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General control line discussion => Open Forum => Topic started by: Juan Valentin on February 23, 2014, 11:27:00 AM
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I would like to know why most stunter wings have leading edge sweep and what would be the optimum amount.
Juan
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I would think it gives the airplane better air/wind penetration than a barn door wing. A side effect is that (explained to me years ago by Jack Sheeks) it effectively makes the nose moment longer. He explained the TLE (true leading edge) was a point halfway along the length of the wing panel. Nose moments are measured from the leading edge. A swept leading edge puts that point further aft.
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LE sweep helps reduce changes in yaw as the model travels around the circle in wind.
I am not sure if there is an optimum amount of sweep to use. Some noticeable sweep is probably better than little or no LE sweep. Somewhere. there is probably a limit of how much Le sweep to use, particularly when the tip chord Reynold's Number starts to become excessively small that any improvements in adverse yaw is offset by increasing inefficiencies with the wing.
Keith
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I look at this from the standpoint of using measurements such as LE sweep to calculate aerodynamic characteristics of airplanes. Our convention is not to use LE sweep, but to use quarter-chord sweep and taper. It makes subsequent calculations easier, as does assuming the earth goes around the sun, rather than the other way around. You can use LE sweep in calculating quarter chord sweep and taper. LE sweep itself comes up in supersonic flow, but not so much in subsonic.
I would think it gives the airplane better air/wind penetration than a barn door wing.
What do you mean by that? Drag wouldn't decrease until you start getting compressibility effects at about Mach .7.
A side effect is that (explained to me years ago by Jack Sheeks) it effectively makes the nose moment longer. He explained the TLE (true leading edge) was a point halfway along the length of the wing panel. Nose moments are measured from the leading edge. A swept leading edge puts that point further aft.
"Nose moment" again. From reading stuff written about stunt, I take it this is a distance. I figure that the term was coined by a guy who didn't know what "moment" means, but wanted to sound authoritative. People have used it ever since. How does it relate to any real phenomena? It gives some roundabout way of relating moment of inertia of an enginean engine's contribution to airplane CG, and it may be an indirect way of figuring the propeller's aerodynamic effects, which I'd like to know, but don't know how to calculate. So now that you've calculated "nose moment", show me what you do with that number.
LE sweep helps reduce changes in yaw as the model travels around the circle in wind.
By slowing the airplane down? I take it you don't really mean yaw, but either sideslip or yaw relative to a line tangent to the circle at the airplane's location. In either case, so what?
Some noticeable sweep is probably better than little or no LE sweep.
For a control line airplane without flaps that does maneuvers in the wind, my guess is that the optimal sweep (measured at the quarter chord) is very noticeable and is negative. I first noticed this with a forward-swept combat plane Gary James gave me, and it really became obvious when I saw Slava Beliaev's airplane maneuvering upwind at the 1985 European Championships. Look at current F2D airplanes. I think the key ingredient is rolling moment due to sideslip.
For airplanes with flaps, there may be some reason not to have a forward-swept flap hinge line. There's the obvious mechanical disadvantage of a severely forward-swept hinge line, but maybe there's some aerodynamic perversion, too. So if you're limited to not much hinge-line sweep, then quarter-chord sweep, hence LE sweep, would just be the outcome of what you pick for aspect ratio and taper.
Somewhere. there is probably a limit of how much Le sweep to use, particularly when the tip chord Reynold's Number starts to become excessively small that any improvements in adverse yaw is offset by increasing inefficiencies with the wing.
That statement requires the reader to make some guesses as to what you're assuming. Are you using the standard definition of adverse yaw?
corrections in red
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Notes and translations to English:
I look at this from the standpoint of using measurements such as LE sweep to calculate aerodynamic characteristics of airplanes. Our convention is not to use LE sweep, but to use quarter-chord sweep and taper. It makes subsequent calculations easier, as does assuming the earth goes around the sun, rather than the other way around. You can use LE sweep in calculating quarter chord and taper. LE sweep itself comes up in supersonic flow, but not so much in subsonic.
Translation: "What? Who cares?" Or, perhaps, "leading edge sweep is not the metric that you care about here".
Aerodynamicists talk about "sweep", meaning the sweep at the quarter-chord point, and "taper", meaning, well, taper. Where a modeller says "leading edge sweep but no trailing edge sweep" an aerodynamics guy will tend to say "taper and sweep", perhaps "taper and sweep so the trailing edge is straight".
What do you mean by that? Drag wouldn't decrease until you start getting compressibility effects at about Mach .7.
"Nose moment" again. From reading stuff written about stunt, I take it this is a distance. I figure that the term was coined by a guy who didn't know what "moment" means, but wanted to sound authoritative. People have used it ever since. How does it relate to any real phenomena? It gives some roundabout way of relating moment of inertia of an engine, and it may be an indirect way of figuring the propeller's aerodynamic effects, which I'd like to know, but don't know how to calculate. So now that you've calculated "nose moment", show me what you do with that number.
In any field of scientific endeavour that has to do with physics, a "moment" is a fancy way of saying "torque", unless you're talking about "moment of inertia", which does sorta relate back to torques and distances. Torque has dimensions of distance times force; talking about a "moment" as something that has distance only is as meaningful to a physicist as saying "my cup is three inches high" without saying how big around it is (about as irritating, too).
I'm slightly more charitable than Howard. I suspect that "moment" came from "moment arm", which does have meaning in physics and engineering, and is measured in inches (or meters). However, a meaningful engine-to-wing moment arm would be measured from the center of gravity of the engine to the aerodynamic center of the wing -- and the leading edge is a good long way from the aerodynamic center.
(balanced snipped)
So, Howard -- you've made statements about wing sweep and performance in the wind. Are you inclined to say what you think does work well in the wind, in your terms?
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A true tapered planform (both LE/TE) will keep the highpoint of the airfoil parallel with the spar.
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A true tapered planform (both LE/TE) will keep the highpoint of the airfoil parallel with the spar.
I am not sure what you are talking about here. Tapered means tapered, the tip chord is smaller than the root chord, nothing more as far as I know. Swept or not swept is as mentioned above, whether the 1/4 chord point (and by implication - the CP) is either straight or swept. Any combination of those is possible.
Most full stunt planes have tapered wings and some sweep. Mostly, this keeps the wing looking about right and in many cases you want to keep the flap hinge line straight for mechanical and trim reasons. The sweep probably helps generate some yaw stability and does cause some dihedral effect (although not much), but I expect it comes out that way because with an appealing taper, flaps = 20% of the chord, and a straight hinge line, it just winds up that way. If you don't want sweep, you probably end up with the hinge line swept forward.
Brett
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Thanks for the translation, Tim
I'm slightly more charitable than Howard.
Unwarrentedly so, but fortunately, as I'm asking you for substantial charity in another endeavor.
I suspect that "moment" came from "moment arm", which does have meaning in physics and engineering, and is measured in inches (or meters). However, a meaningful engine-to-wing moment arm would be measured from the center of gravity of the engine to the aerodynamic center of the wing -- and the leading edge is a good long way from the aerodynamic center.
My guess is that the original phony heard "tail moment arm" somewhere, thought "arm" was superfluous, and also didn't understand why it was measured between the hard-to-measure points it is and decided it could be simplified. The result was a somewhat meaningless measurement given a name that means something else. Then, to make things worse, he figured if there was a "tail moment", there must be a "nose moment", so he made something up. Here we are several decades later wondering what it should mean. I think the engine was customarily located to get the fore-aft CG to come out in the right place without ballast, so the distance from the engine assembly CG to the airplane CG (not directly the AC) might have been a useful number, but I can't think of anything "nose moment arm" could mean, let alone "nose moment".
So, Howard -- you've made statements about wing sweep and performance in the wind. Are you inclined to say what you think does work well in the wind, in your terms?
For combat, a modern F2D plane. For stunt, I'd expect a Firecracker to work well, but for the same reason I thought Don Hutchinson's F-86 would work poorly, and it doesn't. If I had a nice U joint for flaps, it would be interesting to try extreme forward sweep. I think there may be points in being able to keep the tricks opposite the judges regardless of wind vagaries. Meanwhile, I'm standing pat. So, to give a maybe-not-too-satisfactory answer to Juan, an Impact's LE sweep works just fine.
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Juan
I think LE sweep is there just to make the plane look cool. Sorry, just couldn't resist.
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I agree with Mike
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For stunt, I'd expect a Firecracker to work well, but for the same reason I thought Don Hutchinson's F-86 would work poorly, and it doesn't. If I had a nice U joint for flaps, it would be interesting to try extreme forward sweep. I think there may be points in being able to keep the tricks opposite the judges regardless of wind vagaries. Meanwhile, I'm standing pat. So, to give a maybe-not-too-satisfactory answer to Juan, an Impact's LE sweep works just fine.
I think a pair of lucky boxes at the flaps would take care of linkage.
Paul Walker mentioned in his '81 Impact article that he was never going back to a forward-swept flap hingeline, but I cannot remember what he said about reasons, nor would I expect him to necessarily have the same attitude today.
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I think a pair of lucky boxes at the flaps would take care of linkage.
Paul Walker mentioned in his '81 Impact article that he was never going back to a forward-swept flap hingeline, but I cannot remember what he said about reasons, nor would I expect him to necessarily have the same attitude today.
More specifically, he said, "if I ever think about building a swept-forward hinge line please break my arm" or something close to that. Then he did it again on the Mustangs. The reason was trimming issues.
Brett
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I think LE sweep is there just to make the plane look cool.
This is credible. The optimal amount would be that which makes the plane look coolest.
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Great. So it's a myth that quarter chord sweep back aids tracking in windy conditions. (I am straining to understand Howard's terms.) 30s pylon racers are fab looking. Glad to find out that the straight leading edge of these designs can be preserved when stretching this and that to make them effective in CL Stunt.
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Great. So it's a myth that quarter chord sweep back aids tracking in windy conditions. (I am straining to understand Howard's terms.) 30s pylon racers are fab looking. Glad to find out that the straight leading edge of these designs can be preserved when stretching this and that to make a simulation effective in CL Stunt.
Pressed the wrong icon suddenly I'm quoting myself. Feels very strange.
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Great. So it's a myth that quarter chord sweep back aids tracking in windy conditions. (I am straining to understand Howard's terms.)
What's that you call tracking? I am straining to understand your terms.
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I had another model type before Max ... it was called Next. The only difference was larger wing. The Max was orriginaly cloned Next with smaller wing because I saw that the orriginal wing had too much area, but I wanted to reuse root templeate so I did shorter only tip chord by 20mm (less then inch). The result was little more sweepback and little more taper. Since we did several of both models I can tell difference. That model with less swep back gave better chance to set tip weight, changes 0.5g were clearly visible and feelable. The Max was not so easy to see, but it also means it is little more forgiving. So while Next was very well trimable to perfect trim, Max was more universal in different conditions what made him well usable when I go to contest in different altitude or different conditions (when I practice early morning and I must fly afternoon in hot air), I not need to play with tip weight too much. Also side wind does not take him out of the trim so much as did with Next. The reason could be area concentrated close to fuselage while LO guide still on the same distance from CG (taper effect), or maybe dihedral effect like Brett pointed (caused by sweepback). I any case it is visible difference.
http://www.netax.sk/hexoft/stunt/thenext.htm
http://www.netax.sk/hexoft/stunt/the_max_ii.htm
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Is a straight leading edge wing at a disadvantage in CL Stunt when compared to a wing with sweep back? If so, in what way?
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Thanks for all the answers ,I have enjoyed reading all comments and will keep them in mind.I will be saving this thread.
Juan
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Is a straight leading edge wing at a disadvantage in CL Stunt when compared to a wing with sweep back? If so, in what way?
Suggest you read Igor's account posted on Feb 24 at 12:59:07.
Keith
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I read it. Igor is reporting on specific planes. Not a scientific sample. Anecdotal. Problem with much opinion expressed on these forums. Howard seems to contradict these conclusions. I am hoping he will elaborate. As far as anecdotal observations. I have seen at least one stunter with a nearly straight leading edge do the pattern in roaring winds. Finished 7th at the NATs that time. Finished 7th again a few years later. For aesthetic reasons I am interested in straight leading edge (or nearly straight leading edge) wings. Since they match the aesthetics of 1930s pylon racers. Planes I find fascinating.
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I do not see too much contradiction, Howard certainly means properly trimmed model, and I say the difference is how to reach that trim ... so we are speaking about two different things :- )))
When I observed this property, I asked myself what is better, I did not answer myslef, but in any case I was more successfull with that with shorter tips. Alex Schrek used even shorter tips and the same had Richie K. I think they both went back to Max planform lately, so it is certainly not "the more - the better".
However I can imagine the rectangular wing can have also some advantages, for example I can imagine that it will not tend to roll in hard turs. So pilot with lower skill which cannot do all corners of the same radius (for which is model trimmed), can also benefit from such wing, but differences are tiny
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I read it. Igor is reporting on specific planes. Not a scientific sample. Anecdotal. Problem with much opinion expressed on these forums. Howard seems to contradict these conclusions.
Not quite correct Dennis. Scientific examples can have multiple outcomes. You are looking for a single definitive answer which in and of itself is not always scientific. The definitive answer for wing sweep is NOT absolute,it is relative. Consequently Igor's observation,(which is part of the scientific method by the way) is completely correct RELATIVE to his set of parameters.
That is, the key to wing sweep is part of a set of parameters that,taken together produce a certain outcome. Maneuvering aerodynamics is a complex business that demands study and experience to get right.
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Right. Igor. I agree with you. I didn't think your discussion focused on whether or not leading edge sweep back was of benefit in CL Stunt airplanes.
I don't know why you would conclude that a reduction in body roll is of benefit to the less skilled flier, not so to the more skilled flier. In any case, I think we can agree that a flier who edges close to top five is of above average skill. Within a hair of demonstrable top 5 skill. I am talking of Dan Banjok and his Vista. A near straight leading edge plane. Total sweep back of 1/2" from center to tip. Miniscule on a 60" span thick airfoil model. I am interested in knowing whether anyone made a systematic comparison of the performance of sweep back vs non-sweep back models flying at typical stunt speeds. Side note: combat planes that need to be aimed accurately and are flown in all kinds of wind conditions, use straight leading edge wings.
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I don't know why you would conclude that a reduction in body roll is of benefit to the less skilled flier, not so to the more skilled flier.
I mean something else ... more skilled flier can do equivalent corners all the time. So he can benefit from model which is good at just that one radius and does not matter what model does if he does corner for example tighter (model usually tends to roll out) ... while less experienced flier, which sometimes comes to stress, and simply once does corner tighter and once weaker, will benefit if model does not rooll in such case and if he pays little penatlty of some worse property of somethig else, does not matter, because he will not feel it too much anyway.
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My first recolletion of the terms "Moments" as generally (OK, erroneously) applied to CL Stunt aircraft came from the MAN atricle that accompanied George Aldrich's Nobler article. The distances from the engine thrust washer to the leading edge of the wing at the root, was described (erroneously) as the "nose Moment". The distance from the flap hinge line to the elevator was described (erroronously) as the "tail moment". I recall a diagram with dimensions describing those parameters.
I think these terms simply stuck in the CL Stunt community. It's entirely possible that George got them from somewhere else (erroneously).
At any rate, I would say that while they certainly are not engineering discriptions, they have been adopted to actually mean some specified linear dimensions that, while not used in any meaningful aerodynamic calculations, can certainly be used to describe a particular general arrangement of the physical elements of a CL stunt aircraft.
As such they do have a generalized purpose that has come to mean something in the Stunt community, and therefore any criticism aimed at their use simply means that the folks leveling the criticism are being "Prudish" technocrats that actually do know what is meant by their usage in general terms but insist on trying to show everyone else that they are too smart to acknowledge that changes,or additions, in general terminology do and can coexist with numerically generated engineering reality.
Besides, sometimes the real engineering terms don't do much better at describing the actual physical function of the surrounding world except in numbers (sometimes erroneously). Especially since they are understood only by a very small portion of the population.
I've learned to just smile and accept reality. After all, the ultimate level of education is Philosophy is it not? Isn't that why they call it PhD. <= <=
Randy Cuberly D>K
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I remember that diagram in the GMA article, Randy. What has me a little confused is stuff I recall from the Zaic books, where Frank Zaic showed how to calculate tail volumes, both horizontal and vertical tail volumes. Seems to me that he measured from the "quarter chord" of the wing, but maybe I've forgotten that detail, and he referenced from something else. That didn't make any sense to me. I could see referencing from the MAC or even high point of the airfoil, but I better stop before Howard gets upset with the terms I'm using being all wrong... LL~ Steve
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I'd think that taper would help in turbulence, where the upsetting moment is proportional to the spanwise distance from the CG to the mean aerodynamic chord, and the restoring moment is proportional to the spanwise distance from the CG to the leadout guide. Rectangular wings also aren't as structurally wonderful: there's more load out toward the tip, which makes for a higher bending moment at the wing root, and the spar isn't as deep at the root, so the forces on the spar at the root are even greater. The rectangular wing might be more prone to twisting, too. The upchuck is that the structure for a rectangular wing would need to be heavier than for a tapered wing. Maybe you'd get some hinge moment benefit from constant-chord flaps. I don't know.
If a rectangular wing looks cool to you, I think you should use it.
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I remember that diagram in the GMA article, Randy. What has me a little confused is stuff I recall from the Zaic books, where Frank Zaic showed how to calculate tail volumes, both horizontal and vertical tail volumes. Seems to me that he measured from the "quarter chord" of the wing, but maybe I've forgotten that detail, and he referenced from something else. That didn't make any sense to me. I could see referencing from the MAC or even high point of the airfoil, but I better stop before Howard gets upset with the terms I'm using being all wrong... LL~ Steve
Probably a quarter of the way back on the mean aerodynamic chord. That has actual physical significance.
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As such they do have a generalized purpose that has come to mean something in the Stunt community, and therefore any criticism aimed at their use simply means that the folks leveling the criticism are being "Prudish" technocrats that actually do know what is meant by their usage in general terms but insist on trying to show everyone else that they are too smart to acknowledge that changes,or additions, in general terminology do and can coexist with numerically generated engineering reality.
Besides, sometimes the real engineering terms don't do much better at describing the actual physical function of the surrounding world except in numbers (sometimes erroneously). Especially since they are understood only by a very small portion of the population.
Obviously I disagree. Whoever coined some of those terms was using words the meaning of which he pretended to understand, but didn't. So he came up with measurements with no physical significance, no standard definition you can look up, and names that mean something else. So if you are describing a set of measurements for a bunch of airplanes, you are better off drawing an airplane cartoon with distances shown and labeled "a", "b", etc. or saying, "distance from the thrust washer to the wing root leading edge measured at the side of the body" than by using "nose moment", which could mean a measurement to the wing root, to a point halfway down the leading edge, or something else. You can communicate better by describing things without using technical terms than you can by using technical terms ambiguously and a lot better than you can by using technical terms wrong.
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Obviously I disagree. Whoever coined some of those terms was using words the meaning of which he pretended to understand, but didn't. So he came up with measurements with no physical significance, no standard definition you can look up, and names that mean something else. So if you are describing a set of measurements for a bunch of airplanes, you are better off drawing an airplane cartoon with distances shown and labeled "a", "b", etc. or saying, "distance from the thrust washer to the wing root leading edge measured at the side of the body" than by using "nose moment", which could mean a measurement to the wing root, to a point halfway down the leading edge, or something else. You can communicate better by describing things without using technical terms than you can by using technical terms ambiguously and a lot better than you can by using technical terms wrong.
I have to agree with Howard here,
I visit several photography sites,, its a real crapshoot to communicate because people dont use the proper terms for things
so when you respond you never know whether they are refering to the real definition, or the one they imagine it to be
words have specific meanings,, to communicate you must use the words that refer to the proper topic,,or risk confusion
its like stating the wing percentage thickness is it with or without flaps,,
stating the tail "moment" (sic),, is it from the CG or the flap hingeline,,
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Obviously I disagree. Whoever coined some of those terms was using words the meaning of which he pretended to understand, but didn't. So he came up with measurements with no physical significance, no standard definition you can look up, and names that mean something else. So if you are describing a set of measurements for a bunch of airplanes, you are better off drawing an airplane cartoon with distances shown and labeled "a", "b", etc. or saying, "distance from the thrust washer to the wing root leading edge measured at the side of the body" than by using "nose moment", which could mean a measurement to the wing root, to a point halfway down the leading edge, or something else. You can communicate better by describing things without using technical terms than you can by using technical terms ambiguously and a lot better than you can by using technical terms wrong.
Balloney Howard...read what I wrote again!
It has nothing to do with using technical terms wrong. Those "technical terms" exist only in the "misusage" described therefore they could be simply described by the definitions given for them as "New physical descriptive terms". I think the drawing supplied in the article gave them their definition.
You certainly have the right to disagree...you also have the right to be wrong in your thinking.
Relax you can't change the fact that the terms as used by a given community of people and understood as a standard description of something, colloquial or not, has meaning to that community. No matter how wrong YOU think it is!
However if asked to calculate meaningful answers from that colloquial data...you can certainly laugh a lot!
Randy Cuberly
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I have to agree with Howard here,
I visit several photography sites,, its a real crapshoot to communicate because people dont use the proper terms for things
so when you respond you never know whether they are refering to the real definition, or the one they imagine it to be
words have specific meanings,, to communicate you must use the words that refer to the proper topic,,or risk confusion
its like stating the wing percentage thickness is it with or without flaps,,
stating the tail "moment" (sic),, is it from the CG or the flap hingeline,,
Hi Mark,
Well, if you're talking about the names of physical objects, like calling a lens a thingamajig, you're right. But for the purposes of our discussion which is about technical terms...what I said to Howard applies to you also.
Randy Cuberly
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You certainly have the right to disagree...you also have the right to be wrong in your thinking.
I'm not, though, of course.
So a person new to stunt (not that there are any) confronted with the term "nose moment" would need to find a 60-year-old magazine article to find its definition, whereas if he wants a definition of "moment", he could find a consistent one in any physics or mechanics textbook or in a zillion places on line.
More confusing than "nose moment" is when a term's real meaning is close to what the user means, but not quite. Not to pick on the Colonel, but "LE sweep helps reduce changes in yaw as the model travels around the circle in wind." is an example of that. I knew he couldn't have meant yaw relative to a fixed axis system, the usual definition of yaw, because that angle changes inversely proportional to lap time. Maybe he meant yaw relative to the tangent to the circle. That would be what you'd see at the handle. No, if he's thinking of Cnβ, that would be wrong, and if it were true, it wouldn't be a virtue. Maybe he meant "helps reduce changes in sideslip". Cnβ would do that, I guess, but if you have enough line tension to control the airplane, I'd think that Clβ from sweep would cause more trouble than Cnβ would cause good. So I was confused. If it's clear to you, please explain it to me.
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I'm not, though, of course.
So a person new to stunt (not that there are any) confronted with the term "nose moment" would need to find a 60-year-old magazine article to find its definition, whereas if he wants a definition of "moment", he could find a consistent one in any physics or mechanics textbook or in a zillion places on line.
More confusing than "nose moment" is when a term's real meaning is close to what the user means, but not quite. Not to pick on the Colonel, but "LE sweep helps reduce changes in yaw as the model travels around the circle in wind." is an example of that. I knew he couldn't have meant yaw relative to a fixed axis system, the usual definition of yaw, because that angle changes inversely proportional to lap time. Maybe he meant yaw relative to the tangent to the circle. That would be what you'd see at the handle. No, if he's thinking of Cnβ, that would be wrong, and if it were true, it wouldn't be a virtue. Maybe he meant "helps reduce changes in sideslip". Cnβ would do that, I guess, but if you have enough line tension to control the airplane, I'd think that Clβ from sweep would cause more trouble than Cnβ would cause good. So I was confused. If it's clear to you, please explain it to me.
Howard,
What you're forgetting is that 98% of the people on this forum have no idea what the Hell you are talking about and don't understand anything you have said...but did get the jist of what Keith ment by Yaw... I definitely do not agree with his conclusion but did understand what he meant. But then I probably know him a little better than you do and talk to him more often.
I would never try to explain it to you!
Bottom line is don't be such a bully you'll get your point across better if you simply realize you are talking to intelligent people who don't understand your language...you have to speak in theirs if you want them to understand...if you can't do that it simply means you're a good engineer and a lousy reference for normal folks!
Peace!
Randy Cuberly
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For those folks questioning a rectangular configuration for a CL Stunt wing either for better or worse I would simply post this picture of Kaz Minato's Classic entry at last years VSC.
Very Beautiful airplane and it flew very very well! If there was any disadvantage there, it certainly wasn't obvious and was "in the noise".
Randy Cuberly
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What you're forgetting is that 98% of the people on this forum have no idea what the Hell you are talking about and don't understand anything you have said...but did get the jist of what Keith ment by Yaw...
I wrote that to describe my thought process in trying to figure out what Keith meant, and I daresay I used the language correctly. He used a technical term when a description in lay language would have served him better. No, I don't think anybody got the jist of what he "ment" except by accident.
I definitely do not agree with his conclusion but did understand what he meant. But then I probably know him a little better than you do and talk to him more often.
So what did he mean and how could you tell?
I would never try to explain it to you!
My guess is that you can't.
Bottom line is don't be such a bully you'll get your point across better if you simply realize you are talking to intelligent people who don't understand your language...you have to speak in theirs if you want them to understand.
This is exactly my point. It's particularly onerous if "your language" is a private one made up of words that mean something else. Don't say "nose moment". Say "the distance between..." . If you mean "the sideways angle between the direction the airplane is pointed and the direction the air is blowing on it", say that if you want a general reader to understand it.
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Randy has pointed something out here that needed to be pointed out. I think the original question was, why do most stunters have a swept leading edge and how much sweep is enough. I was making a joke when I said it looked cooler but maybe that was a small factor in the swept back leading edge. There may very well be some aerodynamic advantages to have the leading edge swept back but as Randy said, they need to be explained in terms and language that the other 98% can understand. The skill of the pilot has a lot to do with how the plane goes through the pattern also. Often dicussions that evolve from a relativly simple question that was originally asked, get so far out in the brainiac sphere that I sometimes think that a foreign language is being spoken. Whenever I start reading a thread that insterests me for whatever reason and all of a sudden I am looking at calculus and formulas that I have no idea what they mean, I just give up on the thread and go elsewhere. A person who asks a simple question like what does uniflo mean in a gas tank and gets an answer that is a lesson in physics from someone whose intentions are good but does not know how to relate to this person who might be an insurance salesman, is most probably going to just give up and not want to seem dumb because he cannot even understand the language of physics or formulas and feel intimidated and not ask any more questions because of thinking he is appearing as dumb.
I think it is great that we have a group of individuals on here that are extremely bright in their fields and have a tremendous amount of knowledge in math, engineering, physics and aerodynamics that they can share with the other 98% of us..we are indeed fortunate. But as Randy previously stated, unless you respond in language and terms the 98% of us can understand, things get lost in translation.
I have read these threads that are posted on here sometimes by these individuals and after i have read the thread, I have no idea what they are talking about and seek out a post and responses I can relate to.
We are very fortunate to have these bright minds among us...just dumb it down a little for us poor slobs in the 98 %
Mike
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A true tapered planform (both LE/TE) will keep the highpoint of the airfoil parallel with the spar.
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I am not sure what you are talking about here. Tapered means tapered, the tip chord is smaller than the root chord, nothing more as far as I know. Swept or not swept is as mentioned above, whether the 1/4 chord point (and by implication - the CP) is either straight or swept. Any combination of those is possible.
Most full stunt planes have tapered wings and some sweep. Mostly, this keeps the wing looking about right and in many cases you want to keep the flap hinge line straight for mechanical and trim reasons. The sweep probably helps generate some yaw stability and does cause some dihedral effect (although not much), but I expect it comes out that way because with an appealing taper, flaps = 20% of the chord, and a straight hinge line, it just winds up that way. If you don't want sweep, you probably end up with the hinge line swept forward.
Brett
I was referring to the planform of the wing and where the CP (Center of Pressure?)- as per your ex. 25%, can be either swept fwd, straight or swept aft. If you plot out the high points, you get this.
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Howard is absolutely correct...and as usual, this belongs on the engineering board. That anyone expects this question to have a convenient "home remedy" answer is unfortunate. I don't care whether one WANTS it to have such an answer; it DOES NOT.
Now that the majority have tuned out to beliebve what's comfortable, I'll @#$% uphill or into the wind with the rest.
FIRST, it is not reasonable nor more "understandable" to use technical terms wrong and then state that you know what they actually mean to the masses. Nose moment means the torque around the center of mass exerted by the sum of the moments (torques) ahead of it. NOTHING MORE! If you choose it to mean the "distance" from the "whatever" to the leading edge, it is still absolutely meaningless, because it does not describe accurately what actually happens when you place a weight there. You can kid yourself all you want and suggest that it's healthy for others to think this way, but it is inaccurate in any inferences you may choose to draw from such characterizations. Forces that act ahead of the c.g. exert torques on the plane that are proportional to their distance from the c.g., NOT the leading edge. There is significant and quite measurable difference, and they have resulted in numerous errors, for instance, in adding prop extensions on light weight engines for certain purposes. These have resulted in historically disadvantageous tail sizes and lengths.
Hinge to hinge measurements too are not proportional to what really happens when tail moments and volumes are changed. Such measurements are irrelevant to real-world happenings. The only reason they seem - that is SEEM - to work is that most stunters have settled on the same approximate configuration, and hodge-podge solutions in trim "cure" design mistakes.
These are the effects relevant to the question, and their analysis and use are not all simple and NOT always easily understood.
1) Wing taper determines MAC placement, which in turn determines how far in on the span the a.c. lies. The more the taper, the further inboard the a.c. lies, until the taper ratio is zero (pointed wing), in which case the theoretical a.c lies at 1/3 the half span. In reality, all a.c.'s lie inboard of their computed value, because of tip losses and resulting lift distributions. This is significant to wind gusts, which is why more highly tapered wings like the "Firecracker's" are preferred in Australia and why elliptical wings are considered better in the wind (gusts). Leading edge sweep also moves the a.c. further aft of what any "home remedies predict; the famous icon of stunt design mentioned above once made that mistake and apparently wrote off a viable design, built later successfully by others who then placed the c.g. appropriately (you do not place the c.g according to root chord with any significant leading-edge sweep). Taper allows wings to approximate more closely the proved ideal of elliptical lift distribution (although idealized root bending moment calls for a variation). The limit is dictated by Reynolds numbers near the tip - too short a tip chord leads to inefficiency, flow separation, and tip stalls.
2) Spanwise-straight or swept back hinge lines should be more stable in yaw on normally tapered wings, since the forward yawed wing will usually have less lift and drag than the aft one with the more perpendicular hinge line and more projected (usually) planview area.
3) in order to achieve the straight hinge line and still have reasonable taper, the leading edge must be swept back. If flaps are reasonably proportioned (talk to Ted, Howard, or Brett) then the amount of sweep is determined by preferences of efficiency and wind (gust) performance. Sweep back causes a dihedral effect while otherwise stabilizing a wing in respect to yaw, due to drag. The dihedral effect causes complications in roll with gusts, and there is always a yaw-roll couple, meaning simply that if you cause either yaw or roll, you almost always get the other too.
4) Control line leadout position relative to rake helps diminish the yaw and roll effects. A lot of control-line fliers don't care. Some do.
Ultimately, it is comfortable for people to claim that these things like hinge-to-hinge or "nose moment" (whatever that actually is supposed to mean) measurements are significant, but they are not meaningful past the point that in a "normal" stunter, a longer one of these measurements means that the proper and significant measurement is also longer. HOWEVER, they are NOT proportional, and such fictitious "accepted" measurements, when actually used quantitatively, give the wrong answers, which are then gleefully accepted as meaningful, after trim has been applied to mask their shortcomings.
Do we always have to denigrate people who just try to use perfectly understandable terms by bastardizing these terms and casting aspersions on the character of people who use them correctly and post over and over all that's needed to truly understand? She-e-e-e-sh!!!
SK
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This is all my fault for mentioning moment. Back in 1969, I used to build listening to the stereo. My favorite song was by Jay and the Americans titled This Magic Moment. I guess it just stuck with me.
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I was referring to the planform of the wing and where the CP (Center of Pressure?)- as per your ex. 25%, can be either swept fwd, straight or swept aft. If you plot out the high points, you get this.
So it wasn't taper, it was sweep, that you were referring to.
Brett
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Howard is absolutely correct...and as usual, this belongs on the engineering board. That anyone expects this question to have a convenient "home remedy" answer is unfortunate. I don't care whether one WANTS it to have such an answer; it DOES NOT.
Now that the majority have tuned out to beliebve what's comfortable, I'll @#$% uphill or into the wind with the rest.
FIRST, it is not reasonable nor more "understandable" to use technical terms wrong and then state that you know what they actually mean to the masses. Nose moment means the torque around the center of mass exerted by the sum of the moments (torques) ahead of it. NOTHING MORE! If you choose it to mean the "distance" from the "whatever" to the leading edge, it is still absolutely meaningless, because it does not describe accurately what actually happens when you place a weight there. You can kid yourself all you want and suggest that it's healthy for others to think this way, but it is inaccurate in any inferences you may choose to draw from such characterizations. Forces that act ahead of the c.g. exert torques on the plane that are proportional to their distance from the c.g., NOT the leading edge. There is significant and quite measurable difference, and they have resulted in numerous errors, for instance, in adding prop extensions on light weight engines for certain purposes. These have resulted in historically disadvantageous tail sizes and lengths.
Hinge to hinge measurements too are not proportional to what really happens when tail moments and volumes are changed. Such measurements are irrelevant to real-world happenings. The only reason they seem - that is SEEM - to work is that most stunters have settled on the same approximate configuration, and hodge-podge solutions in trim "cure" design mistakes.
These are the effects relevant to the question, and their analysis and use are not all simple and NOT always easily understood.
1) Wing taper determines MAC placement, which in turn determines how far in on the span the a.c. lies. The more the taper, the further inboard the a.c. lies, until the taper ratio is zero (pointed wing), in which case the theoretical a.c lies at 1/3 the half span. In reality, all a.c.'s lie inboard of their computed value, because of tip losses and resulting lift distributions. This is significant to wind gusts, which is why more highly tapered wings like the "Firecracker's" are preferred in Australia and why elliptical wings are considered better in the wind (gusts). Leading edge sweep also moves the a.c. further aft of what any "home remedies predict; the famous icon of stunt design mentioned above once made that mistake and apparently wrote off a viable design, built later successfully by others who then placed the c.g. appropriately (you do not place the c.g according to root chord with any significant leading-edge sweep). Taper allows wings to approximate more closely the proved ideal of elliptical lift distribution (although idealized root bending moment calls for a variation). The limit is dictated by Reynolds numbers near the tip - too short a tip chord leads to inefficiency, flow separation, and tip stalls.
2) Spanwise-straight or swept back hinge lines should be more stable in yaw on normally tapered wings, since the forward yawed wing will usually have less lift and drag than the aft one with the more perpendicular hinge line and more projected (usually) planview area.
3) in order to achieve the straight hinge line and still have reasonable taper, the leading edge must be swept back. If flaps are reasonably proportioned (talk to Ted, Howard, or Brett) then the amount of sweep is determined by preferences of efficiency and wind (gust) performance. Sweep back causes a dihedral effect while otherwise stabilizing a wing in respect to yaw, due to drag. The dihedral effect causes complications in roll with gusts, and there is always a yaw-roll couple, meaning simply that if you cause either yaw or roll, you almost always get the other too.
4) Control line leadout position relative to rake helps diminish the yaw and roll effects. A lot of control-line fliers don't care. Some do.
Ultimately, it is comfortable for people to claim that these things like hinge-to-hinge or "nose moment" (whatever that actually is supposed to mean) measurements are significant, but they are not meaningful past the point that in a "normal" stunter, a longer one of these measurements means that the proper and significant measurement is also longer. HOWEVER, they are NOT proportional, and such fictitious "accepted" measurements, when actually used quantitatively, give the wrong answers, which are then gleefully accepted as meaningful, after trim has been applied to mask their shortcomings.
Do we always have to denigrate people who just try to use perfectly understandable terms by bastardizing these terms and casting aspersions on the character of people who use them correctly and post over and over all that's needed to truly understand? She-e-e-e-sh!!!
SK
Serge,
If you wish to deal in absolutes, the one correct thing you said is that your discourse belongs on the engineering board!
Why not take it over there.
Randy Cuberly!
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Serge,
If you wish to deal in absolutes, the one correct thing you said is that your discourse belongs on the engineering board!
Why not take it over there.
Randy Cuberly!
You're welcome to address anything you feel to be incorrect here - 'probably ought to. As for taking it elsewhere...
1) I didn't put this thread here.
2) I've covered all these on the other boards, including "over there". You can use the search function here and on SSWF to find the informatiuon.
SK
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My favorite song was by Jay and the Americans titled This Magic Moment.
I like the guitar lick on the Drifters version.
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Randy has pointed something out here that needed to be pointed out. I think the original question was, why do most stunters have a swept leading edge and how much sweep is enough. I was making a joke when I said it looked cooler but maybe that was a small factor in the swept back leading edge. There may very well be some aerodynamic advantages to have the leading edge swept back but as Randy said, they need to be explained in terms and language that the other 98% can understand. The skill of the pilot has a lot to do with how the plane goes through the pattern also. Often dicussions that evolve from a relativly simple question that was originally asked, get so far out in the brainiac sphere that I sometimes think that a foreign language is being spoken. Whenever I start reading a thread that insterests me for whatever reason and all of a sudden I am looking at calculus and formulas that I have no idea what they mean, I just give up on the thread and go elsewhere. A person who asks a simple question like what does uniflo mean in a gas tank and gets an answer that is a lesson in physics from someone whose intentions are good but does not know how to relate to this person who might be an insurance salesman, is most probably going to just give up and not want to seem dumb because he cannot even understand the language of physics or formulas and feel intimidated and not ask any more questions because of thinking he is appearing as dumb.
I think it is great that we have a group of individuals on here that are extremely bright in their fields and have a tremendous amount of knowledge in math, engineering, physics and aerodynamics that they can share with the other 98% of us..we are indeed fortunate. But as Randy previously stated, unless you respond in language and terms the 98% of us can understand, things get lost in translation.
I have read these threads that are posted on here sometimes by these individuals and after i have read the thread, I have no idea what they are talking about and seek out a post and responses I can relate to.
We are very fortunate to have these bright minds among us...just dumb it down a little for us poor slobs in the 98 %
I went off on my "nose moment" tirade, leading the thread away from the original question. Here's a try, although other people have said the same thing while I was writing this:
Leading edge sweep doesn't affect much directly. Stunt planes have it because the wings are usually tapered and the flap hinge line is usually pretty straight. I gave a couple of reasons for taper above, and you gave a better one, although it doesn't apply to Dennis. I think wing sweep back is bad; Keith thinks it's good. I can explain why I think it's bad. It's not awful, though, and not having experimented with way-swept-forward flaps, I'll accept the conventional wisdom that they would do worse things than the sweep does, so I'm building another Impact. That still doesn't answer the question of what's the optimal LE sweep. Maybe what we should have done from the get-go was to rephrase it as, "what's the optimal taper, given the usual stunt plane aspect ratio and a straight hinge line?" Igor came closest to answering that. I don't know the answer.
To address your objection, alas some of this stuff is kinda complicated, and to show why it is what it is takes some math. Try showing somebody without using math why his airplane will turn more easily for a given CG if his battery and motor are in the same place than if the battery is on the CG and the motor is way out in front of the airplane. I haven't seen much beyond high school math here, and I don't think anybody should apologize for using high school math. One thing that annoys me is guys "simplifying" stuff when their knowlege of the subject is so shallow that they have no alternative. One guy writing in a recent Model Aviation started with something like, "I know this will annoy engineers out there, but I'm going to explain this without using math." As I expected, he then went on to reveal that he didn't know beans about what he was “explaining”.
I have a friend who wrote a technical book and seemed to have math minimization as an objective. Sure enough, scanning through the book you don’t see much math. It’s all there, though. He just put everything into highfalutin vector operators so the math was packed in tight like matter in a neutron star. This isn’t pertinent to this conversation, but I thought it was amusing.
I don't like the term "dumb down". I hope you mean that folks should put more effort into explaining something to the intelligent reader who’s not in on the jargon. Things that can help are to avoid using esoteric technical terms when possible, not to use technical terms the meaning of which the user doesn't understand, and not to use private jargon.
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I like waking up feeling ignorant, even a little stupid. Means there's something to try and figure out. Think about. It's the action of trying that feels good.
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I think wing sweep back is bad; Keith thinks it's good. I can explain why I think it's bad. It's not awful, though, and not having experimented with way-swept-forward flaps, I'll accept the conventional wisdom that they would do worse things than the sweep does, so I'm building another Impact.
Howard,
Do you really really think wing LE sweep back is bad? I was going to ask you then, why do you build your CLPA airplanes with swept back LE edges? But then, I guess you sort of answered that conventional wisdom (whatever that is, like - where is this conventional wisdom?) sort of says that it is better than say having "way-swept-forward flaps".
Now, some of this has already been addressed in one form or another. But one thing to consider is to understand why full scale aircraft use tapered wings. And tapered wings means that generally, there will be LE sweep-back to some degree. It is my understanding that there are several reasons for wing taper. One is structural. A wing with taper can be built lighter than a non-tapered wing of the same area each designed to the same strength specifications because the tip loads on the center structure are less with the tapered wing (washout and/or washin notwithstanding). Another reason is that a tapered wing is closer to a more optimal elliptical wing planform without the fabrication difficulties of building an elliptical wing. The tapered wing comes closer to giving elliptical lift distribution across the wing than a straight wing working on the premise that elliptical lift distribution is good because tip losses are minimized and drag is reduced. (I have my own thoughts about elliptical wings on CLPA models, but I will not get into that here.)
And as has been suggested here, some may feel that a tapered wing (which sort of results in LE sweep) is more attractive. So, go for what looks good.
An interesting experiment would be to build two stunt ships. Equal span, equal areas, equal moments, same weight and same power package. The only difference would be one has a non-tapered wing, the other with a tapered wing with the amount of taper "normally" seen on CLPA models (probably not less than a taper ratio of 0.6 or 0.7). Which one would have a better square turn? I would suspect that a good pilot would determine that the tapered wing will present a better square maneuver. And I think the reason for it is that there is a reduction in tip losses in the turns with a tapered wing. There may be less drag involved, but drag experienced by a maneuvering CLPA model is not necessarily a bad thing.
Howard, I am not trying to argue with you, nor am I going to get into the discussion about whatever is the difference between side slip and yaw.
Keith
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Howard thank you for taking the time to address my concern about explanations sometimes getting above some of our heads. I do not like the term "DUMB DOWN" either and it was a poor choice of words to make a point. God knows there is too much dumbing down going on in the country now. I guess what I really was trying to say is that I look at this as a hobby and a relaxation outlet for me. I cannot and will not speak for anyone else. In most cases I am able to take what I need and seek from the information that is posted here most of the time. THe posts that I cannot relate to for whatever reason I just skim over and go on. I guess the old adage of if you ask someone what time it is and they tell you how the watch is made might apply to what I was trying to say.
In any case, I am glad we have folks like you and the others who have taken the time to post in this thread to unselfishly offer advice and share knowledge whether is gets to technical for me or not. I do appreciate in particular your sense of humor Howard as it can be a bit warped like mine at times.....
Mike
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More specifically, he said, "if I ever think about building a swept-forward hinge line please break my arm" or something close to that. Then he did it again on the Mustangs. The reason was trimming issues.
Brett
That is correct. I had built a new very light plane for the '82 season. It was another "Frustrations End" geometry but in the low 50 ounce range. It flew reasonably well but always had yaw in harder corners that I could never trim out, and it became a real annoyance to me.
The next plane took that same geometry and simply straightened the flap hinge line. It totally solved the yaw issue. By straightening the hinge line I gave the wing more taper, an effectively longer nose length and shorter tail length. This plane was the original "Bad News". The Impact series followed that straight hinge line.
The Mustangs used some "minor" hinge line forward sweep. They also had a more forward CG and they didn't have significant yaw issues.
I still use straight hinge lines on the electrics.
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Howard,
What you're forgetting is that 98% of the people on this forum have no idea what the Hell you are talking about and don't understand anything you have said...but did get the jist of what Keith ment by Yaw... I definitely do not agree with his conclusion but did understand what he meant. But then I probably know him a little better than you do and talk to him more often.
I would never try to explain it to you!
Bottom line is don't be such a bully you'll get your point across jbetter if you simply realize you are talking to intelligent people who don't understand your language...you have to speak in theirs if you want them to understand...if you can't do that it simply means you're a good engineer and a lousy reference for normal folks!
Peace!
Randy Cuberly
Bully you call Howard....
You better go back and read what you have written.
Sad.
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Do you really really think wing LE sweep back is bad? I was going to ask you then, why do you build your CLPA airplanes with swept back LE edges? But then, I guess you sort of answered that conventional wisdom (whatever that is, like - where is this conventional wisdom?) sort of says that it is better than say having "way-swept-forward flaps".
I don't think of LE sweep as an independent variable. Data I've seen such as in NACA Report 1098 are given as functions of quarter-chord sweep and taper. I think sweep is bad because of rolling moment due to sideslip. The more sweep a plane has, the bigger the tendency to roll changes as maneuver placement relative to the wind changes. There are other design considerations that outweigh this, so the optimal stunt plane probably has some sweep. There's the flap problem. To make rolling moment due to sideslip go away, flaps would need to be swept forward 30 degrees or so. I haven't found any data on the aerodynamic effect of way-swept-forward flaps, nor do I know how to calculate it. I just intuitively think it would be bad. I have intended to make a plane like that to find out for 35 years. It will have to wait another few months, at least. Another disadvantage of swept forward wings is that the nose gets long, as Dick said above. In 1983 I switched from a straight LE to a straight quarter chord on my F2D planes to shorten the motor mounts. It seemed to be a good trade, but in retrospect I should have lightened the tail. Of course, the issue of sweep effect maneuver placement relative to the wind will be moot when we can use 2.4 GHz radios to shift ballast.
Where's the conventional wisdom? One sees few airplanes on Saturday at the Nats with 30 degrees forward sweep in the flap hinge line.
Another reason is that a tapered wing is closer to a more optimal elliptical wing planform without the fabrication difficulties of building an elliptical wing. The tapered wing comes closer to giving elliptical lift distribution across the wing than a straight wing working on the premise that elliptical lift distribution is good because tip losses are minimized and drag is reduced. (I have my own thoughts about elliptical wings on CLPA models, but I will not get into that here.)
Good point. I forgot about that one. To cancel that disadvantage, you'd need to bump up the aspect ratio of the rectangular wing a little, which would add even more structural weight. I look forward to hearing your elliptical thoughts. Elliptical wings look so cool.
And as has been suggested here, some may feel that a tapered wing (which sort of results in LE sweep) is more attractive. So, go for what looks good.
The rectangular wing looks more attractive to Dennis. He should be able to make up for its structural weight penalty with originality points.
... equal moments...
You're messing with me, aren't you, Col.?
Howard, I am not trying to argue with you, nor am I going to get into the discussion about whatever is the difference between side slip and yaw.
Sorry, Keith. I was on a tear about language abuse, and yours was the first target I came to.
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Bully you call Howard....
You better go back and read what you have written.
Sad.
A bully he is, on backwards he said my canopy was.
Derek
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Just for some perspective from the full size world, I have some significant time in the LET Blanik L13 which has swept forward leading and trailing edges. One of the most well connected, well balanced planes I have ever flown. A pleasure to fly aerobatics in. (well, at least till the wing spar AD :( )
Kim
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Marske Pioneer III - 42:1, so far?
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Bully you call Howard....
You better go back and read what you have written.
Sad.
Some of Howard's Jive Combat Team rhymes, can be pretty intimidating!! LL~
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Right. Igor. I agree with you. I didn't think your discussion focused on whether or not leading edge sweep back was of benefit in CL Stunt airplanes.
I don't know why you would conclude that a reduction in body roll is of benefit to the less skilled flier, not so to the more skilled flier. In any case, I think we can agree that a flier who edges close to top five is of above average skill. Within a hair of demonstrable top 5 skill. I am talking of Dan Banjok and his Vista. A near straight leading edge plane. Total sweep back of 1/2" from center to tip. Miniscule on a 60" span thick airfoil model. I am interested in knowing whether anyone made a systematic comparison of the performance of sweep back vs non-sweep back models flying at typical stunt speeds. Side note: combat planes that need to be aimed accurately and are flown in all kinds of wind conditions, use straight leading edge wings.
Hi Dennis,
FWIW, Bob Hunt once judged a flight of my Johnson "little s" powered Chief at a VSC and told me years later it was one of the better flights he had ever judged. Nothing much straighter than a Veco Chief leading edge!
My Imitation was the best airplane I ever designed to fly well easily and it had the least taper of any of my designs (save the very straight winged Doctor/Medic EMT designs). None of my "competition ships" had so little taper because it looked ugly. Didn't say I was smart, did I!!!
Ted
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The more sweep a plane has, the bigger the tendency to roll changes as maneuver placement relative to the wind changes.
I am not sure, but I remember some text or may be NACA report showing several properties of yawed wing with sweepback (pressure distribution, CP position, bending moment etc ...). I think somewhere in conclussion was written that sideslip does not make expected sidewise shift of centre of pressure. Additionally we are flying circular path, it can also change situation as the effective span make speed differences on tips lower. It will be nice to make some simulation and find real center of pressure with reaspect of side wind on circular path.
The effect of side slip also varies with angle of attack.
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...Bob Hunt once judged a flight of my Johnson "little s" powered Chief at a VSC and told me years later it was one of the better flights he had ever judged...
Ted
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I saw that flight. Bob wasn't kidding. It was textbook.
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Just for some perspective from the full size world, I have some significant time in the LET Blanik L13 which has swept forward leading and trailing edges. One of the most well connected, well balanced planes I have ever flown. A pleasure to fly aerobatics in. (well, at least till the wing spar AD :( )
Kim
Nice to see our airplane in our newsletter comming from Canada :- ))
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My first recolletion of the terms "Moments" as generally (OK, erroneously) applied to CL Stunt aircraft came from the MAN atricle that accompanied George Aldrich's Nobler article. The distances from the engine thrust washer to the leading edge of the wing at the root, was described (erroneously) as the "nose Moment". The distance from the flap hinge line to the elevator was described (erroronously) as the "tail moment". I recall a diagram with dimensions describing those parameters.
I think these terms simply stuck in the CL Stunt community. It's entirely possible that George got them from somewhere else (erroneously).
At any rate, I would say that while they certainly are not engineering discriptions, they have been adopted to actually mean some specified linear dimensions that, while not used in any meaningful aerodynamic calculations, can certainly be used to describe a particular general arrangement of the physical elements of a CL stunt aircraft.
As such they do have a generalized purpose that has come to mean something in the Stunt community, and therefore any criticism aimed at their use simply means that the folks leveling the criticism are being "Prudish" technocrats that actually do know what is meant by their usage in general terms but insist on trying to show everyone else that they are too smart to acknowledge that changes,or additions, in general terminology do and can coexist with numerically generated engineering reality.
Besides, sometimes the real engineering terms don't do much better at describing the actual physical function of the surrounding world except in numbers (sometimes erroneously). Especially since they are understood only by a very small portion of the population.
I've learned to just smile and accept reality. After all, the ultimate level of education is Philosophy is it not? Isn't that why they call it PhD. <= <=
Randy Cuberly D>K
Bravo, Randy.
My definition of a valuable post is that somebody can read it in English he understands and employ the information in a positive manner to improve his performance at the flying field. Snarky criticism in and of itself seldom fulfills that standard.
I agree, it can't hurt any of us to learn more precisely accurate descriptions/definitions, etc. of aerodynamic subjects but, it is my belief, that any attempt to point out the technical fallacies of a given post should include helpful commentary to not only illuminate the fault but to advise what is accurate and what the enhanced effects might be at the flying field from employing the technically esoteric but precise terminology as opposed to the apocryphal language of the lay pilot.
Ted
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I have to agree with Howard here,
I visit several photography sites,, its a real crapshoot to communicate because people dont use the proper terms for things
so when you respond you never know whether they are refering to the real definition, or the one they imagine it to be
words have specific meanings,, to communicate you must use the words that refer to the proper topic,,or risk confusion
its like stating the wing percentage thickness is it with or without flaps,,
stating the tail "moment" (sic),, is it from the CG or the flap hingeline,,
Mark,
Although your points are well taken, taken literally they pretty much eliminate everyone from participation on the forums besides Howard, Igor, Brett, Serge and maybe a couple of others.
While if, like Brett, they can do so in language decipherable to the non-cognoscenti, such a site might be more valuable from a precision standpoint it would also be pretty much a bore since--without the foolish commentary which generates the high brow responses--there wouldn't be much to read. Almost all of the wisdom which arises in these threads is the result of responses to the "foolish" input from people who just like to be involved in the discussion. Without those triggers I wonder how many threads there would be in our treasured fora????
I just don't like "snark". I much prefer information that helps the now foolish become less so. Anybody that hasn't seen the improvement in the "average" stunt flier since the advent of the forums just hasn't been paying attention...to say nothing about those way above average types that are currently kicking some pretty serious "good old boy butt" of late.
Ted
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My definition of a valuable post is that somebody can read it in English he understands and employ the information in a positive manner to improve his performance at the flying field. Snarky criticism in and of itself seldom fulfills that standard.
I agree, it can't hurt any of us to learn more precisely accurate descriptions/definitions, etc. of aerodynamic subjects but, it is my belief, that any attempt to point out the technical fallacies of a given post should include helpful commentary to not only illuminate the fault but to advise what is accurate and what the enhanced effects might be at the flying field from employing the technically esoteric but precise terminology as opposed to the apocryphal language of the lay pilot.
I have read a lot of expert advice on these fora that I flat out don't understand. For example, I never learned what stunt people mean by "power", nor if they all mean the same thing. I only knew they didn't mean power. What if the writer and reader don't have the same private definition? There is no place the reader can look it up. In such a case, no, I can't include helpful commentary, because I don't know what's being said. You think I should just shut up, but I figure if a guy with more background in flight mechanics than the usual reader can't make heads nor tails about some flight mechanics advice from an expert stunter, he might do a service to his fellow readers by saying, "Huh?". I don't think I'm the only person who doesn't understand. We agree that it's best to use language decipherable to the non-cognoscenti. Instead of "lift", it's better to say "force perpendicular to the flight direction" or even something wordier if you need to be more precise. We evidently disagree whether it's OK to use a technical term not to mean its standard definition, but to mean something we're guessing that the reader thinks is its definition. If the reader has a different definition than you're guessing, or if he looks the term up in a book or on the Internet, he won't understand what you mean. If one uses a technical term, it's easy enough to look it up to see if it's what he thinks it is. Heck, I just looked up "cognoscenti".
Also, I don't think that all these posts should have to be universally accessible. I have learned a bunch from Igor, Frank Williams, etc. here, talking cognoscenti talk. Sparky thinks we should take such vile language to the Engineering board, which is OK with me.
Meanwhile, I could be nicer, but it's against my nature.
Snarker in Chief
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Mark,
Although your points are well taken, taken literally they pretty much eliminate everyone from participation on the forums besides Howard, Igor, Brett, Serge and maybe a couple of others.
While if, like Brett, they can do so in language decipherable to the non-cognoscenti, such a site might be more valuable from a precision standpoint it would also be pretty much a bore since--without the foolish commentary which generates the high brow responses--there wouldn't be much to read. Almost all of the wisdom which arises in these threads is the result of responses to the "foolish" input from people who just like to be involved in the discussion. Without those triggers I wonder how many threads there would be in our treasured fora????
I just don't like "snark". I much prefer information that helps the now foolish become less so. Anybody that hasn't seen the improvement in the "average" stunt flier since the advent of the forums just hasn't been paying attention...to say nothing about those way above average types that are currently kicking some pretty serious "good old boy butt" of late.
Ted
I followed you up to 'non-cognoscenti', but I didn't know what you meant. So I stopped listening. ::)
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I am not sure, but I remember some text or may be NACA report showing several properties of yawed wing with sweepback (pressure distribution, CP position, bending moment etc ...). I think somewhere in conclussion was written that sideslip does not make expected sidewise shift of centre of pressure. Additionally we are flying circular path, it can also change situation as the effective span make speed differences on tips lower. It will be nice to make some simulation and find real center of pressure with reaspect of side wind on circular path.
I just looked at the ancient NACA Report 1098 that I keep referencing, and indeed that's what it says. The authors recommend that those data be used only to extrapolate from characteristics of airplanes for which there's wind tunnel data, and that they give the largest change to be expected. I have done some experiments with combat planes. The sweep effect exists, but I haven't quantified it.
The effect of side slip also varies with angle of attack.
The 1098 data show it as proportional to angle of attack. So on a windy day, flying a great circle path on the upwind side of the circle is probably safe, but you might not want to do either inside or outside loops upwind.
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Howard. Help!
On my new plane I lengthened the nose moment, added power, and now it doesn't track good.
Now what do I do?
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Good point. I forgot about that one. To cancel that disadvantage, you'd need to bump up the aspect ratio of the rectangular wing a little, which would add even more structural weight. I look forward to hearing your elliptical thoughts. Elliptical wings look so cool.
You're messing with me, aren't you, Col.?
Hi Howard,
Regarding the first point above, we are talking about stunt ships with elliptical wings. I agree. Elliptical wings do look good. Years ago, I had a series of these things and I had some of my initial successes in competition with them. I definitely have some thoughts about them regarding CLPA. (There are photos from the 60's recently posted in another section of this forum but since this is a thread on LE sweep, there is no need to post them here.) This can be a subject we can discuss some quiet evening coming up in August. (I tried to get on that same airplane with you out of Chicago.) I also have some comments about stunt ships with "higher" aspect ratios than usually seen on our CLPA airplanes, something else outside the scope of this thread. I also have comments about stunt ships with wings with more sweep back than usually seen out our CLPA airplanes, something else outside the scope of this thread.
Now the other comment was in regard to my term "equal moments". Given the technocratic perfection of this thread, I guess I should have known better than to use that term when I was trying describe a hypothetical pair of CLPA models that only differed in taper ratio. They were to have equal spans, equal weights, equal wing areas, equal tail areas, same power plants, and same trim for flying the best pattern (if that can be achieved). AND, they were to have equal nose lengths (measured from "some technically acceptable reference point on the wing to the nose) and equal tail lengths (measured from "some technically acceptable reference point on the wing to another acceptable reference point with respect to the horizontal tail). I carelessly called out that this otherwise identical pair of CLPA models except for taper ratio would have equal moments. (Also, to save you the bother of pointing out that there could not really be such a pair of "identical stunt models except for taper ratio", I am fully aware that the differences in airfoil percentages because of the differences in the root chords and differences in the tip chords cannot be fully accounted for as being "identical". So forgive me for not being as descriptive as I should have been when I called for "equal moments". But my "opinion", not based on any hard data, is that the CLPA airplane with a "typical" taper ratio found on our stunt models (say around 0.7) will perform the CLPA pattern better than the otherwise similar CLPA model with no taper. At least, it has been my experience that it is easier for me to fly a better pattern with that.
Keith
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I followed you up to 'non-cognoscenti', but I didn't know what you meant. So I stopped listening. ::)
Cognoscenti? I thought this thread was about aerodynamics, not sniffing gears!
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Hi Ted,
Yeah. I think Dan's plane flies pretty well. The Vista. Even looked good a few years back. We dig the the thirties pylon racers. Most of them had rectangular wings with Carl Goldberg looking Buster tips. Looks good to us. A Brown B2 with swept back leading edge. Ugh.
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Hi Dennis,
FWIW, Bob Hunt once judged a flight of my Johnson "little s" powered Chief at a VSC and told me years later it was one of the better flights he had ever judged. Nothing much straighter than a Veco Chief leading edge!
My Imitation was the best airplane I ever designed to fly well easily and it had the least taper of any of my designs (save the very straight winged Doctor/Medic EMT designs). None of my "competition ships" had so little taper because it looked ugly. Didn't say I was smart, did I!!!
Ted
Based on this input, I just measured my Skylark I used at VSC last year. It has a 1/4 chord that sweeps aft 0.8 degrees. That's not much, and it flies well.
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I just looked at the ancient NACA Report 1098 that I keep referencing, and indeed that's what it says. The authors recommend that those data be used only to extrapolate from characteristics of airplanes for which there's wind tunnel data, and that they give the largest change to be expected. I have done some experiments with combat planes. The sweep effect exists, but I haven't quantified it.
The 1098 data show it as proportional to angle of attack. So on a windy day, flying a great circle path on the upwind side of the circle is probably safe, but you might not want to do either inside or outside loops upwind.
OK, I found it after all, now I read it and I see it is not so consistent for example CP does not move sidewise but rolling koefficient is positive ... probably needs more reading ... may be later
http://naca.central.cranfield.ac.uk/reports/1955/naca-rm-l54k15.pdf
Yes I understand what you mean and I agree it should be so, but that report says something else, that is what I wanted to point out
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Howard. Help!
On my new plane I lengthened the nose moment, added power, and now it doesn't track good.
Now what do I do?
Now, when I read this thread, I learned you need more lift ... VD~
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I followed you up to 'non-cognoscenti', but I didn't know what you meant. So I stopped listening. ::)
Sorry, Curare. One of my lifelong pleasures has been looking up interesting sounding words I don't know the first time I see/hear them and afterwards often try to use them appropriately when the occasion arises. Sort of a hobby, like building stunt ships. Most of the world finds stunt boring as well and also looks the other way when they see grown men playing with their funny looking toys (unless, of course, the toys are built by companies with fancy names like Apple, Callaway or Porsche, that is! y1 #^ n~)
Ted
p.s. Cognoscenti are "people in the know" on some, often arcane, subject. With the "non" attached to it, of course, the implication is the reverse...sort of the condition into which this thread has devolved. My actual thought was that, without those whose knowledge base is empirical (based on, concerned with, or verifiable by observation or experience rather than theory or pure logic[per a Google search]) rather than book l'arnin', Sparky's pages would be pretty barren. It is their empirical (if technically flawed) observations that drag the Cognoscenti off their lofty perches to enhance the the manner in which the empirically trained refine their understanding and, ultimately, improve the manner in which they inform others. Sort of a classic win, win arrangement.
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I have read a lot of expert advice on these fora that I flat out don't understand. For example, I never learned what stunt people mean by "power", nor if they all mean the same thing. I only knew they didn't mean power. What if the writer and reader don't have the same private definition? There is no place the reader can look it up. In such a case, no, I can't include helpful commentary, because I don't know what's being said. You think I should just shut up, but I figure if a guy with more background in flight mechanics than the usual reader can't make heads nor tails about some flight mechanics advice from an expert stunter, he might do a service to his fellow readers by saying, "Huh?". I don't think I'm the only person who doesn't understand. We agree that it's best to use language decipherable to the non-cognoscenti. Instead of "lift", it's better to say "force perpendicular to the flight direction" or even something wordier if you need to be more precise. We evidently disagree whether it's OK to use a technical term not to mean its standard definition, but to mean something we're guessing that the reader thinks is its definition. If the reader has a different definition than you're guessing, or if he looks the term up in a book or on the Internet, he won't understand what you mean. If one uses a technical term, it's easy enough to look it up to see if it's what he thinks it is. Heck, I just looked up "cognoscenti".
Also, I don't think that all these posts should have to be universally accessible. I have learned a bunch from Igor, Frank Williams, etc. here, talking cognoscenti talk. Sparky thinks we should take such vile language to the Engineering board, which is OK with me.
Meanwhile, I could be nicer, but it's against my nature.
Snarker in Chief
Howard,
No way do I think you should shut up. You and a few others bring informed expertise that is bullion for those who would excel at things aerodynamic.
Which is exactly why you should write informative articles on the subjects which would inform rather than inflame those who share your passion for model aircraft but lack your excellent technical background. If you were to do so, however, I would encourage that you utilize language which those who could value from your contributions can understand and recognize that, at the average age of those readers, are unlikely to be willing to go back to school for five or six years to learn the prerequisites for understanding at the level with which you are prone to inform. Tough to do but not as destructive to the common weal as belittling competent modelers whose real world expertise hasn't been devoted to the subject they find of interest--yet who like to opine on their empirically learned wisdom. More or less the idea behind special interest web sites
Your thought of a devoted board hosted by and restricted to commentary from the people you mention would be an excellent way to go about providing that information. I bet Sparky could be talked into providing the access and necessary band width or whatever it takes. It would also put all of the valuable information in a single location which would simplify access to those who truly want to understand how these things work. I encourage you to initiate discussions that would turn your idea into reality.
You might want to include an "in only" mail box for readers to ask questions from which you could choose the subject matter for each resulting commentary. When I wrote the (most likely incorrect) column for Model Aviation for four or five years questions from readers were my primary source for subject matter. Might be equally valuable for your Expert Panel.
Ted
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I have to look up "snarky".
Having read all the criticism and pseudo criticism last night, I spent a couple hours typing a post to meet the criteria requested. I defined key terms in this thread, pointing out those that are misused and the mistakes to which they lead. I stated why they were necessary to understanding. I then stated precisely as I could what was relevant to stunt design and trimming and their relation to sweep. I did not post for the following reasons:
1) I realized I'd already posted this information before.
2) It was too long.
3) I just didn't give a darn anymore after reading all the flack above.
SK
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" Quote from: Paul Walker on February 25, 2014, 09:33:37 PM
Howard. Help!
On my new plane I lengthened the nose moment, added power, and now it doesn't track good.
Now what do I do?
Now, when I read this thread, I learned you need more lift ... Devil "
LOL I thought that more practice was in order !! :-)
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Serge,
Snarky: "Testy or irritable" according to my Websters Unabridged Dictionary. H^^
PS: I don't know about the rest of the readers but I'm "IMAO" at this column. And I'm learning something (what I don't know) about airplanes..............No, people! LL~
Jerry A.
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looks right flies right
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Based on this input, I just measured my Skylark I used at VSC last year. It has a 1/4 chord that sweeps aft 0.8 degrees. That's not much, and it flies well.
Hi Paul,
I expect that was a "needle"...to which my only mea culpa excuse would be that Dennis was asking only if stunt ships with essentially constant chord (non-swept leading edges per the original subject of the thread) could not be competitive with their more aesthetically pleasing cousins. To which I provided examples of very good flying airplanes that didn't conform to the swept leading edge norm. My way of saying heck yes they can be competitive.
Here I tend to agree with Howard. I think tapered and/or swept back leading edges are ubiquitous simply because, to the vast majority of us, they look better. Oh, another good flying essentially constant chord airplane was Bob Emmett's Howard Ike which is, like the airplane's Dennis favors, a classic Gee Bee era racer.
Ted
p.s. Yes the Skylark flew well. My best guess is that it would only take .02 degrees less sweep to optimize its response rate as biased by Coriolis force, thus allowing maneuvering flight at greater than 4 seconds per lap VD~ H^^.
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Hi Paul,
I expect that was a "needle"...to which my only mea culpa excuse would be that Dennis was asking only if stunt ships with essentially constant chord (non-swept leading edges per the original subject of the thread) could not be competitive with their more aesthetically pleasing cousins. To which I provided examples of very good flying airplanes that didn't conform to the swept leading edge norm. My way of saying heck yes they can be competitive.
Here I tend to agree with Howard. I think tapered and/or swept back leading edges are ubiquitous simply because, to the vast majority of us, they look better. Oh, another good flying essentially constant chord airplane was Bob Emmett's Howard Ike which is, like the airplane's Dennis favors, a classic Gee Bee era racer.
Ted
p.s. Yes the Skylark flew well. My best guess is that it would only take .02 degrees less sweep to optimize its response rate as biased by Coriolis force, thus allowing maneuvering flight at greater than 4 seconds per lap VD~ H^^.
Roger that Captain!
Gee, I thought classic planes were supposed to fly fast. Dang, another thing I got wrong!
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p.s. Yes the Skylark flew well. My best guess is that it would only take .02 degrees less sweep to optimize its response rate as biased by Coriolis force, thus allowing maneuvering flight at greater than 4 seconds per lap VD~ H^^.
Well now, we need to better understand the impact of the polar vortex coupled with the variables created by electric motors and all of those pesky electrons that envelop the model when being driven by either left hand or right hand props. It really becomes necessary to optimize LE sweep-back and to tailor that with the LE radius of the horizontal stabilizer. Maybe deBolt was on to something with his 80 mph Stunt Wagon with its short "moments".
Keith
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I was going to post again but had a senior "moment" and forgot what I was going to say. HB~>
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Ted I was with you all the way, but I was indulging one of my hobbies, which is making asinine groanworthy jokes to lighten the mood.
As a bit a layman, I can tell you that discussions on this board occasionally stray from my realm of knowledge, but if that happens, I only have to do some googling and I can find enough information to peice together the crux of the argument.
As an engineer it does make things difficult if the nomenclature used is incorrect or misleading.
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Ted I was with you all the way, but I was indulging one of my hobbies, which is making asinine groanworthy jokes to lighten the mood.
As a bit a layman, I can tell you that discussions on this board occasionally stray from my realm of knowledge, but if that happens, I only have to do some googling and I can find enough information to peice together the crux of the argument.
As an engineer it does make things difficult if the nomenclature used is incorrect or misleading.
Curare,
No worries. Your point (and Howard's) is well taken but the underlying problem is pretty much irreparable.
The problem arises due to the unintended but no less effective development of an "arcane" language among the handful of stunt devotees around the world who, over a period of 70 or so years, have used certain words in a consistent fashion, notwithstanding their meaning in the language used by others (engineers, for instance) that has become accepted and understood by the "tribe". That these meanings differ from the meanings ascribed by other tribes is pretty much irrelevant (a huge percentage of words in the nominally "English" language have, over time, assumed a variety of meanings that must be understood via the context in which they are used. Power, for instance is used to describe a force, a deity, coercion and, almost certainly others that don't come immediately to mind. All meanings correct in their context.)
Just because stunt fliers are a small tribe doesn't make the words in their "language" wrong. Their words mean nothing more than what the tribe knows them to mean. It's not surprising that those whose mother tongue is different can find the stunt tribe's definitions irritating but it means nothing more than they aren't yet conversant in the tongue (or prefer not to speak the language which is, of course, their right).
In stunt, IMHO, it is important to note that George Aldrich, who wasn't to the best of my knowledge an aero engineer, pretty much wrote the code for the tribe with the Nobler 60 or so years ago and, despite subsequent language difficulties, not a great deal of importance has been divined since. Every top stunt ship all these years later is pretty much a thinly disguised Nobler, whatever the pedigree of the "designer"...and I happily include myself among those who has poached on George's territory in print.
It hardly seems necessary to me to excoriate one another because we don't all speak the same language when those with the greatest speech impediments are often perfectly capable of beating the socks off of our Stunt Shakespeares.
Ted
*(Arcane definition: known or understood by very few; mysterious; secret; obscure; esoteric: She knew a lot about Sanskrit grammar and other arcane matters.)
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Well now, we need to better understand the impact of the polar vortex coupled with the variables created by electric motors and all of those pesky electrons that envelop the model when being driven by either left hand or right hand props. It really becomes necessary to optimize LE sweep-back and to tailor that with the LE radius of the horizontal stabilizer. Maybe deBolt was on to something with his 80 mph Stunt Wagon with its short "moments".
Keith
Exactly, Kernel! See you soon.
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Cognoscenti? I thought this thread was about aerodynamics, not sniffing gears!
Actually, Tim, Cognoscenti is an Italian wine. A pink, I think. n~ n~
Ted
p.s. That's probably not true; although I don't speak Italian so who knows?
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Serge,
Snarky: "Testy or irritable" according to my Websters Unabridged Dictionary. H^^
PS: I don't know about the rest of the readers but I'm "IMAO" at this column. And I'm learning something (what I don't know) about airplanes..............No, people! LL~
Jerry A.
Thanks for the def. I hadn't looked it up yet. You probably already know most of what there is to be learned about people here. Ha! Now that I've finished glassing my model with 45o bias weave and epoxy and made the annual mess, I'll have time to work off the irritability in sanding,...and sanding,...and probably sanding. That's before I sand through something and fix it, but sometimes that doesn't happen ('didn't happen on a few occasions recently).
Well, I should get a little bit "on topic." So a remark: I think that a well-conceived and built plane with a "Hershey-bar" shaped wing can stunt just fine. However, as I and others have posted from time to time, there are advantages to tapered wings that often outweigh their disadvantages, especially as models increase in size. Keith covered at least two of them. Another tapered-wing advantage that is more or less epitomized by the elliptical wings is resistance to lateral gust upsets. Tapered wings also probably recover from yaw quicker and I think (Howard will correct me, I'm sure) have less yaw-roll couple. That means that I think that the tapered wing will roll less with a given yawing motion (Howard?).The strange thing about leading-edge sweep is that despite its drawbacks and those of any concomitant wing sweep, mentioned above, it does accomodate spanwise-straight trailing edges, which some reports I've read indicate increase the efficiency of given wings. If the designer can get past the elementary mistake of picking a.c.'s and/or c.g.'s from just looking at the root, there are interesting compromises possible. Also interesting - to me anyway - is that the calculation of MAC and a.c. for elliptical wings at any sweep is much easier than for straight tapered wings, although you can easily have the a.c. and MAC calculated at sites on line, as has been posted often. That's what I do.
SK
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Roger that Captain!
Gee, I thought classic planes were supposed to fly fast. Dang, another thing I got wrong!
Don't get too down on yourself, Paul. What the heck, you've gotten a few things right over the years. Glad I could help you out on this one. H^^
Ted
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"Moments"
Howard,
Now I am really lost. Reference is made to the most recent issue of Model Aviation, , March 2014. page 126 for the "FF Sport" column. There is a photo of a stick and tissue FF Scale model of the Vindicator. Included in the caption is the statement "It has good wing area and MOMENTS..." (Emphasis added.)
Gad, what on earth does that mean? Surely, FF guys understand appropriate terminology used in aeronautics.
Keith
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I dunno Keith. I have my good moments, too. Mostly on the practice field -- I'd like to have more of those good moments in official flights.
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I dunno Keith. I have my good moments, too. Mostly on the practice field -- I'd like to have more of those good moments in official flights.
Tim,
Exactly my point! #^ #^
If every word had only one definition, Webster's voluminous volume would be a puny pamphlet. y1 y1
Ted
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Exactly my point! #^ #^
If every word had only one definition, Webster's voluminous volume would be a puny pamphlet. y1 y1
Actually I think it'd be way bigger, and there'd have to be a "word inventor guy" in every community.
Either that or we wouldn't fly model airplanes -- we'd be flying "well they're not really birds but they're more like little toy wagons that fly through the air, y'know".
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Hehehe, you'd be suprised how many languages call aircraft "flying things" :D
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...
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Dang. I look for an insightful post by one of the reliable model-techie types, and instead I find that some idiot has pulled the thread off topic.
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(http://media.tumblr.com/tumblr_lsx3v0sb4x1qzbl7f.jpg)
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Mark,
Although your points are well taken, taken literally they pretty much eliminate everyone from participation on the forums besides Howard, Igor, Brett, Serge and maybe a couple of others.
While if, like Brett, they can do so in language decipherable to the non-cognoscenti, such a site might be more valuable from a precision standpoint it would also be pretty much a bore since--without the foolish commentary which generates the high brow responses--there wouldn't be much to read. Almost all of the wisdom which arises in these threads is the result of responses to the "foolish" input from people who just like to be involved in the discussion. Without those triggers I wonder how many threads there would be in our treasured fora????
I just don't like "snark". I much prefer information that helps the now foolish become less so. Anybody that hasn't seen the improvement in the "average" stunt flier since the advent of the forums just hasn't been paying attention...to say nothing about those way above average types that are currently kicking some pretty serious "good old boy butt" of late.
Ted
Ted,
respectfully,, were people to take a few minutes to understand the accurate usage of the words a great deal of the "snarky" responses would be eliminated. Most come from the misuse rather than any inherent snarkyness of the writers.. I agree some people can describe things using "non technical " terms,, but usually it leaves more room for missinterpretation.
I dont see how using proper verbage would eliminate anyone from the discussion, it would allow more people to communicate since we are talking apples and apples,, If you call me to ask why your pictures are so dark, and I ask what aperture and shutter speed you are using,, and what your ISO setting is,, and you say,,k I push the button on the camera and it goes click, but the number is 60,,, how on earth can I help you,, relatedly,, ISO on a camera relates to the sensors gain ( light sensitivity) but in other worlds it means "in search of" so you do have to use the right terms in the right place,,
and as a gentle nudge, S?P, your use of non-mainstream words of the 5 dollar variety could be taken in the same way using proper aero terms is,, IOW,, if ya dont know, look it up and enhance your knowledge.. I always enjoy reading your posts because most times there is a word that forces me to use google at least once,,
The same holds true for Igor, Howard and some others,, they discuss something and it forces me to use my brain to understand,,( and google) and that is a good thing..
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I like snarky. Like the old aftershave commercial. Whack whack wake up.
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Sooo, getting back to sweep, it seems like we do this for looks and either way works. I'm ok with that because the "look" adds or detracts from the illusion of the maneuvers.
What about airfoil thickness tapper? If you are at 18% root thickness what happens aero wise if the tip is 20% or 10%? How far can you go? I had a wing that my uncle built in the 50's that was 2 1/4" at the root tapered to 3/8" at the tip. It looked cool but how would that work for todays designs?
Best, DennisT
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Dennis I built something like that as a teen but as a combat ship. It turned like a demon due to the thick center section generating gads of lift but had little roll stability. If not careful engine torque could try to roll it. I learned then to keep the tips at least equal to, if not thicker by percentage than the root so that the tips don't stall first. One must also be mindful of where the high point occurs by percentage in relation of root to tip.
Dave
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Sooo, getting back to sweep, it seems like we do this for looks and either way works.
I agree that either way works well, but the question should be what works best for what purposes.
I re-read the whole thread and realize that my last post was somewhat redundant in that the point about taper moving the a.c. inboard had already been addressed quite early by Howard and maybe Keith. Anyway, I think this point is valid and makes taper relevant more than just aesthetically. I remember the old Smoothie ads referring to "windy weather" performance, and I have talked to others who feel that their more elliptically shaped wings are more stable (for Howard, 'less prone to upsets' or 'prone to milder upsets') in gusts. To me that seems to be because the elliptical wing has the furthest inboard a.c. of any normally accepted wing. Also I note that the more extremely tapered designs like the "Firecracker" are prominent at the top of the lists in Australia. Note also what elliptical and highly tapered wings have been on top in classic there.
So here are more extreme examples of useful taper. I hope that you'll forgive my using borrowed internet-posted pictures, a couple from Stunthangar members. The first picture shows a straight-tapered wing with the same a.c. position as an equivalent elliptical wing superimposed on a "Firecracker". The second is the Bond "Bandolero", with extreme taper. The third shows the 2013 Classic winners "down under": Palmer T-Bird, Rondinelli "Venus", and extreme-tapered Aldrich "Magnum." Configurations may be coincidental due to other reasons (Bob Palmer is quite popular there), but I think it shows that the accelerated-taper elliptical wing is very much at home in that element.
edit: I've added a final picture of my short-lived high-aspect-ratio model from 2007, which featured a highly tapered wing. It flew better than I expected in mild gusts for an Aspect ratio of over 6:1
I usually double taper mine in order to ensure that section thicknesses remain constant or increase just slightly spanwise for the reason stated above and for consistency.
SK
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I like waking up feeling ignorant, even a little stupid. Means there's something to try and figure out. Think about. It's the action of trying that feels good.
Well Dennis I too wake up feeling ignorant, and even a little stupid. Except I won't say that I like it! But like you I try to think about whatever I'm thinking about and to figure things out. Sometimes I succeed.
Mike, I like swept leading edges too!
Topic is a good one.
If this were a pissing contest, Howard and Brett the winners! Serge, start your @#$^%^(*&^%$ UPHILL!!!
Doug
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This is credible. The optimal amount would be that which makes the plane look coolest.
I Dissagree . it Should look @#$% Hot .
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If this were a pissing contest, Howard and Brett the winners! Serge, start your @#$^%^(*&^%$ UPHILL!!!
Doug
Hmmm... 'have to admit, having awakened not feeling particularly brilliant this morning, I have no idea what this means. Was there a pissing contest back in 2014? What does the rest mean?
SK
Edit: Oh, wait! I just re-read what I wrote myself. Ha! Now I know what it means. 'still not fully aware of the quote's intent in new context, but at least I know what I meant by my part. Thanks for reading.
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One thing I don't believe anyone mentioned is wing thickness at center and tips on the tapered wing and a non tapered wing. Most but not all tapered wings have thinner wings at the tip than straight wings do. I think this seems to help our models with tapered wing fly better then straight wings. When I used the term tapered I am meaning leading edge sweep. Models like the Juno and a well known Australian model have sweep in both the leading edge and trailing edge and have very thin tips. These models seem to have very good all around performance but especially in the wind.. My conclusion from my experience is leading edge sweep ON FLAPPED MODELS does fly better than straight wing models.
That is my answer to the original question. ~^
NOTE In the answer above I used the term "I" meaning it is my personal feeling not a proven answer.
Ed
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oops
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I would like to know why most stunter wings have leading edge sweep and what would be the optimum amount.
Juan
Just copy ThunderGazer.
MM