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General control line discussion => Open Forum => Topic started by: Mike Griffin on November 29, 2022, 09:04:51 AM
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What is the difference between a swept back leading edge and a straight leading edge in respect to how a model will handle or perform? Most of the modern stunters have swept leading edges and there must be a reason but I am not sure as to why. When I got back into flying control line a few years ago, I built a Pathfinder which has a straight leading edge and a trike gear and it flew very well. Joe Gilbert can perform miracles with a Ringmaster but if you remove the pilot from the equation, what is the design advantage to the swept back compared to the straight?
Mike
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The swept wing looks cool. The aerodynamic comparison is complicated.
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In George Aldrich's article abut his Nobler,he said it was for stability, as opposed to the Chief wing, which is the basis for the Nobler, his words not mine. See his interview. D>K
I'll agree with Ty here, and I will add that in my years of reading I have read the theory that a swept leading edge of a certain number of degrees will have the same stabilizing effect as as certain number of degrees in dihedral. As I was coming along from my beginnings in stunt, I remember discussions and articles about a swept leading edge will turn better than a straight leading edge, and the stabilization factor works into how well a model will lock back into level flight also. One design that I can think of where leading edge sweep is towards the excess side is the Skydancer that I used to see at VSC every year. I think it was a popular southwest design back in the day. I think Windy explored this with his Sidewinder design, and it was a pretty steep leading edge sweep along with being fairly low aspect ratio. Four inches is what comes to mind on the sidewinder as far as how much sweep it had. There have been several classic stunt and combat designs that were almost jet like in appearance , the Super Sweep being one I think that Walter Umland made a few kits of. I think that most modern designs that have some sweep have settled into the 1 to 2 inch range or some variation, just judging from how they look. When you go too far then lead out position tend to get tricky when building the wing and then exiting the tip at a good spot. I think we all have some favorite model that has a constant chord wing that flies well and is easy to build because all the ribs are the same size except for allowing for sheeting purposes. That's my take on the situation.
Type at you later,
Dan McEntee
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I believe the most important thing you need to know about tapered/vice "straight untapered" wing configuration is more basic...basically, that the fore/aft location of "the wing" is where the "mean aerodynamic chord" is located. This (the MAC) is roughly the point at which "lift" is "felt" by the airplane. As the taper increases the location of the MAC moves toward the fuselage. Here is a link I cut and pasted from a search for it ("How to find the MAC (mean aerodynamic chord of an airfoil").
The "MAC" is the fore aft location of where the plane "feels" the lift to be generated with respect to the entire aircraft...not where the wing "plugs into" the fuselage!!! Thus, much of what the designer/builder/pilot of a stunt ship must consider when designing, trimming etc. of a "new" design must take into account where that "MAC" is located.
Check out that link I provided to see if that clears up your questions. Although I've flown airplanes as diverse as small hand launched gliders to a "full of folks and fuel" B-747 I am not a trained aerodynamic wizard and am reluctant to pontificate much beyond that basic info above, but...I'm pretty sure the reason for tapered wings is related more to structural integrity and aspect ratio performance issues than "stability". What taper does do is bring the center of lift closer to the fuselage which is likely valuable with respect to roll control in turbulent weather.
Let's see if some of the guys with expertise want to modify/add anything.
Ted
p.s. Just as an FYI, a straight/untapered wing, by the way, is known as a "constant chord" wing.
pps: Just a guess here but I expect the fact the tapered wing brings the MAC (the spanwise center of lift per wing) closer to the fuselage for the same amount of wing area reduces "roll axis" stress in crosswinds and, since we fly in circles that include direct crosswinds twice every lap they will be less likely to wag the wings at the pilot twice each lap.
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Unless the straight wing plane truly has no tapered flaps attached like on a Jamison, Humongous, Skyray, Doctor, Medic, then the tapered fixed flaps on a Flite Streak or moveable tapered flaps on the Pathfinder, and Twister, create a swept wing...Forward swept.
The quarter-chord line which includes the flaps, sweeps forward root to tip.
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One thing I noticed with straight leading edges , is in slightly bumpy or slightly gusty air , the tips move - yaw - bounce - rock , a trifle .
Which can be good , as it is indicative of the imediate atmosphere to the model aeroplane . Might be called ' feedback ' even .
Like felling lumps bumps & ripples with stiff old motorcycle suspension , triumph ducati & the like . Where the soft wallowy ones absorbe it and twist and weave and swerve all over the place ,
being Hondas .
SORRY . ;D
The ' SWEPT ' Ive seen refered to as lateral or longitudeinal DIHEADRAL . As in - it steadies the plane in YAW , also less apt to rock & drag the tips - weave , dutch roll etc .
SO ,, the Straight Wings good but untidy , and the swept smoother & tidier looking , but maight be less ' feedback ' in the imediate sense . :P
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Heavy Weather Sailing Tips - Control Roll, Pitch, and Yaw
CRIKEY , might be some applicable data / theories , involved , here . https://www.skippertips.com/public/2178.cfm
As in the air & ocean aint concrete , so they both move around a bit , and arnt entirely disimilar , being made by the same bloke . ;)
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My understanding and experience with leading edge sweep is it dampens yaw oscilation quickly and more smoothly than a straight leading edge. In good air you likely wouldn't tell much difference however in gusty conditions where the airplane is prone to "swimming" from side to side as it takes gusts from every angle it might make some difference. When in 'level' flight the airplane is flying at a very shallow angle of attack so the leading edge sweep will have something of a dihedral effect I think.
Dave
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Wing sweep is often misunderstood. It is an angle formed between the lines of the aerodynamic enters of wing panels, NOT the angle at the LE. A "rule of thumb:" the "aerodynamic center, or ac" of (at least a symmetrical) airfoil is at 25% of its chord (including any movable flap's chord.)
Consider a Ringmaster-like wing - say 11" root chord, 9" tip chord or so. Straight LE. Consider aerodynamic "tips" at the outermost rib... Root ac is 2 3/4" back of LE and tip ac is 1 3/4" back: the ac sweeps forward root to tip 1 inch.However, if ac is straight across from tip to tip: there's NO aerodynamic sweep. The root LE is 2 3/4" ahead of ac, and tip LE 2 1/4" ahead of ac. Sorta like a Mustang planform, no? A Ringmaster-type's ac does sweep, but it's forward sweep!
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" A Ringmaster-type's ac does sweep, but it's forward sweep!"
In gusty conditions the RM is probably the most stable plane you'll ever fly. Could we have missed something that was there all the time?
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" A Ringmaster-type's ac does sweep, but it's forward sweep!"
In gusty conditions the RM is probably the most stable plane you'll ever fly. Could we have missed something that was there all the time?
Hi Frank,
At my skill level, I really cannot tell a lot of difference in the way the model handles if I am flying straight or slanted (swept back) leading edge airplanes. I was just curious of what difference it made if you take the pilots skill level out of the equation. Guess I was asking a question regarding aerodynamics that, again, at my skill level really is not an issue. Let's take for example, a really skilled pilot flying expert. He has a choice of flying something like a Pathfinder or Ringmaster or a SV11 or an Impact. Based purely on the design of the wing, will the two models (say the Ringmaster vs SV11) handle differently (they probably will) and if so, why? I get lost a lot of times on here when technical discussions take place because I am not trained or skilled enough to really understand what is being said. Guess if was looking for something in layman's terms that would give me the answer to my question. Maybe there is no simple answer, I do not know.
Mike
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Hi Mike
Let me clarify a bit .... I didn't mean to imply that all along I knew that the "forward sweep" of a RM was the reason I perceived it to be more stable in the wind than other planes. Lou pointing out the forward sweep, registered with me as it might be the reason I liked the RM in the wind. I had thought it might be something to do with the elliptical tail area. Quite honestly I don't know why the RM is preferred in terrible conditions. Is is just the smaller size of the model compared to "fuller size" stunters that makes if better conditioned to gusts. The test of course would be maybe a junior nobler versus a RM. Match the size and eliminate size as a parameter. Better yet, compare a standard RM with an identical RM with the le swept and not the te. That might be an interesting experiment. I do feel, from my experience, that flying a standard RM in horrible conditions seems much easier than other planes. There have been people who have flown the larger (576) RM to a place on the FAI team when conditions deteriorated. Is it the sweep, or am I the only one who has noticed the stability of a RM in gusts?
Frank
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Hi Mike
Let me clarify a bit .... I didn't mean to imply that all along I knew that the "forward sweep" of a RM was the reason I perceived it to be more stable in the wind than other planes. Lou pointing out the forward sweep, registered with me as it might be the reason I liked the RM in the wind. I had thought it might be something to do with the elliptical tail area. Quite honestly I don't know why the RM is preferred in terrible conditions. Is is just the smaller size of the model compared to "fuller size" stunters that makes if better conditioned to gusts. The test of course would be maybe a junior nobler versus a RM. Match the size and eliminate size as a parameter. Better yet, compare a standard RM with an identical RM with the le swept and not the te. That might be an interesting experiment. I do feel, from my experience, that flying a standard RM in horrible conditions seems much easier than other planes. There have been people who have flown the larger (576) RM to a place on the FAI team when conditions deteriorated. Is it the sweep, or am I the only one who has noticed the stability of a RM in gusts?
Frank
I really appreciate the input Frank. This all makes for a very interesting discussion.
Mike
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Just to clarify, the original question was about leading edge sweep BACK. Not WING sweep forward. I would think that there IS a difference
Type at you later,
Dan McEntee
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I'd really like to hear what Brett has to say on this....
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Just to clarify, the original question was about leading edge sweep BACK. Not WING sweep forward. I would think that there IS a difference
Type at you later,
Dan McEntee
Thank you Dan. That is correct.
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Guess if was looking for something in layman's terms that would give me the answer to my question. Maybe there is no simple answer, I do not know.
(https://qph.cf2.quoracdn.net/main-qimg-eb45a00a93c76c8d435c0df25e94584f-lq)
IF the Max thickness was at , say , 33 % chord - at the root .
say , 25 % chord - at the tip .
IF it was a straight plank wing ( assume ) the center of lift would presumably angle forward going outward .
Around the 70's & 80's a lot of planes ran a differant root & tip airfoil percentage and high point percentage ( of thickness and chord distance )
mainly stated to stop or improve tip efficency ( avert premature stall ) and get less increased drag in turns .
This is where having the flaps stop prior to reaching the tip is tried as a effort at cleaner wake there , with less tip wobble .
(https://i.servimg.com/u/f18/19/07/72/97/tm/ringma36.jpg)
part of the stabilty / steadyness , is the ' MASS ' distribution . Area & Moment ( distance ) . Being About Even . Maybe a tad more forward , perhaps ? .
so sidewinds dont throw a yaw into the equation . Like the would if it only had one end ( effectively ) The TAPERED PLANFORM I think alows the air to
SQUEEZE the flight without catching on anything much .
So you dont get turbulent vorexes dragging it round .
Some dry summer days you can see wakes like you can sometimes see the shimmering of a thermal . And OBSERVE the wake etc etc . just .
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TO Dan's Post #14: I only mentioned the forward sweep of the wing bcause it is technically there. An oddity, that's all.
Leading edge sweep is usually small enough that it doesn't much matter - SIG Zlin, Skydancer and few others aside. For 'usual' flight and prop direction, large sweep and a sharp right yaw could 'present' a longer inboard panel span to the airflow than the 'foreshortened' outboard panel. That could shift more lift and associated drag towards the inboard panel... possibly showing as right roll and left yaw.
At an extreme that could resemble hinging: inboard wing roll up (in the 'lift" direction) and (likely less noticeable) nose yaw in. Disturbing if it happens, but usually very quickly done and ended. And there are many (usually) much stronger forces to restrain deviations.
Effect on Ringmasters? Most over the years have been fairly high powered and hefty for their size. Sweep alone - LE or whole wing - probably doesn't much matter. I haven't heard whether it stays true for the recent superlight editions. The fairly large side area may also be involved.
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Wing sweep is often misunderstood. It is an angle formed between the lines of the aerodynamic enters of wing panels, NOT the angle at the LE. A "rule of thumb:" the "aerodynamic center, or ac" of (at least a symmetrical) airfoil is at 25% of its chord (including any movable flap's chord.)
Yep. Sweep of the LE itself might be of interest in supersonic flow, but not for us.
For 'usual' flight and prop direction, large sweep and a sharp right yaw could 'present' a longer inboard panel span to the airflow than the 'foreshortened' outboard panel. That could shift more lift and associated drag towards the inboard panel... possibly showing as right roll and left yaw.
At an extreme that could resemble hinging: inboard wing roll up (in the 'lift" direction) and (likely less noticeable) nose yaw in.
I think that's a good way to look at it: the flow is more perpendicular to the upwind wing.
Dan mentioned the similarity between dihedral and sweep. Positive dihedral will roll the wing in the direction opposite sideslip (the angle the relative wind blows on the airplane). Sweep also rolls the wing in the direction opposite sideslip, but multiplied by lift: if you're flying a swept wing airplane downwind, it will roll out in both inside loops (+ lift, + rolling moment) and outside loops (- lift, - rolling moment) as if it has too much tip weight. If you do either an inside or outside loop on the upwind side of the circle, you'd be better off with forward sweep. Equation 7.64 of https://apps.dtic.mil/sti/pdfs/ADA319978.pdf shows the rolling moment effect of sweep. y/b is the spanwise location of the wing center of pressure that "Ted" mentioned. I think the other interesting thing about that equation is the use of capital lambda (Λ) for sweep angle.
Thereby hangs a tale. I always thought sweep is bad and wondered how the Skydancer and Don Hutchinson's F-86 worked so well. I spent the night at Tim Just's house on the way back from the February Tucson contest. Tim retires much earlier than I, so I stayed up snooping in his library. I found to my delight (and later stole) George Palmer's favorite textbook, Airplane Aerodynamics by Dommasch, Sherby, and Connolly. I came across the drawing below, showing that the prop blast has a negative dihedral effect that could cancel some of the effect of sweep. Wow. Engine offset makes it even more confusing.
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Before we take this thread too far into the weeds let's get to the real reason most of us use swept leading edges. They look cool.
Ken
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As a teen who tended to get buried in aerodynamics, I decided all that theory doesn't often apply to our tiny, slow aircraft. Stick with what works.
Fly Riley Wooten's constant-chord Demon and Sneeker (with some sweep) in a 25-mph wind and maneuver upwind. Concentrating wing area near the center of the wing will be an easy decision.
Dennis
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I'm trying to reach out to Chuck Smith who's an Aero Engineer he'll have an answer to swept vs straight leading edges. This time of year Chuck sometimes runs south where he Charter Captains fishing boats.
Steve
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I'm trying to reach out to Chuck Smith who's an Aero Engineer he'll have an answer to swept vs straight leading edges. This time of year Chuck sometimes runs south where he Charter Captains fishing boats.
Steve
I'd be interested in an engineer's analysis but wonder if theory isn't better applied to larger objects than our typical creations. Back in my college days I built quite a few combat models of varying shapes and sizes. In my own experience constant-chord wings are much less stable in the roll-axis, if you will, in strong winds. The higher the aspect ratio, the greater the problem.
As the saying goes: your own mileage may vary.
D>K
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A visual representation is always nice to illustrate what we are discussing.
I have attached a simple drawing showing the outline and quarter chord line of the basic flavors of wings often used in stunt.
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I believe the most important thing you need to know about tapered/vice "straight untapered" wing configuration is more basic...basically, that the fore/aft location of "the wing" is where the "mean aerodynamic chord" is located. This (the MAC) is roughly the point at which "lift" is "felt" by the airplane. As the taper increases the location of the MAC moves toward the fuselage. Here is a link I cut and pasted from a search for it ("How to find the MAC (mean aerodynamic chord of an airfoil").
The "MAC" is the fore aft location of where the plane "feels" the lift to be generated with respect to the entire aircraft...not where the wing "plugs into" the fuselage!!! Thus, much of what the designer/builder/pilot of a stunt ship must consider when designing, trimming etc. of a "new" design must take into account where that "MAC" is located.
Check out that link I provided to see if that clears up your questions. Although I've flown airplanes as diverse as small hand launched gliders to a "full of folks and fuel" B-747 I am not a trained aerodynamic wizard and am reluctant to pontificate much beyond that basic info above, but...I'm pretty sure the reason for tapered wings is related more to structural integrity and aspect ratio performance issues than "stability". What taper does do is bring the center of lift closer to the fuselage which is likely valuable with respect to roll control in turbulent weather.
Let's see if some of the guys with expertise want to modify/add anything.
Ted
p.s. Just as an FYI, a straight/untapered wing, by the way, is known as a "constant chord" wing.
pps: Just a guess here but I expect the fact the tapered wing brings the MAC (the spanwise center of lift per wing) closer to the fuselage for the same amount of wing area reduces "roll axis" stress in crosswinds and, since we fly in circles that include direct crosswinds twice every lap they will be less likely to wag the wings at the pilot twice each lap.
I have reached out to Chuck, hopefully he surfaces. Going back to Ted's earlier post above, he discusses MAC, the Mean Aerodynamic Chord as the point where the airplane feels the lift along the fuselage and not necessarily the point of intersection where the wing connects. I'm going to shoot from the hip here but the question of a swept vs straight wing brings to mind when swept wings began showing up. Lift and CG play a close part toward the stability of the plane. Drastically swept wings were for the most part showing up with the introduction of the jet fighter. Fighter engines were stuffed in the rear half of a fuselage resulting a very aft CGs. Doesn't it appear to over come this the rear sweep moved the MAC to accommodate the change in CG to maintain forward stability? There's much that goes into a wing's performance, especially understanding laminar and turbulent effects. Not having been schooled in aerodynamics and understanding Reynolds Number relative to a wing, the sweep, chord change, airfoil thickness and taper leaves me wondering if there really is a single answer to the question of the performance difference between as straight LE vs a rear swept wing. It is an interesting topic.
Now back to fighting my head cold.
Steve
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Hi Guys,
As Howard mentions (It's good to listen to Howard because he knows his stuff) unless we're getting transonic the leading edge sweep itself is probably the last thing that's going to affect a stunt ship at the speeds we fly. The main reasons we sweep wings is to get them clear of the shock cone and put the CG where we need it.
Other than that, it really doesn't matter. There are plenty of aircraft with swept-forward wings (I've flown one and I can tell you it handles exactly as an airplane should), generally done to control the CG with varying loads - the Blanik sailplane is a great example.
NASA also built the "scissor wing" plane which pretty much settled the sweep argument. In flight one wing was forward and the other backwards!
Taper is something different and has to do with induced drag and how efficient the wing is. In theory, an elliptical wing has the lowest drag for subsonic aircraft. In practice, however, and eliptical wing is expensive, complicated and sometimes too heavy to build. Good news though, is that a tapered wing can get pretty close to the efficiency of an elliptical wing. In aerospace engineering there's a little term we put in the drag polar equation for a plane called the "Oswald Efficiency Ratio/Coefficient" that accounts for how well the wing mimics an elliptical wing and is based on the taper ratio, aka the ratio of root to tip.
Dihedral is the most misunderstood phenomenon in aviation as far as I can tell. I've written some articles about it and apparently I'm not very good at explaining it without a lot of math - so I'll try a simple explanation. Dihedral affects Dutch Roll stability, i.e, how the aircraft responds, free of any control inputs, to a sideslip. Also, don't ask me what the Dutch did to get naming rights. Dihedral is really there to move the wing vertically towards the center of the fuselage. Again, sans math, if you look at low wing transports the wings go up and high wing transports the wing goes down. Small planes like Cessnas break this rule by having high wings and a little positive dihedral. This is for a practical reason - to have the fuel at the tank pickups. A Cub has the tank in the fuse - and hence no dihedral.
Now, all that said, there is a notable exception - tailless aircraft, something I spent a lot of time on. As previously noted by an earlier post, there is a yaw stabilizing effect to a swept wing. It's predictable and funny thing is here at my desk are some balsa hand gliders I built years ago to demonstrate there's an optimum angle for the wing sweep on a sub-sonic flying wing. I'd put up pics but given the latest in aircraft development they're probably considered ITARS controlled, LOL! You can throw them like a Frisbee, and they will instantly settle down to stable forward flight. But- this sweep angle is much more severe than we'd expect to see on a stunt ship.
As all this relates to Stunt - meh. Wing loading, tail volume, CG and thrust are paramount in my book. Airfoil matters a lot less than anyone will be willing to accept provided the leading edge isn't sharp. For a symmetrical wing the airfoil is mostly there to streamline the internal stucture. ALL symmetrical wings have the same lift curve regardless of thickness or shape. At the extreme ends of the curve they differ some but we don't operate there. Sweep is a non-issue other than too much and you have a CG problem.
IMHO, Al Rabe was the guy who figured out stunt airfoils back in the late 70's. In level (or straight vertical) flight the airfoil doesn't matter. What does matter is that there is as smooth an upper surface with the flap deflected as possible. Al was also the best builder I've ever had the pleasure to meet. We'd all be flying ships like his today if we could build them.
Summation:
1) If we all spent as much time actually building and practicing as we do posting on internet forums about aerodynamics we'd be up to our armpits is Bergers and Fitzgeralds.
2) It doesn't matter because there is no "perfect" stunt design. I've come to the conclusion that it's highly personal and what works great for me might not work for you. I've had others fly my ships and tell me they were "unflyable", yet I can still grease a decent pattern when I put mind to it. I've flown other people's ships and wonder how they even flew them level even though they did quite well with them. My best advice: build a lot, fly a lot, and figure out what works for you.
3) "Once in a while you get shown the light in the strangest of places if you look at it right" -R Hunter.
Peace out,
Chuck
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Sorry dudes, double post.
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... 2) It doesn't matter because there is no "perfect" stunt design. I've come to the conclusion that it's highly personal and what works great for me might not work for you. I've had others fly my ships and tell me they were "unflyable", yet I can still grease a decent pattern when I put mind to it. I've flown other people's ships and wonder how they even flew them level even though they did quite well with them. My best advice: build a lot, fly a lot, and figure out what works for you.
3) "Once in a while you get shown the light in the strangest of places if you look at it right" -R Hunter. ...
Great response Chuck!
My Crash Combat designs from 1958 pictured below - wings were a sheet of plywood with something of a Clark Y airfoil on top. As Duke Fox wrote to a friend several years ago after many complaints, "Quit worrying - go flying!".
The Reynolds numbers on our models are tiny ...
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It doesn't matter because there is no "perfect" stunt design. I've come to the conclusion that it's highly personal and what works great for me might not work for you. I've had others fly my ships and tell me they were "unflyable", yet I can still grease a decent pattern when I put mind to it. I've flown other people's ships and wonder how they even flew them level even though they did quite well with them. My best advice: build a lot, fly a lot, and figure out what works for you.
Kind of. This line of reasoning ("everyone is different and so find xxxx you like and practice till you can't stand up") is typically, or almost universally, used to excuse or rationalize not making necessary changes to get better. Based on my rather extensive experience, there is very little variation in "personal preference" among the most competitive, and all those things that make people think they have a special need is just a matter of not being willing to make the changes necessary to improve. Because in many cases, making this change might make you go backwards for a while.
You can't just learn to live with a weakness and try harder to overcome it, because someone else will try just as hard but not have as many obstacles, and beat you. You cannot "out-practice" anyone to try to work around a problem.
I note that you used Igor and David as examples of not wasting time on what you consider trivial discussions. Whether anyone knows it or not, you couldn't have picked two less applicable examples. Igor is well-known as one of the most sophisticated engineers in stunt, to the point that his controllers are the standard for electric, and what he is doing is so far beyond most people's understanding that he doesn't get enough credit. And having flown with David for the last 35ish years, and knowing his history, he had these discussions going back to when he was a kid, with Ted, Gary McClellan, and his father all having absolutely endless discussions about exactly these sorts of topics. Read the Imitation article, particularly part 1, to see how far ahead of the game they were even then. David grew up in that environment and while he doesn't spend a lot of time telling you about it online, thats because he knew the answer 50 years ago.
I have noted (and Ted has told us all for years) about flying other people's airplanes, and finding it amazing how well they do. That is not personal preference, that is a combination of overcoming flaws by brute force. That's swell, you can overcome some problems, but that doesn't mean that is the only way they can do it, or that even a small extra problem can be overwhelmed by more effort - because other people put in the same or more effort, and don't have a problem.
I have flown many *competitive* airplanes, that is, airplanes that win or finish in high positions in the NATS or Team Trials, from the most accomplished designers and trimmers. You know what you find - that they *all fly very much the same* and have no significant vices that you have to "overcome" or better suits someones "highly personal" preferences. You might expect that with Ted, David, Paul Walker, and I. We did a fly-around last weekend, David, Jim, and I - aside from slight neutral differences, no real vices and fly very much alike.
But, when Bob Hunt and I can fly each other's airplanes and they fly nearly identically, when we have *absolutely nothing* in common in terms of design history, natural talent, flying experience, that wouldn't be expected using the personal preference theory. Last time we did that, mine was a super-thick wing, medium-heavy wing loading, piped 61 airplane and Bobby's was a super-light electric with a wing half as thick. They flew the same. Bob has a 100x my natural talent, practices all the time. I can barely walk to the center of the circle most days and fly 100 flights a year, most of the time. I have done stuff like this a lot, there are *very minor* differences, but for the most part, everyone has converged on the same feel and response, there aren't any significant personal differences.
So, you are *sort of* right that the answers are pretty obvious with casual examination, the idea of "highly personal" characteristics is, frankly, about as wrong as it could be, and is almost always used to rationalize trying to trudge on without making any of the changes you need to.
Brett
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I recall a conversation with a local expert flier who said that a flap hingeline that was other than straight caused a LOT of trimming problems. The last design of his that I recall with swept forward flap hingeline was what I refer to as the "PW-51", way back in the Saito era. The two B-17's may also, but that was earlier, and I'm not sure about them.
My aerodynamic theories come from my years of competing in Free Flight, mostly F1A. Basically, a tapered wing results in a smaller tip chord and reduces the tip vortex, said to be a major cause of drag. It also happens to increase the aspect ratio, which was good for FF, but not so much for stunt, unless the root chord is increased. For stunt, I think the reduced tip vortex is a big deal, especially when flying in conditions where you have wake turbulence problems...like here. Flite-Streak-ish wingtips have become more popular, and should reduce the tip vortex further. Would look silly on a Hellcrate or Mig-ish, though they'd look normal enough on a Reno Racer type of decor. y1 Steve
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Ah Brett, never change, we love you.
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... So, you are *sort of* right that the answers are pretty obvious with casual examination, the idea of "highly personal" characteristics is, frankly, about as wrong as it could be, and is almost always used to rationalize trying to trudge on without making any of the changes you need to.
Brett
Ah Brett, never change, we love you.
Normally, I suspect you can take to the bank anything Brett posts here …
Many moons ago, I designed and built a very successful combat model. Quite a few flyers in the upper Midwest asked for plans, which were produced - and later, a foam wing version kit even surfaced.
Virtually everyone who built one complained it was nose heavy. I dunno … worked for me, is that a personal preference that works? They would have said the same thing about any of my other combat models … that routinely brought home the trophies.
Dennis
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Ah Brett, never change, we love you.
Uh, thanks. But this "personal preference", which might be true in the small, is definitely not true in the large, but it is a very easy way to convince yourself not to make the changes you need to, too. "My wrist is different" is a classic example.
Brett
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Normally, I suspect you can take to the bank anything Brett posts here …
Many moons ago, I designed and built a very successful combat model. Quite a few flyers in the upper Midwest asked for plans, which were produced - and later, a foam wing version kit even surfaced.
Virtually everyone who built one complained it was nose heavy. I dunno … worked for me, is that a personal preference that works? They would have said the same thing about any of my other combat models … that routinely brought home the trophies.
I know for certain that in stunt, one of the biggest traps is thinking as suggested - that you need something different from everyone else. Sometimes, people just don't know any better, practice until they get very good, without any references, don't know how much better it could be. When they finally get one flight on a good airplane, they are all over the place, and then convince themselves that this means that they are somehow a special case, and that they need whatever weaknesses their system has. In fact, it would take them some time to overcome the bad habits they have developed, during which they will feel very uncomfortable and not fly as well. But, if they continue on, they are going to get stuck.
It's very easy in stunt because it's so difficult to get things to work at all, that once someone gets something reliably through patterns in most conditions, they are very hesitant to change anything because it was so hard to get it even that good.
I will tell you and everyone else right now, you cannot "work around" even pretty small weaknesses or problems by brute force, because someone else will work just as hard. I can think of several hallmark examples that I decline to mention, not having a bomb-proof mailbox.
Again, it's just advice, no one has to take it. No one can say they weren't warned.
Brett
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I know for certain that in stunt, one of the biggest traps is thinking as suggested - that you need something different from everyone else. ...
Brett
The fallacy in that, Brett, is that some of us never thought much about what works for "everyone else" ... Personally, I gave a lot of thought to the way I wanted to fly, then designed and built accordingly. And my own personal observations over the years have convinced me lots of practice will beat aeronautical theory most days when it comes to our (extremely low Reynolds numbers) models.
Dennis
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The fallacy in that, Brett, is that some of us never thought much about what works for "everyone else" ...
I am not sure why you think that is a "fallacy", at least in stunt, it is *absolutely mandatory* to pay attention to and understand what other people are doing, why, and whether you can take advantage of it or not. Not necessarily copy, but know what they are doing and what effects it has.
You can get to be a pretty good local expert just using your own resources, that's what I did, and I would have won every local contest for the decade of the 90s if it wasn't for Ted Fancher. But winning a bunch of local contests isn't the goal, ultimately its about fighting it out with the best pilots to ever fly the event, and it is my considered opinion that you can't do without understanding how other people succeed - or fail.
As before, I am just giving my best advice and most considered opinion, I think it is worth something because I have managed pretty well over the years with what could be argued is the least natural talent of any NATs winner ever. I am not complaining about my lack of talent, because I am willing to admit to my limitations and do something about it.
Recognizing your own blind spots/weaknesses/demons and doing something positive to address them is even MORE important. And based on innumerable case studies over the years, including myself, pretty darn difficult.
Brett
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My best advice: build a lot, fly a lot, and figure out what works for you.
I took a different approach to stunt. I picked a design that was successful for somebody else, and that's all I've flown. I guess you're right. I've built six of them now and I still lost the Nats this year. Maybe I should try a Fierce Arrow.
The Reynolds numbers on our models are tiny ...
So finish that sentence you trailed off with an ellipsis and explain the implications of boundary layer physics to stunt stability and control. Specifically, show us how it invalidates the effect of sweep given by equation 7.64 of the above-referenced USAF document (or the analogous explanation of the textbook of your choice).
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Oh goodness, boys ... can you explain why an overweight, Fox 35 powered monster with a flat sheet of plywood for a wing can perform reasonably well? (Hint: it's not an F-104.)
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Oh goodness, boys ... can you explain why an overweight, Fox 35 powered monster with a flat sheet of plywood for a wing can perform reasonably well?
That airplane was competitive with known expert combat fliers (PTG, Howard, the Clevelands, etc) flying typical equipment?
Brett
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That airplane was competitive with known expert combat fliers (PTG, Howard, the Clevelands, etc) flying typical equipment?
Brett
Gosh Brett, I learned about 200 years ago as a high school wrestler that must of us put our pants on one leg at a time. Must we take ourselves so seriously? "known experts"?
Remember Chuck Yaeger flying the MiG-15 against an F-86 Sabre in mock dogfights? When the Sabre pilot complained that Yaeger always won with the MiG, they switched planes - and Yaeger kept winning, but with the Sabre.
When it comes to Combat, I'm betting those "known experts" could have won flying almost anything. Heck, I once won a combat match in practically gale-force winds flying a Ringmaster - with a Fox 35 up front and only the inboard wing for lift - by getting several cuts on my opponent.
My point is simply this: all the aeronautical theory in the world seems to me to have rather little significance when applied to our small vehicles. Your opinion may be very different, and that’s fine.
Peace. Have a great day!
Dennis
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I was at a combat contest today. Lots of planes. I didn't see anyone flying flat sheets of plywood. I guess empirically, since we are bashing science here, that still says that good airfoils work better. And by extension, that low speed aerodynamics are real physics, too. Of course, anyone was free to bring plywood as long as it had the required shutoff....
On the other hand, we have periodically run an "Orange Crate" contest here in SoCal. Guys have to quickly build whatever they can from supplied flat boards that could have come from an old orange crate. (We used to have lots of orange groves around....) The aero on one of those is pretty bad. But you can get them to fly with enough horsepower and the right handlaunch.
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LL~ LL~ LL~
Me thinks some here take the discussion much too seriously. After spending 7-1/2 years in a research lab, I'm not about to "bash" science. But I may point out its limitations. When existing "science" can't explain our observations, we simply change "science".
If I understand what some here seem to suggest, what is the perfect stunter? Surely if we all apply existing theory, there can only be ONE perfect stunt design. What is it?
Dennis
PS: Check out the aerodynamic theory of bumble bee flight. Write it down, in fact, because a year from now it may be very different - https://www.scifacts.net/animals/bumblebees-fly/ (https://www.scifacts.net/animals/bumblebees-fly/)
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Science. Well, back in my college physics days, scientists couldn’t explain why atoms stayed together, so they determined an unknown force was at work - and it was often called “spirit”. I guess the term currently in use is “strong force”.
Yes, please don’t bash the exacting field of science.
y1 y1 y1
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https://www.scifacts.net/animals/bumblebees-fly/
These guys could use a good editor: of/off, to/too, etc. Their writing is slightly "unpolished" and they apparently can't tell the difference between a honey bee and a bumblebee in their video. I know that many engineers are bad writiers, but at least they could have someone else read it before they post it. :P
Apologies for the interjection, please continue the squabble..... ;D
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"...all the aeronautical theory in the world seems to me to have rather little significance when applied to our small vehicles."
Nope. No science-bashing there. But it seems odd that you would support your statement about the irrelevance of aerodynamics by citing uncertainties in atomic theory.
Modelers have an amazing ability to iterate configurations from prior work; from demonstrated performance in the prior article combined with hopeful modifications. Most without any meaningful analysis. That's ok, it's a hobby. And most people in the hobby have little or no aerodynamic training. But to then by extension to say that analysis and proper design are not useful or "have rather little significance?" That confirms that someone is just changing cosmetics, or has their own internally rational aero theory, or is simply making random changes out of curiosity. That's still ok--it's a hobby. But to then suggest that we disparage the actual physics by substituting the hyperbolic "flying plywood theory" needs to be called what it is.
You might enjoy reviewing how much research and testing went into the Mars helicopter. There were some really interesting videos of some of the design issues and the test program. Also a pretty small vehicle. And no, the teams involved didn't just "wing it" considering the enormous effort it took to get it there.
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"...all the aeronautical theory in the world seems to me to have rather little significance when applied to our small vehicles."
Nope. No science-bashing there. But it seems odd that you would support your statement about the irrelevance of aerodynamics by citing uncertainties in atomic theory.
Modelers have an amazing ability to iterate configurations from prior work; from demonstrated performance in the prior article combined with hopeful modifications. Most without any meaningful analysis. That's ok, it's a hobby. And most people in the hobby have little or no aerodynamic training. But to then by extension to say that analysis and proper design are not useful or "have rather little significance?" That confirms that someone is just changing cosmetics, or has their own internally rational aero theory, or is simply making random changes out of curiosity. That's still ok--it's a hobby. But to then suggest that we disparage the actual physics by substituting the hyperbolic "flying plywood theory" needs to be called what it is.
You might enjoy reviewing how much research and testing went into the Mars helicopter. There were some really interesting videos of some of the design issues and the test program. Also a pretty small vehicle. And no, the teams involved didn't just "wing it" considering the enormous effort it took to get it there.
Dave, were we sitting together enjoying a soda we'd probably have a great conversation. I think you've completely misinterpreted much of what I've written, or I've done a poor job of 'splaining. English really is a fairly precise language.
I'm merely stating the Reynolds numbers on our models are pretty darn low. Correct me if I'm wrong!
That said, it would seem to follow that much of the theory that applies to a Boeing 747 probably has little relevance when applied to your Flite Streak. True or False?
Incidentally, I was an aero engineering major for the first 2 years of my college experience. Three of my flying buddies from our small town in Southern Minnesota finished the program. And the closest of that group retired not long ago from many years of advanced research at Northrop Grumman. Some of the stories he tells are considerably less about theory and more closely "Just do it and we'll see what happens".
I started reading every book I could find about aerodynamics at the age of 10. Started designing my own airplanes a few years later. But - in my own experience - I've learned a lot more about our models by simply trying instead of relying on theory.
I know from actual experience the last thing I want in an airplane maneuvering upwind in a 25mph wind is a constant-chord wing. No theory needed.
I know from actual experience another thing I don't want in that situation is a high aspect ratio wing. No theory needed.
I know from actual experience that low aspect ratio wings will tend to be stronger structurally and less prone too warps than high aspect ratio wings. No theory needed.
Kudos to those who rely on theory, design accordingly, and make it work.
And - since we're told any deviation from the optimum is a mistake - just what is the optimum stunt design?
[One of the "Gods" who posts here with the initials BB insisted in another forum some years ago that PAMPA could have the newsletter commercially printed at the same cost per copy whether the quantity were 20 or 2,000 ... So even "theory" seems to produce mistakes!]
D>K]
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Incidentally, I was an aero engineering major for the first 2 years of my college experience. Three of my flying buddies from our small town in Southern Minnesota finished the program. And the closest of that group retired not long ago from many years of advanced research at Northrop Grumman. Some of the stories he tells are considerably less about theory and more closely "Just do it and we'll see what happens".
I started reading every book I could find about aerodynamics at the age of 10. Started designing my own airplanes a few years later. But - in my own experience - I've learned a lot more about our models by simply trying instead of relying on theory.
Back in 1982, I participated in a few Douglas Aircraft DC-9 wind tunnel tests at the Rockwell blow down wind tunnel in El Segundo, CA as one of the data systems operators. (We had newer PSI quartz air pressure transducers. Rockwell's data system was geared to the older and slower Scani-valve systems. We could gather a lot more data points quickly with the newer system, reducing the number and length of blows to do the testing. In one or two days with that instrumentation and our portable data system, we gathered the same amount of data that would take the older system about a week of testing.)
On one of the tests, they were doing boat tail studies. One, a chisel looking tip was tried. That concept was made factual in the planes manufactured in the latter 1980's. I gathered that the design engineers were as you say, "Just do it and we'll see what happens".
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Back in 1982, I participated in a few Douglas Aircraft DC-9 wind tunnel tests at the Rockwell blow down wind tunnel in El Segundo, CA as one of the data systems operators. (We had newer PSI quartz air pressure transducers. Rockwell's data system was geared to the older and slower Scani-valve systems. We could gather a lot more data points quickly with the newer system, reducing the number and length of blows to do the testing. In one or two days with that instrumentation and our portable data system, we gathered the same amount of data that would take the older system about a week of testing.)
On one of the tests, they were doing boat tail studies. One, a chisel looking tip was tried. That concept was made factual in the planes manufactured in the latter 1980's. I gathered that the design engineers were as you say, "Just do it and we'll see what happens".
Love it! My good friend Tom would agree ... LL~
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If I understand what some here seem to suggest, what is the perfect stunter? Surely if we all apply existing theory, there can only be ONE perfect stunt design. What is it?
My point earlier was that they have already converged to a very small range of options, and they generally (when trimmed and powered properly) fly very similarly - so, any of them are about the same. They aren't plywood flat plates, and they aren't ST60 planes with conformally-mapped Nobler airfoils, and they aren't straight-winged.
The range of variation for "personal preference" is extremely narrow, you can't just grab anything and practice till your arm gets tired and hope to compete. Most of the things we argue about are trivial differences that get swamped by construction/power/trim, or just don't make much difference.
As always, no one is compelled to pay any attention and are always welcome to prove me (and the rest of us) wrong. I guaranteed that I never, ever, beat anyone with my superior natural talent, physical fitness, or by out-practicing them, because I don't have an advantage in any of those areas. So, I should be easy pickings.
Brett
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I should be easy pickings.
LL~
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I sincerely appreciate all of the input on this post that I started. Since I am not good in math and have zero education or training in aerodynamics, physics and engineering, I did not understand some of it. I guess I was just looking for a simple answer as it pertains to flying our models. Some designs have a barn door type wing with a straight leading edge and others have a tapered wing with a leading edge that is angled back. Most of the top fliers (pilots) seem to prefer models with the swept back leading edges as compared to a wing with a straight leading edge. My question was Why? Is there any advantage of one wing design over another because the sweep or lack of on the leading-edge configuration. If you take a Humongous and an SV11 and put it in the hands of a top stunt pilot flying the same pattern, will the design of the wing have anything to do with how the pilot scores or does it all depend on the skills of the pilot?
Mike
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I am not good in math and have zero education or training in aerodynamics, physics and engineering, I did not understand some of it.
Bottom line: just listen to what Brett says, and fly what Fitzgerald flies (or just copy it and change the shape of the rudder, move the canopy forward or back and then claim you designed it.) ;D
If you go back and read Gialdini's write-up for his Olympic way back when in American Modeler, take note of his dumbbell drawings and discussion.
This probably isn't quite correctly written: think of how a tapered planform wing has progressively less area per each inch of span as it moves out towards the tips compared to a constant chord wing. In "upset" conditions it will roll less than a constant-chord wing simply because it has progressively less area. It's an area times moment arm (from the center-line of your fuselage) thing. You may have noted that, in general, constant chord wings fly pretty choppy in bad wind conditions. Years ago at Brodaks I watched Dr. Reuben fly his Pathfinder in bad air conditions. It was rolling, and hacking, and puking all over. The next flight was his son, Stevey, flying a Cardinal Evo. That thing came around the circle flying flat liike it was on rails. Same wind conditions. Staright chord versus tapered chord.
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Bottom line: just listen to what Brett says, and fly what Fitzgerald flies (or just copy it and change the shape of the rudder, move the canopy forward or back and then claim you designed it.) ;D
If you go back and read Gialdini's write-up for his Olympic way back when in American Modeler, take note of his dumbbell drawings and discussion.
This probably isn't quite correctly written: think of how a tapered planform wing has progressively less area per each inch of span as it moves out towards the tips compared to a constant chord wing. In "upset" conditions it will roll less than a constant-chord wing simply because it has progressively less area. It's an area times moment arm (from the center-line of your fuselage) thing. You may have noted that, in general, constant chord wings fly pretty choppy in bad wind conditions. Years ago at Brodaks I watched Dr. Reuben fly his Pathfinder in bad air conditions. It was rolling, and hacking, and puking all over. The next flight was his son, Stevey, flying a Cardinal Evo. That thing came around the circle flying flat liike it was on rails. Same wind conditions. Staright chord versus tapered chord.
Thank you Scott. That helped.
Mike
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Bottom line: just listen to what Brett says, and fly what Fitzgerald flies (or just copy it and change the shape of the rudder, move the canopy forward or back and then claim you designed it.) ;D
I note that the only thing I said of any consequence was to not use "personal preference" as a rationalization for doing something wrong or less-than-your-best. That is a classic trap, maybe the most insidious of the common traps you can fall into.
What makes a good stunt plane, and how they fly, has converged to a narrow range. We still argue about stuff, but it's over minutia that are far more subtle than most people are concerned with - since almost everyone, including NATs qualifiers, has trim/power issues so profound that it just swamps the minor details.
Otherwise there was a lot of very good information from everyone, and the basics of the question originally asked about wing planforms were answered long ago.
Brett
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the only thing I said of any consequence was to not use "personal preference"
Oh no! But my personal preference is to just listen to what Brett says....so now I'm in an unending conflicting do-loop! ;D
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Oh no! But my personal preference is to just listen to what Brett says....so now I'm in an unending conflicting do-loop! ;D
Yes, I can see your dilemma. Time to reboot.
Brett