stunthanger.com
Design => Engineering board => Topic started by: Avaiojet on September 14, 2014, 01:40:04 PM
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I have this sport scale stunt model on my drawing board. Actually a drawing program.
I'm thinking a degree or a half degree of positive wing incidence.
With the symmetrical airfoil it may be a good thing?
I don't know enough about CL design to be sure?
Anyone building positive wing incidence into their models?
Thanks in advance.
Charles
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First, as usual, there's the obligatory statement: if you were to read posts by other people you would already know the prevailing opinion.
Second, in all the times I've been looking at stunt planes, all I have ever seen for wing incidence has been dead level. Some author's recommend a hair (1 degree or so) of positive (nose down) incidence to the tail plane. Some people also recommend a hair (1 or 2 degrees) of down-thrust on the motor, IF it rotates the "normal" direction (CCW as you look at the front of the plane). You DO NOT want this if you have a CW-rotation ("pusher") prop.
So far I've only ever built my planes with 0-0-0 thrust, incidence, and tailplane angle. This may not be the absolute tip-top optimal arrangement, but it's been working pretty well for me.
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First, as usual, there's the obligatory statement: if you were to read posts by other people you would already know the prevailing opinion.
You could say this to just about anyone who Posts a question. I'm sure, over the years, all topics have been covered.
I read some Posts. Much about how the model looks inverted, nose up - nose down, and other interesting comments.
I wanted something a bit more solid.
I believe if 0-000 can work for you, then it can work for me.
R/C I wouldn't be asking the question.
Thanks for the reply.
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I have this sport scale stunt model on my drawing board. Actually a drawing program.
Charles
if it stays on the drawing board then a working answer matters little.
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Some author's recommend a hair (1 degree or so) of positive (nose down) incidence to the tail plane.
Just to clarify, in my brief visit, I think Tim means the nose or leading edge of the stabilizer is up, which pitches the plane's nose down. The opposite causes problems (like hunting) in level flight.
Also, positive wing incidence upright is negative incidence inverted for that sport stunter. Additional asymmetry between upright and inverted handling isn’t desirable. With flaps, there is already a positive wing incidence in both kinds of level flight, anyway, due to up-elevator providing downward deflected flaps. So, engine-wing-stabilizer incidences are 0-0-0, 0-0-positive, negative-0-0, or negative - 0 - positive. Any wing incidence relative to the fuselage will require engine and stabilizer adjustments to create one of these sets of relative incidences. I think that there's a trade-off between engine down-thrust and positive stabilizer angle.
SK
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Just to clarify, in my brief visit, I think Tim means the nose or leading edge of the stabilizer is up, which pitches the plane's nose down. The opposite causes problems (like hunting) in level flight.
Yes, Tim meant that one ought to bias the stabilizer so that the nose of the whole plane tends to pitch down. Assuming that one knows what one is doing, which Tim does not feel he does, so he uses 0-0-0 thrust, incidence and stabilizer bias -- even on those occasions when he speaks of himself in the first person.
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Just to clarify, in my brief visit, I think Tim means the nose or leading edge of the stabilizer is up, which pitches the plane's nose down. The opposite causes problems (like hunting) in level flight.
Ah, hunting! As in the model hunts for a steady direction to resolve conflicting inputs?
Seen that and down thrust seems to cure it.
Thanks Serge.
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Ah, hunting! As in the model hunts for a steady direction to resolve conflicting inputs?
Seen that and down thrust seems to cure it.
Thanks Serge.
Though 0,0,0 is the standard that can always be trimmed out to work some what acceptably, here seems to be a lot of fiddling with the controls, and handle to cure hunting, and other unwanted inputs.
I've found, after reading Bob Whitley's post, "Things that always work", is that if I set my planes up as Bob recommends, I have a much easier time trimming the plane out for proper flight. Seldom, if ever, is there any hunting. as well as other more subtle problems.
Bob suggests 1-2 degrees of down thrust, just enough out-thrust to make sure there is no in-thrust, and 1/2 to 1 degree of positive stab incidence.
It's easiest to use a pair of incidence meters. First establish the wing at 0 incidence, and block the fuselage so that wing incidence is maintained while you work on the thrust line, and the stab incidence. I leave the incidence meter attached to the wing. This allows me to refer to the wings meter, to get the proper down thrust line. To establish the stab incidence, keep the fuse blocked up where the wing remains at 0 degrees, and move the second incidence meter back to the stab, set it up for 1/2 to 1 degree positive. I most often use about 1/2 degree positive, at the stab. Crank in enough out-thrust, towards the out side of the circle.
I have found that I seldom, if ever, have hunting problems, and the plane seem to fly truer with this set of incidences. Of course, this all is based on CCW flying with standard prop rotation. I've not flown CW, or with a pusher prop to have an opinion. H^^
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Even with a 0-0-0 alignment setup a raised thrustline will give tend to pull downwards towards the drag ( I await the correct technical terms for this that will surely come!)
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My theory is that "cross-control" adds stability. Works in Free Flight, anyway. Part of it is also because of "Circular Airflow", per the Frank Zaic book by that name.
Can a 1:1 Scale pilot comment on how it works with side-slipping in something without flaps, like Dad's Citabria? I'm pretty sure he wasn't 'slipping it to comp for side-wind, but for visibility, and also to add drag (since no flaps). Maybe some of it was to make me nervous? Anyway, how stable is the plane when side-slipping? H^^ Steve
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My theory is that "cross-control" adds stability. Works in Free Flight, anyway. Part of it is also because of "Circular Airflow", per the Frank Zaic book by that name.
Can a 1:1 Scale pilot comment on how it works with side-slipping in something without flaps, like Dad's Citabria? I'm pretty sure he wasn't 'slipping it to comp for side-wind, but for visibility, and also to add drag (since no flaps). Maybe some of it was to make me nervous? Anyway, how stable is the plane when side-slipping? H^^ Steve
I would remind all that positive incidence of the wing with respect to the fuselage with a symmetrical wing is pretty much the same thing as downthrust in the thrustline. The only significant difference would be the potential appearance of the airplane in profile in level flight which at one degree would likely be no more noticable than a wing at zero with downthrust built into the engine. I would expect the effects of incidence built into the stab would also be identical to a "zero" wing and a downthrust engine mount. It remains the combined effects of the forces: lift, drag, thrust and pitching moment.
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YES there has been stunters that use positive incidence in the wing , There are many ways to put a stuntship in good trim
My VECTRA (Dreadnought) that I flew in 9 NATs and many other contest, has 1 degree positive in the wing, it has an effective 1 degree positive in the stab /Elev. it also has a precision adjustable semi soft engine mount that is adjustable both in incidence and in out/in thrust. It flew so well the engine has never been changed, so the downthrust is still set a zero
Randy
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YES there has been stunters that use positive incidence in the wing , There are many ways to put a stuntship in good trim
My VECTRA (Dreadnought) that I flew in 9 NATs and many other contest, has 1 degree positive in the wing, it has an effective 1 degree positive in the stab /Elev. it also has a precision adjustable semi soft engine mount that is adjustable both in incidence and in out/in thrust. It flew so well the engine has never been changed, so the downthrust is still set a zero
Randy
What direction was the engine rotating in Randy?
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What direction was the engine rotating in Randy?
Standard IC engine rotation, I had OS OPS and PA engines in it. The plane was built in the late 1980s before people used electric motors and pusher props.
If I had ever used a reverse rotation w/ pusher props, the stab would have been different, and the adjustable engine mount would have been a great trim tool.
Randy
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if it stays on the drawing board then a working answer matters little.
Chris,
Just catching up on an old but important thread. To me anyway. ;D
As you can see, the model is well off the drawing board.
Actually, from the drawing board it went to my computer then back to paper. Contest grade alsa from Tom Morris. LL~
Great input with the replies about incidence, and I appreciate it. Thank you.
I decided to play it safe so I went with 0-0-0.
However, the fuselage and engine are offset.
Carved in stone.
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Even though you have the engine thrust line, wing section and tail all at 0 degrees (or parallel to each other) you still have each of those lines some distance apart and with the thrustline being above the centre of drag (and the wing is the major cause of drag) you will have a slight downwards force under power.
(For a better visual feast on this just picture the old flying boats with the engine up on struts above the wing.)
Landing ...... well that will be different!
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Even though you have the engine thrust line, wing section and tail all at 0 degrees (or parallel to each other) you still have each of those lines some distance apart and with the thrustline being above the centre of drag (and the wing is the major cause of drag) you will have a slight downwards force under power.
(For a better visual feast on this just picture the old flying boats with the engine up on struts above the wing.)
Landing ...... well that will be different!
You land when the engine quits. So I don't know your point?
Under power the model get's trimmed. They all get trimmed under power.
Most stunt ships are built exactly the way my Stuka is. I copied.
I suggest you take a look at a few stunt designs or just design one and build one yourself using others as a guide.
The days of the thrust line, cord line and stab center line, being on the same center line, are long gone.
That was tried in R/C pattern with a few designs. Offered no advantage.
I don't have to picture the old flying boats with the engine up on struts, I owned a Lake LA-4 200T for a good number of years, 1989 to 1995 actually.
Flies just like any other aircraft. Well, almost. ;D
Off topic but...
One of my all time favorite Big Bands, playing a tune I used to play the drums to.
Yes, I was a Jazz drummer, believe it or not.
This tune will make anyone feel better! Well almost. ;D
https://www.youtube.com/watch?v=cFIZwnDLt_4
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You land when the engine quits. So I don't know your point?
The point is that even with a 0 0 0 setup when the model is under power you will get a pitching effect if the thrust line is above the centre of drag.
When the model is NOT under power there is no thrust and by default NO thrustline and NO pitching effect - however mild that maybe (but this was never a serious point to be considered.)
I suggest you take a look at a few stunt designs or just design one and build one yourself using others as a guide.
The days of the thrust line, cord line and stab center line, being on the same center line, are long gone.
So the current world class Yatsenkos have been discontinued long ago?
And the all inline PAW diesel Freebird seems to fly just as well as ever.
What is your point Charles?
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Even though you have the engine thrust line, wing section and tail all at 0 degrees (or parallel to each other) you still have each of those lines some distance apart and with the thrustline being above the centre of drag (and the wing is the major cause of drag) you will have a slight downwards force under power.
I do not think ... you igrone precession and p-factor - both points nose up (for tractor prop) ... so trust line over the wing (or even down thrust or stab incidence) is natural for our planes.
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Yatsenkos at $3K? My interest isn't in that kind of design.
My greatest interest is Warbird models, and If I can get a loop out of them, all the better. n~
Early on, and I mean really early on, I took a liking to the Warbird models designed by Al Rabe. How can you not like and appreciate Al Rabe's work, not to mention his accomplishments. H^^
So, turns out, my Warbird designs, will have that kind of appeal. I'm currently drawing up another design of an unusual Warbird BTW, it's not designed to be at 0-0-0.
Maybe there is a Warbird aircraft at 0-0-0? Not sure about that?
So, If you don't like my first attempt at a Warbird stunt design, the Stuka tank buster, blame Al Rabe, because that's where my influence is comming from. LL~ LL~ LL~
Thanks Al. H^^
http://www.tanks-hangar.com/html/al_rabe_model_kits.html
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I do not think ... you igrone precession and p-factor - both points nose up (for tractor prop) ... so trust line over the wing (or even down thrust or stab incidence) is natural for our planes.
Hi Igor,
I am not ignoring precession or P factor (as the natural counter to to down thrust) but trying to address that if all datum lines are parallel it does not necessarily make the resolved forces act in parallel.
In common terms a 'trimmed' 0-0-0 model is not necessarily the same as a 'trimmed' all inline model, obviously a 0-0-0 model has all datum lines parallel and entertains the possibility of distance between those lines but no angles are involved and an 'inline' model has only one datum line but achieves trim through angling.
(What I dont see is how an all inline model can be in trim unless there is deviance from 0-0-0 somewhere.)
Thats my understanding of it anyway, if I am in error then please set me right.
Thanks.
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The point is that even with a 0 0 0 setup when the model is under power you will get a pitching effect if the thrust line is above the centre of drag.
When the model is NOT under power there is no thrust and by default NO thrustline and NO pitching effect - however mild that maybe (but this was never a serious point to be considered.)
So the current world class Yatsenkos have been discontinued long ago?
And the all inline PAW diesel Freebird seems to fly just as well as ever.
What is your point Charles?
You guys keep getting sucked in...
Brett