Stuka Stunt Main Forum · 29 of 29 known posts recovered
FOR OUR PURPOSES IN PRECISION AEROBATICS, is a relatively draggy airframe (non-retract) loaded against lots of power more desireable than a very clean retract airframe of the same weight and powered to the same lap times?
I wonder is if excess accelleration might be a problem in an event where steady speed is so critical.
OK folks, what do you think?
Jeff W
I've seen you swagger and you don't present enough side area to be a factor. Wish I could say that!
See you at the meeting on the 16th.
Jeff
With my modest size and low hemoglobin, it's good that I have you big guys for shelter from the Minnesota winds.
Kelvin
Igor,
Isn't a balance of pich drag the goal? As long as it is turning equally? If this is accomplished the model is trimmed.
Jeff,
I am under the impression that drag is good, and Al Rabe's ships are a good example of how power/drag are used to climb and maintain energy/control speed up. There are a lot of ways to do this now that the pipe/low pitch prop set-ups are here, as well as the (not understood by me) 4 strokes.
Chris...
you have gyroscopic moment from prop pitching up, you have engine thrust line over the wing drag pitching down, you have gears pitching down, and you have elevator pitching somewhere ...
and now all those moments in level flight are balanced. Gyro moment against drag of landing gears plus engine pitching are very close to balance so tail makes only very small force.
the question is if you can replace one moment by another - for example prop thrust by rag of landing gears ... one can say that yes, but if you fly in wind, half of the lap against and half of the lap down the wind, then at higher speed of air against the wind prop makes smaller thrust thus pitching down is smaller, while landing gears against the wind make more drag and pitching down is stronger - improper balance can lead to hunting
... I do not want to guess WHAT is that proper balance, I only noted that if you change it on "debugged" model, you can come to troubles ... that is all (if we are speaking about competitive model)
I guess you mean specific model, and not design. It seems one could trim a model to fly well with a low drag retractable set-up, using the low pitch prop for braking. The benefits would be appearance/impression and...?
Chris...
every model is "specific" ... no I do not mean anything specific, I mean that combination of engine thrust over the wing and landing gears under is succesfull methode to beat gyscopic moment. If you reteract gears, you will need to kill it by elevator and we know that such a way can lead to hunting or other ill side effects. Could be you can trimm it, could be not. Could be it enough to deflect elevator from neutral to flaps, but could be you will need to cut out also stab ... did you read David's (F) sentence in S/N about stabs and coincidences?
Jim
every model is "specific" I see, the thrust line being above the wing C/L and drag moment of the landing gear is a trim tool against having a totally neutral, and possibly too unstable reacting control feel. This is essentially a trimming tool in the sense of control feel?
Reminds me off rolling in some trim on a full scale ship when flying formation, so I have a bias to stabilize the inputs.
If you
>reteract gears, you will need to kill it by elevator and we
>know that such a way can lead to hunting or other ill side
>effects. Could be you can trimm it, could be not. Could be
>it enough to deflect elevator from neutral to flaps,
This is what could be controlled with a raised leading edge of the stabilizer, or downthrust. Shouldn't be anything that can't be overcome enough to produce a competitive model.
but
>could be you will need to cut out also stab ... did you read
>David's (F) sentence in S/N about stabs and coincidences?
Yes, and I can relate. I would be building a model specifically with retracts, not modifying a current one.
Chris...
That is the question - which one. They are not equivalent, but I wrote it already.
Do not tale me wrong, I do not want to change your mind, I just wanted to note there IS what to solve ... more than only mechanical problems.
Chris...
That's kind of my gut feeling from my full size flying days too.Seems like we kind of loaded power against drag when we needed precise control. Tough to slow down in something fast and clean.
Food for thought.
Thanks,
Jeff
Brett
Make it simple and make it work.
I have a set of plans that shows a slot cut into the profile fuselage with a skinny wheel inside the slot. Only about 1/4" of the wheel hangs out of the slot the rest of the wheel is inside the fuselage. A cart is used to get the airplane in the air the skinny wheel is used only for landing. One idea.
I have been thinking there must be a way to retract landing gears without some type electronic device, battery, servo, receiver, antenna, etc. I have several ideas the one that seems to be the most likely to work without adding a lot of weight to the airplane is to take advantage of some laws of physics, like centrifical force, air pressure, vacuum. What do we have when the airplane is in the air that we do not have when the airplane is on the ground. A 1" diameter thin wall aluminum tube about 4" long can be used to make a air cylinder. Put a piston inside the tube. Forward air speed produces air pressure that can be used to move the piston which can be used to pull up the landing gear. Centrifical force can aid in moving the piston. I tiny venturi device can be used to suck a vacuum on the other end of the cylinder to aid in moving the piston. The landing gear can toggle shut and lock in place like the linkage on a die cast machine. When the engine stops and air speed is slow, air pressure drops, vacuum reduces, centrifical force is less, the landing gear unlocks, gravity take over and the landing gear come out. It might work. And like you said the disadvantages might outweigh the advantages. It could be a fun an challanging project.
Gary Weaver
I've often wondered what Al Rabe's Sea Fury would have looked like with retractables. Interesting picture!
I'm sure it will happen in the near future and should be fun to see.
(at least as long as we don't attach the bellcrank pivot to the retractable gear) ......sorry, I didn't say that.
Jeff
Edit:I didn't mean a retractible Sea Fury (although that would be great), but a high level retractable geared stunter.
Ron B.
F4Fguy
Attached pics are my Macchi 202 #IV from (about) 1974. As I recall,the big change was subjective,it seemed to turn both ways "cleaner".I don't recall any trimming problems,other than slight handle adjustment. The BIG disadvantage was pork. I figure the retracts cost as much performance in wing loading as they gained in inside/outside trim. I don't remember any problem with accelleration,but I've always used as much diameter as I could and reduced pitch to control speed.Unfortunately this Macchi died an early and ugly death so it had very little time on it. I concluded that, at least at that time,the extra complication simply wasn't worth the gains (it DID look neat though!).
Ron B.
VERY NICE! Losing that was a real shame. Guess it proves the good die young.
Jeff
Ron B.
F4Fguy
Chris:
The doors were 1/32" sheet,molded on the wing core before it was sheeted,then covered on both sides with .5oz glass+epoxy. The small door at the wing/gear intersection was linked to the main door to cover the hinge gap.
The details worked well,the main problem was in trying to do this with then available,off the shelf,components. The Rom-Air system was just too heavy,and the mounting required additional structure,all of which added up to 8+oz.even after liberal drilling and filing.
The other thing I didn't mention above,was that I used a three line Roberts system to operate it. Even with solid .014s,the drag was high,and stickiness was a problem. This system is what caused the eventual crash. The bellcrank failed (it folded one of the arms).
All in all, not a very satisfactory experience.
Ron B.
As long as you have the power, some parasitic drag doesn't necessarily hurt anything. This used to be a lot more critical in the good old days, with 6" of pitch, limited power, and 4-2 breaks. But it still works about the same today. The only difference, and it's a whopper, is that you have almost infinite, repeatable control over the engine run. So you see things like Billy's airplanes with super-thin wings and basically designed like gliders, and also airplanes like mine, that have fat wings, and are quite intentionally far more draggy than they need to be. It definitely tames the engine variations.
For the most part, you can make it work either way. Ted and I have discussed this at some length, and I think we have gone a little too far in terms of thick wings and drag. It works, almost too good. Perfectly steady airspeed means significantly varying groundspeed, hence reduced "penetration". If everything is right with the engine, no problem, but it's a little too critical for my tastes.
That's not too surprising, given that the Trivial Pursuit, and the Infinity, were both designed in the 1989/1990 time frame, and are really what I would consider our first attempt at piped design. Our previous piped airplanes were just old ST46 planes with a 40VF slapped in them. If I ever design another 40VF/RO-Jett61 airplane, it will have a thinner wing than the current Infinity. Not much, but some. About half way between the current wing, and the Impact.
Since the topic came up, everybody is in full agreement that *induced* drag it bad no matter what, and anything you can do to improve it without screwing something else up is probably to the good. Unfortunately, the best way to reduce induced drag is to make the airplane lighter, and that involves compromises in terms of rigidity. I've done it both ways, and seen both appraoches and without restarting any arguments, as long as I have access to piped 61s and 40VFs I'm not going to start cutting away any structures just for some minor hypothetical advantage.
Brett
My heart be still I can't believe what I read. Just thought I would drop a note. The nice thing about building now a days is all the new composites that I have to work with. Loosing weight with out structural integrity.
I don't think I'll try retracts though. Too complex for the savings of drag. IMHO
Robert Storick
AMA 12366
Saint Louis,MO.
I am fully up to speed with composite construction. But you can do one of two things - make the same structural rigidity and less weight, or more structural rigidity and the same weight. Since I know there's no particular advantage to building my style of airplane lighter than it is right now, I would use a more efficient structure and try to build it the same weight. Others might do differently, more power to them.
>
>I don't think I'll try retracts though. Too complex for the
>savings of drag. IMHO
There's some dead weight, and there's the reduced reliability. I think you can get around either problem, but I'll take a pass on the idea.
Brett
> " There's some dead weight, and there's the reduced
>reliability. I think you can get around either problem, but
>I'll take a pass on the idea."
>
> Brett
Ahhh, yes! The good old KISS principle - I like it that way too!
Jim Pollock 
Robert Compton
Anybody, EVEN or especially, the original design crew have any comments? I for one wouldn't mind giving it a go. The original stories were that it was very reliable. Must have been for Bill to risk the paint on any of the p47's.
Stunt history about to disappear....
B
News to me - I thought he used the sound-actuated gadget.
Of course, the sound sensor was plenty reliable enough all by itself. It was the mechanical end that made it less reliable.
Brett