Retracting undercarriage for stunt models

I recently spent some time acting as a sounding board for a friend who builds F2C models on the subject of retracts. The ideas he had and subsequently built into a model would apply to stunt models and I wondered why I haven't seen anyone attempting to add retracts to some of these beautiful semiscale models

Regards

Mike

I was wondering the same thing....I would suppose the added weight is undesirable and there is plenty of power to overcome the drag of the fixed gear....so why complicate things?

Tnx, Mike, the "Old Harley Man" [email protected]

Why have retracts?! 'Cause theyre kool!

Retracts have been done in the past. There was a design published in American Modeler in the 60's that has retracts. It was the Crusader.

The retracts were powered through an additional !/2A engine that was attached through a special backplate and used as a pump to fill a plunger tank that pulled up the gear. Once the engine stopped the gera came down and the ship was landed. VERY neat!

Also, people have used 1/2A R?C retracts in stunt ships with some reported success.

I think that the additional weight would be more of a psychological problem that anything else and would love to hear from some of the guys who have solved this tech problem already.

BIGS

" What constitutes the dignity of a craft is that it creates a fellowship, that it binds men together and fashions for them a common language. For there is but one problem - the problem of human relations."

It seems to me that Bill Werwage had retracts in his first Thunderbolts?
The controler on the outboard wing?
I know that Bob Hunt was convinced that the drag advantage far overrode the weight penalty?
My guess is that reliability of the systems chosen was a question?
I think that the twinkies that Winfred creates cry out for them......as do a lot of semi scale single engined models because of the overly long gear to clear big props......
Zambelli has them on a Beach that he is building....

See Ya

The system that Brian Turner designed for the F2C model was powered from crankcase pressure. There was a centrifugal valve that inhibited retraction until the model was flying and the power was delivered using a very light rolling diaphram piston rather than a sliding seal so the system was pretty friction free. The amount of air used was tiny and made no decernable difference to the engine. Of course, on an F2C model there is just one wheel and the linkages are fairly simple. I was imagining the sight of the undercarriage retracting slowly during the climb after takeoff and unfurling after the motor cut. I would look great.
Roland Surugue used retracts on his F2C model and saw a gain of nearly 4 seconds on a race but the system he used was a centrifugal force powered system that proved less reliable.

Regards

Mike

I'm impressed. Really impressed. For F2C the system would need to be really small and light. Not to mention it'd better work! Several times during a heat, too.

LAST EDITED ON Nov-24-04 AT 04:10 PM (CST)
 
There have been a number of stunt ships built with retracts. There was a trick mechanism a few years ago that worked based on a timer and engine vibration. Start the engine and (fill in the number - it was adjustable) seconds later, the gear went up. When the engine quit, the sensor triped and lowered the gear. Very trick. I think Windy had a Z-tron controlled retract system in one of his planes. I also believe Bob Whitely had a semi-scale plane with timer based retracts (Martin-Baker?).

The problem, of course, is weight. It's an extra 5 or 6 ounces to lug around (at minimum).

edit: Peabody beat me to it.

LAST EDITED ON Nov-26-04 AT 00:58 AM (CST)
 
Bob Whitely had retracts in his "Iceman" Rabe Mustang. It's still hanging around somewhere I think.

It was based on a timer and microphone. Had a small battery and light retracts and servo from some usual R/C source.

The scheme went something like this. The engine was started and the switch was turned on, the mike heard the engine and started a timer in which the gear would retract in a set time. Whitely would walk out the lines, signal and takeoff. The timer would run out and signal the gear to retract. After the pattern and the engine quit, the mike would no longer hear the engine and lower the gear.

One big difference with a retract stunter is the vertical CG position shifts dramatically when the gear goes up, so the handle neutral must be set inflight with gear up. A lot of up elevator pressure must be held for takeoff and level flight until the gear retracts, then it falls into trim.

Call 'Ole Iceman up, he'll tell you all about it.

Chris...

PS Thinking about the Rabe Mustang, it might be that particular design with it's deep fuselage, low wing and long landing gear, might have made the trim issue more dramatic than a regular stunt ship with a shallow fuse, mid wing and short gear.

I think retracts are a stellar concept for the c/l enthusiast. Now lets think of a way to make it practical.--< Flite

LAST EDITED ON Nov-24-04 AT 04:17 PM (CST)
 
>I think retracts are a stellar concept for the c/l
>enthusiast. Now lets think of a way to make it practical.--<
>Flite

2 freeflight engine timers. One for up gear and one for down.

EDIT: I would have to agree with Chris it would cause a trimming problem.

It works quite well.

Robert Compton has built several CL stunters with retracts. He uses a little electronic gizzy with a microphone and delay timer on it. You flip the switch on release, and after takeoff delay the gear retracts. When the engine stops running, the microphone senses it and immediately lowers the gear. Someone was selling the controller..

I believe Bob Whitely's ship was the development vessel for the controller.

As for trimming, it was said that at least some of the ships flew just fine or even better with the gear retracted. It certainly looks impressive.

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"When my old man wanted sex, my mother would show him a picture of me." -Rodney Dangerfield

>>I believe Bob Whitely's ship was the development vessel for
>the controller.
>>

Bob Whitley's article Retract C/L "Stang" and the article A C/L Autoretract Controller by Joe Utasi (Jomar Products) was published in FM Sept 1994. I have two of the controler kits and intend to use them at some point. The system relies on the absence of engine noise to lower the gear. My concern would be what happens if someone is flying on an ajacent circle or running an engine in the pit and you run out of fuel? Is ther potential here for a wheels up landing? Hopefully not.

I think the microphone was reacting to vibration at a sensitivity that would make it obvious to the unit when the engine quit. No problem with ambient noise.

Thanks for the magazine info, I forgot.

Chris,

I had Retracks in my old twin that Bart and I flew in Tucson at vsc.That was when it was new in 1967.I didn`t notice any handle ajustment with the gear up or down.I did notice that there were alot less turblence when doing the pattern.Plus it looked cool too.

Gordy
Ps When are you coming to slc?

Gordy,
I thought it had retracts, but you didn't use them at Buckeye in 68, did you? Did that model have two different sized engines too?

I never go to SLC out of STL. That was the old airline. I'll see you more next year though. Are you going to the SW Regionals?

Chris,

You`re right about not using the retracks in 68 but when I got home I did start using them.I had some problems with the timer and fix it.And yes I had a 29 outboard and 35 inboard.It was hard to set the needles on them because the 29 had to be set leaner than the 35.But,once in the air the 29 would drop into a for stroke.I hope you get some flight to SLC.You`ll have a place to stay.I can pick you up at the airport.And no I will not be come to the SW regionals.Sandy`s Mom is on life support right now. Don`t know whats going to happen with her.

Gordy

I believe that one of the Adamisins had retracts on a Tony built some time in the sixties. He didn't discuss (or his article was edited) how the gear was activated.

IIRC, John Davis flew a retract gear stunter at the NATS several years ago.
Bill <><

John Davis had a design called the Arrowplane. He had both retract and fixed gear versions. The retracts were, I suppose, done by servos. He had insulated lines and had a belt mounted battery which he hooked up to raise and lower the retracts. I saw both versions fly and was very impressed by the retracts airplane. One of the two had the wing fold and crashed at a contest I attended. I wasn't flying stunt at the time and thus did not watch as closely as I would today.

Mike:

One of our local flyers has a Sig Mustang and a DeHaviland Mosquito set up with retracts. It's been a while since he's flown either one so I don't recall the system used but anytime the gear is up either one is stunning in the air.

The Mustang is a good round maneuver plane and seems more even on inside vs outside turns with the gear up. I recall that it would wind up and accellerate faster than most stunters if provoked. Makes sense with that clean an airframe. In any case, absolutely stunning in the air.

The Mosquito is big, heavy, flap equipped and could probably do a full pattern with Schwartzennager, Paul Bunyan ( a 15" tall lumberjack legend for you southerners), or Mr. Universe at the handle. The owner, Keith Sandberg, is a very muscular fireman and run's out of arm about halfway through a pattern. Again, it's really neat seeing those wheels flip forward into the nacelles. It is probably the most realistic ship I know with the gear up, flying past at eye level. Much like what the real thing often did in WWII. Now, if we could duplicate the sound of 2 Merlins............

As some of the others said, who knows what technology will allow in the future?

Paul Bunyan ( a 15"
>tall lumberjack legend for you southerners)

15"?

(Remember that "Spinal Tap" movie? )

I've seen the Mossie on one of Windy's Brodak videos.

It was compressed air powered wasn't it?

Tony

>One of our local flyers has a Sig Mustang and a DeHaviland
>Mosquito set up with retracts. It's been a while since he's
>flown either one so I don't recall the system used but
>anytime the gear is up either one is stunning in the air.

Jeff,
The Mossie has an RC controlled system. Keith used an inexpensive RC unit out of a car, on 27mHz, I think. The tx hung on his belt. One channel controlled the gear, and the throttle stick operated a fuel shut-off. Two Fox 35s. I think the last Keith time flew it was last spring when you guys came to RST. It now hangs in the Hobby Towne in Brooklyn Park. VERY impressive!
Kelvin

PS 15 feet.

Some very interesting answers about retract technology here, as well as in the other thread. However, the original question was " I wondered why I haven't seen ... retracts...". The writer mentioned "stunt models". So it appears to me he's talking about competition stunt airplanes ( if I'm wrong, please correct me ). The answer to his question is quite simple.
As a sport flyer you can do what you want. It doesn't matter whether you're successful or not.
As a competition flyer your thinking is different. You consider what can improve your flying; what can improve your scores. As can be seen from all these answers so far, it's quite obvious that retracts don't seem to improve flying characteristics of the airplane noticably, if at all. Maybe they look "cool", but that's not what the competition flyer is interested in. After all, PA is a flying event. Besides, retracts are an additional complex gadget which needs designing, building, trimming, maintaining, etc. Another item which can fail ( you know Murphy's law ?! ). And all that while the gain is quite doubtful.
While the rules do not specifically prohibit retracts, I'm glad to see that the majority of PA flyers agrees to not use them. The more complicated the technology of an event, the less participants. You can easily see the decline of interest in the more technical disciplines ( speed, team race, FAI free flight, too ); some are downright dying. PA ( or F2B worldwide ) is the most popular control line event, and it is so because technology is simple. Highly complex technology will only exclude potential participants ( who would like to fly but for some reasons lack the required skills for high tech ). Only the best can win, oh yes, but EVERYBODY CAN PARTICIPATE. And enjoy!
Antoine de St.Exupery (= famous French pilot, author, philosopher) said: perfection is not where you can't add anything anymore, but where you can't remove anything anymore. You just cannot say it better.
Regards, claus

Hi Claus,

I love your cartoons! And I still remember your great article "Design and Formation" which I transcribed for Stunt News (March/April, May/June 1997).

We need to see more photos of your recent airplanes!

Best regards,

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"I met the surgeon general. He offered me a cigarette." -Rodney Dangerfield