Author Topic: RETRACTS FOR STUNT MODELS???? EZZEST' N' LIGHTEST??? (Read 2945 times)

Shultzie · « **on:** November 21, 2007, 10:54:27 AM »

Years ago...1977 I toyed with using a "Perry Pumper" on my proposed ST.46 powered "Seahawker" with retracts.

After hanger trashin-rashin' with my RC pylon racin buds...I bought the Perry pumper...robart and the lightest AJ by Adjust-o-Jiggity'?

I ran the pumper with success on the ST 46 installed into the Chipmunk (but never ran it with retracts installed...
but still wonder how they would have worked as a power source for the retracts?

Any ideas...Chris McMillin and I are trying to find the lightest, most reliable and consistent method for retracts not only for CL scale but also for stunt?

attached are some photos of my old crap...retract stuff.

Paul Smith · « **Reply #1 on:** November 21, 2007, 11:05:23 AM »

I just saw an article in a 1955 Model Airplane News where somebody claimed to have powered a gear/flap actuator off of COMBUSTION PRESSURE.

A tiny probe made of a stainless steel syringe-needle was put into the head. Combustion pressure worked a diaphram, and of course, had a spring to make the final configuration when the engine quit. Sounds shakey, but a lot simpler than a sound-monitoring system.

Bob Zambelli · « **Reply #2 on:** November 21, 2007, 12:32:59 PM »

I did what AMA21835 said but I used crankcase pressure to control switching. I designed a small diaphragm switch that would trip two DPDT switches when the engine was started but the gear could not retract until a second circuit was completed. That circuit was completed by a damped centrifugal switch. After the plane flew for around 5 seconds, the "retract" circuit was complete and the gear retracted.
When the engine quit, the pressure diminished enough to allow the diaphragm to reset and make the "extend" circuit (bypassing the centrifugal switch.)

Reversing of the motor was accomplished by a simple relay logic circuit.

There were no electronics in the system.

I started this project in engineering school and it was accepted for my master's thesis but I did not complete it.

Bob Z.

My Staggerwing has retracts controlled by a Z-Tron and they function perfectly.

Tom Luciano · « **Reply #3 on:** November 21, 2007, 05:11:25 PM »

Guy's

We had a guy in the Union club in the early seventies flying carrier using retracts. They would go up within a quarter of a lap on high speed and come down for slow speed. Worked well enough for him to win the nats. Michael Hotra was his name. Usually we run into him at our Christmas party I will ask him how it worked. I know they worked on centrifugal force but, that's all I know.

Regards

Tom

Bill Little · « **Reply #4 on:** November 30, 2007, 10:15:06 AM »

Along the "pressure" topic mentioned, Harold Price used a Cox .010 engine as an "air pump" for the retracts on his Crusader back in the '60s.

Dennis Adamisin · « **Reply #5 on:** November 30, 2007, 02:45:18 PM »

Quote from: Tom Luciano on November 21, 2007, 05:11:25 PM

Guy's

We had a guy in the Union club in the early seventies flying carrier using retracts. They would go up within a quarter of a lap on high speed and come down for slow speed. Worked well enough for him to win the nats. Michael Hotra was his name. Usually we run into him at our Christmas party I will ask him how it worked. I know they worked on centrifugal force but, that's all I know.

Regards

Tom

Tom L:
Don't know if yu had a chance to talk to your friend ablut his carrier bird with retracts, but what you describes sounds like the "Centrac" (SP?) system from way back when. The concept was to mount the bellcrank in a slide and retain it at the end of a slot with a spring. At launch (no line tension) the gear would be down. At 1/4-1/2 lap after launch the line tension would be such that the load on the bellcrank would overcome the spring force, the bellcrank would slide (spanwise) in a channel til it reached a sop and the gear would literally be pulled up by the line tension. When someencing low speed flight, the line tension would reduce, the spring would pull the 'crank back to the other end of the slot, and the gear would exxtend.

It is a great concept for a Carrier flight profile. However stunt models do not pull nearly so hard, and sometimes lines go slack - making for some VERY interesting manuver presentations!

Its just a swag but I'll bet that was what was used on your friends carrier model...?

peabody · « **Reply #6 on:** November 30, 2007, 05:10:29 PM »

Years ago I spoke with Bob Hunt about retracts for stunt...He stated that the lack of drag overcame the weight disadvantage, but that reliability was an issue.
I understand that Bill Werwage built on (or two) planes with retracts, but did not compete with them?

Windy's "bomber" twinkies cried out for them.

Bill Little · « **Reply #7 on:** December 01, 2007, 12:17:02 PM »

Quote from: peabody on November 30, 2007, 05:10:29 PM

Years ago I spoke with Bob Hunt about retracts for stunt...He stated that the lack of drag overcame the weight disadvantage, but that reliability was an issue.
I understand that Bill Werwage built on (or two) planes with retracts, but did not compete with them?

Windy's "bomber" twinkies cried out for them.

Billy's original razor back P-47 was set up for retracts and was working with Dean Pappas on a system. AFAIK, Billy never trusted them enough for competition.

Willis Swindell · « **Reply #8 on:** December 07, 2007, 06:16:00 PM »

I remember Walt Perkins and Walt Williamson using the spring loaded bellcrank in a Team Racer, the Papa Taca in the late 60’s at the Nats. It worked great in practice but it landed on its belly in the heats, guess Walt was pulling to hard for the landing gear to fold down. I can remember that but what did I have for breakfast?

Willis

Air Ministry . · « **Reply #9 on:** December 20, 2007, 09:55:03 PM »

Balloon in a cylinder connected to the muffler pressure line.with a few other bits in there .

One of mines got a catch off 3/4 down.to kick a downlock off,and a cable and a rubber band.
and one or two other bits in there.

Only problems my two four blade prop will only have two blades on one side if I use it, As once its up its up.
One doesnt bounce landings with this system though .

Chris Edinger · « **Reply #10 on:** January 01, 2008, 03:19:09 PM »

You mean no one has designed an electrical system operated from a remote contorl switch??? in todays world that seems the easiest solution.. but im not up to date..

L0U CRANE · « **Reply #11 on:** January 01, 2008, 05:07:17 PM »

Schultzie, and everbody...

When thinking of retracts for stunt, coupla things need some numbers work...

How much force will you need to operate whatever gear retract bit you use? That sliding bellcrank mount for line-pull retracts that Denny A(?) mentioned would make for a pretty exciting stunt flight. I can just about see the gear waving in and out of retracted position in the overhead figures...

Remember, in level flight, our CLPA models pull somewhere around or over 3g outward. You'll have to pull that inward retracting wheel and strut up against that. A decent RC servo may work for a straight-flying model, but we have that circular flight path to deal with. (...Didn't say outboard wheel, since some planes, including the Spitfire and Grumman Mohawk retracted the mains outward from the fuselage. That makes the inboard wheel the inward moving one.)

Not saying it can't be done... The old white nylon Goldberg retract units had a little coil spring in tension to help counterbalance axle and wheel weight. It was a sort of "over-center" thing, that pulled most when the gear was heaviest to the linkage, and you needed help. About 30 years ago, I flew two models with those Goldbergs as retract units, and it worked. I set up that balance spring with the model held inboard wing vertically up. (Lotta work to set up the whole system, and some concern about reliability, but looked great!)

And, where are you going to put the pieces? There isn't a whole lot of spare space in a stunter, unless you are Al Rabe, or Ron King, or one of a very few others...

And, where are you going to get the force to operate the thing? I don't think a fuel 'pumper' like the Perry puts out a whole lot of psi. If it gives you 2psi, and you need 4 lbs of push on the linkage, you need a piston area of 2 square inches (about 1.5" diameter), not considering leakage, seal losses, friction in the 'cylinder', etc. A bigger modern servo can honk out the push, but they weigh more.

A possibility might be timed crankcase pressure, like on Cox TeeDees and the old ENYA and ST engines that had a brass screw closing a tap hole into the case about 180° away from the center of the venturii. ...Might give you near 10psi. Or an air bladder as used in Combat for fuel, another pretty high pressure source. Maintenance could be "fun"?

Triggering the action? With reliability, easy maintenance AND simplicity? A nice challenge, there...

But the stunters I have seen in the air, with all-up, do look great.

wmiii · « **Reply #12 on:** January 01, 2008, 11:14:09 PM »

I seem to remember that Bob Whitely had a P-51 with retracts that worked well.

Walter

Alan Hahn · « **Reply #13 on:** January 02, 2008, 11:11:39 AM »

I would think one "easy" way for retracts is to buy one of the electric timers that we use for electric CL. The Zigras and JMP-2 timer (if it is still available) have an output for a retract servo. The timer will retract the gear some seconds after takeoff, and then lower them some seconds before. You could also add a servo for a throttle

and never have overruns anymore too!

L0U CRANE · « **Reply #14 on:** January 03, 2008, 08:01:05 PM »

Walter, to your Post #14:

Bob Whitely used an on-board controller that:

-- was switched on by the launching buddy upon release for takeoff...

-- waited a timed few seconds to start retraction...

-- kept the servo circuit either locked out, or in retract mode, until things got quiet (i.e., engine stopped)...

-- then switched to gear-down mode, and put them down.

I seem to remember some anxiety as the gear-down system didn't kick in immediately the engine stopped making noise. Sort of the "does she or doesn't she?" getting-up-on-tiptoes kind of thing as the glide continued to descend...

... and descend ...

and then, FINALLY! - wheep/click, and the wheels were once again ready to save that expensive prop.

Worked consistently, in the flights I saw. But, then, Bob Whitely is not just your ordinary builder/flyer.

RAM Electronics, I think t'was, made the actuator controller, with an adjustable delay from switch-on to gear-up triggering, and a sort of microphone that kept it in gear-up mode while it could hear the engine roar, then dropped to gear-down mode when things got (relatively) silent.

I picked up one of the units back about then, and seem to remember the instructions suggested that you could test the setting of the retract delay by making a loud noise for the 'microphone', with your voice, for the delay time. When you stopped after the gear retracted, you could prove the system by watching the gear extend...

Bob's P51 was BEAUTIFUL!! in the air!

Still leaves unanswered what you have to put aboard that will receive and act on the controller's triggering signals... Seems to require:

1) A servo strong enough to operate a...

2) gear retracting mechanism, and the ...

3) linkage to both mains, or both+tailwheel, or all three (mains and nose wheel), and a ...

4) battery with enough oomph to drive the servo.

5) And, some provision to have access to most of the above for trivial little things like recharging the battery, adjusting (or reconnecting) the linkages (making sure they do not stay at high-drain loaded condition because of binding or obstruction), tuning the controller, general maintenance and testing, and inspecting the works.

It is also nice to have a gear retraction gizmo that mechanically locks the gear in its full-down and full-up positions, so that the servo isn't loaded to do that. (Can you say, "dead battery"?...within one flight?)

With today's (arsonist-inspired) LiPO batteries, the weight of power aboard may be much reduced. With some of the silly, but functional, things being done for Indoor (f'Gawd's sake!) RC and "Park Flier" toys, some of the other elements may be available, if you wear a ski-mask or balaclava and hit the - hack, kaff - RC section of the "Hobbye Shoppes" that gobbled up our once beloved LHS's.

You'd still need a fairly robust retract/extend gizmo, and a servo with the grunt to do the loads to it.

AND factor for the 3+g sideways that goes with our circular flight regime.

Worth it? Most likely. BUT you'd need to get so involved in the minutia that a lot of the joy of flying stunt becomes second priority.

Will Hinton · « **Reply #15 on:** January 10, 2008, 01:51:53 PM »

I bought one of the controlers like Bob used on his P-51 when they first came out but never used it. Just didn't get around to it, I guess. It, like you say, works on sound level. When the ship is launched the pit man turns on the switch and an adjustable timer retracts the gear after the time expires. Then the sound of the engine keeps the gear up until the engine quits and the unit then extends the gear. The batteries can go in the outboard tip.
If anyone would like to have this unit I'll be more than glad to sell it for a few bucks. Just enough to cover shipping is enough as I never plan to use it myself. Lemmeknow.
Blessings,
Will

Rudy Taube · « **Reply #16 on:** January 10, 2008, 11:56:01 PM »

Alan, in reply #15, has the perfect solution for the retract controller. The JMP ECL timer has a simple outlet plug that would go to the retract servo, and another plug that would plug into a small battery. The gear is programed to retract 10 sec. after TO. It is easy to set the timer to lower your gear at any time you want. Like Alan said, you could also have it shut down your engine (using a simple spring loaded wire, released by the retract servo, shutting off the fuel by squeezing the fuel line) at a time set by the pilot. This would shut off your engine at say: 5 min 40 sec (or whatever), and lower the gear at the same time.

I am surprised that more PACL flyers don't use this timer shut off device all the time. It is not just the obvious advantage of never having an overrun, and knowing EXACTLY when your engine will shut down, but the REAL advantage would come from being able to put enough extra fuel in your tank so that the tank never gets down to that dreaded low point toward the end of the flight where it changes the mixture during the last few maneuvers. This way you could always have that extra x oz. needed to have a consistant engine run right up to shut off. :-) ..... Or you could just fly ECL and not worry about it at all? Sorry, I could not resist.

The JMP timers are about the size of a postage stamp, weigh almost nothing and are very easy to use. They only cost about $36 and are available, in stock today, at:

http://www.bsdmicrorc.com/

Almost all modern retract systems have a simple "lock" up and a lock down so that the servo is not holding against the G loads. With our relatively small PACL planes, only <4 lbs. there are many light weight, small retracts available. With a small servo in each wing, and using a JMP timer, it would be an easy setup. .... I hope someone does it. I think it would be cool, and might be worth the effort in PA. I just wish I was not so lazy, I would do one myself!

Regards,

Bob Zambelli · « **Reply #17 on:** January 11, 2008, 06:19:26 AM »

Rudy - you can indeed buy small lightweight retracts that lock in both positions.

I bought some by Robart, model 600 as I recall. Very simple and light with short input throw.
Any servo with reasonable force should do the trick.

Bob Z.

Ted Fancher · « **Reply #18 on:** January 13, 2008, 09:48:02 AM »

Re retracts for stunters ... and whether it's a good idea or not.

The alleged desirability of retracts is to "reduce the drag" the landing gear creates. It has somehow been assumed that drag is inherently undesirable and that performance would improve if it is reduced. That is an aviation "axiom"!

One must remember, however, that most of our "axioms" come from the world of full scale aviation. Probably 90+% of the mission in full scale planes is to get them to go farther faster and more efficiently (burn less carbon). The very best way to achieve the maximum in that area is to reduce the drag to only that necessary to accomplish the mission.

This is because drag's only "negative" is that the more of it you have the more thrust you need to produce up front to overcome it. (Al Rabe had the discussion many years ago, by the way).

When you think about stunt you think of a few things right up front. 1.You don't want to fly any faster than you have to. 2.You want as much power up front as you can utilize. 3. You don't really care if you have to use another oz or so of fuel to finish the pattern. 4. You don't want to add unnecessary, non-productive weight (more fuel for more power is "productive"). 5.You want the airspeed to be as consistent as possible to simplify flying the pattern accurately.

One item common to achieving each and every one of the above is the positive value of a reasoned amount of drag!

There are two fundamental types of drag ... parasitic (or "form") drag, caused by the shape and frontal area of tvehicle, etc. ... and induced drag, caused by the production of lift. Of the two the former is essentially constant for a given speed and the latter, induced, can change dramatically as a result of the amount of lift necessary to perform the tricks in the pattern.

Let's deal quickly with induced drag first 'cause it's not really germane to the discussion. Within reason, induced drag should be kept as constant as possible because it is variable and "will" have an effect on the airspeed of the vehicle and the timing of maneuvers, etc. A subject for another day.

Landing gears have nothing to do with "induced" drag, but a lot to do with "parasitic" or form drag.

The drag associated with the gear will effect the items listed above in the following general way; all of which are basically to our advantage ... or, at least, not detrimental to our mission.

1. Will moderate our airspeed and make the ship less able to accelerate in windy conditions.

2. Will allow the engine to run at a higher power setting without excessive speed and in a better location on the torque curve while doing so.

3. Will allow the advantage of more BTUs in the fuel tank to produce that increased power.

4. Leaving out the retract mechanism will reduce the weight of the airplane thus improving performance, especially in high G maneuvers (I know, I know, Sparky and I have this argument all the time. I have never, however, advocated not achieving the best reasonable wing loading achievable with a reasonable amount of effort [not always the lowest, however])

5. Having a high ratio of parasitic to induced drag will mitigate the airspeed changes during maneuvering because the engine will be performing (again) closer to the best location on the horsepower and torque curves.

In other words, I think the bigger question is not how to best produce functional retracts (for stunters), but whether we should do so.

Ted

p.s. Might be fun to attack the various aspects of this post in more detail if anyone is interested. It really is a good "entre' " into the whole field of stunt airplane design.

Bill Little · « **Reply #19 on:** January 13, 2008, 12:20:55 PM »

Hi Ted,

Beyond any aerodynamic sort of discussion, I have never wanted to experiment with retracts simply because I would be guaranteed a malfunction on an Official Flight!

(and I don't get nearly enough of those already! LOL!)

Chris McMillin · « **Reply #20 on:** January 13, 2008, 01:26:26 PM »

Quote from: Ted Fancher on January 13, 2008, 09:48:02 AM

Re retracts for stunters ... and whether it's a good idea or not.

The alleged desirability of retracts is to "reduce the drag" the landing gear creates. It has somehow been assumed that drag is inherently undesirable and that performance would improve if it is reduced. That is an aviation "axiom"!

One must remember, however, that most of our "axioms" come from the world of full scale aviation. Probably 90+% of the mission in full scale planes is to get them to go farther faster and more efficiently (burn less carbon). The very best way to achieve the maximum in that area is to reduce the drag to only that necessary to accomplish the mission.

This is because drag's only "negative" is that the more of it you have the more thrust you need to produce up front to overcome it. (Al Rabe had the discussion many years ago, by the way).

When you think about stunt you think of a few things right up front. 1.You don't want to fly any faster than you have to. 2.You want as much power up front as you can utilize. 3. You don't really care if you have to use another oz or so of fuel to finish the pattern. 4. You don't want to add unnecessary, non-productive weight (more fuel for more power is "productive"). 5.You want the airspeed to be as consistent as possible to simplify flying the pattern accurately.

One item common to achieving each and every one of the above is the positive value of a reasoned amount of drag!

There are two fundamental types of drag ... parasitic (or "form") drag, caused by the shape and frontal area of tvehicle, etc. ... and induced drag, caused by the production of lift. Of the two the former is essentially constant for a given speed and the latter, induced, can change dramatically as a result of the amount of lift necessary to perform the tricks in the pattern.

Let's deal quickly with induced drag first 'cause it's not really germane to the discussion. Within reason, induced drag should be kept as constant as possible because it is variable and "will" have an effect on the airspeed of the vehicle and the timing of maneuvers, etc. A subject for another day.

Landing gears have nothing to do with "induced" drag, but a lot to do with "parasitic" or form drag.

The drag associated with the gear will effect the items listed above in the following general way; all of which are basically to our advantage ... or, at least, not detrimental to our mission.

1. Will moderate our airspeed and make the ship less able to accelerate in windy conditions.

2. Will allow the engine to run at a higher power setting without excessive speed and in a better location on the torque curve while doing so.

3. Will allow the advantage of more BTUs in the fuel tank to produce that increased power.

4. Leaving out the retract mechanism will reduce the weight of the airplane thus improving performance, especially in high G maneuvers (I know, I know, Sparky and I have this argument all the time. I have never, however, advocated not achieving the best reasonable wing loading achievable with a reasonable amount of effort [not always the lowest, however])

5. Having a high ratio of parasitic to induced drag will mitigate the airspeed changes during maneuvering because the engine will be performing (again) closer to the best location on the horsepower and torque curves.

In other words, I think the bigger question is not how to best produce functional retracts (for stunters), but whether we should do so.

Ted

p.s. Might be fun to attack the various aspects of this post in more detail if anyone is interested. It really is a good "entre' " into the whole field of stunt airplane design.

Hi Ted,
Yeah, you are right. All of your points are valid.
But, it looks cool.
You have always built some of the nicest, well proportioned models in stunt, with great paint schemes and details. Your stuff doesn't suck and isn't ugly. So I know you understand the WOW and COOL factor of someone wanting to do it.

Whitely's Mustang was to obviously make his model more scale. It worked and looked the part. On a regular stunter, it would be, well... just adding some more cool. Especially if it not only didn't hurt performance, but actually added to it.

Interesting...

Chris...

PatRobinson · « **Reply #21 on:** January 13, 2008, 07:30:22 PM »

Hi Guys,
One area where retracts could be functionally useful maybe created by the growing move to bigger engines and to the corresponding bigger props, which in turn, need longer landing gear to provide prop clearance. It would seem to me that this long LG could act like a pendulum hanging underneath the plane,that could possibly ,rock the plane on the roll axis during turns.
At the least, you should be careful of the wheels weight when using longer LG and retracting the gear should eliminate the problem. This might be an area where retracts are possibly, more than just cool, but of course there is nothing wrong with "just being cool"

Question for Ted: If you reduce form /parasitic drag in the overall drag budget could you increase wing thickness by some percentage or fraction of a percent to provide the speed consistency you mentioned. This would slightly increase the form drag of the wing but it would also increase lift and also increase induced drag.
I would also think, increasing wing lift with airfoil thickness should probably be balanced against the airplanes weight because it would probably effect the airplanes wind handling characteristics a little like increasing wing area and reducing wing loading, but not to the same degree.

Now,if you could, as a result of this increased lift, reduce flap deflection slightly there might also be some reduction in the significant drag level that is generated by those deflected flaps. This would hopefully, reduce your overall drag budget or at least keep it close to the same. Hmmmm

Ted, This stuff is coming off the top of my head, so, I could dead wrong in my thinking, but in any event ,it is fun to tickle the old brain cells a little.

Ted, thank for your interesting and thought prevoking post. Good Stuff!

Pat Robinson

Ted Fancher · « **Reply #22 on:** January 13, 2008, 08:06:11 PM »

Quote from: Chris McMillin on January 13, 2008, 01:26:26 PM

Hi Ted,
Yeah, you are right. All of your points are valid.
But, it looks cool.
You have always built some of the nicest, well proportioned models in stunt, with great paint schemes and details. Your stuff doesn't suck and isn't ugly. So I know you understand the WOW and COOL factor of someone wanting to do it.

Whitely's Mustang was to obviously make his model more scale. It worked and looked the part. On a regular stunter, it would be, well... just adding some more cool. Especially if it not only didn't hurt performance, but actually added to it.

Interesting...

Chris...

Chris,

Absolutely no argument with anything you've said. No question it looks cool ... it almost goes without saying that -- especially semi-scale -- stuff would look much better without the gear hanging out (might even make 'em go from "semi" to "truly" in the air).

No, as is my usual want, my comments only dealt with the aerodynamic pros and cons of doing so.

As a matter of fact, the modern one speed powertrains can be set-up so as to mitigate any effects of the reduced drag (bigger props and lower pitches, probably)

Give a little, take a little.

Ted

Ted Fancher · « **Reply #23 on:** January 14, 2008, 05:43:41 PM »

Quote from: PatRobinson on January 13, 2008, 07:30:22 PM

Hi Guys,
One area where retracts could be functionally useful maybe created by the growing move to bigger engines and to the corresponding bigger props, which in turn, need longer landing gear to provide prop clearance. It would seem to me that this long LG could act like a pendulum hanging underneath the plane,that could possibly ,rock the plane on the roll axis during turns.
At the least, you should be careful of the wheels weight when using longer LG and retracting the gear should eliminate the problem. This might be an area where retracts are possibly, more than just cool, but of course there is nothing wrong with "just being cool"

Question for Ted: If you reduce form /parasitic drag in the overall drag budget could you increase wing thickness by some percentage or fraction of a percent to provide the speed consistency you mentioned. This would slightly increase the form drag of the wing but it would also increase lift and also increase induced drag.
I would also think, increasing wing lift with airfoil thickness should probably be balanced against the airplanes weight because it would probably effect the airplanes wind handling characteristics a little like increasing wing area and reducing wing loading, but not to the same degree.

Now,if you could, as a result of this increased lift, reduce flap deflection slightly there might also be some reduction in the significant drag level that is generated by those deflected flaps. This would hopefully, reduce your overall drag budget or at least keep it close to the same. Hmmmm

Ted, This stuff is coming off the top of my head, so, I could dead wrong in my thinking, but in any event ,it is fun to tickle the old brain cells a little.

Ted, thank for your interesting and thought prevoking post. Good Stuff!

Pat Robinson

Pat, This is going to sound silly, I know ... but

I don't have time to get into this right now because we've been invaded by skunks (at least one) under our back deck and we're having the devil's old time trying to get rid of it and the smell inside the house. I've been surfing the web trying to get good ideas but what I find are mostly people like myself with the problem and no solution.

Anybody know a good way to get rid of the darn things and just as important, get rid of the dang smell that permeates everything? We;ve set out bowls of ammonia with cloth wicks under the deck at the suggestion of the SPCA (they think its kind of funny and aren't allowed to do anything "mean" to the nice little black and white kitties. I'm thinking of buying a machine gun.

Ted

Ted Fancher · « **Reply #24 on:** January 19, 2008, 10:46:27 PM »

Quote from: PatRobinson on January 13, 2008, 07:30:22 PM

Hi Guys,
One area where retracts could be functionally useful maybe created by the growing move to bigger engines and to the corresponding bigger props, which in turn, need longer landing gear to provide prop clearance. It would seem to me that this long LG could act like a pendulum hanging underneath the plane,that could possibly ,rock the plane on the roll axis during turns.
At the least, you should be careful of the wheels weight when using longer LG and retracting the gear should eliminate the problem. This might be an area where retracts are possibly, more than just cool, but of course there is nothing wrong with "just being cool"

Good point, Pat. I've never been overly concerned about vertical CG on a "conventional" layout but there's no question if you start throwing bigger and bigger props on such a ship the gear will get longer and the wheels will have a greater effect on both roll and pitch. I've not done any research on the subject but I would expect the roll issue to be nominal (but real) while the effect on pitch might be more dramatic. As you suggest, pulling 'em up out of the way would obviate both issues.

Question for Ted: If you reduce form /parasitic drag in the overall drag budget could you increase wing thickness by some percentage or fraction of a percent to provide the speed consistency you mentioned. This would slightly increase the form drag of the wing but it would also increase lift and also increase induced drag.
I would also think, increasing wing lift with airfoil thickness should probably be balanced against the airplanes weight because it would probably effect the airplanes wind handling characteristics a little like increasing wing area and reducing wing loading, but not to the same degree.

I think Al Rabe's approach (greater frontal area, bombs, etc) would be a better means to absorb the power.

Gotta remember the symmetrical airfoil approximates God's perfect subsonic aerodynamic shape (the teardrop) and increases in the thickness of such a finely shaped item will have a comparatively negligible effect on form drag. Also remember that we only produce as much lift as is necessary to support the weight of the airplane at any given point. Making a wing capable of producing more lift is nice but, IMHO, you shouldn't trim a ship to produce a lot more lift than absolutely necessary in maneuvers. Remember, it isn't the wing's lift that changes our direction of flight in the pitch axis, it is only the means that allows us to do so. The tail directs the pitch attitude and as long as the wing produces the lift necessary to support the "G induced" weight that results from the pitch change everything is honkey dorey.
Now,if you could, as a result of this increased lift, reduce flap deflection slightly there might also be some reduction in the significant drag level that is generated by those deflected flaps. This would hopefully, reduce your overall drag budget or at least keep it close to the same. Hmmmm

In maneuvers that would likely be true. Once again, you'd have to determine how much drag results from developing the necessary lift (fat wing with less deflection vice thinner wing and more deflection). I don't know the answers to those questions but I'll bet Igor or Serge have some data on airfoils close to what we use.

Ted

Ted, This stuff is coming off the top of my head, so, I could dead wrong in my thinking, but in any event ,it is fun to tickle the old brain cells a little.

Ted, thank for your interesting and thought prevoking post. Good Stuff!

Pat Robinson

PatRobinson · « **Reply #25 on:** January 20, 2008, 03:07:29 PM »

Hi Ted,
First, I hope you have now got that skunk problem under control.

Ted , Thanks for your input. I agree that in conventional designs Vertical CG isn't usually an issue ,and at most, the only adjustment, I hear about is guys using heavier or lighter wheels to balance vertical CG.
I see reports of guys using 16" props which moves things clearly outside the box of conventional design so we will have to see how that works out.

I also agree, that an excess of lift is not ideal ,especially in wind.

My post regarding flap deflection comes from the writings of Bill Netzeband articles and Martin Simons book that I remember saying from 0-15 degrees lift increases greater than drag , from 15-25 degrees lift and drag increase equally and 25+ degrees of deflection drag increases more than lift. I also vaguely remember something in NACA data about max lift for a "plain flap" occuring around 30 degrees. 1930's aero data makes for dry reading so my memory on the numbers may not be 100%. Anyway, the point I was trying to make is that the goal of both, the airfoil and flaps is to provide the needed lift it was my hope that reducing flap deflection might keep the drag levels more consistent.

Side Note:( I mean't to bring this up in the last post ,but I forgot )
One of the goals mentioned for big engines and big props is to fly slower and because lift is reduced at the square of speed this means there is an actual reduction in available lift. My question is: Would increasing airfoil thickness be a viable way to restore the level of lift without increasing wing area. The goal in this case, is to recover lost lift rather than increasing overall lift.
Flight testing is probably the only way to refine how well it works, but is the concept valid for those guys out who are looking to fly slower with bigger props?

Ted, Thanks again for your input. This interesting stuff!

Pat Robinson

Tom Luciano · « **Reply #26 on:** January 21, 2008, 07:23:40 AM »

Quote from: Dennis Adamisin on November 30, 2007, 02:45:18 PM

Tom L:
Don't know if yu had a chance to talk to your friend ablut his carrier bird with retracts, but what you describes sounds like the "Centrac" (SP?) system from way back when. The concept was to mount the bellcrank in a slide and retain it at the end of a slot with a spring. At launch (no line tension) the gear would be down. At 1/4-1/2 lap after launch the line tension would be such that the load on the bellcrank would overcome the spring force, the bellcrank would slide (spanwise) in a channel til it reached a sop and the gear would literally be pulled up by the line tension. When someencing low speed flight, the line tension would reduce, the spring would pull the 'crank back to the other end of the slot, and the gear would exxtend.

It is a great concept for a Carrier flight profile. However stunt models do not pull nearly so hard, and sometimes lines go slack - making for some VERY interesting manuver presentations!

Dennis,

We finally had our Christmas party last Thursday due to weather issue's. Spoke to Bill Hotra builder of Mike's carrier plane at 91 years young this gentlemen is sharp as a tack. Yes, you are correct he used a design very similar to what you speak of. Another member chimed in and said around that same time there was a guy flying stunt using retracts and they worked quite well but, he could not remember who it was. I will do some more poking around to see who it was. By the way I understand all the negative technical points that come up with this but RETRACTS have a definite WOW factor.

Tom

Mark Scarborough · « **Reply #27 on:** January 21, 2008, 01:41:58 PM »

Just a couple points from my limited perspective. I have long lusted after retracts, especially since I have a thing for Scalish stunters. (Randy Powell, dont tell Pat about my retract fetish he will disown me!) The long gear legs can be accomodated simply by tweakign the leadouts position vertically, as in use dihedral or locate the leadouts vertically in the wing tip as needed to offset the weight. Incidently dihedral has the same effect as lengthening the gear legs for prop clearance with the benefit of loosing an inch of so of springy wire in the gear leg.
My largest issue with retracts on a stunter ( I am actually a supporter of the parasitic drag is good theory) , I would not want my retracts retracting untill after my level flight had been completed. I would be concerned about trim changes during the graded portion of flight, during climb out and level flight. pluss, you have the effect of getting through the level flight, and the gear retracts to say ": ok lets rock I am ready now" then woosh into the Reverse wingove,,,,,

Dave Nyce · « **Reply #28 on:** January 22, 2008, 05:22:27 PM »

Hi Ted. Skunks mate in Feb and March, so it's best to get rid of it soon. You can trap it, but using a foot-hold trap will likely cause it to spray. You can use a box-type trap of 7 x 7 x 24 inch or larger (available from Harbor Freight and many other places). To deter it from spraying, place the trap inside of a sack with the door of the trap at the open of the sack with enough sack available at the front for closing later, but make sure the trap door is not blocked by any of the sack. The sack should have a draw-string for easy closing. Position the trap a short distance from the house, just in case. Near your trash can might be a good place. Bait the trap with sardines or peanut butter near the trigger pedal (but don't use sardines if cats are around, or you may catch them). The trap door closes when an animal is caught. CAREFULLY approach from the back side of the sack and close the open end of the sack. Slowly transport the trap with the closed sack, and the skunk will probably not spray. When in a safe area, the skunk may be dispatched with a .22LR rifle. He will likely spray at that time, and the trap will stink, but at least it's no longer at your house.

Dave

NED-088 · « **Reply #29 on:** February 21, 2008, 07:44:16 PM »

One of my collegues from neighbouring Germany, Uwe Kehnen, has a good description of his take on the subject on his web site: http://www.fesselflug.eu/html/stuntmodel_with_retracts.html
Uwe and I have known each other since we were in our early twenties. Met him at my first contest in Bochum.... must have been 1973 or 4....

Shultzie · « **Reply #30 on:** February 21, 2008, 08:59:31 PM »

Quote from: NED-088 on February 21, 2008, 07:44:16 PM

One of my collegues from neighbouring Germany, Uwe Kehnen, has a good description of his take on the subject on his web site: http://www.fesselflug.eu/html/stuntmodel_with_retracts.html
Uwe and I have known each other since we were in our early twenties. Met him at my first contest in Bochum.... must have been 1973 or 4....

THANKS FOR THAT VERY INFORMATIVE AND EXCITING POST! THANKS KEITH...FOR YOUR HELP ALSO.

Shultzie · « **Reply #31 on:** February 22, 2008, 01:02:48 PM »

Found this old magazine...with Harold's retracts..
WOW! Talk about an engineers mind....(waaaay beyond my imagination or skill)

Thierry SAUNIER · « **Reply #32 on:** March 12, 2008, 04:52:56 PM »

Hi, Friends!
Since I moved to E-C/L now 2 years ago, it was pretty easy to come up with a retract gear. The battery was already in, the JMP Timer has been adapted to my desiderata by JMP himself.
I 'm using the light Robart 600 series retract system with one standard Hitec servo located besides the bellcrank.
My last F2B ship is a semi-scale french Warbird "Dewoitine 520" based on Serge Delabarde's Yak 55. More details and photos on WWW.clacro.de/airplanes.
It's a lot of pleasure when the gear moves in and out slowly by means of an electronic "delay system" .
Of course this airplane is a fully competitive F2B ship.
Be quiet! It sometimes happens to me to play with wet engines and have to clean that bloody oil...
Rgds, Thierry

Shultzie · « **Reply #33 on:** March 12, 2008, 06:01:38 PM »

Quote from: Thierry SAUNIER on March 12, 2008, 04:52:56 PM

Hi, Friends!
Since I moved to E-C/L now 2 years ago, it was pretty easy to come up with a retract gear. The battery was already in, the JMP Timer has been adapted to my desiderata by JMP himself.
I 'm using the light Robart 600 series retract system with one standard Hitec servo located besides the bellcrank.
My last F2B ship is a semi-scale french Warbird "Dewoitine 520" based on Serge Delabarde's Yak 55. More details and photos on WWW.clacro.de/airplanes.
It's a lot of pleasure when the gear moves in and out slowly by means of an electronic "delay system" .
Of course this airplane is a fully competitive F2B ship.
Be quiet! It sometimes happens to me to play with wet engines and have to clean that bloody oil...
Rgds, Thierry

Thanks Thierry... lets give www.clacro.de/airplanes.com a try?
opps...that didn't fly either

Thierry SAUNIER · « **Reply #34 on:** March 13, 2008, 03:29:26 PM »

Hello, Sorry if I made a mistake, here's the web site from Klaus Maikis where he published both my E /CL F2B models:

http://www.clacro.de/

or you type CLACRO in the Google bar
have E fun... Thierry

Shultzie · « **Reply #35 on:** March 13, 2008, 06:47:38 PM »

Quote from: Thierry SAUNIER on March 13, 2008, 03:29:26 PM

Hello, Sorry if I made a mistake, here's the web site from Klaus Maikis where he published both my E /CL F2B models:

http://www.clacro.de/

or you type CLACRO in the Google bar
have E fun... Thierry

WOW! THIERRY...GREAT LOOKING MODELS ON KLAUS'S WEBSITE...INCLUDING YOUR'S!

Shultzie · « **Reply #36 on:** March 13, 2008, 06:49:32 PM »

Quote from: Thierry SAUNIER on March 13, 2008, 03:29:26 PM

Hello, Sorry if I made a mistake, here's the web site from Klaus Maikis where he published both my E /CL F2B models:

http://www.clacro.de/

or you type CLACRO in the Google bar
have E fun... Thierry

WOW!!!!! THIERRY!!!
THAT WEBSITE HAS SOME AWESOME LOOKING EQUIPMENT IN THE GALLERY HUH?
Check out these two examples of some beautifully crafted stunters

Fred Shattuck · « **Reply #37 on:** May 06, 2008, 08:10:30 PM »

I love all this knowledge and experience. It is decided, I am building a new bird with three wire for throttle and retractable gear. our field is very rough, and we use oversize wheels. I like the timer/engine kill combo. wish me luck. FRED

Author Topic: RETRACTS FOR STUNT MODELS???? EZZEST' N' LIGHTEST??? (Read 2945 times)

Willis Swindell

Alan Hahn