Author Topic: Control Throw Ratios for Dummies... (Read 1473 times)

wwwarbird · « **on:** January 25, 2008, 07:56:40 PM »

From the Stupid Question Dept.,

Let's say you have a pushrod in a given location on your bellcrank, and your flap and elevator horns are identical, and each have five holes. Without concerning ourselves with actual throw distance here, is it possible to acheive an accurate 2:1 flap to elevator throw ratio with this simple setup? With this I mean the having the elevator move twice the distance as the flap. Obviously the elevator pushrod would need to be closer to it's axis than the flap pushrod, but where would each pushrod be set on each horn?

Crist Rigotti · « **Reply #1 on:** January 25, 2008, 08:28:17 PM »

The elevator pushrod would go in the flap horn twice the distance as to where it would go into the elevator horn. Thus a 1:2 flap/elevator throw.

Randy Powell · « **Reply #2 on:** January 26, 2008, 12:19:55 AM »

Though I'm not sure why you would want that unless it's a feather light plane. Really feather light. The Cobra I'm flying is designed with a 1:1.5 ratio and it was pretty tough to fly until I moved the pushrod way in on the bellcrank to slow the controls down.

Jim Oliver · « **Reply #3 on:** January 26, 2008, 06:32:25 AM »

Randy,

Not to highjack a thread, but would you please post your final control set up? I have a Cobra short kit waiting for space on the building board.

Thanks,
Jim

wwwarbird · « **Reply #4 on:** January 26, 2008, 05:23:28 PM »

Randy,

My thinking is that this model (the PBY) is going to be on the heavier side, 80 ounces the way it's looking, maybe even a couple more. I know you want the flap movement for the lift, but of course you can really slow the plane down too. With only 700 square inches to work with, I want to maintain the airspeed at all times without the flaps slowing the model down. I'll be searching for a happy medium. I've kind of gone this way with another model, and it seemed to work well. I'm just kind of thinking ahead and "mind-grinding" on it all at this time.

Randy Powell · « **Reply #5 on:** January 26, 2008, 10:02:56 PM »

Jim,

3/4" at the bellcrank. Bellcrank to flap, ~1.3". Flap top elevator, 1" to 3/4"

wwwarbird · « **Reply #6 on:** January 28, 2008, 11:16:25 AM »

Crist and all,

In this particular case I will be having two separate pushrods coming off the bellcrank from the same location, one above the bellcrank and one below it. Would I then want the flap pushrod to connect it's horn at twice the distance from it's axis (hinge line) than the elevator pushrod? Would that actually result in double the travel at the elevator compared to the flap? I know could just set up a makeshift linkage and check this all out, but I just haven't taken the time. I'm on a roll with construction right now and don't want to deviate.

Paul Smith · « **Reply #7 on:** January 28, 2008, 12:50:13 PM »

I believe in the old "two pusrods off the bellcrank" setup.

I put the flap rod on the middle of the bellecrank and the flipper rod in the outboard hole,

The flaps and are adjusted and built into the plane.

You can then tweek the flipper ratio to you heart's content by just working at the back end of the model.

This eliminates the "double trouble" of having ALL the force of BOTH the flaps & flippers go through the short pushrod.

Bill Little · « **Reply #8 on:** February 01, 2008, 10:23:31 AM »

WOW! A title to a thread I could identify with!

Listening to the real *experts* ( a true term of endearment!) I have always heard that the heavier the plane, the more flap you want. For the given reasons of increased lift.

I am always intrigued by the various systems used in Classic planes. 2 pushrods off the bell crank, or one all the way to the elevator and another going back to the flaps, etc., etc..

I truly believe that the modern engines have been the real means for success of the fatter airfoils/heavier wing loadings that fly so well!

Any differing opinions/facts, PLEASE jump in! (I have a new flak jacket.

)

tom hampshire · « **Reply #9 on:** February 01, 2008, 02:47:54 PM »

Hi Bill - No flak jacket required. I agree that more flap travel is the setup for a heavy airplane, with 1:1 flap - elevator travel. BUT, for a classic airplane with a short tail moment (Chief, Nobler, etc.) more elevator travel is required. The reduced tail length makes it necessary to increase the elevator travel and hence lift to generate the same turning moment. With equal flap/elevator travel, even light short tail airplanes don't turn well at all. From level flight, they seem to rise while pointing in the original direction, and after 10-20 feet of flying this way, suddenly turn all at once. Pro stunt? Not hardly. What I don't know about is how to set up an airplane which is both short tailed and heavy. Certainly pushing the CG as far aft as is stable is the first step, and then modify the control throws. Comment welcome. Tom H.

Bill Little · « **Reply #10 on:** February 01, 2008, 03:30:36 PM »

Quote from: tom hampshire on February 01, 2008, 02:47:54 PM

Hi Bill - No flak jacket required. I agree that more flap travel is the setup for a heavy airplane, with 1:1 flap - elevator travel. BUT, for a classic airplane with a short tail moment (Chief, Nobler, etc.) more elevator travel is required. The reduced tail length makes it necessary to increase the elevator travel and hence lift to generate the same turning moment. With equal flap/elevator travel, even light short tail airplanes don't turn well at all. From level flight, they seem to rise while pointing in the original direction, and after 10-20 feet of flying this way, suddenly turn all at once. Pro stunt? Not hardly. What I don't know about is how to set up an airplane which is both short tailed and heavy. Certainly pushing the CG as far aft as is stable is the first step, and then modify the control throws. Comment welcome. Tom H.

HI Brother Tom!

I most heartily agree with you about the Classic planes and more elevator. Everything I have built, for years now, have had one of Tom's sliders on the elevator. And my Werwage I-beams have all needed a quicker elevator set up, even the USA-1!

Setting up a *heavy short coupled plane* is no problem at all!

(get rid of it and build a light one! LOL!!)

wwwarbird · « **Reply #11 on:** February 05, 2008, 05:28:46 PM »

Quote from: wwwarbird on January 26, 2008, 05:23:28 PM

Randy,

My thinking is that this model (the PBY) is going to be on the heavier side, 80 ounces the way it's looking, maybe even a couple more. I know you want the flap movement for the lift, but of course you can really slow the plane down too. With only 700 square inches to work with, I want to maintain the airspeed at all times without the flaps slowing the model down. I'll be searching for a happy medium. I've kind of gone this way with another model, and it seemed to work well. I'm just kind of thinking ahead and "mind-grinding" on it all at this time.

Tom and Bill,

I would be interested in your thoughts or opinions on the above mentioned approach...

Author Topic: Control Throw Ratios for Dummies... (Read 1473 times)

wwwarbird

Control Throw Ratios for Dummies...

Crist Rigotti

Re: Control Throw Ratios for Dummies...

Randy Powell

Re: Control Throw Ratios for Dummies...

Jim Oliver

Re: Control Throw Ratios for Dummies...

wwwarbird

Re: Control Throw Ratios for Dummies...

Randy Powell

Re: Control Throw Ratios for Dummies...

wwwarbird

Re: Control Throw Ratios for Dummies...

Paul Smith

Re: Control Throw Ratios for Dummies...

Bill Little

Re: Control Throw Ratios for Dummies...

tom hampshire

Re: Control Throw Ratios for Dummies...

Bill Little

Re: Control Throw Ratios for Dummies...

wwwarbird

Re: Control Throw Ratios for Dummies...