Correcting turn/corner rate

[Clint Ormosen]

It seems pretty well known that models that have the stab mounted higher or lower than the thrust line will have a different rate of turn inside vs. outside. What I want to know, is it better to correct the turn rate at the handle with line spacing or at the model with elevator bias? I've been successful with either method, but not real sure which is correct. It would seem that the elevator bias would be better because it is actually changing the turn rate and handle spacing is just masking the problem. Usually, on my planes anyway, a handle adjustment is much easier to do. What do others do?

[Dave_Trible]

Clint I've noticed your question has layed here a while without reply so let me give you my take which may be different than others.  Boy, if I could fly the ship for a minute..but ASSUMING;  1. Its properly aligned. 2.  The controls are set up at the more ideal 1-1 flap/elevator throw. 3.  The CG is pretty close to correct for the airplane,  then I'd always adjust the handle bias.  BEFORE you do play with the handle neutral a tiny bit.  Use this to get your bottoms the same height for both insides and outsides.  If it truly is the situation where more is required then move one line at a time up or down at the handle to find the sweet spot.  I've had a couple V tailed ships where the bias was ridiculous to look at but the ship felt equal both ways.  I just don't like jacking with unequal control throws on the airplane.

Dave

[Clint Ormosen]

Thanks for the input, Dave. I'm not really talking about any specific model right now. But this has been an issue with several of my last few Classic ships. The worst I've seen on one of my planes is a Sig Mustang I've been flying. The amount of handle bias needed to get the plane to turn equal is absurd. I've checked stab to wing incidence several times too. All the models I can remember turn tighter outside than inside.

[Derek Barry]

Generally if anything the planes with a higher stab will turn faster inside than outside. I assume this is because of the extra drag above the centerline of the plane? I think the correct fix would be to droop the elevators just a little, maybe 1-2 degrees. I have done it with handle bias but this causes more problems than it solves. I prefer my handle to be as close to equal/neutral as possible.

Derek

[Doug Moon]

It seems pretty well known that models that have the stab mounted higher or lower than the thrust line will have a different rate of turn inside vs. outside. What I want to know, is it better to correct the turn rate at the handle with line spacing or at the model with elevator bias?

Hello,

Are you talking about handle bias or spacing?  The two are different.  Increasing or decreasing handle spacing only increases or decreases your overall leverage.  Changing handle bias will change the "feel" as it adds or removes the amount of wrist movement needed in one direction.  Personally, I would not think this is a good way to go because it doesn’t actually correct any difference in control throw at the plane.  I try to use the handle in what I think is a vertical position.  The amount of movement in our wrist is not equal when talking down and up for a control line handle.  The down movement is actually significantly more than the upward movement available when starting from a vertical position with the arm extended.  But the natural pulling motion from one's bicep in flight accounts for that difference and the brain takes over and equals it out.  It’s actually pretty amazing.

Control differences.

If you are experiencing the same control effect plane to plane then you are building this into your model.  This is normal and just about everyone does this.  I know I do.  When setting up a control system I use a protractor on the side the fuse and adjust the flap pushrod to make sure the throws up and down are equal.  I used to eyeball this in the early days but once I started using a protractor and got the throws really close I was able to predict how the model would feel before I ever flew it.  I do this again at the elevator once the stab is installed.  I don’t know if this is common practice but since I do it on all my planes it is has made things very predictable. 

Once I fly the model I will usually have to shorten the elevator pushrod to even out the turn and get the plane to “lock in.”  This actually changes the flap angle at level flight and changes the AoA of the main wing in level flight. Take a look at some close ups of CL planes in flight.  It is very noticeable on some designs and not so much at all on others.  Over time I have gotten pretty good at predicting the amount of “droop” needed on the bench as I build the same plane often.  If you build different designs then of course just start out with everything equal aand make adjustments as needed during the initial flights.
 

[Steve Helmick]

Isn't some of what Doug is writing about from having the BC biased, i.e., not square to the leadouts, and then the flap pushrod attach point is then biased? Ideally, the pushrod should be attached on a line straight out (or in, if you reverse the BC) from the BC pivot. With mass produced BC's you can't have it both ways. And of course, the LO's are going to be moved around some in trimming. It looks like the better you plan these details, the better off you'll be in the long run.

I have read about some guys pinning the BC at neutral while they are setting up the control system...sounds like a good idea to me. Steve

[Dave_Trible]

Generally if anything the planes with a higher stab will turn faster inside than outside. I assume this is because of the extra drag above the centerline of the plane? I think the correct fix would be to droop the elevators just a little, maybe 1-2 degrees. I have done it with handle bias but this causes more problems than it solves. I prefer my handle to be as close to equal/neutral as possible.

Derek

The accepted explaination has been that in 'up' the stab/elevator is flying in clean air or propwash while in 'down' its working in garbage and blockage of the wing and flaps.  Doug hit on my next thought about handle mechanics.  Maybe you should move BOTH line attachment points at the handle up a notch to get more 'up' advantage.  In other words your wrist pivot point seems too high. In those classic days we also liked our wings to be lower in the fuse to help with the low-to-the-ground illusion.  This worsened the problem too. 

Dave

[Doug Moon]

Isn't some of what Doug is writing about from having the BC biased, i.e., not square to the leadouts, and then the flap pushrod attach point is then biased? Ideally, the pushrod should be attached on a line straight out (or in, if you reverse the BC) from the BC pivot. With mass produced BC's you can't have it both ways. And of course, the LO's are going to be moved around some in trimming. It looks like the better you plan these details, the better off you'll be in the long run.

I have read about some guys pinning the BC at neutral while they are setting up the control system...sounds like a good idea to me. Steve

I use a standard mounted BC, not reversed.  When I start the flap pushrod adjustment I try to have it as straight out from the pivot as possible.  Then I go and make the adjustments to get the throws equal amount in both direction.  The amount of movement from the initial setting is usually pretty small.

I have clamped the BC at neutral during setup before but I find setting the throws equal off the protractor gives me the closet turn rates once it is in the air.  Then the final adjustments bring it all together.  I have had them work right off the bench in the past, but that is kind of rare, and even so I mess with it just to make sure... 

Just like a stunthead, always messing with it.

[Dick Pacini]

Just a thought, has anyone ever tried positive stops on the bellcrank to limit travel?

[Dave_Trible]

Hi Dick.  Never intentionally did that but way back had a plane or two that bottomed out too soon on occasion.  The result is one taut line, one slack line and the airplace doing something strange.  Not something desired.  Most good airplanes require 15 degrees max travel so as long as the controls have say 25 degrees unfettered travel you shouldn't ever bottom out.  I'd not want to feel hitting any stops on the controls. (That's max travel each side of neutral)

Dave

[Clint Ormosen]

Hello,

Are you talking about handle bias or spacing?  The two are different.  Increasing or decreasing handle spacing only increases or decreases your overall leverage.  Changing handle bias will change the "feel" as it adds or removes the amount of wrist movement needed in one direction.  
 

Well, now I'm not sure. I thought I was talking about line spacing. On a hardpoint type handle it would be the distance from the center of the control bar to the "up" line, and center again to the "down" line. I typically move the up line outward and/or the down line inward to correct for a model with a tighter outside turn then inside turn. My question was is this a better solution rather than make the correction at the elevator of the model. In other words biasing the elevator either up or down for a more equal rate of turn.

[Doug Moon]

Well, now I'm not sure. I thought I was talking about line spacing. On a hardpoint type handle it would be the distance from the center of the control bar to the "up" line, and center again to the "down" line. I typically move the up line outward and/or the down line inward to correct for a model with a tighter outside turn then inside turn. My question was is this a better solution rather than make the correction at the elevator of the model. In other words biasing the elevator either up or down for a more equal rate of turn.

I follow you.  I was thinking when you said line spacing meant the distance between the up and down line.  When you talk about moving one line outward or inward in relation to the bar you are talking bias. 

We are on the same page.  I am thinking at the plane is the best place to cure this issue.  But that is just my opinion.  There are a million ways to skin the stunt cat so you want to try methods and pick what works best for you for that particular model. 

[Howard Rush]

Just a thought, has anyone ever tried positive stops on the bellcrank to limit travel?

I did that on combat planes to get the fastest turn in each direction without stalling when I hit full control.  I don't think that would be an advantage in stunt.  I think you'd want as much bellcrank travel as possible.

[john e. holliday]

If a person flies the same plane or the one and only plane all the time, then I think the biasing of the handle would help in some cases.  But, Doug being a great NATS champ should know as well as his coach.   Myself, I fly different airplanes during the time I get out to fly.  Not much fun flying by oneself.  Am trying to get each plane to fly to my liking which I think is getting them to fly the same.   But, there is way too much difference between a flapped plane and a non flapped plane.   My two favorite planes are the Primary Force and the DoodleBug.  Now for me the best flapped planes I had were the Noblers I built, all versions of them.

Sorry Ted, but I should add the Doctor in the equation also as it taught me a lot.  I just don't fly enough.