I have a Hobbico Avistar Select. The ailerons don't move very much. I have soloed many times now and want to know how to increase the throws more. Right now they move only enough to do 1 roll in 3 seconds! Please help me!

Either move the rods farther out on the servo horn, get a longer servo horn, or move the linkage closer to your wing on the AILE torque rods, Also if you have a computer radio you can change the travel ADJ past100%.
later daveo

Avoid setting a computer radio's primary throw rate outside 90% to 110%. If you need more or less... do it mechanically as soon as practical. The servo torque and performance ratings are based on the normal "100%" throw range.

Going down, you decrease power by squareing the decrease in throw. (50% setting on the ATV... you have effectively got 25% power.)

Going above 110% can get into problems with over-ranging the position sensing potentiometer. its only designed to operate within a limited arc. You exceeed that arc and all bets are off on what the servo will do.

This is where computer radios teach bad habits... (and the JR advertizment of setting to 139% is asking for problems.)

The mechanical method of increasing throw in the previous post is correct. You first try to move away from center on the servo arm. IF you can't gain enough throw that way, THEN you try moving closer to the hinge att he control surface. Move one hole at a time at the servo or the control surface. If you have the threaded rod type aileron torque rods... 2 to 3 turns of the nylon adjuster, and move both sides the same amount.

On the Avistar (and some other planes), you can sometimes improve roll rate by just turning the clevices on BOTH ailerons out... moving both ailerons up a little. If the ailerons are adjusted with a slight downward deflection in "neutral" the roll rate suffers, and stalls become more likely to result in spins. Youdon;t have to move the ailerons enough to be easilly visible to make a LARGE performance difference.

FHHuber, I have great respect for you knowledge, as I have read many of your post. I don't understand
your theory on the folowing can you give me some more info. " 50% settings on the ATV... you have
effectively got 25% power" I routinely move mine past 100%. I was of the opinion that was better than
decreasing the mechanical advantage by moving the clevis closer to the control surface. I have a Pizzaz
and 1/4 scale Sukhoi. Both of these need more throw to do 3-D type stuff than I can get without
setting the ATV up or moving the clevises in.
later daveo

What's misleading here is regarding the quality of the servo and resolution. Higher end servos are happy to be pushed to the limits of their throw and that is where best resolution can be attained.

Servos designed to take greater than "standard" throw range... fine, go ahead and use the capability. A Standard servo as used by the average beginner (the ones that come with the average 4 to 6 ch radio system...) is not designed to handle the added travel of exceeding "100%" ATV.

the geometry of the normal pushrod system mathematically can be reduced to a series of levers and fulcrums. When you mechanically decrease throw, rather than using ATV, you increase the effective servo power for the same deflection angle. You also increase the effective precision of control surface movement.

Do a few weight lifting experiments with a servo... tie a 40 oz weight one inch out on the servo arm and then make the servo lift the weight. Move that weight out to 2 inches, and try to get the same servo to lift it the same distance as before. Try 1/2 the weight... then 1/4. (with a "standard" 45 to 52 in-oz servo, only the first and last lifts will succeed.)

You all have some good points. But in hubbers defense I must highly agree. Not only is it fact that using computer radio's to make your corrections to mechanical also brings up one more serious problem. Flutter and servo glitch. Yes with the hitech 100.00 servo you can push them to there limits and keep them happy. But standard 45oz servo's that generally come with a radio. Bad idea? This has been printed in numerous magazine article's since the computer radios have been out. you are answering a question of the beginner. dont give him the easy out he must learn how to make the mannual adj. to ever understand how the setup works. its no different then trimming a new plane. do you leave all your trim levers adjusted all over instead of making the mechanical adjustments to the plane? I hope not!

I have done everything manually. I don't have a computer radio yet. I think I'll just have to get longer servo arms. Thanks for your help.

Engineering aspects aside, Huber did hit on what I feel is the answer to your question which was how to effectively increase the roll rate of your Avistar. The Avistar, Superstar and almost every high-wing trainer roll much bettter by having a greater amount of throw when moving up instead of down. You can do this easily by moving your servo control horn back(away from the control surface) a notch and adjusting the clevis for neutral accordingly. It's easier to see than explain but once you try it you'll see what I mean. It won't take a lot of extra through to make your Avistar roll like a champ! Good luck!

Jeff Benko
Palm Beach Skyhawks

When you say the control horn, you mean the nylon piece on the torque rod, right. If that is what you mean then there is only one hole to put the clevis in.

No, I meant the control "arm" on the servo itself. I'm sorry I said control "horn." I also forgot about the Avistar using only one servo so the method I suggested will NOT will not work. For this, I apologize! It DOES work when one servo is controling one flight surface however. It is possible to move the control arm forward or backward a notch on the servo itself to get more throw either up or down.

In your case I would consider turning the clevis's in a few turns so you do have more up throw than down and cranking down the horns on the torque rods a few turns so you have more throw overall. Don't crank the clevis's in so much that your ailerons act like spoilers however. If you do you will lose lift.

Again, sorry for creating confusion blueangel.

You don't have to apologize, everyone makes mistakes. I had a brand new wing for the Avistar and I am building it now. I am going to try screwing the nylon part on the torque rod a little more. About turning the clevis in, won't that make the aileron stick up and not flat. If it does then it will make really bad spoilers. I understand what you said. I think if I do that even a litttle the ailerons won't go down at all when I bank, they might just go flat. They might even make it need up trim because that is like down elevator.

With the single, centered servo, with the output shaft pointed down: (common trainer wing)

Differential throw can be set up by clippng a 6 arm servo output "wheel."
Clip 3 consecutive arms off, clip the center of the 3 that remain.
The resulting output arms are pointed equally forward with the servo centered. When the (slightly longer than with a straight across output dual arm "wheel.") the natural servo motion will give more positive push (up) deflection than down.

Using a round wheel with no factory holes, you can customize the amount of differential, but getting even throw on both sides takes some care.

If the servo is on the top of the wing, (as in common SPAD aircraft) the V would point back instead of forward to give correct differential.

Huber's suggestion with a clipped 6 arm servo wheel is the way to go. It worked great on a trainer of mine as well as with a Goldberg Cub both using std. servos. The amount of differential is fixed but is close to ideal anyway.

The advantage of differential aileron throw is that by getting more throw from the upraised aileron and less throw from the lowered aileron, you develop less lift and less drag on the outside wing and much less lift but more parasitic drag on the inside wing. This results in less adverse yaw during turns. With strip ailerons, it can pretty much cancel any adverse yaw in turns as there is relatively little adverse yaw with them anyway.

A well designed sport aircraft will have a good balance between dihedrahl and fin and rudder areas that results in a correct amount of roll/yaw coupling and reduces or eliminates the need for any rudder input in normal turns. On these aircraft, differential throw (other than any specified in the plans) will offer little or no benefit.

But differential aileron throw can be very useful in scale aircraft that would otherwise be much more demanding of good rudder coordination during turns and aileron inputs. Broad chord ailerons at the ends of the wing as on a Cub are good examples of ailerons that will cause a large amount of adverse yaw.

Nearly all trainers have a wing with a lot of dihedrahl angle. Yaw on an aircraft will cause the inside wing to advance relative to the outside wing. The advancing wing, if it has a large dihedrahl angle, will experience an effective increase in it's angle of attack and will develop more lift which will in effect decrease the roll rate by attempting to roll the aircraft upright again. With a properly proportioned vertical fin, the aircraft will be overly stable and essentially self righting in roll. (with a large enough rudder in proportion to vertical fin area, the plane can make coordinated turns on rudder alone as is done in polyhedrahled sailplanes) This stability is a good trainer trait but can be a little irritating when your skills improve and you want try some aerobatics. On an overly stable aircraft, differential throw can increase roll performance by again reducing adverse yaw and reducing the tendency of the inside wing to generate additional lift due to the unwanted adverse yaw.

FHHuber idea sounds like it will work, but is also slightly confusing. When you say 6 arm servo "wheel" it throws me off a little. You mean a servo arm with six arms making a star, right? I don't know what you mean by they will be pointing equally foward. Do you mean that the 2 arms left won't make a straight line or they will look like the foward view of a plane with alot of dihedral? If you could clear that up a bit it would might be able to help me better.

As for Air Bear, I have never had the problem of adverse yaw on my plane. It can be flown with rudder because it moves more or less than an inch. The recommended trow for the rudder is, I think, 1/4 or 1/2 of a inch. The plane doesn't have alot of dihedral either. It is made to do basic aerobatics. I understand Air Bears descripsion of adverse yaw and what causes it and everything. That isn't why it doesn't roll that fast. It actually rolls faster than a normal Avistar. I maxed out all of my throws and I still want more. The roll rate still isn't fast though. It is barely 1 roll a second. I am just a regular person who likes to "supe up" their trainer before they get another.

Thanks.

Hi Blueangle, Your Hobbico 40 is a fine trainer, but----- trainers were never ment to do lighting fast rolls. However, most trainers have a lot of yaw/roll coupling (a fancy way of saying that when you deflect the rudder the model will roll in the same direction). If this is true with your Select 40 (and I suspect it is) then you should be able to increase your roll rate by using both your rudder and ailerons together. For instance, if you want to roll left, just push the rudder and the ailerons to the left. Once you get used to this arrangement try momentarily bumping the elevator stick towards the top of the transmitter just as the moded reaches inverted. It will bump the nose up and help to keep you "on line" as you finish your roll.

Thanks rixter. I never thought of that. I know I won't get lightning fast rolls. I just wanted to increase the roll rate a little. The Avistar can do nice snap rolls. It looks like a fighter jet just getting hit by a missle and spiraling down in a very weird way. Thanks again and I will make sure to try that.

Yes, the 6 arm "star" shaped servo arm/wheel (output piece that screws onto the top of the servo output shaft) will end up looking like a very wide V when the clippng is done. The single missing arm location and the center of the 3 other missing arm locations will be aligned straight fore and aft. The 2 remaining arms will each be 30 deg forward of being parallel with the LE of the wing. (360/6 = 60 deg separation of arms. The space between 2 arms would be parallel wth the LE if you put the arm/wheel on the servo, then clip the unwanted arms off.)

You may not need to get a longer arm/wheel... The little white plastic pieces the clevices attach to can be screwed down closer to the wing on the torque rod. Screw both down the same amount SLOWLY making the change. You can go appx 4 turns each side the first try. The shorter distance from the pushrod connection to the hingeline will make the ailern mve more for the same amount of pushrod movement.

Only change ONE thing at a time! Don't swap the straight arm for the angled one AND change the torque rod connection at the same time. Fly it a couple of times between changes.

When you change arms... try for the same amount of upward defletion with the new arm as was obtained with the old one. (It won't be exact... a little more is OK.) Downward movement will be reduced! You will need appx 1/4 inch longer pushrods, or the ailerons will be drooped significantly at neutral.

As sooon as I rebuild my wing I will try all of the suggestions. Don't worry, I will only do one at a time. hanks for clearing up the servo arm issue. Next time I go to the hobby store I will get longer pushrods. Thanks for all of your help.