What can a guy do to reduce the tendency for an airplane to snap out when applying elevator. The specific aircraft ia a 120 size Ohio Sukhoi

If split elevator, make sure both halves are adjusted the same, and operate as one.
Check the balance.
Lessen the throws.
Apply less elevator.

That's about it.

Its probably to much throw.

I have a Smith Mini Plane that does the same thing on high rates. I reduced the throw on low rates until it did not snap then I turned up the high rates boy does it snap and Flat SPIN. I hope this helps. CB

Welcome to planes with big elevators.

Too much throw is normally it. The faster the speed of the plane, the less deflection is needed. Vice-versa, Slower speeds require more defection.

There is a change you could add nose weight and reduce the snap, however do it with throw.

This is a good place to use dual rates or expo. Different pilots, different preferences. Dual rates may work better for the newer pilot.

Set the low rate that flys the plane fine, and if you pull full up, it won't snap. Try this at the top of a loop. Fly the plane a couple of times to dial in the plane. Then set your high rate at any higher rate, so you can experiment with different things.

If you ever wondered why you by these radios with rates, expo, trim reset or computer mixing, this is why.

No rates available. Do it with linkage. Outside hole on control horn and inside hole on the servo.

Good Luck

I had the same problem with my Sig Cap 231 Breitling. It would snap when I applied full rudder on high rates when I was going full throttle. High speed snap.

I know this sounds crazy, but try adding some tail weight. It worked for me.

Here is a way to tell if your plane is truly balanced:

Full throttle flat and level
Pull too a 45 degree upline
Roll inverted

Don't touch the sticks once you are inverted. Do not add down elevator.

If you are truly balanced, the plane should continue inverted on a 45 degree upline. If you are too nose heavy, the plane will start coming down. If your too tail heavy, the nose will rise and the tail will drop.

The guys at Aeroworks came too one of our club meetings and gave us a seminar on how to trim planes. The above mentioned method was one of their procedures for balancing a plane.

The reason you need tail weight, (I think) is because one wing is stalling first at high speed and causing the snap.

After adding tail weight, both wings will stall at the same time. You should be able to come in full speed, flat and level and hog back on the elevator too bring the plane too a full stop and in a hovering attitude.

I did this too my Cap 231 and now it doesn't snap.

Be careful and add tail weight slowly. After the correct balance is achieved, the elevator on these aerobatic planes becomes "SUPER SENSITIVE".

After you have it properly balanced, only then should you add the Exponential. Adding the Expo. on high rates will help you with landings.

I know that the advise I have given goes against all conventional wisdom, but I'm telling you; it works.

gimme a minute too get my flame suit on................... okay, flame away.

Just as everyone said. Make sure that both halves move the same then reduce the throw until it don't snap.

too much throw, stalling the plane.
more of the same.

Rcpilet, I wont flame you but I must say......That is the first time I have EVER heard that one............Im not saying your wrong I'm just saying it sounds a little backwards to me........John

Seems tail weight would only make it worse. I agree with jmulder

I know, adding tail weight to a plane that snaps is completely contradictory too conventional wisdom.

Sounds nuts. I know.

Myself and two other guys have the same Sig Cap 231 Breitling. We all fly together occasionally. And we compare plane setup and engine performance.

I am running a big ST engine in my plane, and the other two guys run a Saito 180.

We all had the exact problem that craftsman described. Same exact problem. High speed snaps with full elevator on high rates.

We started trimming the planes according to the sheet that we got from the guys at Aeroworks. I had to add a boatload of right thrust to mine. And even some down thrust. Other guys had to add lot of down thrust and one guy had to also add a lot of right thrust.

Just try what I described in the above post. Try it BEFORE you mess with the balance, that way you have a reference point. Remember, the balance point that most manufacturers provide is only a safe point for starting out. It isn't written in stone that you must not go beyond those specs provided by the manufac. You'd be amazed at how far back I have some planes balanced. According to the plans and specs from the manufac. ; the plane should not fly, but they fly GREAT!!!

Once again; for checking the balance, use the following procedure:

Full throttle flat and level.
Pull to a 45 degree upline and roll inverted.
DO NOT TOUCH THE ELEVATOR
Plane should continue on a 45 degree upline without changing pitch very much.


If it starts to drop the nose, then you are still nose heavy. If the nose goes up and the tail drops, then your tail heavy.


For right or left engine thrust:

Come in about half throttle- flat and level
pull straight vertical and wait for it to ALMOST stop
Slam the throttle full open and then close it quickly
Do it again
Slam it full throttle and then close it quickly

If your plane torques too the left more than you'd like, then add right thrust. If it's gonna torque left; then it will happen when you slam it full throttle when vertical.

If it doesn't torque left, then your probably fine.

When checking the engine for UP or DOWN thrust, there are a few different methods. I usually try both and come too a happy medium.

Checking for proper up or down thrust is a bit more fun:

Come in flat and level- about 1/2 throttle
pull staright vertical
go Full throttle when perfectly vertical
LET GO OF THE ELEVATOR!!!!!!!!

Watch it and see if the nose comes back onto the top or if it goes towards the belly of the plane.

If your nose comes towards the top of the plane and you would need to add down elevator to keep it vertical, then you need more DOWN thrust.

If the nose falls towards the belly and you would need UP elevator to keep it vertical, then you need more up thrust.

The other way; I usually do the next method after the vertical test

Take it up HIGH.

Start out HIGH-200' or 300'- whatever you consider high
full throttle and flat and level
shut the throttle quickly and let it glide
DO NOT TOUCH THE ELEVATOR
watch it and look to see if it falls quickly

Your plane should glide reasonably well. If it is nose heavy, then it will come down fast and accelerate at an idle.

Keep in mind that aerobatic planes don't really glide very far, but most; if properly built and have reasonable wing loading, will glide for awhile. Any plane that drops like a rock after shutting the throttle is most likely, too nose heavy, has improper engine thrust or has DRASTICALLY high wing loading.

Check your incidence. Incidence meters are great. I use them on every plane I build. But there's no substitute for checking the plane in flight after setting it according to plans.

To check wing incidence:

Take it up REALLY REALLY HIGH- at least 300' maybe more
flat and level1/2 throttle
close the throttle down to a nice idle
put the plane into a VERTICAL dive at idle
TOTALLY VERTICAL
LET GO OF THE ELEVATOR
watch it
pull out and throttle up before you get too close for comfort

What your watching for is to see what the plane does in a totally vertical position at an idle. You must do this Vertical, with the nose pointed DOWN at the ground. Thats why I say- start out HIGH.

If, when vertical, the plane comes down and pulls out to level flight. Then your wing incidence may be positive too much. On a plane that calls for ZERO incidence on all surfaces-(wing, stab and engine), it should come straight down.

Some might just come up towards the top of the plane and creep towards level. It might appear as if you are adding just the slightest touch of UP elevator That might be fine. Depends on the plane.

If, when vertical, your plane tucks towards the belly and starts too come around and push out and go inverted, then your maybe a little on the negative side of the incidence.

Now for my disclaimer: I'm no genius. I read all this stuff in books and heard it from other more experienced pilots than myself. I do each and every one of these tests on all my planes now. Yes, I spend almost a gallon of fuel doing all these tests again and again. Each time; landing and adjusting. Then going through the test again. Sometimes I spend MORE than a galloon of fuel to get a plane right where I like it, but in the end, its money and time well spent.

I only try and adjust one thing at a time. One day I will take a new plane out and only work on engine thrust. Next time I take that plane out to the field, I will only work on balance or wing incidence. The point is; only adjust one thing at a time. And above all BE PATIENT!! (thats the hardest one for me)

Sometimes, you might think you have the engine down thrust right where it should be, then you go and start checking the incidence, and you wind up going back and changing the thrust again to make up for an adjustment that you made to the wing.

Believe me, I've spent a few hours chasing my tail when doing this stuff. But, a little tweak here and a little thrust there; and before too long, your plane is flying like you never thought it could.

Try some of the things I've suggested, you might learn something and it will be fun too. I'll bet your plane will fly nicer when your done, too.

Sorry I got so long on this one.

Remember, every adjustment that you make to the plane is going to affect how it flies.

So, when adjusting your wing incidence, you might totally goof up the way it flies. Then you'll have to go back and re-adjust the engine thrust.

You might have to go through the plane 2 or 3 times and perform all the adjustments again and again.

Every adjustment that you make has an effect on other things.

Balance, engine thrust and wing incidence along with stab incidence all make the plane fly differently. It will take some tinkering to get them all together. Have fun with it.

These aerobatic planes have big elevators so that they can fly 3D or at high angles of attack (high alpha). When properly set-up, you should be able to use all the control throw on any given surface without poor results. If you weren't supposed to be able to Harrier it in or hover with the planes, then the control surfaces wouldn't be as big as they are. Right? Those huge control surfaces are there for a reason. Set the plane up correctly and use those surfaces for what they were designed to do.

after reading that...I'm scared!!!!

OK everyone else had suggestions, I guess I can throw in my two cents.
I had same problem with several planes that I admit to over doing the elevator travel...but that is what I wanted.
My solution that corrects huge amounts of the problem is to increase wing lift at high angles of attack.. How you ask..
Mix with computer radio the ailerons into the elevator. When commanding up elevator, the ailerons drop and reverse for down elevator. It will be a large improvement for no cost..
Almost all my planes are now set up this way.
Down side...make sure you can turn this mix off or landing in the wind will be a ballon on wings!!!