Problem with H9 Showtime 4D 90
 

I have showtime 4D 90 with OS 120AX motor.

It fly great. But i have one problem.

I always need to trim ailerons to the left. If i have straight then my plane will always spin to the right. "Make rolls" It will not spin very fast, but you can not fly like that.

What should i check. Should i check angle of motor. Or anything else. I really don't know. I have checked a lot of things. And everything is straight or have the same angle on left and right side.

RE: Problem with H9 Showtime 4D 90
 

Try setting it on a perfectly flat surface & measure wing & stabalizer squareness , also check measurement from flat surface to the same at different points to see if maybe you have a twist in them.

RE: Problem with H9 Showtime 4D 90
 

Also check the lateral balance. Suspend it from the motor armature and them hold the tail about half way down. You may fine your right wing to be heavy.

RE: Problem with H9 Showtime 4D 90
 

Hey, Ram. I think you hit the nail on the head !!!!

RE: Problem with H9 Showtime 4D 90
 

Here are photos how is need to be to fly straight.

I will go and check weight of the wings now.

RE: Problem with H9 Showtime 4D 90
 

It's difficult to say what the problem is until you do some more testing.

It could be motor torque, mis-aligned surfaces, lateral imbalance, etc.

Torque can also be misinterperated as excess lateral imbalance.

I've seen people at the field fighting with what they though was a lateral imbalance problem, until I showed them that on a downline the problem dissappears...



Try this...

Trim the plane for level flight at 80-90% throttle.

Fly the plane as high as you possibly can.

Then cut the throttle completely, leaving the engine at low idle and point the nose straight down.

Let it fly as long as you can, but leave enough margin to recover safely.

Does it roll on the way down?
Does it pitch to the belly or canopy?

If it rolls in the direction you have trimmed the aileron, then motor torque is what was keeping the plane flying level. By flying it w/o the engine on the downline, you've removed the engine from the equation, so you can see how the plane will fly without engine torque factors.

Report back...

Next are the uplines with stalls...

RE: Problem with H9 Showtime 4D 90
 

I will fly tomorrow like you said. I have tested and both wings weight the same.

RE: Problem with H9 Showtime 4D 90
 

You are right. I have trimmed my fly at almost full speed. And i fly as high as i can. Then go straight down without throttle. My plane will rotate slowly at the way i have trimmed it.

So that means that i have too powerfull engine ?

RE: Problem with H9 Showtime 4D 90
 

The engine is developing so much torque that the trim you set is required to keep the airplane from rolling.

I wouldn't call this "too powerful", rather it's expected behaviour. My Giant UCD even with it's big surfaces & controls does the same thing...


If you trim the plane back so it doesn't roll on the downline, it WILL roll as you run the engine up.


A few things you can do...

- Use a smaller prop with a higher pitch. This will produce more airspeed but less torque. ( you may not like/want this... )
- Use your radio mixing to add a bit of aileron as you run up the throttle.

The latter is probably the easiest if you have a computer controlled TX...

Set a mix so that about 6-8% "mix" is added to the aileron, from the throttle.

In other words, as you run up the throttle the ailerons move to compensate for the torque.

Ideally at 100% throttle you end up with the ailerons as you have them now for level flight ( or so ).

To get it right, you need to establish a neutral point first...

So, take your plane high again, and do exactly as you did before ( you'll need to work quickly of course ).

But this time adjust the trim so that the plane DOES NOT roll on it's way down.

That's your "neutral" position.

Your mixing should be set so that with the throttle at idle ( or even maybe below 30% or so ) the ailerons are at this neutral position.

As you move the throttle stick beyond this, you want the ailerons to move to compensate for the engine torque, effectively keeping the plane level.

This is going to have many positive effects, e.g. loops will flatten out, hovering will be easier, etc.

You'll have to play with the mixing "curve" ( actually it's usually a line..).

Until you have the mix dialed in, leave it activated via a switch.

That is, you want to be able to turn it on and off in flight... just to play it safe.

Once you found the perfect setting, leave it on all the time.

RE: Problem with H9 Showtime 4D 90
 

Thank you for help. I will play with mix next week. You are the first person to find the problem. I have checked and measured whole plane a few times and nothing was found.