Single-Engine Turboprop

[MAFman]

How do I make a single-engine turboprop plane that doesn't want to spin like crazy?

[Echo__3]

Use trim and lower the torque of the rotor. Here is a basic tutorial on single engine propeller plane design. You can get more complicated than this if you want to use a variable pitch design.

 

[Vanamonde]

This is a problem real planes must address. Most of them do it by applying trim. Others rely on counter-rotating propellers. 

[MAFman]

Is there a way to make the trim proportional to the throttle, since changing the torque and/or propeller angle changes the torque on the airframe?

[MAFman]

34 minutes ago, MAFman said:

Is there a way to make the trim proportional to the throttle, since changing the torque and/or propeller angle changes the torque on the airframe?

I have an idea. I can have trim flaps deploy when I turn the engine on, and have deploy angle proportional to throttle.

[Vanamonde]

23 hours ago, MAFman said:

Is there a way to make the trim proportional to the throttle, since changing the torque and/or propeller angle changes the torque on the airframe?

Uh, maybe. But I don't know of a way, myself. So I avoid all that and just use pairs of counter-rotating propellers.

[FleshJeb]

23 hours ago, MAFman said:

I have an idea. I can have trim flaps deploy when I turn the engine on, and have deploy angle proportional to throttle.

This is it. Assign the deploy angle to a KAL-1000, and then assign that to the throttle. I use the same one that controls engine torque and/or RPM, and the blade pitch.

[MAFman]

On 11/7/2021 at 2:45 PM, FleshJeb said:

This is it. Assign the deploy angle to a KAL-1000, and then assign that to the throttle. I use the same one that controls engine torque and/or RPM, and the blade pitch.

The torque of the flaps will change as airspeed changes, though. How do I account for that?

[FleshJeb]

7 hours ago, MAFman said:

The torque of the flaps will change as airspeed changes, though. How do I account for that?

For a given RPM, blade pitch determines your maximum speed. The torque of your trim flaps will be roughly proportional to your speed squared. So a good approximation is that trim flap angle is a function of your blade pitch.

What I recommend for an easier build: Have enough torque to drive your blades at maximum RPM no matter what the pitch is. (Higher pitch requires more torque.)

Then, instead of doing any math, figure out the parameters empirically. So, you would set up your blades on the H&N keys, and your trim flaps on your I&K keys.

Get off the ground and get into level flight at a relatively low sustainable speed (low pitch). Play with your trim flaps until the SAS isn't working too hard to control the roll axis (Roll axis indicator in the middle). Write the pitch and trim numbers down.

Repeat for a medium speed and a close to maximum speed. Set your KAL to your throttle, and manually plug the pitch and trim numbers on the timeline where you want them to be as a fraction of the throttle. You might have to use the curve setting to smooth it out  and shift it around a bit after more testing.

Single-props are always going to be a bit fussy, and the SAS will have to eat up some slop, but you can improve it greatly.

You're going to want trim flaps (or any control surface) large enough that you don't have to deflect them more than 10 degrees, and preferably 5. They'll be much more draggy otherwise.

If you have any more questions, feel free to ask. I'm a bit rusty, but I'll try to help.