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Old Oct 08, 2011, 08:50 AM
Wood Chucker
Lacquerhead's Avatar
USA, TX, Allen
Joined Nov 2009
1,497 Posts
Question
Spoiler pitch change - to trim or not to trim?

Is there a general consensus on whether or not to trim out the change in pitch as spoilers are deployed? If the pitch change is trimmed out is there benefit to that and visa versa? Maybe trim out a little bit of it to avoid overspeed? I'm coming from the perspective of a 2M woodie and soon to be built BoT.
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Old Oct 08, 2011, 11:11 AM
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craigrrr's Avatar
San Diego area
Joined Jul 2006
522 Posts
On my RES planes, I program xmiter to give about 15 degree up elevator max at full spoiler deployment. It does vary with each plane, but I always need a little up elevator to compensate for spoilers.
The spoilers tend to drop the nose on my birds.

I think it is a real good idea to do this:

1. On landing it is one less thing to worry about.

2. At spec altitude it is nice to know that you are probably level when spoilers are deployed.

Craig
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Old Oct 08, 2011, 12:35 PM
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rdeis's Avatar
United States, CO, Colorado Springs
Joined Aug 2003
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Quote:
Originally Posted by Lacquerhead View Post
If the pitch change is trimmed out is there benefit to that
Absolutely.

If the airplane pitches up with spoiler deploy and you don't correct by hand, it will stall. If it pitches down and you don't correct by hand, it will dive and overspeed. Neither of these are the desired behavior when spoilers are deployed.

So, since you're going to do it by hand anyway, having the mixer do it so frees your brain to worry about other things when you're busy (as landing) or don't have all the data (at limits of vision or in the dark.)

Quote:
or vice versa
1> Correcting by hand is good for learning more about the airplane, or building intuitive pilot skill in general.

2> If the pitch response is very non-linear, it may be difficult to program smooth compensation in a mix.
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Old Oct 08, 2011, 12:58 PM
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Russian Federation, Sakha, Yakutsk
Joined May 2006
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Quote:
Originally Posted by craigrrr View Post
On my RES planes, I program xmiter to give about 15 degree up elevator max at full spoiler deployment. It does vary with each plane, but I always need a little up elevator to compensate for spoilers.
The spoilers tend to drop the nose on my birds.

I think it is a real good idea to do this:

1. On landing it is one less thing to worry about.

2. At spec altitude it is nice to know that you are probably level when spoilers are deployed.

Craig

Concur 110%.

Why WOULDN'T you set up spoiler-elevator compensation?!?!?

On my Marauder 1.0, I had it nailed at around 7%. Of course the mix was variable with the spoiler deployment. It was awesome, pop the spoilers and she'd track level as a board. It actually saved my plane when I fluttered off my entire vertical stab and rudder on an aggressive winch launch.

Popped the spoilers and she stayed in a nice, level attitude and kinda 'parachuted' on down...
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Old Oct 08, 2011, 01:03 PM
Wood Chucker
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USA, TX, Allen
Joined Nov 2009
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Thanks for the input. I have mine programmed so that the elevator trim negates any pitch change which essentially makes the spoilers act like speedbrakes. The issue I've been having is getting out of thermals. I don't want to overspeed and risk flutter which I did once at altitude and distance. I don't want to have to fly back with half my V-tail dragging in the wind a second time.

I think the thing for me to do is take out some of my up elevator but not enough to completely negate the pitch change from the spoilers. Basically an increase in rate of decent but not so much as to overspeed the aircraft. Fortunately the change in pitch is fairly linear so programming is very straight forward and behavior is very predictable.

Thanks again for your input gents!
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