I am flying a 40 size pattern plane, and I have begun to experiment with spoilers. Each of the aileron servos bringing the ailerons up. I have increased the up throws several times, only to notice a definate tendency to pitch the nose up, although I have zero elevator mixed in. What is the explanation for this up pitch? I had thought that spoilers simply destroyed lift, and the plane would simply sink faster as I slow it down with reduced throttle and some evevator management. I wonder if spoilers are preferable to flaps in landing? I'd appreciate help in trying to understand what is happening. Thanks

Spoilers spoil lift. They can be put from 30% to 75% chord. On landing and tasks like that they are good to control the flight path of the airplane. They are used with flaps on landing to control the flight path of the airplane. Flaps go out at big deflections to get a lot of drag and some lift. Then you set the elevator deflection to control the airplane attitude, etc. The spoilers then can adjust the vertical position on the flight path without affecting much else. When you touch down all the spoilers come out and keep you there.

When you use ailerons on the trailing edge of the wing on your model and deflect them up you get a nose up airplane pitching moment. Remember that they are located a significant distance from the airplane CG and that is what the moment is about.

They might be spoiling lift but also create the moment. To get rid of lift without the pitching moment you need to move them to 30% to 40% of the wing chord.

To add to Ben's explanation.

Consider what you're doing when the ailerons go up. Rather than spoilers in the classic glider sense you're actually reflexing the trailing edge. If you started with a symetrical wing then you've now got an upside down lifting section. Lifting sections like to pitch nose down. But since it's upside down you get a nose up action.

I really do appreciate these explanations. So,... in order to cause a significant increase of sink rate while maintaining a normal pitch, my guess is that a little down elevator mixed in would tend to balance out the nose up tendency from the "spoilerons". Then, using throttle management, I may be able to almost "harrier" down to the runway and make a nice very short field landing. Does that sound like a reality, or do other things come into play in this scenario?

Think of it like it was a flying wing. Up spoilers is like up elevators (or elevons) on a wing. You'll need down elevator to counter.

The F9F-8 Cougar used spoilers for roll control; they had no ailerons. They were nearly full span and just ahead of the trailing edge flaps. The airplane center of the roll was not on the centerline, it was about a point towards the "UP" spoiler. During landing if one was high on the glidepath the airplane could be lowered to the glidepath by alternately rolling left and right. The up spoiler decreased lift on that wing. Spoilers became popular because on some early jets the ailerons instead of inducing roll they caused the wing to bend which resulted in rolling the wrong direction ( aileron reversal ).

Using the reflexed ailerons (probably a better term than spoilers in this case but I know this is the common usage) may aid your transition to the harrier flight mode but once the nose comes up past a certain point the wing will be totally stalled and you'll be using the controls in a totally new mode as the plane won't be technically flying any more.

CaptJim......What you might want to try is adding spoilers to your wing inside of the ailerons with a separate servo on a separate channel...60%-70% wing chord is a general area of installation......this would increase the sink rate of your plane without compromising roll control........then you could experiment with various spoiler deployment angles to come up with a useable threshold......just my .02 cents worth......Bill....

Here's a mod I did to my Goldberg Chipmunk to slow the landing speed. The front part of the flap rotates up like a spoiler when the rest goes down. It puts a load of drag on the airplane, so much that you usually have to ADD throttle to get to the runway threshold. The old flaps made the nose pitch up and I had to mix in down elevator to compensate. This setup drops the nose, so I've mixed in some down. I'm not sure if the down pitch is from all that drag down low or from blanking out part of the stab and loosing the download, but it's still fully controllable.

another view:

And a sketch of the cross section: