<div>I bought a plane off Craigslist and am rebuilding it. This is alarge vintage style trainer. It is a gasser that has a wingspan of 96", alength of 88", and before I started the rebuild, weighed about 14lbs.I figure it will be able to handle just about any weather and be a perfect plane to teach my 2 sons how to fly.

I have a question about some flaps that are under the wing trailing edgenext to the fuselage. They are in the position that you would traditionally have flaps, are very large, but only go down.The top of the wing does not move. I'll post some photos later.

Are they flaps, orsomesome kind of airbrakes?Should I hook them upto the flapschannel where they can be adjustable, or should I hookthem up to the retracts channel where they will beeither up or down?

These things are controlled with 2 servos connected with a y-harness. The ailerons use 2 servos and I only have a 6 channel radio, so I'll be using all channels available to me. I've not quite figured that part out yet either.</div>

What you are referring to are what theycall split flaps similar to what you would find on many warbirds such as a Spitfire

Yep, split flaps, seen on lots of airplanes, the reason for them being simply that in full size they are easy to build, in small deflections add some lift without much drag, and at large deflections add lots of drag without much more lift, (put simply, I know you can't 'add lift' but it makes the explanation simpler...).
Evan, WB #12.

Sounds like a split flaps. For me it’s better to use it using variable or with 3-position switch. This kind of flaps has more drag compare to other flaps, lesser lift but gives you an advantage at higher angle over the plain one. It delays the separation of airflow on the top at higher angle.

Thanks for the explanation of their advantages over regular flaps. For this plane, they appear to be a better choice over regular flaps. It looks like the person who flew this model knew what he was doing because they look like they were added to the model and not built with them.

I've uploaded a couple of photos.

I wouldn't worry about those having too much affect. They aren't long span nor too much area. Also the dihedral looks to be considerably more than normal for even a trainer. The plane is going to be very stable in the roll axis. Chances are good that it will fight your attempts to turn it with aileron/elevator. It will also have a significant tendency to turn when you yaw it with rudder. It appears to have more dihedral than rudder only trainers and rudder/elevator only trainers had in the early years of R/C.

If you have a picture of the wing when assembled, it'd be good idea to post that. You might discover a need to rig differential into your ailerons. It's actually not hard to do. I've been flying a number of high wing models that didn't have dihedral at all and flying them like a trainer, they all needed differential to even fly like a trainer. Significant dihedral on a high wing plane that has a cambered wing (flat bottom for example) makes the sucker turn in the opposite direction you're trying to turn it with aileron/elevator.

Got a picture?

Here are the photos. The dihedral is actually quite small on the main part of the wing. Note that the horizontal stabilizer as well as the landing gear have a flat bottom airfoil. There were some lead wights attached to the engin (see photo) when I got it. Because the plane is so large, I took the horizontal and vertical stabilizer off and made them removable so that I can fit the plane and my kids in the minivan. I'm sure it is now even more tail heavy, so I am moving the servos and everything else that I can forward.

The way that engine is mounted, to achieve balance without adding any weights at all could be quite simple.

Just stand the engine off with a block of wood. Drill some holes through the block for the present mounting bolts. Glue the block to the firewall. Use some longer bolts and you've got a balanced plane without having to move any present hardware.

That is one unique model, btw.

The dihedral you've got is simply an inverted gull wing. It is basically a HIGH wing.

It sure is!

And yeah, some spacer plates made from basic lumberyard 1/2 and 1/4 plywood could be made up and varnished with some polyurethane varnish to oil proof them and make the model balacing a lot easier.

Some may suggest using tubular spacers on the longer bolts instead of a plate to space the engine forward. I don't like that idea since the four bolts and spacers are basically unsupported. For up to maybe 1/2 inch it would be OK. But any more than that and you've given yourself a source of some possible nasty vibration. And those big gas engines shake like a paint mixer already ! ! ! !