JUst picked up a tower Hobbies Ultimate Bipe. 45” wingspan. Question is, can I use the lower wing as flaps? Will this alter turning characteristics if all ailerons aren’t used for turning?

Yes, it will not roll axial at all. The best setup will be to use all 4 ailerons and when setting them up pay close attention to the throws. You want all 4 to match, same throw up and down.

Your question begs another question:
1. for what purpose are you considering flaps?

Ultimates are great flying platforms across just about all sizes. You shouldn't need flaps to slow an ultimate down to a comfortable landing speed.

With that being said, I have played around with many different configurations of flaps and spoilers as well as crow configurations to see what kind of 3D type stuff mine were capable of.

If you were just looking to use flaps on the lower wing to slow down for landing, you could definitely do that and still have enough authority on the roll axis from the top ailerons in order to control your plane while landing, but I think you will find that your ultimate will slow down nicely all on its own as they are a fairly draggy aircraft. Depending on your radio and receiver, you could also program a mix where the ailerons drop a bit but still work as ailerons too (spoilerons).

Astro

The problem with flaperons ( down for flaperons, up for spoilerons ) is that they tend to promote tip stalls. Reason being is that on an Ultimate the ailerons go all the way to the tip but are usually only about 2/3 span. Imagine you have the flaperons dropped 15 degrees and then add a good dose of aileron control. You could easily stall the outboard section of the wing with the aileron/flaperon with the downward travel. Especially bad with a bipe due to the positive stagger between the two wings. When the bottom wing stalls before the top wing it effectively moves the CG rearward. You can imagine what mess that could create.

If you are worried about landing speed there are better solutions. First and foremost would be to reduce overall weight as much as possible. The other is to not have an overly forward CG. An overly forward CG requires constant downforce on the tail to keep the nose level or as the case while landing slightly nose high. To get this downforce you need up elevator in the form of elevator trim or while flaring for a landing back stick. You need airspeed to make either of those two things work, hence faster landing speeds. Being a big fan of bipes ( I have 3 ) with my favorite scale bipe being the relitivly unknown Reed Falcon. My 54" version is a porky 9 lbs but still lands fairly slow due to having the CG reasonably close to the nuetral point.

Thank for all the info. All makes sense. I will not be using lower wing as flaps.

Flaps on a biplane are kind of like roll up windows on a bicycle. Why?