RE: Concept Fleet Biplane
Flew the fleet for the first time today. After flying the snot out of it today I gotta say it's my favorite bipe!
Covered it with Solartex and painted with Krylon. G38 for power turning a 19x8 wood prop. Weight without fuel is 22lb. That G38 looks pretty small on the nose of this plane and the weight was higher then I expected. Didn't help that I had a bunch of 1/4 scale size servo's laying around that needed a plane. They probably add 1/2 lb of weight more then normal hi-torque servo's. I need not have worried! It flew GREAT!
Broke ground at about 1/2 to 3/4 throttle and climbed out smartly. I had expected this plane to be slow with a narrow speed range, but was pleasantly surprised with the speed between 3/4 and full throttle. Loops are beautiful. Rolls are pretty slow, adding rudder helps. I found myself using rudder quite a bit in turns as well.
Stalls are a non-event. It slows to a crawl, drops the nose straight ahead and recovers. Landing requires some throttle to be carried on final much like any other bipe, but not as much as I expected. Get in ground effect and it will float down to a nice 3 point landing when everything is right. Managed to get a little porpoise on one landing when I tried to stretch it and bounced a little too much on the 6" balloon tires. If I had given it a little goose of throttle it would have settled down.
Landed and checked it out after a few circuits to make sure nothing worked loose. Flew it until my batteries said it was time to park it. I need to add some down thrust to the motor for full throttle trim, but nothing else needs attention. The top wing incidence is +1 deg, the bottom wing is at zero and the horizontal stab is +1/2 a degree.
Ground handling is pleasant. Does not need much up elevator during taxi. Take off run only needs a little up elevator to keep the nose level. I've got a little toe-in on the main wheels and there is no tendency to ground loop at all.
Construction of the basic airframe took 1 month working 2 or more hours each day. Virtually no super glue was used in construction because of the large number of ply and spruce joints. I used mostly Elmer's pro wood glue and 30 minute epoxy. Covering, hinging, radio, painting and motor install took another month and a half working a couple of days a week. The plans and instructions are very good, but some previous building experience is needed. It took 5 1/2 two meter rolls of Solartex to cover it and 6 cans of Krylon.
I deviated from the plans in only a few areas. I made the top wing 1 piece. I scratch built a cowl similar to that used on the Portuguese military version and changed the rudder plan-form to look like the model 7. Just not a fan of exposed radial cylinders and did not like the square rudder shape.
The most tedious part of construction was of course the wings. Each of the 4 wing panels has 2 spars and the center sections for top and bottom wing each have 2 of their own. The box spars must be built from 4 pieces (2ea 1/4x1/8 spruce and 2 ea 1/16 ply sheet). There are 12 spars to be built and if they are not built straight your wing will not be either. Then there are the ribs! Each rib comes in 3 pieces and there are a LOT of them. Once you have a set of straight spars, wing construction actually moves along pretty quickly, even without super glue. I decided early on that I would make the top wing 1 large piece instead of 3 as specified in the plans for added strength and simplicity.
Aside from the spars the most critical areas of construction are the cabane struts and the alignment of the fuselage sides. If the fuse sides are uneven your lower wing will not be correctly aligned. Lots of tweaking was needed to get the cabanes assembled and soldered in the alignment specified on the plans. I still had to do some tweaking when I checked top and bottom wing alignment. Whatever you do, don't enclose the cabanes in wood fairings until you are satisfied with the wing alignment!
Since the only sheeting is the 1/32 ply on the cockpit area sanding was not as much a work as is normally the case.
Covering is a joy with Solartex. The only down side is you have to clear coat it at a minimum to seal out the dirt. If you were going to paint anyway then there is nothing bad to say about it. No priming was needed.
With 2 giant servos in the tail and the batteries, receiver and throttle servo located under the rear cockpit, the CG came out exactly in the middle of the range specified on the plans.
If you love bipes and building the 1/4 scale Concept Models Fleet is a great choice!