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Big_Bird -> RE: Jim Pepino's YMF-5 Waco (12/20/2006 7:23 AM)
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Hi Big Bird - Well I guess it pays to research a plan set before starting to build off them! I really appreciate the tips you have listed here. You mention that you have cut all the ribs. I presume you used the "Basic Rib" planform that he shows on sheet 3. I presume then that you would have used this to modify the length of the center ribs.
Yes, I used the basic rib pattern for shape. What I modified was the placement of the slots for the spars so that they would fit the wing spar spacing shown on the wing plans.
I agree that the top wing should be at -1 degree. My 26% Skybolt - plans by Dario Brisighella - was incorrectly drawn but I set it at the same incidence as the lower wing and it flies OK. But I wish I had set it at a negative 1 degree as I think it would help with some of the "strange things" it does some times! Too hard to change now. However, as a point of interest - I have read that the wings on a number of bi-planes are set at different incidences so that only one wing stalls at a time. I wonder if it matters if it is the top wing or the bottom wing and if Pepino was setting up the top wing to stall first? (Just thinking!)
Several years ago I built Great Planes Giant Aeromaster. I set up the wings as called for on the plans, 0 degrees on both wings. The plane flew good but was a little pitch sensitive. I raised the trailing edge slightly to give the upper wing -1 degree of incidence. Of course that meant adjusting the inter plane struts. The plane then grooved beautifully with no pitch sensitivity. If you can imagine with the wings set this way it is a little like the front wheels of a car having a little toe in. The theory behind having the top wing stall first was that the plane would then pitch down taking the wing out of the stall condition. Most of us don't fly our R/C planes so slow with such a high angle of attack that this would ever be of benefit.
My 1/4 scale Super Cub is from a Balsa USA J3Cub kit that I bashed into the Super version. It's mostly all balsa fuse framing. I used 1/64 ply gussets all over the place aft of the wing and it has held up to many landing errors and lots of water flying. It has a Quadra 41 in it so it has to take lots of shaking as well. I read in a thread somewhere where someone was building the Pica YMF-5 and they said they were glad all the stringers were spruce so you couldn't put a finger through one when picking up the plane. I thought that they must be very "ham handed"! I think hard balsa would suffice.
I have a Dumas electric Waco YMF-5 and I lost track of the number of times I cracked the 1/16" square stringers. On the other hand, the stringers on the big waco are 1/8" x 3/8" and placed on edge. You would probably have to be someone who drug his knuckles on the ground when he walked to regularly break these balsa stringers.I did notice that the bottom wing fairing was not on the plans but I missed how it should fair back into the fuse aft of the wing root and now I see that it couldn't the way he's drawn it. Also I don't like the wing bolt going in at the angle illustrated.
We will have to put a plywood piece in the trailing part of the wing for the bolts to go through and the head of the nylon bolt should fit squarely against this plywood. Of course Jim doesn't show this plywood. I also don't like the way he shows the leading edge of the wing wedging in above the block. The leading edge of mine will get two more nylon bolts.
I think a lot of these things can be cleaned to make this a great model. We'll just have to double check the drawing accuracy before cutting. AMEN, check, check, and re-check.I'm not starting mine until into the new year but I will be making lots of notes on the plans as my buddy is also going to build one with me, so we'll be twins! The heads up you've given me will save us lots a grief. I'd appreciate any updates you find as you progress. Are you planning to do a build here? Probably when I start gluing.
I don't plan to start gluing until all of the parts have been built and these odd items have been corrected. I'm going to build the wings solid so that they don't plug in. I'm putting all of the hardware in so that I can use flying wires if I want to.
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