ORIGINAL: Rcpilot
I couldn't do a project like this without documenting it all. I'm not sure how many of you saw my 4*120 build thread from 2005. I really enjoyed doing that thread and having people follow along with it. Several other guys were building the same plane and contributed great information to the thread.
I've been talking with my best flying buddy. He thinks it will not fly very good with a semi-symmetrical wing. I have my doubts too.
All of the 4* designs fly very well. We discussed doing some experiments with the 4*40 first. One of the things we talked about was to put the top wing on upside down. Then, when you fly inverted, it's all the same. I would need to build my outer cabanes and inter struts with an adjustable bolt so that I could adjust the incidence between flights. We came up with a simple but effective design for this. I could mount the top wing normally--or upside down--and still have complete control over the incidence with a couple turns of a bolt. Would take all of 2 minutes to make those adjustments at the field.
Using the 4*40 as a design platform would certainly be cheaper than the 120. But, I have the wing kit for the 120 already, and I have the plans for the 120. I've got access to power tools (band saw, drill press, scroll saw, disk sander etc...) so scratching the fuse is really no big deal.
Does anybody have any comments on using semi-symmetrical wings on a bipe like this? How do you think it will fly.
How do you think it would effect the flying if that top wing was built upside down, so the flatter part of the wing was on top when flying? It's not something that I WANT to do. Just wondering if it would give the plane a more neutral feel.
Do other bipes have semi-symmetrical wings? Hog Bipe? Balsa USA Pheaton? GP Stearman? Do they all have fully symmetrical wings? Semi-symmetrical?
What are the disadvantages (if any) of going forward and just using the stock airfoil from the 120? It is going to need more negative incidence on the top wing or would the standard -1.0 up to -1.5 degrees be enough?
These are all design considerations that have just hit me. I'm REALLY concerned about the wings now. Don't want to build a plane that wants to climb all the time and takes 1/2 stick to fly inverted.
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It depends upon what kind of performance you are anticipating, as to whether the semi-symmetrical airfoil will satisfy your needs.
Fortunately, the semi-symmetrical airfoil is the best compromise for most types of flying, although I do favor fully symmetrical airfoils the majority of the time.
I flew a Balsa USA Phaeton Biplane (original version) for a couple of years in the early Eighties. I'm a part time pattern pilot, or used to be, and I didn't experience any major disadvantages with its semi-symmetrical airfoiled wings. I do wish the Phaeton had ailerons on the top wing, but I got by with lots of control throw on the lower wing ailerons. I just got by, though.
I did incorporate 1/2 degree of negative incidence in the top wing as an experiment. It turned out to be the best flying biplane I've ever flown. It locked into the groove and performed amazingly well. The 1/2 degree of negative incidence idea was picked up from reading a Don Lowe article in RCM. All of my bipes now get that treatment.
My Phaeton was slightly underpowered with the then new Super Tigre .40S. A sixty would not have been out of place, but I stuck with the .40 and learned a lot about energy conservation. <G>
One thing new biplane flyers must get used to is immediately lowering the nose should the engine quit. Mine had the glide ratio of the Space Shuttle or a dropped manhole cover. You have to fly as though you're playing musical chairs and knowing that the music (of the engine) may stop at any time. Fly upwind and in close, so you can make it back to the field after you recognize that the engine has quit. Cheat a bit and fly your four-stroke with the muffler off on busy days at the field (get a Perry VP-20 shaker pump so you won't miss the muffler pressure). Or use a louder two-stroke.
Ed Cregger