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Old Mar 04, 2013, 05:20 PM
Registered User
United States, NY, Ithaca
Joined Sep 2007
954 Posts
Pat, thanks very much for answering all those questions, it is very helpful. I think I will need to build one this year. Very interesting thread.

I think there are a bunch of issues about incidence that need to get separated. With positive stagger, and the lower wing flying in downwash from the upper, as Rodney says, it is more efficient to use less incidence on the top wing than the bottom.

For maximum stability it's the other way around, as HF says. But I expect the stab to provide the stability, not a whole extra wing.

As far as climbing under full power is concerned, it's a separate issue. People often decrease wing incidence, but that also reduces downthrust. Nothing wrong with just using downtrim. But many designs could use some positive stab incidence to avoid the problem. People don't like to do that, but remember, the stab is usually flying in downwash too.

Jim
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Old Mar 04, 2013, 09:14 PM
Registered User
Tn
Joined Jan 2011
311 Posts
Jim,
I'm going to have to set the plane back up with my meters back on it, because I don't think I would have set the upper wing positive to the lower wing. I have to have my numbers written down wrong.
I right now have my 96" Monocoupe 90A taking up the bench right now, with parts being glued up, so I will have to wait a few days before I can check it.
I have always zeroed my incidences before. except my old Phaetons, I just put the wings on and flew, and they flew great, as far as I'm concerned This time I e-mail some people, and asked what they have set theirs at, and used what they told me they used.
I have had from a 72" Weeks special down to a 16" Canonshot with many between. I had flying biplanes since the early 80's, with them always set at zero, and I have yet to have one not fly good. I have 5 right now, not counting the Phaeton. My new 30" & my old 72" DR1 has all three set at zero, with the stabilizer at +5.5 it's been that way since 90' and flies great. Don't get me wrong, I'm not say they are wrong, I'm saying I don't believe I wrote the numbers down right.

Pat
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Old Mar 05, 2013, 11:57 AM
Registered User
United States, NY, Ithaca
Joined Sep 2007
954 Posts
Pat, I just examined the side fuselage view of my Phaeton plans by drawing two foot lines through the airfoils of both wings. I used the center of the leading edge and the center of the trailing edge of the airfoils of both wings to draw my lines. They are parallel. The stab is a little bit negative to the wings. Did your others need a touch of down trim? I would guess so.

I don't think you can go wrong just putting the top and bottom wing at the same incidence. I know Rodney has done tests that convinced him it's better to have a bit more incidence in the top than bottom. It makes sense and I don't doubt his results. I also know others have gone the other direction and like the easy stall-proof landings they get. Gordon Whitehead who has designed many biplanes for prominent magazines has discussed these two approaches and he always just uses the same incidence top and bottom.

That seems to be what BUSA did, and I'm sure it's fine. I suspect the stab could be made a bit positive, but you can always just use the elevator trim.

The Fokker DR.I is quite a lesson in the effect of downwash isn't it? Modelers can hardly believe the positive stab, but it works. I'm sure that's due to downwash from those three wings.

Jim
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Old Apr 04, 2013, 01:27 AM
Umón Takahashi
Puebla, Pue.
Joined Sep 2008
202 Posts
Hi! Nice job! I have one of this, but it's a kit from 1985. The planes are very old, and I don't have problems with them, but I don't have the assembly manual. Can you sell me yours when you're done with it? Thanks.
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Old Apr 04, 2013, 06:55 AM
Registered User
Tn
Joined Jan 2011
311 Posts
You should be able to just copy the ones I posted it post #24, click on them twice, they will get larger, print them out. Thats how I got those, I didn't have them either.

Good Luck!

Pat
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Old Apr 07, 2013, 08:35 PM
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United States, WI, Lincoln
Joined Feb 2011
3 Posts
Hello, awesome build!

I see some meat scales in the finished plane pics.
Any idea of auw as it is,without covering on.

Have a kit and plan on lighting it for electric / will give me a idea how much i can loose in balsa shavings!:d
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