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Author Topic: P-40B dihedral  (Read 616 times)

Offline Mike Urban

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P-40B dihedral
« on: December 30, 2023, 08:41:30 AM »
Not sure if this is a building question or a design question, but I’ll start here.
I’ve been gifted a Brodak P-40B kit for Christmas. The instructions say if I’m building a sport-scale model to include some dihedral, but if I’m building for aerobatics, to build the wing flat. This contradicts some comments in various P-40B threads I’ve read on this forum, including some from Pat Johnston, who I believe designed the model. Those comments indicate the dihedral is necessary to correct a vertical CG issue, and should be included for any application.

So does anyone have any insightful comments on how to reconcile these comments with the Brodak instructions?  I am a bit confused.

Thanks,
Mike

Online Dave_Trible

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Re: P-40B dihedral
« Reply #1 on: December 30, 2023, 09:05:34 AM »
I'm not directly familiar with this particular airplane but on most all profile models the wing centerline needs to be no lower than about 1/2" below the thrust line.  If any more than that it will end up "top heavy" and want to roll outward in regular upright flight.  This is because the engine is horizontal on the thrust line as well as the tank and fuel load.  To improve scale-like appearance the designer may have made the wing lower but yes,  the tips need to be raised so that the leadouts exit more near that thrust line from the side view.  Dihedral will have no effect on aerobatic flying ability.  On full fuselage airplanes you can get away with as much as an inch offset usually because the engine will normally be inverted so that the bulk of the engine,  muffler and tank is below the thrust line-more in line with the wing centerline.


Dave
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