negative angle of incidence?

[joel greer]

i'm building an arf biplane and need to set the angle of the upper wing to 1 1/2 degrees negative incidence, but the wings don't fit the struts at a angle of 1 1/2 degrees, it's built for an angle close to 0. i'm not sure what the negative angle is for so i don't know how to proceed. put the wing where it fits, or set it at 1 1/2?
joel greer

[DKjens]

All aerobatic bipes I've seen have had instructions for about 1 degree negative in the top wing. I think it may have something to do with the fact that the engine thrust line is so far lower, that you would normally put down thrust in the engine if the top wing were the only wing, but since you also have the low wing, which is not as far below the engine thrust line and usually set to 0 degree incidence, ot the same as the engine, you put the negative in the top wing. I would at least try to get some negative in the top wing.

[stommerd27]

I would do as the directions say. I listened to someone on my ultimate, they told me everything should be set at 0. Well I adjusted the the tail feathers to zero. Now I need a bunch of down elevator to keep it from climbing.

[krayzc]

i have a BG Ultimate and a H-9 Ultimate and both are set up with:

stab +1.5 - 2.0 degrees of up
bottom wing 0
top wing -.5

the stab needs to be slighly raised other wise the ultimate will climb badly on the maiden.

they also carry up thrust on the firewall in the range of 1.5 - 2.0 so that your uplines do not pull towards the wheels. You def want to set up those above things are you will just hate flying this bird.....

stommered if you stab is not glued on you should insert a popcicle stick under the stab that is just about right for 2.0 degrees of upthrust. On both of my Ultimate the tail and stab are removable and I choose to not gue them on. The H-9 Ultimate comes that way from the factory....

[stommerd27]

Yeah it sucks but mine is glued. The guy that told me to do what I did has been building for years so I thought he new what he was doing. I should have gone with my gut instinct and just squared it up and glued it in instead of taking the angle out. It did climb badly when I maidened it but once trimmed it still flew awsome. Oh well some lessons need to be learned the hard way. I will know better when I buy my h9.

Thanks for the info.

[joel greer]

thank you all, this was my first post- this is a great web site! i gotta do this somemore. i,ll b back.

[Rickster]

On a Pitts I try to set the top center of the wing at -1-1.5* and then trim the "I" struts to achieve 1.5-2* on the top wing tips to put some washout in the outboard top wing...

Rick

[Steve Steinbring]

Build a jig to set the horizontal stabilizer at zero degrees. Then set the lower wing to the incidence angle where it should be which in most cases will also be zero degrees. Then shim in the upper wing to the recommended decalage incidence. Once the wings are pre-fitted correctly I then cover the wing center sections with wax paper and bed in the wings to with epoxy paste forming the proper incidence angle in the wing beds.

[Marvan Maxwell]

The reason I have always been told, is to have 1/2 to 1 degrees negative incidence in the upper wing so it will stall last, when the plane is rotated

MarVan