Calculating Incidence, one more time - RC Groups
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Sep 17, 2001, 09:04 PM
Tu ne cede malis
MtnGoat's Avatar

Calculating Incidence, one more time

I know this thread has probably been beaten to death, but I'll ask for some help anyhow.

On my previous scratchbuilds, I've not bothered calculating tail incidence, I'd just set it up so it "looked right" and then use shims to tweak it once I got it flying. Works out OK, I build foamies and the fuse can always stand another go with the knife.

On my latest creation, a speed 600 Skymaster with twin booms, shimming either the tailplane or the booms is about to get twice as complex, for obvious reasons. So I thought I'd ask those in the know here, what's the procedure or rule of thumb?

I notice there's an incidence value one of the data areas in Compufoil when I have my foil up on the screen, is this generally pretty close? Any rules of thumb or tricks appreciated. I'm using a SD7003 with a couple percent camber added to get higher lift lower flying speeds.
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Sep 18, 2001, 06:59 PM
Tu ne cede malis
MtnGoat's Avatar
Come on folks, a yea or nea would be nice!
Sep 18, 2001, 08:13 PM
Ascended Master
Sparky Paul's Avatar
The procedure for twin booms is the same as a conventional plane..
The complexity of the situation is dependent on how the horizontal is attached to the booms.
And if the plane is layed out in the normal manner, the end results will be similar.
Sep 18, 2001, 11:47 PM
Registered User
I set mine up for zero incidence. Block up the fus and Measure from the center of the leading edge, and the trailing edge to get the wings at zero then measure and adjust the stab until the centers of LE and TE are the same height above the surface.

Note that even on a flat bottom wing, the flat lower surface is NOT the incidence line of the airfoil.

Sep 19, 2001, 05:58 PM
Registered User
.... calculating tail incidence..
Thats quite tricky. Take a look at the book Model Aerodynamics
by Martin Simons/Argus Books ISBN 0 85242 915 0

... however to do the maths you need to make quite a few
assumptions and approximations so in the end you still
have to build and test it.

Here's a good question for you. It illustrates the sort of thing
covered in the book....

To maintain a dive you typically need to hold in slight down
elevator or trim in some down elevator. ... so how come the load
on the tail plane is still downwards under these conditions?