Incidence gauge

If your wing is at zero aoa, then you have no lift being generated!

Are you sure about that Eric?

B.

Sorry to but in, but before I get a headache, would someone please tell me if this is right or wrong.
The angle of incidence of a wing is fixed. The angle of attack is variable. Decalage, is the relationship between the angle of incidence of the wing & the horizontal stabiliser ?

Spot on crash!

Eric wrote: If your wing is at zero aoa, then you have no lift being generated!

.......only if the airfoil is symmetrical, if not the airfoil will still generate lift at zero AOA, even if only a little.

Paul.It would seem to me that the plane you are building is designed with very specific lift characteristics. If a proper incidence gauge is required, then you go for it mate. I know i'm not the sharpest pencil in the box, which is why my scratch builds haven't got past the good old 'Clarke Y'. :lol: If you need precision, then you need precision tools.

I think you are mistaking the difference between the centreline of the section, and the flat underside of a simple wing.
The centreline runs from the extreme front of the leading edge - to the (theoretical) point of the trailng edge.
So with the flat bottom at zero, you really have a few degrees of positive aoa relative to the tailplane.
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With a fully symmetrical section at 0 aoa, it is generating lift equally up and down - sum total of zero lift.
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The aoa is controlled by the elevator.
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With a perfectly trimmed craft with a fully symmetrical wing, and thrustline at 0 as well, it should need NO ele trim or deflecton - either way up - to track a straight line.
But of course, being heavier at the front than the back, gravity alone will cause the flight-path to be a parabola - groundwards!
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Throwing in the difference of incidence between top and bottom wings of a biplane is just confusing the issue. Try figuring out the individual aoa of each of a triplanes wings, then figure out the AVERAGE aoa of the combination.

But my wing is undercambered!
Your right crash this one is designed for a specific flight profile and I just wanted to get it set up "sort of correct" from the get go.
I have downloaded a app and I've got a idea to make a crude gauge...I'll report back.

The wing profile doesn't matter. The centreline of the section is still the same - LE to TE.
All the profile does is set the AMOUNT of lift generated for a given aoa. (disregarding airspeed for now!)
Try flying an undercambered wing inverted! :evil:
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Eppler 374 looks like a semi-symmetrical section - until you look at the camber line, I can't recall the proper name for the individual measurements taken from the centreline, to give the profile, right now - but 374 is an undercambered section popular with slope soarers, as it gives high lift the right way up, and good lift inverted, while remaining slim enough for good penetration.
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A very thin profile, heavily undercambered section is very draggy, as well as being very weak, structurally.

If you can find a copy, and can plough through it, look for a book titled
Model Aircraft Aerodynamics, written by Martin Simons.
The isbn is - 1 - 85486 - 121 - 2
My copy is dated 1994, so there may be later versions out there.

No need to buy books, it's all on the net:
NASA

Eric wrote: -
The aoa is controlled by the elevator.
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AOA is adjusted by the elevator, but it's set by the incidence.
Anyway, this started off as a question about incidence meters and is heading towards being dominated by aerodynamics..

Eric

In the attached scan, you can a flat plate aerofoil and at 0 degrees angle of attack there is 0 lift.

On the right of the scan there is another graph for Gottingen 419, this shows the lift being created at a 0 angle of attack, you can see that you need to fly that section at some negative angle of attack to get 0 lift.

Lift is the vertical scale angle of attack is the horizontal scale.

The scan is from the book that you cited.




Regards

Barrie

Glad I asked the original question, its all quite interesting, anyway I've had a go at the seats for the tail plane, had to make a crude jig in order to cut them.

Acording to my calculations the thick end of the wedge needed to be 7.1mm, best I could manage was 7mm! that'll do I think?

using the phone app it seems about right.

No problem with the accuracy of your Vernier micrometer but I am not sure I could say the same about the phone app. Accurate to 1 degree or just 1 significant figure?
Only joking I am sure it will be fine.

I agree Simon, tried a couple of apps on both our phones with simular results, turns out I chap I know has a digital gauge that I can borrow( saves making one) just in case my maths is out.