angles of incidence

[astjp2]

ok, so I went out and measured a prewar vs a post war airplanes for how the wings are mounted on the airframe. I rigged both airplanes and both fly straight and level. I started with a digital level on the horizontal to establish a "0" angle in both airplanes. I used the tool that I have for setting book spec. at 1-5/16" between the front and rear spars.

So I will give you the numbers that I found. First off, the trailing edge on the prewar was even with the top of the fuselage, the post war airplane was about an inch and a quarter with a tape measure. The prewar airplane had 8.50x6 tires and the post war had 8.00x6. Leveling means in the manual in the Hstab.

so the numbers are listed from outboard pilot, inboard pilot, inboard co-pilot, out board copilot in degrees (d=down) in the leading edge from 0 degrees

prewar .1d, 2.6d, 1.6d, .6d
post war .6d, 2.3d, 1.6d, .6d

so I really dont see any difference between the pre and post war airplanes but there is a difference in where the wing root meets the fuselage, so I am wondering if there is a difference in the fuselage longerons which gives the technical difference between the angle of incidence between both airplanes in the TCDS?

So this is actual measurement from flyable airplanes, an .5degrees in my book is negligible on an airplane that was built to +/- an 1/8" and any variations in fabric can change the measurement by .5degrees.

So I will let the tribe stew on this data and let the discussion roll.

Tim

[Scott]

Re: angles of incidence

One among several possible variables is the location of the ribs on the front and rear spars.

The ribs of course changed to stamped ribs for post war and the factory used a jig to position the ribs on the spars. I had some photos of the jigs (can't find them now but I think perhaps Marty sent them to me a few years ago) and I don't think they would work with the built-up ribs. This would mean the factory used a different jig or method of positioning the ribs pre versus post war.

A small change in vertical location of the ribs on the spars results in a relatively large change in angle of incidence (relative to the spar attach fittings and the horizontal stabilizer), and can clearly make a difference in how the wings fair with the fuselage even if the AoI is the same.

[Guest]

Re: angles of incidence

A couple of years ago I made some measurements and posted them at this thread=> http://vb.taylorcraft.org/showthread...ngle+incidence

The data is at post #33 on page 3 and the "jig" I made was put together while looking at the 23012 airfoil cross section such that the angle being measured was the actual angle of the airfoil angle of attack.

I don't know if the data helps but since I had gathered and it seemed it perhaps could help I thought I would mention it.

Dave R

[PA1195]

Re: angles of incidence

Tim: You mention angle of incidence and TCDS in one sentence. Have you found that reference and can you share it? In other publications the AOI has been stated to be 3.8*. I can provide the source(s).

I suggest some further measurements of the dihedral of the ribs over the front and rear spar of each wing. Top or bottom of the wing; the difference reflects wing twist or washout. Use a long flat bar to create an average level line between ribs.

Gary

[astjp2]

Re: angles of incidence

I thought the TCDS said it but it is just a note about wing attach fitting changes...crap I have too much stuff in my mind anymore! I seem to get it messed up MORE AND MORE!

[PA1195]

Re: angles of incidence

Tim it may be time to simplify life, erase some of your RAM, and fly your Taylorcraft. Leaves are turning in Alaska and the birds heading south. I'll take some local pics of the wing trailing edge vs upper fuselage and post.

Here's some sources I found for wing incidence.

Wing dihedral, incidence (3.8*), and washout for test aircraft #5 (Taylorcraft). See Table 1, p. 22: https://ntrs.nasa.gov/archive/nasa/c...9930082385.pdf

Wing dihedral, incidence (3.8*), and variable washout for the test aircraft Taylorcraft. See Table 1, p.28: https://ntrs.nasa.gov/archive/nasa/c...9930083935.pdf

Wing incidence (iw; 3.8*) Table 1, p.47: https://ntrs.nasa.gov/archive/nasa/c...9930084995.pdf

The airframe incidence of 3.8* coincides closely with the highest Lift/Drag ratio for the 23012 airfoil. Probably set for cruise ?: https://ntrs.nasa.gov/archive/nasa/c...9930091610.pdf

Gary