Wing washout measurement

[dkenney1]

Re: Wing washout measurement

This past spring at annual my FBO had laser levels and high tech gear, but the grey haired more seasoned AI said to me, "come on let me show you the simple and better way to make sure this thing is straight". Because the rib was in the way he attached a 1" block of wood to the level at the rear spar and 2 5/16" block at front, some double sided tape at both locations then had at it. During lunch one of younger guys decided to use the tech stuff to prove him wrong, but no difference, except it took 2 hours v 15 minutes to get everything attached and calibrated (communicating with all the sensors) to be able to start reading measurements and adjustments. I'm glad I didn't have to pay for that time. I really learned a lot working alongside Ed doing an "owner assist" annual. This spring will be shoulder harness and flight control rigging.

[PA1195]

Re: Wing washout measurement

Above I posted some stuff about wing rigging and washout. I've since taken a different approach to wing rigging on my plane with VG's. I finished nearly a month's work including checking the wing rigging and test flying. I've come to the conclusion after hours of fun that:

Unless the wing incidence at the root is grossly unequal; and,
Unless the strut fitting placement at the fuselage and wing are grossly unequal; and,
Unless the ribs are precisely formed and uniformly attached to the spars; then,
Using a level (bubble or digital) to precisely determine and set the wash without actual testing is a great waste of time. Or at least it was for me. Here's why.

The former owner, an experience pilot and mechanic, installed lifetime Airframes struts and spent hours setting the wings up per Taylorcraft's and Airframe's method. Upon receipt I flew it a noted the left wing was heavy...like 1/3 from level on the control wheel to maintain level flight. Ailerons were then tightened and rigged but no change. Upon strut removal it was found the adjustment screw was set at one turn in from max extension length on the left, and four turns in from max extension on the right. That repeatedly gave me about 0.5* indicated wash on both wings with my digital level, with the right wing root incidence measured at 0.3* more than the left (ribs not uniform but spar ok?). Still was left wing heavy in flight ball in the middle and the right wing stalled first every time and it wanted to initially roll in that direction.

So we set both rear struts the same...1 turn inboard from max extension and who know what actual washout...started over and tested that configuration.

The result was ball in the middle, control wheel and ailerons level, stall a very gentle straight ahead bob never dropping below the horizon at 1500 rpm with A/S in the 30's on the GPS in all directions in level flight. VG's are installed and absolutely do work with this airfoil. There's plenty of pre-stall warning buffet and the rudder is effective through the stall which is very good. So far the tail doesn't exhibit any tail lightness or heaviness in cruise. That may change with loads on floats.

My last T-Craft without VG's would offer a splendid view of the terrain below during a stall...not with this setup so far but I'm sure it can be provoked in a skidding turn.

Gary

[astjp2]

Re: Wing washout measurement

The washout dimensions get you close. You need the recommended amount of washout because of the stall characteristics of the 23012 airfoil. With no washout, it has a tendency to have a hard break into a nose down attitude, not gentile like a cub. The 23012 without washout also has a very high pitching moment when it stalls, I have read the NACA reports on it ad don't remember all the details but this airfoil is known to have a problem with stalls if not set up right. I set them to the 1 5/16" and then fly it to find what wing is heavy. Then its half a turn in on a heavy wing and half a turn out on light wing at a time until it flies straight. I have been no more than 1.5 turns on both struts on any Taylorcraft I have done. Tim

[PA1195]

Re: Wing washout measurement

The washout dimensions get you close. You need the recommended amount of washout because of the stall characteristics of the 23012 airfoil. With no washout, it has a tendency to have a hard break into a nose down attitude, not gentile like a cub. The 23012 without washout also has a very high pitching moment when it stalls, I have read the NACA reports on it ad don't remember all the details but this airfoil is known to have a problem with stalls if not set up right. I set them to the 1 5/16" and then fly it to find what wing is heavy. Then its half a turn in on a heavy wing and half a turn out on light wing at a time until it flies straight. I have been no more than 1.5 turns on both struts on any Taylorcraft I have done. Tim

Thanks for sharing the experience Tim. It's appreciated.

Like you and many here I've studied airfoils and the 23012 in particular since my first Taylorcraft 41 years ago. Yes it has its plus and minus features, but did find favor in several transport and commercial aircraft for good L/D and low pitching moment across the range of useable AOA. Now with VG's on the wing and tail the beast has been tamed in my experience. I suspect it's due greatly in part because the known and demonstrated flow separation bubble just aft of the leading edge has been reduced or eliminated. Search Google and see pages 269-272 in this text for a discussion: https://www.safaribooksonline.com/li...9780123973085/

Edit: Direct link to Google Books for the pages mentioned above: https://books.google.com/books?id=Xt...20edge&f=false

Theory aside, from what I have gathered from my plane and extensive measurements with a 30" digital level, washout beyond 0.5* isn't possible with "my" Airframes, Inc. lift struts. The dihedral is fixed at about 1.5* (more than factory spec) which limits the range of adjustment of the rear strut. Set to one turn in from maximum extension on each rear strut, the washout is (as best I can measure with the calibrated level between the spars) less than 0.5* on each wing.

As I mentioned above fact trumps theory in my world and regardless of the wing conformation the flight and stall are currently exemplary and relatively benign. I've provoked NACA 2412, 4412, and USA35B airfoils to do far worse in similar circumstances so I'll leave it at that. When the floats are installed I repeat the test flying and report if there's any marked change for the worse.

Gary

[Leenicklas]

Re: Wing washout measurement

When doing the wing washout procedure, is it better/easier/more proper to do it with jury struts on or off?

[astjp2]

Re: Wing washout measurement

Well you can get a few friends to hold the wings for you, but they may get tired after a while��

[astjp2]

Re: Wing washout measurement

Here's an excerpt of a recent e-mail conversation with Terry Bowden regarding wing incidence and initial rigging. I'm posting it only as an opinion as I'm not an engineer and don't pretend it's gospel according to Taylorcraft. It's a "for what it's worth" post only. I hope Terry doesn't find offense in my copying it here. Any comments welcome.

"Hello Terry and thank you for taking the time to reply. I’ll be examining the Taylorcraft I plan to buy tomorrow in Anchorage, AK., and will take a few measurements of the wing rigging if time permits. If not then at a later date.

You know this info Terry, but respectfully here’s my take on all the fog and mystery surrounding rigging any airplane with adjustable wing incidence, and sometimes dihedral. Please correct me if my math below is wrong. This is only fun stuff for me, but I’m not an engineer just a 41 year pilot.

Taylorcraft back then chose to supply field maintenance personnel with a simple tool that could be used when setting wing washout…a 30” level and a reference distance at the outboard rib. Today there are smart digital levels capable of measuring the actual change in fractions of a degree between the root and outboard rib. Same for dihedral and control surface deflections.

For reference here’s some NACA source documents regarding the Taylorcraft and its 23012 airfoil. The lead author on some was Fred Weick who designed the Ercoupe and several Pipers. Hank Jarrett probably referenced #2:

1. http://ntrs.nasa.gov/archive/nasa/ca...9930082385.pdf The Taylorcraft is plane #5.
2. http://ntrs.nasa.gov/archive/nasa/ca...9930083935.pdf A Taylorcraft was the test plane.
3. http://ntrs.nasa.gov/archive/nasa/ca...9930084982.pdf References the Taylorcraft with zero washout.
4. http://ntrs.nasa.gov/archive/nasa/ca...9930084995.pdf The high wing plane is a Taylorcraft.

The design wing incidence at the root is referenced above as +3.8* (airfoil chord line relative to the fuselage longitudinal axis). I tend to believe the sources above. (Note: Later I saw 3*45" referenced in a fuselage print, and 3 3/4* in Chet Peek's book p. 109 when discussing the English Auster. The Auster figure also references a tip incidence of 2 1/2* yielding a design washout of 1 1/4*).

When using a 30” level as a tool, each degree of chord offset is equivalent to 0.52” difference at the front of the level versus the rear. The math is simple: 30” radius x 2 = 60” diameter circle x 3.14 = a 188.4” circle circumference/360 degrees = 0.52” bottom wing to the front of a 30" level offset per degree of change.

If the fuselage is actually built with +3.8* of incidence then that’s a distance of +1.976” at the root (3.8*x0.52”) above the forward end of the level with the fuselage axis also level (ref: horizontal stabilizer).

When measuring the tip wash at 1 5/16” (1.312”) per Taylorcraft’s instructions, we are setting the washout at approximately 1.3 degrees versus the root (1.976”-1.312” = 0.66”/0.52” per degree = 1.3 degrees). (Note the Auster's spec above).

Your 1.250” offset would have resulted in a 1.4* wash. Each 1/16” variance from Taylorcraft’s specs results in approximately 0.1 degree of change (with a 30" level only).

This makes sense to me. I believe the design incidence at the root and the as-built per airplane may vary as some have suggested. That’s why I’d prefer to measure the root angle versus the tip angle on each wing and call any difference the actual washout, especially if it also varies between wings on the same aircraft.

Thanks again for your comments,

Gary"

Hey Gary, did you ever see any data on the prewar angle of incidence vs post war airplanes? I think that I used a post war procedure on a prewar airplane any it maybe gives it a different washout?

[PA1195]

Re: Wing washout measurement

Hey Gary, did you ever see any data on the prewar angle of incidence vs post war airplanes? I think that I used a post war procedure on a prewar airplane any it maybe gives it a different washout?

Hi Dr. Tim. Your question is interesting and deserves a comparison of Pre vs. Post WWII airframe builds. I've not done that but others including you might have developed that data. I guess placing a comparative level across the fuselage attach fittings from leveled Pre <>Post fuselages would note any differences. The frame jigs used by the various Taylorcraft builders probably had variance. Was there an intent to change the incidence specs for the Post models that you've seen or read?

You mentioned rigging procedure. Have they differed over time, and if so, what are the Pre <>Post specs you've seen? Maybe note that here and we can go from there.

Last thought is as I mentioned above...what it boils down to 'for me' is the washout from wing root to tip in degrees. Measure that, set it, then go fly and fine tune. I'll suggest in lieu of factory numbers a starting point of 1* [-0.0*, +0.3*]. Not much wrong with a bit more except possible slight loss of cruise and climb; less may change stall behavior for the worse but slightly add cruise and climb. VG's add another level of variance.

Gary

[Robert Lees]

Re: Wing washout measurement

When doing the wing washout procedure, is it better/easier/more proper to do it with jury struts on or off?

For the initial measurement, leave them on (then if no adjustment is required, you're good to go).
But if the rear strut needs adjusting, you will have to disconnect the jury strut.

If you do disconnect the jury strut, have a good look at the fittings that screws into the wing cross-tube. The threaded fitting is hollow, and the wall thickness is thin at the base of the threads...make sure there are no cracks in it. See attached picture.

(I think Tim has temporarily confused struts with jury struts? )

[PA1195]

Re: Wing washout measurement

It's probably a good idea to look at those fittings. Remove and inspect for corrosion or cracks. After 70 some years of pushing on the struts to move forward or back they may get compromised. Ski ops can take more and harder pushing to reposition the plane.

I was told by mechanics to push at the fuselage or grab the outboard strut to wing junction and avoid the middle spans of the struts. But some days things don't get done the way they should.

Gary

[SpecialT]

Re: Wing washout measurement

... then fly it to find what wing is heavy. Then its half a turn in on a heavy wing and half a turn out on light wing at a time until it flies straight. I have been no more than 1.5 turns on both struts on any Taylorcraft I have done. Tim

Thanks for the post, it took the brain work out of trying to figure out what "wash in" verses "wash out" means and fixed my heavy left wing and constant use of right rudder.

[PA1195]

Some thoughts:

Wash in = wing tip more AOA = more lift. Wash out = wing tip less AOA = less lift.

If right rudder in cruise or under power is required also have a look at the top of the vertical stabilizer. Sight over it and the aligned rudder from the rear and see if an imaginary line through the vertical stabilizer to the top of the cockpit crosses slightly to the left of the center of the cockpit or skylight. Maybe and inch or a little more to the left. Typically they are bent or offset to the left to force the plane to the right to counter prop P-Factor which wants to rotate the plane left under power. A string can also be run along the stabilizer and up to the top of the cockpit. Sometimes that's easier than adding a trim tab to the rudder to accomplish the same adjustment.

Gary

[SpecialT]

150hp and a big prop I figured there is no way I'm going to get away from right rudder in climb or power ops, but the dropping left wing I think was causing some slip. Now at cruise it flys hands off with the ball pretty much center. Now I need an adjustable elevator trim tab.