Wing re-build, washout question

[Robert Lees]

Re: Wing re-build, washout question

...Imagine if I had put a 30 degree twist in and my point becomes more obvious, I think.

I'm not so sure, if only because a 30 degree twist is completely unrealistic. The actual washout (twist) is obviously an awful lot less, and the natural flexibility of the spars, the fabric and the drag/anti-drag wires will absorb any variance during construction.

As a matter of interest, when I recorded the rebuild of my wings, I made the following annotation to these two photos:
"String lines assure the straightness of the spars during trammelling. The right-hand photo shows the wing with a block inserted under the front spar to simulate the wash-out to verify that nothing alters."
(source=http://www.taylorcraft.org.uk/Brey_rebuild-Wing-structural.htm)







and then when I did my next wing, I annotated:
"The next wing is prepared for covering. One of the things very noticeable is a "set" in the wing, after nearly 60 years of washout in each wing."
(source=http://www.taylorcraft.org.uk/Brey_rebuild-Wing-fabric.htm)





I doubt the factory in the 1940's or before or since used blocks to pre-empt washout.

Rob

[Guest]

Re: Wing re-build, washout question

Nice wings, good pics, I am never complaining about having to work in a two car garage ever again!

Dave R

[N96337]

Re: Wing re-build, washout question

Trammeling is to square the bays. If you square them as the wing will fly, they're correct. If you set them level, and then move the wing, they're not going to be far enough off to worry much. The same can't be said about fabric. I can't count how many wings I've seen in areas of high temperature variance, that have loose fabric show up. Partly that is caused by improper step ironing, but I've seen it caused by a wing being built flat, then twisted as well. It's not a big deal to build the thing the way it's going to fly, or pretty close....why wouldn't you want to do that?
John

[Guest]

Re: Wing re-build, washout question

Trammeling is to square the bays. If you square them as the wing will fly, they're correct. If you set them level, and then move the wing, they're not going to be far enough off to worry much. The same can't be said about fabric. I can't count how many wings I've seen in areas of high temperature variance, that have loose fabric show up. Partly that is caused by improper step ironing, but I've seen it caused by a wing being built flat, then twisted as well. It's not a big deal to build the thing the way it's going to fly, or pretty close....why wouldn't you want to do that?
John

We aren't disagreeing but I have done a bad job of communication what I was meaning about being co planar and I don't think I am going to do any better with more typed attempts so I think I will stop.

I agree, square the bays is the point.

Dave R

[LostnSpace]

Re: Wing re-build, washout question

The same can't be said about fabric. I can't count how many wings I've seen in areas of high temperature variance, that have loose fabric show up. Partly that is caused by improper step ironing,

This reminds me of several years ago a guy from south of Atlanta asked me to fly an L-4 in original colors up to OSH and try and sell it, I left it outside the night before I took off, the next mornings was cool and damp, I was shocked at the baggy fabric, after the sun was up a ways and it warmed up, it looked fine, flew fine, got to OSH, was walking around the C-47's/DC-3's early as the sun came up and there was a rudder that looked just like the L-4 fabric, it was shocking to see something like that, I pointed it out to a customer that I was doing a fabric job for, and his first question was, "what's the guarantee mine won't look like this??", thanks for the memories, gary

[flyguy]

Re: Wing re-build, washout question

There is something here in this discussion that I am completely missing. There is an angle that the wings are mounted on the plane relative to the thrust line. Correct? Gives a positive angle of attack relative to that line. Then there is a twist adjustment that is made by tightening or loosening the rear strut adjustment screw. Is there some other angular element that I am missing? Someone clue me in because----

Why would you want to put a twist in the wing when you might have to push the wing in the opposite direction with the strut adjustment in order to correct for aerodynamic rolling tenancy? I have never built a wing up from scratch so I am assuming I have some kind of hole in my knowledge from what I am getting from the discussion here.

[Edwin Otha]

Re: Wing re-build, washout question

Build the wing flat. The fuselage has the incidence angle welded in. I adjust the strut location for the same angle as the fuselage attach. If I have a heavy wing I shorten the rear strut on the heavy wing. Been working for years.
Cotton will be limp on cold days, pretty normal. Poly-Fiber is loose every time you fly, like covering your plane with rubber.
EO

[PA1195]

Re: Wing re-build, washout question

The wing mount incidence at the fuselage is about 3.8* nose up. Subtract from that about 1.5* of washout nose down at the wing tips. The rest is fly and correct with magic.

Gary

[flyguy]

Re: Wing re-build, washout question

OK, I actually didn't know that Taylorcraft wings had a twist to them. Now I think about it though, it sounds familiar. Am I correct to think that the washout is to make the inboard (away from the ailerons) part of the wings stall first. Mine had a repair done to the wingtip on the left side and it appears that the angle out there is off just a bit. Likely why I have had to make larger adjustments on the rear struts.
DC

[PA1195]

Re: Wing re-build, washout question

Here's a discussion of the potential effects of variable washout twist on a Taylorcraft:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930083935.pdf

It can be first set to what specs the factory recommended (http://www.airframesalaska.com/v/vsp...aftinstall.pdf) , or it can be set to an initial twist using a modern digital level. From there flight testing will lead to any further adjustments as previously suggested.

Edit:
Initial washout has been reported to be between 3/4* (Chet Peek's Taylorcraft book pp. 20, 109) to 1.5* in various threads here and from personal communications from owners.
Airframes' diagram of the level's placement relative to the wing spars varies from that shown in the Taylorcraft Service Manual available here (http://www.taylorcraft.org/resources.html)
FWIW my wing's are flat to 1/2* of wash measured with a digital level. I started flat as Edwin suggests above and corrected for excessive left wing lift/right wing heaviness by lengthening the left strut one turn (washed out left wing). Flies and stalls straight and level.
If pilots run out of forward trim at speed and have to push forward on the elevator control to maintain level flight then washout both wings to reduce lift.

Gary

[Guest]

Re: Wing re-build, washout question

There is something here in this discussion that I am completely missing. There is an angle that the wings are mounted on the plane relative to the thrust line. Correct? Gives a positive angle of attack relative to that line. Then there is a twist adjustment that is made by tightening or loosening the rear strut adjustment screw. Is there some other angular element that I am missing? Someone clue me in because----

Why would you want to put a twist in the wing when you might have to push the wing in the opposite direction with the strut adjustment in order to correct for aerodynamic rolling tenancy? I have never built a wing up from scratch so I am assuming I have some kind of hole in my knowledge from what I am getting from the discussion here.

Hi Darrel,

I may have caused that, sorry if I did.

I had been attempting to point out the difference between the theory in geometry that is used to make a rectangle have 90 degree corners (equal diagonal lengths) and the actual practice of it as applied to trammeling.

Very poor job done.

Dave R

[Edwin Otha]

Re: Wing re-build, washout question

I have found that shortening the strut, making it fly more, has a greater effect than lengthening the opposite strut. Much less adjustment is needed. Also in my feeble mind I can't see a reason you would want to lessen the incidence angle outboard of the strut.
All of that NASA stuff is spot-on for critical wing sections, but the little Taylorcraft airfoil isn't too critical. Generally tough to make it stall without some rapid movements. One thing to remember about NASA of the four original operational space shuttles they lost two, 50% failure rate, so look at their information closely.
EO

[PA1195]

Re: Wing re-build, washout question

I'm willing to accept a flat wing, but not a wing with greater incidence at the tip than the root. Even with VG's a tip stall can be interesting. Champs and their offspring have gotten by for years with a flat wing. My Citabrias stalled but weren't vicious.

So starting with a flat wing like I did I lengthened the rear strut on the light wing to maintain decent stall behavior.

Gary

[Hank Jarrett]

Re: Wing re-build, washout question

I have found that shortening the strut, making it fly more, has a greater effect than lengthening the opposite strut. Much less adjustment is needed. Also in my feeble mind I can't see a reason you would want to lessen the incidence angle outboard of the strut.
All of that NASA stuff is spot-on for critical wing sections, but the little Taylorcraft airfoil isn't too critical. Generally tough to make it stall without some rapid movements. One thing to remember about NASA of the four original operational space shuttles they lost two, 50% failure rate, so look at their information closely.
EO

So if you drive a nail and the first one bends you are a 100% failure in driving nails? Even if you proceed to drive several hundred to finish the project with only a few more bends? Wouldn't it be a more reasonable measure to look at the total number of FLIGHTS compared to the number of failures? The failure rate was way too high on the shuttle system, but NASA is in the BUSINESS of taking risks that industry can't afford to.....at least that is what we were SUPPOSED to be doing. NASA is so risk averse now it is a wonder they ever launch ANYTHING.

Hank Jarrett
Retired as lead systems and safety engineer for manned space flight supporting the NASA Engineering and Safety Center

[Edwin Otha]

Re: Wing re-build, washout question

I understand that space flight is risky. Didn't mean to get any ones fur rubbed backwards. EO