Wing washout measurement

[1938BF50]

Re: Wing washout measurement

maybe a little clarification, I taped a 1" block to one one end of a 4ft level and then a 2 5/16" block at 30"(or whatever the spar spacing was. Nothing to measure, just adjust to level the bubble.

[barnstmr]

Re: Wing washout measurement

This thread came just at the same time as I was re-assembling my airplane after RH wing repairs... and I was re-assembling with NEW RH Univair struts and kept my existing LH wing struts. Since the airplane had been flying hands off before the repairs, I decided I wanted to adjust the RH wing to match the same wash-out measurement as the LH wing.

To start out... I adjusted the RH rear strut adjuster screw in the middle of its slot and temporarily bolted it up. I used a 3-foot spirit Level for all the measurements, leveled the aircraft as per the manual. I did not use a string, but instead used my spirit level to check wing incidence measurements. For this, I clamped a retractable tape measure onto the spirit level at the front spar location. I marked the fabric at the rear spar location on Rib #2 both sides and at the first rib outboard of the wing strut attach fittings both sides. This way, I could always come back to the same spot to check incidence. To my surprise, I found that the LH wing was mounted exactly straight on the airplane... no wash out... no wash in. That is.... I found the same incidence measurement at both the #2 rib and the outboard rib. at 1.5/16 inches (positive angle of incidence).

So...
I measured the RH wing and found the wing had only about + 3/8 inch incidence measurement on the outboard rib... and the inboard measured 1.5/16 inch... same as left wing. So... the net twist (wash-out) of the RH wing was 15/16.

I ended up having to adjust the RH rear strut all the way in to its minimum length in the slot in order to match the RH wing with -0- wash out like the LH wing. I attributed this difference due to the mixed manufacturers of struts from LH to RH. I have NOT yet flown the airplane to check the current -0- wash setting for flight characteristics. When I do, I will give a report here. Later-on, I intend to buy new Univair struts for the LH side this summer before my inspection interval is up... so if the airplane flies OK as is now... I will fly as is... then re-check everything at that time. I may also experiment with different degrees of wash out at that time.

By the way... I had my 17 yr-old son Travis helping me. I recommend having at least one other person around to help jiggle the wing when installing strut-bolts in and out. With the whole airplane precariously leveled and the tail propped up on a stool... I was glad to have Travis there helping me watch the airplane and keep from knocking it off the stool... SO if you do try to do this alone as a one-man show... I recommend more suitable jack-stands for the job.

[Hank Jarrett]

Re: Wing washout measurement

Being an engineer I have some ulterior motives to getting accurate measurements of the angles in the wing. I want to do some flight testing on my plane and for the analysis I will be calculating the actual incidence of the airfoil at several points on each wing. I am building a sensitive angle of attack sensor and Pitot that will extend out in front of the wing so that I can measure the actual stall angle of attack and will be able to find the minimum sink angle. We really don't need to know these "bits-o-data" but that is the kind of thing I find to be "fun". Knowing the exact angle that the wing stalls (and how the stall progresses across the span) could allow us to set up things like short field approaches and better angles to attach floats. If I can make the rig easy to attach and remove it would be great to be able to put it on the planes that have the better handling and find out WHY they handle better.
First step is to gather data from a baseline plane and next to check other plane to see how much variance there is.

To quote my old boss, "Sometime, I must explain just how Henry Jarrett has fun."

Hank ;-) Just havin fun!

[barnstmr]

Re: Wing washout measurement

Hank... have you seen the 1950-something NACA report that was the result of extensive flight testing of a Taylorcraft? As I recall, the main objective was to quantify the effects of wash-out, wash-in, slots, slats, and other stall modification techniques.

[Hank Jarrett]

Re: Wing washout measurement

Got a copy right here. That was what got me thinking about additional testing that could be fun. Also where I got the basis for my AoA and Pitot probe. No sense re-inventing the wheel!
Did you see the bubble they put on top of the cabin to see the tufts on the wing? I think I would use a small vid camera.
Hank

[Larry Lyons]

Re: Wing washout measurement

Yesterday I saw the Gopro camera at a Target store! the water proof one too boot. L

[Buell Powell]

Re: Wing washout measurement

Hank,
When you do have those bits of data please keep us posted---since we both have 41 Deluxe models it would be especially great information for me to have. I usually end up doing the adjustments without help but having someone to help with jiggling the wing to replace the bolt or sometimes sliding the strut out of the fitting or back with it perched up to level does seem like a much better idea. If your just checking the washout and it's close blocks on both ends is probably a good way but especially when replacing with different struts one reason I prefer to measure is that it makes it easier to get an idea of how many turns needed to correct the distance -so not as many times of pulling the strut down,adjusting,and re-installing--Also--I like to keep notes-keeping up with the notes sometimes is a different story-I'm not at home right now but somewhere I have the notes of adjusting the new struts for my 41.

[Robert Lees]

Re: Wing washout measurement

<snip>...tufts on the wing? ...
Hank

The tufts one sees on old films of aerodynamic testing are the remnants of creatures called "Bernouli"'s.

These are an ancient type of creature, normally invisible to the human eye, and made of wool, who's sole purpose is to keep things up in the air. Without knowing, we've all seen them in our childhood...they're the lifeforms that keep soap bubbles flying, farts in the bath rising and golf balls ascending.

These little creatures hold hands together to maintain the lift that we know; after all, it's their strength that keeps us up there.

When they are used to keep a wing up (as in our case), all is well. Unfortunately when the wing stalls, their hand-hold fails. The Bernouli's die; the wing loses lift, and the only thing we see remaining is their little woollen arms wafting in the breeze.

So please don't do too many stalls, or you will be killing even more of these beloved creatures.

[Hank Jarrett]

Re: Wing washout measurement

I love the little Bernoulis around my hangar and leave a nice bowl of lifting morning mist for them every time I can. Now everyone should know that spam can drivers do NOT believe in Bernoulis. They think airplanes fly because of Marconies. Marconies feed on bad country music and screechy singing from fat opera divas. I know this because when a Cessna crashes the pilot seems to always be found holding a radio mike praying to Guglielmo Marconi, the patron saint of gabby pilots. If you ever heard one they sound like they are trying out for a German part at the Met.
Hank

Also remember that Bernoulis HATE helicopters. They trap the poor little guys and beat them till they agree to lift their Godless hulls into the air. If there is a Sailplane around a helicopter can barley catch enough Bernoulis to lift off! They seem to just LOVE sailplanes. I never figured out if Bernoulis like balloons and airships or not. Very few seem interested in escaping confinement, but they seem to REALLY loose their temper when there is a lot of Hydrogen around. One spark and they get very violent.

[Mark Julicher]

Re: Wing washout measurement

??
I am really crushed!
I thought the microphone was a primary flight control and that spam can pilots use it to tell their planes what to do.
I also thought that Tesla invented the radio.

there I go thinking again.

[Hank Jarrett]

Re: Wing washout measurement

And I thought Tesla invented the ignition system!
Well, I guess we all just live and learn. ;-)
At least we can all agree that that Taylor guy invented the best danged little airplane ever!
Hank

That would NOT be the Cub. That was the "false start" that LED to the best plane ever. Close but no cigar.

Got to go feed the Bernoulis. They are climbing the walls.

[Hank Jarrett]

Re: Wing washout measurement

Finally got the knees working well enough for a day in the hangar and even found the camera cable so I have pictures of the angle of incidence tool I built.
The tool has two cross pieces attached to the fore and aft stick to solve the problem with the bottom of the rib hitting the stick and messing the measurement up. It also allows the bungees to hold the stick straight on the wing and keep the cross pieces at the front and rear spars. I ran shims under the level to get the angle right and I can now adjust the aft strut and just look over at the level to see when I get it right. Notice the roll of paper towels and napkins because the cross pieces tended to get pulled up by the bungees where the tip curves up. Takes about 2 minutes to attach it to the wing and it never budges when you shake the wing to make sure everything is stable for the measurements. IT's a WHOLE lot easier with a helper, but with the tool, I can do it alone.
Hank

[astjp2]

Re: Wing washout measurement

I have a simple fixture I made that take about 30 seconds to check the washout with a digital level, I used a 1 bolt and a piece of 3/4" angle aluminum riveted together. Hank, send me a PM to remind me to get a picture for you. I also have tools to check wheel alignment. Tim

[Hank Jarrett]

Re: Wing washout measurement

Always interested in seeing new tool ideas. Why not post them so others can make more improvements? Mine worked, and got accurate and repeatable measurements, but sure isn't elegant.
Hank

[PA1195]

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"