Wing washout measurement

[Hank Jarrett]

Hopefully will be just a discussion on how many Angels can dance on the head of a pin. I wanted to make a tool to adjust the washout on the 41 when I don't have anyone to help.
I was going to make a wood stick tool to hold a level against the bottom of the wing while the adjustments were made and allow me to be able to look at the level at the root and aileron break at the same time. The measurement in several manuals says for the level to touch the bottom of the rib at the aft spar and be down 1 5/16" at the front spar 9" aft of the leading edge. All that seems pretty straight forward, EXCEPT that the bottom of the rib is NOT FLAT. If you put the aft edge of the level against the rib at the rear spar it hits the bottom of the rib and ends up about 1 3/4" down. If you set the level at 1 5/16" at the front, it hits the bottom of the rib about 27" back from the LE and is 1/4" below the rib at the aft spar.
All together the total difference is only ~2*, but when I did aircraft design that was A LOT. Anybody know what the incidence angle is SUPPOSED to be at the root and at the start of the aileron? I am really interested in seeing if the incidence is actually the same at both root ribs. I am betting it isn't. They just didn't build them that accurate back them and just trimmed them out to fly straight. Problem is, how do you know how much twist is there if the root angle and aileron rib angle aren't accurate.
How many Angels do YOU think can fit on that pin head?
Hank

See what happens when I can't get out to my plane? I THINK too much!

[Buell Powell]

Re: Wing washout measurement

Hi Hank,
Glad your feeling better! I tape a slide rule 30" from the aft end of the level. Place the aft end just forward of the rear spar-at the first full rib-apx 26" from the tip of the wing.You should be able to hold it at the aft end
for the first few inches before the rib starts to taper upward and see the level bubble. Hope this helps.
Buell

[Hank Jarrett]

Re: Wing washout measurement

One question answered. Based on a NACA test in the musty smelling section of the NASA library they tested roll control and spin characteristics on a Taylorcraft. Part of the base line data was the incidence angle of the wing at the fuselage.
The wing is "supposed" to be at 3.8* based on level as measured at the horizontal stab.
Hank

Doesn't that make everyone feel better? We can all sleep soundly tonight, till we think about how far our planes are out of standard. :-)

I just GOT to get out and actually PLAY with my plane!

By the way, they test controlability at 0*, 4* and 6*. Lots of deep reading. I will pass anything useful along (already found out the slats tested in the second phase were pretty much useless).

[Hank Jarrett]

Re: Wing washout measurement

I actually have a wing rib at home (got to have SOMETHING to play with while convalescing). I was going to use it to make a tool so I wouldn't have to hold the levels while I do the adjustment. The drawing you posted is one of the drawings I have to hold the level, but what is interesting is you can't actually put it against the wing like they show (OK, actually it DOES go against the wing just like that, but the 1 5/16" dimension is MUCH bigger. What I am going to do is put a 1x1 stick span wise for 3 ribs at the front and back spar to stand the level off the wing curve. A fore and aft stick will be glued 90* to the two span wise sticks with a piece of plywood that goes up and holds to the TE and sticking far enough forward for a second ply piece to be wing nutted so it grabs the LE. Couple of wraps of tape to hold the level to the fore and aft wood and it will stay up there all day. A shorter version at the root and a level on top of the stab and I can check all three without moving anything.
Got to get all these measurements right before I build the Pitot extension and AoA extension probe. Nice design info in that NACA report. If you like skylights you should see the bubble they put through the cabin top so they could see the tufts on the top of the wing. Put two sticks out of it and it would look a little like a B-25 top turret!
Hank

Nice way to intimidate the lesser LSAs. ;-) Anyone want a gun turret on top of their Taylorcraft? I think if I try to do some of their tests I will just use a little Vid camera.

[mikerice]

Re: Wing washout measurement

Hank-
we just did the wing tip wash measurement this past Wed. and found the same problem you mention. We leveled the aircraft with the horizontal fins and could not get a level to lie flush with the bottom of the rib.

I had a 1 5/16" block on the level at 30" and it would not work.

What we ended up doing was to carefully hold the level and measure the dimension above the level at rear spar front edge, comparing both sides. This started about 9/16"" on the right and 1/4" on the left. We ended up adjusting both sides to about 7/16".

We flight tested and did not notice much difference to be honest. I can not say if there was any improvement, but I guess we can say the wing wash is equal on both sides, for what thats worth. It seems to fly wings level ok.

Our goal was to eliminate a rudder flying 1/2 ball out to the right, it did not help. Looks like we are going to need a rudder trim tab.

[mikeg]

Re: Wing washout measurement

Food for thought guys, that is where you start. Then you go fly and adjust for your "normal" cruise weight (one or two on board, wing tank/tanks full or empty, etc.) Then wash both wings in or out equally to center the trim tab for your "normal". My '41 DeLuxe cruises at 105, stalls clean straight ahead (ball centered), spins are realative slow (warm weather) and about the same in both directions. Rigging and trimming are fun. The Tri-Pacer manual (as I remember) said to bend the fin to elimate any jaw tendancy at cruise. Works on a T. There-that should start something:-)
Later,
Mikeg

[Buell Powell]

Re: Wing washout measurement

I think I understand what you are saying now. The rib is actually just giving you the shape and same distance from the bottom of the spar--so if you have the ship level-place the level just at the forward edge of the rear spar at level-go out 30" which should give you 9" back from the leading edge and measure 1 5/16" at the forward end up to the wing with the level ball centered and not worry if the level is flat on the rib. Another way to tell is-- If it flys nose heavy- both wings need to be washed in -if it flys tail heavy then both wings need to be washed out. But like Mike stated thats where to start then adjust by test flying and adjusting-

[mike lutz]

Re: Wing washout measurement

I used to tape a 1 inch block on the end of the level and adjusted the rear strut till I got 2-5/16(remember the 1 inch block on the level),then went and flew it.I would if needed put wash-in on heavy wing.I,ve had good results over the years doing it this way.

[Hank Jarrett]

Re: Wing washout measurement

Rigging an airplane can be challenging and a lot of fun if you actually enjoy that kind of thing (I do). You can eliminate a lot of problems through the "back door" and end up with a plane that will fly straight at cruise, but yaw or roll anywhere else. You can "fix" an off center ball with differential wash-in/out and engine shims, but if it is really a yaw problem, a rudder tab makes a lot less drag (so you cruise faster). Sounds like what Mike did by hand is what I want to do with a "fixture" so I won't need help in the hangar. Not many people want to fiddle with the minutia on my Taylorcraft like I do. I can always get help, but I like to avoid the rolling eyes when I get all anal.
Just wait till she is flying again and I want to start doing flight testing to build all the charts for a POH. I will probably drive potential data recorders crazy.
Hank

[Ragwing nut]

Re: Wing washout measurement

how far off the rib or at what angle does not matter if your measuring difference. make a straight edge with blocks at each spar point to keep the staight edge off the center of the rib. take a measurement at the root, then a measurement at the strut, I set the difference at 2* wash or slightly less, never more, too much drag. With that set, tail rigged square, I hand adjust for flight characteristics after that. I hate tabs, so if i have a yaw issue, I adjust aileron position starting with 1/4" droop to correct yaw.

[Hank Jarrett]

Re: Wing washout measurement

The main reason for the rig I am building is I need to be able to do the whole job alone. I usually don't have anyone to hold the blocks and level while I work and everything takes forever every time you have to re-set-up. With the wing clip system the level is in place for the whole process and I can put a level on the stab, one at the root and one at the last full rib outboard all at the same time with no help. The nice side benefit is is stands the level off the wing and avoids the lower rib curve. What amazes me is those drawings showing how to do it have been around since before WW-II and no one ever noticed they don't work as drawn. Not that it would take more than a few seconds for a good mechanic to shrug it off and add equal thickness additional blocks at each spar, but if a "newby" didn't see it, he could put the level tight at one end or the other and end up with 4* of twist or NONE! A stall spin with no twist could get more exciting than any of us want, especially for a guy who was new to aviation. That was the whole reason for the NACA report I dug up. Lots of stall spin fatalities back in the 30s and they wanted to know what was happening.
Hank

[Buell Powell]

Re: Wing washout measurement

Back when my Dad was instructing and these planes were built, spins and recovery was required training. I use the 1 5/16" to make sure the wing tip doesn't stall first in a slow turn and to insure recovery from spins and the fact that is what the manuel states. The drawing works for me but I use a slide rule instead of a block at the front. This works for me to keep up with the distance and amount of turns needed to correct when adjusting. When I re-installed the struts on an F19 that I believe had been set when it was built-both wings checked right at 1 5/16" after taking them apart and reassembling them.

[mikeg]

Re: Wing washout measurement

Rigging an airplane can be challenging and a lot of fun if you actually enjoy that kind of thing (I do). You can eliminate a lot of problems through the "back door" and end up with a plane that will fly straight at cruise, but yaw or roll anywhere else. You can "fix" an off center ball with differential wash-in/out and engine shims, but if it is really a yaw problem, a rudder tab makes a lot less drag (so you cruise faster). Sounds like what Mike did by hand is what I want to do with a "fixture" so I won't need help in the hangar. Not many people want to fiddle with the minutia on my Taylorcraft like I do. I can always get help, but I like to avoid the rolling eyes when I get all anal.
Just wait till she is flying again and I want to start doing flight testing to build all the charts for a POH. I will probably drive potential data recorders crazy.
Hank

Hank,
I actually made something that looked like a prop blade paddle to "tweek" the fin. Didn't take much.
Mikeg

[Buell Powell]

Re: Wing washout measurement

add equal thickness additional blocks at each spar,
Hank[/QUOTE]
That seems like something very worthwhile to add to a manuel.--I use a slide rule taped to the front instead of a block so may be --or add a block at the rear spar and add equal thickness of block to front measurement?

[1938BF50]

Re: Wing washout measurement

Mike Lutz is spot on. It is a simple one person job and works great....nothing to measure. That's exactly how I did mine.