Adjusting Washout

[flyguy]

Re: Adjusting Washout

Apparently the 74 inch prop is not certified/tested for vibration at the higher RPM of the 85. There was quite a discussion here on that subject a while back. Lot of people are using them anyway. Additional vibration would have to be pretty bad to notice it in a Tcraft. Chuckle.

On the full opposite adjustment on the struts; I have close to that condition on my -85. What I can see on my wing is that one of the wingtips is shaped slightly different from the other. I have to look VERY closely to see the difference. With all that leverage, for sure that is part of the reason for the adjustment offset on mine.
DC

[cvavon]

Re: Adjusting Washout

I have a 72/40 sensenich on a c85-12 on my tcraft it will static at 2450 and turn over red line if I let it as far as speed i get around 100 mph at 2450 rps it climbs with full fuel and 290 lbs me at 1200 to 1500 ft per min as tim said the 150 supper cub don't get to far ahead of me. I think you need to take your prop to a good shop and have it checked and maybe pitch it at 42 instead of 40.Also Sensenich pull better then McCauleys do.

[smmilke]

Re: Adjusting Washout

I took some angle measurements and have a couple other pieces of info that may be of interest.

The rib angle measurements were taken 20 inches forward of the trailing edge, on the lower surface of the wing. The horizontal stabilizer was at an angle of 10 degrees. Starting from the innermost rib (roughly 20 inches from the fuselage) and moving outward the measurements are as follows:
Left Right
12----10
11----9
11----9.5
11.5--10
11.5--10.5
10----9.5
10.5--9.5
10.5--9 (difficult to take this measurement as the rear strut was in the way)
10.5--10
11----10
11.5--10.5
12----10
11----10.5

Despite what these numbers might indicate, by looking at the rear strut adjustment the left wing is washed all the way in (min rear strut length), while the right wing is washed all the way out (max rear strut length).

I noticed that looking at the trailing edges near the fuselage the left wing appears to sit lower than the right. Here are some pictures that show the slight difference:



I hope these measurements and observations give you guys some idea of what might be going on here.

On an unrelated note I noticed that the support plate on the rear strut attach is welded further up on the right wing than on the left. Any idea as to why this might be/if it is a structural safety issue if I fly at #1500 gross.

[Hank Jarrett]

Re: Adjusting Washout

With those wing angles this plane should be seriously right wing heavy. Something is wrong and it looks like it is along the whole wing which says the problem is at the root end or fuselage lugs. The next measurement is a little harder but I did it on my plane. You take the wing bands off and measure the angles of the lug holes (front and rear spar attach) on both sides. That sounds impossible with the wings on at first, but you can measure the offset from the bolt threads with a couple of blocks hot glued to a long level so they rest on the threads. The lower one is in contact with the bolt and you measure the other one. The actual angle is irrelevant, but it needs to be the same on both sides! If it IS the same, you have one wing with damage or the attach straps not in the right place (either the ribs are on the spars at the wrong angle or the actual straps are too high or low). If the fuselage lugs are not level with each other, you have a bent fuselage!
Twisting the wing with the struts IS NOT the fix for either of these problems! You are just flying a big propeller with one blade backwards, and that will make a LOT of drag!
I don't know what your IA would say, but you could weld up a new rear spar attach fitting in one wing with the holes offset that would correct this IF THERE IS NO DAMAGE that caused it in the first place. I have seen one wing that was angled like this and the REALLY BAD NEWS was that the plane had tapped a hangar with a wing tip and split the rear spar of the wing. The wing was able to twist up and down as the split opened and closed. It nearly killed the pilot. Have you tried to hold the wing tip and GENTLY twist each wing to listen for "funky" noises? When the other plane tapped the hangar there was NO external damage visible. The paint wasn't even scraped. That wing is a LOT of leverage!
If you have NO DAMAGE to the wing or fuselage and want to make a new rear spar wing fitting you might need a DER to sign it off and the logs would lock that wing to that plane until the wing was rebuilt straight. I would NOT sign for something like that unless I was POSITIVE there was no underlying damage.

Hank

[3Dreaming]

Re: Adjusting Washout

In your pictures you have two different strut attach fittings. If the wings were not built to match each other it could be your problem. The fact that the adjustment is different between sides could be correcting for the miss matched wings. I know this may sound a little simplistic. Move the airplane outside and set the tail up on something to get it near level flight attitude. Center the ailerons. Now step back behind the airplane and look at the wings. You should be able to see the wash out. It will show as more lower surface showing near the wingtips. If they don't look close to the same, then you are fighting a problem with the airframe that needs to be addressed. This is something I started doing with any fresh aircraft coming out of the shop, after taking off and having a very wing heavy airplane one time.

[Hank Jarrett]

Re: Adjusting Washout

I like it. Eyeball trammeling! I used to do this with all my models and it actually works (except an FAA type will probably not like it). If we don't find the real source of the problem soon a full trammel will probably be needed. A little complex but you learn a lot about your plane in one.

Hank

And it is actually kind of fun.

[smmilke]

Re: Adjusting Washout

I got a little more info today. I checked the angles as best I could on the spar attach fittings. The right wing measured 15.5 degrees and the left wing was 16.5 degrees. I set the level on the tops of the two flanges that rest against opposite sides of the spars and tried to get the level closer to the fuselage side of these fittings as that is where they appear to be the most uniform. Despite the precision of these measurements being to .5 degrees, I am not sure the accuracy is really as great as +-.5, due to the difficulty of getting the spacers to sit properly on the uneven tops of the spar attach fittings.

I have some better pictures of the trailing edges with a straight rod continuing on to the fuselage showing that the right wing's trailing edge is significantly higher than the left's.



The most interesting development of the day was noticing a metal tag welded to on of the frame tubes near the right rear spar attach. The tag seems to read "I.A.C. MFG. REPAIR". There are some welds on the tubing near the tag that don't match the other side of the fuselage. What would have warranted welding a tag to the airframe? I have logs going all the way back to the day the plane came out of the factory and there are some mentions of spars being spliced, but I can't find an entry that can conclusively be linked to a fuselage repair/modification like this.

[Guest]

Re: Adjusting Washout

It probably says T.A.C not I.A.C., Taylorcraft Aviation Corporation.

I suspect that it has nothing to with your problem and merely indicates that they spliced a piece of tubing in at the factory.

I would look inside each wing and measure and record;
1) the height of each spar (front and rear) and I assume that you will find that they are the same if they are not then we may have extra arithmetic after step 2
2) measure the distance that each rib lower surface is below the bottom of the each spar (two numbers per rib).

I suspect that you will find that the ribs have been placed differently with respect to the spar's upper surface.

Imagine a plane (mathematically speaking) that sits on a line that follows the top of the front spar and a line that sits on top of the rear spar.

What I mean is that the ribs are different angles with respect to that plane. It may even be that each rib on the same wing has a different angle.

Its a guess but I am guessing that the guy that assembled the ribs on the wings did not pay attention to this.

If the spars are different heights then the calculation needs some adjustment to account for the z distance from the top of the spar to the lift strut fitting attach holes.

Dave

[astjp2]

Re: Adjusting Washout

Prewar vs. post war measurement for the wing attach fittings after a repair? Wing spar fittings were off a little on each side? Does it really matter if you can get it to fly wings level? I would be looking at getting a prop before worrying about the wings....Tim

[waltermrich]

Re: Adjusting Washout

On the subject of rib nailing do you know the height of the rib in relation to the spar , in other words where do they nail on the spar, how much rib is above the top edge of the spar, unfortuately, I removed all of the ribs on my frount spar without measuring that distance, the other wing is covered so i can not check it. I do have a uncovered wing and can use it but it may have been built slightly differently. Thanks for your help.

[3Dreaming]

Re: Adjusting Washout

On the subject of rib nailing do you know the height of the rib in relation to the spar , in other words where do they nail on the spar, how much rib is above the top edge of the spar, unfortuately, I removed all of the ribs on my frount spar without measuring that distance, the other wing is covered so i can not check it. I do have a uncovered wing and can use it but it may have been built slightly differently. Thanks for your help.

I think wing assembly was kind of like paint jobs at the factory. It was how ever they felt that day, some high, some low, and some centered. All that mattered is they made each pair of wings the same.

[waltermrich]

Re: Adjusting Washout

Well there in lies the dilema, Hope that I can make the right wing reasonably close to the left , on 2nd thought I do have lots of photos I can probably get pretty close. Not prefect but what now?

[astjp2]

Re: Adjusting Washout

Fly it

[Hank Jarrett]

Re: Adjusting Washout

But every plane I have seen the lugs were the same side to side! There can be a lot of variance in location, but the symmetry has to be there. Same for the wings. I talked to a guy who built a lot of wings and he said that getting perfectly straight spars wasn't that easy all the time. They would set up the spar and pull a string to find the high and low spot along the span. If the spar arched up some you wanted the smallest gap on top where the highest point on the spar was and the smallest gap on the bottom where the lowest part was. They split the difference so the smallest top and bottom gaps were about the same on the worst spots and all the ribs were placed to stay in line and nailed. Look at some of the old factory photos and you can see the strings across the ribs to get them straight. If you work with the small gaps available on the ribs and one wing spar is way out one way and the other way out the other, you can still trim it out when the spar to fuselage attach fittings are put on by shifting the bolt holes a little. If the fuselage attach fittings are out it can have a lot more impact, and I am afraid that is what we are looking at. One of the aft spar attach fittings on the fuselage looks like it is low. Worst case the vertical tube may have to be cut and the top longeron jacked up until the attach fittings are the same angle on both sides.

Hank

I think wing assembly was kind of like paint jobs at the factory. It was how ever they felt that day, some high, some low, and some centered. All that mattered is they made each pair of wings the same.

[Guest]

Re: Adjusting Washout

But every plane I have seen the lugs were the same side to side! There can be a lot of variance in location, but the symmetry has to be there. Same for the wings. I talked to a guy who built a lot of wings and he said that getting perfectly straight spars wasn't that easy all the time. They would set up the spar and pull a string to find the high and low spot along the span. If the spar arched up some you wanted the smallest gap on top where the highest point on the spar was and the smallest gap on the bottom where the lowest part was. They split the difference so the smallest top and bottom gaps were about the same on the worst spots and all the ribs were placed to stay in line and nailed. Look at some of the old factory photos and you can see the strings across the ribs to get them straight. If you work with the small gaps available on the ribs and one wing spar is way out one way and the other way out the other, you can still trim it out when the spar to fuselage attach fittings are put on by shifting the bolt holes a little. If the fuselage attach fittings are out it can have a lot more impact, and I am afraid that is what we are looking at. One of the aft spar attach fittings on the fuselage looks like it is low. Worst case the vertical tube may have to be cut and the top longeron jacked up until the attach fittings are the same angle on both sides.

Hank

Is the fitting low on the spar or is the rib high?

The ribs have a lot of variability for a small change in nailing position and that is a scenario that can easily occur as evidenced by Walter's comments.

I don't claim to know the answer only suggesting easy things to check and consider based on the trailing edge pictures and rear strut comments & pictures.

I don't have a dog in this hunt.

The prop may be a good place to start I didn't think about the cruise speed issues. While on that subject though I would also look at when/if the a/c has been actually weighed. W & B may be amuck as well.

Dave