Strut angles

[mike lutz]

Re: Strut angles

I bought a set of WagAero struts for my 1940 bc T-craft and they fit like a glove. No problem with angle. What I like about theirs is that the rear struts are the same size as the original rear 40 struts. Heavier tube wall. The front was ever so slightly larger than the original Taylorcraft,s and heavier tube wall also. The fronts appear to be the same size as the Super Cub uses. Welds looked good and workmanship was good. I also have sent two sets of struts in to them for inspection and sealing, and was very satisfied with the service and workmanship. My experience with WagAero has been good. Been a customer of theirs since the 70,s. Just my two cents worth.

[astjp2]

Re: Strut angles

I am still amazed at how much this strut angle issue comes up still, it was only one manufacturer that seemed to have different angles, there is not really a way to get a lot of variation unless the airplane is way out of wack. They were built with a +- 1/8" for a lot of dimensions and about 3 degrees.... if your lower strut attach point is fairly close and the leading edges of the wings are even and straight from each other....there is not enough difference in angle to really affect anything...

[PA1195]

Re: Strut angles

The large angle offset may be found on F-19's and onward. Unless someone has a pre-F-19 with one?

Gary

[astjp2]

Re: Strut angles

The fuselages and wings interchange...so how do the angles change that much?

[PA1195]

Re: Strut angles

The fuselages and wings interchange...so how do the angles change that much?

My suggestion for the F-19 offset came from obs in an earlier thread of several local aircraft, some of which I took pics of the upper strut and wing fitting. I drove around and found the only one with a large strut offset was an F-19. There were other F-19's in the sample. Limited database I know but maybe it'll provoke some further investigation.

Someone (maybe from the Anchorage/Kenai area of Alaska) provided Airframes with a strut with a large offset that they made their example from. Airframes told me it was like 10% or less of what they had sold that needed that change from stock angle. The 10% wasn't backed up with total numbers.

I think it was Dave the mentioned the Feris' may have had a jig that wasn't right somehow (?). Not sure if they had more than one jig otherwise how'd they know if it was wrong?

So to answer your question Tim....maybe some fuselages and wings won't interchange with the factory stock strut angle. Something in a minor percentage is different.

Gary

Standard strut on left; larger offset on right; both F-19's:

[Guest]

Re: Strut angles

Its about 115" along the spar from the spar butt to the attach point for the lift strut.

The lower lift strut fitting is going to be about (14/2)" aft of the main spar, I think I over estimated before.

So the anticipated angle between the lift strut axis and the main spar axis will be on the order of arcTan((14/2)/115).

That works out to about 3.5 degrees.

But that is estimate of only the angle between the axis-es.

There is another angle that may need to be included and that is related to how far off axis the lift strut end fittings are. The worst that can be the (aprox.) is arcTan of the strut width divided the 115" dimension from above.

Its more likely that it is not that much but may 1/5 of the strut width divided by 115. That comes to about arcTan[(3.37/5)/115] or .3 degree. It could be a plus or a minus.

I did not estimate from the attached picture I did it with parts and ruler but I did use the picture to guess where the main spar "fall" along the line between the landing gear attach points. I guessed half way, i.e. I divided 14 by 2. The landing gear attach points are about 14" apart.

Initially I made a mistake on this an forgot to divide a number by 2! Eek, I just corrected it.

Looking at my errors and estimates it seems to me that it is more likely that I overestimated the angle between the axis than underestimated. Real measurements on the plane will be better.

To make 4 degrees the lower lift attach needs to be 8" aft of the spar, to make 2 degrees it needs to be 4" aft of the spar.

I went to the airfield a few days ago and measured. I have to make come corrections to the data above. Text in red needs to be corrected.

I measured parallel to the horizontal stabilizer .

The lower lift fitting is 12-7/8" + 5/8" aft of the leading edge or 13-1/2" aft of the leading edge.

I recall that the spar is 9" aft of the leading edge making the lower lift fitting only 4-1/2" aft of the spar. I will double check the 9" value later today.

So now the anticipated angle between the lift strut axis and the main spar axis will be on the order of arcTan((4.5)/115) or 2.25 degrees.

Checking that 9" number now.

p.s. 9" from leading edge to spar is listed in post #3 of this thread. However my calculations may be off by half the thickness of the spar because that was ignored. If you consider that it makes the angle about +/- .25 degrees. +/- because I am not sure how the 9" dimension was measured. Will look into it later.