compression strut between strut fittings - hopefully my last dumb question

[citabrickr]

Ok, tried the search this time and didn't really come up with anything to help answer this. The "flangeless" compression strut that goes between the wing strut attach fittings on the F21 wing I am finishing up is approx 1/8" shorter than the two shortest "flanged" struts that were removed from the wing. Is there supposed to be a washer or some type of bushing that takes up this gap when installing the threaded rod to assemble? Don't understand why there would be a difference from the "flanged" strut right above it since the distance between the fittings is the same, possibly I have a missing part? Thanks in advance.

[Ryan]

Re: compression strut between strut fittings - hopefully my last dumb question

IS this the tube that you are referring to in this photo? If so, I believe that it is shorter, due to the thickness of the strut fitting itself , and the thickness of the stacking pads on the spars for the strut fitting. My wings are no longer open, so can't see it for measurement, but might be in a position this weekend to find an old spare and measure for you if no one else helps you out. I remeber that tube seemed to rotate somewhat freely around the rod, but was tight between the front and rear fittings where it was tightened down by the rod. There is a spacer that goes between the strut fittings and over the screwed in rod. My wings had a mixed bag of phenolic (probably original) and thin tubing. This is all on a BC12 D, which as I understand should be the same as the F-21, but could be minor differences.

[Forrest Barber]

Re: compression strut between strut fittings - hopefully my last dumb question

That tube with the threaded wire through it helps keep the struts together and is usually loaded in tension. It should fit snug , let me know the length of it and I will check against a drawing or another part.

[citabrickr]

Re: compression strut between strut fittings - hopefully my last dumb question

Yes, it's the one with the threaded wire. Hard to get a measurement now on it because I installed it ( a few times) yesterday but it's about 3/32" shorter than the normal short compression strut with the flanges on the same strut fitting and is loose between the fittings as much as an AN washer is not enough to take up the gap but two are too many. It did snug down with a very tight wire. I found a spacer that had a washer glued to it that goes inside the rear strut attach fitting webs, but found nothing for the front one in my box of parts, which is pretty bare at this point. I'm having a hard time getting the bays back to the 31" +/- 1/32" spec using the same shims that were in each bay before, have to make another 1/16" one for the one at the butt end, add a 1/32" one for another full length one and may have to take one out of another long bay. Don't know how close to spec they built them for real, but I know getting the butt end one right is a must-do. Wish I had the fuselage here to measure up. Thanks all.
P.S. - this wing from the factory had EXTREMELY tight drag / anti-drag wires, almost no deflection possible with 20+ lbs push and a very high note twang (7th fret harmonic on the low E string if you have a guitar handy...). They won't be going back on like that!

[Forrest Barber]

Re: compression strut between strut fittings - hopefully my last dumb question

trammeling is the only way and yes you need the EXACT measurement of the fuselage . I will try to check Tues.
I forgot , I sold the wings I was going to measure. what is the ser# of your ship ; here or Lock Haven?

[Robert Lees]

Re: compression strut between strut fittings - hopefully my last dumb question

Unless the F21 spar strut fittings are significantly different in design to those of the B model ships (which I doubt), the length of the flanged (oval-ended) compression strut that affixes between the spars at the strut fitting is no different to the length of the tube that forms the compresssion strut with the tension wire.

The thickness of the steel strut fittings does not vary, and because as the fittings come out of the lower wing surface they are parallel, the overall tube lengths must be the same.

I can only assume that there is a problem with the parts as originally fitted.

For Forrest's refence, the B model spar "flanged" (i.e. the one between the timber) compression strut is P/No B-A800.

Below is an image of the general asssembly. Note there appears to be a spacer between the two parts of the steel strut fittings.

[citabrickr]

Re: compression strut between strut fittings - hopefully my last dumb question

Unless the F21 spar strut fittings are significantly different in design to those of the B model ships (which I doubt), the length of the flanged (oval-ended) compression strut that affixes between the spars at the strut fitting is no different to the length of the tube that forms the compresssion strut with the tension wire..

Not on this one! This is a factory wing, first time uncovered.

I can only assume that there is a problem with the parts as originally fitted..

Yup, but that's the way I got it. I see a listing that there are potentially 3 different length compression struts? I have 2 different lengths, although they were marked with a paint stripe and there were three different colors, long ones were red, strut attach bay was medium blue...and I forget the butt end one.... Now that all the struts are in the strut attach fitting bay is 1/8" over spec spar center to center (31 1/8"), yes, I double checked the butt end strut and the strut attach bay ones, same length, although the straight tube with the threaded rod was, like I said, about 3/32-1/8" shorter. It's an 1980, F21, s/n #F1006.

[Robert Lees]

Re: compression strut between strut fittings - hopefully my last dumb question

Hmmmmm..

There must be some differences between your 1980 F21 and my 1946 BC12D in the wings that I am not aware of.

To throw a spanner in the works: Will the TC owner not provide you with the answer?

[Ragwing nut]

Re: compression strut between strut fittings - hopefully my last dumb question

should be no difference in that part between planes. spacer between fittings is to keep from crushing the spar and allow you to install strut end with the member tight. only major difference between bc12d and f21 is spars are taller, and spar reinforcements a little different to compensate for higher gross weight.