Jury strut adjustment

[Frank DeBartolo]

There are adjustments on the jury struts just underneath the wing. How is the adjustment made and what is the reason to adjust the jury struts.

Thanks,

Frank D

[Forrest Barber]

Re: Jury strut adjustment

They are there to allow the mid point of the struts to move up and down to align the strut perfectly straight. I level the aircraft and use a tight string on the front of the strut to assure it is straight.
Remove the through bolt at the adjuster and loosen jam nut ( be careful if it has not been done in a while) I make sure the jury struts are perfectly vertical when done. ONCE in a while you have to sacrifice this vertical part if you run out of adjustment. Mayve screw the adjuster clear out and clean all if you ahve to run them in furthur.
Jury struts are to keep the struts straight under load. Very important during outside manuvers

[pftcraft]

Re: Jury strut adjustment

Ahh sooo....I was wondering about the vertical part. We are adjusted all the way in and the strut is "almost" straight. So I guess we'll have to live with the jury struts not being completly vertical...

[flyguy]

Re: Jury strut adjustment

Thanks Forrest, good to know how to do it correctly.
Darryl

[Robert Lees]

Re: Jury strut adjustment

Jury struts are to keep the struts straight under load. Very important during outside manuvers

To be more precise, the main failure mode of strut-braced monoplanes is whereby the struts are subject to buckling (compression). Reducing the effective length of struts, by putting in an intermediate brace (jury strut) reduces the buckling load to 1/4 of an unbraced strut.

That is why our lift struts are so beefy, compared with the tensile loads they are ever likely to see in service.

It is arguable that over 75% of the CSA of struts is to protect against failure in buckling, rather than under tension. Look at a Pitts...all the flying wires are REAL small in CSA. But there is of course no compression on them.

Which is partly why the strut AD is misplaced...any corrosion in the bottom end of our beefy struts is less relevant to the main failure mode (buckling failure), the closer it is to the bottom end. Think of trying to compress the bottom 12" of the streamline wire of a Pitts, difficult, isn't it? But there we are, history is now history.

The clip-wing boys are more au fait with this phenomenon, since they have this paranoia of extra drag from jury struts on shorter struts. Take a look at a clip-wing...most of them without jury struts have HUGE lift struts to compensate for the reduction in the buckling strength of the unsupported lift struts.

Put a small set of jury struts in, and Bob's your uncle.

[Hank Jarrett]

Re: Jury strut adjustment

I tried to get that point across a long time ago but couldn't get an audience. Tried to demonstrate through analysis you could corrode a hole through a strut big enough for your finger and the strut wouldn't fail in normal operation. Never could get the FAA to understand the pile of corroded struts THAT HAD NOT FAILED were proof of the SAFETY of the struts, not the hazard they represented.
Oh well, that's why I went silent in this mess. I'll just wait for the mess to settle out then buy my struts.
Hank

[Forrest Barber]

Re: Jury strut adjustment

I too told of flying a Cub in here a long time ago and was able to crush the rear of the struts with my thumbs and the rear tubes on the elevators too; but she flew nice .... I watched the destruct tests at the Feris factory and know when the failures occur. Front compression tube in fuselage, buckling, rear tube too, strut ends pulling out ; but she all stayed together at 7.5 g's positive and 4.5 negative....