Strut Materials

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Varmint
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Strut Materials

Post by Varmint »

I did a brief search on this, and to my surprise did not find a lot of info on it, though I'm sure it has been a well hashed topic, so apologize for the repeat this will be to some.

What material is used for the Lift Struts and Cabanes?

The plans show the lift struts to be streamlined 2812 tubing sized 2 3/8 x 7/8
and the cabanes to be 1667 streamlined tubing but I don't see any dimensions.
I assume most are using "plain old 4130" streamlined tubing. But in what sizes and wall thickness.

It's my understanding that the lift struts carry much more load in flight than the cabanes so expect the cabanes are smaller, but can't really verify this from the "per plans" material callouts.

Thanks
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Richard Roller
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Re: Strut Materials

Post by Richard Roller »

Regular old 4130 struts are used, as in 34KP
A lot of people are using the extruded aluminum struts from Carlsons, they work well and save some weight.

The struts in the plans are not available anymore.
Varmint
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Re: Strut Materials

Post by Varmint »

Are the cabanes made from the same material as the main lift struts or is a smaller material used?
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KenBickers
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Re: Strut Materials

Post by KenBickers »

I used streamlined 4130 steel for my cabane struts and Carlson's extruded aluminum struts for my diagonal struts. Were I to do it again, I'd use the extruded aluminum for both. The streamlined 4130 steel is quite expensive, but as it happened I already had some on hand. The aluminum is quite a bit lighter and cheaper too.

Cheers, Ken
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taildrags
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Re: Strut Materials

Post by taildrags »

Varmint; I guess your initial question still hasn't been answered... are the cabane struts the same size material as the wing lift struts? My answer, based on the forces that they see, is "no". But just going back to the 1932 Air Camper plans and looking at the relative sizes of those in the drawings, the cabanes are smaller. How much smaller? We don't know because the callouts for them (2812 for the main lift struts and 1667 streamline tube for the cabanes) are tubing nomenclature that is no longer used. I can tell you what the cabanes on my airplane are, but my guess is that mine aren't the same as anybody else's and since I didn't build my airplane, I don't know how they were selected. Maybe a starting point for you though?

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power
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Richard Roller
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Re: Strut Materials

Post by Richard Roller »

Ken Perkins Piet, N34KP, has the following sizes of lift/cabane struts.

All struts are SAE 4130 steel streamline tubes.


forward and aft lift struts: 2.023" x .857", .049 wall thickness, ERT* 1.5 & 1.0

cabane struts: 1.685" x .714", .049 wall thickness, ERT 1.25 & .75

cabane brace: 1.18" x .5", .035 wall thickness, ERT .875 & .4375



NOTE: ERT means equiv. round tube in tension (1st) and compression (2nd).

The above is from my notes on 34KP. I will add that the lift struts L'/p dimensions actually exceed the recommendations for column compression loads, even with jury struts. But they have worked well for 20 years now.
Varmint
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Re: Strut Materials

Post by Varmint »

Thank you fellas for the feedback.

Oscar, it is my recollection that somewhere an article I read about the fact that most of the loads are carried by the main lift struts and very little lift is actually carried through the cabanes was perhaps something you wrote, maybe in a newsletter or something. Is that correct? Perhaps not, its been a while......

Roger, I'm assuming the ERT diameters you gave implies the same wall thickness as the streamlined that was used? (.049 , .049, and .035)

Also, in regard to your statement:

The above is from my notes on 34KP. I will add that the lift struts L'/p dimensions actually exceed the recommendations for column compression loads, even with jury struts. But they have worked well for 20 years now.

What is L'/p (I'm not schooled in this subject)?

Also I'm unclear in that you said the "dimensions exceed recommendations.... even with jury struts"
Although I'd expect the phrase "exceed...... even without jury struts" or "do not meet.......... even with jury struts"

So I'm not sure if you are saying that the lift strut dimensions you cited on 34KP do or do not meet the "rated" compression loads and if that is with or without jury struts. Can you please clarify? I'm clear that in 20 years they have not failed.

Which brings me back to a day, perhaps 30 years ago, when my wife and I travelled to the Kansas City area to look at a Piet project being built by a man whose name I recall as Ken Perkins. A real nice guy and quite a craftsman. I believe he was also an A&P. I was then interested in building a PIet and somehow (don't remember how) I got connected with "Ken". It was all before the internet so he must have been a friend of a friend of a friend kind of referral. I was a young man then and "Ken" (as I recall his name) was not, so I suspect he has passed, perhaps long ago. Some 30 years and 4 airplane builds later my interest has again turned to the Piet - the original homebuilt, in many regards.
So I am wondering if by chance this could be the same plane we are talking about? What I remember most uniquely about this Piet was that he was building the one piece wing (somewhat rare) and that he cut from a thick plate of brass or bronze a "Ford" logo which he affixed to the Model A engine. He was very proud of the Ford plate he had carved and it looked really cool. He also made a couple of "custom instruments" for the front cockpit (which he may or may not have installed). One was basically an empty instrument case containing a pair of dice he had gotten (in Vegas as I recall) which would of course be "rolled" in aero or negative G situations and the other "instrument" was an instrument case which which was internally lined with a cutout from a sectional map and had a small plastic chicken inside that would point the proper direction to go. Sort of a predecessor to the GPS - LOL - and he called it a "Navi-Bird" (Odd the things you remember).

Does this sound like the same plane? Surely there is only one "Navi-bird" out there..........

Thanks
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taildrags
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Re: Strut Materials

Post by taildrags »

Varmint;

You're confusing my responses with those of Richard Roller. Notice the registration numbers of his airplane, N34KP. See those last two letters? Richard now owns and flies the Piet that belonged to Ken Perkins! That is a very interesting "circling around to where it started"!

About the value that Richard referred to, L'/p, that is related to the Euler Buckling Theory for columns loaded in compression. One of the values that is used to evaluate when and if a column might buckle under load is called the slenderness ratio. Picture a wooden yardstick. Stand it on end on a hard surface and begin to press down on it with your hand. At some point, it will buckle, or bow outward, and be unable to sustain any more load. Our wing lift struts are, in effect, slender columns which are loaded in compression under negative G loading such as we might encounter in severe up or down-drafts, or even a very hard landing. We can prevent or delay the buckling of slender columns by bracing them to hold them straight, and that's one of the things that the jury struts do... brace the struts to hold them straight under compressive loading to keep them from wanting to buckle.

-Oscar
Varmint
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Re: Strut Materials

Post by Varmint »

Oscar thanks for the clarification on L'/p and Euler.

Perhaps I should have sent two different replies - I'm not an experience "forum user".

I actually addressed the first paragraph to Oscar and the second to Roger. Sorry for the confusion. :(
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Richard Roller
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Re: Strut Materials

Post by Richard Roller »

Varmint.
A case of needless information, I apologize.
As Oscar noted the "L'/p" reference is to slenderness ratios and how that works with the column loads. And the "equivalent round tube" is a reference to the round tube (same wall thickness) that would react the same as the streamlined tube. All my values come from the " "Analysis and Design of Airplane Structures" by E. F. Bruhn. Printed July, 1943". A copy I acquired when I was needing to learn to analyze the tube fuselage I wanted to use on my Piet project. It came in handy for the wing also.
The tubes that Ken used on his lift struts falls just outside of the recommended slenderness ratio, but have worked well for these 20 years. I'm sure Oscar is much better qualified to explain these things to you. He has helped me several times.
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Richard Roller
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Re: Strut Materials

Post by Richard Roller »

You referenced Ken Perkins. I have the a/c (N34KP) that he was building when you visited, as Oscar noted. I meet Ken about 1994, when we both worked for TWA at the Kansas City overhaul base. I had worked on small a/c before being at the base and Ken needed someone who could get all the way into the tail of his Cessna 150 to buck rivets on the rear bulkhead. We became good friends and I was privileged to be able to help him with his Piet. The man was an artist with any material and an excellent machinist. I learned many things from Ken. I do miss him.
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