Sleeved tube vs single tube

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kirbylee

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For example, the plans call for the landing gear legs to be made of 1"x.058 aluminum tubing, with a 7/8" x.058 tube of equal length inside.
Why not simply use just one single tube with equal wall thickness ? Maybe a 1" x .125.
Without guessing, does anyone know the reason for two tubes instead of one?
 

TFF

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A tube has an inside and outside wall so there is actually two “skins” that the mechanical properties can work through. A solid bar only has one. A tube inside a tube has four. One tube only has two. There is going to be a gain in strength, whatever it is, using one inside the other. Maybe some flexibility advantages too.
 

pictsidhe

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Usually finding suitable tube. With sleeved tubes, you can alter the weight and strength of tube along its length easily by only sleeving the part that needs more strength than a single 058
 

Pops

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Diameter means a lot more than wall thickness in column strength. Adding an inside tube does little to increase the column strength, mostly just adding weight. Weight is the enemy. Work out the column strength on the Euler scale for the dia and wall thickness needed for the LG leg. Then the bearing strength of the aluminum tube and sleeve wall thickness needed and then the rivets needed to attach the tube and sleeve.
IF your landing gear is the Cub type, make sure the column strength of the shock strut is not under strength for side loads as in a ground loop with a tail dragger. Nothing worse than a collapsed shock strut with the wheel folding under the fuselage with a wing, stab and prop strike.
 

wsimpso1

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For example, the plans call for the landing gear legs to be made of 1"x.058 aluminum tubing, with a 7/8" x.058 tube of equal length inside.
Why not simply use just one single tube with equal wall thickness ? Maybe a 1" x .125.
Without guessing, does anyone know the reason for two tubes instead of one?
You got the guy that thinks guessing is to be avoided...

I ran the numbers, a 1 x 0.125 is about 6% stiffer in bending than a 1 x 0.058 plus a 7/8 x 0.058. So the thicker tube is a little stiffer and a little lower stress.

Is the landing gear leg a Wittman style leg (one piece spring leg) or is it part of a suspension system like a Cub? How it is loaded matters to the designer. If it is a Wittman leg and their drop test came in showing enough strength but they needed a few percent more travel, they could get it by going with the sleeved set up. Or maybe the 0.125 was not available when they built the prototype.

I am also the guy who says stick to the plans, so, stick to the plans. Law of unintended consequences usually comes in big time once you start changing things.

Billski
 

Pops

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You got the guy that thinks guessing is to be avoided...

I ran the numbers, a 1 x 0.125 is about 6% stiffer in bending than a 1 x 0.058 plus a 7/8 x 0.058. So the thicker tube is a little stiffer and a little lower stress.

Is the landing gear leg a Wittman style leg (one piece spring leg) or is it part of a suspension system like a Cub? How it is loaded matters to the designer. If it is a Wittman leg and their drop test came in showing enough strength but they needed a few percent more travel, they could get it by going with the sleeved set up. Or maybe the 0.125 was not available when they built the prototype.

I am also the guy who says stick to the plans, so, stick to the plans. Law of unintended consequences usually comes in big time once you start changing things.

Billski
The 6% is about right. Like you, I say stick to the plans. But the designer could have saved a little weight by going to a larger diameter tube with less wall thickness for the strength needed , but so many other things to consider for a very small weight saving so maybe he thought that this was a better way.
 

kirbylee

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You got the guy that thinks guessing is to be avoided...

I ran the numbers, a 1 x 0.125 is about 6% stiffer in bending than a 1 x 0.058 plus a 7/8 x 0.058. So the thicker tube is a little stiffer and a little lower stress.

Is the landing gear leg a Wittman style leg (one piece spring leg) or is it part of a suspension system like a Cub? How it is loaded matters to the designer. If it is a Wittman leg and their drop test came in showing enough strength but they needed a few percent more travel, they could get it by going with the sleeved set up. Or maybe the 0.125 was not available when they built the prototype.

I am also the guy who says stick to the plans, so, stick to the plans. Law of unintended consequences usually comes in big time once you start changing things.

Billski
The landing gear is somewhat like a minimax. Axle runs from wheel to wheel, the gear legs go straight up from the axle, mounts to the plan, and then the tube going from the axle aft and bolts to the plane.
The axle is a 1 1/8"x.058 wall, with a 1 x .058" wall slipped insid of it, and a 7/8 x .058 wall slipped inside it.
The gear legs are 1 x .058" wall with a 7/8 x .058 wall slipped inside of it.
No springs, no bungees, just solid.
As far as sticking to the plans, about the only thing I might change is are cosmetic things and very little else. But I feel sure there will be a little less than a perfect landing one day, and with no suspension at all, I'm thinking the impact could be damaging not only to the plane, but my spine. Sometimes it dont take much. Thanks for replying.
 

wsimpso1

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The landing gear is somewhat like a minimax. Axle runs from wheel to wheel, the gear legs go straight up from the axle, mounts to the plan, and then the tube going from the axle aft and bolts to the plane.
The axle is a 1 1/8"x.058 wall, with a 1 x .058" wall slipped insid of it, and a 7/8 x .058 wall slipped inside it.
The gear legs are 1 x .058" wall with a 7/8 x .058 wall slipped inside of it.
No springs, no bungees, just solid.
As far as sticking to the plans, about the only thing I might change is are cosmetic things and very little else. But I feel sure there will be a little less than a perfect landing one day, and with no suspension at all, I'm thinking the impact could be damaging not only to the plane, but my spine. Sometimes it dont take much. Thanks for replying.
Never have liked solid gear. The things protecting your spine in rough landing are:

Tires deflecting, wheels collapsing, gear legs bending or collapsing. If there is enough energy lost in these, you might damage the plane and still not get to injurious g's on you. Or maybe not... What does the operational history of the MiniMax look like? How close is the MinMax design to this one?
 

Rockiedog2

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The landing gear is somewhat like a minimax. Axle runs from wheel to wheel, the gear legs go straight up from the axle, mounts to the plan, and then the tube going from the axle aft and bolts to the plane.
The axle is a 1 1/8"x.058 wall, with a 1 x .058" wall slipped insid of it, and a 7/8 x .058 wall slipped inside it.
The gear legs are 1 x .058" wall with a 7/8 x .058 wall slipped inside of it.
No springs, no bungees, just solid.
As far as sticking to the plans, about the only thing I might change is are cosmetic things and very little else. But I feel sure there will be a little less than a perfect landing one day, and with no suspension at all, I'm thinking the impact could be damaging not only to the plane, but my spine. Sometimes it dont take much. Thanks for replying.

Wonder what the weight of equivalent strength 4130 would be as compared to all those al tubes inside one another. One of you engineer types can figger that in a couple minutes
 
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