Why round tubes for landing gear?

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Dan Thomas

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Cessna used the flat-leaf spring gear for the mains on all their singles (even the 210) up until about 1970 or so. The 150 and 172 went to the round tapered machined tube. The diameter of the tube was maybe double the thickness of the flat leaf, so they were able to get rid of so much metal that the tube ended up at half or less of the leaf's weight. The 182 went to the tube later. The 180 and 185 and 206 never did. The 210 and 182RG also went to the tube.

Some stuff showed up. The round tube was retained in the inboard fuselage gear casting by a single bolt, 7/16" IIRC. Braking forces would try to rotate the tube, and the bolt would wear. A few actually failed, sheared, folding the gear and messing up the airplane. I started checking ours every 2000 hours or so. Jacked the airplane and pulled the bolts to check them. Expensive NAS bolts.

An imbalanced main wheel would wobble the leg back and forth while landing or taking off or taxiing. The leaf didn't do that. Not unsafe, just annoying. Doesn't do that bolt any good.

Cessna make light aluminum fairings from 2024 for the tube gear. They shaped them into an airfoil, closed at the trailing edges with screws, and held them in position with a bracket at the bottom end and the fairing at the top, and chafe tape on the leg to prevent chafing. Unfortunately, the gear leg flexes along its length and curves, and that thin aluminum tube resists flexing, being a tube, and it cracks up.

Like the flat gear, an entry step was clamped to the gear leg. Water and pollutants got under that clamp and serious corrosion pitting happened, and some gear legs broke. The flat legs are really hard to come by now. Cessna hasn't made them in years except for the current 206, which never used the tube gear.
 

Pops

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I had the same wear on the bolts on the C-150 round gear legs on my F-12. Had to replace the bolts on each leg and the bracket on the main spar had the bolt holes wore and I turned steel bushing and welded on each side of the bracket for more surface area at about the first 500 hrs. No wear after that.

I have a coupe sets of flat main gear legs. I think one is from a 1958 C-172 and the other might be from a C-182. At one time I bought the remaining Cessna 100 series parts from a salvage yard when it closed down. Couple semi-trailer loads. Also still have some doors, fin, elevator, etc.
 

Dan Thomas

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I have a coupe sets of flat main gear legs. I think one is from a 1958 C-172 and the other might be from a C-182. At one time I bought the remaining Cessna 100 series parts from a salvage yard when it closed down. Couple semi-trailer loads. Also still have some doors, fin, elevator, etc.
There are people looking for those legs. Might fund your next airplane by selling them.
 

Pops

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That seems to defeat the point; it's heavier, way more expensive and you don't get any benefit of the streamlining if it's fabric covered.
Bob Barrows streamlines the rear of the Bearhawk LG "Vees . The front legs is a round tube and the rear round tube is streamlined with aluminum of about 4" wide around a 4130 round rods for a frame work. The LG "V" is fabric covered.
 

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N804RV

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Hi,
I'm sure there is a perfectly obvious reason all landing gear are constructed from round tubing, but I don't know what it is. Anyone care to enlighten me? Likewise for wing struts.

Duncan
"The landing gear of the Tailwind represents the one and only area in which Steve broke entirely new ground in its design. Steve can lay claim to two different major patents in landing gear design: The flat gear, the called “Cessna” spring gear and the other being the tapered rod "Wittman" gear as used on the Tailwind (and the Buttercup before it). Although not actually as simple to make in a garage as it appears, the gear is wildly effective and downright clever in the way its twisting and spring action actually aid the gear geometry and help keep an airplane straight on the ground." -Budd Davison ( Wittman Tailwind Pilot Report )

Also, Making a Business out of a Metal Rod -Ken Scott (Kitplanes Nov, 2017)
 
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