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Tube Steel Landing Gear Gauge

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Falcon_H

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Oct 21, 2019
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Hello,


I'm working on a replica of an SE5a and although the fuselage is constructed using wood, I'm considering making the landing gear using steel, so I thought this discussion area would be the best place for this thread. The most common landing gear used on the SE5a was made of White Ash, but many early production planes used steel. The reasons why I am considering using steel is that it would be a bit difficult and expensive to find Ash of the size and quality necessary. I am also almost certain that the steel landing gear would be lighter.

The empty weight of the plane will be about 1450 lbs. and the mgtow is about 1980 lbs.. The plans that I have do not include any information on the early steel landing gear, so my question is what gauge of tubing I should use for a plane of that size. The outside diameter diameter of the tubing will be 1.25 inches.

Thank you for your help!

-Falcon H
 

TFF

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That’s pretty small diameter but I guess it’s about right. It’s going to be thick. 1.25 is about the same as my Starduster at almost half the gross. Just a guess but .120 will be thin. It’s a great airplane. What is going to power it?
 

Falcon_H

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Oct 21, 2019
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Yeah, I'm using the drawings from Replicraft. They can be a little hard to decipher at times, but have a lot of great information.
 

TFF

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The SE5 is a complicated plane. I built the old Top Flight RC one. Much more than the Camel. I have seen the Jack Keabey one and its beautiful.
 

Chilton

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Jersey, channel islands
I expect Billski will be along soon and say this better, but the only way to size this is to run the math for it.

Pazmany Landing Gear for Light Aircraft, or if you feel brave dig in to FAR 23, otherwise you are guessing and that has no place in any part of an aircraft.

None of the maths is dificult, even the FAR gives you half of it, Evans is another good resource for the rest of what youwill need.

Dont build a beautiful aircraft and then break it because of TLAR on the gear.
 

wsimpso1

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I saw this thread earlier, and kept hoping we would get some details on the type of structure of the gear and energy absorption method.

The originals had a simple wooden V on each side attached in two places to lower longerons and an axle crossing from one side to the other. The axle appears to slide vertically within a vertical slot in the bottom of the V's. Bungee shock absorption was common, and may be what was applied.

This system would not likely pass muster on modern energy absorption requirements. The designer has to decide how authentic looking they want the gear to be and then design accordingly. I would think that if one were to keep the looks of the original, streamline tubing for V's would be used or perhaps fab'd up from flat stock and in left and right halves and then welded together. The axle could readily be streamline tube between the V's and welded to suitable axles.

The designer's task is kind of set by the strength of existing longerons and expected landing weight of the airplane. The V's do spread the peak load to two spots along the longerons, but peak load must be within the existing fuselage's strength. Some quality time with Pazmany's Landing Gear Design for Light Aircraft is in the designer's future. Review of how to perform the energy absorption requirements based upon sink rate will be needed. I expect that the design will see a bunch of iteration and adjustments to requirements before a design can be selected. The big issue is that the gear will have to soak up the vertical kinetic energy of the airplane sink rate to the runway plus the potential energy of whatever stroke the bungees allow.

All landing gear design is a balancing act - the gear must absorb enough energy that the system or the attaching structure will survive the landings thrown at, but it will be heavy and perhaps draggy if designed to absorb too much energy. In certified birds, the sink rate is set based upon wing loading, and that landing must result in between 2.5 and 3.5 g's. Any attempt at making an authentic looking gear with bungees might have a very limited stroke, requiring higher peak g's (if the longerons will stand it) and high preload. One of the scary parts is that if you design to too small a sink rate at contact, and the pilot drops it on at higher sink rate than that, the system will bottom with impact on touch down, overloading and damaging the weakest part of the system, which might be the V's, the longerons, the axle, the wheels, the tires... On the other side, if you over specify, you may end up with a robust design that does not look authentic.

Good luck with the design. I hope that you guess well on how much energy to absorb on landing. Welcome to The Monkey House...

Billski
 

TFF

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This is WW1. The gear is essentially two Vs with an axel that spans the full track held on with bungees. First it needs to be history accurate. He is trying to substitute the earlier gear version which was steel instead of wood. His plans don’t have that one.

I think laminated wood would be fine. Most seem to do exposed wood when replicating when a lot were wrapped with covering to prevent splits. If it was wrapped, a lot could be hidden. Metal or wood.
 

Falcon_H

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Oct 21, 2019
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Thank you very much for the help, everyone! I had not heard about Pazmany's book before, so I'm excited to read it!
 
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