Aluminum Plate Engineering/Forming Question

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wsimpso1

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I know Billski prefers steel, but I think you can get a composite leg to work satisfactorily.
Please do not put words in my mouth... Only steel will fit in the space I have in my build. I considered steel, aluminum, glass, and graphite, designing acceptable legs in all four materials. All were too bulky once you had hardpoints designed except for the steel.

I agree that graphite rod can be made to work as gear legs. You will have to get fancy around the anchors and for the axle mounts.

Billski
 

Victor Bravo

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OK, thanks again EVERYONE for participating.

I may have mis-spoken, and I certainly am brilliantly capable of that. What I was really trying to say was that my engineer friend pointed out something obvious that I had not paid attention to:

If a larger percentage of the gear "leg" section was nearly vertical, then on landing impact that near-vertical portion of the gear would not be loaded in classic flexure as much, because the applied load was putting a larger portion of the leg in compression, as opposed to bending.

So the "near-horizontal" portion of the gear arch (that is loaded in more classic bending), would be taking a lot more of the flexing, compared to a straighter section of gear leg.

The engineer in question is a classically trained aircraft stress engineer (British translation "stressman") that came up through the deHavilland aircraft company in the 1960's, with a very high level of training. If it was a simple calculation of a curved beam, he is more than capable. I agree with several posters here that he was probably saying it's far from ideal, and may not be worth the weight... as opposed to telling me it is not possible or too hard to figure out.

Billski thank you, I will take you up on your kind offer in a moment :)
 
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flyboy2160

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VB,
I regardless of how 'tall' the outboard 'near' vertical section is, you still have material spanning horizontally from the vertical load point to the inboard support that is taking bending. An excessive amount of 'near' tall will cost you in weight, but you haven't sketched a crazy looking thing that is dangling way down vertically. Just like the other arched gears, it will have just enough of a vertical outboard part to attach the axle. Then the load will be taken in bending.

Small radii bends generate stress concentrations that are greater than those in a generously curved design. There's no free lunch.

It's easier to make a couple of 'small' radius bends in a piece of metal than to get the bending tooling just right for a large arch, which I suspect is why the small radii metal designs aro so popular. There's also less material in them, so they're a good choice for metal.
 
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pictsidhe

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If you aren't going to mess with heat treatment, the biggest radius that will fit is the way to go. Warm bending will help, but then you have to bend warm.
How do you plan to bend this? I'd be tempted to make a roller bender from big chunks of steel, and borrow the 3200ftlb torque multiplier from work to crank it...
Did you know that Grove makes custom gear? ;)
 

Victor Bravo

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the biggest radius that will fit is the way to go.

How do you plan to bend this?
The "biggest radius" is precisely why I was asking for the minimum bend radius in already-tempered aluminum. I wanted to see if the minimum bend radius was larger or smaller than the actual height of the gear spring. If these two dimensions were equal, then I could make the gear to the same height without heat treating, at the cost of it being "arched" on each end rather than "straight sections".

In the greater Los Angeles area we have many shops with large powered plate rollers that can make a ring out of a strip of thick plate. Bending 7/8 thick high-temper aluminum a quarter of the way around in a circle is not something I'm going to do in my hangar with a Crescent wrench and a handful of bungees.
 

wktaylor

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pictsidhe... 'warm bending' is simply NOT an option... not enough change in strain.

An old fab process for forming fully HT 7075-T6 was 'hot forming'... Rapidly [in ~4-to-5 minutes], raise the local temperature on area of part to be bent up-to ~600F, form, then rapidly air-cool back below 200F. Due to very short duration of exposure, the temperature never permanently affected the HT/temper... but was only suitable for small parts, with lots of insulation due to thermal conductivity of aluminum trying to suck the heat away. Also the operators had to be VERY careful for personal safety.

Victor bravo... RE vertical section of gear-leg [close to axle]. Typical landing and taxi loads [upward, spin-up and braking-drag forces on the tire] relative to a protruding [offset] axel/tire create a 'vertical' and 'aft' shear-load COMBINED WITH vertical/flexural bending [upward] and torsion [bending/twisting aft]. A 'locked-brake' on hard-landing is considered a 'worst-case' design.

Have You seen the Vans RV14 landing gear drop-tests..?
 

flyboy2160

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pictsidhe... 'warm bending' is simply NOT an option... not enough change in strain....
Ok, Ok, I know this is being a Grammar Nazi ( :)Ha! We need a Smiley for Grammar Nazi!), but didn't you mean 'not enough change in the modulus.' That is, the relative stiffness to force. I've looked at hot forming my Ti nose leg, but in order to get a large change in the modulus, I need temps that require an inert atmosphere or post-forming removal of the contaminated outer layer.
 

BBerson

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The "biggest radius" is precisely why I was asking for the minimum bend radius in already-tempered aluminum. I wanted to see if the minimum bend radius was larger or smaller than the actual height of the gear spring. If these two dimensions were equal, then I could make the gear to the same height without heat treating, at the cost of it being "arched" on each end rather than "straight sections".

In the greater Los Angeles area we have many shops with large powered plate rollers that can make a ring out of a strip of thick plate. Bending 7/8 thick high-temper aluminum a quarter of the way around in a circle is not something I'm going to do in my hangar with a Crescent wrench and a handful of bungees.
I think Billski calculated the minimum radius for you in a previous post.
Are you sure 7/8" is needed? Seems thick, what is the gross weight?
 
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Winginitt

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While you are agonizing over the issue of a large bend radius , what is your actual plan on how to execute the bend. Its not really easy to execute two radaii and get them at the exact location you want them from each other.
Its often difficult to keep the bar from getting some twist in it. Also, getting two radaii that are exactly the same can be difficult. Basically to form two large radaii you will probably need to roll them and thats going to take a heavy duty plate roll. Trying to form them by bending them around something will most likely result in irregular bends and possible kinking. I have a 10' sheetmetal brake. I was going to bend some 3/32" steel that was 10 feet long to make a top for a workbench. Couldn't do it even with my wife helping. Ended up putting floor jacks under each handle and alternately jacking them up. The brake was capable, but I wasn't. All I'm trying to say is that its going to take a heck of a lot of ooomph to bend this bar, and you are going to have to control it so it doesn't twist or kink. My suggestion is to find a machine shop with a LARGE plate roll and see if they will roll the bends for you.
Its better to continuously apply pressure at the point of the bending than to apply it at the end points and try to wrap it around something.
I'm not trying to be a smart alec here, but honestly I don't think you are going to get good results or really save any money by trying this method of making a landing gear. Have you thought about purchasing some used landing gear and adapting it, or maybe something moly tubing and damping?
 

Rik-

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Roll forming will be easier than a brake press will be on the 7075. Of course a different grade of Aluminum will make the entire process easier as 7075 machines great but it doesn't like to bend, weld nor hold up to corrosion very well. 7075 is also heavier than 6061 for example.

You'll need to look for a metal fab shop, not a heating/AC shop but an actual metal fab shop that has a roller or press brake that is capable of doing the job and if it's a press brake, be prepared for a crack in the part. They can press brake a radius if you'd not prefer a sharp break. They can just bump it around to match the pitch gauge.
 

BBerson

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You could probably take a 7/8"X 1/2" 7075 bar and bend it around a form or in the air to see if it works. A cheater pipe will do it if you have something like an old big truck frame or a farm tractor or hangar beam to clamp the bar to. A vise will break. I think I formed a 1" X 1/2" 2024 to about a 24" radius or something.
 

Rik-

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Are you looking for strength, price or weight? Pick two.

But if your looking for a gear, it can be made in steel just like they are doing for the Kit Foxes and the Just Air Craft. It doesn't have to be aluminum. 7075 is good if you want a flat part machined, it really machines easy no clogging the end mill at all. But, it's not friendly to forming, welding and it's not light.

You can get some box tube steel and form it far more easily and be as strong to be honest.
 

rotax618

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The Savannah (same as 701) uses a 6061T6 gear leg, the leg can be cold bent using a simple hydraulic pipe bender, I think it is 3/4" but 7/8" makes a more durable UC. The original 701 plans called for 6061 T6, why would you go for 7075 unobtanium?
 

Victor Bravo

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The original 701 plans called for 6061 T6, why would you go for 7075 unobtanium?
Because the original 6061-T6 gears do not hold up nearly as well in service, and do not have the strength-to-weight as the 7075.

And because I'm not interested in walking out of some uninhabitable piece of desert in 110 degree heat, with the Mojave Green rattlesnakes nipping at my plump behind and Wile E. Coyote sharpening his Chef's knife... because I cracked or busted the gear while goofing off.
 
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