Aluminum Plate Engineering/Forming Question

Online metals has 7075 bar, I think they have 4 X 1" maybe, didn't see any 7/8".
$700 or more depending on length.
That Grove gear in post 29 appears to be about 12 feet long. A larger radius might need more than that 12 feet possibly. I wouldn't want to ruin it with too many botched bending tries.

 

7075 x 7/8 x 4 x 144 is $249 at

https://www.midweststeelsupply.com/store/cart.php

 

That looks like a good price, but it says "stock price $2600 and $249 each (might need to buy the whole sheet?)

 

Let me rephrase a bit. Would the stresses of regular use become concentrated in such a way as to make this configuration likely to fail horribly?

 

You could find out what it would cost to heat treat. You may find oven time an acceptable expense or Your friend may throw it in the oven with other items being heat treated for a friend rate provided you do all the work on it. It is common to anneal or purchase in annealed condition heat treatable materials to bend and/or form them and heat treat after working.

 

Ok, I have a BSME and an MSME with a lot of training and successful experience doing structures. Stress concentrations are normal business. This is straightforward stuff. What makes you think something way weird is going on in this simple system?

Billski

 

If you stress all of it to the same level, you will need a certain volume of material. make it longer by making it a funny shape, less cross section. Though wastage from tapering it will confuse the issue.

 

I think I would assemble the gear into a 1" x 4" I beam.
Using 1/4" x 4" caps that are easy to bend. And 1/2" bar for the web. With bolts or solid rivets about 1" apart.

 

I just wanted to know if doing it the way I had it in the picture would suck or not.

 

Suck? Jeez man, have some confidence.

Usually, most schemes can be made to work, it just becomes a matter of cost/weight/packaging/style. OK, on airplane parts, add in aero drag. There are successful flat spring landing gear legs with vertical attachments to the fuselage and then bent outboard then bent back to vertical where a standard landing gear axle is attached. So, your scheme can work - similar things have been done. It might turn out to be heavier or draggier or whatever, but it can be made to work. The devil is in the details - that is where we find one scheme is more expensive and/or heavier and/or does not fit and/or looks bad and/or is draggy. So you look at other options and keep doing it until you find one that is acceptable.

A couple things about airplane landing gear that folks forget - how do you attach it to the airplane? You want to select the system that makes for the best overall solution, not just the lightest detail someplace. Sometimes a less than optimal piece in one place makes for the optimal system.

Billski

 

I'd be tempted to use a different and solid core. Perhaps a plastic. An I beam will be lacking in torsional stiffness. It would be a whole lot easier to form a gear if made in laminations...

 

Yes, an I beam is lower in torsion, but has plenty. The center can be wider if needed. It could be full solid at the wheels.
A box beam has excellent torsion but twice as many rivets. Just depends what the designer wants. A box beam or I beam could be significant deeper and significantly lighter.

 

No. If you go online and actually add the cut size you want to your cart, just the much lower cut piece price is in the cart.

 

I've bought from them a few times. Great folks to deal with. Good prices and shipping. They pack stuff up really well too. That is much appeciated by me.

 

I'm pretty confident it would work well from just eyeballing it and picturing how the curve would flex, or I wouldn't be suggesting it. I just wanted a second opinion on it in case I missed something.

 

Thanks for the link, I tried that but the cart button wasn't working.
I think shipping 12 feet is still very expensive for most of us. I try to order below 8 feet for UPS ground.

 

There is a 90+% chance that whatever I use will be mounted using the standard Zenair gear mount. Billski is correct, one section being better, leaving other sections less than ideal.... is not worth a large modification. A bolt-in replacement that fits the existing fuselage is 10X more desirable to me.

 

Please explain why you would want to do that?

How so? Stiffnesses are all related. EI is bending stiffness and GJ is torsional stiffness. J = I1 + I2 where the 1 and 2 directions are perpendicular to each other. G is a function of E. They are interelated, and things that increase EI also tend to increase GJ.

Might be possible - How would you connect the lamination together and keep them together against the shear loads?

For spring gear legs, it is just way more straighforward to bend the legs out of stock, then saw to planview shape.

Billski

 

Compare the torsional stiffness of a box section and and an I section of equal bending properties.
Yes, shear resistance is going to be a big design consideration.

 

Significantly lighter I agree with. Depth will depend on your limit strain in the caps, which depends on the sprung curvature you want.