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 Post subject: Streamline tubing
PostPosted: October 14, 2008, 4:37 pm 
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After looking at JackMcCornack's kineticvehicles control arms it seems to me that construction of lower control arms with Streamlined tubing would not be all that hard. Basically you would build it just like Jack has done, even replicating the joint of the rear control arm, front control arm joint. I am not sure how much would be gained in terms of areodynamics by doing this but it seams that it would look "slimmer". Thoughts?

http://www.aircraftspruce.com/catalog/m ... amline.php

milo


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PostPosted: October 14, 2008, 5:28 pm 
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I like the looks of that, but does it have a thick enough wall? I'm no mechanical engineer and haven't researched this yet, but it seems a bit thin...

This was a good find, I'm looking forward to hearing other thoughts on the suitability.

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PostPosted: October 14, 2008, 5:29 pm 
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I believe its all in the cost. That tubing costs 20x as much as regular rectangular steel.

Jack's design is a neat revelation. He discovered and explained how rectangular tubing is actually more efficient in an airstream then round tubing. The mathematical details are in another thread, but the essential point is that with it being rectangular, the air flows around the longer (even if they are square) tubes better then regular round tube.

It is a great idea, IMO, while still maintaining the essence of "locost". If that aerodynamic tubing wasn't an arm and a leg per foot, then one could certainly use it to great effect. Thing is...the stuff is ridiculously expensive.

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PostPosted: October 14, 2008, 5:40 pm 
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Found the thread

http://locostusa.com/forums/viewtopic.php?t=4421

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PostPosted: October 14, 2008, 5:52 pm 
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The streamline tubing is .049 which is about 17 gauge, Jacks are .065 which is almost 14 gauge so it is thinner. I am not sure of the significance of it's thinness.

Yes it is more expensive but in reality you are only buying 4' of the stuff so we are talking an extra $100. Sure it's not the "locost" spirit but neither is IRS or Wilwood anything.

As I understand it the aerodynamic gain in 1x2 rec is having a smooth long surface along the path of airflow. the fact that it has right angled edges is not part of it's gain, the fact that it has a longer cross section parallel to airflow is. It's just an assumption but my guess is that streamlined tubing built for planes is more... streamlined :D.

Don't get me wrong, I think the "gains" of using this stuff is limited at best, however (and this is no offence to Jack, I love those lower control arms, they take the spirit of form and function further than most things) I think they just look a little dumpy. I was debating the merits of chroming them to make them look smaller but then I stumbled upon this stuff which compared to chroming the arms is cheaper.


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PostPosted: October 14, 2008, 7:37 pm 
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Just idle curiosity, but for elaborately shaped suspension arms (e.g. a CF cover for a round steel tube), would it be worth making them wing-shaped rather than tear-drop, to provide downforce? Or is it an effect that would be swamped by easier-to-make improvements?


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PostPosted: October 15, 2008, 12:17 pm 
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Anything is possible.

If you notice from the other post, there was a brief discussion regarding covering tubes with foam, then shaping them. All these ideas are possible, and would be neat to see.

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PostPosted: October 15, 2008, 1:02 pm 
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Wouldn't 4130 be a challenge for most of us to use anyway? Back purge and heat treat?

-S.


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PostPosted: October 15, 2008, 1:12 pm 
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You don't need to backpurge or heat treat 4130. One of the main factors driving the development of 4130 back in the day was its ability to be used in the "as welded" state. With that said, if you can back purge or heat treat its not going to cause any harm.

Your only change will need to be to your filler material; instead of using ER70 wire you will want to switch to ER80. The ER70 fillers are all 70ksi minimum. 4130 is generally stronger than that so the weld will become the limiting factor in the strength of the part.

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PostPosted: October 15, 2008, 2:23 pm 
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This is what we do on F Atlantic lower wishbones. These are carbon fiber but could be made in fiberglass. We have Algie composites fab them. They are split at the rear so you can apply over the arm and just helicopter tape together.
Image
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PostPosted: October 15, 2008, 2:43 pm 
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00000:

Little wings are not efficient, so you don't want to try making downforce with
them. ( In general ).

Miles:

Looks like a clean suspension. I like the simple cover for the inner wheel face too. I see the cover on the wishbone tube, but it looks like the tubes are oval section too. Do you know what thickness and size the tubing is? Just looking for rough idea of what they consider acceptable in FA.

I am so used to looking at those long arms, that the short ones on sevens look kind of wrong now. I wonder if there is really any downside to making a locost a few inches wider and using cycle fenders on the rear...

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PostPosted: October 15, 2008, 9:51 pm 
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I'm just saying that that's damn pretty. I really like the look of slim flat girls, err... I mean tubing.

Milo

PS. I apologize for the juvenile comment above, in fact it's not even that true, but I couldn't resist. Sorry again.


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PostPosted: October 16, 2008, 4:06 pm 
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The suspension arms are oval crush tubing from Swift, Pat Prince makes the same arms in aero tubing. I dont know what the wall thickness is but we have a large box of bent arms and I could cut some and measure for you. We were saving them to remove the hard points. The pushrods have strain guage sensors attached for data. Prince would be the guy for fabricating (albeit unlocost).


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PostPosted: October 16, 2008, 4:46 pm 
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In the world of locost extremes, I still think we can do this super-cheap while still getting the aero we want.

Take round (or rectangle) tubing, and get some stiff foam, like swimming pool "noodles", and cut a shape that fits over the tube with the proper teardrop shape and size. Then, use R/C airplane covering material and wrap the foam, then use a heatgun to shrink and bond the cover to the foam. This should give your shape with very minimal extra cost.

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PostPosted: December 4, 2008, 8:19 pm 
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I do like the sound of the above post. Foam and skin them sounds great. Do ppl really think these lil arms will make much of a difference though? We're talking very miniscule would be a fun project though. I love the wheel cover on that Formula car.

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