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Curt.Thompson(at)verizon.
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 Posted: Sun Jan 10, 2010 9:03 pm Post subject: Fork tube analysis and prospective stainless steel substitut |
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On my plans built CH701, I have been polishing a few of the parts like the landing gear and front fork. I was wondering if I could replace the front fork tube with stainless steel parts and get a similar look. I would need to make sure that the replacement had the same strength as the original. So, with the help of my son, we did a SolidWorks analysis of a 4130N tube, 2 inch diameter, 21 inches long with a 0.065” wall. The top is solidly anchored and a force is applied horizontally at the bottom. Here is a link of the simulation video that SolidWorks made:
http://www.youtube.com/watch?v=w8uamuysV_8
The video ends when the fork tube fails. It took a force of 540 lbs. As you can see, the tube bent a lot before it failed. If you make the fork tube stronger you are likely to move the loads elsewhere and it will break somewhere else.
One thing comes to mind here, if you bend the front axle and lock up the wheel you are going to see a lot more than 540lbs. There was a picture on this list over a year ago that showed a bent fork tube after what was claimed to be a normal landing. I don’t know how common this problem actually is.
We substituted the fork tube with T-316L stainless steel in the simulation. It took a wall thickness of 0.250” before we arrived at a similar result. Since that would make the fork tube about four times as heavy, I have decided to stay with the 4130N of the plans. I may go up one notch in thickness of 4130N though. I might also replace the front axle with a solid shaft. On the shaft I have now, I machined bushings and welded them in place.
Curt Thompson
Redmond, WA, USA
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bobkat
Joined: 07 Sep 2008
Posts: 143
Location: Bismarck, ND
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| Posted: Tue Jan 12, 2010 3:54 pm Post subject: Fork tube analysis and prospective stainless steel substitut |
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Yep, land it like a taildragger and use the nosewheel only for taxiing. The nosewheel is plenty strong.
[quote] ---
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lgold(at)quantum-associat
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| Posted: Mon Jan 18, 2010 9:21 pm Post subject: Fork tube analysis and prospective stainless steel substitut |
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Thank you for the analysis Curt. Looks like Chris Heintz picked the best way to go from a weight, strength, and cost standpoint.
FYI, when the front gear folded, (the one I posted a year ago) it did do some damage to the firewall, which also had to be replaced.
From: owner-zenith701801-list-server(at)matronics.com [mailto:owner-zenith701801-list-server(at)matronics.com] On Behalf Of Curt Thompson
Sent: Sunday, January 10, 2010 9:01 PM
To: zenith701801-list(at)matronics.com
Subject: Fork tube analysis and prospective stainless steel substitute
On my plans built CH701, I have been polishing a few of the parts like the landing gear and front fork. I was wondering if I could replace the front fork tube with stainless steel parts and get a similar look. I would need to make sure that the replacement had the same strength as the original. So, with the help of my son, we did a SolidWorks analysis of a 4130N tube, 2 inch diameter, 21 inches long with a 0.065” wall. The top is solidly anchored and a force is applied horizontally at the bottom. Here is a link of the simulation video that SolidWorks made:
http://www.youtube.com/watch?v=w8uamuysV_8
The video ends when the fork tube fails. It took a force of 540 lbs. As you can see, the tube bent a lot before it failed. If you make the fork tube stronger you are likely to move the loads elsewhere and it will break somewhere else.
One thing comes to mind here, if you bend the front axle and lock up the wheel you are going to see a lot more than 540lbs. There was a picture on this list over a year ago that showed a bent fork tube after what was claimed to be a normal landing. I don’t know how common this problem actually is.
We substituted the fork tube with T-316L stainless steel in the simulation. It took a wall thickness of 0.250” before we arrived at a similar result. Since that would make the fork tube about four times as heavy, I have decided to stay with the 4130N of the plans. I may go up one notch in thickness of 4130N though. I might also replace the front axle with a solid shaft. On the shaft I have now, I machined bushings and welded them in place.
Curt Thompson
Redmond, WA, USA
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