| Yes: Thanks to all of you responding on the mail, and contributing to my questions. The mounting that has to be build is , is for a tri-gear setup and apologies for not mentioned it. Just want to know more or less the OD for the majority of the design but understood that this is more complex and design is more critical for my Vision (composite) fuselage. We will design a mount based on the info received from all of you. Luckily i took over 3 years ago a unfinished project of a Rans airframe and cut it into pieces. Believe i have almost enough material for the majority of the mount.Sorting out the wall thickness of the same OD’s sizes.There is quite a difference in weight, between the different wall thickness of the same OD’s but “overkill” is better than marginal. Will come back to you on the design on the group. Thanks again and happy building for all of you.
Sent from my iPhone Le Roux Breytenbach On 23 Jul 2020, at 16:12, Ernest Christley echristley@att.net <flyrotary@lancaironline.net> wrote:
I was reading just last night in Sport Aviation that as a member of the EAA, you can get a copy of Solidworks that will do stress analysis. Has anyone done this with a motor mount?
On Thursday, July 23, 2020, 9:32:33 AM EDT, Charlie England ceengland7@gmail.com <flyrotary@lancaironline.net> wrote:
Hi All members:
The 4130 chromemoly seamless pipe for the engine mount.
What is the appropriate size for building a engine frame, as the included drawing of Paul L. ( copyright P.L )
The outside diameter and wall thickness ?
7/8 Inch OD x 0,069 “ Wall thickness ?
or 0.120 W
1 inch x OD ?
Cant find any specifications for such a design.
Sent from my iPhone
Le Roux Breytenbach --
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For perspective, the RVs with up to an IO360 use 3/4" x 0.049" tubing. But as Bobby & Andrew pointed out, crippling is the most critical issue, and all of the RV's tubes that are loaded in compression are much shorter than the bottom-most tube in that pic. I'd be most concerned about that tube; the pair that are arrowed wouldn't concern me that much.
Those aren't the only issues; you need to look at the load paths within welded joints, also. The strongest welds are the ones that are stressed along their length. A tension load perpendicular to a weld line is kinda 'worst case'. You obviously want to avoid loading tubes in bending, but there are situations where it *might* be acceptable, or even better. Ex: there are some 'bed mounts' (what that drawing effectively shows) for some Continental 6cyl engines that use a much larger horizontal member (left arrow in the pic), and attach the compression member (bottom most tube in the pic) near the mid point of the horizontal member. This loads the horizontal in bending (requiring upsizing), but shortens the bottom compression member a lot, reducing crippling loads on it. 'Everything is a compromise.' ;-) Be sure that your airframe's 'stock' motor mount doesn't include a horizontal member between the two upper firewall attach points. RVs don't need the tube, but some composite or wood designs might not have the compression strength across the top of the fuselage that's needed to resist those two points trying to come together under positive G loading.
Something I *wish* I could have done with my mount is to incorporate a feature found on some radial engine mounts. They often have the 4 firewall attach points being a U shaped bracket bolted through the bottom of the U, to the firewall, and the motor mount termination a vertical tube at each corner. By pulling the bolts on the top & bottom of one side, the entire mount & engine can be swung to one side to service stuff on the
firewall or the back side of the engine. Trickier to do with a mount like a taildragger RV, which has the gear leg sockets incorporated in the mount.
I was fortunate enough to have two different engineers, both with structural experience, critiquing my design attempts, and one of them is also an excellent welder.... :-) If you can find an engineer or structures guy to look over your shoulder, it would be a good thing.
Charlie
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