Engine mount tube thickness?

[FoxbuilderWill]

I have been looking for info on the early model kitfox motor mounts and i know the tube diameter is 1/2" but don't know what the thickness is? Anybody have that info?

[HighWing]

Not sure on the original mount, but I made my own mount on my latest Model IV and used .049" from Aircraft Spruce.

[fathom]

Where did you find plans to fabricate your mount? Or did you reverse engineer based on an existing one?

[FoxbuilderWill]

Not sure on the original mount, but I made my own mount on my latest Model IV and used .049" from Aircraft Spruce.

Thanks for the reply. I made an assumption perhaps incorrect that since the spools are 3/8" and most of the tubing in the mount is half inch that a wall thickness of .065 would allow the tubes to be welded to the spools without any gaps.

By spools i mean the little 1" long 3/8" outer diameter .26 inner diameter tubes that the bolts go through to bolt the mount to the airframe.

[HighWing]

First, My mount was a custom mount to correct some W/B issues because of the gap closures and fairings on the elevator and rudder. I had about 7 lbs back there that at eleven feet seriously compromised my baggage weight allowance. I wanted the engine a couple of inches forward of where it normally is. I understand the thinking behind the thickness - welding issue. I used TIG and it helps a lot getting penetration thin to thick.

The fabrication was pretty much fit and weld. Using an engine stand, I positioned the engine where I wanted it relative to the fuselage and essentially closed the gap. For posoitioning, I used a high lift transmission jack from Harbor Freight with some modifications for adjusting alignment to support the engine and wood supports to position the fuselage. I made my own doughnuts for dampening and used a ring mount on the engine. With the extra spacing it worked, but with coolant hoses and other items needed behind the engine, a ring mount would be very difficult if not impossible, using the standard Model IV dimensions.

Searching through my build photo collection, I can't find anything that might help design wise. I did find one picture that I used to get a close alignment with regard to vertical placement and longitudinal alignment. That picture is attached. Center Line copy.jpg

[FoxbuilderWill]

How did you make your own donuts? What material etc?

Also have some questions about annealed vs normalized 4130. From what i can see ACS 4130 steel plate is annealed, and i haven't looked into it for sure but I think the round tubing might be normalized. I'm not going to weld the mount personally i'll have someone else do that but if some of it is normalized and some is annealed what then? Even if it is all normalized do you have to heat treat it after?

[jrevens]

Hi Will... FWIW, normalized 4130 is considerably stronger than the annealed condition. Many welded steel aircraft structural components are fabricated from 4130 N, but it is not normally re-heat treated after welding. It is usually good practice to stress-relieve a structure that has been arc welded (TIG or MIG) after welding, usually with an oxy-acetylene flame. This seems to be ignored by some fabricators. The need to do that varies with the design of the structure.

[HighWing]

How did you make your own donuts? What material etc?

I used urethane rubber - the type used for making rubber molds. It comes as a two part liquid that cures after mixing. I had to make molds for getting the shape I needed.
I dont remember the shore hardness I used.

[FoxbuilderWill]

Ok thanks for the replies.

New question, similar topic. I have the motor off my bird and have a nice flat leveled table that I set the motor mount on and put a framing square with the short side flat on the table with the long side sticking up see pic so that i could measure the thrust line angle. According to my slightly rough measurements the thrust line is angled up .5 degrees. Does this sound right to you guys? Mount came off a model 1 kitfox that as far as i know was factory standard for all rotax equipped aircraft. There was a 532 on this mount when i bought the plane. 20190313_184709.jpg

[HighWing]

When I built my mount, I did some research that strongly suggested that - at least with - the Model IV I was working on was built with zero offset horizontally and vertically. That is what I went with. The airplane flies very similarly to my first IV. The picture I posted was essentially taken to establish the thrust line and where it should be located in its vertical relationship to the airframe.