Engine Mount Mis-alignment 1

[hilltopkid]

I'm working on a homebuilt aircraft. The engine we were shipped was pre-attached to it's mount. When we tried to install the 4130 mount to the 4130 cage structure of the airplane, we found the mount did not fit. In fact the left and right bottom holes were at least 1/2 inch too wide on the mount. To move the mount holes inward so we could insert the AN6 bolts, we had to use a racheting strap with much pressure.

The top left and right bolt holes in the mount were mis-alligned by even more, maybe an inch. But, because of the design of the mount, we could push those two bolt holes on the mount into alignment by hand.

Is this safe? Should we trust a mount which is under such stress from mis-alignment?

Can the mount be stress-relieved by removing all the paint and heating with a torch to a dull red and let cool? We have a friend who is a retired master welder who says he can help us.

Thanks.

 

[rb1957]

if you're pushing something by hand to make it align, i figure you're only applying <100 lbs force ... this is not great, not recommended but probably not fatally weakening the structure.

aligning something with a "racheting strap" sounds way more of a problem ! i'd rather see one of the holes filled with a freeze fit plug, drill an oversize hole, and bush it. possibly 1/2 the difference and rework both sides.

i'd stay well away from the torch.

 

[berkshire]

hilltopkid (Aeronautics)
You need to go back to the drawing and measure the dimensions of the holes of the framework of the fuselage,
and the holes on the engine mount without any stress on either part and see which one is incorrect. You are dealing with a triangulated structure and in order to move something, a length of one of those lower components needs to change.
Now that you have used a ratcheting strap on the structure, go back and look at the tubing in the weld joint areas, for paint flaking off and bulges in the tubing.

You say you can move the top mounts into position by hand.
are these individual tubes going from the top mounts to Dyna focal or lord mounts on the engine?
If that is the case you may need to change the angle on the mount plates. I would certainly get the maker of the engine mount involved in this and ship it back to him if necessary.
B.E.

 

[dik]

Swingpress?

Dik

 

[MikeHalloran]

Uh, ".... did not fit." is where you should have stopped installing the engine and broken out the good measuring tools, so you could figure out whose problem it was.

Now, you've made it your problem.

If you think forcing engine mounts into alignment is a good idea, or even an acceptable idea, just Google "AA191".

From my perspective, both the engine mount and the airframe are now scrap, and should be cut into little pieces, unrecognizable as part of an airplane, before going to the junkyard.



Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

hilltopkid,

You paid for a properly designed and manufactured engine mount and airframe, so that's what you should expect. The engine mount should mate to the airframe without forcing it into shape.

Any stress you impart into the mount structure by forcing it into position will be additional stress the structure is not designed to take.

All welded tube structures, like your engine mount, have residual stresses present due to the uneven expansion/contraction heating cycles created during the welding process. These stresses are normally relieved after welding (in an alloy steel part) through a thermal stress relief process. Since your life may depend on the structural integrity of that welded part, I would not recommend performing this stress relief yourself with a torch.

What I would recommend is that you carefully measure the mount, and carefully measure the airframe, then contact the manufacturers of both items to establish which part is non-compliant.

Good luck.
Terry

 

[berkshire]

tbuelna (Aerospace)
If it is a home built, Hilltopkid may well be the manufacturer of the airframe.
If I understand his post correctly he only tweaked the engine mount not the fuselage.
So if the positions of the mounting holes on the fuselage are correct, then the problem lies with the engine mount.
If the holes on the fuselage are not correct to the drawing,then he needs a custom manufactured mount, and should give the engine mount manufacturer a template taken from the fuselage mounting holes.
Any way you slice it he has trouble.
B.E.

 

[FieldTeam]

Hilltopkid did not say if the engine will align to the mount now.
It sounds like he got the correct engine with a mount made for a different aircraft.
I hope he is not thinking of returning the mount and not letting the manufacturer know of the stress the mount was put through. "hey, I got the wrong mount, here are the measurements I need.....cool, I'll send you the correct mount and you send me that one back...." then some sucker down the line gets the gem!

AA191 was caused by a management decision to streamline their procedures and a maintenance department that did not have the stones to put a halt to it. the pylon attach fittings were damaged due to damage from maintenance procedure....it would have all fit together if they were doing it correctly.

 

[thruthefence]

Years ago, while working for as a General Aviation A & P mechanic, I was called upon to replace the arm that articulates the cabin plug type door on an American B727. (My company was the 'contract maintenance' for the airport). The proper procedure was to disassemble the door frame to the point where the arm could engage the cam inside the frame. I had tech support on the phone, and they advised they had "developed" a procedure where the arm could be inserted, and then twisted into position with a large pair of 'channel lock' pliers,( mole grips to you Brits) and the trip can launch, with it's 100 souls, "on time". In 'eyeballing' the dimensions of the cam slot & arm,and doing a 'dry fit' with no tools,I decided I was having no part of this project. I got the "tech guys" back on the phone, and was subjected to a line of abuse I hadn't heard since boot camp. The station manager then got on the phone, and then HE subjected me to threats & abuse, though in a little more genteel way. I again got on the phone, and was told, (and I'm paraphrasing) to "force that God-Damned arm into place & be done with it! Act like a man instead of some F***ing P***Y, so those those folks in the aircraft can get home!" I paused a minute, and replied, "yeah, kinda like you folks did with that pylon mount on that DC10?" Got real quite, and the prick on the other end of the line said "do what you gotta do", and hung up. The station manager got a crew over from Dallas to do the repair, never found out how it was accomplished.I was expecting a bunch of grief over this, but never heard a word. I did tell my supervisor, and he was on my side.

Forgive this long post, but the point is, as has been stated before in this thread, is that expedience has no place around aircraft.