EM12 Extrusion Loads/Sizing

[TParker]

Does anyone have/know of any loads analysis done for the engine mount extrusions (EM12) and their attachment to the fuselage? Or are there any examples/pictures of this joint failing or being damaged due to overloading (like in a hard landing)?

I've seen others have increased the vertical web of the EM12s or substituted steel in anticipation of a heavier engine and I was curious if the extrusion was actually the limiting factor or if it was something else like the bolts that attach the EM12s to the rest of the structure, or failure or the composite structure itself. The plans state a max engine weight of 246 lbf and a max vibrating weight allowable of 286 lbf; I presume that number came from some analysis (available?).

I'm further curious as to how much the bolts contribute to this system as this implementation seems a bit strange to me; in that:

1. If the bolts are intended to carry tensile loads, using small OD (AN960-416L) washers against relatively soft spruce doesn't seem effective
2. If the bolts are intended to carry shear loads they're likely to split the spruce and the shear handling capability of the fiberglass is also likely low
3. This installation is significantly different from the wing attach, where an aluminum puck is used to transfer loads into the composite

Any insight here would be appreciated. TIA.

[Kent Ashton]

This beef-up (pic) is pretty common and seems to be adequate for bigger engines.  http://www.longezpush.com/chapter-1423-engine-mount/

Similar mounts here   http://www.aryjglantz.com/2017/05/center-section-spar-install.html

I have seen steel angles substituted for the aluminum or two 1/4" 2024 angles used.  Also mounts made from 1" X 1/8" wall steel tube.  A solid piece of steel is welded into the square tube and drilled for an engine mount bolt.  Those are probably overkill.

The only failures I can recall are overload-cracking of the plans aluminum angles where the 1/4"(?) mount bolts go through the angles.   The angles can be removed and replaced.

Edited March 12, 2020 by Kent Ashton

[TParker]

Thanks Kent. I've got some issues in this area (EM12 to fuselage) that need attention and I'm trying to figure out how I want to address them.

8 hours ago, Kent Ashton said:

...

The only failures I can recall are overload-cracking of the plans aluminum angles where the 1/4"(?) mount bolts go through the angles.   The angles can be removed and replaced.

Do you mean the bolts that attach the engine mount to the angle? Or the bolts that attach the angle to the fuselage?

I saw that you built yours like the Cozy, what did you do on forward side of the firewall? Particularly interested in how you tied in the lower mounting points. Apologies if details are in your thread and I missed it.

 

[Kent Ashton]

14 hours ago, TParker said:

Do you mean the bolts that attach the engine mount to the angle? Or the bolts that attach the angle to the fuselage?

I saw that you built yours like the Cozy, what did you do on forward side of the firewall?

In the pics I've seen, the bolts through the aluminum angles begin to elongate the holes in the angles, then the angles start to crack.  Never seen bolt failure or elongation of the holes in the engine mount tubes but I don't work on other people's airplanes--just look at pics.  🙂

I think it would be hard to convert the plans mount angles to Cozy style firewall mounts.  The Cozy has extra layups inside the firewall and outside overlapping the outside of the fuselage.  A few pics of the bottom inside here http://forum.canardaviation.com/showpost.php?p=70747&postcount=64

I think the plans EZ mounts are OK, just need to be beefed up.  As far a repairs go, I haven't worked on those plans mounts but I would think I'd get in there with a die-grinder and grind away the bad stuff and lay up new angles and glass.  I know that has been done a few times.

Edited March 13, 2020 by Kent Ashton

[Countach74]

Just got done doing this. Grind into sides of turtledeck, strake fillets for uppers and cut rear part of fuel dumps then sides of fuselage for lowers. Welded u shaped 1/8 dia. Rod to the heads of correct grip length bolts. Floxed these in. Now have studs sticking out with no chance of spinning.