6061-T6 engine mount?

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Sylvain

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Hello gentlemen :)
I am presently building a Double Eagle from Leonard Milholland. I will install the HKS700E engine that is my workshop and I am planning the build of my engine mount.
I of course consider to make it in 4130 tubing but I am also considering making it with 6061-T6 angles, bolted, not welded.

I would appreciate any opinion and advice on the subject!
Sylvain Belanger
Montreal QC Canada
 

TFF

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I would think that the fuselage had to be welded, so it would be better to not switch materials. I don’t know how a hks mounts. Does it need to be changed to make it easier?
 

Sylvain

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I would think that the fuselage had to be welded, so it would be better to not switch materials. I don’t know how a hks mounts. Does it need to be changed to make it easier?
The engine will be mounted on an aluminum plate, I have the plans and drawings from greensky.
The fuselage is completed, I did the welding myself. So once the engine mount design done, not much a problem for me to fabricate it.
 

TFF

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I looked at a picture and saw it was a bed mount. I would be inclined to make it steel tube. I think making it aluminum would end up with a bunch of bolts that really shouldn’t be there. Probably a lot thicker stuff than expected, too; along with worst case, steel being better in a fire, heavens forbid.
 

Bigshu

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Hello gentlemen :)
I am presently building a Double Eagle from Leonard Milholland. I will install the HKS700E engine that is my workshop and I am planning the build of my engine mount.
I of course consider to make it in 4130 tubing but I am also considering making it with 6061-T6 angles, bolted, not welded.
I would appreciate any opinion and advice on the subject!
Sylvain Belanger
Montreal QC Canada
Hummel does it with an aluminum motor box. Solid rivets, if I remember correctly. The pic is for a half VW on an Ultra Cruiser, but they have a similar design for the full VW powered H5. You can weld up a mount if you like, but they do provide for the sheet metal approach as well.


1642112183576.png
You can get a better idea from their website, but I think the drawing gives the gist of this approach. It's a bed mount, secured to the forward fuselage with angles, bent sheet and solid rivets. Lots of them flying.
 

proppastie

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Unless you are able to stress analyze your design it would be better to copy an existing design for a similar weight horsepower engine
 

wsimpso1

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steel being better in a fire, heavens forbid.

I have heard the concern with aluminum mount structure over fire before too. Several levels and a couple of points to cover:

First level fire is an exhaust leak, which is fairly likely. 1500 F gases washing over everything nearby and temps dropping some as other air under the cowl mixes with it. Seems to me that you would have to postulate a leak from one pipe at a time, and consider the mount components in that wash to be with the rest of the system needing to be capable. Repeat for all exhaust pipes and make sure that on any one leak, the engine stays put. You are probably OK with looking at it one pipe broken at a time. More than one pipe broken begins to get pretty unlikely;

Next level is a broken oil or fuel line feeding fuel to hot surface and burning. Again, you would have to review failures at all the likely points and the fire leading from that spot, wiping out the mount in a region. Follow all the possible single point failures to make sure the engine would stay restrained;

Last level is crankcase failure and ignition of engine sump oil. This is a pretty bad one as it can melt the crankcase. On the good side, it will take a while to melt the crankcase before it can start melting the engine mount - you had better be on the ground before cylinders start making their own way out of the cowling.

All in all, I suspect that the proper precautions are firesleeved oil and fuel lines, a firewall forward fuel cutoff, and a welded steel tube engine mount. Oh, and do not do like one of SDS's clients, and build the exhaust system from aluminum tubes... That last one is way up there on the "let's try something stupid" list.

Billski
 

TFF

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Not total melt down, but if you had a leak that started enough of a fire that cracked a leg of the mount. You just don’t want it to snowball. This is a simple plane at least. No need to go crazy.

There was the Viking that totally burned up when the fire first took out the PLeads and fuel in the system kept the engine running long enough for the fire to spread. Not an engine mount issue, but you don’t know where it might go.

A friend fixed this plane. A kid was flying this thing solo. It’s about the what if.
 

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proppastie

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A friend fixed this plane.
backfire when starting and you will get a nice fire .......same with pumping the accelerator pump when trying to start and you get a backfire.....although unless there was lots of fuel on the ground it probably would not be as spectacular as a fire of the movie plane.
 

TFF

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The kid was flying with the float bowl loose. As long as the fuel was pumping it would be bad. A kid in the pattern will have the boost pump on all the time. Panic for someone with 15 hours total time is almost assured. My friend had quit working on the plane years ago because the owner was cheap. He ended up working on it again that time because the owner had burned other mechanic bridges and it was back to his turn.
 

wsimpso1

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I do not BS like that... Look up the crash of N551RD. Aluminum exhaust manifold material cited. Ross Farnum of SDS has written about it too. Exhaust gases blowing on his wires were why the engine cutout. Ross has since including shielding for the engine sensor wiring...


Have fun.

Bill
 

raytol

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I think that the FARS and JARS should be re-written to ban any aluminium in critical components in the engine bay!
Same as using nyloc nuts, plastic cable tie's, batteries mounted in the engine bay and a host of other things that are easily
changed during the design phase but harder to change later.
 

wsimpso1

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I think that the FARS and JARS should be re-written to ban any aluminium in critical components in the engine bay!

Harrumph. The really rare under cowl fire still results in an emergency descent and dead stick landing - big risk is not substantially reduced by this proposed change. Wouldn't it make far more sense to reduce odds of undercowl fires in the first place?

Billski
 

TFF

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I think calling out a 210 or a Bonanza is not in the right context. If you wanted to make an engine mount for a Cub out of aluminum, you are not thinking monocoque construction, you are thinking angle. This mount is for a 4130 tube fuselage . Let’s go inconel or titanium. If needed, we can really go overboard for something that should be as simple as rain.
 

Lucky Dog

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I build custom engine mounts for one and two place ultralight type aircraft, usually for folks who are swapping engine types. I am a better than most gas and TIG welder, but almost all of them are aluminum angles and plates, bolted together. If you do the numbers, aluminum and steel structures have almost identical strength to weight ratios. Steel tubes take up less space and welded tubes are simpler structures to build. The disadvantage of small-diameter, thin wall steel tubes is welding tabs to attach substructures often weakens and can warp them - a double reduction in strength. Drilling small steel tubes, for instance, to pop rivet a windscreen or an access hinge, invites crack propagation - equally bad. So all the attachment points for accessories and such must be engineered into a steel tube engine mount. By contrast, to attain similar strength and durability, aluminum parts must be significantly thicker and wider members, it is practical, then, to drill, rivet and bolt attachment points (within reason) to your engine mount structure without detriment. Bolting the mount together ensures that the strength of the members is not diminished by welding, and fatigue tests show that lightweight bolted or riveted aluminum structures last longer and are more reliable than welded aluminum configurations. Check out Robert Baslee's (Airdrome) aluminum engine mount designs as a starting point. Since you are fluent in both mediums, chose the one that gives you the most options and you'll be good to go.
 
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MACOWA

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Hummel does it with an aluminum motor box. Solid rivets, if I remember correctly. The pic is for a half VW on an Ultra Cruiser, but they have a similar design for the full VW powered H5. You can weld up a mount if you like, but they do provide for the sheet metal approach as well.


View attachment 120489
You can get a better idea from their website, but I think the drawing gives the gist of this approach. It's a bed mount, secured to the forward fuselage with angles, bent sheet and solid rivets. Lots of them flying.
Hello Bigshu. I am building an Ultra cruiser. Power will be a Rotax 503 mounted plugs down, B box up, to match the thrust line. Do you know of anyone that has done this using this motor box ? Any Ideas ?
 
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