6061-T6 engine mount?

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Bigshu

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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 ?
All the Hummels I've seen are VW powered. They're almost all metal motor box mounts, but Dennis Brooks used a welded mount for his H5. Works great. Dennis has built and assisted building on a few UCs. I'd reach out and pick his brain. He's a super nice guy. Good you tube videos as well
 

MACOWA

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I saw that one too. Craftsmanship ? The plan is to run the 503 plugs down. hanging out the bottom. Perhaps suspending the bed plate between two fabricated aluminum beams like the ones used on the JU-87 could be a solution. It might help the rocking couple vibration these inline twins produce and also clear the intake/exhaust stuff that hangs out of both sides of these motors. Guess I'm going to see how many pencils I can wear out.
 

Bigshu

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I saw that one too. Craftsmanship ? The plan is to run the 503 plugs down. hanging out the bottom. Perhaps suspending the bed plate between two fabricated aluminum beams like the ones used on the JU-87 could be a solution. It might help the rocking couple vibration these inline twins produce and also clear the intake/exhaust stuff that hangs out of both sides of these motors. Guess I'm going to see how many pencils I can wear out.
I think I'd wait and see what the Hummel guys come up with. Are you looking for more hp than a 1/2 VW can supply? The V-twins I've looked into claim 35-42hp. They're pretty massaged, but still only putting out 4K rpm to make that.
 

MACOWA

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I've spoken with the Hummel builder assist guys a couple of weeks ago, (These guys are sharp ! ) Their sugestion was to try a pretty much standard welded tube type fire wall mount. I have built two of these in the past. What with the Rotax D/C twins having intake & exhaust components hanging out all over the place. The proper geometry for this type of birdcage mount is almost impossible to attain without interference. The one that I
used on the 377 / J-3 Kitten had dampened fasteners at all attach points. It vibrated a lot. The Scott Castler twins are not only the design power plant for the U/C they are beauties. Rumor has it that the 45s are on hold due to crankshaft mod's and the 37 just isn't enough. as this plane must pull floats. I have a zero hours 503 DC/DI built by Bill Larsen at OAD, With a new Powerfin prop attached. It's a beauty too Besides, I already own it. Considering the limited wing area of the Ultra cruiser 52 HP, might be just about right.
 

Bigshu

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I've spoken with the Hummel builder assist guys a couple of weeks ago, (These guys are sharp ! ) Their sugestion was to try a pretty much standard welded tube type fire wall mount. I have built two of these in the past. What with the Rotax D/C twins having intake & exhaust components hanging out all over the place. The proper geometry for this type of birdcage mount is almost impossible to attain without interference. The one that I
used on the 377 / J-3 Kitten had dampened fasteners at all attach points. It vibrated a lot. The Scott Castler twins are not only the design power plant for the U/C they are beauties. Rumor has it that the 45s are on hold due to crankshaft mod's and the 37 just isn't enough. as this plane must pull floats. I have a zero hours 503 DC/DI built by Bill Larsen at OAD, With a new Powerfin prop attached. It's a beauty too Besides, I already own it. Considering the limited wing area of the Ultra cruiser 52 HP, might be just about right.
Sounds like you're on top of it, but I think to get lowest weight, stick to the plans, meaning aluminum engine box. How much will the floats and supports weigh?
 

MACOWA

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Looks like the choice has been made. Lori from Hummel called a couple of hours ago and told me that the complete motor box kit is being shipped in the same crate as the rest of the fuselage kit, that's 6 weeks before I expected it ! Besides the thought of deviating from a well proven design has always made me a bit edgy, In that I think we concur. Looks like it's time to innovate rather than fabricate. Looks like the floats and attach will weigh about 52 pounds. there is also the elimination of the landing gear, wheel, brake, and tire weight.
 

Bigshu

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Looks like the choice has been made. Lori from Hummel called a couple of hours ago and told me that the complete motor box kit is being shipped in the same crate as the rest of the fuselage kit, that's 6 weeks before I expected it ! Besides the thought of deviating from a well proven design has always made me a bit edgy, In that I think we concur. Looks like it's time to innovate rather than fabricate. Looks like the floats and attach will weigh about 52 pounds. there is also the elimination of the landing gear, wheel, brake, and tire weight.
I don't remember you ever saying, but are you trying to be part 103 legal? They don't make any allowance for extra weight of floats like LSA does, do they? Gear, wheels and brakes probably won't come out to 52 pounds, so you might be up against it for weight.
 

reo12

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Floats are accounted for in part 103. "(1) Weighs less than 254 pounds empty weight, excluding floats and safety devices which are intended for deployment in a potentially catastrophic situation; "
 

Marc Bourget

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Fatigue was touched upon, above. Due to the mass and vibration, I suggest the prudent builder, assembling with bolts (instead of driven rivets), should employ precision sizing methods.

For my wing attach fittings to the spar, AN bolts were acceptable in strength, but the production tolerances were so varied, that I bought a series of reamers, stepped up in .0005" increments. I drill and install bolts, one at a time. After initial drill, I would ream to ensure 0.00 to -.0005 interference. Navy Tech Report showed significant increase in strength and huge increase in fatigue resistance.

Your results with an engine mount should be much greater.

YMMV
 

MACOWA

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I don't remember you ever saying, but are you trying to be part 103 legal? They don't make any allowance for extra weight of floats like LSA does, do they? Gear, wheels and brakes probably won't come out to 52 pounds, so you might be up against it for weight.
I don't remember you ever saying, but are you trying to be part 103 legal? They don't make any allowance for extra weight of floats like LSA does, do they? Gear, wheels and brakes probably won't come out to 52 pounds, so you might be up against it for weight.
Yes they do, It's 60 pounds including the attach. I am indeed building for part 103. As was the case for the last two projects. The J-3 kitten made it, the Quicksilver MX did not. Everyone flying a legal ultra light is as you say "up against it." It costs $1000 to be caught heavy. No appeal.
 

pfarber

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Wait, exhaust gases melting aluminum? Like thick plate Al?

Wow, just wow.

Next is fires from a fuel leak melting Al? Is that in Part 21? We need to get rid of fuel in wings becuase it might explode or catch fire.

Wow. Just wow.
 

Mad MAC

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For my wing attach fittings to the spar, AN bolts were acceptable in strength, but the production tolerances were so varied, that I bought a series of reamers, stepped up in .0005" increments. I drill and install bolts, one at a time. After initial drill, I would ream to ensure 0.00 to -.0005 interference. Navy Tech Report showed significant increase in strength and huge increase in fatigue resistance.
That would be why one should use NAS close tolerance bolts, they cheaper than a bunch of reamers.
 

raytol

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I have a motorglider that had an oil fire. Everything that was thin aluminium was melted. The pitch change lever was aluminium but 1/4 inch thick and it melted! The block and heads were ok. Stainless steel stuff was untouched. The plastic in the Nyloc nuts was burnt and I could turn them easily with fingers. All the cable ties vaporized. Be careful for what you wish.
 

wsimpso1

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Wait, exhaust gases melting aluminum? Like thick plate Al?

Wow, just wow.

Next is fires from a fuel leak melting Al? Is that in Part 21? We need to get rid of fuel in wings becuase it might explode or catch fire.

Wow. Just wow.

Being real.

EGT's run over 1400 F, 6061 lose a huge fraction of strength at 775 F, starts to melt at 1080F, is fully melted at 1205 F.

Imagine a single point exhaust system failure. They happen. A prudent designer really would make sure that the engine will stay on the airplane after any one exhaust system leak. Imagine a crack, open joint, broken weld, and the exhaust flow from it.

So, the designer would be prudent to design so that they could blow torch any one spot a few inches in diameter and still keep the engine attached.

Protecting for this need not be an awful thing. For instance, an engine hung from four places is probably going to retain the engine with one point compromised, but a three point attachment might get really floppy and the engine may depart the bird with one gone. A 1/4" aluminum plate will stay put longer than a 0.035" sheet both because of more mass and more thermal conduction away from the hot spot.

Let's also remember you may have the blowtorch running a while before you discover it, and may want the engine for a while after that before you would willingly shut it down.

Or one can ignore it and trust to the ballistic recovery parachute. To do this, make sure that a blowtorched mount and engine in the process of departing the airplane does not compromise either the cockpit or the 'chute.

Billski
 
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Bigshu

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Imagine a single point exhaust system failure. They happen. A prudent designer really would make sure that the engine will stay on the airplane after any one exhaust system leak. Imagine a crack, open joint, broken weld, and the exhaust flow from it.
The OP is talking about a Hummel Ultra cruiser, which has the cylinder heads and exhaust outside the cowling, So there's not much chance the exhaust will cause trouble for the mount, whether it's welded tube or a riveted box structure. Lots of Hummels flying with aluminum engine boxes, Haven't heard of any engine box failures. Even in enclosed cowling designs, I'm not familiar with mount failures from heat being a significant fraction of cited causes of accidents. Designers should consider these types of potential failures, but I'm not sure how much brain work has to go into it. There must be lots of other potential failures that have a much higher likelihood than exhaust leak engine mount failures.
 

wsimpso1

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The OP is talking about a Hummel Ultra cruiser, which has the cylinder heads and exhaust outside the cowling, So there's not much chance the exhaust will cause trouble for the mount, whether it's welded tube or a riveted box structure. Lots of Hummels flying with aluminum engine boxes, Haven't heard of any engine box failures. Even in enclosed cowling designs, I'm not familiar with mount failures from heat being a significant fraction of cited causes of accidents. Designers should consider these types of potential failures, but I'm not sure how much brain work has to go into it. There must be lots of other potential failures that have a much higher likelihood than exhaust leak engine mount failures.
Point taken. That the heads and the entirety of the exhaust system on the Hummel's is outside the cowling then makes the analysis simple for birds of that type, does it not?

Our threads tend to drift and take on more breadth than just the OP's topic. Far more readers get into our threads than just the OP, and many of them with thoughts on airplanes different from the OP's. Responses that are more broad have validity. Omission of comments just because they do not apply to the OP could leave readers not thinking about what a parted exhaust system can do to things under the cowl...

Billski
 
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