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Engine basics => Engine set up tips => Topic started by: Jim Oliver on December 24, 2024, 05:30:43 PM
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Good evening and Merry Christmas!!
I'm looking for info on prop/fuel/tank size for a PA 75 with a Jett header muffler. Any help much appreciated!
Jim
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Tank size, one pint.
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put 'PA 75' in SEARCH H^^
orin googlesearch ,and it'll get them ,
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put 'PA 75' in SEARCH H^^
orin googlesearch ,and it'll get them ,
Actually, that was no help...........
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Actually, that was no help...........
That's because, as far as I know, no one is running it with a muffler. You're starting from nearly scratch. There are two obvious ways to go - 5-6" of pitch with an ENORMOUS prop (presumably a wood two-blade, maybe 14-15-16"), or 4.5-5 with maybe a 13.5" 3-blade. It will probably turn even more diameter, but presumably any larger would be prohibitive on the corners. Too small and you will not have enough control over it with just the muffler.
Brett
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That's because, as far as I know, no one is running it with a muffler. You're starting from nearly scratch. There are two obvious ways to go - 5-6" of pitch with an ENORMOUS prop (presumably a wood two-blade, maybe 14-15-16"), or 4.5-5 with maybe a 13.5" 3-blade. It will probably turn even more diameter, but presumably any larger would be prohibitive on the corners. Too small and you will not have enough control over it with just the muffler.
Brett
I think I have read of some using a muffler. The only one I'm sure of is Keith Trostle in his Martin-Baker MB-5 that he built a few years ago, but I don't know how much, or if he's flown it. If I'm remembering correctly, he had a exhaust manifold converted to a muffler, and maybe Bob Whitney did the work for him?? Maybe Keith will see this and fill in the blanks.
Type at you later and MERRY CHRISTMAS!!
Dan McEntee
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Thanks Brett and Dan for those helpful comments:)
I'm thinking that the 75 is too much of a good thing........also concerned about prop diameter and not enough ground clearance.
Regards,
Jim
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Dan Banjock runs the 75 on a header muffler in his Turbo Raven that seems to run well when I see Dan fly. It’s been a couple years.
The 75 on a pipe is an amazing motor and is very forgiving if you set it up correctly.
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Dan Banjock runs the 75 on a header muffler in his Turbo Raven that seems to run well when I see Dan fly. It’s been a couple years.
The 75 on a pipe is an amazing motor and is very forgiving if you set it up correctly.
Was going to chime in with the same note. Banjock's runs great. I launched him a couple times this summer and the motor run was perfect. I know he runs it on a 3-blade but don't know anything else.
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Dunno if thisisit .
https://www.youtube.com/watch?v=W8PBaCokwr8
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I doubt if thatsit.
Quite a clear asymmetry, lean in outsides. And the engine doesn’t really react but stays lean during longer maneuvres, like 8’s. Sounds like a poor thermal balance. L
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Quite a clear asymmetry, lean in outsides. And the engine doesn’t really react but stays lean during longer maneuvres, like 8’s. Sounds like a poor thermal balance. L
The asymmetry is something we fought on any number of schneurle engines over the decades. I have no specific information but just from the reaction I would guess he has a stock-like venturi (asymmetry) and is trying to deal with it by softening it by lowering the compression (delay in returning to a 4-stroke). That's not a thermal issue, it is a classic "low compression" symptom, and the fact that going hard lean in outsides and not pile-driving him into the ground also suggests low compression. Lower it enough and it will go lean and stay lean till it runs out - the classic runaway.
I know what I would try to adjust it, maybe it would work, but Dan probably knows what to do and this is what he wound up with.
Brett