HP VT49 MAX RPM ADVICE PLEASE

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HP VT49 MAX RPM ADVICE PLEASE

Postby boz » Thu Sep 09, 2010 11:10 am

I ran a new Austrian HPVT 49 today for the first time. The book that came with it says 500-15000 RPM. I was running a 12x6 prop and although it was running a bit rich I got it up to 8000 RPM after two tanks but I don't think it will go anywhere near the 15000 RPM mentioned in the book. What do you guys think I would get max RPM running a 12x6 prop ?
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Postby chiefss » Thu Sep 09, 2010 1:56 pm

It will if you use a smaller prop. RPM is based on prop size. 8000 is probably right for a 12x6
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Postby propwobble » Tue Oct 26, 2010 7:18 pm

Performance is not always about RPM anyway. Prop for the application.
:)
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Postby chiefss » Tue Oct 26, 2010 9:30 pm

Propwobble. It's been a long time.
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Postby propwobble » Wed Oct 27, 2010 4:23 pm

chief, Yes been awhile. Ever notice how engine makers are liberal with their RPM figures? Kind of hard to imagine an HP four stroke turning 15,000 with any prop.
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Postby chiefss » Wed Oct 27, 2010 8:27 pm

That's true with the poppet valve engines. The VT has a rotary valve and can turn that fast but then it doesn't do what it was designed for. Turning a reasonably large prop at slower speeds. I have a HP 49and it will turn a small prop that fast but I think I think that is well past the max horse power curve.

Why spend the money to turn a little prop at high speed. Buy two cycle to do that.
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Postby propwobble » Thu Oct 28, 2010 1:48 pm

I'm a bit surprised to hear that in spite of the lack of valve float. What size prop did it take to reach that magical 15,000. I always think of the practical application, I suppose I should have used the word " efficiently" .

The little drive tower does look cool. It would be really special if hooked up to to overhead cam desmo poppet valve setup. Dream on......
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Postby chiefss » Thu Oct 28, 2010 4:39 pm

It was small and it wasn't MY engine but a friends. We wanted to see just how fast it would turn. I think we used a nine inch prop. The little beggar was screaming it's heart out and they are quiet engines. We flew his plane with an 11x7.5 turning about 8500 RPM which worked just fine.

My 49 is still NIB.
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Postby Gnu » Sat Oct 30, 2010 11:59 am

Possibly the mfr's 15,000 rpm rating is what it considers the engine's physical limit prior to becoming shrapnel.
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Postby chiefss » Sat Oct 30, 2010 1:19 pm

That is definitely NOT how the manufacturer rates horsepower.
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