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<< Lancair Builders' Mail List >>
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Micah Froese writes in response to my statement about a dodge
488 cid engine that can be turned at 2500 RPM at 26 in MP for a very
loooong time.....
It sure could be turned for a very long time, and that is what it would take
to get off the ground. At 26 in. MP it would be way over that RPM.
My response is: MP has almost nothing to do with RPM. You can
have 15 in. MP at 5000 RPM or 30 or more { if its supercharged}
in. MP at 1500 RPM, it all depends on how you have the engine
loaded. On an airplane this would be controlled by prop pitch.
Micah then wrote: Take a look at the horsepower/RPM chart for
the Viper 488 and see how much,or should I say little,power is
being developed at the RPM.
I must admit that I am at some what of a disadvantage hear, because
I was unable to find a HP/RPM chart for this engine on the internet,
but I was able to fined HP- torque specs at peaks.
450 HP @ 5200 rpm
490 ft lb torque at 3700 RPM
Both of these RPM levels are to high for prop use, so I will use the
pick-up truck variant of this engine as an example.
300 HP at 4000 RPM
450 ft lbs of torque at 2800 RPM.
2800 RPM is at a useable RPM for airplane use, so I will use this
figure. And keep in mind that this engine has a cam profile that
is optimized for higher RPM use than that of an airplane. If a cam
was installed that was more optimized for a maximum 2700 RPM,
these torque figures would be higher.
450 lbs of torque will move a plane of lancair size off the runway
quite smartly I think. But I'll go back to the original reason for my post.
Modern auto engines are built to much higher standards and to
withstand much higher peak loads than that of your average L or C
and for the prices that L&C are charging, they should be all but
indestructible.
Mark Lally ES
LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
Builders' Bookstore: http://www.buildersbooks.com/lancair
Please send your photos and drawings to marvkaye@olsusa.com.
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