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>
> Bill, I think Ed was saying that if you
pitch the prop to absorb 243HP
> at 3157, then it will be producing
?160HP? at ?2000RPM?. You're engine
> will be turning 5700 with the
prop at that RPM. The question is, "Will
> 5700 engine RPM produce
160HP or greater?" If you don't get >160HP at
> 5700 RPM, you'll
never be able to get TO the 243HP that is sitting there
> waiting for
you. A CSprop would let you feather it past the lower RPMs
>
and bring you into the sweet nirvana where you manifolds tuning works at
> its maximum. With a fixed pitch prop, it may be questionable
until you
> build one and try to run it.
>
> How'd I do,
Ed?
>
>
Better job of explaining it than I did, Earnest.
Thanks
Yes, it doesn't matter what HP you produce at 6000,
7000,8000 or 9000 rpm if the load of the prop at some point before those points
is more than the engine can produce. The load on the prop goes up as the
rpm^3 (following found on the internet)
Taking these three points, the power in watts required to drive a
prop would be:
Watts = Const * rpm^3.0 * diameter ^4 *
pitch
Therefore, a small increase in rpm raises the amount of
power needed considerably to meet the load. Of course, as you point out so
well, Ernest, a variable pitch prop permits you to change the pitch factor in
the equation reducing the power needed at any specific rpm.
If your pitch is small enough (load low enough)
there is no doubt you can reach your manifold airflow design limit, but
for a useful pitch then the engine must overcome the prop load at every lower
rpm point to keep revving into that golden zone.
So there are really only two factors I can think of that
will cause a engine from continuing to accelerate to higher rpms under
load.
1. The load is too great for the power being
produced at an rpm
2. The induction system (intake/exhaust) has choked
at that rpm (see 1.)
At least that's the way appears to me. So if Bill's
beautiful design can produce the HP to over come a realistic prop load (72x88?)
up into the 6500 rpm range (where apparently all the valves in the auto manifold
are open) then I think he will have a good chance of making his goal of
9000.
If I wanted to absolutely ensure that my
engine could reach that golden rpm range of 240HP, then I believe a variable
pitch prop is the only way to ensure that (or a gear box {:>)).
Certainly, if you have a fixed pitch prop whose diameter and pitch producing a
sufficiently small load factor (which might be too small to be useful) to can
also reach it.
I believe the question Bill will need to answer if
his manifold is going to become a product is "What is the maximum
prop load that can be place on an engine with his manifold and still permit the
engine to climb into the golden RPM range". I think he will further
have to determine this in terms of prop diam and pitch (and perhaps # blades) so
that the requirement can be translated into "airplane speak"
{:>)
I am rooting for his success - naturally I would only run
8000 rpm with his intake on my older 13B, but I would be happy with that
{:>)
Ed.
Ed
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