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Mark,
I did some algebraic manipulations to find HPL based on a
selected HPD (tube diameter) and got an answer. However, I am
somewhat skeptical of it although it does tend to fit with the general theory of
larger dia pipes = shorter lengths.
By arbitrary selection an diameter - you
automatically select the rpm factor in the equation (but, its hidden
in the HPD value). The way you check what your new rpm sweet spot
with the arbitrary diameter is to vary the rpm in the first set of equations
until you get the length determined by manipulated equation.
So the revised equation for 1.8" dia tubes gave 27.58"
inches for the HPL. You vary the rpm value in the first equations until
you get an HPL of 27.58" and you get an rpm of approx 7900 - so I agree,
probably too high for your configuration.
Ed
Sent: Saturday, November 20, 2010 11:18 AM
Subject: [FlyRotary] Re: Exhaust Calcuations
Ed,
OK, that answers my question. By going with 1-7/8" OD pipe (.049
wall), it would be tuned for about 7800 rpm. Obviously, this is too high
for our purposes. I'll go with 1-5/8 (.063 wall) to shoot for 6700 rpm
peak power. This is typically the rpm I see on ground roll and early climb
before I start adjusting the prop down to a lower rpm to transition to cruise
climb.
Have you used the header designer tool available from Burns Stainless?
You need to know all the timing numbers, rpm, etc. I may give it a
try and see what I come up with. I have a test p-port housing that I made
up to see if the tube could be welded to the inner liner. So, I can use
that with a spare rotor to verify the EVO and EVC numbers.
Mark
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