Quote:
Originally Posted by SEE
Thanks guys, just one qestion. At alt 17K and above, the manifold pressure in Clods Spit Mk1 drops significantly (less than 2 Ibs per Sq.in.) - full throttle - straight and level - The boost cut out has no effect as pointed out earlier in the thread. So, based on the above - this appears to be incorrect for that altitude?
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You got me curious so i set forth to investigate this by converting some units and making a couple of simple comparisons
My personal conclusion is that while i can't be sure if it's accurate because i don't have original performance specs, +2 boost is nothing to scoff at in the wider sense of things.
First of all boost is measured in relative units, it's PSI above the normal sea level ambient pressure or in other words, zero boost means full throttle at sea level in a non-supercharged engine.
To put this in perspective, +0 boost would be equivalent to about 1 Ata (for Luftwaffe aircraft) or 29.92 inches of mercury (for USAF aircraft)
According to conversion tables, 1 psi = 2.036 inHG = 0.068046 atmospheres.
I don't know if Ata units correspond exactly to standard atmospheres, but here's how it looks thus far with relative boost measuring:
1 atmosphere = 29.92 inches Hg = +0 psi boost
If we measured absolute psi we'd get:
1 atmosphere = 29.92 inches Hg = 14.696 psi (absolute)
If this gets confusing, just keep in mind that boost is like setting the scale arbitrarily: +0 psi boost = 14.696 psi absolute
Following this train of thought we have:
+2 psi boost = 16.696 psi absolute (14.696 absolute + 2 from the boost) = 1.13609 atmospheres = 33.993 inHg
If we keep in mind that variants of late war fighters with turbo-charged engines like the P-47 were limited to about 42 inches Hg, getting the equivalent of 33.99inHg from a supercharged Merlin (no turbos involved) is not shabby at all.
Like i said i don't know how accurate it is, it's just that it doesn't seem implausible when making comparisons to later designs. I know this doesn't answer your question in a satisfactory manner, i was just in the mood for some investigating until someone with more accurate data can pop in
