Originally Posted by
Volume
Is that another inaccuracy of the (interim) report? Do they actually mean the BMEP when they say "the captain stated that the manifold pressure was low" ?
Do they mean the BMEP indicators when they say "the manifold pressure gauge, which is a dual indicator for the left and right engine, was removed, repaired and refitted to the Aircraft" ?
There's nothing which suggests that mix up. I only pointed out that the BMEP wasn't mentioned in the report to keep readers from assuming that our discussion of BMEP gauges indicated there was reason to believe that there was a problem involving BMEP.
Originally Posted by
Volume
Does manifold pressure mean anything on these high power piston engines? Is it as important as on a typical SEP with CS Propeller?
Yes, it is every bit as important as it is on a simpler, normally aspirated piston engine with a CS prop. MAP is the primary indication for setting power.
Originally Posted by
Volume
Or is BMEP the parameter you use to manage engine power?
Not really, power settings are made by MAP and RPM. BMEP is useful as it is a measurement of output, vs MAP which is a measurement of input. Input doesn't necessarily equate to output, depending on condition of the engine, etc. As an example, if you were to turn off the magnetos in cruise in the DC-6, the RPM would tend to remain the same because of the CS prop. MAP is a function of supercharger speed and throttle opening, and because the RPM is the same and you haven't changed the throttle setting, MAP indication will remain the same. and fuel flow would remain the same. But obviously, even though you have the same manifold pressure, you aren't getting the output you want. Aside from aircraft feel/handling/performance, the only instrument indications of the power loss would be BMEP and your cylinder heat temps would be decreasing. BMEP was used to verify power output, and on the DC-6, if you had the same MAP and RPM on all 4, and one BMEP was noticeably lower than the other 3, that was an indication something wasn't right. Also, BMEP was used as a primary indication for leaning the fuel mixture in cruise. We would lean until BMEP peaked, then decreased by 12 psi. That represented about a 10% drop, when meant we were operating Lean of Peak, but that's a whole separate discussion.
Originally Posted by
Volume
Is the removed and repaired unit somehow linked to the autofeather system?
Not exactly, as I said, there's no indication that the references to the MAP gauge were in error. There's no direct link to the Autofeather System, so an MAP gauge error wouldn't affect the operation of the autofeather system.