Our group decided to invest in a Norvic replacement engine for our Robin DR400. The old engine was burning a lot of oil and our engineer was making noises that he was not happy to carry on signing it off “on condition”, as it had passed it’s TBO.
Those with an engineering background migh be able to answer this thought :Was the old engine producing the same power output as the new engine?
If you think about the old engine being worn and the piston rings letting a certain amount of fuel combustion past the rings, does it mean therefore we possibly had to advance the throttle further to get the same number of revs?
Or does it mean that any two engines, one knackered and one not, still produce the same power output if they are both run at the same revs?
Lycoming 0-360-A3A normally aspirated (cauburettor) fixed pitch prop.
If the engine in the same type of airplane and with the same prop develops the same RPM on take-off then it actually does pretty much develop the same power. Continental made some tests and they found out that while oil consumption will be high even engines with very low compression ratios like 30/80 will still develop their rated power, or almost.
Continental once made a test where they removed one or multiple piston rings which brought the compression leak down test to something like 20 / 80 psi then ran it on a dyno. IIRC, the engine made over 90% of it’s rated power although it was burning copious amounts of oil.
A “tired” high time engine is often not really so tired .
That said, you could have easily made a simple before and after test by loading the aircraft to given weight then do an all out timed climb to say 10,000 ft. Do the same with the new engine installed being careful to choose a day and time that matchs closely the temp & baro of the baseline run.
Here’s the blurb:
In fact, Continental Motors actually ran a dynamometer test on an IO-550 whose compression ring gaps had been filed oversize to intentionally reduce compression on all cylinders to 40/80, and it made full rated power.
