Dave Martin wrote:
On Friday 28 October 2005 02:03, Vassilii Khachaturov wrote:
In a real gravity-fed Cessna, there are 2 aspects relevant to the engine
problems resulting from negative Gs that I was told about by the
instructors. One is the fuel flow (tanks/carb/engine intake manifold)
and the other is the oil flow that has gravity-induced return of the oil
into the sump. If that stops, it's as disastrous as oil leak --- permanent
damage can be done. (As opposed to just engine out due to momentary fuel
absense which goes away as soon as one pulls back up and the gravity is
restored).
This is quite true but it only becomes a problem after a few seconds of
sustained *negative* G as opposed to zero G. (Some 152 Aerobats have inverted
oil systems to prevent this all together).
I have more information on the survivability of engines starved of oil but
it's probably not relevant here ;)
As for the clearing the climb path, I was told to do some gentle S-turns
rather than pushing over the nose in order not to screw up the airspeed
and hence the time-to-climb calculations, as well as be less nauseating
for the passengers (of course, if executed in a properly coordinated
matter).
We were training in a busy traffic area (EGBE UK) where other aircraft in
unexpected places were a regularity. Typically we would make one check before
reaching 650' QNH and turning crosswind. The trick to making the check is to
leave the trim set to climb and just push forward momentarily while scanning
ahead for anything resembling your own aircraft. Typically, aircraft would
re-stabilise in its nominal climb in 10 seconds or so - not an issue when
climbing for the training circuit.
I can quite safely say that while you would have 'your heart in your mouth' as
you pushed forward, it was certainly not even a zero-G motion and the engine
certainly wouldn't waiver.
Also, in low-G manouvers such as a high-AoA entry to an incipient spin or a
0-G pushover where very low positive G (certainly lower than 0.3G) is
sustained for maybe 2 to 3 seconds, the engine would behave as in the cruise.
Having flown the manouvers during PPL training (not required but none the less
useful) I am adamant that the IO-200 will experience no power-loss down to a
small fraction of a G even when sustained for several seconds.
Thanks for the feedback, I'll change that.
Harald.
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