> is rated for 95 HP continuous; 100 HP for 5 minutes
> (is there another version of the 912S?).
>
> Anyway, this comps to 5.65% speed increase, 95 verses 80 HP, per Hoerner.
>
> Aircraft), presents a graph which would put the speed increase at about 7%,
>
Sounds like plausible and well argued aerodynamics to me.
6-7 % would be about 7 1/2 knots.
In my case I'd hope for 114 + 7 1/2 = 121 knots at 5000 rpm (17 1/2 degree fixed
prop)
This would give me an average point to point (practical) cruise of over 115
knots
on a calmish day, using the 912S.
I also know it's pretty difficult to make a fair assessment of true cruise
performance.
In my case, it took me ages to get it right and I had to be really hard on
myself.
It's so easy to overestimate by, say descending during the test, or failing to
take into account
of side wind components, to say nothing of head and tail wind compensation.
Also, wind at 1000 ft comes from a different direction than wind over the
ground.
There are days when I'd go back and forward for an hour at a time, writing down
GPS
results on a scrap of paper, trying my best to hold a track over the ground, and
desperately
trying to hold a fixed rpm and a fixed altitude.
Can anyone publish a _rigorous_ set of rules to be followed when measuring
cruise
performance ?
I'd like to see if I've neglected anything.
Another way to get a useful result would be to keep a note of all point to point
times (excluding
taxi, takeoff, climb, decent) between airfields with known separation. As time
passes,
an average transit speed would emerge. You could usefully put this on flight
planning documentation
to forecast an arrival time (105 kts ?). Recently, I've found this to be really
accurate.
One other thing I've discovered is that my ASI is wildly optimistic,
unfortunately. (over 7 knots
in the new configuration).
*Well done* to those who can cruise around all day at 150 knots. I'd really,
really, like to
know _exactly_ how it's achieved on such low HP and low fuel burn. At this point
in time,
I just don't understand how it's possible. I'm looking forward to the next
newsletter to see what
modifications have been suggested.
Then of course I'd like to copy them, if I'm persuaded !
alan
It'd take me longer to cruise to Scotland at 120 kts, than at 105 kts. I'd have
to stop
for fuel.
--
Alan. D. Stewart
14 Goddard Way 'phone : +44 1245 264186
Chelmer Village work : +44 1473 607571
Chelmsford, Essex CM2 6UR email : alan.stewart@cableinet.co.uk
office email : alan.d.stewart@bt.com
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