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RPM of Heli OS.91SZ-H vs. Aero.91FX

Old 01-13-2007, 07:06 PM
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Default RPM of Heli OS.91SZ-H vs. Aero.91FX

Hi Fellows,
I agree with popular comments but some of the comments still try to ignore the difference between
two "quite the same" enignes with a Very Different Price, for example OS.91FX and OS.91SZ-H.
Lets not ignore the fact the heli guys most likely prefer heli engine and pay lot more, Why do they
do that; they are not stuid indeed ? As for the bhp, I believe what I see on the tachometer with the
same propeller, and fuel; here are results for 14x6 APC, 12% nitro, 6% castor, 14% aerosave oil,
both engines at open exhaust: OS.91FX: 12000-12500, and OS.91SH: 13500-14000.
Please comment on this big(!) difference which reflects the difference in the catalog data too; that
spells out in thurst difference between about 5.8-6.1kg vs. 7.2-7.6 kg force which makes the plane
flying visibly in a different manner. And those numbers are real thing one can measure, it is in fact
very simple to measure and not just advertising data on paper only. Also the third needle is of
pretty good importance for the power torque; few are who can do power torque with regular
two-needle carburator with the usual unstable transition. Thus, there migh be something else behind
the difference between Heli and Aero engine, what that might be, compression ratio, more precise
porting, more precise timing, or what ? [sm=spinnyeyes.gif]

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