[NSRCA-discussion] OS 91FX or 120 AX for Focus sport

[J N Hiller]

I recommend the 1.20 AX. It will turn a bigger prop, which offers a more
efficient HP - Thrust conversion. I am flying advanced with a 9+lb airplane
powered with the 1.20 AX and a 16-10 APC. I am getting away with the 16-10
but I feel I am pushing the upper limit. It would probably be more
comfortable with a 15-10 or 16-8. It is probably more power than needed in
lower classes but throttle management is one of the things we need to learn
and the sooner the better, besides the extra power will be most welcome in
adverse weather conditions.
Jim Hiller

-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of Shoval
Aviv-BAS036
Sent: Thursday, June 26, 2008 10:24 AM
To: nsrca-discussion at lists.nsrca.org
Subject: [NSRCA-discussion] OS 91FX or 120 AX for Focus sport

Hi All,
I'm fairly new to pattern flying. I'm considering to buy the Focus sport and
want to "keep it simple" with the engine. I know the Focus was design for YS
110 but for cost/ simplicity reasons i am considering the OS 91 FX or the OS
120 AX. In the OS web site they claim that the 120AX is 20% more power but
when I compare efficiency it looks like the 91FX wins. Its 6% more efficient
in power to Wight and 16% more in power to displacement. Am I missing
something? Practical RPM misleading numbers? What would be your
recommendation?


120AX
91FX
Displacement (Cu in)
1.2
0.91
Weight (gr)
650
550
Output (BHP at RPM)
3.1 at 9000
2.8 at 15,000
Cost
250
200



output/ weight
0.004769
0.005090909
Output/ displacement
2.583333
3.076923077


Best Regards,
Aviv

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