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HelicopterEngines Plugs Mufflers Fuel › y.s. 80 gear ratio
09-07-2003 08:56 PM  14 years agoPost 1
RRLL

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Israel

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Did anyone try a lower gear ratio than 8:1?
I'm using the 8:1 ratio with very good results but want to try and get more flying time on each tank.
30% fuel + zimmerman muffler.

What do you think about 7.5???? (for F3c only)

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09-08-2003 01:51 AM  14 years agoPost 2
Dr.Ben

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Richmond, VA, USA

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Wayne Mann and Dwight Shilling ran 80's @ 7.9:1 in their Calibers with 30% nitro with good results.

I SERIOUSLY doubt you'll be able to keep your headspeed up when loaded heavily in aeros using a ratio as tall as 7.5. Also FYI, Cliff Hiatt tried as tall as 7.6 (or was it 7.5....) and found that to be a bit too tall for even the YS91. The C-Spec will handle a ratio in the mid sevens just fine, but that wasn't your question.

Ben Minor

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09-08-2003 02:43 AM  14 years agoPost 3
karlk

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Petaluma, CA

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Ben, any idea how the YS80 does with the 8.18 ratio & 15% fuel? I'm considering the YS91 for my Tempest 3D, but I really don't need gobs of power. I run the OS91 SX in my Nova off 15%, 7.57:1 ratio, & about 1800 head speed. Nice & quiet, and ample power.

Since the 80 is cheaper & easier to get, it got me thinking....

-Karl

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09-08-2003 04:35 AM  14 years agoPost 4
Dr.Ben

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Richmond, VA, USA

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Karl,

I'll tell you first hand that the Tempest head with 700mm blades, an 80 on 8.18, and 20% fuel pushes the motor pretty hard. It ain't at all pretty if the weather is especially hot and humid. 15% won't help that issue. I really needed the 91 to be able to get through the FAI schedule adequately. There's just so much blade out there coupled with the 195mm bolt hole spacing on the Tempest head. If you try the 80, I'd be more inclined to suggest either the 8.36 or 8.45 ratio to gear the engine down a bit. I think that combo might work OK for you.

Wayne and Dwight were using 7.9 with 700mm blades and a wide grip spacing, but they were also using 30% nitro AND I can tell you for a fact that their engines were running balls to the wall -fully needled in.

Ben Minor

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09-08-2003 06:03 AM  14 years agoPost 5
karlk

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Petaluma, CA

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Thanks Ben. I think I'll just go ahead and get the 91. It doesn't make sense to spend another $150 for the gearing (my Tempest is 8.18) so I can save $50 on the engine. I have an OS91SX I can use in the meantime if I have a hard time finding a YS91.

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HelicopterEngines Plugs Mufflers Fuel › y.s. 80 gear ratio
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