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Old Jun 19, 2012, 09:02 PM
North Simcoe Flyers
Canada, ON, Midland
Joined Jan 2012
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New Saito rpm help

So I have a new saito 125 that I have been breaking in... After following the initial break in process as stated in the manual... I have now ran about a gallon of the cool power 15% through it... With a 16x8 APC prop the highest RPM I can get is about 8500-8800.... Does this sound right? Or does the motor need more time to reach full RPM... Manual states that max RPM is 11000.....

The motor still seems to be running quite rich but as this is my first glow I'm not really too sure... Solid amount of smoke, with some fuel slowly dripping from the exhaust..... If I lean out the main needle anymore it starts loosing rpm while wide open..

What do you guys think?
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Old Jun 19, 2012, 09:23 PM
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Chicagoland
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Maximum RPM stated in the manual is the maximum allowed before wear or failure becomes an issue.

The prop determine how fast the engine will actually run. Large props results in lower RPM. Horizon says the benchmark APC 16x6 turns 9k, so your engine is doing just fine.

The engine will probably take some more time to break in, but it's probably pretty close to maximum power. Do not run the engine lean of peak RPM. This can result in detonation (a rattle or clatter sound) and quickly damage the engine. The Saito manual is very clear about tuning the needle 200-300 RPM rich of maximum RPM.

Greg
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Old Jun 19, 2012, 09:48 PM
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A 16x8 is normally considered to be the prop for the 1.50 and 1.80, as Greg suggested a 16x6 or 15x8 would put you at 9,000 plus a few.
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Old Jun 19, 2012, 11:28 PM
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Originally Posted by i tobor View Post
16x6 or 15x8 would put you at 9,000 plus a few.
this!
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Old Jun 20, 2012, 01:06 AM
North Simcoe Flyers
Canada, ON, Midland
Joined Jan 2012
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Thanks so much guys.... I originally had a 15x8 on it but I was concerned about airflow over the elevator as this motor is in a hanger 9 hellcat 60... The cowling is so huge so I went to the 16x8 after the first couple tanks were put through the motor.... Just help stop the plane from nosing over when taxing on the grass field at my local club... The bigger prop really helped getting more air over the elevator...

If I wanted to stick with the 16x8.... What if I went with a lighter prop, would that help increase the rpm a little? I was thinking of a Xoar Carbon Fiber prop... I have a few xoar props and they are almost half the weight of an equal sized APC? Or does the weight of the prop have little effect on rpm speed?
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Old Jun 20, 2012, 06:00 AM
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USA, NH, Alstead
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I run Xoar 16 x 6 on most of my Saito 125's; also 17 x 4 on my Saito 125 profile 3D planes. Both are a good fit. RPM's in the high eights maybe low nines depending on how rich I leave it.
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Old Jun 20, 2012, 06:55 AM
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United States, TX, Leander
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Thats about right for that prop. I run 16x8 on my 120's. I also dont tune for every last bit of rpm. Out of four 120's, two of them have over 200 hours run time on the original parts. I prop all my 4-strokes for 8000 to 9500 rpm.
Edwin
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Old Jun 20, 2012, 07:05 AM
Engine Category Manager - EVO,
United States, IL, Champaign
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Quote:
Originally Posted by Ayeager View Post
Thanks so much guys.... I originally had a 15x8 on it but I was concerned about airflow over the elevator as this motor is in a hanger 9 hellcat 60... The cowling is so huge so I went to the 16x8 after the first couple tanks were put through the motor.... Just help stop the plane from nosing over when taxing on the grass field at my local club... The bigger prop really helped getting more air over the elevator...

If I wanted to stick with the 16x8.... What if I went with a lighter prop, would that help increase the rpm a little? I was thinking of a Xoar Carbon Fiber prop... I have a few xoar props and they are almost half the weight of an equal sized APC? Or does the weight of the prop have little effect on rpm speed?
Ayeager,

You should be fine with that prop as long as you run it 2-300 rpm rich as the manual states. The higher pitch prop will unload more in the air than a lower pitch prop so the in air rpm will likely be close to each other.

I would choose the prop to use more on the in air performance of the aircraft ( ie preferred top speed, climbing ability, the ability to slow down for landings etc) rather than these ease of taxiing the airplane in the grass. To fix the taxiing problem you might consider more elevator throw with higher expo rate on a "taxi and takeoff" dual rate or flight mode position.

The Hellcat is a great airplane and with the 125 in it you have some serious horsepower for the weight. Have fun with this!

Pete
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Old Jun 20, 2012, 07:50 AM
North Simcoe Flyers
Canada, ON, Midland
Joined Jan 2012
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Thanks Pete I will give that a shot... I have had the hellcat in the air a few times now.. And she really screams... Big lazy loops at half throttle... And when she comes down in a dive at full throttle... Well... Let's just say scale performance is thrown out the window.. Lots of fun!!

Anyways thank you to everyone with your help!
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Old Jun 28, 2012, 11:17 PM
North Simcoe Flyers
Canada, ON, Midland
Joined Jan 2012
176 Posts
So I have ran two gallons through the saito now... And have switched back to a 15x8... Max rpm is sitting at about 8800-9000 rpm.... Idle is at 2200.... But a small problem has seemed to developed... Mid range throttle has a slight hesitation... It doesn't stall... But it's notable.... Also the rpm jumps around from 5400 down to 5000 and back... It's only a fraction of a second.... But like I said noticeable... And it wasn't doing it before... Any thoughts?
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Old Jun 30, 2012, 06:51 AM
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Normally when the rpm "hunts" it due to being slightly lean, at 5,400 to 5,500 it has to be the LS needle that's lean but not by much. The hesitation and rpm hunting says it the LS needle. Here's what I would do, I'd set the HS needle at absolute peak, then set the LS needle starting with it 1/8th turn richer than you are now, you very well hit the sweet spot right there. Trying to set the LS needle with the HS needle 300 rpm rich will having you chasing both needles all over the place.
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