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  #21  
Old 06-29-2012, 12:22 PM
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First off I'm doing this in a RV with a non-counterweight O-360, so that eliminates any concerns about counterweights flying off.

Second, the CAFE report wasn't conducted with mogas and since the octane is lower, the burn is much faster hence PPP occurs earler. Retarding the timing is appropriate in that case. The vast majority don't experiment with this stuff because most people are content to just kick the tires and go.
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  #22  
Old 06-29-2012, 01:00 PM
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Default HA!

I thought you were planning for the Rocket! DOH! Thanks for giving us ALL the information.

Best you talk to Les Dowd about non-CW vs CW cranks & their effects on the prop & crank. Their is a pulse amplitude limit on every prop, with the wood versions tolerating a much higher amplitude.

In ANY case, use a F/P wood prop so your crank & prop are up to the job. I would recommend against doing this with a metal prop of any type.

Carry on!
Mark
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  #23  
Old 06-29-2012, 06:39 PM
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Tonight I went for a little jaunt around the area and did some very unscientific testing. Starting at the normal cruise settings I use 2300,25" I pulled the prop back to 2000 and back to 25" due to the expected rise in MP, and all seemed well. CHTs stayed the same, EGTs dropped considerably. When I pulled back to 1800 the EGTs dropped 200+ degrees. The CHTs never budged (analog steam gauges unfortunately.) Pulled the prop all the way out and it got down to 1600 RPM. Thats as far as it will go.

The EGT drop was not unexpected but I was surprised by the amount.

Everything felt fine, a little bit more of a slow shake at 1800. 2000 seemed to be about perfect.
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N9187P PA-24-260B Comanche, flying
N678X F1 Rocket, under const.
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  #24  
Old 06-30-2012, 08:44 AM
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Quote:
Originally Posted by F1Boss View Post
Hey Bob:

Most of the big round stuff cruises at 1800/25-28", LOP.

Seems to me the most of the big round stuff like the R-2800 have planitary gears and the tach is reading prop rpm if memory serves.Depending on application that engine was built with one of several gear ratios.
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  #25  
Old 06-30-2012, 08:54 AM
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Quote:
Originally Posted by dhammer View Post
Seems to me the most of the big round stuff like the R-2800 have planitary gears and the tach is reading prop rpm if memory serves.
That is how I remember things also.
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  #26  
Old 06-30-2012, 09:40 PM
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The "big round engines" that I have flown all read engine RPM. (R-3350 in a Skyraider, R-2800 in a Corsair.) V-engines read engine RPM as well.
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  #27  
Old 06-30-2012, 09:42 PM
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Default If you have a smartphone...

consider using a vibration meter ap for this testing. I haven't done any low rpm testing, but I clearly documented improvement after balancing my prop with an android ap called "vibrometer". I placed my phone on the glare shield propped up against the center support brace (slider). I'm sure there is a similar ap for the apple folks. High amplitude can't be good at any frequency we're talking about..
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  #28  
Old 07-01-2012, 05:13 AM
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I had some time just jollying around the traps today, at 28+" MP and 2400/2300/2200 it did not make any significant difference, and I must qualify this.

All operations were LOP, so this takes MASS AIRFLOW being the dominant factor out of the equation.

Now I know there is subtle theoretical differences in drag and prop efficiency, but to be honest it was hard to tell.

2300 and 2400 were just fine, in fact I found 2400 was smoother although it may be just prop balance. even though we balance at 2300, but this was 100 hours ago and due for checking.

Find a sweet spot for smooth operation
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  #29  
Old 07-01-2012, 05:44 AM
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Some of us also have prop limits:

DO NOT OPERATE ABOVE 22 INCHES
MP BELOW 2350 RPM. O-360-A1A:
OPERATION ABOVE 2600 RPM IS
LIMITED TO TAKEOFF, IOF-360-A1A:
MAXIMUM ENGINE SPEED LIMITED TO
2650 RPM

When I'm just tooling around I find 18-20" works well with about 2300, anything less than that is just not as smooth.
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Last edited by Walt : 07-01-2012 at 05:47 AM.
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  #30  
Old 07-01-2012, 06:58 AM
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Bob, give yourself an edge. Contact Lycoming and ask for guidance on a knock sensor installation. You're an electronics guy so it shouldn't be hard to do. Vibratory and detonation risks are real; a knock sensor would give you a handle on one of them.

Quote:
Originally Posted by RV10inOz View Post
I had some time just jollying around the traps today, at 28+" MP and 2400/2300/2200 it did not make any significant difference, and I must qualify this.
Full throttle? That's aggressive. I assume you pulled to LOP before reducing RPM?
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