Can the O320 handle 2800 RPM Cruise
 

I posted in another thread about my prop experimenting. I have an O-320 with a Catto prop. I am getting around 197 MPH TAS or so at 2800 RPM at 8K DA. I can go LOP and it drops to 2700 / 190 MPH.

While I am happy with the 2700 RPM setting and speed, I am wondering if I can wind it up to 2800 if I am in a hurry. It only burned another .7 GPH or so and could see myself making that trade-off. I have seen some people saying that the O-320 has no problem turning that RPM on a continuous basis. 2800 at that altitude was indicating about 80% power.

I am hoping to hear from those with experience in this area. Can the O-320 handle 2800 or is that creating a potential for problems. The prop is rated at either 3000 or 3300. I can't recall which was on the placard.

Larry

Looks like you will save eight minutes over a tank of fuel. Not such a great savings.
The engine can handle it as can be seen in race planes, well over 2,800 rpm.
Now running lop at 80 percent power, Not to happy about that one.
Enjoy your rv. Like I say, hi or low, fast or slow, right side up or up side down. Total fun. :D

TBO
 

For how long might be a concern; I wouldn't expect it to make it to tbo running like that. You wouldn't drive your pickup around at full throttle would you?

As Turbo eluded Id be concerned about leaning out at greater than 75% power or running LOP at more than 65% power, IIRC.

Sounds like your prop is pitched right. But if that is a typical cruise alt (or lower) and you like running WOT, perhaps you should coarse it up a notch.

My -9A was just like that... I think back to my 172 days and there was no way you could over speed that engine at those altitudes, straight n level.

My opinion is the RVs have such a wide speed envelope how could you possibly get the perfect fixed pitch prop! Still beats a 172 though:D

https://www.google.com/search?q=cobr...NtK2LcI6FrY%3D

Has an O-320. Was a Reno racer for a time, then flew airshows quite a bit. A close friend of my neighbor did the airshow flying. It sounded like 'the other' F1 race when it was flying. Close to 4k rpm in airshows; well north of 3k rpm cross country between shows. (Yes, that's a cut-down metal prop; don't try this at home. :-) )

Overhaul frequency will suffer, but the engine doesn't seem to care from a reliability standpoint.

Having said that... One mile per gallon would be pretty painful inefficiency for me. I wouldn't worry about it if a few minutes made a difference on a particular flight, but wouldn't want to pay for the gas on a regular basis.

Now, if your prop will give you that much rpm if you go up a couple of thousand feet, you should be able to drop back close to your 75% fuel burn, get 75% power at a higher altitude, and gain the speed/efficiency advantage of thinner air. Then your only 'hit' would be slightly faster wear due to higher rpm.

Charlie

Thanks for the input. I am happy with it being a bit fine pitched, as I can get closer to 2700 at higher altitudes for better efficiency. I am set up with O2 and plan cruise closer to 10K+ I would expect to take the economy LOP at 2700, but could envision weather scenarios and such where I want every bit of speed I can get. Just looking for options.

When I go LOP and RPMs drop to 2700 I am at 75% power. My interpretation is that the 75% guideline is the running state not the starting state before leaning. Furhter, Dan Horton posted some interesting test data on detonation. It showed no detonation at any mixture setting with a 2700 / 26" configuration. In my example, my MAP was under 25." It seems that the detonation risk increases as you get over square. This is logical, as the engine is "working" harder. High MAPs relate directly to "load" and my experience with auto engines is that most bad thing happen under heavy loads (low vac / high MAP).

Larry

The EZ Community has been running a big fleet of O-320's propped to allow 2,750 -2,800 RPM cruise for decades. Mine runs 2750 WOT at 15,500. Mahlon and the crew at Mattituck told me don't worry about it. My Red Gold overhaul came after 2,200 hours on a std Mattituck overhaul at mostly high RPM cruise. Mahlon told me the engine was perfect inside and could have flown a thousand more hours. High RPM, low manifold pressure operations is easy on the engine. What Mahlon did warn me about was high very high RPM descents (like above 3,000) at very low throttle settings as they felt the it loaded the piston rings "wrong".

I always fly LOP at WOT cruise. ALWAYS

EZ's "require" high RPM cruise to permit enough static RPM to get the things off the ground - no propwash over the elevators to assist in elevator authority/rotation.

I guess if speed is your only priority, but what about Noise and comfort ?

R/M
 

Lots of history with the 0 360 in aerobatic airplanes turning 3500 r/m. No significant history of any problems that could be considered r/m related. Most overhauled at 1200/1400 hours, rarely any problems found at teardown. The 0 320 is even better, shorter stroke means less wear.

I've heard the only potential "issue" with high RPMs can be valve "float", where the standard springs don't quite keep up the necessary rotational timing. But I don't think that's an issue till you get closer to 3000 RPM. I think Lycoming considers "over speed" is 110%.

Deek is absolutely right about the EZ fleet running hi RPMs for thousands of hours of history.

Lets not forget about all those Lycoming helicopter engines running at elevated RPM - some with the same TBO as the aircraft versions