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Max Continuous RPM IO360 (180hp) - RV6

F

fbrewer

Well Known Member
Members,

I currently operate my IO-360 with a maximum RPM of 2700 and then reduce to 2450 rpm for climb an cruise.

But, I cannot find any specific limitation.

In the Lycoming Operating Manual (IO-360-M1A) I can find no specific limitation of MAX continuous RPM at cruise.

It hints at 2450 being 75% power, but no real state limitation.

What are your thoughts on MAX continuous RPM at cruise in the IO-360?
 
OH boy.

I don't think you are going to like any answer on this one because there are so many things to consider on this subject. If you have a type tagged engine an aftermarket kit engine., How well is it balanced, what compression is it. WHAT YOUR COMFORTABLE WITH, and so on and so on. Your are talking about an EAHB here I hope. Most of the books with list 2700 to 2750 as a good top end red line. Then "RED LINE" is another long topic. If you race, those figures are some what higher. In the field I think most people are comfortable with the 2700 to 2750 numbers. But it is your call with your engine in your EXPERIMENTAL. Yours, R.E.A. III # 80888
 
fbrewer said:
In the Lycoming Operating Manual (IO-360-M1A) I can find no specific limitation of MAX continuous RPM at cruise.


What are your thoughts on MAX continuous RPM at cruise in the IO-360?
Click to expand...

You cant find a limitation because in the vast majority of cases, there isn't one. If you want to run your engine at 2700 for every hour of it's life, then you can. The engine is designed with adequate cooling and lubrication to handle 100% power without limitation.

In most cases where there is a limitation, it's really the prop that the LIMFAC. In some cases it's structural, and in some cases its regulatory (noise). You will note that there are several 360 variants that have a max RPM of 3200... These are generally Helicopter engines, but share virtually identical internal components. And in some cases, the rods and crank are the same part numbers as the "airplane" versions, yet have these higher numbers.

So generally, feel free to spin it up to "max" and leave it there as long as you need to.
 
2700 is perfectly fine. FP set-ups often cruise high rpm.

4-bangers have natural intensified resonance bands between 2600 and 2700 and 2100-2300. Hartzell recommended avoiding continuous operation therein with their heavy aluminum clubs. But that's a prop restriction, not engine, and isn't an issue with composite props that better adsorb vibrations.

I firewall everything until I reach my chosen altitude them dial MP and RPM to suit, set mixture. Lower RPMs are more comfortable for me in cruise; cruising at 2700 would drive me nuts (nuttier?) unless I really, really, want to make max HP. Then there's a world of efficiencies, temp control, yada, yada, to consider. YMMV.

Root around AvWeb for Jim Deacon articles on engine operation. Highly educational.

John Siebold
 
Rated (recommended) red line RPM is the max. anytime (continuous, take-off, etc.)
Max continuous power is 75%..... what ever combination of RPM and MP gives you that power value.
Experimental is not limited by these limits.
Many RV's with fixed pitch props run high RPM with low to moderate MP at altitude to help narrow the compromise gap when compared to the performance attainable with a constant speed prop.
A benefit of a constant speed is that you can get 75% power at a variety of MP and RPM combinations.

With a constant speed (and being able to run lower a lower RPM in cruise) you get the benefit of lower noise level.
Often a slightly lower oil temp.
Slightly lower internal parts wear per hour of operation on the engine. Etc.
 
It all depends on which prop you are operating- for example the Hartzell 7496 blades used on an O-360-A1A should only use 2700 rpm for takeoff and reduce to 2600 rpm afterwards. I believe this is stated in the prop manual but I don't have it in front of me. Here's what Vans says-
https://www.vansaircraft.com/pdf/Hartzell_c2yr.pdf
 
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Like Scott said, 75% (not rpm) continuous is a conservative limit, though IIRC, some engines have been rated for continuous operation at rated power.

Get a Lycoming operating manual and look up the rpm required for 75% power at around 8000 feet altitude.

edit: The rpm limit with various props is a *propeller* limit; not an engine limit. Significant difference.

Check out:
https://www.google.com/search?ei=ZZWqWrSULaLGjwTCp7jADQ&q=cobra+biplane+racer&oq=cobra+biplane+racer&gs_l=psy-ab.3..0i30k1.7976.9720.0.10251.7.7.0.0.0.0.199.987.0j6.6.0....0...1c.1.64.psy-ab..1.6.969...0i7i30k1j0i8i7i30k1j0i7i10i30k1.0.2m9uyjkBs3Q
(Cobra Reno biplane racer using a Midget Mustang I fuselage)
This plane flew airshows for years after its Reno career. O-320 (with a metal prop). Typically ran 3000 to 3300 rpm on cross countries to/from airshows, and close to 4000 when racing or flying airshow routines.

Charlie
 
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Whether the limit is an engine limit or prop limit is not the point. The title says "Max continuous RPM". You cannot ignore the prop limitation.
 
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fbrewer said:
Members,

I currently operate my IO-360 with a maximum RPM of 2700 and then reduce to 2450 rpm for climb an cruise.

But, I cannot find any specific limitation.

In the Lycoming Operating Manual (IO-360-M1A) I can find no specific limitation of MAX continuous RPM at cruise.

It hints at 2450 being 75% power, but no real state limitation.

What are your thoughts on MAX continuous RPM at cruise in the IO-360?
Click to expand...

Let is talk about this from a classic engine design standpoint. That was based on piston speeds, 2200 ft/min for short run high power, 2000 FPM for longer term intermittent operation and 1800 FPM for true 24/365 continuous operation. The limits are based on many issues including advertised life, expected life, warranty, fuel consumption etc.

1800 fpm is 2468 rpm for the 360. You are at the right range for that. Compared to 2700, your ring grooves will be cooler, piston thrust forces lower, and valve guide temps cooler. Maybe Vlad will tell us what he runs to get 3000 hours if life!

All that being said, much depends on the specific engine and it's actual operational limitations. This Lyc is from the older era but does use modern rings.
 
0 360

In the era when 180 hp fixed pitch Pitts was the dominant aircraft in competetion, those engines survived 3300-3500 rpm for 1200 hours, which was the aerobatic TBO in that era.
The geared engines in various Lycoming powered fixed wing airplanes survived at rpm's in the 3500 range. The TBO on those engines was much lowere but not necessarily related to the high rpm. Aircraft with the geared Lycomings included Twin Bonanza, Queen Air, Aero Commander, P Navaho and Helio.
 
The IO-360 is type certificated engine. The FAA's Type Certificate Data Sheet is a nice thing to become familiar with. The FAA has TCDS available on line.

It does indeed list your engines RPM limitation. In all likelihood, you already knew it....its 2700 RPM. Some variants have some different limitations....I saw a 2400 RPM, and a 2900 RPM for the HIO variations. There are lots of other nuggets of info you might be interested in besides RPM.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/299fa3d6aef0ba048625821e0072188a/$FILE/1E10_Rev_28.pdf
 
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