[brad walton]

What are the dangers of running high RPM's aside from more fuel consumption and higher rate of engine wear? I ask because I have a Catto 3 blade and Superior IO360 and I can easily reach Van's numbers for an RV-8 at 8000 DA and 2700 RPM's. But I have a considerable amount of throttle left and could go faster if willing to exceed the 2700 RPM redline Superior suggests and accept the higher fuel burn. At WOT, I can exceed 2700 up into the teens altitude.

 

[Toobuilder]

It's not usually the engine itself that's the problem, but the prop (or prop/engine combination). For example, the (H)IO-360 on the -8 that I fly is rated at 205 HP at 2900 RPM, but I would not swing the Hartzel that fast as a matter of course.

The Reno and acro guys often run at 3000 RPM or higher with fixed props.

Lots of fuel, and shorter TBO are the main drawbacks.

 

[RVDan]

Think of engine life in terms of inches of piston travel. The faster you turn the engine the less time it will operate before wear takes it's toll.

If you can get proportionately more speed from the extra RPM's so you travel the same distance per RPM, than it is break even. This is not likely though.

The higher surface speeds will also likely reduce life even more as the lubricants get pressed to their limits.

Another advantage for a CS prop.

 

[Low Pass]

Good points already listed. All dynamic loads (those resulting from things moving) increase exponentially with speed. Just keep that in mind.

 

[Rupester]

I have a Catto 3 blade and Superior IO360 and I can easily reach Van's numbers for an RV-8 at 8000 DA and 2700 RPM's. But I have a considerable amount of throttle left and could go faster if willing to exceed the 2700 RPM redline Superior suggests and accept the higher fuel burn. At WOT, I can exceed 2700 up into the teens altitude.

FYI ... A lot of us with Catto 3-blades (in different model RVs, either 0-320 or 0-360) find we can easily exceed 2700rpm at 8000+. I, for one, throttle back to keep it 2700 or under, per engine builder's recommendation.

 

[airguy]

Sounds like you need a little more prop...

 

[brad walton]

Good points all. Thank you. I guess that is what I expected to hear. Not sure if I need more prop if I am getting Van's numbers at 75% power/ 8000 DA. Maybe, but it is a compromise. I would hate to give up the current great rate of climb and at less than 2800 RPM's I can easily exceed Van's numbers. I have been cruising at 2450 RPM's on less than 8 GPH ROP 6000 to 8000 DA and getting about 162 knots. But clearly not using anywhere near 75% power with that burn rate. And yes, that is where a constant speed prop would be of benefit.

 

[Robert Anglin]

To pitch or not to pitch.

The points made above are very good ones. The dynamics of a prop engine unit are complex. In the old days with a factory engine I would say keep the RPM's down to the called out spec.. Today you have a nice well balanced engine and a light weight wood core prop. It is a good engine prop match to go up 1500 RPM's over 2700 with. However it sounds like you are pitched just on the outside of the box on the climb side with this prop. A very good prop and good people that made it. For my money I would call Catto and ask them if they would re-pitch it a little for you, but don't go overboard as it sounds like it is close to what works for your application. Yours as always R.E.A. III #80888

 

[n5lp]

I have a Sensenich 72FM8 metal prop that is about like that. I have come to like it. I have to pull the throttle back until quite high altitudes to stay below 2700 RPM in level flight but it climbs better that way and I still keep up with other RVs just fine until the descent. If I really want to go fast the option is there to go up to 2850 or so and embarrass the constant speed folk, not that I would ever really do that. I have not and do not want to repitch it.

 

[alpinelakespilot2000]

Craig Catto repitched me from 2850 rpm to about 2720 rpm. I gave up nothing significant in the climb but can now pretty much run WOT which adds efficiency value and also allows for better fuel distribution on my carbed engine. That, in turn, seems to result in more balanced CHTs and also greater ability to run a bit further toward LOP.

 

[N434TM]

I also think you need a bit more prop, if it were me.

Regarding high rpm, over 2700, I do it only for racing at Reno or testing for racing at Reno. It is very satisfying when this engine gets in the upper range. Everything seems to come alive and really starts to run! The fuel burn obviously being ridiculously high, the other thing to watch is oil temp. RPM = Heat I have my setup to just keep it in the yellow by the end of the race. Not too much air, not too little, perfect. So something to consider, or at least keep an eye on.

 

[jrs14855]

overspeed

1000 hours in a Pitts S1, all aerobatic flights were 3300-3500 rpm, never backed off on the power except for spins, snap rolls and to stay below Vne.
Engine had perfect compression at 1000 hours, never any metal in screen. Oil changes every 20-25 hours. O 360A4A with PS5C carb.
The typical cross country racers that I have talked to with fixed pitch are running 3000-3100 r/m.
Reno gold biplane racers by the sound are running 33-3500 r/m.

 

[N941WR]

Mel, help me out here...

I believe Lycomings are designed to make TBO at 75% power while running on the redline.

 

[n5lp]

Mel, help me out here...

I believe Lycomings are designed to make TBO at 75% power while running on the redline.

I am not near as smart as Mel, but I have never seen anything from Lycoming that would indicate a reduced recommended TBO on our typical engines due to operation at less than 100% rated power at 100% rated RPM.

 

[SHIPCHIEF]

I'm understanding the 'total inches of piston travel until worn out' concept, but I would like to consider that cold air compressors last darn near forever.
I think all of us agree that cylinder head temp is a big factor.
One major diesel manufacturer determines TBO by fuel used. The model I'm familiar with was expected to burn 440,000 gallons of fuel to reach overhaul.
(that would take us a while )
You may re-think your position. You might have the perfect prop right now.
Short takeoff, great climb, excellent standard cruise, and a very powerful dash. RPM of 2900 for those periods won't be a problem if the head temp is cool enough.
More pitch might make the landing a tad longer?

 

[Walt]

I am not near as smart as Mel, but I have never seen anything from Lycoming that would indicate a reduced recommended TBO on our typical engines due to operation at less than 100% rated power at 100% rated RPM.

Lots of info out there on this, do you really think you can run your engine at 100% rated power and have it last as long as one run at 65% power?

Just one quote from the Lycoming flyer:

For maximum service life, maintain the following
recommended limits for continuous cruise operation:
(a) Engine power setting - 65% of rated or less.
(b) Cylinder head temperatures - 4OO?F. or below.
(c) Oil temperature - 165?F. - 220?F.

 

[n5lp]

Lots of info out there on this, do you really think you can run your engine at 100% rated power and have it last as long as one run at 65% power?...

Personally, I doubt it and did not say that. I stand by my statement.

 

[brad walton]

Saturday 1-11-14

Yesterday, two on board, almost full fuel, 4000 DA, WOT, 2790 RPM, I was able to get 186 KTAS. So far I have only done this for short periods of time. Most of the time I am at 60% power or less for fuel burn and engine wear reasons. I do make sure my CHT are well below 400F and oil below 200F.

 

[Walt]

Personally, I doubt it and did not say that. I stand by my statement.

Lycoming repeatly makes the statement that operation at the "recommended" power settings will allow an engine to reach TBO.

Show me a single aircraft POH that recommends 100% power operation at anything other than TO and I will concede.

I can show you many statements, like the one below from Lycoming, that conflict with your statement.

"Operation at the recommended cruise RPM settings should
allow the engine to reach TBO if it has regular oil changes, is
operated within normal temperature ranges and is well cared
for by pilots and maintenance personnel. Longer engine life may
be expected from most engines when the operator is willing to
sacrifice maximum performance for conservative cruise operation
in the 60% to 65% power range."

 

[Toobuilder]

I think we are all smart enough to realize that "TBO" is more of a regulatory number than an operational absolute. And most will concede that an engine run easier will generally last longer than an engine run harder.

That said, I believe you could bolt a 180 Lycoming to an irrigation water pump or generator at sea level and run it at 180 HP for 2000+ hours with proper cooling and clean oil. In fact, stationary engines have one of the best operational lives possible because of the stable temps and low cycle times.

Frequent, long, and stable flights are the biggest determinant to engine life. I have no hard data to point to, but I'd have to opine that a fixed pitch Lycoming that does frequent long cross country flights buzzing at 2900 RPM is going to live a longer life than a whole bunch of the infrequently flown, "low time" offerings available at the local FBO.

 

[SHIPCHIEF]

Brad, you might have the perfect prop. Test again at 8000 DA and 12000 DA
and report back!
This is a subjective area, but it takes Horsepower to get speed. HP is about linear with RPM, so you are getting more power than a constant speed prop equipped plane, whose governor limits the engine to 2700 RPM.
Few people cruise at full throttle, the fuel consumption is too high. If this is you, then enjoy the usual 160 KTS and keep that high power speed dash up your sleeve for the occasional SARL race.
If Bob Axom were alive, he would be commenting here!

 

[David Paule]

....Few people cruise at full throttle, the fuel consumption is too high....

With a constant speed prop, and above 8,000 feet, I'd expect that people cruise at full throttle fairly often. I do.

On a trip, it's routine for me to take off at full throttle and leave it there. At cruise altitude, drop the rpm to what I want and leave it there. For the descent, I'll pull back on the throttle to a low-cruise setting and reduce rpm to a low-cruise setting for a gradual fast-cruise descent. I'll have to reduce throttle periodically, of course, as the air gets thicker and the manifold pressure increases. In the pattern at the destination, bring the throttle back as needed while the rpm goes to the go-around setting. From that point, the prop stays fixed and the throttle is used. Of course, I lean and make it richer as appropriate.

Remember that I fly from Colorado. Your field might be below 5,000 feet and that might affect your procedures.

Dave

 

[SHIPCHIEF]

Yes David,
That's true. Especially for constant speed prop equipped aircraft.
I cornered myself into thinking of common local flights.
I fly my Thorp T-18 at full throttle just about everywhere I go, because it has an O-290 and my wife and son both have RV-4s with O-320s. They have to lollygag to 'let' me keep up! It runs 2650RPM @4000DA,but when I let the nose down a smidge, I don't mind if it runs up to 2900RPM
I'm not concerned about running at or 10% above 2700 RPM, given Mahlon's comment about helicopter engines running at higher RPMs yet being filled with many of the same parts as aircraft engines.
That being said, higher RPM is more fatiguing to the pilot.

 

[Mel]

Mel, help me out here...
I believe Lycomings are designed to make TBO at 75% power while running on the redline.

Lycomings are indeed designed to reach TBO @ 75% power. Typically 2700 rpm @ 5,000' is very close to 75%.
I don't like to use the word "redline". I prefer to use "rated" rpm. Redline seems to infer that you should never exceed that value. I don't think that is the case here. Maybe I missed it but I don't remember seeing anything in the Lycoming manual saying "never exceed 2700 rpm".
Obviously running any engine harder will result in a shorter TBO. However, most Lycomings, if properly cared for, will exceed 2,000 hrs. easily.
I've seen many run well into the 3K hrs.
I got over 2800 hrs. out of my first run, and even then every part I removed met better than serviceable specs.