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Highest safe RPM for fast cruise

dwilson

Well Known Member
Simple question, but haven't found an answer yet.

What is the highest RPM suggested for cruise in my RV10 IO-540 D4A5. (The one Van's sells with the fancy roller tappets)

I like the speed I get out of 2400 RPM. Is 2500 safe? how about 2600?

Thanks,
 
Safest? You can safely run to your maximum rated rpm of the engine all day long within limits. You might not like your efficiency however. Also, your prop has recommendations for maximum and continuous operation.
 
Safe RPM limits

When you say "safe" consider that Lycoming says the plane can go to TBO running at 2700RPM continuously.
I run 2300-2400 usually, there really isnt an unsafe RPM on the high range (well unless its higher than the designed 2700RPM), unless of course your CHT's start to climb into the mid 400F range.
Pascal
 
Good information

When you say "safe" consider that Lycoming says the plane can go to TBO running at 2700RPM continuously.
Pascal

Can you please give me a reference for this information? So far I haven't been able to find that particular piece on info in the Lycoming publications.

Thanks
 
When I was racing my aircraft I was interested in this discussion about 2700 continuous rpm. During races, 30 to 45 minutes usually, I would run flat out full power. I called Lycoming and spoke with one of the more experienced engine guys there (old guy). He told me that that although they are rated for 2700rpm, for maximum engine life, they suggested that 10 to 15% of the total time at max rpm would be advisable. This worked for me as racing was a small percentage of my total flying. For typical flights I use full rpm until 500' and then back off thus my total percentage running at full power was still relatively low even with the four or five races a year that I participated in.
 
There it is!!!

I see the entry for "Rated speed RPM." I did not know exactly what that set of words meant. It sounds like it means "go for it if you are willing to pay for the gas!"

Thanks,
 
tach time versus real time

Keep in mind tach time, what TBO is based on, "runs" faster at the higher RPM...so you will get to that wonderful destination perhaps a bit faster AND for sure your major overhaul bill even faster! :) But when it comes to safety, what you really asked about, I concur with others, if the cylinder temps are <400 F and oil temp is good you can run all day at 2700. I have never come across a limitation or warning for continuous operation of a IO-540 at 2700 RPM.
 
Keep in mind tach time, what TBO is based on, "runs" faster at the higher RPM...so you will get to that wonderful destination perhaps a bit faster AND for sure your major overhaul bill even faster! :)

True, but unless you are flying an airplane in a Part 135 operation (which experimentals can't do), the actual engine time (tach or otherwise) is meaningless and not binding regarding when you do an overhaul.
In fact, with careful operation and maintenance it is easy to go well beyond recommended TBO and then choose to do an overhaul based on condition.

Having said that, I agree in theory that higher RPM's might make the overhaul be required sooner, but I know of many instances of engines flown regularly and run hard but kept within Lyc. recommended limits, to have gone hundreds of hours past other engines that were babied all the time.
 
I'm flying a Continental these days. It's pretty routine to fly the IO-520 at 2500RPM for cruise. It has the same max recommended RPM - 2700 - as the Lycoming. Accumulated experience with LOP flying is showing that LOP operations have more to do with engine longevity than RPM or other operational considerations. Of course Continental cylinders are another issue - but that is not an RPM related issue.

The advanced engine management course in Ada, OK teaches "WOTLOPSOP" - wide open throttle, lean of peak, standard operating procedure. Their point is that if the engine is operated LOP not much bad can happen. But there are many important caveats: fuel flow must be balanced (usually means GAMI injectors for Continental engines), no induction leaks, high fuel flow (higher than Continental's recommendations in fact) on take off and in climb, etc. Leaning in climb is conservative - maintain same EGTs as on takeoff with full fuel flow. Maintain full RPM until cruise - then 2500 or whatever the engine likes (throttle wide open). "Big Mixture Pull" to lean of peak. It's lean of peak operation that gives efficiency and protects the engine - cylinder pressures can't get into the danger zone.

As others have said, the main reason to pull RPM back from 2700 is to reduce fuel flow, increase efficiency overall. That last few knots costs a lot of gas.

Not a recommendation by any means - sharing what I've experienced.
 
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An interesting consideration is the O-470-R versus the O-470-U. The -R model runs to 2700rpm with low compression Pistons making 235HP and has a TBO of 1500 hours. The -U model runs to 2400rpm with higher compression Pistons making 235HP and has a TBO of 2000 hours. This is all IIRC. Interesting how the TBO depends on rpm.

Also, while TBO is required for part 135 operations and not for part 91, I think the people talking about TBO are more referring to the time before an overhaul is needed due to condition more than the time before ov Rahul is needed because of regs.
 
An interesting consideration is the O-470-R versus the O-470-U. The -R model runs to 2700rpm with low compression Pistons making 235HP and has a TBO of 1500 hours. The -U model runs to 2400rpm with higher compression Pistons making 235HP and has a TBO of 2000 hours. This is all IIRC. Interesting how the TBO depends on rpm.

Also, while TBO is required for part 135 operations and not for part 91, I think the people talking about TBO are more referring to the time before an overhaul is needed due to condition more than the time before ov Rahul is needed because of regs.

Doesn't the R run at 2600 and U at 2400? That is what the Conti literature reports. Also, can be many differences with pistons, rings, inserts, cases, . . . the list goes on. So, we have talked about this before, but each engine as different weaknesses that might affect/yield a different TBO. RPM included.
 
Doesn't the R run at 2600 and U at 2400? That is what the Conti literature reports. Also, can be many differences with pistons, rings, inserts, cases, . . . the list goes on. So, we have talked about this before, but each engine as different weaknesses that might affect/yield a different TBO. RPM included.

Actually, I think you are right that it is 2600. There may be other factors, but the internals of he engine are pretty much the same. The rpm is the major difference that increases the TBO.
 
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