Ovation cruise RPM selection

[r0ckst4r]

I was wondering what people's opinions were on cruise RPM selection.  The cruise chart gives power settings for 2300, 2400, and 2500.  I've heard some people talk about lower RPM settings being better in the long run for engine life and it by the chart is seems to use slightly less fuel.  Is there a reason to set the prop at higher RPMs?   Any difference in speed using a different propeller RPM for a given power setting (ie 75% power)?

[carusoam]

O1... max rpm 2500rpm... set it and for get it...

The MAPA manual has a perfect explanation for all things IFR flying and the O (and other Mooneys)

O3 powered Mooneys... 2550... because any faster... the economics of fuel aren’t worth it... unless you a have a corporate fuel card...

 

you will never know the difference in terms of engine wear vs. rpm...

Higher rpm, burns more gph... heat may be a challenge...  so be aware how to handle heat...

Some people like to descend with a slower rpm... lower drag...

Same issues for climb... 2700 rpm is great... FF is large, heat needs to be managed...

PP thoughts only, not a CFI or mechanic...

Best regards,

-a-

[M20S Driver]

Full throttle,  2400 rpm LOP over 7000 feet, and  2400 to 2500 rpm at 75 deg ROP with 20-22 inch MP in short flights. 

The 2400 rpm LOP is more quiet and less vibration and kinder to my pocket.  It gives me 172-176 Knots TAS .  Most of my short flights are 2400  75 deg ROP 65% power or less.

Bob Minnis commented that you can fly the io550 at 2700 rpm all day and not damage it as long as you can afford the fuel.

 

Driver

[ilovecornfields]

I think some have argued that the O3 prop is most efficient at 2550 RPM. I like 2300 RPM WOT. Seems that the engine is smooth and happy at that setting and if I’m going far I can really get the MPG up that way. I could get there a few minutes faster by burning a lot more fuel but not really worth it 99% of the time.

[PMcClure]

If I want to get somewhere fast, I cruise at 2500. With pax on board I may fly 2300. It’s quieter And smoother at 2300. But 2500 is in the green so I see no reason you couldn’t fly there all day if you wanted. The difference in fuel efficiency isn’t enough to concern me. I have never had anyone complain about noise and vibration at 2500 but have had several comments about how smooth it is at 2300. Mine is limited to 2500, some ovations can go up to 2700.

[r0ckst4r]

Thank you for the information.  Yes, I should have clarified this is an O1 IO550G.  It also has a TKS prop if that makes any difference.

[Cruiser]

Mike Busch recommends high MP and low RPM for best efficiency .

This is the IO-550  Continental graph on friction HP loss. Notice you lose about 7 HP to friction going from 2200 RPM to 2400 RPM. 

[PT20J]

IO-550 has 4.25" stroke x 2 per revolution /12 in/ft x  100 rpm x 60 min/hr x 2000 hr / 5280 ft/mile = 1610 miles of piston ring travel over engine life per 100 rpm

[GeeBee]

Your fuel economy will be better at low RPMs because each cylinder has more time to extract the BTU value of the fuel provided. While BMEP will be higher, your engine can take it. That said, there is a Continental SB not to go below 2300.

 

 

[Mooney217RN]

I have the Ovation 3.  I fly it in cruise at full manifold pressure, 2450 RPM.  Going any more on the RPM gives you nothing in the way of speed increase.  It just tosses fuel out the exhaust as far as I am concerned.  I generally fly around 10,000' MSL.

[r0ckst4r]

From what I've been seeing it doesn't seem that there is any benefit to cruising at higher RPM.  Maybe I'll try some experimentation on a long flight to see if my TAS changes but if all things are equal 2300 looks like the best choice on paper.

[StevenL757]

Optimal cruise RPMs...

• IO550G - 2500RPM
• IO550N - 2550RPM

These coming from Bob Minnis (Minnis Aviation)...former engineering director at then-TCM (Continental)...one of the co-designers of the IO550 platform, and creator/former STC owner of the Ovation3 upgrade.

Regular flight-testing has proven these to be the best RPM settings across the board.  Any lower RPMs than these have not proven to “save” the engine or allow it to run any more efficiently.

[Niko182]

My plane seems to start vibrating once i go below 2450. I dont know if its because i went from a 2 to a 3 blade prop, or because the lord mounts are original from 99. They will probably be switched out this annual.

[M20S Driver]

5 minutes ago, StevenL757 said:

Optimal cruise RPMs...

• IO550G - 2500RPM
• IO550N - 2550RPM

These coming from Bob Minnis (Minnis Aviation)...former engineering director at then-TCM (Continental)...one of the co-designers of the IO550 platform, and creator/former STC owner of the Ovation3 upgrade.

I noticed that you have an O3 and used the name "Minnis" (AKA IO550 god).  Do you mind sharing your cruise numbers LOP and ROP and  settings for low attitude short flight?  Anything you can share would be greatly appreciated as education or refresher

[r0ckst4r]

17 minutes ago, StevenL757 said:

Optimal cruise RPMs...

• IO550G - 2500RPM
• IO550N - 2550RPM

These coming from Bob Minnis (Minnis Aviation)...former engineering director at then-TCM (Continental)...one of the co-designers of the IO550 platform, and creator/former STC owner of the Ovation3 upgrade.

Regular flight-testing has proven these to be the best RPM settings across the board.  Any lower RPMs than these have not proven to “save” the engine or allow it to run any more efficiently.

Do you have any links to more information about this?

[carusoam]

Gents...

When it comes to talking to key people for awesome lessons about the Mooneys we fly...

Put Bob Minnis on your list...

He knows all things IO550... and TopProp...

And speaks as if you have known him a while...

I had the opportunity to speak with Bob while spec-ing out my IO550(N)... and selecting the thin bladed TopProp of the Acclaim...

In the end I got a personalized version of a power plant that I wouldn’t have been able to figure out on my own...

Eight years later... still pretty happy.

So... Bob is not a god. But he does shine pretty brightly.   

 

If I understand properly... Bob may be speaking at a fly-in in Florida later this year...(?)

There is some really interesting facts about what the IO550 was designed to do... and can do... Bob delivers all the details...

Best regards,

-a-

[StevenL757]

7 hours ago, M20S Driver said:

I noticed that you have an O3 and used the name "Minnis" (AKA IO550 god).  Do you mind sharing your cruise numbers LOP and ROP and  settings for low attitude short flight?  Anything you can share would be greatly appreciated as education or refresher

I'll take "low-altitude" as 8000 feet in this case as a benchmark, so in that case, I'm seeing...

• 2550RPM, 23in MP, 50LOP --> 172-175KTAS
• 2550RPM, 23in MP, 50ROP --> 180-182KTAS

Airplane has TKS, no A/C, and an NY164 TCAS antenna above the cockpit, so speeds are reduced versus many other Ovations out there.

For any altitudes lower than 8000 in cruise, plan to reduce MP to a max of 23 inches, dial back to 2550RPM, then lean to LOP or ROP as desired.

For @r0ckst4r's reply above, Bob Minnis shared this information through many 1:1 consultations with me from 2013-2014 as I was preparing to replace my "G" engine.  There really isn't anything from him directly online that I can find; however, he welcomes e-mails and phone calls about this topic at any time.  You're always welcome to call and/or e-mail, introduce yourself, and ask him similar questions.  As others have stated here, he's incredibly passionate about what he does after all these years, and will be happy to discuss.

Steve

[MIm20c]

9 hours ago, r0ckst4r said:

Thank you for the information.  Yes, I should have clarified this is an O1 IO550G.  It also has a TKS prop if that makes any difference.

Might want to check your systems. I’m going to take a wild guess and say you are looking at the heated section of the prop not TKS boots. This makes a difference when preparing to enter icing conditions. The hot prop needs to be turned on in addition to the tks to work properly. 
 

We normally cruise at 2400 or 2550. I’ve found the oil consumption can be slightly higher at 2550+ when flying above 12k (high rpm/low available Mp). 

[Guest]

There was a Canadian with a Lancair Columbia 300 who flew some amazing distances by running the 550 engine down to around 1600 RPM with no apparent harm to the engine.  Victoria BC to Toronto Ontario was one common flight.

Clarence

[ohdub]

31 minutes ago, M20Doc said:

There was a Canadian with a Lancair Columbia 300 who flew some amazing distances by running the 550 engine down to around 1600 RPM with no apparent harm to the engine.  Victoria BC to Toronto Ontario was one common flight.

Clarence

I worked him into Buttonville once, couldn't believe that he'd made it from Victoria non-stop. Also couldn't imagine why he'd want to do that non-stop!

[M20S Driver]

5 hours ago, StevenL757 said:

I'll take "low-altitude" as 8000 feet in this case as a benchmark, so in that case, I'm seeing...

• 2550RPM, 23in MP, LOP --> 172-175KTAS
• 2550RPM, 23in MP, ROP --> 180-182KTAS

Airplane has TKS, no A/C, and an NY164 TCAS antenna above the cockpit, so speeds are reduced versus many other Ovations out there.

For any altitudes lower than 8000 in cruise, plan to reduce MP to a max of 23 inches, dial back to 2550RPM, then lean to LOP or ROP as desired.

Thanks for the data Steve.   Do you use 50 deg for LOP and ROP?

Masoud

[StevenL757]

9 minutes ago, M20S Driver said:

Thanks for the data Steve.   Do you use 50 deg for LOP and ROP?

Yes.  Edited my post above to include that...thanks.

[Niko182]

3 hours ago, M20Doc said:

There was a Canadian with a Lancair Columbia 300 who flew some amazing distances by running the 550 engine down to around 1600 RPM with no apparent harm to the engine.  Victoria BC to Toronto Ontario was one common flight.

Clarence

Do you have any info on what he got fuel flow wise with a power that low?

[M20S Driver]

16 hours ago, Cruiser said:

Mike Busch recommends high MP and low RPM for best efficiency .

This is the IO-550  Continental graph on friction HP loss. Notice you lose about 7 HP to friction going from 2200 RPM to 2400 RPM. 

Does anyone have access to the prop efficiency chart for 3 bladed top prop?   It would be interesting to analyze the above chart with the prop chart.

[carusoam]

Looks like you can get 10% more HP running it up to 3krpm too...

Got to love the IO550!

Best regards,

-a-