Ovation Critical Altitude

[Fipdublin]

For the Ovation drivers out there. Based on the book power settings, I haven't  been up high enough yet to run out of MP. What seems to be that altitude for you?

[gsengle]

What do you mean run out of MP? You start losing it at maybe 2500 and by say 6500 you can no longer get 24...

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[Fipdublin]

I'm usually flying at 9000 or 10000 feet. Using the power settings for 65%, there is still plenty of black knob to push in at that altitude. Just wondering at what altitude you can run 65% and max out your throttle.

[gsengle]

I always run full throttle that's most efficient, when I'm up above 5k. Then lean appropriately.... Not sure why I'd ever pull back the power at those altitudes, so, no idea...

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[carusoam]

Since MP is a function of altitude in our NA engines and MP drops off at 1" per 1000'...

It's a PIC decision of how high you want to go balanced with how quickly you want to go somewhere...

My favorite altitudes are 11k' and 12k'. WOT, 5°F LOP, No bottled O2, and a lot of spare potential energy.

Best regards,

-a-

[Txbyker]

I ran some numbers on my last flight all WOT, OAT 18C, A/C off, 80 gallons,

LOP 8000 ft, 22.3MP, 2400RPM, 171kts, 13.1gph

ROP 8000 ft, 22.5MP, 2400RPM, 174kts, 18.3gph

LOP 9000 ft, 21.5MP, 2400RPM, 169kts, 12.7gph

ROP 9000 ft, 21.5MP, 2500RPM, 177kts, 17.1gph

Interested to see what others may be getting.

Russ

[Fipdublin]

Thanks.

At 9000 If I use the visor power settings for 65%, 2400 RPM, I think the MP was round 20", 14.2 gph,(ROP), 170 true.

[Jeff_S]

That actually seems a bit slow for that fuel burn. Did you pull throttle back to 20" for some reason? I guess that would slow you down but it's not the most efficient way to run the engine. Realize that above 8500' you cannot generate more than 65% power at any setting so you can run the engine wherever you want and not worry about detonation. 

I have to admit I don't pay any attention to the visor charts -- even though now with my sunglasses/readers I can actually see them again!   I'm a WOT/LOP guy at any cruise altitude unless I'm just loafing around to burn dinosaur juice.

[kortopates]

If the intended question was how high can the Ovation go, that's generally referred too as the Service Ceiling - which is actually the altitude at which Vy climb rate drops to 100FPM. Of course it will even go a bit higher to its Absolute Ceiling (max altitude the aircraft can sustain level fight) - but you likely won't find any data on that. The Service Ceiling though is in your POH and is just a bit over 20K Feet in ISA conditions at max gross.  Critical altitude doesn't apply to normally aspirated engine since its the altitude ceiling at which the engine will no longer produce 100% power when exceeded - which is sea level for a NA aircraft. If you've only been up to 9 or 10K so far, you have lots of usable altitude above you but will need supplemental O2 to take advantage of it above 12.5K.

[Cruiser]

On 5/17/2016 at 11:53 AM, Fipdublin said:

I'm usually flying at 9000 or 10000 feet. Using the power settings for 65%, there is still plenty of black knob to push in at that altitude. Just wondering at what altitude you can run 65% and max out your throttle.

If I understand the question correctly, You will run out of MP about 14,000' above that altitude you cannot maintain 65% power. The Ovation will operate well above that altitude on less power however.

[THill182]

I think I understand the original question, as I have been wondering the same; for reference, attached is the power-setting chart for the 310hp Ovation.

According to what I have read about running the IO550 LOP, presumably, above 9000 ft or so there is no Red Box because the engine doesn't make enough power.

BUT that after paying for a premature engine overhaul, I "baby" my engine, and usually don't run above 65% power in cruise. According to the power chart, this happens somewhere at/above 12,000 ft. That is actually consistent with my observations, i.e., I can get more MP at 9,000 ft (or above) than what is listed in the power chart for 70% power.

I actually made my own simplified power chart (see PowerAt2600RPM-M20R, attached) to figure out what 65% power means when running LOP, relative to my original 270HP and now converted 310HP.  I usually try not to exceed 21.5 Inches of Mercury while cruising at any altitude, and then run LOP and lean using standard procedures to 50 degrees LOP. I then use the attached table to verify that I am below 65% power (at/below 13 gph ff). 

Usually, I can get 65% power all the way up to 10,000 ft or above... Above 9,000 ft that gives me 170kts or better (note that I have  a TKS system and air conditioning, both of which slow you down a bit).

 

Hope that clarifies things a bit. Curious what others think of this procedure, and or experience regarding engine operation on engine longevity.

 

 

 

 

 

[gsengle]

Personally I think that's overly conservative....

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[carusoam]

A couple of questions regarding the math...  (It is still early, forgive me if I missed something)

1) What is the baseline HP for an O, 270 or 280 hp?

2) The STC inconveniently left out a column for 65% power.  Did you just average the two columns together (60&70)?

I had one engine OH in reserve. That got used up. This engine needs to last a long time.

Best regards,

-a-

 

[Cruiser]

2 hours ago, THill182 said:

BUT that after paying for a premature engine overhaul,

can you tell us more about this? Are you suggesting you had problems because of how you ran the engine?

[THill182]

Regarding the "math" (how to convert fuel flow to HP when running LOP), we had a discussion about this here:

Regarding this being a bit "conservative": Absolutely! I enjoy flying, and 10 minutes or less time saved on most flights isn't worth pushing my engine for me.

However, I have a "bad" history of engine work. There is a long story, but the short of it is that when I bought the plane used with a few hundred hours, the previous pilot ran it according to book numbers (ROP, and 75%). I continued the same, and saw very high CHT's and also burned a lot of oil. At well under 800 hours I had cracked cylinder heads and a top overhaul. Since then I am running LOP and at "reduced power".  Recently I have seen some interesting fluctuation perhaps in oil usage, but overall the engine has been doing well for over a thousand hours.

 

I don't know what the best practices really are, other than pushing the engine less is probably better than more, and flying often is good...

 

 

 

[Mcstealth]

On May 17, 2016 at 0:48 PM, Txbyker said:

I ran some numbers on my last flight all WOT, OAT 18C, A/C off, 80 gallons,

LOP 8000 ft, 22.3MP, 2400RPM, 171kts, 13.1gph

ROP 8000 ft, 22.5MP, 2400RPM, 174kts, 18.3gph

LOP 9000 ft, 21.5MP, 2400RPM, 169kts, 12.7gph

ROP 9000 ft, 21.5MP, 2500RPM, 177kts, 17.1gph

Interested to see what others may be getting.

Russ

How much lop, how much Rop?

[Jeff_S]

THIll, you've obviously done some in-depth analysis and I agree it's fun to be a test pilot in that way. More interesting than just boring holes into the sky. But I can't really tell from your chart where there is allowance for density altitude differences, which will factor in both non-standard temps and increasing altitudes. It seems a bit complicated to try to follow this chart rigorously in-flight. But the guidance from GAMI folks and Mike Busch has always been that there is no red box above 8500' density altitude, meaning that no NA engine will produce more than 65% power at those altitudes. How are you determining that you can get 65% power up to 10,000'?

And absent pulling out your chart, do you have any general rules of thumb that you use? For me, if I'm trying to get anywhere, I'll pick the best cruise altitude for winds and terrain, then I'll fly 2500 RPM if I'm into the wind, 2400 RPM if the winds at my back, WOT all the time and LOP to achieve 173-175 KTAS. This invariably has me between 14.5 gph at lower altitudes and 12.5 gph up high, with CHTs in the low 300s. That seems about conservative enough for me, and easy to administer.

[THill182]

37 minutes ago, Jeff_S said:

THIll, you've obviously done some in-depth analysis .......For me, if I'm trying to get anywhere, I'll pick the best cruise altitude for winds and terrain, then I'll fly 2500 RPM if I'm into the wind, 2400 RPM if the winds at my back, WOT all the time and LOP to achieve 173-175 KTAS. This invariably has me between 14.5 gph at lower altitudes and 12.5 gph up high, with CHTs in the low 300s. That seems about conservative enough for me, and easy to administer.

First let me say: I am strictly an amateur -- the computations were mostly to satisfy my own curiosity and I have no idea if they are really meaningful.

Having said that: I was curious because I routinely would get more MP than what the standard charts said. Obviously, outside conditions (temps, pressures) have a lot to do with that. Also, I am using the K&N air filter and they claim you get up to one Inch more MP than the off-the-shelf standard filters (I never verified that myself with before-after tests; see http://www.challengeraviation.com/accessories.html ).

Running LOP, where you burn (almost) all gas, I understand that the HP that is generated is mostly a linear function of fuel flow (FF). Since I fly in cruise at 2,600 RPM I just wanted to know for myself how different FF's convert into percent-power based on the original 270HP my engine used to have (Ovation II) and after the 310HP conversion.

Anyway, I also see CHT's in the low 300s LOP, with about 12.5 gph at altitudes above 7000ft or so. My speeds are perhaps 3-5kts less which happened after I added TKS (wing is no longer as efficient). One difference is that I will pull back the power at lower altitudes so I also end up with 12.5 gph or so (below 13 gph); again that is my "weirdness" being overly conservative (when I fly low I usually don't go far, so it doesn't matter; on long x-country trips I usually go above 10,000 ft unless weather doesn't permit it).

It seems from this discussion (and others) that one of the operational differences is that most other Ovation drivers choose a lower RPM for cruise (2400, 2500); I always cruise at 2,600. Not sure if that will have an effect on longevity. My engine does run exceptionally smooth at that RPM. 

 

 

[THill182]

On ‎5‎/‎17‎/‎2016 at 0:48 PM, Txbyker said:

I ran some numbers on my last flight all WOT, OAT 18C, A/C off, 80 gallons,

LOP 8000 ft, 22.3MP, 2400RPM, 171kts, 13.1gph

ROP 8000 ft, 22.5MP, 2400RPM, 174kts, 18.3gph

LOP 9000 ft, 21.5MP, 2400RPM, 169kts, 12.7gph

ROP 9000 ft, 21.5MP, 2500RPM, 177kts, 17.1gph

Interested to see what others may be getting.

Russ

That is what I wonder about: So first, I get pretty much the same numbers. Very similar.

But when you look at your MP at 9000ft (21.5), according to the M20R performance chart, the max MP listed at 9,000ft is 21.1. Clearly you can get more. I always thought that the performance charts above 8000 ft show WOT, and so the max MP you can get out of your normally aspirated engine...(?)

[Cruiser]

A couple of things I can think of about the 310 HP upgrade.

The engine is the same. There is nothing different in the IO550G. 

The change that gives the extra horsepower is the increase in maximum rpm from 2400/2500 to 2700. So, the performance should be identical for the three different configurations BELOW the maximum rpm limits. (changes due to propeller efficiencies excepted)

[Robert C.]

OAT of 18C at 8000 is well above standard adding about .4 to mp if I understand the chart correctly which is about what Russ seems to report.

[Fipdublin]

Lots of great information thanks for the continued discussion . What a great aircraft. I'm coming over from a C182 so I think you all must know how impressed I am about the efficiencies and speed of the m20r.

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[Txbyker]

On May 22, 2016 at 1:35 AM, Mcstealth said:

How much lop, how much Rop?

I was running -25 for LOP and 100 for ROP.

[THill182]

8 hours ago, Fipdublin said:

Lots of great information thanks for the continued discussion . What a great aircraft. I'm coming over from a C182 so I think you all must know how impressed I am about the efficiencies and speed of the m20r.

The M20R is a great travelling plane; much more efficient than the C182. I came from a C182RG many years ago. If I were to give advice about some gotcha's:

1. The engine needs to be babied; study and be conscious of temperatures, power settings, etc. There is lots of info out there (e.g., Deakin's articles on how to run the big-bore Continental). My 182RG had a Lycoming O540 which pretty much was bullet proof, and you just ran it "however"; can't do that with the IO550G.

2. Landing took some getting used to for me. Speed control is critical for landing the M20R. The most common M20R accident by far is bouncing on landing, and then hitting the prop. Landing the M20R is not difficult at all, but you cannot force it onto the runway when your speed is too high to land. I never had to go-around in my C182RG; I had to go around in my M20R on a few occasions when I couldn't make the landing speed work. Practice will automate that over time....

 

Else: Great choice!

[mike_elliott]

9 hours ago, Fipdublin said:

Lots of great information thanks for the continued discussion . What a great aircraft. I'm coming over from a C182 so I think you all must know how impressed I am about the efficiencies and speed of the m20r.

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Coming from a 182, Consider spending a few hours with a Mooney instructor to learn the fine points of that great airplane. It will pay dividends in the long run, possibly save you some huge $