Pwr Settings for O3 drivers

[vasco]

i have been reading on another board that the 550 engines are more efficient at lower RPM, like 2300 in cruise. My typcical settings are:

1.  Full power until i start my descent

2.  Reduce prop from 2700 to 2550 after 1500' AGL

3.  2500 for cruise. 

i typically get 179-183 ktas buring 11.5 to 12.5 gph at 11-13000' in cruise.  Would i be better running at 2300 versus 2500?  i thought i would ask before playing with the settings.  Thanks in advance for feedback.

 

[carusoam]

Vasco,

 

Are you running 50dF LOP or peak at 13,000ft?

 

I think you will see slightly improved efficiency (nmpg) at lower rpm, but it will be produced at lower overall air speeds.  I believe, the lower rpm setting at max available mp will result in lower % power.

 

If you are looking to maximize your fuel use...LOP and low rpm are a combination that allows for maximum burn of your precious gas.  It won't be the fastest way to get anywhere though...

 

Best regards,

 

-a-

[Cris]

Vasco "a" is correct in his thinking IMHO. Here is the flight supplement chart for the O3 which uses the Midwest Mooney STC http://www.deltaaviationllc.com/Nav%20Page/ovation3/Ovation3%20STC.pdf. As a practicle matter you should typically climb at 2700 RPM for safety but you will need to keep the airspeed up in order to keep the CHT at or below 400 df particularly on a hot day. Others will advise below 380 df but in most cases you will not be at that temp for very long. These engines are made to operate WOT without an issue at 2700 rpm particularly for the 1st minutes of a flight. Climbing at  the lower RPM defeats the purpose of this engine's STC & takes longer. In cruise you will not want to fly at 2700 due to the noise & fuel burn & a more typical RPM is what the standard Ovation uses ie 2550 max. Personnally  I lean in the climb as you should & your initial burn will be close to 30 gph droping off as you gain altitude to approximately 20 GPH. In cruise I generally vary the RPM LOP to give me 190-195 knots with 330 on the CHT at 11-12 K.  As the tailwinds increase I decrease the RPM but never below 2200 to keep me at my target airspeed. Obviously headwinds change the formula in the opposite direction but that is why you have an O3. Fuel burn will vary based on the supplement above. Cris  

[Cris]

The page in the supplement to which I am referring is page 9. 

[vasco]

Thanks guys.  I will try leaving the prop at 2700 until cruise and 2550 in cruise on my next flight.  Yes, i fly 40-60 LOP, but i am only getting 179-183 ktas in cruise.  What is your fuel burn at cruise?

Thanks again!

[Cris]

Vasco -Power settings, fuel consumption, and endurance should be computed using the M20R performance charts n your POH. This is as per the 310 HP STC flight manual supplement. The STC is a little sketchy on some figures. As an example cruise climb is shown at 2550 RPM & 24 In. but no airspeed is indicated whereas the R chart shows 2500 & 24 at 120 kts. Another differance is best angle Vx. The 310 STC shows 2700 @ 75 knots wheras the R is 2500@ 85 Kts. Typical differance between ROP & LOP is 1.5-2 GPH depending on power setting, Alt Temp etc. So as an example from the R book 75% power at 7500' with 10 D OAT equals 190 Kts. @ 16 GPH ROP. & 14.5 GPH LOP This is at 2500 RPM. Above 9000 & 2650 RPM you are unable to maintain 75% power so I would think that at 12/13 K & 2300 RPM you are only producing 55% power. The 310 STC at 2550 for that alt would give you 60% @ 17.9 in. & 14.3 GPH ROP and about 12.3 GPH LOP. With all of the above we are talking true airspeed but I typically target ground speed hoping for a friendly wind at altitude which is the only reason to be there except for terrain. One last point is that your numbers for true air speed are if anything above the book for the R performance charts especially LOP. Of course it depends on the temperature at alt. when you were flying but keep in mind that you are really running out of power at those alt's & you only exacerbate the problem if you reduce RPM. You are already WOT so keep your RPM up if you want higher airspeeds & of course accept higher fuel flows. With that said you can use your NMPG on your fuel computer to adjust for the best efficiency.

[Parker_Woodruff]

Quote: vasco

Thanks guys.  I will try leaving the prop at 2700 until cruise and 2550 in cruise on my next flight.  Yes, i fly 40-60 LOP, but i am only getting 179-183 ktas in cruise.  What is your fuel burn at cruise?

Thanks again!

[ghovey]

What fuel flow are you getting on climbout at 2700/WOT at sea level at 100 kts? I currently run at 29.2 but I continue to have high CHT on climbout so I have to reduce climb or rpm. In speaking with the GAMI engineers they told me to have my A&P increase the fuel flow to the low 30's. i use GAMI injectors, 05 O3.

[ghovey]

What fuel flow are you getting on climbout at 2700/WOT at sea level at 100 kts? I currently run at 29.2 but I continue to have high CHT on climbout so I have to reduce climb or rpm. In speaking with the GAMI engineers they told me to have my A&P increase the fuel flow to the low 30's. i use GAMI injectors, 05 O3.

[carusoam]

Ghovey,

 

For comparison,

 

Yesterday in nj....

I have the O1,  max output 2500 rpm, 23.0 gph, 100 kias, 1,100 fpm initial climb rate, 1400 egt, 380 cht

 

Best regards,

 

-a-

[carusoam]

Ghovey,

 

Check your fuel flow #s.  30 gph in an IO 550 seems a bit high?

 

I read Chris' performance charts for comparison.

 

Let me know what you see in your charts.

 

Best regards,

 

-a-

[ghovey]

Carusoam,

The STC of the Ovation 310 which I have states that max fuel burn at 2700 rpm is 150-160 lbs or approximately 26.7 gph.  There are no numbers on the Cruise Power Settings chart amending the POH.  I don't think that is enough fuel to keep my engine CHT's under 400.  The main problem is that I have one cylinder that runs 50 degress hotter, but it is #3 on climbout and #5 in Cruise unless I dial the rpms back to 2400 and then everything runs within 10 degress of each other.

[carusoam]

Ghovey,

The major change of the 310 STC is the higher rpm limit.

200 more rpm, about 8% increase in rpm over the O1.  NA engine should ingest about 8% more fuel.  WOT at SL going up to 2700 rpm.

 

HP difference is 280 vs 310.  Approximately 10% more fuel burn expected using this calculation.

 

For the most part, if you operate at 2500 rpm, your numbers will probably overlay the pre STC change.

 

Some difference should be expected by the different prop, but probably on the order of a couple of percent.

 

as for excess heat, you are burning 10% more fuel, and not increasing cooling capability, that I am aware of.

 

I am still operating / leaning in the blue zone on the ships EGT during climb.  I accept whatever CHTs come with that.  I might see low 400s briefly.

 

If I want to flush more fuel through the system, lean lower than the blue zone.

 

Are you familiar/using the blue zone?

 

Best regards,

-a-

[Cris]

The fuel flow on take off will be close to 30GPH with the 310 HP STC. if properly set up. I realize that the book calls for less but as a practicle matter these IO 550 G engines are set up for the fuel flows of the IO 550 N specs. I know this from spending a couple of days at Midwest Mooney which holds the STC. Anyone interested might want to call them directly for their advice. I worked with Mat who has done many of these conversions. In terms of climb/cruise  "a" is correct  that if one operates the engine like the Ovation 1-2 one will get pretty much the same performance plus a few knots due to the prop. To keep the climb temps at 400 D you have to increase the airspeed to 120 or so & accept a reduced climb rate on a hot day. That is not necessary for the first few minutes so you will get spectacular climb rates & safty initially. The Continental Operation Manual calls for full rich during climb with a max temp of 420 D but I personnally lean at the blue zone (after 2-3 k' from sea level) like "a" and keep the temps as close to 400 as possible. So Ghovey based on your fuel flows which are low for this STC & your temp differentials I'd say your fuel system definitely needs to be adjusted. It would not surprise me to find that some mechanic at along the way reduced the fuel flow thinking he was putting the engine into the correct "specs." If you are near Flora Ill give Midwest a call. Like someone else pointed out this engine will produce best performance at 9000' & below to get the 78 percent book power.

[ghovey]

Carusoam,

I am familiar with the "bluezone" concept although on the G1000 I am not sure where it is since there is no blue zone on my EGT or CHT scales.  There is a white bar around 1450 egt that I lean to when I have climbed above 5000 and am in cruise climb at 120+ knots.  With a fairly full airplane this is around 800-600 fpm as I climb from 5-10k.  Out here in California I regularly fly between 10 and 14k because of terrain and ATC preferences.  The CHT issue is problematic on initial climbout.  After I level out to a cruise climb the CHT is usually around 400-405 on the hot cylinder. 

[ghovey]

Cris,

Thanks for the tip on Midwest

[Cris]

I'd say your CHT is to high in cruise but suspect you are ROP. Try running LOP & see if it doesn't end up around 340F at 11 K. 

[carusoam]

ghovey,

I can't find the details on my blue box, but I don't think it is as high as 1,450.  The blue box is somewhere in the range of 150 to 200dF ROP.  I recall a discussion on the Garmin system vs. the simple blue box.  I think it was left out of the earlier versions.  I don't recall why.

The Mooney 02 AFM makes reference to leaning to the blue box in the performance charts, and has garmin panels.

Check out pages 5-31 and 5-18.  These are take-0ff distance and speed distance charts where this reference is made.

"Set EGT to top of blue arc as required" 

Unfortunately, I am out of town and don't have access to my key details. My manual has not been pdf(ed) yet.  I only have a low definition photo showing where the blue box is....

Cris, do you have the Garmin panels, with a blue box?

Best regards,

-a-

Further reading indicates that the "operational procedures for maximum fuel efficiency" page 5-3.

Leaning after the climb: Set throttle, rpm, then lean mixture (from full rich).  "at this point the mixture is full rich from the climb"

My guess is O1 uses the blue box technique, O2 on uses full rich technique.  Getting STC fuel flow settings from Midwest seems like a good starting point.

 edit again: Climb instructions on page 4-11 indicate climb full rich or white bar on EGT.....

[carusoam]

Add these to the discussion...

Mooney uses 5.82 #/gal for fuel density.

Green range for the fuel flow gauge is 0 to 30gph

 

These were two details from the O2 AFM....

 

Best regards,

 

-a-

[Cris]

-a- I think you have done the same research I have seen. My Eagle has a blue box  on the EGT, I do not have the Garmin 1000. I do see in the latter APM's the same references that you make. There is something about the white box on the Garmin #? MFD which I took to mean the same as the blue box on the earlier EGT's. The higher 2700 RPM's for climb are going to require higher fuel flows which might be the reason that full rich is referenced.

[Shadrach]

Quote: carusoam

 

Ghovey,

The major change of the 310 STC is the higher rpm limit.

200 more rpm, about 8% increase in rpm over the O1.  NA engine should ingest about 8% more fuel.  WOT at SL going up to 2700 rpm.

HP difference is 280 vs 310.  Approximately 10% more fuel burn expected using this calculation.

This is the major issue. 10% more power does not equate to 10% more fuel. It equates to 10% more fuel + whatever additional fuel is required to manage the combustion event to maintain reasonable CHTs.

For the most part, if you operate at 2500 rpm, your numbers will probably overlay the pre STC change.

Some difference should be expected by the different prop, but probably on the order of a couple of percent.

as for excess heat, you are burning 10% more fuel, and not increasing cooling capability, that I am aware of.

Right, which is why more fuel flow is required to increase cooling capability. 

I am still operating / leaning in the blue zone on the ships EGT during climb.  I accept whatever CHTs come with that.  I might see low 400s briefly.

This may work out fine for you, but just remember - the only thing that is really cooling an exhaust valve is it's very brief contact with the valve seat and the heat dissipation that comes with it; the cooler the seat, the better. Low 400s on a regular basis (even for a short time) are not ideal for long term engine health...

If I want to flush more fuel through the system, lean lower than the blue zone.

Are you familiar/using the blue zone?

 

Best regards,

-a-

 

[ghovey]

I just got back from KSDM (San Diego) to KHND (Henderson NV).  500' elevation at departure, 20 degrees centigrade, fuel flow at 2690 rpm,  aircraft weight 2900, , wot on climbout was 27.2 gph.  At 85 kts and over 1500 fpm climb, high CHT was 420 so decreased climb/increased speed to 120kts 800fpm and Cht fell to 400.  After a couple thousand feet pulled the rpm back to 2550 and with cruise climb/ 120 kts cht was just under 400. Pulled rpm back to 2400 and cht fell to below 380-the 2400 rpm setting was tried on departure from KHND, 2400ft and fuel flow was around 25gph and cht never got above 390 at 27 degree oat.  The rpm seem to have much more impact on cht than any other factor. Cruise- At 11,000, 2540 rpm, LOP about 35 degrees, 12.2 gph, 174 TAS, CHt down around 310-330. At 10,000 35degrees LOP usually 12.5 gph, 175 TAS and low CHT.  at 2400 rpm and TAS drops to 170. 

It seems that I may need to adjust the WOT fuel flow to around 30 gph.  

Also the white box on the G1000 is 1400-1450 egt.  One problem I have with the EGT is that there are individual probes for each cylinder but the single EGT number shown on the first page of the engine monitor on the MFD uses a different probe located lower down on the manifold and it reads about 75degrees hotter than the individual EGTs.  There is a white box on the front page and one on the second page but with two sets of entirely different EGT readings.  Either way on climbout I lean to the white box on the front page (the higher EGT number).  But I run LOP using the second page and the individual cylinder readings to find that last cylinder that peaked and then lean 35degrees.  I don't run LOP below 10,000 feet unless I pull the  rpm and throttle below 70% power. 

[Cris]

Ghovey- You got it right. The rpm's drive the cht temps all else being equal. I had a short flight Thurs. on an 85 D day at 100' elevation. RPM was 2690 & fuel flow was 32 GPH with the cyl temp at 402 D thru 2000'. You really need the higher fuel flow at max operating rpm. I don't recall the climb rate but I'll go back & confirm the figures for you when next I fly. This was a real issue at the MAPA PPI I last attended but I do not recall why it was so important to have the higher fuel flows. I  seem to remember it is vital for cooling at ROP as well as getting the full performance but there was something else I'll have to check my notes.. I get similar performance as you in terms of CYL LOP at the reduced RPM's & I suspect that Ovation owners in genenal do also. "a " you want to chime in on this? 

[carusoam]

 

Cris and ghovey,

 

I think you are right on target with your numbers.  Higher RPMs generate more combustion events in the same amount of time.  This drives up heat energy in the cylinders as indicated by higher CHTs and EGTs.

 

Do you have EGT to go with you data sets?

 

The 30 gph target (or so) should be verified with Midwest the STC holder.

 

The excess fuel flow will be applied directly to cooling during ROP.  it's expensive, but only lasts a few minutes overall.  Accidentally burning things up would certainly be more expensive.

 

I am only slightly surprised by two different egt sources from the factory.  Since it is a relative measurement and selected by MAC it represents what they had in mind for leaning.  With your "real" engine monitor, you can identify how many degrees ROP the white box really is.  The assumption is that ROP at original rpm target is the same for the new higher rpm.  leaning during climb is a rough measurement compared to leaning during cruise.

 

My initial concern with this topic is, going too rich could lead to flooding, drowning, lead build up, and poor running during full rich / low power operations.

 

Following the STC seems to be best guidance.

 

AFM indicates 450 CHT is in the green.  Staying safely lower when possible is a good idea.  

 

Leaning/enrichment below the white box (at alt) will indicate delta cht per excess gph.  

 

Consider a simple Experiment: Keeping everything constant, change ff by one or two gph with mixture knob, record change in cht and egt.  Of course, comparing during climb really makes this a complex task.

 

Somebody here will be quick to point out that we can control EGT with mixture.  It may do surprisingly little to control CHT.

 

The knobs we have to decrease CHTs: airspeed, MP, rpm, mixture.  

 

If you want max climb and low egts: use wot, max rpm, Vy,  full rich.  If CHTs are still too high, increase a/s, followed by lower power setting etc.

 

Key thing here is "what is full rich"?  Originally set by MAC, needs to be updated to match STC.

 

Best regards,

 

-a-

 

[jhbehrens]

Hi

Following advice from Justing at Midwest M20 I have full power fuel flow set up at 27.5GPH in my 310HP Eagle.

There is a good article on this topic here http://www.avweb.com/news/savvyaviator/SavvyAviator_65_WhatsYourFuelFlowAtTakeoff_199805-1.html

And TCM instructions for fuel flow setup are here http://www.tcmlink.com/pdf2/SID97-3E.pdf

Jorgen