Power settings at altitude

[Cruiser]

In order to tryout my new Oxymiser cannula I took a flight climbing up to 14,500' the other day. I have never flown above 10,000 MSL before. Along the way I continually leaned the mixture to maintain a constant 1275°F EGT. My cylinder temps were holding steady at 325°F. When I leveled off and an closed the cowl flaps the cylinder temps jumped up to 350°F.

I decided to try setting LOP on the JPI analyser and to my surprise when I started to lean, the engine immediately began running rough. I think the JPI was totally confused but I ended up richening the mixture and the JPI showed 20°F LOP. I don't know if that is correct because I never really saw a peak EGT. The engine smoothed out and EGTs were about 1410°F and FF was 7.9GPH. I was as low as 6.5GPH at one time.

By continually leaning the engine in the climb did I end up on the lean side of peak before I reached altitude? Anyone else flying their M20J at 14,000 or higher how do you setup for power at this altitude? I was WOT 2600RPM

[Piloto]

When headed from KFXE to TJMZ in Puerto Rico I climb to 15,000 feet (Airway MEA is 14,000) just before passing GTK. My typical power setting is full throttle and 2400 RPM. I lean ROP to about 1350F EGT. Depending on OAT my average CHT ranges from 360 to 380F. I get about 8.5gph and 155KT TAS. I never set to LOP overwater, roughness makes me uneasy when there is no coast line in sight.

José

 

[Mooneyland]

If you guys spend a lot of time above 10,000', then I would suggest looking into Gami injectors. Gami's work their best on the 231 engine, but I've seen some on the IO-360 that perform very well especially for LOP running. Right now you can only lean to the hottest (number 3) cylinder but the Gami's flood that hot one with fuel to cool it down and thus you can lean to all four cyls w/o running rough. The engine also runs cooler LOP that way and gets better fuel economy. You should see between 1/2 to 1 GPH in savings while making your engine run smoother and happier.

Last I checked Gamis for the 4 banger's run around $800 plus install which goes fairly quickly. Above 10,000' I usually set RPM at 2600-2650 and all the MP I can get. The nice thing about an injected engine is the faster it turns, the smoother it usually is and aside from the prop, 2600 RPM is not a lot of RPM for an engine; so that never concerns me to run 'em that high, and the faster you can go at those high altitudes, the more stable the airplane is in that thin air.

I hope this helps some.

Regards,

richard zephro mooneyland.com

[KSMooniac]

Cruiser, by leaning to maintain 1275 in the climb you did not end up on the lean side of peak up high.  Perhaps you leaned too quickly for the JPI to "keep up".  I've done a few flights at 16k over CO and keep WOT, 2700 RPM, and lean to best power.  You cannot hurt our 201 engines up that high with the mixture knob since they're not producing much power, so don't worry about that.  All that you need to do is watch the CHTs because the thin air does not cool them as well as at lower altitudes.  I would start by trying to find 40-80 ROP or so up high, and if the CHTs creep up above 380, then lean from there until they cool down.

If your engine ran rough at any setting leaner than 1275, then perhaps you have an induction leak.  If it is very slight, then it is possible that it would not manifest itself as rough operation when you lean at higher power settings, but could show up as a rough idle or when leaning at high altitude (ie low power).  If you suspect that, then I would suggest repeating the GAMI lean test at a low power setting (say 50%) and at a higher power setting (say 70-80%) and see if you note any roughness.  Recording the data should point to the cylinder(s) that might be giving you trouble.  I recently R&R'd all 4 of my cylinders, and ended up with an induction leak from one of the rubber o-rings on an induction tube that got misaligned during installation.  The engine ran fine LOP at 80% power, but idled poorly.  Fixing the leak fixed the idle problem.

[Cruiser]

Quote: KSMooniac

Cruiser, by leaning to maintain 1275 in the climb you did not end up on the lean side of peak up high.  Perhaps you leaned too quickly for the JPI to "keep up".  I've done a few flights at 16k over CO and keep WOT, 2700 RPM, and lean to best power.  You cannot hurt our 201 engines up that high with the mixture knob since they're not producing much power, so don't worry about that.  All that you need to do is watch the CHTs because the thin air does not cool them as well as at lower altitudes.  I would start by trying to find 40-80 ROP or so up high, and if the CHTs creep up above 380, then lean from there until they cool down.

If your engine ran rough at any setting leaner than 1275, then perhaps you have an induction leak.  If it is very slight, then it is possible that it would not manifest itself as rough operation when you lean at higher power settings, but could show up as a rough idle or when leaning at high altitude (ie low power).  If you suspect that, then I would suggest repeating the GAMI lean test at a low power setting (say 50%) and at a higher power setting (say 70-80%) and see if you note any roughness.  Recording the data should point to the cylinder(s) that might be giving you trouble.  I recently R&R'd all 4 of my cylinders, and ended up with an induction leak from one of the rubber o-rings on an induction tube that got misaligned during installation.  The engine ran fine LOP at 80% power, but idled poorly.  Fixing the leak fixed the idle problem.

[KSMooniac]

Unfortunately I didn't take any notes....going from memory I was somewhere in the 120-130 KTAS range at 7 GPH or perhaps a bit less LOP.  I have not done any flight testing per se at altitudes in that range...I just climbed up and cruised.

[N57039]

Cruiser, I use the same climb profile that you used, i.e. a constant ROP mixture (about 1275 - 1300 dF). Once at cruise altitude I close the cowl flaps, dial the prop back to 2500 and lean to LOP. At altitudes above 8000' leaning to 5 dF LOP works fine. I think you went way leaner than this when you got roughness during your test. You don't need to rush to find peak, and the JPI is fast but not instantaneous. Fuel flow and TAS will be altitude dependent. Holding 350 dF on the CHTs should be no problem even on hot days.

[jlunseth]

On the issue of the engine temp increasing once you close the flaps, my admittedly very limited experience is with my new 231.  We also had that issue flying the plane home from KSDL, where I purchased it.  I am told by the Mooney Service place that currently is working on the plane, that the cowl flaps need to be set by the mechanic to trail slightly open.  If they close tightly the engine compartment will warm.  We had to open the cowl flaps to the detent (half open) position to cool down at altitude (15,000).  A Cessna 210 friend of mine who lives in NM says his mechanic tells him the same thing.  Cowl flaps need to be set to trail slightly open in the summer, then can be set to fully close in the winter.  Not an adjustment you can make from the cockpit though. 

[The-sky-captain]

Quote: jlunseth

On the issue of the engine temp increasing once you close the flaps, my admittedly very limited experience is with my new 231.  We also had that issue flying the plane home from KSDL, where I purchased it.  I am told by the Mooney Service place that currently is working on the plane, that the cowl flaps need to be set by the mechanic to trail slightly open.  If they close tightly the engine compartment will warm.  We had to open the cowl flaps to the detent (half open) position to cool down at altitude (15,000).  A Cessna 210 friend of mine who lives in NM says his mechanic tells him the same thing.  Cowl flaps need to be set to trail slightly open in the summer, then can be set to fully close in the winter.  Not an adjustment you can make from the cockpit though. 

[KSMooniac]

I think it is a fairly common thing for the 231 drivers...it might even be in the manauls somewhere.  I believe the 252 has an electric cowl flap motor that allows infinite positioning so you can really fine-tune it to keep the CHTs in check.

(I'd rather have a manual/vernier-style control instead of another heavy motor that could fail, personally)

[KSMooniac]

If I roll-my-own TN kit, I plan to do exactly that.  I imagine it would be simple to do on a 337 provided you have a friendly FSDO that still uses their brain.  I haven't found the need in the 201 yet, but I'm not surprised the tightly-cowled turbo Mooneys need it in the thin air up high.  I think the loss of density is faster has a greater negative effect on cooling than the positive effect of the cooler temps up there.

[Parker_Woodruff]

Quote: JimR

I can't say that I "need" a vernier cowl flap control, per se, but it would be nice to have more than three options for setting them. Perhaps more importantly, a vernier control would presumably be more substantial and less susceptable to damage during entry and egress from the cockpit, as my cowl flaps are always open for ground operations and the handle sticks way out and is in the way.