M20K - technique flying high Altitudes

[NicoN]

My co-owner recently flew FL160 with our M20K (GB-ENgine).

He complained that the engine does not produce 100% HP at this altitude and expected full power until at least FL170.

Also, it was difficult to keep the CHTs under control.

He reported, he had to use full rich, cowl flaps half open.

According to EDM830, as usual #2 cylinder was hottest with 386F, EGTs  between 1290 and 1380, TIT ~1430. FF ~18.7

Speed is not available at the moment, GPS-Alt was roughly 17000ft.

Is this normal? I have no experience with those altitudes.

 

 

Edited July 24, 2019 by NicoN

[kortopates]

With the unmodified fixed (bolt) wastegate engine, I recall critical altitude at a DA of 15,700' (from memory). The Merlyn fixes that and the intercooler will bring down the CHT's at altitude.
(I also answered your partners question on Savvy, see that for a more in-depth explanation.)

Sent from my iPhone using Tapatalk

Edited July 24, 2019 by kortopates

[CaptRJM]

Agreed. Critical altitude on stock system is 15,700. The GB motor is notorious for running hot anyway.

Merlyn Black Magic upper deck controller will boost Critical Altitude. Before I installed a Turbo Plus Intercooler CA with just the Merlyn was around 19,500. 

Cylinder 2 will always be the hottest as it has the worst airflow and the oil cooler is immediately behind it. Also, the highest you go although air temperature is lower there are fewer air molecules to cool the engine. Running the cowl flaps in trail will enhance the volume of cooling air. 

[81X]

I’m assuming this is a non-Merlyn non-intercooled GB engine and if so, this sounds like somewhat normal behavior (second hand knowledge).

I flew my LB, intercooled, Merlyn’d 231 at 15k home from OSH on Wednesday and only had to trail flaps as I got further south/later in the morning (warmer OAT) while burning about 12.5GPH ROP at 28”.  I am able to develop full power (36”/23GPH) at that altitude with about 25% throttle travel remaining.  

 

While this may be years off for you, having a factory reman done when it’s time for overhaul will get you the LB with the bigger induction which will help with cooling.  Add in a Merlyn and Intercooler and you’ll get even better cooling/detonation margins, get a much higher critical altitude, reduce/eliminate turbo bootstrapping(surging) and be closer to a 252 config which has a proven superior engine setup. Also as a bonus, TBO will go to 2,000 from 1,800.  

[NicoN]

Okay, thank you.

Is flyinig LOP still okay in FL150-170? Or is it mandatory to stay on the ROP side for cooling?

[gsxrpilot]

4 hours ago, NicoN said:

Okay, thank you.

Is flyinig LOP still okay in FL150-170? Or is it mandatory to stay on the ROP side for cooling?

You'll get BETTER cooling flying LOP at that altitude. I fly my 252 regularly between FL200 and FL260. At those altitude while ROP I have to keep the cowl flaps full open. If I pull back to LOP, the CHT's drop 30° across the board. And I can close the cowl flaps.

This shows all the settings. You can see I'm LOP at 9.4 gph.

[Danb]

Paul now that’s efficiency what other certified plane can top those numbers across the board, I didn’t see MPG must be pretty damn good..

[gsxrpilot]

15 minutes ago, Danb said:

Paul now that’s efficiency what other certified plane can top those numbers across the board, I didn’t see MPG must be pretty damn good..

Here's the photo with the MPG. The 252 truly is a special airplane.

[flumag]

not for me. Here my flight yesterday back from Oshkosh at 17000ft. 

very stable after the climb. cowl flaps closed. 4 hours 15 min for 745NM. But the M20K has Intercooler and Merlyn wastegate.

[ArtVandelay]

not for me. Here my flight yesterday back from Oshkosh at 17000ft. 
very stable after the climb. cowl flaps closed. 4 hours 15 min for 745NM. But the M20K has Intercooler and Merlyn wastegate.

Boy your oil pressure is low?


Tom