First time ROP ops in a J

[0TreeLemur]

In five years flying our C model, I read the ROP/LOP discussions with some amusement and more than a little ignorance.   A C is hard to run reliably LOP.  I did it once, westbound over central Kansas with the stars aligned, moon in the right phase, and the universe in harmony.  Normally I ran the engine 80 to 100F ROP, which used fuel at about 10.3 to 10.5 gph for 140-143 KTAS.

Since acquiring our new-to-us J model in January, I've only flown it LOP in cruise, because it lets me.  It's easy to do.  Do the "Big Mixture Pull" and enrichen 'til smooth.  Trues out at about 148 knots and 8.3 gph.  Smooth.  Quieter. CHT's 280-310F.  Very efficient.

Sunday I departed a bit late for my trip to Miami from Tuscaloosa because I forgot something at home.  30 minutes late to be exact.  The rush was caused by a TFR scheduled to go into effect at 17:15Z over Montgomery/Selma.  I took off at 16:30Z.  Because of this, when I reached top of climb at 9,000 ft I decided to run ROP for the first time get out of the soon to activate TFR on my route of flight.

Looking at the handy-dandy but hard-to-read performance chart on the sun visor, I figured that best power ff for WOT at 9k and 2500 rpm was about 10.5 gph.   Dialed that in.  She trued out at 158.  That's 15-18 knots faster than our C model at the same fuel flow!  That's pretty cool.   Now I get it.   If you want to haul a$$, go ahead.  If you want to fly more economically and burn ~20% less fuel for only a 6% reduction in cruise speed, do that.

 

[Nippernaper]

Exactly. My J matches your speeds and fuel flows just about right on.


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[cwaters]

This is just about what my J is at also, for reference im dialing in on the EDM 900 Lean find function. Mine seems to be really happy at a FF of 8.3-8.5gph LOP and 10.5-11.2ROP depeding on altitude and MP setting on the ROP side. most the time im running WOT on my climb (based in CO so my WOT on the ground is only putting me in the 22-23in range and 80% power)