LOP RPM

[jetdriven]

Mike, do you lean to the point of stumbling on the ground when you advance power?  Do you never let RPM get below 1000 on the ground? Climb at "target EGT," and then lean to Target + 50-75F above 5K feet? Run LOP until the power reduction on downwind abeam numbers, and then set near peak?   Are they worn out massive plugs?  Ours look like the tailpipe, light tan. Take a look at the tailpipe.

 

target in our J is ~1285 degrees. Thats sea-level 15C 29.92 takeoff full rich mixture.

[Shadrach]

Quote: 201er

At my last oil change I had my mechanic check the plugs and he gave me the usual line of "looks like you're running a bit too rich, try leaning it some more." How is that possible when I've been flying almost exclusively lean of peak (except climbs) since my last plug cleaning? Or is that just a standard line they read to everyone? Is it possible to get the apperance of too rich by running too lean? Or is being too rich in the climbs enough to give this apperance?

[KSMooniac]

Quote: jetdriven

Scott, if you keep the FF the same while LOP and lowering RPM, it requires richening.  It may mess up your test.   The engine will make more power with more RPM, and hence more thrust, and speed.  Try this,  Go WOT at 1000 AGL up there, and leave all 3 knobs to the firewall.  You should see 160-169 KIAS after about 90 seconds.  Now, pull the prop back, try 2450 RPM.  wait a minute, and then record that value.     You can do it at 5K feet too, but down low, you can make more horsepower.  It wil be interesting, but I bet you lose 3-4 KIAS bringing down RPM.   You couls also do a time to climb to 5K feet.  2700 vs 2500 RPM.

[garytex]

The other thing that may be going on with the few tenths of a gallon more fuel to produce the same power may be the additional friction and pumping (air) losses at higher RPM.  These can be seen on graphs of simply motoring (turning with an external power source) an engine with no combustion.  It takes more energy to turn the engine faster.