Rocket fuel flow head scratcher

[Eraaen]

So, my last two cross country trips. Run up's, taxi , take off, climb, cruise all normal. I’m always FL 180-190. 3200/2400 and keep TIT 1530-1540 at about 22-22.5 gph. Here is the problem. When ATC starts brining me down and I start pulling back the throttle 100 pr min to prevent shock cooling (I typically leave mix n prop alone)

The last two flights as soon as mp gets below around 29 down to below 25. The fuel flow will jump to 30gph.  The engine sounds normal, cht, egt, tit, seem to be as they should. It’s just the indication of fuel flow that freaked me out.

I did pull the top and verify both high and low fuel pump set screws were still tight. Any ideas?

[1980Mooney]

2 minutes ago, Eraaen said:

So, my last two cross country trips. Run up's, taxi , take off, climb, cruise all normal. I’m always FL 180-190. 3200/2400 and keep TIT 1530-1540 at about 22-22.5 gph. Here is the problem. When ATC starts brining me down and I start pulling back the throttle 100 pr min to prevent shock cooling (I typically leave mix n prop alone)

The last two flights as soon as mp gets below around 29 down to below 25. The fuel flow will jump to 30gph.  The engine sounds normal, cht, egt, tit, seem to be as they should. It’s just the indication of fuel flow that freaked me out.

I did pull the top and verify both high and low fuel pump set screws were still tight. Any ideas?

If the fuel flow is actually materially higher than you normally observe at a particular altitude/MP/throttle/speed, shouldn’t you also see a material difference in the temperatures that you normally observe?  You say “cht, egt, tit, seem to be as they should.”  

[Pinecone]

https://www.avweb.com/ownership/shock-cooling-time-to-kill-the-myth/

 

[1980Mooney]

7 minutes ago, Pinecone said:

https://www.avweb.com/ownership/shock-cooling-time-to-kill-the-myth/

 

Interesting article but it doesn’t seem to have anything to do with the OP’s question of higher observed fuel flow. 

[N201MKTurbo]

You should use avgas not Rocket Fuel 

[N201MKTurbo]

I would agree, if the TIT doesn't change, it is hard to imagine the FF is changing that much. It may be an anomaly in your FF sensor.

[Will.iam]

2 hours ago, Eraaen said:

So, my last two cross country trips. Run up's, taxi , take off, climb, cruise all normal. I’m always FL 180-190. 3200/2400 and keep TIT 1530-1540 at about 22-22.5 gph. Here is the problem. When ATC starts brining me down and I start pulling back the throttle 100 pr min to prevent shock cooling (I typically leave mix n prop alone)

The last two flights as soon as mp gets below around 29 down to below 25. The fuel flow will jump to 30gph.  The engine sounds normal, cht, egt, tit, seem to be as they should. It’s just the indication of fuel flow that freaked me out.

I did pull the top and verify both high and low fuel pump set screws were still tight. Any ideas?

You need to clarify cht, egt, tit, seem to be as they should for 30gph fuel flow or the 22-22.5gph fuel flow you had at cruise. I. E. If the fuel flow really did go to 30gph your egt and tit would drop immediately I would guess tit would be in the low 1200’s. That much fuel going into just 25” mp would be an extremely rich fuel mixture setting and should be noticeable to verify if the fuel flow meter is indeed working correctly or giving false values. 

[Will.iam]

2 hours ago, Eraaen said:

So, my last two cross country trips. Run up's, taxi , take off, climb, cruise all normal. I’m always FL 180-190. 3200/2400 and keep TIT 1530-1540 at about 22-22.5 gph. Here is the problem. When ATC starts brining me down and I start pulling back the throttle 100 pr min to prevent shock cooling (I typically leave mix n prop alone)

The last two flights as soon as mp gets below around 29 down to below 25. The fuel flow will jump to 30gph.  The engine sounds normal, cht, egt, tit, seem to be as they should. It’s just the indication of fuel flow that freaked me out.

I did pull the top and verify both high and low fuel pump set screws were still tight. Any ideas?

You bought a rocket to go fast what are you doing pulling back the throttle on descent? Get that time back you lost during the climb to 18,000ft. J/K but lowering your RPM’s to 2200 will slow you down a little compared to running at 2500 or so and at 2200 the engine is torquing more with the air than pulling you forward. Think of a 10 speed bicycle when you go down a hill you can peddle like mad with very little resistance in a low gear (2700 rpm) and maybe not even be able to peddle fast enough to even keep up with the speed or you can peddle with more resistance in the highest gear (2200 rpm) this still keeps a load on the engine and prop so you don’t have to worry about the “prop driving the engine” when you have the governor set at a low RPM. 

[Pinecone]

On 10/10/2024 at 11:09 AM, 1980Mooney said:

Interesting article but it doesn’t seem to have anything to do with the OP’s question of higher observed fuel flow. 

Just an addendum for his comment about his power reduction scheme for shock-cooling.