FF versus TAS

[KLRDMD]

This morning I collected some data for your enjoyment. Stuff like this helps me determine where I want to put the engine parameters for various flights. As a general rule, I'm not in a big hurry, but at the same time if I'm going too slow I may as well drive. My cutoff is about 160 KTAS. Much below that and I feel like I'm sitting there forever, much above that and I have to have a good reason to burn that much fuel. Here are iPad screen shots from this morning's commute. 7,500 ft cruise, temperature was -1ºC initially, then 0ºC later. Full manifold pressure gave me 22.6" and the RPM was set at 2400 throughout. I simply chose a fuel flow, let it stabilize 2-3 minutes and calculated TAS with the Utilities part of WingX, images reproduced below. They are at 16.0 GPH, 15.0 GPH, 14.0 GPH, 13.0 GPH, 12.0 GPH and 11.0  GPH. By 11.0 GPH the engine was very LOP and the cycle to cycle variation was noticeable. To get much below 11 GPH I will probably need to go higher or reduce MP.

This afternoon I'll go home at 8,500 ft and will look more closely at what the engine monitor calculates as % power since I set LOP as the default a few days ago. Tomorrow I have a longer flight that will be done at 10,500 ft so I'll gather data on lower fuel flows then and I'll gather data in 0.5 GPH increments.

Each 1 GPH reduction in fuel flow only reduced my TAS by about 2 knots until I got to 11GPH. Peak temperatures occur around 14.5 GPH. 

[Guitarmaster]

Excellent! I need to go do this in my 310! Thanks for sharing!

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[Marauder]

Excellent! I need to go do this in my 310! Thanks for sharing!

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I’m glad you used the word “need”. You’ll “need” it.

Still shunned...


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[M016576]

1 hour ago, KLRDMD said:

This morning I collected some data for your enjoyment. Stuff like this helps me determine where I want to put the engine parameters for various flights. As a general rule, I'm not in a big hurry, but at the same time if I'm going too slow I may as well drive. My cutoff is about 160 KTAS. Much below that and I feel like I'm sitting there forever, much above that and I have to have a good reason to burn that much fuel. Here are iPad screen shots from this morning's commute. 7,500 ft cruise, temperature was -1ºC initially, then 0ºC later. Full manifold pressure gave me 22.6" and the RPM was set at 2400 throughout. I simply chose a fuel flow, let it stabilize 2-3 minutes and calculated TAS with the Utilities part of WingX, images reproduced below. They are at 16.0 GPH, 15.0 GPH, 14.0 GPH, 13.0 GPH, 12.0 GPH and 11.0  GPH. By 11.0 GPH the engine was very LOP and the cycle to cycle variation was noticeable. To get much below 11 GPH I will probably need to go higher or reduce MP.

This afternoon I'll go home at 8,500 ft and will look more closely at what the engine monitor calculates as % power since I set LOP as the default a few days ago. Tomorrow I have a longer flight that will be done at 10,500 ft so I'll gather data on lower fuel flows then and I'll gather data in 0.5 GPH increments.

Each 1 GPH reduction in fuel flow only reduced my TAS by about 2 knots until I got to 11GPH. Peak temperatures occur around 14.5 GPH. 

That’s per engine, right?  So when you say 11gph, you’re actually burning 22?

 

edit: wait a second- did I miss something?  Are you flying a Bo now?

Edited January 22, 2019 by M016576

[KLRDMD]

Just now, M016576 said:

That’s per engine, right?  So when you say 11gph, you’re actually burning 22?

An S35 Bonanza only has one engine . . .

[M016576]

Just now, KLRDMD said:

An S35 Bonanza only has one engine . . .

Just noticed that!  I thought you were still in the Baron!  Nice!

[KLRDMD]

5 minutes ago, M016576 said:

Just noticed that!  I thought you were still in the Baron!  Nice!

It has been about a week and a half.