Matt,

 

If Lorn is using ram air, the increase in IAS from 139 to 152 would increase the ram pressure (theoretical is about .22" Hg for that speed change) and the prop going by more often might also be a slight boost to inlet ram pressure.  He didn't mention any throttle change.  His AOA would have decreased a bit too.

 

Grayhawk

 

In a message dated 6/25/2010 3:49:00 P.M. Central Daylight Time, matt.hapgood@alumni.duke.edu writes:

Why did MP change with fuel/RPM change?

Matt

On Jun 25, 2010, at 1:59 PM, Lorn H Olsen <lorn@dynacomm.us> wrote:

> 06/22/10 I was flying from Detroit to Ft Lauderdale at 11,000. With nothing else to do, I thought that I would take a few measurements.
>
>   Condition   LOP Lo      ROP Hi
>   ---------   --------    ---------
>   11,000 IA   2,350RPM    2,700 RPM
>   13,000 DA   19.3"MP     19.8"MP
>   30.08 "Hg   6.0 GPH     8.6 GPH
>   12°C temp   139 kts IAS 152 kts IAS
>   35°F dewpt? 168 kts TAS 183 kts TAS
>   1,670 lbs
>
> For a 43% increase in fuel, a 9% increase in airspeed doesn't sound like much. However, 183 kts airspeed at 13,000 ft density altitude, no matter how you do it, is great.
>
> The LOP reading at .435 BSFC comes out to HP = 36 * 6 * .435 = 94.0 HP or 94.0 / 160 = 59% power.
>
> Comments appreciated.
>
> Lorn
>
> --
> Lorn H. 'Feathers' Olsen, MAA, ASMEL, ASES, Comm, Inst
> DynaComm, Corp., 248-345-0500, mailto:lorn@dynacomm.us
> LNC2, FB90/92, O-320-D1F, 1,700 hrs, N31161, Y47, SE Michigan
>
>
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