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Induction Air Temp and Charge Distribution

 
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lhusser



Joined: 15 May 2019
Posts: 1

PostPosted: Fri May 17, 2019 13:09    Post subject: Induction Air Temp and Charge Distribution Reply with quote

Hello,

I'm new to the group. I own an Cessna 195 with Jacobs R-755A2...so, by default, an Aircraft Engine History enthusiast.

I'm looking for references in order to help solve a debate within the 195 community. Is there a meaningful efficiency gain using carb heat in cruise? Many run these engines with CATs from 70-130F, then leaned. I've found a NACA TR or War Report that had test data for a 9 cyl. wright, where they measured EGTs (or O2?) as a proxy for charge distribution on a test stand at varying charge temperatures. They found a significant gain, from what I remember: 90F for best power (probably increasing MP to account for lower charge density) and something like 100F for best economy. However, I have not been able to find that report searching the NACA database.

Is anyone familiar with a reference (NACA or otherwise) that has hard data?

I've played around with varying CAT/RPM and MP, and have not seen a meaningful increase in miles per gallon with the use of carb heat.
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sithomas



Joined: 01 Jan 2019
Posts: 9

PostPosted: Wed May 22, 2019 09:35    Post subject: Reply with quote

I haven't got any experience with the R-755, but from what I have gleened from the BeechTalk forum was that the efficiency increase is more due to the increased turbulence in the induction from having the carby heat cracked open, rather than a benefit from the hotter inlet charge.

FWIW they also say that the early E-185/E-225 can also gain some efficiency from having the throttle ever so slightly closed - again due to increased turbulence.

If you are looking for increased efficiency, this could be a good segway into the ROP/LOP debate Very Happy


Simon
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