Ross:
I often wonder about BSFC as a relation to degrees LOP. THe data really doesnt exist for 4 cylinder lycomings. I do have a graph supposedly from Lycoming that shows peak BSFC at 50 dF LOP. But the curve is flat from 20-50 LOP. Our plane completely falls on its face below 50 LOP. Down low below 3000' its no big deal, 100 LOP is fine qe have excess MP available. I wonder if I can even make 75% (150 HP) power LOP at altitude. It would take 9.9 GPH and for us almost always thats ROP. I havent seen it yet. I always end up 8.7-7.8 GPH depending on altiitude and 145-150 KTAS. It seems the airplane is happiest around 120 KIAS regardelss of altitude.
EDIT: with the 25 degres of timing there is much morm "oomp" while LOP. We also modified our style of flying to 10-20 LOP and not 130 KIAS is the norm, and FF is ~9 GPH below 4K, 8.8-8 GPH between 4-8K. At 9500 its 7.8 GPH.
The airframe equation seems that further from max L/D the more you pay in drag. But the engine's efficiency at 40% power to maintain that speed (L/D MAX) is below its max efficiency range as well. So the engine likes 55-65% power to maintain a .39 BSFC but the airframe likes the equivalent of 40% power. There is a balance somewhere. I think our typical 8.7 GPH 62% power LOP at 8500' is actualy a bit slow, we could make nearly the same trip burn flying faster.
Byron
1977 201 N201EQ
SN 24-0162
Quote: Shadrach
Hi Norman,
Being that you're doing your thesis, I would like to see more about how you're using SFC relating to mixture, rather than just taking Gami's estimate. I believe that the lowest BSFCs occur at fuel air ratios significantly lower than would be utilized at 25LOP (more in the range of ~35-65LOP, engine dependent). Moreover, Gami may or may not have been taking airframe efficiency into consideration when they came up with that number (I've personally don't recall 25LOP given as a "best SFC target, excepting for in this thread.). I don't believe that the power level that generates the lowest BSFC in a specific engine necessarily correlates to the most efficient power setting for a given airframe (discussion limited to normally aspirated engines). I think that you already understand this and it will be a significant part of your thesis. However, In addition to flat plate area, I'd like to see how you're accounting for the increase in induced drag that can result from lower IASs at the reduced power levels being used to attain the lowest SFC. It seems to me that those values would change with altitude and from airframe to airframe. Thanks!
P.S. Do you still want the climb table from my M20F POH, or are you only wanting M20J info?