The 600-750 shp PT-6 engines operate at cruise around 270 pph which equates to about 40 gph of Jet-A. Their takeoff fuel flows are around 350-plus. Economy cruise is about 230 pph/35 gph. The smaller/older -20 engines such as used in many conversions of old recips only make about 500 shp and burn about 25% less.
My 170B gained about 100 lbs since it left the factory and was restored. Although not painted, it has full interior poliamide primer, which I'm told is quite heavy, and helps explain it's aft C.G. (Scales showed 703-L, 720-R, 149-T with full fuel/oil. Subtracting 222 lbs of fuel leaves 1352
Operating Weight, to which must be added payload for flight.)
Many operators forget that their calculated E.W. also subtracted unuseable fuel/oil (42.25 lbs) and so they likely operate about that much overweight when they think they are at gross. My E.W. is 1303.75 lbs.
If the math is correct, it appears my E.W. C.G. is at 55578 MOM/ 42.63 ARM. ....which makes it dang near impossible to ever get my airplane into the Utility Category (and another reason besides unnecessary stress that I've never spun it.)
So I guess
wingnut is correct.... that poliamide is
heavy.
Good thing my exterior stripes are
RED.
Anyway, with a EM7655 prop it uses lots of runway and has a low ROC when it's loaded down on a hot day.
I have an EM7652 prop I intend to install for flight testing before this summers' vacation to Bardstown, and I hope to
document the differences carefully in an article. I'm waiting for a pretty day convenient for a helper to take measurements and times on level pavement. I expect to gain TO/Climb at the penalty of cruise and fuel-burn.
The thing everyone wants to know is exactly what effects a particular prop-pitch change will make, and that's a difficult thing to nail-down because of other variables, including individual prop-condition and engine performance. The prop I'm planning to use, measures full-length and has only 200 hrs and no visible defects on it since ovhl. My engine is mid-time at 900 hrs and runing good with fair compressions, so I'm hoping the results will prove useful.
The bottom line is that I suspect the best/cost-effective mod to make to a standard airplane for better short-field performance (STOL may be a misnomer in these aircraft) will be the propeller, coupled with a serious weight-reduction program. Cruise performance will be compromised.
You want better cruise and lower fuel burn? Give up on the shortest runways.
