Page 20 - Index

Using Flight Planning Software for Performance Comparisons
Winds Aloft HELP
FL280 ISA(-41) Comp
FL260 ISA(-37) Comp
FL240 ISA(-33) Comp
FL220 ISA(-29) Comp
KCOS0500
288/017 +14 -016
297/013 +15 -012
297/008 +16 -008
294/010 +16 -009
KCOS0400
277/021 +14 -017
282/019 +15 -017
286/015 +16 -014
296/014 +16 -013
KCOS0300
268/029 +13 -022
276/026 +14 -021
285/019 +15 -017
297/018 +15 -017
KCOS0200
282/029 +10 -026
290/024 +12 -022
297/019 +13 -019
302/018 +12 -018
KCOS0100
293/023 +09 -022
296/018 +10 -018
296/015 +11 -015
300/016 +11 -016
Avg. Trip Winds=>
-21 Headwind
-18 Headwind
-15 Headwind
-15 Headwind
FLT TIME==>
ABOVE MAX ALT.
3:08(+00) 232TAS
3:04(-04) 235TAS
3:03(-05) 234TAS
Fuel Burn==>
---
96.0 Gal.
98.3 Gal.
101.1 Gal.
-21 JetPROP
Winds Aloft HELP
FL280 ISA(-41) Comp
FL260 ISA(-37) Comp
FL240 ISA(-33) Comp
FL220 ISA(-29) Comp
KCOS0500
288/017 +14 -016
297/013 +15 -012
297/008 +16 -008
294/010 +16 -009
KCOS0400
277/021 +14 -017
282/019 +15 -017
286/015 +16 -014
296/014 +16 -013
KCOS0300
268/029 +13 -021
276/026 +14 -021
285/019 +15 -017
297/018 +15 -017
KCOS0200
282/029 +10 -025
290/024 +12 -022
297/019 +13 -019
302/018 +12 -018
KCOS0100
293/023 +09 -018
296/018 +10 -018
296/015 +11 -015
300/016 +11 -016
Avg. Trip Winds=>
-20 Headwind
-18 Headwind
-15 Headwind
-15 Headwind
FLT TIME==>
ABOVE MAX ALT.
2:54(+00) 252TAS
2:56(+02) 244TAS
3:00(+06) 236TAS
Fuel Burn==>
---
95.4 Gal.
94.5 Gal.
95.3 Gal.
-35 JetPROP
Most popular ight planning software has pro les set up for the various engines on the various
airframes. This makes it easy to contrast block-to-block times and fuel burn expectations among different engines. In this example, I have used FltPlan.com to compare the -21 and -35 JetPROP (under the same conditions) in a ight from KSJO to KCOS. As you can see, the difference in performance is negligible.
available values, the difference in power is only seen when the engine becomes “temp-limited,” meaning that the limit of power available is limited by the ITT, not torque.
Every turbine driver knows that an engine will become temp-limited at a certain altitude (dependent upon temper- ature), and the smaller engines will be- come temp limited at a lower altitude. It is only then that the difference in torque between the larger and smaller engine becomes apparent. As an example, the -6 powered B100 I operate will develop the same torque as the -10 when depart- ing my home airport (KJSO, 670 ft. field elevation). Both airplanes will takeoff equitably, and both will climb equitably through about 10,000 MSL. However, the -6 version will become temp limited earlier than the -10 version, and then the -10 version will develop more torque for the rest of the flight, climbing better and cruising faster.
The altitude where the engine is temp- limited becomes critical for the pilot who operates from high-density altitudes. I’ve departed Santa Fe, New Mexico (KSAF, 6,348 ft. field elevation) in the summer heat and was temp limited on the takeoff roll in the -6 powered B100. Had I departed on that same day in the -10 powered B100, I probably would not have been, and the takeoff performance and climb would certainly be better with the bigger engine. So, if you operate out of high-density altitude airports, you might be one of the few who would want to more strongly con- sider the bigger engines available on a particular airframe.
But there is a catch here. Remember, what comes around goes around...if you purchase that smaller-engine airplane for a lesser price, the market will almost always want to pay you a smaller price when you sell, and there will be fewer buyers for that smaller-engine airplane when you do sell. My advice? Seek out
the best example of whatever type air- plane you wish to purchase and nearly disregard the type of engine. Find the one with the right avionics, nice paint/ interior and excellent maintenance pedigree. If that airplane happens to be a small-engine version, great! There will be some wonderful efficiencies that you’ll grow to appreciate.
Stay tuned for my next article where I will explore the reverse: why bigger engines are worth considering. T&T
•
Joe Casey is an FAA-DPE and an ATP, CFI, CFII (A/H), MEI, CFIG, CFIH, as well as a U.S. Army UH-60 standardiza- tion instructor/examiner. An MMOPA Board member, he has been a PA46 in- structor for 16-plus years and has accu- mulated 12,000-plus hours of flight time, 5,500 of which has been in the PA46. Contact Joe at: www.flycasey.com, by email at joe@flycasey.com, or by phone at 903.721.9549.
18 • TWIN & TURBINE
October 2018