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Re: [LML] LOP vs ROP Climb: Time and Fuel Burn
(LIVP)
I did this trial to answer a nagging question for me: what is the
cost and penalty of ROP vs LOP climb. To make the comparison as
similar as possible (reduce the confounding variables), I kept MAP
(34.8") and RPM (2500) the same, as well as OAT, wind (direction
of climb) and distance downrange. The VSI was chosen to produce
at least a minimum 500 fpm climb (notably required by ATC), hence a
lower forward IAS when LOP. The goal was a comparison, not
necessarily the most efficient ROP climb compared to the most
efficient LOP climb, although this sounds like it might be an
interesting examination.
If I climbed ROP at 152-157 KIAS, the CHT would have been much
higher, much sooner. As it was, I could not maintain CHT
<410*F at 160 KIAS during the ROP climb. Of course, if I
throttle back (to 26"-27", 2500 RPM), this might produce the
same VSI as the higher LOP MAP given I've reduced my ROP horsepower,
but then I've still got unconsumed (and wasted) fuel exiting the
exhaust manifold, and for what HP gain?
Regarding the ROP fuel burn of 34.2 gph vs WOT 45 gph (on take
off), my engine is set to feed the recommended 45 gph at 38.5"
MAP, 2700 RPM to produce the rated 350 HP. These numbers,
particularly the ROP 34.2 gph, were at 34.8" MAP 2500 RPM full
mixture, not WOT. An interesting footnote is that these engines
are rated for continuous operation at WOT 38.5" 2700
RPM.
How many pilot are climbing out to altitude at MAP 38" 2700
RPM and 140 KIAS (and 2000 fpm)? This is an interesting idea,
not something I've tried (or was taught). Colyn's numbers
suggest it would get one to altitude quick enough that the CHT2 might
not be an issue (he sees 380*F), despite the reduced forward air flow,
and still have similar fuel consumption as 34.8" 2500. This
would be a bonus.
I'd welcome some comments about people's ROP climb numbers
typically used.
Jeff L
LIVP
Next you might run ROP at the same
performance numbers as you had LOP (152-157 KIAS and 600-900 fpm VSI)
and see what the fuel burn is. You probably will use a
significantly lower MAP to get equivalent performance. I bet
26-27" MAP. That may significantly impact the difference
you found in fuel economy.
I think your
full rich FF is (way) too low.
How ROP are
you at 34.2gph?
I believe
continental specs for full throttle (38") are
43gph.
For overhaul
economy it would be good to get it up there.
I have mine
set at 45gph for 38"/2700rpm.
I don't know
what temps that would give at 160knots
but at 140
knots the hottest cylinder is 380 and it will climb at 2000fpm (not
that I do that a lot)
If you want
to use those numbers it takes 5 minutes to do that climb which would
be 3.75 gallons.
switch to
cruise @260 knots at 16,000 and I think you burn another 1.38 gals for
a total of 5.13.
...so maybe
a little less bad than you said.
but somehow,
a gallon and a half doesn't register compared to the build cost,
insurance, training, etc.
if I'm
feeling environmentally responsible I just think how much fuel I saved
by not owning a turbine....
Itıs curious to me that you experienced
higher CHTs at ³Rich.²
Have you tried just climbing out at 38 MAP?
On 3/9/09 10:41 AM, "Jeffrey Liegner, MD" <liegner@embarqmail.com> wrote:
Here's some analysis on time to climb and fuel consumption
in my LIVP during a controlled ascent of 10,000' (from 6000' MSL to
16000' MSL) in both Lean of Peak (LOP) and Rich of Peak (ROP) engine
configuations.
This test occurred over Pennsylvania 3/7/09, fixed heading (350*),
fully configured and stabilized in level flight (6000' MSL) at 34.8"
MAP and fuel flow, followed by a pitch up (over a known GPS reference
point) and climb (to 16000' MSL) either LOP (18.2 gph) or ROP (34.2
gph). Winds were light out of the northwest (a quartering
headwind), remained consistent during both tests; temps were above
ISO. The test was conducted over a 32 min span of time.
Engine: TSIO-550E.
Lean of Peak (LOP) Data:
10,000' climb at 34.8" MAP
Fuel flow 18.3 gph (estimate 100*F LOP)
Time Required: 11:28 min
Distance Downrange: 30.9 nm
Airspeed during climb: 152-157 KIAS (Calculated Groundspeed: 161)
Indicated VSI: 600-900 fpm (Calculated: 870 fpm)
Fuel Burn: 3.5 gallons (confirmed with totalizer)
Highest CHT Temp: 360*F (CHT2)
Rich of Peak (ROP) Data:
10,000' climb at 34.8" MAP
Fuel flow 34.2 gph (Mixture full in)
Time Required: 9:07 min
Distance Downrange: 26.5 nm
Airspeed during climb: 160 KIAS initially, but 165 KIAS last 1:30 min
due to CHT2 >410*F
Indicated VSI: 1000-1400 fpm (Calculated: 1100 fpm)
Fuel Burn: 5.2 gallons (confirmed with totalizer)
Highest CHT Temp: 412*F (CHT2)
Bonus Data in Level Flight after ROP climb:
Immediate LOP to 18.3 gph
Proceeded to 30.9 nm down range
Additional time required in level flight: 1:17 min
Additional fuel required in level flight (LOP): 0.4 gallons
Total time to reach 30.9 nm down range: ROP 10:24 min (versus LOP
11:28 min)
Total fuel burn to reach 30.9 nm and 10,000' gain: ROP 5.6 gal (vs LOP
3.5 gal)
My personal conclusion:
LOP during climb consumes 37% less fuel and only extends travel
time 11%.
CHT are much better LOP during the climb.
Jeff Liegner
LIVP in New Jersey
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