Wren 44 TurboProp Users Manual. Copyright Wren Turbines Ltd February 2008 Page 18
Fuel Consumption and Flight Time Endurance
Fuel Consumption
Fuel consumption means the quantity of fuel required to achieve the specific power level
indicated. For fliers, it is not such a useful figure as it is a single setting quantity and doesn’t
represent actual flying. The full power figure is useful as an indicator of the worst case maximum
consumption figure and the likely minimum flight time achievable. Endurance basically means
how long a plane can fly under power for a given quantity of fuel, including take-off and landings –
there must be at least one of each of these for every flight!
The fuel consumption of the turbo-prop unit is proportional to the power used and for most fliers
this will vary considerably depending on the type of aircraft and duty undertaken. A slow flying
glider tug might use full power for one minute and then reduce to quarter power to circle for
several minutes and land. A fast sports type aircraft might use full power extensively during its
flight including prop hanging and full power ascents. A scale type model might use full power for
just a few seconds for take-off and never use full power again in the flight.
So fuel consumption figures must be used sensibly with an eye on how the engine is operated.
Fuel tank capacity
The duty cycle anticipated of the aircraft will impact the choice of fuel tank capacity. There is little
point carrying around 3ltrs of fuel if the flying requires only 0.4 ltrs per flight. Equally there is no
point having a 0.5ltr tank for a fast aerobatic aircraft that is required to perform an eight minute
show slot (it won’t!).
In general we recommend a compromise tank size for most aircraft of 1.5ltrs (50oz) which should
allow plenty of flight time (8mins+) and assures a reliable supply of fuel and a decent reserve to
keep the system filled.
It is not good practice to choose too small a tank as you run a greater risk running the tank dry
which will allow air to enter the fuel system. This can be difficult to remove afterwards and can
make the system unreliable if air bubbles remain. If you plan a lot of high power manouvers
and/extra long flights then a 2ltr tank may be a better option. It is sensible to allow for about 25%
extra capacity from your requirement to ensure consistent fuel supply.
Fuel Consumption in ml/min to Engine
RPM
0.0
40.0
80.0
120.0
160.0
5
5
1
0
0
1
3
0
1
6
0
1
8
0
1
9
5
Engine RPM x 1000
F
u
e
l
c
o
n
s
u
m
p
ti
o
n
i
n
m
l/
m
in
Fuel Consumption Fl/oz to Engine RPM
0.0
1.0
2.0
3.0
4.0
5.0
6.0
5
5
1
0
0
1
3
0
1
6
0
1
8
0
1
9
5
Engine RPM x 1000
C
o
n
s
u
m
p
ti
o
n
i
n
f
l/
o
z
p
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r
m
in
