PFR - Aerospace Engineering Sciences Senior Design Projects ...

Project Final Report – CUDBF April 30 th , 2009
ASEN 4028: Aerospace Senior Projects
The Neu 1110 2Y motor was chosen because it meets all the requirements at the lightest weight.
In order to increase the torque provided by the motors and increase the efficiency at cruise, the
motor is geared using a gearbox. The two options available for the Neu 1110 motor are a 4.4:1
and 6.7:1 gearbox. According to Electricalc [21] ,amp draw by the Neu 1100 motor using a 4.4:1
gearbox is 60 amps compared to a 24 amp draw with a 6.7:1 gearbox. Since the propulsion
system was designed to utilize up to 40 amps per motor, the 6.7:1 gearbox was eliminated.
Therefore a 4.4:1 gearbox was chosen to provide more torque and increase the efficiency of the
motor at cruise. The motor and gearbox can be seen in Figure 53.
Figure 53: Neu Motor and Gearbox
8.3.2 Propeller
The propeller choice was driven by the requirement to produce enough thrust in order to make
the 100ft takeoff while providing the most efficiency at cruise. The limiting factor in the overall
propeller size was ground clearance. The main landing gear were designed to be 7” long,
allowing the 5.75” water bottle to be stored under the wing while maintaining approximately 1”
of clearance from the ground. Due to the 5° incidence angle from the nose gear, the ground
clearance available for the propeller is 8”. In order to reduce the overall landing gear size and
weight, the size of the propeller was limited to 14”. This allows the propeller to spin freely while
still maintaining 1” of clearance from the ground. The 1” of ground clearance from the propellers
are sufficient even during a crosswind landing since the propeller is inboard of the landing gear.
Thin electric propellers with diameters from 12-14” and of all different pitch were considered.
The lower the propeller pitch, the more static thrust is generated on takeoff. However, the higher
the propeller pitch, the more efficient the propeller is at cruise. The propeller sizes shown in
Table 16 were tested at the maximum theoretical power of 800W (20V and 40 amps per motor
(80 amps total)) which can be obtained from the battery pack. It is important to note that while
the battery pack can deliver up to a total of 80 amps (40 amps per motor), the propulsion system
was sized based upon the assumption that a maximum of 60 amps can be obtained. The battery
pack can only deliver 80 amps immediately after charging (while the battery pack is still hot).
However, due to the unknown waiting time at the competition flight line, the battery pack may
not be used for up to 30 minutes of it being charged, consequently reducing the maximum amp
draw to 60 amps. In order to generate the required thrust of 8.0lbs total at only 60 amps, each
motor must be able to produce 5.33 lbs at 40 amps.
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