PFR - Aerospace Engineering Sciences Senior Design Projects ...

Project Final Report – CUDBF April 30 th , 2009
ASEN 4028: Aerospace Senior Projects
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Equation 11: Weight-to-Power ratio for cruise speed.
In Equation 11, is the dynamic pressure based on the ambient density, and cruise velocity,
is the parasitic drag,
is the takeoff thrust to cruise thrust ratio, is the Oswald efficiency
factor of the wing, is the aspect ratio of the wing,
is the ratio of the cruise weight to the
takeoff weight, is the wing loading and
is the cruise speed. A detailed list of the
assumptions and values used to size this aircraft can be seen in Appendix F. The equations used
to do the performance sizing were obtained from Roskam [11] .
The design point chosen from this design area is also marked in the plot. This design point gave
a wing loading, W/S of 2.1 lb/ft 2 and a weight to power ratio, W/P of 0.047 lb/lb ft/s. Using an
estimated gross takeoff weight of 15lb, the wing area necessary from the wing loading was
determined to be 7.14 ft 2 . The power required from the weight to power ratio was determined to
be 530 W. The performance sizing shown demonstrates that a number of designs that meet all
the performance requirements for stall, takeoff and cruise are feasible, and an optimized design
can be created that would maximize the cruise speed while keeping the weight to power ratio
small.
7.1.4 Propulsion Feasibility
To ensure that the propulsion system can meet all the design to specifications, a feasibility study
was conducted. The two major requirements to verify are the 100 ft takeoff distance and the
maximum 4 lb battery weight. The rest of the requirements can be verified by inspection. In
order to make the 100 ft takeoff, the thrust required from the motors was calculated. The
equation for takeoff distance is in Equation 12.
S
LO
=
g * ρ * S * C
L
2
1.44 * W
*{ T − [ D + µ * ( W
r
− L)}
Equation 12: Takeoff Distance Calculation
To simplify the equation, it is assumed that drag, D is very small compared to thrust and that the
coefficient of friction, µ of the landing gear wheels is negligible. This yields the simplified
version solved for thrust in Equation 13.
r
54