Phase II Final Report - NASA's Institute for Advanced Concepts

Planetary Exploration Using Biomimetics
An Entomopter for Flight on Mars
effects of blowing as demonstrated in the wind tunnel has yet to be achieved through the study
team’s CFD efforts, though this too is an area slated for follow-on work.
Consider a baseline conventional fixed wing vehicle (one wing set) with a one meter wing span
and having aspect ratio of 5.874 (similar to that of the Hawk Moth-based Entomopter wing) flying
near the surface at a speed of 100 meters per second. Its wing area is 0.142m 2 (1.532ft 2 ).
Reference atmospheric conditions on the Mars surface are: density = 0.0000279 slugs/ft 3 , atmospheric
pressure = 0.11475psia, and temperature = -20.4F. At a typical fixed wing lift coefficient
of 1.0, that vehicle can carry 1.04kg (2.3lbs.) gross weight (approximately 2.8 Earth kg (6.2lbs.))
if Mars gravity is taken as 37% that of Earth’s). That represents a wing loading of only 7.3kg/m 2
(1.5lb/ft 2 ) due to the low density and pressure compared to aircraft flying on Earth at perhaps
342kg/m 2 (70lb/ ft 2 ) to more than 488kg/m 2 (100lb/ft 2 ).
Based on the same pneumatic aerodynamic data used for the terrestrial pneumatic Entomopter
(previous wind tunnel data for a GTRI circulation controlled wing model with the same aspect
ratio), a C L of 5.3 is attainable (this is steady-state data, not flapping, which will be larger, as
discussed below). Assuming that the two-winged Entomopter has the same total wing area and
aspect ratio as the one meter conventional wing, giving it a reduced wing span of only 0.646m
(2.12ft) per wing. At the same high flight speed (100m/s), this blown Entomopter can lift 5.53kg
(12.2lbs.) on Mars (15 Earth kg (33lbs.)). Or, if one assumes the two aircraft have the same wing
area and a gross weight of 1.04kg (2.3lbs.) from above, the blown Entomopter can reduce the
required flight speed from 100m/s to 43.4m/s, i.e. the dynamic pressure is reduced from 7.3kg/
m 2 (1.5 lb/ft 2 ) to 1.387kg/m 2 (0.284lb/ft 2 ). Lastly, if we assume that both aircraft (aspect ratio =
5.874) fly the same flight speed (perhaps a lower value of 50m/s speed) with 1.04kg (2.3lbs.)
gross weight, the blown Entomopter can do it with a total wing area of only 0.107m 2 (1.156ft 2 )
or a wing span of 0.56m (1.84ft) per wing set, compared to the span of 1.83m (6.0ft) and area of
0.569m 2 (6.126ft 2 ) for the conventional wing. The size reduction possibility is clear, however
this also has implications in that were the wing to remain the same length, it could be flapped at
a slower speed, thereby accommodating the effects of inertia and strength of materials.
Finally, using a slot height geometry of such a size as to obtain the blown C L = 5.3 requires a
C L = 0.40. At the flight speed of 100m/s, q = 7.333kg/m 2 (1.502lb/ft 2 ), and the required total slot
blowing weight flow = 0.0076kg/s (0.0168lb/s), jet velocity = 538m/s (1765ft/s) and blowing
pressure is 0.18kg/cm 2 g (2.5 psig), mainly due to the very low external atmospheric pressure
and temperature on Mars.
An additional valuable comparison can be made if appropriate wing loadings are considered
along with the required flight speeds. The terrestrial pneumatically-blown Entomopter design
with two wing sets (i.e., 4 wing panels: 2 front, 2 aft) has a wing loading of 3.554kg/m 2
(0.728lb/ft 2 ). For a 1m span Mars Entomopter with 2 wing sets scaled to that wing loading and
an aspect ratio of 5.874, a flight weight of 1.01kg (2.24lb) can be achieved. The conventional
aircraft with the same weight and aspect ratio and one wing set has a wing loading of twice that,
or 7.13kg/m 2 (1.46lb/ft 2 ). Figure 3-134 shows the flight speeds required for each aircraft at
those wing loadings, as well as double the wing loading for each vehicle. The conventional aircraft
with C L =1.0 requires a speed of 98.4m/s to support that weight in level flight, while the
same weight pneumatically blown Entomopter with attainable C L = 5.3 can fly at 30.2m/s. C.P.
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Phase II Final Report