SAWE Report - Cal Poly San Luis Obispo

4 Stealth Considerations
As mentioned by the RFP, the aircraft is required to meet a stealth requirement. This is a very
important driver for the aircraft. The entire design is influenced by this consideration equally as
much as aerodynamics. There are many low observable considerations to be taken into account.
The first and most obvious is the radar cross section (RCS).
From the aspect of RCS, there are many drivers for an aircraft. The majority of the radar return
comes from the shaping of the aircraft. The fuselage is constructed from flat sides and constant
radius curves. The sides are kept at a 60° angle from the horizontal and the bottom is kept flat
(Figure 4.1). This is desired because, as later shown, the footprint of the aircraft remains small.
Another feature is the canted tails. This keeps the surfaces in the empennage section from
creating 90 degree angles. This is important because the 90 degree angle would radiate RF
energy directly back in the direction of the source. The leading edge sweep is 40°. This creates
spikes well off of the frontal aspect of the aircraft. All other leading edges are kept swept at this
same angle in order to minimize the magnitude of the frontal spoke. The 15° look up angle was
considered the most important aspect of the RCS. The majority of the threat encountered will be
below the Vendetta. This implies that they will be looking up at the aircraft, not from the front.
This is where the majority of the stealth considerations were taken into account. (See Figure 4.1)
The Low observability requirements are not only for RCS. In fact, the RFP specifically specifies
“Balanced Observables”. Aside form RCS, IR accounts for the next highest threat. Emissivity
matching can reduce the IR signature of the aircraft. The Vendetta will be coated with a material
with similar emissivity as the surroundings, aiding in the disappearance of the aircraft to an IR
sensor. The actual odds of becoming invisible to the IR sensor are fairly unrealistic due to the
cold surroundings. The aircraft is shadowed by what is essentially space at 50,000 feet. It is
hard to hide a warm object when backlit by a cold space. The other stealth consideration in this
area is the nozzles. These are axisymmetric nozzles that are proven to have lower IR signatures
than the axis symmetric option. This, combined with the frontal look-up threat direction
minimizes the impact on IR stealth.
40° LE Sweep
All other Surfaces
Matched
Hidden Canted
Verticals
60° Facet
Figure 4.1 - Stealth Considerations
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