XV-15 litho - NASA's History Office

Jim Weiberg’s leaf blower became a
casualty in the quest for advancement
of tilt rotor aircraft technology. The leaf
blower was replaced with a commercial
blower having metal fan blades and an
electric motor. This new smoke generating
system functioned well and provided
the smoke needed for the flow
visualization study.
The flow visualization data revealed
that near the wing tips, as expected,
the proprotor wake impinged on the
wing upper surface and spilled over
the leading- and trailing-edges of the
wing in a chordwise direction (figure
56). As the smoke was moved to the wing midspan position, it showed that the
proprotor wake was also moving in a spanwise direction toward the fuselage
(figure 57). With the smoke source moved further inboard, it was seen that the
flows from the two proprotors moved spanwise toward each other and combined
above the fuselage centerline, turning vertically upwards to form a “fountain
flow” above and along the aircraft’s longitudinal plane of symmetry (figure 58).
These observations confirmed the inboard flow observed from the tuft study
mentioned earlier. Furthermore, the large air mass involved in the over-fuselage
fountain flow created a large downward force which accounted for the higher
than expected download in the hover mode of flight. As explained later, this
fountain flow was also found to contribute to the nonuniform distribution of
noise around the hovering tilt rotor aircraft.
Sidestick Controller
Among the many decisions made early in the development of the TRRA was the
cockpit control configuration. Simulation and flight evaluations by Bell and
Government pilots resulted in the selection of a helicopter-type power lever for
rotor control and a conventional center stick and rudder pedals for longitudinal,
directional, and pitch control inputs. The tall center stick, however, with its masscenter
several inches above its pivot point, introduced undesirable dynamic
effects (called “bobweight” motions) during maneuvers. This issue, coupled with
the possible interference of the center stick with crew station structure (instrument
panel), problems with cockpit ingress or egress, and the general interest in
conserving limited cockpit “real estate,” led researchers to investigate the use of
a sidestick controller as the principal flight control for the developing military
JVX tilt rotor aircraft (later called the V-22 Osprey). The principal concerns with
this type controller were whether it would be able to provide the same level of
control as the conventional center stick, and whether it could perform adequately
Figure 58.
Inboard flow visualization
showing “fountain flow”
above fuselage.
(Ames Photograph
ACD-0804-3.1)
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