XV-15 litho - NASA's History Office

Figure 55.
XV-15 during short takeoff
performance test.
(Ames Photograph
AC82-0723-22)
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all identified elastic modes at all airspeeds and altitudes examined. The most significant
and technically difficult objective of the TRRA project and the goal set
nearly 30 years earlier during the XV-3 project had finally been achieved.
Short Takeoff Investigations
In August, 1982, the Ames TRRA Project Office continued performance and handling
qualities evaluations of the XV-15, aircraft N703NA. This included investigations
of the tilt rotor’s short takeoff performance (STO) characteristics. To vary the
weight and center-of-gravity (c.g.), lead-shot-filled bags were placed in the fuselage
and lead plates were affixed at the nose and tail of the aircraft. Following a
series of evaluations at various c.g. locations, a number of flights were conducted
to assess STO performance at high gross weights. Because of the high risk
involved, these tests were performed at the sparsely populated and remote Crow’s
Landing Naval Auxiliary Landing Field (NALF), located about sixty miles from
Ames. With the aircraft at or near the maximum takeoff gross weight, and the
nacelles positioned at a preselected angle, the pilot released the brakes as the proprotors
were brought to the desired torque level. The aircraft was then rotated for
liftoff at a target ground speed and an attitude for maximum rate-of-climb was established
(see figure 55). The aircraft position was measured using a laser operated by
Ames Flight Operations Division personnel and contractors. The tracker utilized a
laser retro-reflector mounted on the landing gear pods of the aircraft and the data
were recorded for later correlation with aircraft data. Even at the maximum gross
weight of the XV-15, the short takeoff operation was a rapid and very dynamic
maneuver. This investigation enabled the effect of nacelle angle on STO performance
to be evaluated. Too high an angle (at reduced torque to simulate a condition
for which only STO and not vertical takeoff was possible) resulted in lower rates
of acceleration, therefore extending the ground roll before liftoff could occur. Too
low a nacelle angle provided improved ground roll acceleration, but the reduced
vertical lift vector from the proprotors delayed the liftoff. It was determined (for
the XV-15 at its maximum takeoff
gross weight, and at approximately 60
percent of the normal power) that the
optimum nacelle position for minimum
ground roll to clear a 50-foot obstacle
was 75 degrees. Evaluations of this
type verified the capability of the tiltrotor
aircraft to perform short takeoffs at
gross weights well above its vertical
takeoff gross weight, adding an important
performance capability to this new
aircraft type.
As often happens in developmental
work, a totally unforeseen incident
involving a critical proprotor hub