XV-15 litho - NASA's History Office

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Nose weight
Top:
Figure 61.
Typical cross section of the
XV-15 metal blades.
Bottom::
Figure 62.
XV-15 Advanced
Technology Blades
configuration variations.
Steel spar Stainless steel skin
Basic cuff
Extended cuff
Cuff extension
Cuff off
Eccentric bushings
Aluminum honeycomb core
Basic tip
Swept tip
Square tip
Trailing edge block
that the proprotors would be too highly
loaded, i.e. operating too close to aerodynamic
stall, to provide adequate
reserve thrust for control when operating
in hover at high gross weights.
This could result in a reduction of control
effectiveness or the need for a substantial
increase in power when operating
at the high gross weight condition.
Flight tests of the XV-15, however, did
not indicate deficiencies. The metal
bladed proprotor, although sized for a
smaller aircraft, performed well at all
XV-15 operating weights and flight
conditions. While performance was
satisfactory, another problem emerged
that could threatened the future of the
XV-15. This was the possibility that
one or more blades could become
unserviceable or unflightworthy due to
mishandling or deterioration of the
blade’s structural integrity.
Concern centered on the aft blade section,
an aerodynamic fairing constructed
of a lightweight aluminum honeycomb core covered with a thin steel skin
(figure 61). Over the first few years of aircraft operations, minor surface damage
was incurred due to ground handling. More significantly, small areas of separation
of the bond between the skin and the honeycomb was detected on several
blades. While the size of these “voids” was monitored during frequent inspections,
the discovery of a rapid growth in size or an unacceptably large separation
area could render the blade unusable for flight. The limited number of spare
blades (two right and one left) meant that the loss of two left flightworthy blades
would ground an aircraft.
Part of the TRRA Project Office advanced flight research program goals was the
“investigation of alternate or advanced proprotor configurations.” This was consistent
with the Project Office’s perceived need to replace the blades, both to assure the
continuation of flight testing and to explore the application of new materials technology.
The activity, to design, build, and flight test a new set of proprotor blades
for the XV-15, was known as the Advanced Technology Blade (ATB) project.
Although there were no immediate prospects for funding an upgraded transmission
that would allow a larger amount of the installed engine power to be used
(providing a significant enhancement of the XV-15’s performance), the ATB proj-