Pilots Fly Further, Carry More Ordnance, Land Better Under
Difficult Conditions
The U.S. Army is leveraging cutting-edge technologies from its
Science and Technology Directorate (S&T) to give the Block III
Apache aircraft increased power, lift, maneuverability and
hard-landing ability, service officials said.
The Army S & T community, a subset of the Assistant
Secretary of the Army for Acquisition, Logistics and Technology
(ASA ALT), has been developing the Rotorcraft Drive System of the
21st Century (RDS-21) Face Gear Transmission and High Performance
Shock Strut (HPSS) advanced landing gear; these technologies are
giving the next-generation Apache the ability to buy back
performance lost when the aircraft added the extra weight that went
along with enhanced mission equipment packages.
"With these technologies, pilots can fly further and carry more
ordnance. They can land better under difficult conditions with no
damage to the aircraft," said Mac Dinning, team leader for aircraft
survivability, Aviation and Missile Research, Development and
Engineering Center (AMRDEC).
The empty weight of the Apache A model is 10,267 pounds,
compared to the 11,800-pound D-model Longbow Apache; the heavier
Apache carries significantly improved targeting and sensing
capabilities but lacks the transmission-to-power ratio and
hard-landing ability of the A model. The Block III Apache is being
engineered such that an advanced, high-tech aircraft at the weight
of the D model can have the power, performance and landing
abilities of an original A model Apache.
"When the Apache was first developed in the mid-70's it had
specific operational requirements -- for hard landing and for lift
capability to lift a certain payload at a certain vertical rate of
climb at forward speed. Over the years we have added a lot of
capability to the aircraft in terms of mission equipment packages
such as sensors, and all of that has added thousands of pounds of
weight to the aircraft. So now the empty weight of the aircraft is
much heavier and if we are still going to carry something close to
the full weapons capability, we start losing the capability of the
landing gear," said Dinning.
"In terms of technologies specific to buying back vehicle
performance they had in the A model before adding all of the
weight, the RDS-21 gear box and Shock Strut are the two most
significant ones to add back capability the Apache had with the A
model and lost with the D."
The RDS-21 improves efficiency because the transmission combines
the output torque of two engines into a single power torque
transmission, Dinning said. "The RDS-21, with the split
torque gear capability, is allowing us at no increase in
transmission weight to pass significantly more torque through the
transmission up to the router. This gives us the lift capability we
need to carry the full weapons and fuel load to get missions done.
It is a hardware system that is taking the output torque from two
engines and is combining them into a single torque into the shaft
of the router," said Dinning.
On the other side of the aircraft, the High Performance Shock
Strut advanced landing gear ... also entering LRIP this year as
part of the Apache Block III aircraft ... gives the aircraft hard
landing abilities at a D model empty weight of 12,800-pounds.
The key feature of the HPSS is a variable metered orifice which
allows hydraulic fluid to move from one area to another at a
controlled rate, Dinning said. "The technology used on the Shock
Strut is a variable metered orifice that allows the aircraft to
adjust to the weight load of the aircraft and tailor the
deceleration. Typically what happens with hydraulic shocks is there
is a load in one end of the shock and it is reacted to by fluid
that is prevented from moving from one reservoir to another. With
the metered orifice, fluid is able to move from one reservoir to
the other at a controlled rate as a function of pressure. You want
to control the decelerating force so the aircraft can absorb energy
across the airframe," said Dinning.
"Now you have the ability to tailor the deceleration profile to
safely land at significantly more weight than we have now. It
slowly absorbs the energy and decelerates the aircraft from a
certain synch rate to a hard stop."
The HPSS can be retrofitted onto the AH-64D model Apache,
service officials said. "The High Performance Shock Strut
technology was developed because the basic structural design gross
weight of the AH-64D had increased, and therefore the crash
performance of the shock struts were no longer optimal," said Bryan
Pilati, Aerospace Engineer (AATD). "The HPSS is a new valve design
qualified as a retrofit solution to the current shock strut. This
technology restores the crash performance of the second stage to
its original performance requirements."