Future design requirements and
trends to overcome challenges of
helicopter operations
BY
Wg Cdr (Retd) NS Krishna YSM
WHAT ARE THE DESIRED QUALITIES IN AN IDEAL
AEROPLANE?
Ideal Aero plane
Helicopters
Aero foil design for high lift or
high speed
Wing adaptable for various
stages of flight
Should be Trimmable
Usually symmetrical.. Neither
high lift or high speed
NO.. In addition, various part of
rotor move at different speeds
NO
Fuel Efficient
Fuel efficiency per seat is over 5
times a A 320
HA HA HA
Minimum noise
Minimal Loss of Power
Substantial losses by the time
power is delivered to Rotors
Ideal Aeroplane
Minimum Drag
Sealed and capable of being
pressurized
Effect of Controls-Minimal
Cross couplings
Helicopter
Very draggy, primarily due to
gearbox
Not designed to be pressurized
Should be statically and
Dynamically stable
Range –should be large
Each movement cyclic, collective
and rudder pedals has a primary,
secondary and tertiary response
Dynamic unstable.. Diverges
rapidly
Very limited ranges
Vertical/short Takeoff and
Landing
YES YES YES!!!!
• Helicopters are different from planes.
•An airplane by it's nature wants to fly, and if not
interfered with too strongly by unusual events or by a
deliberately incompetent pilot, it will fly.
•A helicopter does not want to fly. It is maintained in the
air by a variety of forces and controls working in
opposition to each other
•If there is any disturbance in this delicate balance the
helicopter stops flying; immediately and disastrously.
This is why
•airplane pilots are open, clear-eyed, buoyant
extroverts
•helicopter pilots are brooding introspective
anticipators of trouble.
So, why fly helicopters at all?
Helicopters differ from Aeroplanes in that
they :•
•
•
•
•
Can Hover
Can move sideways and backwards
Can fly very slow without stalling
Can fly very low to avoid radar detection
Can maneuver in small spaces
MAIN USAGE OF HELICOPTERS
• Usage in civil is mainly for operations to/from
places where big landing surfaces cannot be built
• Mountains
• Offshore oils rigs
• Emergency Medical Services from unprepared
accident sites to nearest
Hospital ( roof top or
nearby helipad)
• Trump Towers to JFK Airport
• Disaster relief
Exotic Civil Uses
• Policing and Traffic management
• Helitourism.. Such as ride to the Grand
Canyon
• Lifting heavy tree logs from
Jungles or mountains to
nearest processing plants
• HT cables laying
• Cattle rounding
• Clearing water logging
and snow from runways
MILITARY USAGES
• Casualty Evacuation – Remember M*A*S*H? OF
course you would not.. Even I was a kid then!!
•Battlefield Air Support – Fighter Aircraft cannot fly low
and slow as required
•Anti Tank- Very effective as
they can use a fire and
forget missile, and duck after firing
• Air Superiority– ie protect
own troops and tanks from
enemy helicopters and fighters using ATAMs
• For direct attacks , as a Command post and for
transporting troops during Anti Terrorist operations
“ The helicopter approaches closer than
any other vehicle to the fulfillment
of mankind’s ancient dreams of the
flying horse and the magic carpet”
– Igor Sikorsky
• However, during all these roles,
helicopters face certain operational limitations
– Speed
– Relatively costlier due to
• Fuel Inefficiency in terms of seat per mile
• Relatively lower payload capability
• Lower cabin volumes for the same AUW
– Maintenance intensive due to more rotating parts
– Noisy- this is more noticeable as helicopters operate close to
ground
– Adverse weather operations in hills and to helipads carry great
risks
FUTURE TRENDS OF
HELICOPTER DESIGN
SEEMS UGLY IS
BEAUTIFUL!!
• All the future trends are towards :– Overcoming Speed limitations
– Reducing Noise
– Improving Power to Weight ratio
– Using Fly BY Wire and advanced Autopilots to
artificially improve stability while retainingg
maneuverability.
– Improving fuel efficiency
– All weather capability
VTOL X PLANE : A PROGRAM BY US DOD
• VTOL X-Plane challenges industry and innovative engineers to
create a single hybrid aircraft that would concurrently push
the envelope in four areas:
– Speed: Achieve a top sustained flight speed of 300-400 kt
– Hover efficiency: Raise hover efficiency from 60 percent to
at least 75 percent
– Cruise efficiency: Present a more favorable cruise lift-todrag ratio of at least 10, up from 5-6
– Useful load capacity: Maintain the ability to perform useful
work by carrying a useful load of at least 40 percent of the
vehicle’s projected gross weight of 10,000-12,000 pounds
• Several companies have been funded for initial research, after
which a short list will be made for competing for US Govt
contract
EFFORTS TO INCREASE SPEED
• Speed in helicopter is limited because :– Dissymmetry of lift between advancing and
retreating blade
– Forward Control limits being reached as flap back
is overcome
– Retreating blade Stall
– Compression effects on advancing tip
ALL CURRENT PROJECTS ADDRESS THE ABOVE
ISSUES
Trends in Speed Improvement
Eurocopter X3
• Compound helicopters
– – 253 KTs
– Uses two puller propellers
with differential pitch to provide antitorque
– Stub wings offload rotors by 40-60 %, also
preventing retreating blade stall
– Rotors are slowed down to prevent drag from
advancing blade tip
Trends in Speed Improvement
Sikorsky X2 ( S (& Raider)
• – 260 Kts
– Rigid Contra-rotating rotors about 2 ft apart
– Rear prop provides most of
forward thrust requiring very
little forward tilt of rotors
– Resultant vibrations damped
by active dampers
– Instability countered by FBW
and highly advanced AP
Trends in Speed Improvement
Bell V280 Valor
• Designed for 280 Kts
• Tilt Propellers at ends of a
straight wing
• Since control laws would be
very complicated, specially
for transition f rom hover
mode to forward flight, it has
triple reduntant FBW system
• V tail for maneuverability
• Range of 2600 nm – highest
of any new development of
Future Vertical Lift ( FVL)
aircraft
Boeing Concept :Phantom Swift
• Employs a wide, blended
body incorporating two large
lifting fans, which are
covered in forward
flight.
• It has ducted fans in
swiveling nacelles at
the end of the short
wings.
• Boeing has already built
and flown scaled-down
model of the Phantom Swift.
Avatar
Planes?
My Take? The Avatar helicopter/plane looks deadly, but
cannot possibly be ideal for high speed!
• Stub wings cannot give much lift
•Rotors look too draggy for high speed
•Rotors have very little tilt, and no propellor to give
forward speed
•DON’T SEE WHERE THE FORWARD THRUST IS COMING
FROM
FUSELAGE SIZE
•The space required for landing is
determined by the rotor diameter and
length
•Requirement of an anti torque
Tail Rotor and a supporting tail
boom decreases available space
for the cabin
•Usable cabin space is steadily
increasing with alternate
solutions for anti-torque
•These solutions could enable shuttles from
heliport to heliport between city centres
carrying 100 plus passengers
Trends in Rotor Blades
• New thoughts in Rotor Design are required for
– Optimising
blade performance
in advancing and
retreating sides
– Reduce vibrations
– Reduce noise
• “Smart” blades, which change shape Chordwise, or camber
wise, are being developed
• These use Local Mod of aerodynamic characteristics of a
blade such as flaps, slots and boundary layer control to
optimise performance across the full revolution in forward
• Smart Blades use piezoelectric actuators–mechanical devices
incorporating a material that changes shape when subjected
to an electrical field
Trends in Rotor Blades
FLAPS- FOR MODIFYING LIFT
AND REDUCING VIBRATIONS
DROOP - FOR PREVENTING
DYNAMIC STALL ON
RETREATING SIDE AND
REDUCING VIBRATIONS
GURNEY FLAPS- FOR
INCREASING LIFT ON
REREATING SIDE
SLOTS FOR RE-ENERGISING
BOUNDARY LAYER
Trends in Rotor Blades
• NASA , in collaboration with Boeing and DARPA, has tested
smart blades in a wind tunnel.
• However, there is a long way to go as there are many
challenges
– Weight and Space constraints
– Centrifugal loads
– Reliability ( more than 10000 flight hours at failure rate < 10-9
per hour)
• Challenge greater for actuator which need to work more than once
during a rotation cycle, for eg those used for active vibration control
– Failures must not result in uncontrollability or adverse decrease
in performance
A SMART TEST PILOT WOULD BE VERY CAUTIOUS FLIGHT TESTING
THESE!!
Efforts towards Reduction Of Noise
Sources of Noise
DESIGN TRENDS FOR REDUCTION OF NOISE
• Modulated Blade Spacing
– Frequencies in equally spaced blades are related to
spacing
– Modulated blade spacing reduces noise by
• Lower peak sounds
• Distribution of acoustic energy over wider spectrum of
frequencies
• Reduced tip speed
• Tip redesign mainly for reducing vortices and
reducing noise impact of blade passing through
vortices
• Aerofoil tailoring as in smart blades
OTHER INTERESTING AREAS OF NEW DESIGNS
Engine power
•
Use of Silicon carbide ceramic materials in turbine blades
• Electric Distributed Propulsion
– One/Two main engines producing Electric power and
charging batteries
– 6-8 ducted propellers driven by batteries and producing
thrust
– Very light weight super conducting cables
– Management according to flight mode
• Take off- use power
• Cruise – charge
• Descent – idle/windmilling
• Land - use
OTHER INTERESTING AREAS OF NEW DESIGNS
• Increasing of the AFCS autonomy
– Possible A/RPC problems.
– Clear definitions of when pilot has override needed
• Low Visibility Flying
– Autonomous Landings based on LIDAR and Hybrid Nav
systems with a specified RNP ( Required Navigational
Performance)
– Tactile cues
• Pilot wears a vibrating vest
• As the pilot comes into land, if a drift starts, say on his
right hand side, he would feel a vibration on his right
hand side.
Electric Helicopter
• The e-volo VC200 has become the first electric helicopter to make a
successful maiden flight, with multiple flights lasting several
minutes and reaching heights of nearly 22 meters high.
• Together with 18-rotor blades and a disassemblable architectural
system, the volocopter has been designed to host two passengers
for distances of up to 100km and a flight altitude of up to 6500 ft.
• Equipped with a sophisticated automated control system requiring
minimum piloting skills
Click here
• I have covered a few of the design efforts already in progress
• However the biggest problem facing helicopters today is adverse
weather operations
• Most of the current aids available, such as EGPWS, Autopilot
coupled modes, etc are still not enough to prevent Controlled
Flight into Terrain ( CFIT) as pilots often delay or are unable to
process all the information available
• No effective landing aids while landing at helipads in low
visibility
• Potential exists to develop autonomous systems using LIDAR
etc to fly in adverse weather in hills, or take over/suggest
action when a potential CFIT situation is imminent.
• signal
•Research and academic institutions, such as IIT K ,
could look into the needs of the hours, concepts of
the future and conduct research to enable this vision
•I leave you with a video outlining a possible futuristic
military scenario, which may possible give you some
thoughts on the direction design efforts need to take
•Aviation 2050 Vision