National Aeronautics and Space Administration 

NASA AERONAUTICS RESEARCH ONBOARD 

DECADES OF CONTRIBUTIONS TO TILT ROTOR AVIATION 

1950s—1990s 

AEROELASTIC STABILITY 

COMPUTATIONAL FLUID DYNAMICS (CFD) H v F NOISE DATABASE 

H Applies also to commercial aircraft 

v Applies also to military aircraft

 F Applies also to general aviation aircraft 

4 

1 2 

8 DATA ACQUISITION SYSTEM 9 WIND TUNNEL TESTS H v F 10 TILT ROTOR PROOF OF CONCEPT 

5 PROPROTORS 

6 FLIGHT CONTROL SYSTEM 

3 COMPOSITE STRUCTURES H v F

7 DISCRETE NACELLE POSITION CONTROL SYSTEM 

www.nasa.gov 
 

 

 

1. Computational Fluid Dynamics (CFD) 

Starting in the 1970s, NASA began developing sophisticated computer 

codes that could accurately predict the flow of fluids, such as the 

flow of air over an aircraft’s wing, fuel through a space shuttle’s main 

engine, or the complex interactions between a rotorcraft’s main rotor 

blades, fuselage and its tail rotor. 

Those ideas and codes became CFD, which today is considered a 

vital tool for the study of fluid dynamics and the development of new 

aircraft. CFD greatly reduces the time and cost required for designing 

and testing nearly any type of aircraft. 

NASA-developed computer software products are critical for modeling 

the tilt rotor in both hover and airplane modes. 

2. Noise Database 

Rotor blades generate noise and vibration inside and outside all rotary 

wing aircraft including the tilt rotor. NASA research validated that noise 

levels could be reduced with the aid of advanced rotor designs and 

new flight path approaches. 

3. Composite Structures 

NASA first partnered with industry during the 1970s to conduct 

research on how to develop high-strength, nonmetallic materials that 

could replace heavier metals on aircraft. Gradually, these materials 

have replaced metals in helicopter fuselages and rotor blades, and 

have become critical for reducing the weight of vertical-flight vehicles. 

4. Aeroelastic Stability 

During the decades of research conducted by NASA on the development of tilt rotor aircraft, a key area of study was discovering ways to 

prevent the unstable flexing of the tilt rotor, its wing and pylon. As a 

result, NASA developed a system of unique actuators that dampen 

motion and lessen instability in the proprotor. 

5. Proprotors 

NASA research enabled development of a combination, highly-twisted 

propeller/rotor that provides the thrust needed for vertical lift as well 

as forward flight. The blades of this propeller/rotor were eventually 

constructed from stronger, lighter and quieter composite materials. 

6. Flight Control System 

The ability to operate a vehicle in both vertical and horizontal modes 

of flight required a revolutionary flight control system. NASA research 

enabled the development of a system that blends and phases flight 

controls for both helicopter and fixed-wing airplane modes of flight. 

The system includes a tilt rotor pilot station with controls for pitch, roll, 

yaw and thrust in all modes (helicopter, tilt and airplane). 

7. Discrete Nacelle Position Control System 

NASA research enabled development of a system that would automatically advance a tilt rotor’s nacelles to new positions at modest rates 

so that the pilot could focus on primary flight control. The discrete 

nacelle position control system, used today on the Bell/Agusta 609, 

makes operation of tilt rotor aircraft more predictable during instrumented flight and approach to landing. 

8. Data Acquisition System 

During the tilt rotor research program, NASA developed a digital data 

acquisition system that could capture multiple streams of wind tunnel 

and flight test data. The system was able to withstand the oscillation 

forces generated by test apparatus while still accurately capturing and 

transmitting pressure, temperature, load, torque and position data. 

9. Wind Tunnel Tests 

NASA wind tunnels were, and continue to be, used to test tilt rotor 

models and research aircraft for: aerodynamic performance; structural 

load capacity; mechanical, electrical or hydraulic systems performance; aeroelastic stability; and noise reduction. 

10. Tilt Rotor Proof of Concept 

Flight tests using the XV-15 tilt rotor research aircraft and simulations 

conducted by NASA, the U.S. Army and Bell Helicopter were vital to 

proving the feasibility and practicality of the tilt rotor concept. Decades 

of research from the tilt rotor program led to production of the world’s 

first operational tilt rotor, the V-22 Osprey for the U.S. military, and the 

first civil application, the Bell/Agusta 609.

www.aeronautics.nasa.gov 

NL-2008-12-012-HQ