Zolomuro No eBook available Lulu. These articles will add to the body of knowledge that Ray has helped to grow so well. Helicopter Aerodynamics 2 by Ray W. Torque Fay In Autorotation. A Tale of Luck in Helicopter Design. Flight Testing to New Helicopteer.
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Each week online, we will reprint a selection from those columns. The laws of physics that govern aerodynamics do not change. Our understanding of them is somewhat improved — but not yet perfect. Advertisement Three fields of endeavor have helped make us smarter since then. The first, a fairly new one, is computational fluid dynamics CFD. The second is wind tunnel testing, and the third, that only standby, flight-testing. He can now program the very basic equations governing fluid dynamics almost down to the molecular level.
He can also quickly sole the equations without making many of the assumptions that had previously been needed to make the old computational methods practical. Currently this capability is used to design new rotor-blade airfoil sections that can go to high angles of attack before stalling and to high Mach numbers before suffering from compressibility effects. High-speed computers allow the designer to account for the complicated interactions between shock waves and boundary layers that affect these characteristics.
This information is also essential to make good noise estimates from a rotor in given flight conditions. Additionally, it helps in estimating pressures on the portions of the fuselage and the tail surfaces in the rotor wake. And it helps to determine how the wake may affect the flight path of a missile that is launched from hover or low-speed flight. This field was just in its adolescence in Several theoretical approaches had been proposed that varied from fairly simple to quite complicated, but since the computer power to work the latter methods was not yet available, it was the fairly simple methods that were receiving the attention.
This is because it is very difficult to experimentally measure the velocity field in and around a rotor in order to get data with which the computer results can be correlated. Some progress along these lines has recently been made in wind tunnels through the use of a piece of sophisticated measuring equipment known as a laser velocimeter. At this time, the equipment is so bulky that it must be mounted at the side of the wind tunnel to probe the fluctuating velocity field at points just above or just below the rotor disc.
In the future we should expect that it can be mounted on the rotating hub and focused at a spot just in front of the blade element to measure its true angle or attack — not only on wind-tunnel models but also on full-scale helicopters in flight.
Wind-tunnel testing Helicopter engineers are sometimes accused of not taking as much advantage of the wind tunnel as their fixed-wing brethren.
But the fixed-wing folk commonly use such testing to make their aircraft fly as helicopters do — at low speed. They place their airplane models in the wind tunnel in their landing and takeoff configurations, with an emphasis on developing flaps and control surfaces to ensure safe airport operations. For this type of testing, only a part of the wind tunnel time is spent testing for cruise or maximum speed. These couplings are also of concern on hingeless rotors. Another wind-tunnel function in the helicopter industry has been in developing new rotor-blade airfoil sections.
The next generation of airfoils, which are more slab-sided, is flying on prototypes like the EH Industries EH and the Boeing technology demonstrator. Thus special tests are done with airfoil models that can be rapidly oscillated in both pitch and plunge to simulate what actually happens on a rotor in forward flight. The information, in turn, helps compute the thrust and power for an entire rotor. Whirl towers do, therefore, help the engineers gain confidence in their design, as well as make changes before building the full-scale aircraft.
Flight testing No matter how high the confidence level in a completed design, flight-testing almost always produces some surprises. Over the past 25 years, such surprises have provided much knowledge of helicopter aerodynamics. For example, the excessive trim chance through transition with a large, fixed, horizontal stabilizer was discovered in flight testing; first on the YUH Black Hawk and then on the YAH Apache.
This anomaly probably could not have been discovered any earlier by either CFD, wind tunnel testing, or even simulation.
Both aircraft had to be fitted with a moveable stabilator to avoid excessive pitch up during low-speed flight. Rotor masts were subsequently extended. This image was originally published with R. But unexpectedly, the befits applied to the retreating side was well; the tip could be flown to a higher angle of attack before stalling than could the original, unmodified blade. In , Westland Helicopters Ltd.
The results of other surprises from flight testing can be seen on helicopters in the forms of spoilers, slats, ventral fins, tip plates, and stabilizer trailing-edge modifications, which were not in the original design. In my opinion, neither CFD nor wind tunnel tests cold have predicted the potential problems or helped ver much in the solutions.
Conclusion So, the tools to study helicopter aerodynamics have greatly improved over the years. But they are not a cure-all, and good helicopters can still be designed without extensive use of wind tunnels and large computers for CFD.
Perhaps the best example is the helicopter with the current highest production rate, the Robinson R It was developed with neither. Receive the latest rotorcraft news right to your inbox.
Ray Prouty: Progress in Helicopter Aerodynamics
He was In addition to his achievements in the technical field, Prouty was known for his generosity and commitment in sharing his knowledge with others, in particular students and new engineers. His lectures, articles, papers and books have helped educate generations of rotorcraft engineers. He remained there until , and then worked at Sikorsky Aircraft as a helicopter aerodynamicist, - He was a stability and control specialist at Bell Helicopter - , then group engineer for helicopter aerodynamics at Lockheed Aircraft - He taught helicopter aerodynamics courses throughout the world after retirement. Prouty is a Grand Elder of the helicopter industry.
Helicopter Aerodynamics Volume I
Each week online, we will reprint a selection from those columns. The laws of physics that govern aerodynamics do not change. Our understanding of them is somewhat improved — but not yet perfect. Advertisement Three fields of endeavor have helped make us smarter since then.
Helicopter Aerodynamics And More Helicopter Aerodynamics by Ray W. Prouty
AHS Mourns the Passing of Ray Prouty