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I'm very interested in simplifying the mechanics of helicopter design and their safety factors. Most specifically, coaxial helicopter designs and their simplistic nature. I've done a lot of historical research on autogiro and helicopter design concept development, and have thus concluded that the coaxial design has some most favorable attributes. The Sikorsky "XH-59A or S-69" coaxial helicopter design of 1978 is a design point in favor. It was once thought to be the fastest (compound) helicopter ever built, capable of 322 MPH, using a 36 foot rigid (ABC) advanced blade concept rotor system. There were problems with the twin vertical/rudders and horizontal/elevator size and design that could have been remedied! Combining the Westland Helicopter U.K. "swept back blade tip design" with the Sikorsky S-69 overall coaxial design would make for a great non-conventional helicopter! Stan Hiller was on the right tract back in his "XH-44 and UH-4" coaxial helicopter design rigid rotor system 1940's days! I admire Mr. Hiller greatly, for he did not follow the "calf-path" design methodology, he explored all rotor system design concepts for himself (the Sikorsky S-69 rigid-rotor design is proof of Hiller's success). The Russian Kamov Coaxial Helicopter models are the only present coaxial helicopters in world existence! I make an analogy, I think of the Kamov like the Russian AK-47 rifle (much in demand by all our U.S. Special Forces: Army, Navy Seals & Air Force Commandos), they're both design built for reliability, rigidity and overall less maintenance! I've started an archives of every coaxial helicopter design ever built through flying prototype and have designed an experimental coaxial helicopter of my own. Compound helicopters were designed and developed to increase helicopter forward speed. They pay for the higher speed in a decrease in vertical take-off and hovering capability, since the wing interferes with the airflow through the rotor; then, too, the added weight of its structure reduces the payload capabilities. The tilt-prop designs were another step forward on the increase speed scale; the large models were capable of 300 to 400 mph. This system proved inferior to both the helicopter and compound helicopter in vertical take-off and in hovering ability; their propellers were not as an efficient rotor systems. Control in hovering flight was not as good and payload that could be lifted vertically was much less (for the same power) than with a helicopter. Also, the vertical take-off of the tilt-prop designs were more of a strain on the engines than that of a helicopter. VTOL aircraft are not as safe as true helicopters due to not having autorotational capabilities in an engine failure, these aircraft are completely dependent on their engines for vertical and horizontal vented thrust. Advantages of coaxial over conventional helicopter designs: 1.) Excellent maneuverability, 2.) Good ground clearance, 3.) Better liflting capability per main rotor diameters than single rotor configurations (approximately 1.75% greater increase per given rotor diameter), 4.) As vertical separation of the coaxial rotors increase (between 10 to 25%, right at 17.5% of one rotor radius), they approach the power efficiency of a isolated single rotor configuration in forward flight. At 10% or less of the rotor radius vertical rotor separation, a 1.41% increase in induced power is required. As rotor separation approaches or reaches 25% of rotor radius, the harder the lower rotor has to work to develop and maintain its share of rotor thrust. "Vertical separation of rotor wakes determine efficiency." 5.) Coaxial configuration helicopters also avoid the tendency of the single rotor helicopter to roll during high speed flight. A rotor's advancing blades combine their rotational speed with the helicopter's forward airspeed to produce increased lift on one side of the rotor; the retreating blade, in contrast, subtract their rotational speed from the helicopter's forward airspeed and produce less lift. The resulting asymetrical lift at high speed produces roll forces that increase with forward airspeed. Coaxial helicopters whose rotors turn simultaneously in opposite directions, in contrast, present an equal number of advancing and retreating blades on each side, thereby neatly avoiding this problem, 6.) Coaxial helicopters utilize all their power to generate lift and directional or forward thrust, instead of 15 - 20% power loss due to power required for anti-torque tail rotors, 7.) Coaxial Helicopters require less maintenance and weigh less due to having a shorter tail section, no tail rotor: drive system, gear box, collective or its control system, 8.) Coaxials are easier to control in high cross-wind or tail-wind conditions due to their balanced main rotor torque and shorter tail sections. Conventional helicopters, due to their long tail sections, tend to wind vane and can run out of positive tail rotor pedal for anti-torque yaw control, 9.) Coaxials are safer, there's no chance of yaw or directional control loss due to tail rotor failure or possible tail rotor mishaps, 10.) Coaxial helicopter are a more compact design due to the smaller length tail sections based on the radius of smaller diameter rotor disc requirements and 11.) Coaxial designs also offer a greater (c.g.) center of gravity payload range. Note: Past coaxial helicopter designs, especially of the 40's lacked
development of vertical/rudder tail fins for aid to differential collective
for lateral (OGE & IGE) yaw control and a horizontal/elevator for
aid to cyclic pitch control at cruise speeds. In place of differential
collective, the use of a braking system to engage either one or the
other of the concentric rotor shafts to offset rotor torque for yaw
control needs further design exploring. Both aided systems for yaw and
pitch control, I employ in my coaxial helicopter design.
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Coaxial
vs. Conventional Helicopter & Tilt-prop VTOL designs
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I would love to write something about the aerial stunt work in either
Feel free to email me information or attachments or fax me materials
Thanks in advance. Sincerely, Stewart Wolpin Stewart Wolpin
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I am an avid air show fan.....After years of Internet research on air shows, I only today found this site....are you a magazine? How may I subscribe? Thank you
804 275 0064
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I have read the story of Mr. John O'Grady on your website. I was Sincerely Marlow Ben
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I am looking for information to organize a gliding summer in Turkey. Does anybody knows about flying conditions and autorisations to obtain. Thanks in advance.
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Does anyone have comprehensive list of Ultralight / Microlight models
which Roger
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after all we prepared some pictures from our 23rd Ljubljana Cup, I'm
shure you will enjoy looking pictures and remember very nice feeling
from Ljubljana Cup.
See: 26.10.2001: Photo gallery of the 23rd Ljubljana Cup Take your time and look at the pictures! Regards!
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| OTHER ARTICLES OF ASI NOVEMBER
2001 ISSUE | Editorial |
From The Secretary General's
Desk | Air Waves |
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