Hiller VZ-1
| Hiller VZ-1 | |
|---|---|
.jpg) VZ-1 in flight |
|
| Type: | Micro helicopter |
| Design country: | |
| Manufacturer: | |
| First flight: |
February 1955 (unbound) |
| Number of pieces: |
3 (6?) |
The Hiller VZ-1 Pawnee (factory designation Model 1031) was a vertical take-off and landing aircraft made by the American manufacturer Hiller Helicopters Company , which can be viewed as a miniature helicopter in terms of its structural design . At least three prototypes were built. The recently (2019) popularized Flyboard Air by Franky Zapata represents a similar development . Here, however , jet engines are used instead of the rotors driven by piston engines .
history
First of all, it should be noted that the development of the VZ-1 is shown in the literature to be highly contradictory. Harding (1990) and Jim Winchester (2005) (cited by Aviastar), Aerofiles and Jay P. Spenser (2003), for example, only list three units built, while Hiller's website describes the construction of six machines. However, it is undisputed that only two copies received the Army designation VZ-1 (see designation system for aircraft of the US Army from 1956 to 1962 ) and a military serial number .
prehistory
At the end of the Second World War, Charles H. Zimmerman began developing a vertical take-off aircraft, which was nicknamed the Flying Shoes . wore. This was a tubular steel platform with two small two-stroke four-cylinder engines from a targeting missile that powered propellers pointing upwards. The pilot buckled his feet and increased the engine speed with a twist grip. The control was carried out by shifting weight ("kinesthetic" control) by leaning the pilot in the desired direction of flight.
Stanley Hiller visited Zimmerman in Connecticut and had his aircraft brought to California for testing at his company. At the beginning of 1948 the Flying Shoes arrived in Palo Alto, where the first tethered flights could be carried out close to the ground. The two uncoupled motors made it difficult to deliver even power to the two propellers; the failure of an engine would inevitably have led to a crash. The tests were stopped in 1948 and only resumed after the Office of Naval Research (ONR) approached Hiller and commissioned him on September 17, 1953 to develop an improved version (Model 1031) in which the jacketed propeller concept by Alexander Satin was taken into account should. In addition to Hiller, de Lackner also received an order to build a flying platform, which, however, used open rotors. The program was supervised by the ONR on behalf of the US Army.
Model 1031
In September 1954, the construction of the Model 1031 (still without military designation and serial number) was completed. The VTOL research aircraft was supposed to investigate the usability of the ducted propeller as a drive unit and the potential military value as a tactical reconnaissance and transport vehicle. The first prototype was given the temporary Army designation YHO-1E . The first untethered flight was carried out in February 1955. The first prototype had a superficial resemblance to the de Lackner HZ-1 developed at the same time , which also used two small piston motors to drive counter-rotating propellers located below the platform. In the model 1031, however, the propellers were covered (see ducted propellers ).
The hover behavior of the flying platform was relatively stable. When flying forward, it also showed a self-stabilizing behavior, making it almost impossible to tip over. At the same time, however, this feature limited the forward speed to 26 km / h. In this concept model, each of the two two-stroke engines was still driving a rotor, which would have led to total control failure if one engine had failed.
Model 1031-A
The Army was so impressed by the flight performance of the device during testing that they commissioned another, modified specimen in November 1956, which was to be used for a mission evaluation. The variant now called VZ-1 (Model 1031-A, US Army serial number 56-6944) differed from the first version by adding a third motor and a propeller casing with a larger diameter. The machine had its maiden flight in 1958. Both motors now acted together on both rotors. In the event of an engine failure, there would be a quick descent, but no loss of control. Instead of the now no longer possible control method around the vertical axis by means of differential speed control of the motors, movable air baffles were installed in the air inlet. Due to the low engine power, this version could only be operated in the area of the ground effect .
Model 1031-A-1
Hiller determined that the circular surface loading of the two rotors was too high for the Model 1031-A , whereupon longer rotor blades were used. However, this made the construction of a larger, third platform necessary, which was now named Model 1031-A-1 (56-6945) and flew for the first time on November 20, 1957. At this point, the US Army took over the US Navy contract with Hiller. Although the new platform could now operate outside of the ground effect thanks to the new rotors with a diameter of 2.13 m, there was now another problem. Due to the greater weight, the center of gravity shifted so far down that control by shifting body weight was only effective to a limited extent. The increased weight also led to a reduction in flight stability, which could not be compensated for by shifting the pilot's weight. In addition to increasing the pilot's position, a gyro stabilization system that came from the Hiller UH-12 helicopter was then installed. This system was connected to baffles that were now arranged in the propeller outlet and could actually improve the stability considerably. A soldier's shooting demonstration on the platform showed the stable flight behavior very clearly. When flying forward, however, unpredictable vibrations occurred even in light winds that could not be compensated by the stabilization system.
The three machines provided a lot of information about VTOL flights in general and about the properties of ducted propellers in particular. In the end, however, the concept of the flying platform was too cumbersome, too slow and mechanically too fragile to be of any real value for combat use. The further development was stopped and by 1963 all copies had been shut down. One machine is on display today (2019) in the Udvar-Hazy Center of the National Air and Space Museum .
More copies?
According to a source, the US Army placed an order for three further developed copies of the VZ-1, which should also use three (more powerful?) Engines. This requirement made it necessary to increase the rotor diameter again to 2.44 m. However, this led to a further exacerbation of the control problems, so that kinesthetic control was no longer possible. Hiller tried to increase the stability by extending the rotor casing and also developed a more conventional control system in which a pilot operated a control stick in a seated position that was connected to the air deflectors. Although this design achieved a higher forward speed, the remaining control and instability problems remain unsolved.
construction
The VZ-1 is a one-man mini helicopter in which the pilot stands on a round frame under which two counter-rotating coaxial propellers rotate in a cladding made of fiberglass composite material. The diameter of the propellers was increased in several stages from 1.53 m to 2.44 m. Initially in the air inlet and later in the outlet stream, eight movable baffles were also attached to improve lateral stability. Control was carried out by the upright pilot by simply shifting his weight in the desired direction of flight, also known as kinesthetic control . The speed control of the motor was designed like a motorcycle with a simple throttle grip.
The second machine had a simplified control panel. The last VZ-1 had a much higher propeller casing than the first two machines and a circular landing skid instead of the previous three and four point landing gear. The controls were now also designed similar to those in a helicopter.
See also
literature
- Stephen Harding: US Army Aircraft since 1947. Airlife Publishing, 1990, ISBN 1-85310-102-8 , pp. 144 f.
- Leonard Bridgman (Ed.): Jane's All The World's Aircraft - 1955–56. Samson Low, Marston & Company, London 1955, p. 269.
- Jim Winchester: The World's Worst Aircraft. 2005.
- Jay P. Spenser: Vertical Challenge: The Hiller Aircraft Story. 2003. Quoted from www.secretprojects.co.uk (accessed August 11, 2020)
Web links
- Brief description of the history (accessed on August 11, 2020)
- Description on hiller.org (accessed August 11, 2020)
- "The Sky-High Invention" including a description of the control system on howtoadvice.com (August 11, 2020)
- Flight recordings of the first machine on youtube.com
- second machine (larger jacket diameter) of the Smithsonian
- Replica of the Hiller VZ-1 PAWNEE (in original size) in the helicopter museum in Bückeburg
Individual evidence
- ↑ Description at aviastar.org (accessed on August 11, 2020)
- ↑ Description at aerofiles.com accessed on August 11, 2020
- ↑ Description on hiller.org (accessed on August 11, 2020)
- ↑ Photo of the Flying Shoes
- ↑ Steve Lehto: The Great American Jet Pack: The Quest for the Ultimate Individual Lift Device , Chicago Review Press, 2013. from excerpt online
- ↑ Tied "test flights" (accessed on August 11, 2020)
- ^ John M. Andrade: US Military Aircraft Designations and Serials , Midland Counties Publ., 1979, p. 176
- ↑ Demonstration of the flight behavior of the Model 1031-A-1, from minute 1:30 (accessed on August 11, 2020)
- ↑ Last version with high propeller casing (accessed on August 11, 2020)
- ↑ Description on airandspace.si.edu (accessed on August 11, 2020)
