Bölkow Bo 46
| Bölkow Bo 46 | |
|---|---|
 Bölkow Bo 46 V1 in the Helicopter Museum Bückeburg |
|
| Type: | Experimental helicopter |
| Design country: | |
| Manufacturer: | |
| First flight: |
January 30, 1964 |
| Commissioning: |
Development stopped in 1965 |
| Production time: |
was never mass-produced |
| Number of pieces: |
3 prototypes |
The helicopter type Bölkow Bo 46 was a project of the German helicopter manufacturer Bölkow Developments KG . A prototype Bo 46V1 with the registration number D-9514 was built from 1961, which also flew in Neubiberg on January 30, 1964. The program was discontinued in early 1965. The Bo 46 helicopter was based on the principle of the Derschmidt rotor.
Principle of the Derschmidt rotor
"Normal" rotor
The lift is generated by the rotor that wing centered by the centrifugal force to rotate about the rotor axis. The lift is generated by the curvature and the corresponding pitch of the blade profile (collective pitch), the propulsion by a cyclic pitch of the rotor blades per revolution. As a result, the rotor disc inclines in the direction of propulsion and the helicopter flies forwards, sideways or backwards, depending on the controlled, cyclical adjustment of the blade profile. The term rotary wing aircraft is therefore more technically correct.
The rotation gives the rotor blades a constant flow velocity. Added to this is the flow caused by the forward movement, which is added up when the rotor blade is advancing - rotating in the direction of flight - and subtracted when the blade is moving back. A normal rotor therefore has flapping and swivel joints on the so-called rotor head . They allow the blades to move up and down within limits in the longitudinal direction and to move forwards or backwards from the radial direction within the rotor disc. Even with the so-called rigid rotors, the rotor blades take part in these movements due to the elasticity of appropriately shaped rotor heads or rotor arms.
The helicopter designer must now ensure that the outer blade tips on the leading blade do not get into the supersonic range (Mach 1.0). This would cause stalling and collapse the lift at the blade tips. In addition, the noise level rises sharply due to the sonic boom on the leading sheet, and the sheet is mechanically extremely stressed.
It has proven to be physically optimal to set the constant rotor blade tip speed, which is a function of the rotor speed and the rotor diameter, at about 0.7 Mach. There remains about 0.3 Mach (about 300 km / h) for a forward speed. Helicopter rotors therefore all turn at the blade tips in the range of 700 km / h. Conversely, the helicopter has its natural limit at forward speed of around 300 km / h.
If you want to fly faster, you have to reduce the rotor speed, compensate for the lower lift from the wings and / or use an additional propeller for propulsion, an effort that reduces the payload to uneconomical values, like the tests with the so-called compound helicopters from various manufacturers - u. a. also at Bölkow / MBB, with the Bo 105 , if only for record purposes - have consistently confirmed. Recently, however, this statement has been called into question again by new developments such as the Sikorsky X2 or Eurocopter X3 .
Derschmidt rotor
Due to the swivel joint, the rotor blades already perform a slight swivel movement against or with the air flow in the direction of flight, but this is limited and dampened with - mostly hydraulic - dampers.
Dipl.-Ing. Hans Derschmidt had been pursuing the idea since 1946 and had a patent for moving the leading rotor blade back to the air flow much further and the returning rotor blade leading forward according to the air flow. This would reduce the blade tip speed and this gain could be used to increase the airspeed. Derschmidt expected forward speeds of such helicopters of up to 500 km / h. As a side effect, the aerodynamic load / power on the leading and trailing rotor blades would be more evenly distributed with fewer vibrations.
Derschmidt therefore increased the pivoting movement on the rotor blade to up to +/- 40 ° per revolution and depending on the speed. In the hover, the swivel movement was practically zero, at full speed on the forward blade down to −40 ° and analogously + 40 ° on the returning blade. Derschmidt was aware, and that was the content of the patent, that all movements had to be harmoniously coordinated with one another (in resonance) in order not to generate any additional kinematics or aerodynamic loads. You would have canceled out the positive effect. He proved the principle theoretically and experimentally, found advocates in science and research, and Bölkow agreed to develop the rotor and a helicopter with Derschmidt as an employee and appropriate funding from the Ministry of Research and the Ministry of Defense. A rotor system with a diameter of 6 m for test bench tests and a rotor system with a diameter of 10 m for flight operations in the Bo 46 helicopter program were built.
Bo 46
The project was given the designation Bo 46. It is not known what the regularity behind this designation was for the Bo 105, which was being developed in parallel, and the earlier Bo 102 and Bo 103 models .
The fuselage of the Bo 46 was given a streamlined, aerodynamically favorable shape, similar to a wing airplane. There were two seats next to each other in the cabin. A photo can be seen on the website of the helicopter museum in Bückeburg, where the prototype is also on display. The interest of the military was no accident. The qualities of the helicopter as a weapon of war had already been recognized at that time, which later led to demands for anti-tank helicopters. In its technical approach, however, the Bo 46 was still an experimental system and would only have been "militarized" in a further step.
After promising tests with the test stand rotor, the flying system was ready for its first flight at the end of 1963 / beginning of 1964. The first attempt at levitation showed serious problems with the controllability. Changes made to the control hydraulics quickly (doubling the hydraulic pressure ) brought no improvements. Only broader studies showed that the system was dependent on very precise and fast position control without dead times . Extensive changes were necessary and there were further hover flights in the autumn of 1964. It turned out that the interaction of the system was too complex and too sensitive to dare to fly forward even in hover flight without the rotor blades swiveling back and forth. After failures with the test stand rotor, which also showed material problems, the program was discontinued.
Today the speed limit of the helicopter is accepted because of its different qualities in peaceful coexistence with the fixed wing aircraft . The last attempt in US with the Kipprotorsystem Bell-Boeing V-22 the characteristics of the helicopter with those of the surface plane to join, also had to contend with many technical problems. However, despite the difficulties, the project continued. The first machines were delivered to the US Air Force in 2005 , and some examples have been in combat with the US Marines in Iraq since September 2007 . Also, Bell and Agusta still working on their civilian tiltrotor aircraft BA609 , which made its maiden flight successfully of 2003. Strictly speaking, these two types are not helicopters, but convertible aircraft . This also applies to the Bell V-280, which is currently in development . The experimental samples Sikorsky X2 and Kamow Ka-92, the prototype Sikorsky S-97 and the new development Sikorsky / Boeing SB-1 are, however, flight wipers .
Logbook entries of the test pilot
Entry in the logbook of the test pilot of the Bo 46, Wilfried von Engelhardt :
- February 14, 1964: first attempt to lift Bo 46
- October 27, 1964: four successful Bo 46 hovering attempts, total flight time 3 minutes
- October 28, 1964: four hover flights. Log entry "sluggish but controllable". Total flight time 18 minutes
- October 29, 1964: two landings from a height of more than 3 meters. A total of 13 minutes of flight time
Whereabouts
Of the three originally built machines, only the Bo 46 V1 with the registration number D-9514 still exists. It can be seen in the helicopter museum in Bückeburg .
Technical specifications
| Parameter | Data |
|---|---|
| Rotor diameter | 10 m |
| Number of rotor blades | 5 |
| Takeoff mass / TOW | 2400 kg |
| Engine | Turbomeca Turmo IIIB |
| power | 590 kW (approx. 800 PS) |
| projected speed | 450-500 km / h |
See also
Web links
Individual evidence
- ↑ Entry ( Memento of the original dated December 2, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. at Eurocopter
- ↑ Entry at bayerische-Flugzeug-historiker-ev
- ↑ Entry at hubschraubermuseum.de
