Bölkow Bo 46
The helicopter type Bo 46 was a project of the German helicopter manufacturer Bölkow developments KG. It was from 1961 a prototype Bo 46V1 built with the registration D - 9514, which also flew in Neubiberg on 30 January 1964. The program was discontinued in early 1965. The helicopter Bo 46 based on the principle of Derschmidt rotor.
Principle Derschmidt rotor
" Normal " Rotor
The lift is on the rotor generated by that wing of the centrifugal force centered rotate about the rotor axis. The buoyancy is determined by the curvature and the appropriate employment of the blade profile is generated ( collective employment ), the propulsion through a cyclic pitch of the rotor blades per round. Thus, the rotor disk tilts in the direction of the propulsion and the helicopter flies forward, sideways or backwards, depending on the controlled cyclic pitch of the blade profile. Technically correct, therefore, is the term rotorcraft.
By the rotation of the rotor blades maintain a constant face velocity. Added to this is still the incoming flow by the forward motion, which is the leading - rotating in the direction of flight - summed rotor blade and the retreating blade subtracted. A normal rotor has therefore impact and swivel joints at the so-called rotor head. They allow the blades to move in the longitudinal direction within limits up and down inside the rotor disc in the radial direction, forwardly or rearwardly. Even with the so-called rigid rotors, the rotor blades make these movements by the elasticity with correspondingly shaped rotor heads or rotor arms.
The helicopter designer must now make sure that the outer blade tips at the leading blade is not in the supersonic (Mach 1.0 ) advised. This would produce stalls and let collapse the lift at the blade tips. In addition, the noise level rises through the sonic boom at the leading sheet substantially, and the sheet is mechanically extremely stressed.
It has been found to be physically optimal constant rotor blade tip speed is a function of rotor speed and the rotor diameter, to set at about 0.7 Mach. There are still about 0.3 Mach ( about 300 km / h) for a forward speed. Therefore, helicopter rotors rotate all in the range of 700 km / h at the blade tips. Conversely, the helicopter has in the forward speed its natural limit of about 300 km / h
If you want to fly faster, you have to reduce the rotor speed, to compensate for the case is less buoyant by wing and / or attach an additional propeller for propulsion, an expense that reduces the payload on uneconomic values , as the experiments with the so-called Compound helicopters of different manufacturers - inter alia even at Bölkow / MBB, with the Bo 105, if only to record purposes - have consistently confirmed. Recently, this statement is contested by more recent developments such as the Sikorsky X2 into question.
Derschmidt rotor
The blades fully perform the pivot joint, even a small pivotal movement relative or with the air flow direction of flight, but with - is limited and damped shock absorbers - usually hydraulic.
Dipl. -Ing. Hans Derschmidt since 1946 pursued the idea and had a patent on the advancing rotor blade the air flow much further yielding vorzuschwenken voreilend back and the retreating rotor blade according to the air flow. Thus, the blade tip speed would be reduced and this profit be used for increasing the airspeed. Derschmidt expected to 500 km / h possible forward speed of such helicopters. As a side effect aerodynamic load / performance at the leading and hurrying back blades with less vibration would be more evenly distributed.
Derschmidt therefore increased the pivotal movement on the rotor blade at up to / - 40 ° per cycle, and depending on the speed. In the hover the pivotal movement was practically zero, at full speed at the leading sheet to -40 ° and 40 ° at the analog retreating blade. Derschmidt was aware, and that was the content of the patent, that all movements had to be harmoniously matched with each other ( in resonance ) to kinematic and aerodynamic produce no additional charges. You could have the positive effect zunichtegemacht again. He pointed the principle theoretically and experimentally by, found advocates in the science and research and Bölkow agreed with Derschmidt as an employee and matching funding from the Research and the Department of Defense to develop the rotor and a helicopter. It has a rotor system with 6 m diameter for bench tests and a rotor system with a 10 m diameter for flight operations in the helicopter program Bo 46 built.
Bo 46
The project was named Bo 46 Which law hid behind the same designation to located parallel in development, for example, Bo 105 and the previous patterns Bo 102 and Bo 103, is unknown.
The fuselage of the Bo 46 received a streamlined, one wing aircraft similar sleek and aerodynamic shape. In the cabin were two seats side by side. A photo can be seen on the website of the Helicopter Museum Biickeburg, where the prototype is also issued. The interest of the military was not for nothing. The qualities of the helicopter He had then already recognized as a weapon, which then also later in receivables led to anti-tank helicopter. The Bo 46 but was still in the technical approach, an experimental system and would have been " militarized " only in a further step.
After promising experiments with the test rotor was 1963/Anfang end of 1964 the flying system ready for its maiden flight. The first attempt to float serious problems in the controllability showed. Hastily implemented changes to the hydraulic control (doubling the hydraulic pressure ) brought no improvements. Only broader investigations showed that the system had to depend on a very accurate and fast position control without dead times. Extensive changes were needed and it came in the fall of 1964 to further hovers. It was found that the system already in hover without the forward and backward pivoting of the blades in his interaction was too complex and too sensitive to dare to forward flights. After failures with the rotor test rig, which still aufzeigten material problems, the program was discontinued.
Today the speed limit of the helicopter is accepted with the fixed wing aircraft because of its other qualities in peaceful coexistence. The last attempt in the USA with the Kipprotorsystem Bell - Boeing V-22 to connect the properties of the helicopter with those of the surface plane, had to contend with many technical problems. Despite the difficulties, the project was continued. The first machines were delivered to the U.S. Air Force in 2005, and some copies have since September 2007 with the U.S. Marines in Iraq in combat. Also, Bell and Agusta are still working on their civil tiltrotor aircraft BA609 which 2003 its first flight successfully completed.
Whereabouts
Of the three originally built machines exist alone nor the Bo 46 V1 with the registration D - 9514th They can be visited in Helicopter Museum Biickeburg.