Our heavyweight helicopter equal in the world does not have
In Rostov started production of the most load-lifting rotary-wing car The Russian holding «Helicopt[...]
Negative drag
In Chapter 2 we described how upwash can occur at the tips of swept wings. When this happens, the resultant force vector is tilted forwards, so that negative drag, or thrust is generated. It is also possible to create a negative contribution
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Fig. 4.20 Creative Canard: the Vari-Eze designed by Burt Rutan Design features include wing-tip winglets doubling as fins, composite materials, and a nose wheel that can be retracted in flight, and for ground parking, as shown. Amateur pilots would probably get away with forgetting to lower the undercarriage; a common error A maximum cruising speed of nearly 200 mph, with a stall speed of 55 mph, despite a mere 6.77 m span, make this an attractive alternative to conventional designs |
to drag by bending the leading edge downwards. A low pressure is produced on the top of this drooped surface either by attached or vortex flow, and as it is facing forward, a negative contribution to drag results. The droop of the leading-edge needs to be matched to the flight conditions, and so, a movable leading-edge flap is required. The leading-edge flaps on the Eurofighter Typhoon shown in Figs 8.3 and 10.8 may be used for drag reduction as well as high lift production.
Clearly, it is not possible to pull oneself along by one’s bootstraps, and such a negative drag contribution can do no more than reduce the overall drag.
In supersonic aircraft, it would be possible to produce genuine overall negative drag or thrust by burning fuel to heat up and raise the pressure in the wake. However, there would be considerable practical problems in implementing such a system.
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Speed (m/s)
Fig. 4.21 The variation of drag with speed for a typical light aircraft
Note how the trailing vortex drag reduces with increasing speed while the boundary layer drag rises. The resulting total drag therefore has a minimum. Flying slower than the minimum-drag speed would require an increase in thrust
