Graham Warwick / Washington DC Light Aerial Multipurpose Vehicle will be powered by ultra-efficient turbofans in the cruise

Boeing Phantom Works is seeking funding to develop a novel aircraft that uses simple pulsejets for vertical take-off and landing (VTOL).

The Light Aerial Multipurpose Vehicle (LAMV) uses pulsed-ejector thrust augmentor (PETA) engines for only 90s on take-off and landing. Small ultra-efficient turbofans are used in the cruise.

In the PETA concept, multiple pulsejets are mounted vertically in augmentor ducts running along the sides of the LAMV's fuselage. The ducts entrain freestream air, which augments the thrust of the pulsejets. The unsteady exhaust produced by a pulsejet draws in more air than the steady exhaust of a conventional jet, increasing the augmentation ratio.

"We can get augmentation of 1.6:1 with steady flow, but 2-plus with unsteady flow. We can double the thrust of the pulsejet, which is the pump for the ejector," says John Skorupa, senior manager strategic development, advanced airlift and tankers. Because it is essentially a simple tube, the thrust-to-weight ratio of a pulsejet is already high, at around 10:1.

The Phantom Works has studied several sizes of pulsejet, ranging from one producing 50lb thrust (0.2kN) at 150Hz, to one producing 1,000lb thrust at 60Hz. The smaller pulsejet is 0.9m (3ft) long and 25mm (1in) in diameter, while the larger is 3m long and 200mm in diameter. Higher thrust - and therefore longer - pulsejets could be accommodated in a fuselage by "bending" them, Skorupa says.

Boeing has shown two concepts. One has a 700kg (1,540lb) payload, removable wing and empennage and the other is a more conventional aircraft with a 1,600kg payload, 260kt (482km/h) cruise speed and a 2,000km (1,080nm) range.

Skorupa says the exhaust velocity of the pulsed-ejector thrust augmentors would be similar to the rotor downwash of a helicopter, and temperatures would be low, compared to other jet-lift VTOL designs, at around 80°C (175°F).

Source: Flight International