Bill Gunston's conceptual stealth aircraft designs

[Weaver]

A thought's just struck me about how you could reconcile the BG design with the fan-size problem using Martin's reverse-flow suggestion. Suppose the engines are mounted backwards in the rear fuselage with a reverse-flow intake, and all four nozzles are hot? The engines have normal-sized fans, but bifurcated jetpipes. The upper half of each jetpipe runs forward, over the wing box and weapon bay, and then down to the front nozzle on the same side. The lower half of each jetpipe runs across the fuselage, behind the weapons bay, to the opposite rear nozzle. The advantage of this is that, unlike the two-nozzle RIVET design, a single engine failure in the hover takes out two diagonally opposite nozzles, giving a "flat fall" rather than a violent roll. It does mean a lot of space taken up by jetpipes, but then they can be bent or "squashed" (within limits) to recover some space-efficiency.

[martinbayer]

Weaver,

interesting idea! I played a little more with possible options for the RIVET concept as well and wondered what an arrangement of four identical engines would look like, with the two towards the front of the plane possibly installed at some upward angle to the horizontal to facilitate integration. Fan diameter of the individual engines would be further reduced due to the lower required throughput and thrust, and nozzle flow losses would be lower than in extended exhaust ducts. Individual engines could be throttled or cut to compensate for failures at the opposite corner of the thrust quadrangle during VTOL maneuvers, or to increase fuel efficiency during cruise. On the other hand this alternative obviously increases complexity and decreases overall reliability, the smaller engines lower overall efficiency and increase dead mass during cruise, and the inlet ducting would be fairly complex. Still an intriguing thought though...

Martin

[PR19_Kit]

The lower half of each jetpipe runs across the fuselage, behind the weapons bay, to the opposite rear nozzle. The advantage of this is that, unlike the two-nozzle RIVET design, a single engine failure in the hover takes out two diagonally opposite nozzles, giving a "flat fall" rather than a violent roll. It does mean a lot of space taken up by jetpipes, but then they can be bent or "squashed" (within limits) to recover some space-efficiency.

Wasn't there a similar sort of idea put about when the P1154 was being planned? One of the umpteen versions proposed, I think an FAA shipboard version, had two engines and cross-over jetpipes/exhausts so the aircraft could keep flying straight and level long enough for the crew to eject on case things went TU.

Having seen the test BS100 engine at Yeovilton I'm astounded that they could come up with such an idea looking at the size of the PCB driven front nozzles, they are HUGE!

[rickshaw]

Wasn't there a similar sort of idea put about when the P1154 was being planned? One of the umpteen versions proposed, I think an FAA shipboard version, had two engines and cross-over jetpipes/exhausts so the aircraft could keep flying straight and level long enough for the crew to eject on case things went TU.

Yes there was.  I remember seeing a diagram of it in a book about Rolls-Royce, I think it was many, many moons ago.  It had what I thought were very seriously complicated trunking, with trunks going over one engine to the other side and vice-a-versa.  IIRC it was for a twin-Spey powered P.1154.