Is this only how far we've come? I may have surpassed my 90th birthday but I haven't lost my critical faculties. This Airbus Military A400M is a brute at 70t empty. With a 30t load and 15t fuel remaining (half that at brake release and maximum take-off weight) it can stagger up to FL310 (31,000ft/9,500m) and cruise impressively at 400kt (740km/h) with a comparatively modest lift coefficient of 0.544 and only 517kg/m2 (106lb/ft2) wing loading by my calculations. How so? Well despite the hype, the Ratier-Figeac FH386 propellers are not that impressive. The tips sweep a 16m (55ft) arc at 14 rev/sec so the M0.72 speed limit coincides with these tips going supersonic...the old problem. The spinner is there to overcome disk solidity at the blade roots as always and its bluntness or sweptness is a function of solidity, nothing more. Making the necessary adjustments for the number of blades, disk diameter, activity factor and whatnot, the propeller efficiency is still only 85%, albeit across a very wide band of speed. The advance ratio is 3.28 at sea-level indicated airspeed for a coefficient Cp of 0.55, yes a massive 10,700hp (8,000kW) (effective shaft horsepower?) where the mighty Tyne could "only" muster 6,100hp. But apart from broadband speed, a dual 3m four-blade prop from 1944 could do exactly the same. Is this all that 60 years' of progress has been able to come up with - oh and a 25% reduction in specific fuel consumption? James Scott Isleworth, Middlesex, UK
Joint Strike Fighter puzzle I spotted an advert (Flight International, 7-13 September) that featured a picture of the Joint Strike Fighter in hovering flight, which means I have to amend my original belief that the lift fan is much nearer the aircraft centre of gravity than the jet nozzle. Assuming that the centre of gravity is just forward of the main landing gear vertical struts, the lift fan and nozzle appear to be equidistant from it. Equally, since the power to weight ratio of the engine fitted to all variants is presumably greater than unity (excluding the full war loads situations), the conventional models, after taking off along the runway, can accelerate vertically, with 100% of the aircraft weight effectively carried by the jet nozzle. So the puzzle remains, to me at least - what is going on in the VTOL mode? The pilot rotates the jet nozzle through 90° to a point straight down, couples a rather substantial lift fan (which is shut down in wing borne flight) to the engine low-pressure compressor shaft, extracting an enormous amount of power from it in the process, somehow splitting the total resulting thrust equally between them, without apparently upsetting the basic operating parameters of the engine. There is no doubt in my mind that they do it, but how? Perhaps Uncle Roger or one of his nephews can help? The relevant information can't still be secret, can it? J A Kendal Wokingham, Berkshire, UK
The comfort of engines With due reference to James Wilkins "Single-engine champion" (Flight International, 26 October-1 November), I would prefer to think of myself as more "old-fart" than "old-guard". Personally, however admirable the Pilatus PC-12, the more engines scattered over the wings and fuselage the happier I, as "self-loading cargo", become! Andy Adams Pevensey, East Sussex, UK
The comfort of crews Congratulations are indeed due to Capt Gennotte, flight officer Michielsen and flight officer Rofail for their consummate skill and teamwork in saving the DHL Airbus A300 at Baghdad in November 2003. They also displayed in abundance those most human of qualities: innovation, determination and the will to carry on living, which no computer is likely to be able to reproduce in the foreseeable future. Let us therefore keep human flight crews where they belong - in the cockpit. The day I have to use a remotely crewed aircraft is the day that I stop flying. Paul Barker Uckfield, Sussex, UK
Can Rutan improve? Burt Rutan's supporters are still not understanding my point. Any comparison to the NASA/Alan Shepherd mission is bogus, as Shepherd was in a vehicle representative of one to follow, capable of true orbit and re-entry with all the associated dangers and technical challenges. The Rutan team has not built a vehicle capable of orbit or re-entry, nor has it any stated ambition to do so. The prize claimed did not require this. Furthermore, if Virgin can market suborbital lobs, then that is what the derivative vehicles will do. What is needed is a further competition for orbital flight and safe return, then Rutan's team might stretch its legs and NASA might be shown for the bloated, incompetent organisation these correspondents believe it to be. Peter Johnson Gloucester, UK
Source: Flight International
