henry@zoo.toronto.edu (Henry Spencer) (07/05/89)
From: henry@zoo.toronto.edu (Henry Spencer) >When the F-111 first came out, it had a _terrible_ problem with engine >stalls. The engine would stall during ground engine runs, even. This >was due to a bad inlet design... In fairness, it should be added that the intake design would probably have been fine for a turbojet, but this was the first use of a turbofan in a fighter and nobody realized that turbofans cared more about smooth flow. Mind you, nobody had made any particular effort to find out whether turbofans had the same inlet-compatibility characteristics as turbojets. The engine manufacturer thought it was the inlet's problem, the inlet designers thought it was the engine's problem, and the USAF thought that because the contract said it had to work, it would. It's also noteworthy that British designers working on swing-wing aircraft had looked at the F-111 and expressed reservations about the placement of the inlets. (Rough flow is a particular problem with the F-111 because the inlets are well aft under the wings, and there is a lot of fuselage ahead of them to mess up the flow.) Actually, the Brits had reservations about a number of aspects of the design; if you compare the F-111 with the later Tornado, you can see some of them. Nobody listened. (Oh, all right, a sampler... F-111 intakes too far aft under wings; Tornado intakes are forward on fuselage sides. F-111 wing pivots too far outboard; Tornado pivots are in fuselage. F-111 fuselage bottom useless for stores due to undercarriage retraction; Tornado undercarriage retracts into *sides* of fuselage, leaving underside free for weapons. Except for its smaller size -- despite a reputation as a big aircraft, Tornado actually isn't much larger than an F-18 -- the Tornado is what the F-111 should have been.) The most interesting aspect of the whole thing was that production rolled along steadily despite glaring evidence of problems. The definitive fix for the inlet problems involved significant structural changes, and by the time it was sorted out, something like the first 50% of the production F-111s were too far along to incorporate it. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu
IA80007%MAINE.BITNET%CUNYVM.CUNY.EDU@CUNYVM.CUNY.EDU (Martin E. Kader) (07/15/89)
From: "Martin E. Kader" <IA80007%MAINE.BITNET%CUNYVM.CUNY.EDU@CUNYVM.CUNY.EDU>
I agree that the F-111A had problems with the inlets and compressor
stalls when it was in the pre-production and production stage of its
development, but these problems were corrected by the time the D, E, and
F variants were developed. But, I must take exception to your comment
about the Tornado being the plane the F-111 should have been. If you are
comparing the F-111A to the Tornado, then I say there is no comparison.
That comparison would be like comparing a '65 Corvette with an '75 Corvette.
Now, if you want to compare the F-111F to the Tornado, then I say the
F-111F is the better aircraft. The F-111F has a max weapons load of
31500 lb and the Tornado has a max load of 20000 lb. The F-111F has a
combat radius (hi-lo-hi) of 1480 km, the Tornado's combat radius is 1390 km.
The service ceiling for the F-111F is 60,000 ft and the Tornado's is 50,000 ft.
Maximum speed at high and low altitude is about the only thing these aircraft
have in common, high: Mach 2.4, low: Mach 1.2. I think the F-111F is the
aircraft the F-111A was meant to be.
Martin E. Kader
University of Maine at Augusta
IA80007@MAINE.BITNET
IA80007@MAINE.MAINE.EDU
(Information taken from _The_World's_Great_Attack_Aircraft_, Gallery Books,
New York, NY, Aerospace Publishing 1988.)