henry@zoo.toronto.edu (Henry Spencer) (03/22/91)
From: henry@zoo.toronto.edu (Henry Spencer) >>>F-102 - top speed was much less than expected. Research into the problem >>>resulted in the "area rule"... > > What is this "area rule" I haven't heard of it and I am curious. Actually, the original statement was a bit inaccurate, if I recall rightly. The area rule slightly pre-dated the F-102, but the F-102 was what really brought it to everyone's attention. It is more than slightly embarrassing when a fighter contractually obligated to reach Mach 1.5 can't go supersonic at all... The simplest statement of the area rule is that the cross-sectional area of the aircraft, measured in the plane perpendicular to the direction of motion, should change smoothly from nose to tail. (In fact there is an ideal curve for it, and the details change slightly when speed significantly exceeds Mach 1, but that's the general idea.) The F-102's problem was that the bulge in cross-sectional area contributed by the delta wing came at a point where the fuselage was still big and fat too, so the graph of c-s area came to a horrendous peak near the rear. The fix was to slim the fuselage down as much as possible there, and *add* fuselage bulk further aft to smooth out the abrupt drop in cross section behind the wing; the result, the F-102B, did meet the speed specs. Some other aircraft of the time have more or less obvious measures taken to smooth overall cross-section where the cross section of the wing peaks. This is, for example, why the B-58's fuselage slims down aft, and why its inboard engines are mounted very far forward on long pylons while its outboard engines are mounted very far aft. More modern aircraft tend to pay attention to the area rule in more subtle ways, and ostentatious fuselage taper isn't common. -- "[Some people] positively *wish* to | Henry Spencer @ U of Toronto Zoology believe ill of the modern world."-R.Peto| henry@zoo.toronto.edu utzoo!henry
johnm@vme.heurikon.com (John Mahoney) (03/23/91)
From: johnm@vme.heurikon.com (John Mahoney) >to a horrendous peak near the rear. The fix was to slim the fuselage down >as much as possible there, and *add* fuselage bulk further aft to smooth >out the abrupt drop in cross section behind the wing; the result, the >F-102B, did meet the speed specs. I don't seem to recall there ever having been an F-102B. I was under the impression that the speed problem was discovered on the prototype XF-92 and the design changes were incorporated into the F-102A. Even the two-seater 102 was labelled the TF-102A, if memory serves. I'm pretty sure that the follow on, instead of being the F-102B, was the venerable F-106. (IMHO one of the sexiest looking airplanes ever built!) Or am I just having another one of those pesky memory faults?
henry@zoo.toronto.edu (Henry Spencer) (03/25/91)
From: henry@zoo.toronto.edu (Henry Spencer) >From: johnm@vme.heurikon.com (John Mahoney) >I don't seem to recall there ever having been an F-102B. I was under the >impression that the speed problem was discovered on the prototype XF-92 >and the design changes were incorporated into the F-102A. Even the two-seater >102 was labelled the TF-102A, if memory serves. I'm pretty sure that the >follow on, instead of being the F-102B, was the venerable F-106. (IMHO one >of the sexiest looking airplanes ever built!) Or am I just having >another one of those pesky memory faults? I think you need to get somebody to run diagnostics on that memory. :-) However, you did get some of it right, and I goofed on the designation... The XF-92 did not discover the problem because the 92 was subsonic by design. The first two 102s were YF-102s (there was no XF-102); first crashed early, but problems in transonic performance were already evident; second confirmed them... with production 102s (admittedly, meant for use in the development program) already on the line. Months of frantic work produced a drastic redesign, prototyped as the YF-102A, a rebuild of 102 number seven. This one reached Mach 1.2 without difficulty. Some problems were found on the way to 1.5, but it was eventually achieved. The production aircraft, based on this design, was the F-102A. The trainer was the TF-102A. An advanced version using the J-75 engine was originally put under contract as the F-102B, but ended up being almost totally different and became the F-106 instead. -- "[Some people] positively *wish* to | Henry Spencer @ U of Toronto Zoology believe ill of the modern world."-R.Peto| henry@zoo.toronto.edu utzoo!henry