Air intake like in the MIG-15 or the F-86 Sabre. Modern fighters, like the F-22, have two intakes under the wings close to the fuselage. I’m sure there’s a good reason for why the front intake was abandoned, I’m merely curious what those reasons are.
My guess is that most modern fighters use two jet engines for more power and with that configuration a front intake wouldn’t work. Also, that the nose is the best place for radar equipment and an intake there would be in the way.
You may notice on that F-22 that there are two engines; each needs its own air intake. On single-engine fighters, such as the F-16, the nose contains radar and other equipment that is helpful to have in the nose of a plane, so the intake is moved down.
I’m sure someone else will cover aerodynamic issues.
The US and several other partner countries are currently developing a new aircraft called the Joint Strike Fighter. There was a competition in the late 1990s for the design of the plane. One of the entries in the competition featured an air intake for the single engine fighter that was somewhat closer to the nose inlet of years gone past.
In the case of modern single-engined fighters (e.g. F-16), I think it’s because mounting the intake under the nose gives room for a larger radome, and therefore a more effective radar system. The early jet fighters you mentioned had very limited radars. I’m not sure what the pros and cons are from an aerodynamic point of view. However, it is possible to build a very fast jet with a front intake: http://en.wikipedia.org/wiki/English_Electric_Lightning
Front intakes allow radar to see the compressor fan of the engine which gives a nice fat return signal. Chin and side intakes bury the engine in the fuselage and use curved ducts to route intake air to it hiding the compressor fan disk from radar.
QFT. Also, because of the intricate surfaces inside a jet engine, the radar cross-section (RCS) is large over a wide range of frequencies. (Basically, any edge that’s an equal multiple of the wavelength gives you a strong return in that wavelength, and inside the engine, you can find edges of nearly every relevant length).
Even in old front intake aircraft the engine was in the back, so they were actually buried further from the intake so I really don’t think radar cross section was the issue. See this image. Also take a look at the intake of a Mig 15 and you can see a very obvious dam routing the air around the cockpit; there is no line of sight to the engine.
Also there were a few front intake aircraft with two engines like the Mig 19, so I dont think that was it.
The F9F Panther as an example of the same era had wing root air intakes. However there are no examples from that time of the big side intakes with deflector plates like became common later on - see the F4.
My understanding is that there is an aerodynamic cost to a front intake as the air supplying the engine is traveling a long and often convoluted path. Those early fighters were mostly nose mounted gun equipped and I know they had to play with gun placement to avoid engine problems from sucking in gun exhaust.
Most later aircraft with side intakes had a number of aerodynamic improvements, such as “area rule” which narrowed the body at the wings and intakes, because the wings effectively widened the fuselage. The basic rule of aerodynamics is minimizing cross section, and I suspect the engineers at the time of the early jets thought that side intake would increase cross section where front intakes would not. I think better understanding of aerodynamics allowed them to get around this and design side intakes that would not deliver too serious a penalty.
As radar became a more common feature that nose real estate became much more valuable as well.
So what was the advantage of the Lifting Body design? I get the idea that the lift is provided by the body, making wings unnecessary except as control surfaces, but what advantage did the design supply? Stealth? Efficiency? Resilience?
As above, the reasons are 1) making room for a radar, 2) simplifying getting the air path past the cockpit, and 3) (relative) stealth.
The last reason was not an issue in the 60s, but it’s the show-stopper reason you probably won’t see a pure open-mouth F-86 style fighter again.
The original Mig-15 & F-86 did not have radars at all. When they later invented a radar that would fit in a fighter-sized airplane they had to re-work the intake a bunch to find a spot for the antenna. Compare the pix of the radar-equiped F-86D here http://en.wikipedia.org/wiki/F-86D_Sabre with those of the other non-radar F-86 models here http://en.wikipedia.org/wiki/F-86
One of the key limitations of the modern F-16 is that the radome is not very large. For any given level of technology, radar range & acuity is proportional to the antenna area. The F-16’s antenna is barely 1/3rd the area of the F-15’s, becasue that’s all that will fit in that small nose.