Several issues:
- Modern IR missiles are just about as effective at tracking targets from head on as from behind. That wasn’t true at all in the Viet Nam era. But even back in the 1980s we routinely shot the bad guys once as we’re closing head-on then if they don’t blow up we’d maneuver as required to get pointed at them again. Since the enemy fighter pilot is doing the same thing, that amounts to *almost *a traditional WWII style dogfight *after *the initial exchange of fire head-on.
After the initial pass, it’s not so much that you have to get directly behind the other guy. But you do have to point generally towards him for a few seconds. And given the speeds and angles available, that’s easier to do when you’re going in more or less the same direction. i.e. if he’s traveling ~90 degrees to your path, he’ll flash across your nose from the far left to far right much more quickly than the missile can lock onto or follow. So each pilot’s goal becomes to generate enough spacing between yourself & your target plus enough alignment of flight paths that the apparent angular rate of the other guy is slow enough that your radar and/or missile seeker can obtain & hold lock long enough to get a valid shot off.
- Air to air missiles are fast, but they’re not that much faster than the jets themselves. It’s not like a tank and a tank main gun where the tank goes 30 mph and the tank’s shell goes 6000 mph, a 200 to 1 ratio. For fighters it’s more like the jets go 500mph and the missile goes 2500mph, a 5 to 1 ratio. What that means is the range of the missile strongly depends on the relative speed of the shooter and target. Also, most dogfight missiles have very fast burning motors. Rather like a bottle rocket. They accelerate very quickly (1-3 seconds) to their max speed then the motor runs out and they coast the remaining 80% of the way to the target. As they go along, they’re slowing down. The slower they go the less maneuverable they become. Eventually they slow enough to simply fall out of the sky.
Made up numbers: If we imagine two jets cruising along at the same altitude, speed, and direction, with the target in front and the shooter behind, the effective range might be, say, 3 miles. IOW, from 3 miles back, the missile has the oomph to accelerate away from the shooter against a 500mph relative wind, close the distance to the target, and still be going fast enough to maneuver effectively at the end. The bad guy probably doesn’t get away. During the 15 seconds the missile spent covering the 3 miles between them, the two aircraft advanced 2 to 4miles across the ground. So the missile covers 6-7 miles across the ground.
Take the same shot from 4 miles back and the missile is just about out of oomph when it gets there. Even if the target is a lumbering bomber, it could bank gently and evade the missile. Provided they knew it was coming.
Take the same shot from 5 miles back and the missile doesn’t even get there; it runs out of closing speed before it get to the target, then falls stupid to the ground.
Now, take the same shot from head-on. Instead of a 2500mph missile trying to close the unchanging distance to a target against a 500mph headwind, it’s aimed at a target which is getting closer to the launch aircraft at a combined speed of 1000 mph.
Now you might be able to take a shot a 10 miles and still have a strongly maneuverable missile when the target and missile get near each other. And you could take a 15 mile shot against a bomber and still have a weakly maneuverable missile when the range gets to zero.
3. If you had a rearward firing missile, when it first leaves the aircraft it’s flying tail first relative to the air. The motor has to accelerate (decelerate?) the missile from backwards 500 mph to zero to forward 2500 mph relative to the air. And the control fins have to be able to steer both flying ass first and nose first as well as at very slow speeds while making the transition from backwards to forwards flight.
That’s not an easy problem to solve.
4. For a rearward firing missile you’d also need sensors, e.g. radar, that point that way to detect and track incoming aircraft. We’re working on so-called “all aspect” radars and other sensors, but that’s still aways in the future.
All in all, given current tech rearward firing missiles are a bad solution to a problem that doesn’t much need solving.
Fast forward 40 years from today and I can easily imagine something sorta like a WWII P-63 or Mosquito with good speed, better maneuverability than a transport, but less than a dedicated fighter, all-aspect sensors, and directed energy (e.g. laser) weapons in turrets which can fire all-aspect as well.
Given those kinds of sensors and weapons, the need for very high maneuverability falls away. We’re left needing speed, and a big enough aircraft to carry the weapons & sensors and the fuel to power them. Which at least at first will require something a bunch bigger than, say, an F-15 or F-22, much less an F-16 or F-35 sized aircraft.