How come we seldom see these technologies in air combat?

In My Humble Opinion
1

I’m wondering about the scarcity of ramfan engines in missiles and of ventral/dorsal radar pods on fighters. I’ll explain what I mean and how I guess they might be useful. If I’m mistaken about parts of it or you see ways it could be useful, I’d like to know that.

Ramfan engines in missiles:
What I mean is a jet engine which uses a booster instead of a compressor stage and uses a turbine and fan to generate its thrust.

Not having a compressor is usually unsuitable for aircraft since aircraft need to be able to go from low speed to high speed repeatedly and ram engines need to go at least at Mach 0.5 to generate significant thrust. Ram engines are therefore particularly vulnerable to engine stall.

Missiles, however, only need to go from low speed to high speed once. This can be achieved by putting a solid propellant booster in the combustion chamber or duct which can provide sufficient speed for the ram effect to compress incoming air. Fuel is then added to the ram-compressed air which combusts, the energy is taken by the turbine and transmitted to a fan which propels the missile forward which compresses the air through the ram effect and so on.

What’s the point, you may ask? First, my guess is that the compressor stage represents a significant part of a jet engine in terms of cost/weight/volume.

Second, it would eliminate any mechanical element forward of the combustion chamber(s). The turbine could either directly or through reduction gear behind the turbine transmit the energy to the fan.

Third, it would provide the specific impulse of a fan engine with, depending on whether a high or low bypass ratio is used, speeds of Mach 0.8 to Mach 2.

The lower price (than compressor-using engines), high range and high speed would presumably make it most suitable for fast cruise missiles and anti-ship missiles.

Radar pods on fighters:

You’ll have to use your imagination to grok what I mean. Look at these 2 pictures:
Imgur
Imgur

See the 2 gray bars, one on top, the other at the bottom and forward? Imagine them as phased arrays which can swivel left to right and are encased in radar transparent pods.

Note that the bottom one points somewhat forward.
What’s the point? Radars benefit from having a large size across their most important axis. In this case, bearing is usually more important than elevation. Elevation usually only has 20km of possible value variation, bearing, much more. Hence, having a wide array is more beneficial than a tall array. It’s difficult for fighters to have an array which is both wide and front-facing since they’re built like bullets

By putting a radar array in a dorsal or ventral position, a fighter can increase antenna gain and use lower frequency bands (which have greater range and anti-stealth performance) while retaining sufficient accuracy.

Also, unless I’m mistaken, fighters will often try to notch enemy radars. I.e.: the fighter puts the enemy radar on his 3 o’clock or 9 o’clock so that it’s not moving towards or away from the enemy radar at any significant speed. This makes it difficult for the enemy radar to use the Doppler effect to pick out the fighter from the background. This is the position in which a dorsal/ventral radar would excel.

In addition, it can make it easier for platforms to work together. With a dorsal/ventral pod, a fighter can keep its radar pointed at a target at a constant distance for extended periods of time to function as a spotter/illuminator for an ally.

I’m guessing that a radome would be unsuitable for the kind of brisk maneuvering a fighter may have to do.

2

AIUI, many fighters won’t turn on their own radars in combat, but will rely on AWACS which is a far distance away, thus remaining “nose cold.”

Might the proposed dorsal radar cause brain damage? (For that matter I always wondered why AWACS radar doesn’t affect the crew sitting just 15 feet below it.)

3

I’m not sure I’m really understanding the point of a ramfan.

In a typical jet engine, the air goes through a compressor, fuel is injected into the air and ignited, and then through a turbine. The air leaving the back of the engine is going much faster than the air entering, which pushes the engine forward.

There’s also a ramjet. It doesn’t have a compressor; as it moves forward, the shape of the inlet compresses the incoming air. Then there’s a combustion chamber. And because there’s no compressor it doesn’t need a turbine. Like other jet engines, the air coming out the back provides thrust, but it needs to be moving to work at all.

So what’s the point of a ramfan? From your description, the air comes in the front of the engine and gets compressed. Fuel is added and burned. Then the air goes through a turbine (which slows the air down) and a compressor (which speeds it back up). Why not just leave the turbine and compressor off entirely and have a ramjet?

4

Why aren’t there missiles mounted backwards so it doesn’t matter if the enemy gets on your tail? Why don’t they mount anti-missile guns so you can shoot down incoming missiles and not have to try to evade in the first place? (or anti-missile missiles if the guns have too short a range)

Lots of questions about air combat besides why aren’t the missiles more efficient. And if you think about it, only a handful of countries are even building cutting edge combat aircraft (3 I guess - EU, USA, Russia) so maybe it’s not a matter of making the best aircraft possible but just making something that beats (or keeps up with) what the other guys have.

5

It enables you to have a fan without having a compressor.

You want a fan for high fuel efficiency which translates to high range. Fan engines have higher specific impulse than ramjets.
You want to spare having a compressor if you can because 1) it’s a missile, it’s not like you can spread the cost over many uses 2) If it’s carried by aircraft, weight and volume are at a premium 3) Not having a fan, compressor stage or shaft in front of the combustion chamber might allow interesting/streamlined design. People who are knowledgeable about jet engines might chip in here.

My understanding is that they’ll use the radars of other aircraft to get in the same area as the target but I don’t know if an AWACS has enough accuracy to guide a missile 400km away against an enemy aircraft or if an E-8 can illuminate a ground/surface target from 200km away.

6

AIUI some modern AAMs do have the ability to launch and U-turn to go hit targets behind the launching aircraft.

7

Besides the efficiency bit, IIRC Ram-fan engines are not terribly responsive through a wide range of airspeeds. Aerial combat requires that you have high response at whatever energy state you happen to find yourself.

Dorsal and ventral radar are added weight and complexity to little gain. For specialist purposes, ventral imaging and radar might be used, but that’s generally for reconnaissance.

8

The P-61 had a turret that could put four .50 machine guns on a guy behind you. It interfered with the aircraft so much that they were often removed. To heck with that for me, I’d want to discourage someone from sneaking up on my airplane from behind.

Wouldn’t those radar bars interfere with flight, or be torn off at high speed?

9

LSLGuy answered the first question a few years ago.

[QUOTE=LSLGuy]
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.

[/QUOTE]

10

Can’t decide if joking or serious…

Gun turrets are LONG gone as useful ACM devices. They’re only retained on combat helicopters for ground attack, and mostly there because helicopters are relatively slow, and can make use of them.

Combat aircraft radar is mounted behind streamlined structures.

11

My understanding is that for combat aircraft, responsiveness is indeed critical since brisk maneuvers will bleed off energy which then needs to be gained back quickly. For munitions, less so. No missiles will make a hard turn then try to gain speed, make another brisk turn then try again to increase its speed. Most missiles either burn at a pretty constant speed or have a very intense acceleration period(s) and then burn out.

Through what mechanisms do those gains occur in reconnaissance? I would have thought that higher antenna gain, the use of lower frequency bands while retaining sufficient accuracy and the possibility of maintaining the beam on target while remaining at the same distance would translate well to combat spotting/illuminating.

12

My point being that it would be really nice to be able to shoot at a guy behind you.

13

Has a ramfan like you describe ever been built and tested? I can’t find anything about it online. I’m not sure we know exactly what its specific impulse would be.

I can still see a couple of issues with it.

The fan on your ramfan missile is going to need some sort of inlet. The extra efficiency when it’s used may be more than offset by the extra drag from all the times you carry it around and don’t use it.

In air-to-air combat, a fast missile may be just as good as a long-range one. If your missile goes mach 2 and the thing you’re shooting at goes mach 1.9, the missile will need a long range to catch up to its target. If your missile goes mach 3 it will catch the target sooner, and cover less distance before it does.

14

Missiles also have to function from whatever energy state the launching aircraft possesses, and are in fact, often highly maneuverable, especially those refered to as “Dog Fight” miisiles (AIM-7, AIM-9, K-13, etc.) As I understand, ram engines generate extremely little thrust below Mach 0.5, yet that’s a speed at which a combat aircraft may find itself. So, similar conditions apply, both from maneuver and from energy points of view.

The gain to which I was referring was “gain in utility,” not gain in resolution. In reconnaissance, the combat aircraft won’t be looking for other aircraft - they’re examining the terrain to locate, classify, and map enemy assets. Either dedicated internal pallets will be swapped out for other sensor or electronic warfare options, or exteranl hard points will be used. And, of course, some aircraft are dedicated solely to this purpose, where the weight and complexity is part of a specific and limited purpose.

15

That’s what wingmen are for.
Any backward-firing missile would have significant problems in designing its center of pressure. If its center of pressure is behind its center of gravity (relative to where the missile points) and it’s launched facing backward when the aircraft is traveling, then (relative to airflow), its center of pressure will be in front of its center of gravity which will lead to funny results for onlookers.

16

Video example of the high degree of missile maneuverability which modern AAMs bring to the table (including shooting at someone whom is about to be behind you):

17

Thanks for your input, Tranquilis. I continue to argue the case here not because I don’t think that what you say makes sense but because I don’t know if your disagreement comes from me not explaining my idea well enough or my ideas not being sound.

They’re highly maneuverable but they’re not expected to repeatedly accelerate from many energy states. They only accelerate once. Note that those two missiles don’t have compressors, they use the same thing for acceleration as what I mentioned. As for ram engines having very little thrust below Mach 0.5, that’s why I mentioned using a solid fuel booster in the chamber(s)/duct to make sure the missile gets to sufficient speed to get enough ram effect.

Do we agree that you want a compressor to be able to gain speed repeatedly from any energy states and that if you only have to gain speed from any energy state once, a solid fuel booster can be enough?

I understood that the gain was in utility but gains in resolution and antenna gains are also gains in utility in combat aircraft

Are AWACS , E-2, E-3 and E-8 not a sort of recon/surveillance aircraft? E-2 and E-3 do look for other aircraft. E-8 can look for moving ground targets. The setup I describe could provide the speed and maneuvrability of a fighter with the antenna size of an E-2. It might be particularly useful for aircraft like the EA-18 Growler or as a mini E-8.

18

If the target aircraft can get behind the missile, can the missile turn around and fly quickly enough to hit the target?

If the two aircraft are flying fast, how about dumping twenty pounds of ball bearings out the back for the other guy to run into at Mach I?

19

Well, letls put it this way: Innovative minds have been looking at ACM for a lot longer than either of us have, and they’re not using those technologies. There’s a reason.

Item: Each manever would disrupt airflow in the nozzle of a ram, so yes, that’s very much a factor. Second, if you’re going to make the missile MORE complex by adding additional thrust elements, you’ve made the missile heavier (thus slower) and more complex (thus more likely to fail) - not things that pilots are going to appreciate.

While basically correct - presuming you don’t need to deal whith shifting angles of attack due to continual manuever - I want to know: if you already have a booster in place, and it’s more than adequate for combat, why would you want to complicate things? Because that’s what we’ve got - A rocket motor (booster) handling combat, quite effectively.

You’re adding weight and complexity to no useful purpose.

Those are NOT tactical combat aircraft. Nor are they recaonnasiance craft - they’re battlespace command, control, and serveilance which is a very different niche, and you will only see them near the FEBA if someone has really screwed up.

20

It does not need to be a missile, but it would add weight thats not really useful for anything else. One defense, was to drop a bomb so that the enemy fighters would fly into the blast radius. If you have read Dale Brown’s fictional flight of the old dog, then you would remember the aerial mine. The only problem other than functionality, or the actual pk value of a weapon, would be that its only good for one thing, and something to actually hang on a bomber.

40 years of jet fighters and no one has come up with a rear firing missile, other than a james bond movie. So i presume we are skipping it entirely and going straight to pilots with lasers (*) on their heads , lol.

*Not speaking of the off axis snap shot thingie