WI: F-108 Rapier Enters Service

[Delta Force]

The North American F-108 Rapier was the original platform for a variety of technologies that would later be seen on other American military aircraft. Its two General Electric J93 engines would have propelled it to Mach 3, and although they never flew on the F-108 or the B-70, they were later developed into the General Electric GE4 for the Boeing 2707 supersonic airliner (both of which were themselves canceled). The Hughes AN/ASG-18 radar and AIM-47 missile were America's first pulse-doppler radar and long-range missile systems, respectively, and they formed the basis for the AN/AWG-9 and AIM-54 Phoenix radar/missile system later used on the F-14. An infrared search and track system was also planned.

Clearly a lot of performance and technology in one aircraft, which would have been akin to a MiG-31 a decade or two earlier. If the Rapier had entered service, what kind of impact might it have had on military and commercial aviation? Could the F-108 find a niche in the USAF, perhaps being diverted from Air Defense Command to TAC or SAC? Would a fleet of a few dozen or more public knowledge Mach 3 aircraft have accelerated the development of high speed flight, leading to earlier supersonic airliner and spaceplane development?

 

[sharlin]

The technical problems are comprehensive for a mach 3+ aircraft, whilst its performance may say MiG-25 with a Foxbats radar etc its still incredibly niche and would probably be a HUGE resource hog to build and maintain.

 

[Riain]

I think it would be a failure in the same way the Space Shuttle was a failure: it worked great, it just didn't have a job to do.

Either way, I want one.

 

[Delta Force]

I imagine when the Soviet Mach 3 bomber threat fails to materialize there will be various grand schemes for using the planes already built for other purposes. The question is who ends up flying them, and doing what? Might they become strike-reconnaissance aircraft in the truest sense? The AIM-47 was modified to produce the AGM-76, which could be of interest to TAC and SAC. TAC could have a good tactical strike platform if the AIM-47/AGM-76 is developed with different seekers, and SAC could have a platform for peeling back enemy air defenses (both interceptors and radar sites) to create strike corridors.

 

[sharlin]

Hmm...carrying all that ordinance reduces really their one big 'thing' raw balls out speed. Instead of the Blackbird how about the Rapier being the recon aircraft for the USAF?

 

[cpip]

Hmm...carrying all that ordinance reduces really their one big 'thing' raw balls out speed. Instead of the Blackbird how about the Rapier being the recon aircraft for the USAF?

Well, the dimensions are pretty similar. So the F-108 ends up converted into the RF-108, kind of like the A-5's evolution into the RA-5?

 

[sharlin]

Makes sense, I dunno if its got the range of the Blackbird which would limit its uses and keep it from being strategic recon but it could be a form of theater recon. Lets say you've got a squadron of them based in...err..Italy, they can use their speed to zip over somewhere like Libya at high altitude and speed like the Blackbirds did and then come home again.

 

[Riain]

What could the F108 do in Vietnam? Could it find use as a fighter there, perhaps getting an exemption from the restrictive ROE due to it's unique nature and capabilities?

 

[Delta Force]

Hmm...carrying all that ordinance reduces really their one big 'thing' raw balls out speed. Instead of the Blackbird how about the Rapier being the recon aircraft for the USAF?

The missiles are carried internally in a rotary bay, so they are a weight issue instead of an aerodynamic/drag issue. One thing that's interesting about AIM-47 development is the proposal for a dual-mode sensor (radar and infrared), which was rejected due to the diameter and weight increase. However, there were plans to create a folding fin AIM-47 for the F-12 (an interceptor variant of the CIA A-12), which had a smaller weapons bay. Perhaps if both were adopted the AIM-47 could be even more capable with a smaller impact on F-108 performance. It would probably cost a fortunate, but active radar/passive radar/IR tracking would make the missile very difficult to deploy countermeasures against.

In the form of the AGM-76 and similar missiles, the AIM-47 (or at least its airframe) might be an interesting option for equipping B-58s and other aircraft. The Iraqis used Tu-22s to carry out supersonic toss bombing attacks in the Iran-Iraq War, and with an extended range guided missile similar hit and run techniques could be used tactically. According to this site (which has a good overview of other AIM-47 derivatives, and the other Falcon missiles), there were proposals for a ground attack variant of the AIM-47 that would have achieved a CEP of 6 meters (optical) or 15 meters (radar guidance) with a range of 50 miles.

Well, the dimensions are pretty similar. So the F-108 ends up converted into the RF-108, kind of like the A-5's evolution into the RA-5?

We think alike. In my Jet Age timeline I was working on a few months ago, I had the F-108 butterfly the A-12/SR-71. I don't remember if it was the RF-108 or RS-108 though. I think it would be much easier to make a reconnaissance variant of an interceptor than an interceptor variant of a reconnaissance aircraft. A branching development into separate fighter/attack and reconnaissance aircraft might lead to F-108 airframes and their derivatives being used in more unique "one off" roles, as a high altitude Mach 3 complement to the RC-135 Rivet Joint aircraft.

What could the F108 do in Vietnam? Could it find use as a fighter there, perhaps getting an exemption from the restrictive ROE due to it's unique nature and capabilities?

Strike-reconnaissance seems likely if things are as restrictive as they were in our timeline, although it could still be a useful role. I suppose the real trick would be getting the enemy to keep their radars on after picking up the distinctive signature of an aircraft screaming over Indochina at Mach 3 and 80,000 feet. I'm not sure if the AAM system would have been usable against the small fighters used by the North Vietnamese, but if possible it could certainly clear the skies of enemy aircraft in addition to shutting down and/or destroying missile sites.

A PoD which sees the F-108 deploy to Vietnam might also see the F-102 and F-106 see more widespread use in attack and air supremacy as well. I think I've read about the F-102 being used to fire AIM-4 infrared missiles at campfires and trucks in Vietnam (and even about the future President Bush Jr. considering volunteering for that program), and there were proposals for developing the F-106 into a true multirole aircraft or a cheaper platform for the AIM-47 system than the F-108.

None of this will of course save high speed and high altitude aircraft and attack patterns in the long term, but it could be interesting if the USAF develops techniques for radar guided Tu-22 style attacks instead of techniques using television, laser, and other forms of optical guidance.

 

[Coiler]

What could the F108 do in Vietnam? Could it find use as a fighter there, perhaps getting an exemption from the restrictive ROE due to it's unique nature and capabilities?

I don't think it'd have much capability as a fighter over Vietnam. The positive-ID issue is still there, as are the issues of new high-performance missiles in a rough environment. There's also the problem that if the North Vietnamese down some with careful sneak attacks or lucky SAM hits, you've just made the PVO a whole lot more dangerous once they examine the wreckage. If the Air Force insists on using it, I can see its main use being that of a makeshift AWACS thanks to its extremely powerful radar.

 

[Grey Wolf]

What could the F108 do in Vietnam? Could it find use as a fighter there, perhaps getting an exemption from the restrictive ROE due to it's unique nature and capabilities?

Well it has a GUN which would have been useful!

Best Regards
Grey Wolf

 

[Herzen's love-child]

The Rapier only made sense for its intended mission. It would not have been good if the Blackbird was nerfed by the Rapier's deployment. The former flew faster, higher, farther,stealthier than the f-108 and was imminently suited and adaptable to being the fantastic strategic reconnaissance platform it was.

 

[Delta Force]

Well it has a GUN which would have been useful!

It has a very heavy cannon armament for a Mach 3 missileer, but the wing loading is quite low for modern jets as well (102,000 pounds maximum weight and 1,865 square feet of wing area gives a wing loading of 54.69 pounds per square foot). It doesn't have the highest thrust to weight ratio, but such low wing loading could make it quite maneuverable at high altitudes. The B-36 was rumored to be capable of outmaneuvering early jets at higher altitudes.

The Rapier only made sense for its intended mission. It would not have been good if the Blackbird was nerfed by the Rapier's deployment. The former flew faster, higher, farther,stealthier than the f-108 and was imminently suited and adaptable to being the fantastic strategic reconnaissance platform it was.

That's true, but the question is if that extra performance is worth the additional research and development costs and more expensive airframes. More F-108 variants can be built if the SR-71 isn't pursued.

 

[Grey Wolf]

It has a very heavy cannon armament for a Mach 3 missileer, but the wing loading is quite low for modern jets as well (102,000 pounds maximum weight and 1,865 square feet of wing area gives a wing loading of 54.69 pounds per square foot). It doesn't have the highest thrust to weight ratio, but such low wing loading could make it quite maneuverable at high altitudes. The B-36 was rumored to be capable of outmaneuvering early jets at higher altitudes.

Wouldn't surprise me about the B36. I've seen videos of what these early strategic bombers (inc B47, B52) planned to do to deliver their payload, a manoevre that looks insane for an aircraft of that size but one which was practised successfully numerous times.

Best Regards
Grey Wolf

 

[Herzen's love-child]

It has a very heavy cannon armament for a Mach 3 missileer, but the wing loading is quite low for modern jets as well (102,000 pounds maximum weight and 1,865 square feet of wing area gives a wing loading of 54.69 pounds per square foot). It doesn't have the highest thrust to weight ratio, but such low wing loading could make it quite maneuverable at high altitudes. The B-36 was rumored to be capable of outmaneuvering early jets at higher altitudes.



That's true, but the question is if that extra performance is worth the additional research and development costs and more expensive airframes. More F-108 variants can be built if the SR-71 isn't pursued.

It might have made for a fine Mig-25 killer but if we talk of the Rapier as a fighter, most of its opposition were far more maneuverable at low to mid altitudes. I don't see it as having any pragmatic use for a cannon. How good would its look-down shoot-down capabilities have been in its era?

Different versions perhaps there might have been had there been a Soviet high speed bomber threat and relevance was seen for the B-70. I always thought that the Rapier rode on the Valkyrie's coattails -- if the latter went down, it would follow the Rapier would too.
The Rapier as a specialty tactical recon platform? As a fighter to hold the high ground in an air war? An extended body model (with cupholders ) for a longer legged recon plane to supplant the Blackbird? (Grrrr!)

 

[CalBear]

Almost no real impact. It would be an aircraft without a mission (rather like the MiG 25) except for breaking "official" world records (anyone who believes the actual records for altitude, speed, rate of climb, or the rest of the book for air breathing aircraft hasn't been paying attention since the Kennedy Administration).

It would illustrate what was already understood, MACH 3+ isn't useful for combat aircraft in anything but very narrow circumstances.

 

[Delta Force]

It might have made for a fine Mig-25 killer but if we talk of the Rapier as a fighter, most of its opposition were far more maneuverable at low to mid altitudes. I don't see it as having any pragmatic use for a cannon. How good would its look-down shoot-down capabilities have been in its era?

Different versions perhaps there might have been had there been a Soviet high speed bomber threat and relevance was seen for the B-70. I always thought that the Rapier rode on the Valkyrie's coattails -- if the latter went down, it would follow the Rapier would too.
The Rapier as a specialty tactical recon platform? As a fighter to hold the high ground in an air war? An extended body model (with cupholders ) for a longer legged recon plane to supplant the Blackbird? (Grrrr!)

Considering that aircraft with shorter ranged missiles didn't carry cannons in this era, it is indeed strange the F-108 carried one at all. A Mach 3 interceptor with 100 mile range missiles shouldn't be getting close enough to use cannons.

As for its look down/shoot down mode, it performed well in tests, but I'm not sure how realistic the tests were. The AIM-54 Phoenix performed very impressive feats in tests but never achieved any kills (at least in USN service). It's thought that some of the problems with the AIM-54 may have been due to a combination of their expense (limiting tests) and their perception as super missiles (making tests seem unnecessary), causing them to not keep up with developments in enemy aircraft. The missiles themselves were quite aged when the USN used them as well (early to mid-1970s construction, mid to late 1990s use).

Almost no real impact. It would be an aircraft without a mission (rather like the MiG 25) except for breaking "official" world records (anyone who believes the actual records for altitude, speed, rate of climb, or the rest of the book for air breathing aircraft hasn't been paying attention since the Kennedy Administration).

It would illustrate what was already understood, MACH 3+ isn't useful for combat aircraft in anything but very narrow circumstances.

The performance envelopes are rather speculative for most modern aircraft. Even the SR-71 and MiG-25 are still classified, except for being somewhere over Mach 3 and probably 80,000 feet.

Mach 3 aircraft are definitely niche, but some of those niche roles could attract funding and attention in the 1960s, especially strike, reconnaissance, high altitude research/ASAT, and commercial aircraft.

 

[Just Leo]

Considering that aircraft with shorter ranged missiles didn't carry cannons in this era, it is indeed strange the F-108 carried one at all. A Mach 3 interceptor with 100 mile range missiles shouldn't be getting close enough to use cannons.

Specification states that it carried 4 20mm cannon, type unspecified, but no information on where they were to be fitted. Any ideas?

 

[Matt Wiser]

An RF-108, a high-speed photo recon aircraft for TAC, would work. TAC would have loved to have an aircraft almost as fast as an SR-71, and more responsive to in-theater recon needs. The RF-101 and RF-4C (later) would still handle the down and dirty tactical recon mission.

 

[DD951]

Specification states that it carried 4 20mm cannon, type unspecified, but no information on where they were to be fitted. Any ideas?

If it was to carry 4 20mm cannons, I'd guess that they'd probably be M-39s, although a search for cutaways & diagrams online didn't show anywhere it would look like they could go, and scans of the Standard Aircraft Characteristics sheets from 1958 & 59 available online list no gun armament, just a few Falcon missiles in an internal bay, yet the wiki article cites to the USAF Museum online fact sheet, which lists 4x20 mm cannon & 108 unguided rockets, or 4,000 lbs bombs.

If the museum didn't just make a mistake, then any guns would probably have to be mounted on a tray that would mount in the weapons bay, they were originally planned but deleted early in the design process, or the program was cancelled before the designers found a place to squeeze them in.