General Dynamics F-111 Projects

[hesham]

A good report,

https://ocw.mit.edu/courses/16-885j-aircraft-systems-engineering-fall-2004/4fe291673f88543ed6940d68a43cf0da_f_111_final.pdf

 

[Grey Havoc]

Thought I had copied the below from the IMI Program topic over to this thread ages ago:

Here's one of the first news reports at the time on the insertion of the F-111 into the IMI requirement: Now an Air Defence F-111 (Flight International, February 9th, 1967)

YET ANOTHER VARIANT of the ubiquitous GD F-111 is under consideration in Washington by the Department of Defence—this time as a long-range intercepter to replace the ageing F-102 and F-106s of Air Defence Command.
The development is being considered in competition with Lockheed's Mach 3 F-12 project, on which small-scale spending is continuing through the next financial year.

Prospects for the long-range F-111 intercepter depend in part upon the
feasibility of the AWACS (airbornewarning and control system) aircraft for
which Boeing and Douglas are now making contract definition studies based
upon the 707 and DC-8 airliners respectively.
The AWACS system is necessary to provide detection and control at
ranges far beyond those of ground-based radars. The AWACS concept is heavily
dependent upon the development of airborne radars which are sufficiently
discriminatory to direct and track lowflying aircraft against the background of
ground return. Development of these "overland" radars is in hand, with five
different types due to be evaluated incompetition this year.

So a decision on a USAF F-111 intercepter (the problematical F-111B
intended for the USN is, of course, primarily an intercepter version) remains
a fairly distant possibility. If indeed it is adopted, it will be a great feather in
the cap of GD, which will then be providing variants of the same basic aircraft
for the USAF's three major combat commands—Strategic, Tactical and Air
Defence.

 

[flateric]

A beauty from ePay

 

[Trident]

Here's a drawing, source unknown:

Is it just me, or does that drawing depict Spey engines?

 

[BlackBat242]

Is it just me, or does that drawing depict Spey engines?

Yes - as the F-111K was the proposed UK version for the RAF, just like the F-4K (Phantom FG.1 for the RN) it was to use the afterburning Spey to increase UK content.

 

[BROF]

Not at all. The F-111K had the same P&W TF30-P-3 as the F-111A. Changes were limited to avionics, weapon-bay arrangement, heavier-duty LG from the FB-111A, non-swiwelling outer wing pylons, and an FR probe instead of flying-boom receptacle.

 

[A Tentative Fleet Plan]

F-111K used TF-30s, Speys were investigated but were dropped due to the cost of modification.

 

[Trident]

Exactly, that's why I thought it was so unusual - they were considered, but I was always under the impression that they would ultimately have been delivered with TF30s.

 

[apparition13]

F-111K used TF-30s, Speys were investigated but were dropped due to the cost of modification.

I was under the impression it would be pretty straightforward a swap given it was done in the A-7. What was the issue in the F-111? Or was the A-7 not as simple a change as I thought?

 

[A Tentative Fleet Plan]

Dr Richard Moore's article, F-111K: Britain's Lost Lost Bomber for Air Power Review Volume 18 No.3 Autumn/Winter 2015 has this to say, unfortunately I don't know what sort of modifications the Mk.2K avionics would have had.

 

[Scott Kenny]

The A-7D/E makes it sound like a TF30-Spey swap wasn't that involved. At least not compared to what was needed in the F-4K!

The big problem was that the British requirement was for F-111D or better avionics fit.

 

[Yellow Palace]

I was under the impression it would be pretty straightforward a swap given it was done in the A-7. What was the issue in the F-111? Or was the A-7 not as simple a change as I thought?

Straightforward doesn't mean there's no cost whatsoever - presumably as the TF30 did what was required, the money was felt better used elsewhere.

 

[Trident]

Another question - is there any detailed description available of what type of intake the FB-111H was going to use? It looked weird to me in the drawings I've seen and I had mostly come to the conclusion that they were simply inaccurate depictions of vanilla F-111 quarter-cone intakes. But then the RCS pole model apparently did have the same kind of shape, best I can tell is that it might have been an inward-turning (inverse-design internal compression) type. These are pretty commonly seen in hypersonic concepts recently but would be equally applicable to lower Mach numbers if you were looking to squeeze out the last drop of efficiency in supersonic cruise. Boom Supersonic's SST was going to use them at one point, IIRC.

Still, pretty risky move at the time - seems the lessons of the Triple Plow saga hadn't quite sunk in.

 

[F119Doctor]

I was thinking more like early 2000s, but almost guaranteed out of service by 2010.



PW still had the tooling to make parts, so if you threw money at them you can get all the F111s using the same engine. Probably call it the F-111H or J for the rebuilds to common avionics and new engines.

In the mid 1990s, there was several proposals to extend the life of the F-111F including the propulsion system. Both the F110-GE-129 and F100-PW-229 were considered. The real issue with the TF30-P-111 engines was that the AB nozzles were just worn out and beyond economical overhaul. P&W ended up proposing scaling the PW-229 AB duct and nozzle and adapting it to the TF30-P-111 as the most cost effective path.

The interesting thing was that performance analysis indicated that both the -129 and -229 would provide faster acceleration in the middle of the flight envelope, but both would have lower top speed at both low and high altitude. And both burned more fuel during subsonic cruise. The TF30, especially the later -100/111 version, was well matched to the F-111 mission.

 

[sferrin]

In the mid 1990s, there was several proposals to extend the life of the F-111F including the propulsion system. Both the F110-GE-129 and F100-PW-229 were considered. The real issue with the TF30-P-111 engines was that the AB nozzles were just worn out and beyond economical overhaul. P&W ended up proposing scaling the PW-229 AB duct and nozzle and adapting it to the TF30-P-111 as the most cost effective path.

The interesting thing was that performance analysis indicated that both the -129 and -229 would provide faster acceleration in the middle of the flight envelope, but both would have lower top speed at both low and high altitude. And both burned more fuel during subsonic cruise. The TF30, especially the later -100/111 version, was well matched to the F-111 mission.

I read somewhere that the TF30 Tomcats had a higher top speed than the F110 models as well.

 

[F119Doctor]

I read somewhere that the TF30 Tomcats had a higher top speed than the F110 models as well.

To be fair, I believe the F-14 variable inlets were locked into a fixed position on F110 powered versions to reduce maintenance costs. This would have limited their high altitude high Mach performance. Lower right corner performance would have been unaffected by the fixed inlets.

 

[Trident]

Also the locked glove vanes, that might have increased supersonic trim drag.

 

[aim9xray]

To be fair, I believe the F-14 variable inlets were locked into a fixed position on F110 powered versions to reduce maintenance costs. This would have limited their high altitude high Mach performance. Lower right corner performance would have been unaffected by the fixed inlets.

No, I strongly don't believe so. The vari-ramp bleed dump on top of the inlet module was fixed at 100 sq in early in the program - in the 1970s (the actuator was replaced by a fixed link). By the 2000s, the aircraft was operationally limited to 1.8 mn for various reasons. With operational loads, there was probably no way you could get up to the speed'o'heat, any way. Come to think of it, I would have to question whether the nearly permanently-mounted LANTIRN pod was itself was cleared to 2.0 mn.

 

[F119Doctor]

No, I strongly don't believe so. The vari-ramp bleed dump on top of the inlet module was fixed at 100 sq in early in the program - in the 1970s (the actuator was replaced by a fixed link). By the 2000s, the aircraft was operationally limited to 1.8 mn for various reasons. With operational loads, there was probably no way you could get up to the speed'o'heat, any way. Come to think of it, I would have to question whether the nearly permanently-mounted LANTIRN pod was itself was cleared to 2.0 mn.

You may be right about the F-14B/D inlet ramps being active. I had read other posts indicating they had been locked, but the F-14D Dash-1 available on Google made no mention fixed ramps, fully describing their variable function, and emergency procedures when they malfunctioned

 

[sferrin]

To be fair, I believe the F-14 variable inlets were locked into a fixed position on F110 powered versions to reduce maintenance costs. This would have limited their high altitude high Mach performance. Lower right corner performance would have been unaffected by the fixed inlets.

I seem to recall it being in the upper right corner.

 

[sferrin]

No, I strongly don't believe so. The vari-ramp bleed dump on top of the inlet module was fixed at 100 sq in early in the program - in the 1970s (the actuator was replaced by a fixed link). By the 2000s, the aircraft was operationally limited to 1.8 mn for various reasons. With operational loads, there was probably no way you could get up to the speed'o'heat, any way. Come to think of it, I would have to question whether the nearly permanently-mounted LANTIRN pod was itself was cleared to 2.0 mn.

Or the AGM-129 being cleared for supersonic external carriage. They thought the B-1B might get supersonic with AGM-129s on the OUTSIDE?

 

[F119Doctor]

I seem to recall it being in the upper right corner.

You missed the point - the TF30-P-100/111 in the F-111F had higher thrust in the lower right corner than either the -129 or -229, where any inlet scheduling would have minimal impact.

 

[sferrin]

You missed the point - the TF30-P-100/111 in the F-111F had higher thrust in the lower right corner than either the -129 or -229, where any inlet scheduling would have minimal impact.

Right. I was just referring to the Tomcat specifically. Any idea why the TF30 performed better at high speed? (Whether F-14 or F-111.) I'd initially thought it had a lower bypass ratio than the F100/110 but it looks like it's higher so I'm stumped.

 

[F119Doctor]

Right. I was just referring to the Tomcat specifically. Any idea why the TF30 performed better at high speed? (Whether F-14 or F-111.) I'd initially thought it had a lower bypass ratio than the F100/110 but it looks like it's higher so I'm stumped.

I really don’t know why. The higher bypass would allow higher AB fuel flow, the lower overall pressure ratio might allow higher core performance under ram conditions without having to cut back for diffuser case pressure limits, the low rotor mounted low compressor might add to core performance under high inlet temperature conditions.