F-111B Conversion Part Four - Cockpit

 

 Currently a work in progress.

 

The seven F-111B cockpits differed in two major ways: ejection seats or crew escape module; and the Phoenix Airborne Missile Control System (AMCS) was installed or not.

The first three F-111Bs (BuNos 151970, 971, and 972) had ejection seats because qualification of the crew module did not support the aircraft manufacturing schedule. See https://tailspintopics.blogspot.com/2016/07/f-111ab-ejection-seats.html.

As far as I know, only the F-111Bs used by Hughes for its Phoenix system test program had the Phoenix system displays and controls installed. These were BuNos 151971, 972, and 152715 (152714 was also operated by Hughes for a time, reportedly for pilot checkout and proficiency flying). This included the Vertical Display Indicator Group (VDIG), which consisted of a large TV-like presentation (Direct View Indicator, similar to the one in the A-6 Intruder) and a head-up display (Precision Indicator).

This is the instrument panel of BuNo 151972. The head-up display is just visible above the glare shield.

 The left console forward:

 The left console aft:

 Center console:

 

 

 The right hand console from the F-111B flight manual (the top of the control stick for the AMCS cursor is just barely visible in the first photo):

 

The Vertical Display Indicator Group (the PI extended through a slot in the glare shield):

The VDIG was essential to the Phoenix system control, one of its several modes:

All the other F-111Bs had Grumman-designed substitutes: at least two variations of a large, mostly blank, sheet metal panel in the right hand crew position, one the same shape and dimensions as the Phoenix system installation; and a gyro-driven, three-axis attitude indicator and separate flight instruments in place of the VDIG for the pilot.

This is the cockpit of BuNo 152715 prior to the installation of the Phoenix system. Note the sheet metal equivalent of the system in the right hand crew position and the large artificial horizon in place of the VDIG:

This is the cockpit of BuNo 151973 that was used by Grumman for various flight-test requirements. The right side panel in this case is flush with the pilot's instrument panel. Red-orange designated flight test instrumentation or calibrated instruments. The orange handles with black stripes on either side of the center console activated the ejection of the crew module.

 

This is the cockpit of BuNo 151974 that was eventually used for at-sea evaluation aboard Coral Sea. Note that the right hand panel is the same as the one initially installed in152715. The big aeronautical map on the lower half of it is centered on the Long Island, New York area.

 The instrument panel of 151974 with another variation of a substitute for the VDIG:

This is the stripped cockpit of BuNo 152714 after it was stricken with yet another variation of the right hand instrument panel that included provisions for several flight instruments, possibly including an altimeter (it almost certainly never had the Phoenix systeme installed even though it was assigned to Hughes for a time).

 

The Cat 4 Conversion Set R72016 provides parts for the first three F-111Bs including the Phoenix instrument panel and the ejection seats.

F-111B Conversion Part Three - Inlets

Thanks to the generous assistance of Jim Rotramel (an F-111 Weapons System Officer and mission planner, he is the author of Operation Eldorado Canyon: The 1986 US Bombing Raid on Libya), I'm declaring victory on this post although it is still subject to change from time to time as a result of new information or realization of errors.

An unexpected F-111 issue was the significant time and effort required to develop the engine inlet, an unintended consequence of combining a little-used quarter-round configuration bounded on one side by the fuselage and its top by the underside of the wing with the first attempt at adding an afterburner to a turbofan jet engine, the Pratt & Whitney TF30. It was a non-afterburning low-bypass turbofan engine being developed for the Navy’s subsonic Douglas F6D Missileer.  The turbofan configuration—the first few stages of the compressor were significantly bigger in diameter so air accelerated at its periphery bypassed the combustion process and flowed aft past the turbine section into the tailpipe—was developed to power civil airliners, reducing fuel consumption in cruise. Fuel efficiency was essential for both the USAF and USN applications, long range for the former and time on station for the latter.  The Air Force’s Mach 2 requirement necessitated an afterburner and a variable-geometry inlet that managed the air volume and velocity over a wide speed range to the engine requirements and limitations. resulting in a quarter-round, variable-geometry inlet spike and cone. The TF30 would be the first turbofan engine to be fitted with an afterburner; the Spey was the second. Both the TF30 and the Spey proved to be finicky about the quality of the air provided to them relative to an axial-flow engine, prone to compressor stalls. It also didn’t help that the bypass air channel increased the susceptibility of the compressor to stall due to the afterburner light-offs. Modifications to both the inlet and the engine became necessary.

One feature of the original inlet was the cowl position for low versus high-speed flight. For takeoff and landing (in the event of the need to wave off), the pilot was to position them forward (extended/open) so there was a large vertical opening into the engine inlet duct to provide additional air for maximum thrust. The control philosophy evolved during early flight test. Tragically, the cowl-position switches were mis-set before the takeoff of Ship 4 (BuNo 151973) on 21 April 1967. This F-111B had a three-position switch (Store/Open/Close) cowl switch for each engine. Store was for ground use only (it overrode the landing gear handle position) to close the cowl if desired. Open extended the cowl if the gear handle was down. Close retracted an extended cowl when the landing gear handle was up. As a result, the cowl would be open when the landing gear handle was down. Unfortunately, the takeoff was made with both switches in the Close rather than Open position, possibly because it had been left in the Close position after the previous flight. As a result, seven seconds after the landing gear handle had been raised after takeoff (it took that long for the jack-screw actuator to close them), there were compression stalls on both engines, significantly reducing thrust. The attempt to eject the crew capsule just before the airplane crashed beside the runway failed when the ejection handle malfunctioned. Both Grumman test pilots were killed.

General Dynamics did all of the inlet development work. The F-111B inlet configuration varied as GD made progress in reducing compressor stalls). These consisted of the original inlet, a subsequent short-lived improvement, and two that were approved for USAF production: Triple Plow I and Triple Plow II. The first three F-111Bs (BuNos 151970, 971, and 972) were built with and retained the original F-111A inlet. Four and Five (BuNos 151973 and 974) first flew with an early modification of the original inlet. Five subsequently received the Triple Plow I inlet. Six (BuNo 152714) initially flew with an early configuration Triple Plow II inlet, which was replaced with one almost identical to the production Triple Plow II inlet (the difference was two suck-in doors instead of three).  Seven (BuNo 152715) received that inlet as well.

This updated and corrected illustration summarizes the various iterations flown on the F-111Bs. 

The original F-111B inlet was the same as the first F-111A's.

 

It was the inlet on BuNo 151970, 971, and 972. However there were subsequent modifications. The first were vents on the bottom of the cowl aft of the inlet to discharge the splitter plate bleed and then underwing ducts rather than simple vents to discharge the glove bleed.

The inlets on 151973 and 974 had a different splitter plate (the bottom was level, not angled upward) and ducts under the cowl to discharge the splitter-plate bleed. There are now vortex generators in the inlet (note the ones on the spike) to provide a more uniform and consistent flow of air to the engine.

The ducts under the wing have been eliminated. My guess is that the glove bleed for these particular inlets was discharged out of enlarged vents in the top of the wing glove.

The next set of F-111B inlets resulted from GD's "Triple Plow" development program. The name reflects the fact that the inlet now removed low-energy boundary layer air from entering it slightly differently from the lower glove surface and inlet splitter plate, directly diverting it rather than internally redirecting it, i.e. plowing it away like some of the fuselage boundary layer air. This is Triple Plow I (note the array of vortex generators inside the inlet):

 BuNo 151974 was modified with the Triple Plow I inlet at some point before its at-sea evaluation aboard Coral Sea. The most notable difference between the original inlet and the Triple Plow I was a kink at the top of the splitter plate that moved it farther outboard from the fuselage.

 The new splitter plate also extended slightly aft of the inlet compared to the original one (note that 151974's Triple Plow splitter plate was not painted gray like its first one):

Triple Plow II had a greater offset of the inlet from the fuselage due to the thicker boundary layer at Mach 2.5. As a result, no splitter plate was required. Another change was the replacement of the powered auxiliary air opening in favor of spring-loaded doors that positioned themselves aerodynamically depending on aircraft speed and engine thrust.

Except for the length, the spike/cone configuration and function was never changed. It provided management of the air to the engine at high transonic and supersonic speeds with its variable geometry.

At low transonic and below speeds, the spike was positioned all the way forward and the cone collapsed. At supersonic speeds, the spike moved aft and the cone expanded to control the speed and volume of the air being provided to the engine.

BuNo 152714 first flew with a variant of the Triple Plow II inlet that retained the splitter plate, which no longer has the kink as the spike has been moved outboard. The cowl no longer translates fore and aft, the required opening being replaced by two aerodynamically actuated doors rather than the three on the USAF production Triple Plow II inlet.

Note that spike extends farther forward of the Mach sensor and has been moved outboard closer to it. The splitter plate was subsequently removed but the fuselage not repainted accordingly.

The doors appear to have been added to existing cowls.

Craig Kaston Photos

BuNo 152715 first flew with the splitter plate removed but again, with only two doors on the modified cowl. 

One problem with the Hasegawa/Hobby 2000 kits with the Triple Plow II inlets is that the spikes appear to have not been lengthened compared to the Triple Plow I's.

Hobartville Hobbies in Australia sells seamless Triple Plow I and II inlets/ducts in 1/72, 1/48, and 1/32 scales. Their website: https://www.hobartvillehobbies.com.au. I can't vouch for their accuracy, quality, or fit but the illustrations look good and depict the vortex generators in the ducts that would be difficult to add to the parts in the plastic kits.

F-111B Conversion Part Two: Landing Gear

 A work in progress

The nose gear of the F-111B was very different but so was the main landing gear to a degree. As it happened, with two exceptions, the landing gear of the first three F-111Bs (BuNos 151970/71/72) was essentially identical to the landing gear on production F-111As, making the landing gear in the Hasegawa/Hobby 2000 kits usable as-is for them The two exceptions were that the nose gear on BuNo 151972  was damaged in the first of its two emergency landings and replaced with an F-111B nose-tow gear (at some point prior to its retirement, an F-111A nose landing gear was reinstalled) and the different aft main landing gear door on all seven F-111Bs.

BuNo 151972 with a nose-tow nose landing gear:

The aft main landing gear door was originally identical on the prototype F-111As and Bs. During extension and retraction it was articulated on two pairs of links so that on extension it swung down and back, remaining parallel to the bottom of the fuselage.

One pair of links was attached to pivot points on the main landing gear trunnion to which all its other parts were attached, one on either side of it, just below its pivot point on the back of the wheel well. The other pair were attached on the door just outboard of the first pair and to pivot points on each side of the wheel well. When the landing gear was extended or retracted, the door was driven by the first pair of links and remained parallel to the bottom of the fuselage when extended and retracted by the second pair of links (idlers).

Note that the trunnion on the 172 Hasegawa/Hobby 2000 kits is an open frame that should be covered with a thin piece of plastic.

A montage to illustrate the shape of the links and the location of the door: 

Apparently the rigging of the original aft main landing gear door was both finicky and subject to going out of adjustment, requiring a gear swing to remediate. As a result, early in F-111A production/operation, the door was simply mounted on the back side of the trunnion. This required that about six inches be removed from the back end of the door to clear the bottom of the fuselage when the landing gear was extended, so when it was retracted, there was a six inch wide opening on the bottom of the fuselage aft of the door.

This is the arrangement on all the F-111 kits except for the Revell, which has a simplified version of its original articulation. All seven of the F-111Bs flew with the original door, although in production it seems likely that it would have been mounted on the trunnion as well. While no aftermarket F-111B main landing gear tires are available, the F-111 kit tires can be narrowed and reduced in diameter accordingly.

All of the F-111Bs after the first three were delivered with the Navy landing gear. The F-111B main landing gear was the same as the F-111A’s and subsequent shore-based F-111s with the exception of the tires and the aft main landing gear door. At some point, to minimize a tipback problem in service, at least BuNo 152715 was modified to move the main landing gear wheels eight inches aft.

The Navy nose landing gear was completely different, however, except for the tire size. It was redesigned to add the nose-landing-gear tow and hold back for catapult launch as well as the Automatic Carrier Landing System radar corner-reflector. Both the strut and its actuation reflect the requirement that the nose landing gear react both the hold back and launch loads. Although no aftermarket F-111B nose landing gear is available, scratch building one is relatively easy.  Except for the wheels, the USAF nose gear isn't much use in that regard, though.

 Note that its shock strut angles forward (this is 151970 with the USAF nose gear) and ends well above the tire; the red markings on the nose wheel door were there to verify that the gear was fully extended:

 The Navy nose gear had a somewhat longer (the shock strut extended down to the axle) and beefier shock strut; the retraction actuator was also much beefier and attached above the shock strut piston:

 The Navy nose gear strut was mounted vertically (note the location of the wheel relative to the nose landing gear door):

 Ready to launch (the trail bar would hold the airplane back at full thrust and then release at the fitting to the strut when the catapult fired, remaining on the ship for reuse):

 The radar reflector was attached to the scissors so when the strut was extended in flight, it was raised to be vertical and above the right tire. Note the amber approach light, indicating to the LSO that the pilot is at the proper angle of attack.

 

F-111B Conversion Part One

A matrix of the seven different F-111Bs by Bureau Number is provided HERE along with a illustrations of the features and/or links that describe them.

There have been a few 1/72 and 1/48 conversions released to convert an USAF F-111 kit to the F-111B configuration. Most were only partial representations and there were only a couple of decal sheets available. Nevertheless, Bill Gillman (Navy Bird) was able to make do with them: Click HERE and HERE

 HERE is another 1/72 build by DrPlastic in 2012 using the Pete's Hangar conversion set (not recommended even if you could find one).

All of these conversion options have been eclipsed by the recent CAT 4 release of mostly 3D printed parts and a comprehensive decal sheet and instructions for any of the first three F-111Bs, which diverge the least from the production USAF F-111s. Click HERE for a description of the sets and a source.

These are the 3D-printed ejection seats provided in the CAT 4 1/72 conversion set R72016 that provides the majority of changes for the first three F-111Bs. The protective cover in front of the upper and lower ejection handles has been removed on the left seat.

 
There are various F-111 kits that provide a basis for that but their quality and build-ability varies significantly. I’m only familiar first hand with the 1/72 alternatives; however, Googling “1/48th F-111 kits” will result in the many detailed reviews that will provide a basis for selection.

Four 1/72 kits were originally issued, reissued as variants, and also distributed by other kit manufacturers:  

- Hasegawa/Hobby 2000: Unless your standards for accuracy and build-ability are low, these are the only acceptable starting point (also, the CAT 4 conversion sets are designed for them).

- Esci/Ertl/AMT/Gunze/Italeri: Disappointing in accuracy and fit but buildable (full disclosure, Paul Boyer binned his attempt at it)

- Revell/Monogram: The first release provided parts for both the development F-111A and F-111B airplanes. It was quite accurate in shape for those aircraft except for, ironically, the F-111B nose. The landing gear was retractable but necessarily simplistic as was the interior of the separable crew module. Later releases deleted the F-111B option.

- Airfix/MPC/Heller: Minimal detail (e.g. cockpit, no wheel wells), and the crew module is a separate, ill-fitting assembly

Note that one significant difference in some kits is the wing span but CAT 4 has created a conversion (R72025) for the low-aspect-ratio wing that was present on the F-111A/D/E/F to the higher aspect-ratio F-111B wing (the F-111C/G and FB-111A had the same wing span as the F-111B).

 Other options are DIY and using the wing extensions from the original Revell F-111A/B kit.

 Do It Yourself (degree of difficulty reduced if you glue the flaps and slats up and scribe the ones on the extension):

 Revell Kit Wing Tip Extensions:

 However, the CAT4 modification includes the extension of the trailing edge flaps and leading edge slats, which would be difficult to accurately represent deployed otherwise.

Another consideration is the two different lengths of the engine shroud aft of the afterburner. Both of these were present at one time or another on all of the first five F-111Bs and the ones in the Hasegawa kit are all long and configured with “feathers” that resemble those on variable-area afterburner nozzles, unlike the smooth exterior of the shrouds on the F-111Bs (my guess is that the feather configuration was added to reduce the hoop stress from thermal expansion). CAT4 provides a shroud length option or the kit shroud feathers can be filled and smoothed to the F-111B configuration.

All of the F-111 kits will have the USAF landing gear. As it happens, the first three F-111Bs flew with them but the remainder were delivered with the very different Navy nose landing gear and main landing gear wheels. Also, except for the Revell, the F-111 kits do not have the original retractable aft main landing gear door flown on the first seven F-111Bs.

The engine inlets also varied among the kits with some overlap of those on the first seven F-111Bs (General Dynamics was responsible for inlet development; Grumman was roughly one inlet modification behind in production). As noted on the Conversion Set Application matrix, which specific F-111B you model will determine which Hasegawa/Hobby 2000 kit to buy.

The F-111B cockpits were notably different. The first three F-111Bs had ejection seats. All had flight controls only on the left hand side. The F-111Bs delivered to Hughes for Phoenix system installation (151971/2 and 152715) had the right side instrument panel provided in the CAT 4 set R72016 but the remainder had a flight-test-only substitute with few instruments and switches.

To be continued in Part 2