Training the Right Stuff

Mark Frankel and I have written a book on the development and operational history of U. S. Air Force and Navy jet trainers.

It will be available in May 2016. For more information, see:

http://www.schifferbooks.com/training-the-right-stuff-the-aircraft-that-produced-americas-jet-pilots-5914.html

Republic R-46?

Okay - it's a bogus designation, based on the Navy practice of designating a research aircraft with its identifier for the manufacturer and the manufacturer's model number of the design, e.g. Douglas D-558-1 Skystreak. (Also see http://thanlont.blogspot.com/2010/07/navy-research-aircraft-designations.html) In this case, it was Republic's AP-46, the Air Force's XF-84H informally known as Thunderscreech, a flying test bed for supersonic propellers. While the model number is correct, an R for Republic is conjecture on my part. Neither it nor its predecessor, Seversky, was apparently ever assigned a manufacturer's designation by the Navy.*

I first read of the Navy's prospective involvement in the program in the 3 May 1954 issue of Aviation week, which stated that the XF-84H was to fly in August. It also stated "the Air Force will use the plane to check supersonic propeller characteristics" and, of more interest to me, after being "fitted with another type Aeroproducts propeller, it will also undergo Navy carrier trials".

As it happened, it didn't fly until July 1955 and there was no Navy testing. In fact, there was very little Air Force testing, since the two XF-84Hs only flew a total of 12 times, making precautionary landings on 11 of those occasions. As a test-pilot friend of mine once noted, it doesn't take long to take a close look at a hot horseshoe.

I had assumed that the Navy's interest in the airplane, if true, had been as a backup for the Douglas A2D Skyshark, which was powered by the same Allison T40 turboprop engine.

However, the timing was way off, the XA2D having first flown in May 1950. Also, its engine was more or less unsatisfactory from the get-go, suggesting that the Navy's backup for the A2D, if it had one, would have used a different one.

I just now took another look at the XF-84H program since Steve Ginter has released the latest in his excellent series of monographs on Navy and Air Force aircraft.

To order from Steve (he makes a few more bucks that way) see http://www.ginterbooks.com/AIRFORCE/AFL219.htm

There aren't many details about the Navy's involvement, but by happenstance, John M. Leonard updated his fascinating online article (http://www.enginehistory.org/Allison/XF-84Propulsion.html) about the XF-84H propulsion system for the latest issue of the American Aviation History Society Journal (Fall 2015). If you're not a member, you should be. This issue alone is worth the price of a year's subscription.

He describes what little is known about the Navy involvement, which was basically the funding of design and whirl test of an Aeroproducts six-bladed, two-row propeller beginning in late 1949 or early 1950. This is a picture from his AAHS article:

The aft (bottom, as depicted here) propeller is obscured in this picture. The propellers were nine feet in diameter and separated by about 18 inches longitudinally. The aft propeller was offset by 15 degrees and, surprisingly, given the amount of torque involved, rotated in the same direction. I assume that the shock waves from the front propeller dictated this configuration.

In the late 1940s and early 1950s, the Navy was interested in a supersonic propeller in order to get more range and endurance from a fighter with with jet performance, not to mention the takeoff and wave-off benefits of the propeller.

As far as I know, the Navy never got as far as assigning a Bureau Number to its AP-46, which would have been the third one built. Instead, the Air Force reportedly agreed to install the Navy gearbox and propeller in the second XF-84H after its initial flight test. That, of course, didn't happen.

* Seversky did propose a carrier-based variant of its P-35 to the Navy in 1937 and furnished one, free of charge, for an evaluation that included the Brewster F2A Buffalo and the Grumman F4F Wildcat. Seversky promoted it as "NF-1", signifying Navy fighter number one, but it was civil registered and as far as I know, not assigned a Bureau Number or Navy designation. For one thing, it was on loan from Seversky and not owned by the Navy. The Navy reportedly referred to it as the XFN-1. This is possible—albeit only informally since the designation had previously been assigned to a Naval Aircraft Factory fighter, BuNo A8978, several years before and the Navy rarely reused a designation even when, as in this case, the NAF design wasn't built. According to several websites, the P-35 evaluated by the Navy was modified by the Naval Aircraft Factory and therefore designated XFN-1; I suspect that this is a conflation of the two designations leading to an erroneous conclusion. For one thing, the Grumman XF4F-3 was assigned BuNo 0383 and the Brewster XF2A-1, 0451. If the NAF did modify the P-35 and it was assigned a BuNo, it would have almost certainly been higher than 0451, not 1,400 BuNos lower in the previous A series.

Carrier-Based Airplane Self-Boarding

Mark Nankivil passed along the following from Jack Abercrombie:

While watching the Banshee at  https://www.youtube.com/watch?v=khVPlD2rNfc, which shows a ground crewman exiting on the right side. the question occurred to me—on which side of most top-entrance jet aircraft are built-in steps, left or right? And what about external, crew chief erected boarding ladders?

Which got me to thinking. It turns out that carrier-based propeller-driven fighters tended to have the boarding provisions on both sides of the fuselage, like the F6F Hellcat.

These big engines needed to be warmed up. This allowed a crew chief to do so if desired and then climb out of the cockpit on one side while the pilot climbed in from the other.

The F4U Corsair had a similar arrangement, but eventually the boarding provisions on the right side were somewhat more user friendly than the ones on the left, as with this F4U-5P that had a boarding step extending out from the fuselage.

 The earliest jets were a mixed bag. The FH-1 had boarding steps on the right side but not on the left.

Note that there was a non-skid patch on the nose landing-gear door for the first step with the left foot.

The FJ-1 had boarding steps on both sides (there was also a door that opened on the left side as there was on the right).

Since boarding provisions were heavy and jets didn't need to be warmed up, my guess is that it was quickly determined that only access was required from only one side. But which side?

The F6U Pirate was boarded from the left side.

But the F3D was boarded from the right.

As was the XF2D-1 as Jack noted:

(Note that the landing gear door was not used as a step.)

However, the production F2H was boarded only from the left, with the gear door again serving for the first step.

 The F9F Panther was also boarded from the left side, which was now standard.

With the advent of bigger jets with a nose-high stance for low-speed lift like the F7U-1 Cutlass, providing for self-boarding began to be a challenge.

Ladders were still anathema on the carrier, but widely used ashore.

There were only two exceptions to the self-board requirement. One was the A4D Skyhawk. Self-boarding was one of many things left off in the pursuit of minimum empty weight (also see http://thanlont.blogspot.com/2011/09/self-boarding-for-douglas-skyhawk.html). The other was the F4D Skyray. In the latter case, both the mockup and the prototypes featured self-boarding from the left side.

However, by the time the XF4D was ready for at-sea carrier qualification, it had more of a nose-up stance and a ladder (mounted on the left side) was needed to reach the cockpit.

Somehow Douglas convinced the Navy to forego F4D self-boarding, probably because its contemporary, the A4D, didn't have self-boarding and used a similar ladder, (different than the one shown above) that could be attached only to the left side of the fuselage.

Similarly, the F3H Demon, which was delivered with self-boarding capability (see http://thanlont.blogspot.com/2009/06/self-boarding.html for the XF3H and http://thanlont.blogspot.com/2008/05/i-had-hoped-to-find-picture-like-this.html for the F3H), was allowed to have ladders even aboard carriers as was the F7U-3, which probably avoided several broken bones or worse (note that the F7U-1 steps have become pegs with a giant step required from the engine nacelle to the first peg and another from the second peg to the cockpit).

Why access from the left side? My guess is that given the primitive fuel controls of the first jet engines, a pilot's first start or two during his initial checkout in jets needed to be demonstrated and/or closely monitored in order to avoid overtemping the engine. Since the throttle was on the left side of the cockpit, the instruction by an experienced pilot or crew chief needed to be from the left side of the airplane. 

Carriers and Tricycles

Except for a few very early biplanes, for many years airplanes had tail wheels, not nose wheels, even though the latter made landings less likely to result in excursions off the runway or worse. The reasons were compelling. A nose gear was more likely to break during a landing (or even a takeoff) in the former pastures that were used for landing fields, it was heavier than a tail wheel, and before the adoption of retractable landing gear, resulted in more drag in cruise flight.

However, paved runways eventually became the rule rather than the exception. Retractable landing gear made the nose-landing-gear drag penalty disappear. The nose landing gear arrangement also became of benefit during the takeoff roll of a multi-engine airplane: in the event of an engine failure, the pilot was more likely to be able to keep the airplane headed down the runway if it had a nose wheel to help resist the turning moment. In fact, it was more widely incorporated on early bombers like the B-24, B-25, B-26 etc. than fighters. (One exception was the P-38 but the configuration of the former wasn't really suitable for a tail wheel and it was also multi-engined.)

Another exception was the Bell P-39. It's unique inline arrangement of cannon, cockpit, and engine provided room for a nose gear and the need for nondisposable weight up front for balance reasons.

The Navy's preference for a tail-wheel configuration was so strong, that when it agreed to consider a carrier-based variant of the Army's new fighter, it insisted on it. The resulting Bell FL-1 became a taildragger.

For more on the brief history of the XFL-1 Aerobonita (as well as a summary of the history of the development of—and the engine manufacturer's struggle for supremacy between—the air-cooled versus liquid-cooled airplane engine and the Navy's ongoing interest in the liquid-cooled engine) see my monograph;

It is available from Steve Ginter here: http://www.ginterbooks.com/NAVAL/NF81.htm

The Navy didn't completely forswear the nose-wheel configuration any more than they did the liquid-cooled engine. In August 1939, they went to the trouble of converting a Lockheed Junior to have a nose gear (it was fixed and the main landing gear had to be moved aft as well) and conducting successful at-sea trials aboard Lexington (CV-2).

Douglas won contracts during World War II for two single-engine carrier-based attack planes with nose landing gears, the SB2D and TB2D:

 

My guess is that the advantage was that heavy bombs and torpedoes didn't have to be positioned at an angle to be attached to the airplanes. A small quantity of BTDs,  a development of the SB2D, were built for evaluation. Douglas quickly replaced it with an all-new design with a tail wheel, the BT2D, which became the AD Skyraider.

The Ryan FR-1 also needed a nose wheel because it had a jet engine in the tail. From time to time, it was a poster child for the benefit of not having a nose landing gear during a carrier landing (as well as proper location of the attach point for the tailhook).

Nevertheless, the nose wheel configuration also went to sea on the Grumman F7F Tigercat, albeit rarely and not without incident:

The F7F's main contribution to carrier-based aviation was the need for the development of a crash barrier that was compatible with airplanes with nose landing gears. See http://thanlont.blogspot.com/2010/10/barriers-and-barricades-one-more-time.html

Jets, of course, all but had to have a nose landing gear for various reasons. There were a few exceptions early on, even one that was carrier based, the Supermarine Attacker.

For more on twin-engine carrier-based airplanes with nose landing gears, see http://thanlont.blogspot.com/2010/11/one-if-by-land-two-if-by-sea.html

TailDragger Transition

Mark Frankel and I are in the process of finishing up our book on U.S. Air Force and U.S. Navy trainers, Training the Right Stuff. It will be published by Schiffer in the spring.

One major feature of the new post-World War II trainers was that they had nose wheels (tricycle landing gear) rather than tail wheels (taildraggers). Landing an airplane with a tricycle landing gear was a lot less likely to be dramatic because it was directionally stable. A taildragger was not, some more inclined to swap ends than others, but none that didn't bear watching, particularly in a crosswind. There were other advantages to the tricycle landing gear, such as being able to see where you were going when taxiing or beginning a takeoff. (For more on tail draggers and in particular the "ground loop", see http://thanlont.blogspot.com/2014/10/tricycles-are-for-kids.html

One shortcoming of an all-tricycle training fleet was that there were still taildraggers in use. However, most had dual control or dual-control variants, including the P-51 Mustang. And transitioning to a taildragger was somewhat easier if you already knew how to land. In the military, if an aviator had gotten that far, he would be less likely to be off optimal (airspeed, rate of descent, and alignment with respect to crosswind and runway) on short final and quicker to correct a problem like a swerve or a bounce.

What hadn't occurred to me, but did to Frank Williamson, was how did a Navy pilot go from the tricycle-gear T-28 into the AD Skyraider? The Navy didn't have any with dual controls (the Air Force did later on, since the AD-5 had dual-control provisions). The answer was advanced training at Navy squadron VT-30 at Corpus Christi.

Richard Adams via Phillip Friddell

Walt Fink was one of the aviators to do so:

Been there and done that in July 1962. Skyraider "Fam" at VT-30 consisted of five AD-6 (single-seat, because that's all we had—no Fat Spads) "flights"—that in quotation marks because on the first one, we didn't ever get airborne. It was a ground exercise to acquaint us with the taildragger mentality but we prepared for it like we were going flying, with all our gear, complete pre-flight briefing, complete pre-flight of the airplane, etc. After engine start, our instructor led us from the VT-30 line to the run-up area. We followed along, spreading the wings. Once there, we went through all the checks of prop, mags, hydraulics and such. Then he led us on a taxi-around tour of NAS Corpus Christi, looking not unlike elephants on parade, so we could get a feel for what it was like with the tail wheel locked and then unlocked, making turns, etc.

The final part of that first "flight" was that each of us taxied  onto the runway and when we got permission for "takeoff", we held the brakes, stick full back, and ran the R-3350 up to 30" of manifold pressure. Then we released the brakes and without adding power, got a little feel for how much right rudder it took to keep the nose pointed straight down the runway. I don't remember how fast we actually got—enough to get the tail light, anyhow—before we aborted the takeoff and discovered how much left rudder it took to maintain directional control. Then we taxied back to the line, folded the wings, and went through the shutdown procedures. We probably spent 45 minutes or so from start to finish.

Our first real flight was the next day and lasted about two hours, terminating in one landing. The following day, FAM-2 was spent on landing practice: my logbook shows I made 11 landings that consisted of 10 touch-and-goes and one full stop. The third flight was the same and the fourth one was six touch-and-goes and a full stop. The airplane was a beautiful flying machine but it took a little getting used to landing and directional control. By the way, we three-pointed the landings; the bird was heavy enough that it stayed where it was planted.

That was it for "basic fam" but of course we learned a little more with each successive flight. Those four Fam flights were followed by two formation hops, three Tac/Acro flights, and then we got into weapons delivery, day and night navigation, night formation, instruments, and finally FCLP (Field Carrier Landing Practice) and CQ (Carrier Qualification at sea). Total AD flights in my logbook at VT-30 were 44 with no incompletes or repeats.

Robert Hansen also went through the transition: I remember adding power and when the tail lifted off the runway, we cut power. That was an exciting point because you had to change rudder to account for the change in torque. Sometimes it was very colorful and there was an occasional "ground loop". When the flight returned from the first airborne flight, instructors were known to line the windows to watch the "first" landings, which also were colorful at times.

The Gutless Cutlass?

3 September 2021: Revisions made as a result of additional research

 Some airplanes just don't get any respect. The Vought F7U Cutlass suffers worse than most: "Ensign Killer", "the engines put out less heat than Westinghouse's toasters", "Gutless Cutlass", and so forth. And then there's the iconic photos and video of the VF-124 F7U-3 ramp strike:

Yes, that is the LSO sprinting across the deck to get out of the way, which he did. Contrary to what's reported in various places on the internet, he wasn't hurt and there were no serious injuries to anyone else on deck. The pilot was killed.

In fact, the F7U-3 had about the same thrust-to-weight ratio as its contemporaries, the F9F-8 Cougar and the FJ-3 Fury, albeit in afterburner. And that's even though Westinghouse did not meet the original engine-thrust specification. Unfortunately, it was the first fighter with afterburning engines that the Navy took to the carrier. Most pilots did not understand, much less appreciate, the tradeoff involved. Their initial perception was that "dry" engine thrust was only 2/3s of thrust in afterburner and using afterburner involved the burning of prodigious amounts of fuel, significantly limiting range and endurance.

However, there were weight and performance benefits of substituting a small jet engine with an afterburner for a big jet engine with the same thrust without afterburning and Westinghouse did subsequently deliver J46 engines with the originally promised thrust.

This reliance on afterburner for "full" power would not have been quite so evident but for the fact that the Cutlass lacked a horizontal tail. It therefore required a big, thick wing for low-speed lift since no horizontal tail precluded the use of trailing edge flaps: there was no means of counteracting the pitching moment change that was caused when they were lowered. This is a comparison of the F7U-1 and the F-86.

As a result, at low speed on a low, flat approach to an axial deck carrier, pulling the stick back to increase angle of attack actually decreased lift initially. The subsequent increase in lift was accompanied by a very large increase in drag. From the flight manual: "To change angle of attack alone results in excessive loss of altitude, and the rate of descent is so difficult to control as to preclude safe answering of altitude correction signals from the Landing Signal Officer."

So to recover from being low or settling meant adding thrust, preferably even before the pilot got low or settling began. Unfortunately, the relatively low military thrust and high drag at the angle of attack required to attain a low approach speed meant there wasn't much excess thrust unless the afterburner was used. Which was problematical with the early afterburners. From the flight manual again: "Because increases in angle of attack from flight conditions such as making a turn, stopping a rate of descent, and initiating a climb increases the drag, caution should be exercised to assure that the airplane is accelerating prior to entering the aforementioned maneuvers. (A waveoff) must be initiated relatively early because selection of (afterburner) is accompanied by a thrust delay lasting up to two seconds. For the first three seconds following power increase, better airplane acceleration is attained in military power; after three seconds a marked acceleration advantage is obtained in (afterburner)."

The horrific F7U-3 ramp strike was actually preceded by a routine approach and landing by the pilot. The accident investigation determined that the airplane was above the maximum approach weight when it crashed, which meant it was even heavier on the first, successful, landing. However, on the second approach the pilot got low and was slow to respond to the LSO's "come on" signals.

Another frequently repeated and undeserved observation was that the Cutlass had a "weak" nose landing gear. There were several incidences of nose gear collapses (including a fatal one) but they almost entirely due to either pilot error (landing short or long, resulting in an overload of the nose gear actuator when the nose wheels hit something) or mis-set/malfunctioning arresting gear/barrier engines, the abrupt stop again overloading the nose gear actuator. This Cutlass ran off the runway in Japan:

Contrary to another widely repeated canard, the nose landing gear strut never failed upward and speared into the cockpit, ejecting the pilot. There was one carrier-landing incident when a barrier malfunction caused an overload of the nose gear that caused the airframe attach point of its extension/retraction actuator to break loose. The upward movement of the fitting knocked the canopy off, which armed the ejection seat, and then it hit the seat's firing mechanism, ejecting the pilot. The aft side of the ejection seat headrest was modified as a result so it would only fire if the pilot pulled the face curtain.

The belief that the Cutlass was underpowered stems from the Navy's decision to repurpose the F7U-3 as a fleet air defense fighter armed with guided missiles. The addition of Sparrow I missiles, the requisite fire control system, and additional internal fuel resulted in a significant increase in weight; however, the Navy elected not to also add more thrust since the resulting F7U-3M was considered to be a placeholder until the Sparrow III armed F3H-2 completed development and qualification. That version of the Cutlass was therefore considered to be "under powered" although the thrust was adequate for the mission, particularly since its deployment was from angled-deck carriers employing a descending approach rather than a flat one. There were no incidents due to a lack of thrust.

Ironically, the F8U Crusader's handling qualities on approach were at least as challenging as the F7U's and its accident rate not much better even though it only deployed on angle-deck carriers. However, supersonic performance combined with outstanding endurance meant it was revered instead of reviled and ridiculed.

The Crusader pilot reportedly boltered with a badly damaged aft fuselage and was sent to the beach, where he landed without incident.

Post-War Eastern TBM Variants

29 August 2020: Added clarification of TBM-3J

25 July 2015: Added  background information on the TBM-3P

19 July 2015: Updated with additions, corrections, and other changes.

Rick Morgan (http://rickmorganbooks.com/index.html) and I have continued to explore the poorly documented post-war history of the various variants of the Eastern Aircraft TBM-3. The Navy still had lots of them after the war. Since they were big and easily modified, they were readily adaptable to other missions besides torpedo, glide, and level bombing that were their raison d'etre.

Most were modified from TBM-3Es. In most cases, the addition of the E would simply mean the addition of electronic equipment, in this case provisions for carrying the APS-4 radar on a stores pylon under the right wing. However, the designation is also associated, possibly coincidentally, with a redesign by Eastern to reduce weight by about four hundred pounds. One of those changes was probably the location of the tailhook, which had been internally housed on all TBFs and prior TBM production.  Most TBM-3Es delivered from Eastern probably had the external tailhook. This is an example.

There is evidence that the weight reduction effectivity in production (like the tailhook change, deletion of tunnel gun provisions and some armor, etc.) was not the same as for the APS-4 provisions. As a result, the first production -3Es did not have the external tailhook. It is also possible, even likely, that TBM-3s were subsequently modified to the E configuration (i.e. APS-4 provisions) at Navy repair and overhaul facilities but retained the internal tailhook.

Based on the information provided on Joe Baugher's invaluable listing of Bureau Numbers (see http://www.joebaugher.com/navy_serials/navyserials.html) and elsewhere, it appears that one TBM-3E production lot used a block of Bureau Numbers from a cancelled BuAer contract:

Bureau Numbers                 Mfg Number                Model

22857-23656                       1-800                            TBM-3

68062-69538                       801-2277                      TBM-3

85459-86292                       2278-3111 (834)           TBM-3E

53050-53949                       3112-4011 (900)           TBM-3E

91107-91752                       4012-4657 (646)           TBM-3E

These out-of-sequence BuNos explain why many "older" TBM-3Es, i.e. with 53XXX BuNos, are configured with an external tailhook even though its effectivity reportedly occurred at either BuNo 85566 or 86175. It also explains erroneous statements to the effect that most TBM-3Es did not have the external tailhook when in fact most do.

For sure there are TBM-3Es with the APS-4 radar and an internal tailhook. In his comment below, Pablo Montero provided a link to this example, which is reportedly a VMTB-234 Avenger circa 1945. It looks like there is an E at the end of the type designation on the vertical fin but as is frequently the case, the BuNo cannot be read.

The next interesting issue is the alphabet soup of TBM-3 variants. A suffix was used when a change was "major" and intended to be permanent, with occasional exceptions (see TBM-3J below). Note that there was no TBM-3B or -3C whereas there was a TBM-1B and -1C; this appears to have been because B stood for a British version and C was apparently an armament change (the -1C deleted the single cowling mounted machine gun in favor of one in each wing outboard of the propeller arc). There was a TBM-1D with a permanently mounted APS-3 radar on the right wing, which is apparently why the similar -3 conversions were designated -3Ds. These were a late-war modification to add an APS-3 radar on the right wing and ECM (Electronic Counter Measure) equipment. The gun and associated hardware was removed from the turret and the lower compartment by VT(N)-90  to reduce weight since its primary mission was night attack.

Some other well-known variants:

TBM-3W: A late-war modification to add an APS-20 radar in a large belly-mounted radome for airborne early warning. Some were converted from TBM-3s like 89471 so it had an internal tailhook.

Some were converted from TBM-3Es like 53894 so it had an external tailhook.

TBM-3R: A Korean War-era modification for COD (Carrier On-board Delivery); see http://tailhooktopics.blogspot.com/2013/01/tbm-3r-cod.html

TBM-3S: A post-war modification to remove the defensive armament and add ASW mission equipment. It was teamed with a TBM-3W variant to provide submarine hunter-killer capability as a placeholder for the AF Guardian. There were variations in the mission equipment and the canopy modification (one was designated TBM-3S2 to distinguish it from the 3S). Note that a crewman now occupies the compartment aft of the pilot.

TBM-3U: A TBM-3 modified to tow targets and for general utility use. All offensive and defensive hardware was removed and a tow reel was permanently installed in the aft fuselage. The tow target was presumably streamed out from the former stinger gun location just ahead of the tail wheel.

Note that BuNo 69400 was probably delivered from Eastern as a -3 and subsequently modified to carry an APS-4 radar pod under the right wing.

TBM-3J was a TBM-3E with provisions for installation of a tow target reel. The concept was that it could deploy with an air group and provide tow target services when required. It was therefore not, as can be found on internet, a TBM-3 equipped for all-weather operations, i.e. with wing and tail surface deicing.

Less well known and sometimes misidentified are the TBM-3N (see http://thanlont.blogspot.com/2015/07/tbm-3n-versus-tbm-3q.html) and TBM-3Q (see http://rickmorganbooks.com/tbm-3q-avenger.html). For example, as Rick points out in his excellent post on the latter, it did not have a belly-mounted radome like the TBM-3W as usually stated in TBM books and online summaries.

And then there are the TBM variants for which we have yet to find documentation, much less photographs. Through the magic of copy and paste, these are identified on many web sites as follows:

TBM-3H: TBM-3 modified for surface search radar

TBM-3L: TBM-3 equipped with a retractable searchlight in bomb bay

TBM-3M: TBM-3 conversion as missile launcher

TBM-3P: TBM-3 conversion for photo-reconnaissance

Of these five, for sure the TBM-3P and TBM-3L are correctly identified per Navy documentation dated November 1944.

The TBM-3P was a TBM-3 "equipped with a trimetregon (sic) camera". Rick Morgan has found "less than 10" in CASU (Carrier Aircraft Service Units) pools in San Diego and Pearl Harbor in the 1946 Allowance Lists (some are listed as TBM-3EP, which suggests that "TBM-3Ps" were converted from TBM-3s). CASUs were repair and maintenance centers at some naval air stations; they were also a storage point for airplanes that could be issued to squadrons to replace attrition. The trimetrogon camera installation actually utilized three cameras, left and right oblique and vertical, taking pictures simultaneously. This is the installation in a B-17 (see https://historicairphotos.wordpress.com/2014/05/21/trimetrogon-photography/)

The pictures overlapped so they provided complete coverage from side to side.

The TBM-3P camera installation was probably located in the lower (radioman's) compartment. Since mapping, as opposed to strike-damage assessment, was not a primary air-group mission, the TBM-3P was probably little utilized and appears to have had a short career. No pictures of one have been identified as such.

The same document lists the TBM-3L as a "TBM-3, 3D, or 3E equipped with a searchlight mounted in the bomb bay". Note that the TBM-3D had provisions for a searchlight mounted on a pylon under the left stub wing but since this was "detachable", the suffix L did not apply. (In any event, utilizing the bomb bay for this purpose seems counterproductive, which may be why there aren't too many pictures of the type—I have yet to see one.)

The description of each of the other two TBM variants is dubious. A Navy History and Heritage Command document (HERE) does not list the H and the M and identifies the J as a "utility plane", which it was since it could be configured with a tow-target capability.

At the time, the suffix H was used to designate an airplane modified to be a "hospital", i.e. to transport wounded personnel. That's a possibility, although no TBM-3Hs have been identified. There was reportedly a modification of the TBM-3W's radar to optimize it for submarine-snorkel detection but this would have, if anything, probably resulted in a modification to the existing designation (there is a TBM-3W2, for example).

There may have been TBMs with deice boots but they were not designated TBM-3Js. As noted above, these were TBM-3Es modified with provisions for target towing, the forerunner of the TBM-3U. However, they retained the carrier-basing and ordnance capability; as a result, the designation of a TBM with this capability depended on whether the tow equipment was installed or not! See the June 1947 issue of Naval Aviation News.

The TBM-3M, if there were any, was more likely a modification for weather reconnaissance like the PB4Y-2M, which was the purpose of the suffix at the time. None have been identified.

On the other hand, there are a couple of TBM modifications that we have pictures of but little or no additional information. The first is something in the bomb bay of  TBM-3E BuNo 91704 in a picture provided by Jim Hawkins via Steve Ginter. It looks like there is an opening at the bottom of the aft end of the pod and what might be static discharge wicks or antennas on the bottom of the pod. It could be an early ECM pod installed on this TBM for inflight testing.

Another is a TBM marked as a -3E, reportedly BuNo 69465 at Pax River on 18 January 1946, provided by Jim Sullivan (the TT on the cowling indicates that it was assigned to the Tactical Test division at the time). It was reportedly an attempt by Eastern to compete with the new single-seat BT—soon to be changed to A for attack—airplanes from Douglas, Martin, et al.

TBM-3N versus the TBM-3Q

I was recently asked if I had any pictures of a TBM-3Q. First, I had to refresh my memory of the type, one of several modifications of TBM-3Es, a veritable alphabet soup of repurposed Turkeys.

The TBM-3E was the last production model, redesigned in detail to reduce weight and add provisions for an APS-4 radar pod under the starboard wing.  The Eastern Aircraft Division of General Motors built 1,480 as the war was winding down and Navy contractors were completing the development of various single-engine attack airplanes like the AD Skyraider that would replace it and the Curtiss SB2C. The most obvious external difference was that the tailhook was stowed under the aft fuselage rather than within it.

The TBM-3Q was one of the first carrier-based airplanes configured specifically for electronic reconnaissance although it retained its ordnance-delivery capability so ELINT (short for electronic intelligence) was more of a collateral duty. It could also be used to "home-in" on enemy ships and shore-based defenses that utilized radar and jam the capability.

I found this picture of two "TBM-3Ns" on the excellent web site of the National Naval Aviation Museum (http://www.navalaviationmuseum.org/).

I thought that they were actually TBM-3Qs because they did not have turrets (according to one online description of the TBM-3Q, a characteristic of this conversion) and had ECM (Electronic Counter Measure) antennas identical to those on the Martin AM-1Q and the various Douglas Skyraider Qs.

I so informed the museum's library staff and got the immediate and polite response that to the best of their knowledge, the Ns did not have a turret and the Qs did. Another strike against online research.

The TBM-3N Radar Operator's position:

It appears that the TBM-3N was a postwar -3E modification to perform night and all-weather attack missions with updated electronic countermeasure avionics as a placeholder for the forthcoming Skyraider. Rick Morgan looked at some postwar location lists and estimates that no more than 30 conversions were accomplished. He found that some were assigned to the air groups linked with FDR (CVB-42) and Saipan (CVL-48) in early 1947 and early 1947/8 respectively. However most were operated by the night composite squadrons that provided detachments to deploying air groups, first VCN-1 and -2 and then their successors, VC-3 and -4. (For a brief summary of the role of composite squadrons, see http://thanlont.blogspot.com/2013/12/composite-squadrons-and-detachments.html.) TBM-3Ns were also operated by the two Fleet All-Weather Training Units, the Pacific (the two pictured above, circa 1950) and Atlantic

This is a picture from the files of the National Naval Aviation Museum of a VCN-2 TBM-3N landing on Philippine Sea in 1948.

 Note the lack of a turret.

There was wartime precedence for the removal of the turret for night attack (and in fact, none of the Navy candidates for its postwar carrier-based attack requirements, day or night, had defensive armament). VT-90N removed the turret hardware (but not the enclosure) from its TBM-3D's in late 1944 or early 1945 to lighten them. If you look closely at the turret, you'll see that a crewman is sitting there, sans machine gun.

Note that the -3D was optimized for night attack with an APS-6 radar hard-mounted to the wing and various ECM antennas. Why was it not a -3N? Good question. For my attempt to unravel the World War II Navy airplane designation suffix history, see http://thanlont.blogspot.com/2014/03/navy-aircraft-designation-suffixes-redux.html and the links therein.

So what did the TBM-3Q look like? Larry Webster came up with this picture of one in an old Japanese aviation enthusiasts' magazine.

It has the aft-fuselage antennas like those on the TBM-3N but also retains the turret.

Rick Morgan was also exploring this question as well. His TBM-3Q post that resulted is far more detailed than the one I was coming up with. See http://rickmorganbooks.com/tbm-3q-avenger.html.

Your guess is as good as mine as to why the turret was retained on the -3Q. Mine is that there was a risk that the focus of its intention to collect electronic information for future strike-mission planning might take umbrage at the fact. As it turned out, several unarmed land-based "spy" planes were shot down during ELINT missions. For incidents involving the U.S. Navy, see https://www.nsa.gov/about/_files/cryptologic_heritage/publications/coldwar/dangerous_business.pdf

Rick Morgan opined that they retained the turrets because they were assigned to VT/VA squadrons that were primarily equipped with TBM-3Es that retained the turret. Since they could be assigned to day strikes along with the other Avengers in the squadron, their crews wouldn't want to be be defenseless in that event, much less likely to be singled out initially because of the lack of a turret.