by Tommy H. Thomason

Friday, December 23, 2011

Where's His Parachute?

In the typical picture of an Air Force pilot on the ramp going to and from his airplane, he is wearing a parachute. Navy pilots, rarely after flight school.  At some point before mid-July 1944, probably much earlier, parachutes were left in the cockpits of carrier-based airplanes, doubtless to avoid any possibility of a parachute opening accidentally on the flight deck. From the 1 July 1944 issue of Naval Aviation News, page 33:

In order to make strapping in less of a hassle, the pilot was provided with a parachute harness to wear to and from the airplane. It had two straps hanging down from the shoulders with clips at the bottom to attach to the parachute pack in the seat pan.
The crotch straps dangling down from the bottom of the harness were often left unattached for comfort while walking to and from the airplane.

This separate harness seems to have disappeared after the war but the parachutes still remained in the cockpit as evidenced by this Marine FJ-2 pilot saddling up.

The torso harness was reinvented by Douglas for use with the A4D ejection seats. Astronaut Alan Bean has a picture of him in one on his website,  http://www.alanbean.com/naval_aviator.cfm
(He's also wearing an anti-blackout or g-suit.)

 The torso harness became standard at some point with the Martin-Baker ejection seats.

For much, much more on flight suit gear, see: http://heritageflightgeardisplays.wordpress.com/

Wednesday, November 16, 2011

Lockheed P-80A Carrier Trials

As a result of a Jared Zichek Navy P-80A post in Retro Mechanix (see http://retromechanix.com/ for his web site), I took a trip in the way-back machine to a Tailhook Topics column in an IPMS Update:
Jared posted some terrific pictures that he found at the National Archives providing details of the modifications involved. See http://retromechanix.com/lockheed-p-80a-for-the-u-s-navy-1945/ (I don't know how he keeps coming up with some of this stuff; I've been there many times and never seen this particular report.)

The pictures solve a mystery for me. It turns out that the tailhook was installed in a recess on the bottom of the fuselage. One unusual aspect of the installation is that the pivot point for the tailhook was on the aft end of a bell crank that tilted down when the tailhook was lowered. As a result, when the hook is down, it appears to be externally mounted. The arrangement kept the hook from damaging the fuselage, since the bell crank lowered the front end of the hook so the aft end hit a transverse bumper on the bottom of the fuselage if it happened to bounce or be pulled that high. All that will make more sense when you look at the pictures that Jared has posted.

Another unusual aspect of the modification was that the airplane could be attached to the catapult shuttle with either a pendant, which attaches to only one point on the aircraft, or a bridle, which attaches to two points. The bridle arrangement was the most common up until then, mainly because the landing gear represented two strong points to attach a bridle to and stores on the centerline made it difficult to find a place to locate a pendant.

Both bridle and pendant configurations were evaluated for catapult launch of the Navy's P-80A. The bridle cable was attached to a hook on each wing and passed in front of the catapult shuttle.

The pendant was shorter and therefore lighter as well as easier for the deck crew to attach: one end was looped around the catapult shuttle and the other to an attach point on the bottom of the forward fuselage. However, there was some concern that the launch would be more exciting with the pendant if the airplane was lined up a bit crooked or offset relative to the catapult track.

In shore-based testing, the bridle was found to cause too much nose-up pitch at nominal accelerations and end speeds. At 2.6 g and 75 mph end speed, the tail pipe came within four inches of the deck.

The pendant did not cause a pitch up but was found to ding the aircraft on release; however, this was attributed to the shore-based catapult installation that had a track sunk below ground level. No problem was encountered with a non-perfect lineup.

In the shipboard trials aboard FDR on 1 November 1946, Marion Carl made four deck runs (starting from virtually the fantail) and two catapult launches at fairly light gross weights and about 35 knots wind over deck. All were satisfactory.

The drawing incorrectly depicts a tall thin mast in front of the windscreen (see http://tailspintopics.blogspot.com/2016/02/lockheed-p-80a-carrier-trials-mea-culpa.html). The side view drawing above is also incorrect with respect to the location of the forward end of the tailhook and its overall length. I had assumed that the tailhook would be attached forward of the fuselage break from a structural standpoint. The pictures on Jared's website referenced above provide a much better idea of the installation and show it to be attached aft of the fuselage break.

Rumor has it that the P-80 was ready for carrier trials before the McDonnell FH-1 Phantom was. According to one account, the P-80 team had to wait for the Navy's jet fighter to be first to operate from a U.S. carrier at sea. (As in many other things associated with aircraft carriers in those days, however, the Brits were the first to fly a jet to and from one.)

You'll note that the airplane does not have tip tanks. The Navy determined that the P-80's carrier suitability was marginal without them and unacceptable with them. See http://retromechanix.com/lockheed-p-80a-for-the-u-s-navy-1947/

Several minor modifications are required to accurately represent the P-80A. For one thing, it did not have an ejection seat. The windscreen was about nine inches farther aft than later P-80s and aft end of the canopy ended in a point, not a half-round "tail." The landing light was located in the tip of the nose rather than on the nose landing gear and the pitot, on the upper leading edge of the tail fin, not under the forward fuselage. A wire radio antenna ran from the canopy to the leading edge of the vertical fin.The red turbine warning stripe was not yet used. However, my guess is that it did have red lines around the flaps on the upper wing surface. My notes say that the airplane was AN512 light gloss gray, something very close to FS 16492 according to Dana Bell. Based on fuselage station drawings provided by Gerry Asher, this is my best guess at the windscreen location of the A and the B/C airplanes:
Also, when the windscreen was moved forward on the P-80B to provide clearance for an ejection, the sliding portion of the canopy was lengthened so that its aft end remained in the same place as on the A.  Cutting the "tail" off the end of the F-80C canopy and sanding it to a point will approximate the P-80A canopy. For the correct length, you'll have to shorten the sliding canopy by cutting about six-seven inches off the front of it.

Note that the P-80A canopy had structure spanning the side rails aft of the cockpit opening and fittings at the lower front corners that lifted the forward end up as it slid aft. (The gunsight is not shown.)
Created from illustrations provided by Gerry Asher
Photo by Gerry Asher of Navy P-80A BuNo 29689

This inboard profile of the P-80A forward fuselage shows the instrument panel located at the base of the windscreen, the cantilevered gun sight, and the bucket seat:
The location of the aft cockpit bulkhead, instrument panel, and flight controls were the same relative to the airframe as in the P-80B's and C's. The gun sight appears to have not been as cantilevered in the ejection-seat equipped P-80s, retaining the same relationship to the windscreen.

This is my conversion of the 1/72 Airfix P-80 kit:

I vacuformed a new canopy using the Airfix canopy modified to be a master.

The 1/72 new Sword P-80A/B kit provides both the bucket seat for the A as well as the ejection seat for the B, but unfortunately the windscreen location and sliding canopy are only provided for the B.

Gerry Asher provides 1/48 and 1/72 P-80A conversion kits as well as 1/48 details and decals for the Navy carrier-trials P-80. This is his build:

He also sells many other conversion kits and decals for the Lockheed P-80/T-33/F-94 series as well as other jets of that era. Contact him for a list of his kits at gmasher@netzero.net and also ask to be added to his email list.

Lockheed proposed production of a carrier-based P-80B but the Navy already had a plateful of jet fighters in work. In 1946 or 1947, the Navy obtained another P-80A and a P-80B from the Army for missile chase (and destroy, if necessary) at Point Mugu. See http://herschpahlbooks.com/dedications/cliff_weirick.htm.

In early 1948, the Navy realized that an expeditious transition to jet fighters required more airplanes sooner than Grumman and McDonnell could build them. The solution was to buy 50 P-80Cs from the Air Force to “train pilots and maintenance personnel in operation of jets.” These were stock 50 P-80s (49 P-80C-1-LO and 1 P-80C-5-LO), designated TO-1s since the Navy considered them to be trainers and they were not carrier capable. They were assigned BuNos 33821-33870. They were all originally based in the San Diego area, “to simplify problems of maintenance and logistic support”. VMF-311 received 12 and operated them from MCAS El Toro, California. VF-6A, to be redesignated VF-52, initially received 24. In effect, both squadrons functioned as the initial jet transition training units. The rest of the P-80Cs were held in reserve for attrition.

Note the pitot under the forward fuselage, dielectric panel on the nose, windscreen set farther forward on the fuselage, ejection seat, etc.

Sunday, October 23, 2011

F3H Beaver Tails

I've updated the F3H entry with pictures and an illustration of the two different beaver tails and also a picture of the two 20 mm cannon modification: http://tailspintopics.blogspot.com/2010/11/f3h-demon.html

Wednesday, October 19, 2011

Yankee Tractor Rocket Escape System

The retrofit of the Air Force A-1 Skyraiders, both single seat and wide body, with the Stanley Aviation Corporation Yankee escape system is fairly well known. As it turns out, this was a Navy initiative and at least two squadrons had their aircraft modified with this capability, VA-25 (Coral Sea) and VA-152 (Oriskany). It is properly described as an extraction system as opposed to an ejection seat, since the seat stays in the aircraft and the pilot is pulled out by the rocket as opposed to being pushed out.

VA-25

VA-152

The retrofit was fairly simple. VA-25 reportedly had all 12 of its aircraft modified midcruise in a couple of weeks at NAS Cubi Pt, Philippine Islands in November 1967 while Coral Sea was off the line. It basically consisted of a rocket located under the canopy behind the pilot's head and a different seat/headrest. The rocket was connected to two ten-foot lines that were attached to the pilot's parachute harness.

The rocket was installed to the right of the existing canopy actuation mechanism.
(Note that this mechanism was usually covered by canvas before the Yankee seat was installed.)

When the pilot activated the system by pulling a D-ring located between his thighs, the canopy was jettisoned and the rocket tilted upward and fired, extracting the pilot out of the cockpit. This is a test using a civil-registered T-6G.
The system was rated for zero airspeed and zero altitude but only with zero sink rate and zero pitch/roll. A zoom climb was therefore recommended before jettisoning the airplane.

Although light weight, the extraction concept was only appropriate at the relatively low speeds usually attained by propeller driven aircraft.

For more stuff on the Yankee seat, see:
http://skyraider.org/skyassn/otherpics/cole/Yankee.jpg
http://skyraider.org/hook/dashonet/yankee.htm
http://users.bestweb.net/~kcoyne/frame_sg.htm (Click on the Stanley "Yankee" button well down in the left column )

For a comparison with the original seat, see http://tailspintopics.blogspot.com/2013/11/ad-1-skyraider-standard-vs-extraction.html

Thursday, October 6, 2011

AD Skyraider Modeling Notes

I was excited to read about Aero Research's new product, Modelers' Guide to the Skyraider by Jay Sherlock.
It cost $15.95 plus shipping. For a description and to order, see http://www.aeroresearchcds.com/book_shelf.htm

I am very pleased with the content based on a quick read through. Jay has done a great job of delineating the differences between the several variants of the Skyraider and the plastic kits that represent it. However, it is not comprehensive, particularly with respect to the interior and photo coverage of details. For that, I recommend that you supplement it with the excellent Walk Around A-1 Skyraider by Ed Barthelmes and Richard S. Dann.
(I've done some work on the AD-5, including the various interiors, which is provided here, http://tailspintopics.blogspot.com/2009/12/widebody-skyraider.html)

In his kit reviews, Jay mentions the non-uniform pylon spacing but doesn't illustrate it.
The stick on one of the pylons is the strut to brace the wing when it is folded.

He also mentions the presence and absence of nose flaps, but unless I missed it, again you're on your own. There were six slightly curved segments that were hinged on the circumference of the cowl ring so they could be folded back along the interior of the cowl.


There was a cutout in the upper inner edge of the flaps at the three and nine o'clock position, presumably to clear the magnetos on the nose case when the nose flaps moved between the open and closed positions.

Dave Cantrell provided the following photo of an AD cowl with the nose flaps open.

Note the "pin" indicator for nose-flap position sticking out of the cowl at 11 o'clock. There was a single cockpit spring-loaded switch for both cowl and nose flaps - open/off/close. They automatically went full open after touchdown via a landing gear squat switch. The cowl and nose flaps could be closed after shutdown with the cockpit switch overriding the squat switch. However, they all went full open the next time electrical power was applied, as on engine start. The nose flaps closed after the cowl flaps were fully closed and opened fully before the cowl flaps started to open. The nose flap indicator on the cowl ring stuck out the most when the nose flaps were fully closed; I think there was a color band on it to indicate that they were fully closed. You could, of course, tell when they were fully open because the cowl flaps, which you could see, started to open then. Cowl-flap position was predicated on cylinder head temperature but basic guidelines were full open for ground operation, takeoff and go-around; full closed for cruise and let down; full open or partially open for climb depending on the cylinder-head temperature. I don't know how much the nose flaps were used other than after shutdown, but they appear to have been removed or disabled on non-Navy applications.

He writes that the 1/72 Airfix A-1J kit has a number of shape errors in the tail. I'm not sure what he's referring to but one oddity that is actually not an error is the offset and shape of the vertical fin. Airfix went to a lot of trouble to depict it. Douglas drawings of the AD (SACs and company display models) show the vertical fin angled to the left, in some instances specified as three degrees.
It's not easy to see on the airplane. I just had the chance to literally look over the AD Skyraider at the National Naval Aviation Museum at Pensacola. It's pretty obvious when you know where to look but doesn't show up well in a photograph:

Note that the pitot is actually offset to the left of the centerline and the spine of of the fuselage curves back to the right. The appearance of an airfoil lifting to the right is exaggerated by the rudder being slightly displaced as if left rudder was applied.

Why the asymmetry? High power at low speed and a high angle of attack (e.g. during a wave off) requires some right stick and a lot of right rudder. The torque rolls the airplane to the left, requiring right stick; right rudder also helps keep the right wing down. (If the airplane is on the ground, more torque results in yaw to the left due to the higher load on the left main gear wheel.) More importantly, P factor yaws the airplane to the left. (These power-induced trim changes are offset to a small extent by the swirl effect of the prop wash, which pushes the tail to the right but also rolls the airplane to the right.)

Two other design conditions of interest for the vertical fin are minimum-trim drag in cruise flight and not requiring excessive rudder trim changes in the low-power, high-speed dive.

The fin being angled to the left is, in effect, automatically applied right rudder during a wave off when the air accelerated through the propeller disc hits the fin. However, the XBT2D-1/AD-1 SAC drawings and the AD-1 display model drawing clearly show the fin with an asymmetric airfoil that would lift to the right (left rudder) as a function of airspeed/prop wash, although it is still angled to the left (right rudder). That the fin has an asymmetric airfoil is not so obvious in the AD-5/6 display model drawings or later SACs.

My guess is that the airfoil shape provided lift as a function of speed and therefore offset the lift provided by the angle of attack of the fin, so little trim was required in cruise (medium speed and prop wash) and/or a dive (high speed and low prop wash). Or maybe it was the other way round. Or the draftsman made a mistake and the fin is not only angled to the left, it has an airfoil shape lifting left. Or the AD had an asymmetric airfoil early on but not later.

I haven't seen anything definitive on the Skyraider's sonobuoy/searchlight pod used for ASW. This is my best guess so far (the AD-5 stores pylon is shown; the AD-4 pylon was smaller and the stores attach points were farther aft):
I don't intend that any of the above discourage you from buying Jay's book. It is a great companion for the Walk Around by Ed and Rich.

Friday, September 30, 2011

F-111B Aft Main Landing Gear Door

It turns out that there's an F-111 main landing gear maintenance trainer at the Chanute Air Museum in Rantoul, Illinois with the original aft main landing gear door and the Curator there, Mark Hanson, was kind enough to take pictures of it. I've posted a couple of them, one heavily annotated, HERE. (Note: I subsequently revised the annotated picture because I had incorrectly guessed what the hidden portion of the aft main landing gear door leading edge idler looked like.) I'm still working on a more accurate illustration of the mechanism than this one, which turned out to be a pretty good guess as to the moving parts:
Since then, I've renamed Link A as the aft main landing gear door bellcrank and Link B as the aft main landing gear door leading edge idler.

TF-1/WF-1 Forward Fuselage Change from S2F-1

Click HERE for my guess at the differences between the forward fuselage of the S2F-1 and the TF-1/WF-1.

Saturday, September 10, 2011

F-4 Flap/Stabilizer Change

Because the original design was intended for a somewhat lighter aircraft, the F4H (F-4) Phantom II wing underwent some subtle changes in development to provide more lift to go with the increase in gross weight. The first of these were the addition of the inboard leading edge flap and boundary layer control to the sixth F4H. (See HERE and HERE.) Note that I've added information from Craig Kaston about the  earliest changes to the stabilator. Also see: http://tailhooktopics.blogspot.com/2012/11/f-4-stabilator.html

As on all airplanes that don't have the highest level of pitch stability augmentation, the F4H stabilator created down load in most flight conditions. The original stabilator had a symmetrical airfoil.

Because the F4H was short coupled, as carrier-based airplanes tended to be for compact parking on deck, an early modification of the original stabilator added notable negative camber to increase the download available. (Note the zig-zag line at about 20% chord where the cambered leading edge was added on this interim stabilator.)
This was the sixth Phantom aboard during early at-sea trials. Note the cutout in the bottom of the rudder due to the stabilator trailing-edge-up travel being provided at the time.

The Phantom's gross weight continued to increase over time with upgrades, fixes, additional equipment, etc. It was clear that with the next round of improvements planned for the F-4J, another lift increase would be required. Step one was obvious, drooping the ailerons when the flaps were lowered: 16.5 degrees was determined to be adequate from wind tunnel test.

As expected, the droop resulted in more nose-down moment with the flaps extended, too much as it turned out. The problem was most obvious with the increase in nose wheel liftoff speed and the inadequate pitch control power after catapult launch and during bolters. Additional wind tunnel tests established that elimination of the inboard leading edge flap (added during development as noted above for increased lift) reduced the nose-down moment at nose-wheel liftoff speeds and turned out not to affect lift at approach speeds.

Although eliminating the inboard leading edge flap was beneficial, it was inadequate. Further wind tunnel tests indicated that the stabilator was stalled at nose wheel liftoff speed. As McDonnell engineer Bill Weber remembers it, "We tried a matrix of planform and area changes to correct the problem and finally determined that adding a fixed leading slat would delay the stall and could fix the problem. (Note: These wind tunnel tests were conducted without a simulated jet exhaust - later tests with jet effects indicated that the slat did not delay the stall and the improved stabilator power was probably due to an increase in effective area.)"

Even before the wind tunnel tests of the slotted stabilizer were accomplished, McDonnell program management decided to fabricate a slotted stabilator by adding a fixed slat to the leading edge of the existing one and flight test it. Bill Weber again: "As a consequence flight tests of the slotted stabilator took place very shortly after we had wind tunnel results. In any event the flight tests demonstrated that the problem had been fixed. We used the same configuration changes to fix a similar problem on the F- 4E which didn't have aileron droop but had a more forward C.G. due to the installation of the gun."

Although created for the F-4J, which first flew in June 1966, the drooped aileron and associated changes (the slotted stabilator and the elimination of the inboard leading edge flap) were of benefit to the F-4B as well. The package of changes was incorporated with Block 26 production, the first of which was BuNo 152995 that first flew in March 1966, and retrofitted to most of the surviving earlier F-4Bs over time.


Retrofit involved the development, qualification, and approval of a different package of drawings and other documents for use by the Naval Air Rework Facilities before crash-damaged and overhaul-due F-4Bs would get these changes. I've read that "by late 1971 or early 1972 it would have been rare to see a F-4B without these modifications, except perhaps in RAGs or Marine reserve units." For sure the slotted stabilator was present on F-4Ns coming off the Bee Line at North Island. The first F-4N flew in June 1972.

This is an F-4N, which is an upgraded F-4B. Note the drooped ailerons and fixed inboard leading edge along with other detail changes to the original B configuration.

Thursday, September 8, 2011

World War II ASW Schemes versus the Norfolk Scheme

In January 1943, the U.S. Navy directed that its combat airplanes be painted in a new, complex camouflage scheme that utilized counter-shading and counter-shadowing. (Sometimes referred to as the tri-color scheme, it actually involved more than three shades.) It took some time for the Navy airplane manufacturers to switch over to the new requirement, no doubt in part because they had to figure out exactly how to implement it and then get Navy approval for their design.

In the meantime, the Navy had to repaint airplanes that had already been delivered and for a time, those being delivered. It appears that a goodly number of these repaints were done at Norfolk, Virginia to a standardized and somewhat different scheme than the ones that the manufacturers would come up with. It is characterized by the Sea Blue upper surface color extending almost straight down on the side of the fuselage to the leading and trailing edges of the wing and relatively less Sea Blue on the side of the fuselage than the eventual production schemes. In this example, the TBM? on the left has the factory paint scheme and the TBF? on the right is the Norfolk scheme.

Click HERE for my prior discussion of it and more examples.

ASW Schemes I and II were implemented by the Commander Aircraft, Atlantic in July 1943 but not covered by a Navy specification until June 1944. In a recent discussion on one of the modeling websites of these schemes, I began to wonder if I hadn't mistaken at least one picture of an aircraft with an ASW scheme for an example of what I term the Norfolk scheme.

ASW Scheme I: For use in areas where the prevailing weather was clear or clear with broken clouds (the southern United States seaboard, Gulf of Mexico, Caribbean, and South America). This was a topside of nonspecular Dark Gull Gray, sides of nonspecular Light Gull Gray, and bottom of Gloss White. The side surfaces in the shadow of the wings and horizontal tail were to be painted nonspecular Insignia White. In a gray-scale picture, it looks very much like the blue tri-color scheme.

ASW Scheme II: For use in areas where the prevailing weather was overcast of heavily clouded (the middle and northern United States seaboard and the North Atlantic). This was a topside of nonspecular Dark Gull Gray, sides of nonspecular Insignia White, and bottom of Gloss White. The difference between it and Scheme I was the use of White rather than Light Gull Gray on the sides.

In both Scheme I and II, the leading edge and inside of the cowlings, propeller domes, and propeller blades (out to the inner edge of the cowling opening) were to be painted nonspecular Insignia White.

However, the examples are somewhat confusing. This is a picture of SBDs from VMS-3, which was based in the Virgin Islands (rough duty).
It would seem that these airplanes should be in Scheme I (Light Gull Gray on the sides) since they're based in the South Atlantic. Instead, the sides appear to be white, which is Scheme II. One theory for this discrepancy is that the anticipated basing of the airplanes was not the same as their actual assignment. Note that the extension of the top color directly down to the wings is very similar to the Norfolk scheme in this example as well as the two that follow.

This is an example of Scheme II provided by Steven (Modeldad) Eisenman:
The white sides are pretty unmistakeable.

This is an example of Scheme I (Light Gull Gray sides) provided by Steven:
Note the white propeller dome in both cases as well as the early rocket launchers; a hole made by a rocket was an effective way to keep a surfaced submarine from submerging to the relative safety of the depths.

The picture that got my attention was this one:
It was also cited as an example of the ASW Scheme I. However, based on the fact that it has a circle and star national insignia, (and does not have the white-painted propeller dome and inner blades) my guess is that it's an example of the Norfolk tri-color scheme, since the start of the transition to the star and bar insignia predated the multi-color ASW schemes:
n.b. A two-tone white ASW Scheme was reportedly used on the TBFs, if not the F4Fs, of VC-9 when it deployed aboard Bogue in early 1943 to the North Atlantic. However, I haven't found a picture that clearly shows no grey on the Avengers. This one, provided by Steven Eisenman, of TBFs on Card that was possibly taken in July 1943 is the best evidence of that scheme on TBF that I've seen so far.

Tuesday, August 16, 2011

Early F4H Redux

It turns out that there was a change to the tailhook and the deletion of a fairing behind the tailhook that I hadn't noticed. There was also a change to the stabilator that was brought to my attention by Craig Kaston. I've updated the second early F4H entry, HERE, with a drawing and a couple of pictures that illustrate the changes to the tailhook and the deletion of the fairing. I've updated the first early F4H entry, HERE, to illustrate the stabilator change.

Thursday, August 11, 2011

F9F-6 vs. 8 Cougar Redux

I've updated this entry, HERE, in response to a question about the difference in the length between the F9F-6 and the -8 as provided on the interweb—and also in Steve Ginter's monograph Number 66, Grumman F9F-6/7/8 Cougar Part One—of 16 inches versus the eight inches that I show. I also updated the planform view of the F9F-5/6/8 to reflect the eight-inch increase in length of the -8 compared to the -6.

Sunday, July 31, 2011

Douglas Low-drag External Fuel Tanks

13 September 2016: For the earlier 150 and 300-gallon tanks, see http://tailspintopics.blogspot.com/2016/09/things-under-wings-post-war-external.html

30 July 2016: I added some discussion about the 400-gallon tank.

27 July 2012: I added a few more example pictures of the different sizes of standard Douglas-design tanks and an evaluation of the accuracy of the tanks in some 1/72-scale kits here: http://tailspintopics.blogspot.com/2012/07/douglas-low-drag-external-fuel-tanks.html

7 August 2011 Update: Gerry Whiteside provided some first-hand information on the fin attachment arrangement, which I have incorporated.

3 August 2011 Update: I made some changes to the 150-gallon tank based on a drawing provided to me by Craig Kaston. It corrects the number and location of frames and the 14-inch lugs, as well as adding the 30-inch lugs. Note that on 2 August, I also added some Don Hinton pictures of the 300-gallon tank..

In the early 1950s, Douglas created a series of low-drag external fuel tanks and bombs. The latter became the  Mk 8X series. The tanks came in three standard sizes: 150, 300, and 400-gallons. The number and orientation of the fins varied depending on the airplane and pylon station. The 150-gallon tanks, after appearing initially on the A4D-1 and early F4Ds, appear to have had limited operational use although the Douglas AD Skyraider and Grumman F9F-8 Cougar were qualified to carry them and the AD-5W often carried one of them. The 400-gallon tank was primarily carried by later models of the A4D Skyhawk and was also the basis for the Douglas D-704 in-flight fueling store, which was often referred to by the Douglas design number, and carried by the AD tankers for maximum giveaway.

While the bombs became standard across the board, the 300-gallon fuel tanks were primarily utilized by Douglas aircraft: the AD Skyraider, A2D Skyshark, F3D Skyknight, F4D Skyray, and A4D Skyhawk. The other Navy aircraft that deployed in the 1950s like the F3H Demon, FJ-3/4 Furies, and F7U Cutlass carried custom low-drag tanks. Later fighters also had to be equipped with unique tanks to maximize the amount of fuel that they could carry: the F4H/F-4 wound up with two, a huge 600-gallon one on the center-line station and/or 370-gallon tanks on the outboard wing stations. However, the Douglas 300-gallon tank configuration did become standard on the Grumman A-6, Vought A-7, and Lockheed S-3.

The number and orientation of the fins could be easily changed to the configuration required for a particular airplane's requirements. I had guessed that the aft end of the tank would have to be rotated to mount fins at 45 degrees. Gerry Whiteside provided the following:

I was in A-7's (VA-82) and we used the same tanks. The longitudinal slots (at 0, 90, 180 and 270 degrees on the A-7 tanks) are the mounting points for the fins and the vertical slots (at 45, 135, 225 and 315 degrees) are for access to the mounting nuts for the bolts that attached the fins. For the A-7 there was a different fin configuration for the outboard stations (1 and 8) versus the inboard stations (3 and 6); (stations 2 and 7 were dry and for nukes).

Every once in a while, somebody asks about these or compares/contrasts the tanks available from different kit manufacturers. I don't have much but here is a comparison of the 150 and 300-gallon tanks. I drew the 150-gallon tank from a Douglas engineering reference drawing for the A4D; the 300-gallon one was done by a Vought predesign engineer once upon a time. The shapes can be considered to be close to the actual tanks. I was particularly surprised and pleased to see that the fin on the Douglas drawing was exactly the same as the one on the Vought drawing.

I did have Navy documentation for the 300 and 400-gallon tanks:
Unfortunately, the fin isn't shown for the 400-gallon tank but the span shown suggests that it used the same fin as the other two tanks.

30 July 2016 Update: I'm not convinced that the shape of the 400-gallon tank shown in the drawing above is exactly representative of the fielded tank. For sure, both the A4D and the A3J appear to have carried a tank with a less pointed nose, probably ending at the station 0 shown on the drawing.

The A4D tank (the aft end was also bobbed to allow access to the hell hole in the aft fuselage):
The A3J tank:

The A3J tank also appears to taper more going aft than the drawing, although not as much as shown on this North American A3J-1 multi-view drawing for modelers and aviation enthusiasts.
This may have been careless drafting although it's possible North American intended for the A3J to have a bespoke tank like the area-ruled ones on the F11F and the nonstandard external tanks on the F4H. Comparisons with D-704 refueling pod drawings were inconclusive but favored the 400-gallon lines.

However, a comparison of a pretty good North American drawing of the tank on another, more detailed multi-view drawing with the 400-gallon tank drawing above suggests that it might in fact have had slightly more taper. Or the North American draftsman was inaccurate.

2 August 2011 Update: Don Hinton photos of the 300-gallon tank on the F4D at the National Museum of Naval Aviation at Pensacola.
Note that because of parallax, etc. it wouldn't be wise to try to use this to establish the shape of the tank.

The tip of the tank is a little bulbous and definitely not pointed.

Note the 30-inch lugs, sway braces, and connections to the pylon.

Note the vertical and longitudinal slots on the aft end of the tank for installing different fin configurations as described by Gerry Whiteside above.


The silver rectangle on the top of the tank is a data plate.

When a tank required the "X" orientation of the fins, as on the S-3 shown here (from a crop of a Christopher Ishmael picture found HERE), the aft end of the tank was rotated 45 degrees.

As a bonus, here is the Navy documentation for the D-704 store:

 For more on the inflight refueling store, see http://tailspintopics.blogspot.com/2015/06/things-under-wings-inflight-refueling.html