By Tommy H. Thomason

Tuesday, January 31, 2012

Carrier-Based Airplanes Weigh More

Carrier landings are one reason. Not only is the airplane carrying a tailhook attached with structure to allow it to pull on the airplane with two to three times its landing weight,  a nose gear that can pull the whole airplane down the catapult track, a wing folding arrangement, extra wing area, etc, the landing gear has to withstand twice the sink rate of a land-based airplane and not always symmetrically or straight ahead.

The touchdown shown above puts quite a bit of side load on the landing gear. In order to minimize the weight of a landing gear that could withstand it, the engineers who designed the F-14 incorporated a unique load link between the main landing gear strut and the fuselage that was established after the gear was extended.

After the landing gear strut extended into position, a T-fitting on the side of the strut swung up to engage a receptacle located inside an opening in the side of the fuselage.

Why the Rube Goldberg (Heath Robinson to the Brits) arrangement, you might well ask? That's illustrated by a comparison of the Grumman A-6 and F-14 main landing gear struts. They are very similar in overall length, diameter, and attachment to the fuselage even though the F-14 landing weight was 50% greater. If anything, the F-14's side brace at the top of the strut looks less sturdy (i.e. heavy) than that of the A-6.
As often happens with innovative designs, there was an unintended consequence that wasn't apparent in development, qualification, or service test or even in initial operational use. Presumably engineering took into account the splaying loads generated on touchdown that are at least partially mitigated by the lateral friction of the tire against the landing surface. They doubtless took into account that some landings would occur where the tire's resistance to sliding sideways was minimal, such as a touchdown zone coated with rubber deposits and wet from rain.

They might have been aware of the anti-skid coating applied to metal aircraft carrier decks that would have been even more resistant to splaying than a concrete runway.. But what they apparently didn't know, according to Craig Kaston, was that the coating wore down during a six-month deployment and was not necessarily renewed, particularly in the landing area. The result was much more frequent and severe instances of side loads being reacted by the fuselage fitting, with damage eventually becoming apparent in the bulkhead located at fuselage station 569 to which it was attached.

Craig Kaston: "The remedial action was two-fold: ensure that the anti-skid was not allowed to wear down to the deck plates; and inspect and repair the damaged Tomcats. Some aircraft had to have the cracked aluminum milled out of the bulkhead and reinforcing plates added; all had the bulkhead modified in increase corner radiuses and shot-peened (cold worked) to reduce residual stresses and toughen the material. These changes were made to aircraft in production. About ten years later, the material of the 569 bulkhead was changed from high-strength aluminum to titanium in the new-build F-14Bs and Ds delivered from Grumman."

Monday, January 16, 2012

What was the Bell Aircraft F2L?

This is another one of those works-in-progress, since I don't have everything nailed down yet. However, I have enough bits and pieces to start with.

The first Bell Aircraft Navy fighter was, of course, the XFL-1. I've written a monograph on it for Steve Ginter's Naval Fighters series. It's pretty comprehensive if I do say so myself and addresses some common misconceptions about the Airabonita. It's available from Amazon and others.

Some have written that the P-59A was the F2L (more on that in a minute). The Navy History Center lists two F2Ls with BuNos, the XF2L (90060 and 90061) and the F2L-1K (91102 and 91103). The XF2L is stated to be canceled P-63s*, which sort of makes sense because those Bureau Numbers were used to contract for the L-39s, swept-wing configured P-63s. (For more on the L-39s, see

The F2L-1Ks were postwar modifications of Army P-39Qs as drones. These were flown at NAS Cape May, New Jersey. I don't have any pictures yet. A Navy History Center list includes the crash of an F2L in 1946. It turns out that there were two crashes, both F2L-1Ks being flown from the cockpit. BuNo 91102 had an engine failure in the pattern at Cape May and was dead-sticked to a wheels up landing. While operating from NAAS Chincoteague, VA, BuNo 91103 apparently had a brake lock and rudder jam after the disconnect in flight of the remote control system and went off the runway during the landing. Both airplanes were strikes.

These F2L-1Ks may have been preceded by an XTDL-1 (another P-39 modification) that wasn't given a Bureau Number, which would be rare but not unknown or they may have originally designated or intended to be designated TDL, which makes more sense than F2L, since the airplanes were to be used operationally as target drones, not fighters. Although some references list as many as seven were created, it appears more likely that only two P-39s were converted and the remainder cancelled.

Back to the P-59A. In 1941, when the Army asked Bell to design and develop its first jet airplane, Bell had a contract with the Army for the XP-59. It was to be powered by a P&W R-2800 driving a contrarotating pusher propeller. It had reached the mockup stage and was also being proposed to the Navy.
Photo provided by Niagara Aerospace Museum

Note the inlet in the nose for cooling air to the R-2800 and the cannon or machine gun barrels at the front of the tail booms. The stand reads Proposed Navy VF Fighter Spec. SD 112.18. F2L does not appear, although of course this would have been its designation if the Navy had contracted for it.

Some of the mockup pictures include the words "Proposed Navy Fighter" and in others, like this one, Navy Fighter has been carefully erased.
Photo provided by Niagara Aerospace Museum

Lest one think that it was pictures of the mockup of the Army airplane with captions added for the Navy's benefit, a picture of the mockup's cockpit shows the presence of a chart board, which was a Navy requirement.

When the Army contracted with Bell for a jet airplane in December 1941, it did so with the designation XP-59A, presumably using the same contract as the now unwanted XP-59. It was, of course, a completely different configuration. The objective was to add a layer of secrecy to the program.

The Navy obtained two YP-59As and three P-59Bs for its evaluation and pilot familiarization. This is the first Navy YP-59A, as received in late 1943.
It was given BuNo 63960. It was subsequently repainted in the Navy tri-color paint scheme. Note that it does not have guns.

At some point after that, it was brought up to production P-59 standard (square wing tips, ventral fin, etc.) and repainted again, this time with yellow wings for some reason.
Tom Doll collection via Rich Dann

Note, however, that the designation marked on it is "YP59-A".

One theory behind a Navy designation of YF2L for its YP-59A is the existence of the F2L-1Ks to provide misdirection. This almost certainly wasn't the case given that the Navy's drone P-39 program was later in time. Somewhat more plausible is that the YF2L designation was a subterfuge equivalent to the Army's use of the P-59A designation since the XP-59 had been proposed to the Navy. If so, the Navy doesn't appear to have used it in any documents found to date. Its P-59s are always referred to as P-59s.

The Navy also kept pretty good track of assigned designations so it seems likely that the post-war contract for P-39 drones would have used the designation F3L if F2L had been used in the early 1940s for the Airacomet, unless the designation was not a subterfuge but the program considered so secret that the designation was never revealed...

*Bell reportedly proposed a carrier-based P-63. It's conceivable that these Bureau Numbers, originally assigned to an RY-3 Privateer contract, might have been intended for that evaluation before they were used for the L-39s. However, they seem to be too high for that possibility.

Saturday, January 7, 2012

Portable Air-Start Cart

In the early days of jet airplanes, there weren't very many air-start carts at civil airports or some military fields either. This wasn't a problem when jet engines were started with electric motors like piston engines. However, electric starters were heavy so they were replaced on many jet engines in the late 1940s by a small turbine that required high pressure/volume air that spun the engine up to start rpm.  This meant landing at an airport without an air-start cart meant being stranded until one could be located and made available.

The Navy's solution was a start unit that could be carried as a store shaped like a World War II external fuel tank, shown here on an early production Douglas F4D Skyray:

It incorporated a amall AiResearch jet engine, designed as an APU (Auxiliary Power Unit), to provide the air. Panels were opened or removed to expose the APU inlet and exhaust, the attachment of the air hose, and the control panel.

Also stowed within the cart were the hose, wheels, and a handle to pull it along like child's wagon.

The handle also steered the front wheel and when raised vertically, braked it. One source of entertainment for the ramp rats was to start the APU up, staddle it like a horse, and push the handle forward. The thrust of the APU would start it rolling. This practice was, of course, prohibited.

The pod was often present at airshows at civil airports, carried there and back on a standard external stores pylon.

It remained useful to the Blue Angels up through the retirement of their A-4s powered by the J52 with an impingement starter:

Also see

Sunday, January 1, 2012

Project Steam

The superiority of airplanes powered by jet engines was bad news for the carrier navy. Jets required a lot of fuel, which meant bigger and heavier airplanes, and didn't provide much thrust at low speeds. Both dictated the need for a more powerful catapult.  Unfortunately, the hydraulic catapult was pretty much at the top end of its capability. The U.S. Navy had evaluated a German design for a hydrogen peroxide powered catapult (it was used to launch the V-1 pulse-jet surface-to-surface missile) using both hydrogen peroxide and steam but dropped it in favor of developing one that used gun powder. An explosive charge had been used to launch seaplanes from cruisers and battleships since 1925 and was projected to be the simpler and require less space and weight.

Just in time, Colin Mitchell perfected the steam catapult. See After a demonstration, the Navy immediately bought five, one for test at the Philadelphia Navy Yard, and two each for Hancock and Ticonderoga. Hancock was completed first, recommissioned on 15 February 1954, and so it was that only a few months later, in June, she sailed out into the Pacific waters off San Diego in support of Project Steam, an at-sea evaluation of its new catapults.

There was no question that the steam catapult was superior in throw weight.  The question was the compatibility of jet engines with the steam catapult among other operational issues. So the Navy gathered up samples of the newest versions of carrier-capable aircraft they had and launched them from Hancock, including sending a couple of F7U-3s cross country from Patuxent River.
(Photo by Maurice Duke)
Many of the test subjects, however, were from West coast squadrons, flown by fleet pilots, not NATC pilots. Although FJ-2s were assigned to the Marines and almost never deployed on aircraft carriers, this VMF-235 Fury could be considered a stand-in for the FJ-3, which was to be assigned to Navy fighter squadrons:
(Photo by Maurice Duke)
The F9F-6 was evaluated as well.

Similarly, although F3Ds only rarely deployed on aircraft carriers, this VX-4 F3D-2M carrying four Sparrow I missiles made for a relatively heavy test subject:

Propeller-driven airplanes were included in addition to the jets. An NATC Flight Test S2F (note that the catapult pendant has been tied on so as to minimize the number required and shorten the time to hook up for the next launch):
(Photo by Maurice Duke)
Other aircraft launched included the AD-5 and F2H-3/4.

And just recently, duh, I discovered that AJ Savages were also part of the trials, albeit later in the year (this picture was dated 28 September 1954):

The trials were extremely successful. One of the significant attributes of the steam catapult was that it provided acceleration for most of its stroke and there was little snatch load at the beginning of the stoke, making for a much more comfortable launch. This was particularly appreciated at night.