By Tommy H. Thomason

Wednesday, October 29, 2014

Hard to Replace

The Douglas AD Skyraider proved hard to replace in the U.S. Navy. For decades, jets couldn't match its combination of size, endurance, and payload capability. It was eventually supplemented but not completely replaced in one of its missions, nuclear strike, since it was not as survivable as a jet.

The Douglas A4D Skyhawk was therefore specifically optimized for that particular mission, "one man, one bomb, one way". The Scooter, however, fell short of the Skyraider's range until the introduction of inflight refueling and buddy tanking.

The next mission for which a replacement was developed was all-weather attack, the province of the AD-5N.

This was accomplished with the bigger and more expensive, albeit more capable, Grumman A-6 Intruder.

However, because of its endurance and load-carrying capability the single-seat Skyraider continued to be a major part of the carrier strike force up through the first few years of the Vietnam War. At some point, it was given the nickname Spad, which was a World War I fighter. Some say it was to identify it as a Single Place AD, as opposed to the wide-body multi-place AD-5, for deck spotting purposes but my guess it was just to recognize it as an anachronism in what was otherwise an all-jet air wing.

The single-seat Navy ADs were finally replaced in the attack role with a jet of similar mission capability, the Vought A-7 Corsair II.

(The last ADs deployed on carriers were the EA-1Fs, which served through December 1968, providing electronic countermeasure; Skyraiders continued to be operated by the USAF and the Vietnamese Air Force up through the end of the Vietnam War.)

All those jets are long gone from the U.S. Navy, replaced by various McDonnell/Boeing F-18s. Two, the A-4 and the A-7, were also operated by foreign air forces. The last of the A-7s was just retired by Greece.
 Giovanni Colla Photo

The aircraft it replaced in the U.S. Navy, however, the A-4, continues to serve in Argentina as the A-4AR;
Jorge Alberto Leonardi Photo

in Brazil as the AF-1;

and for Singapore as an lead-in trainer, the A-4SU.

I doubt that the Scooter will outlast its replacement's replacement, the F-18, in a military air force but it's possible that they will still be flying as Warbirds after an F-18 lands for the last time.

Saturday, October 25, 2014

Tricycles Are For Kids

Although most airplanes now have a landing gear with a nose wheel, for many years after the Wright brothers' first flight almost all had a tail wheel instead. The tail wheel arrangement was lighter/cheaper, lower drag before landing gears began to be retractable, and more appropriate for landing on relatively unprepared surfaces (airfields were once actually fields, nephews). Its only drawback was a lack of directional stability on landing rollout, which would sometimes result in what was known as a ground loop, particularly if there was a crosswind.
Tricycle landing gears with nose wheels were directionally stable on landing roll out and therefore less likely to turn and bite the inattentive or clumsy pilot. Moreover, they provided an extra prospective benefit on takeoff for multi-engine airplanes. In the event of an engine failure in the takeoff roll before the pilot raised the nose to lift off, the nose landing gear provided increased directional control compared to a tail wheel, particularly if the tail wheel was off the ground for better acceleration. As a result, even before World War II, multi-engine bombers (e.g. the B-24) and fighters (e.g. the P-38) began to have nose landing gears.

The single-engine Bell Aircraft P-39 had a nose landing gear as well, in part because the engine was located behind the pilot, providing room for one.
However, when Bell proposed a variant of the P-39 to the Navy as a carrier-based fighter, one of the changes required by the Navy was to what was then known as a "conventional" landing gear.
Nevertheless, the Navy had evaluated a twin-engine airplane with a nose landing gear, the one-off XJO-3, at-sea in 1939 and all of its subsequent carrier-based multi-engine airplanes would have nose landing gears. (See
The Navy also contracted with Douglas for two different single-engine torpedo bombers with nose landing gears during World War II, the BTD
and its humongous brother, the TB2D.
(BT meant that the airplane's primary mission was as a dive or level bomber and its secondary mission was as a torpedo bomber; TB meant that its primary mission was as a torpedo bomber - the TB2D was to carry as many as four torpedoes - and its secondary mission was as a level bomber.)

I haven't been able to find a Douglas justification for the nose-wheel landing gear arrangement. My guess is that it made loading of torpedoes and 2,000-lb bombs a little easier because of better ground clearance and they could be lifted into place more or less level, instead of having to be tilted nose up to fit in a bomb bay or be aligned with cruise-flight air flow.

The Blackburn Firebrand torpedo bomber featured a two-position torpedo mount that provide both level load/ground clearance and low-drag alignment once in flight.

The nose landing gear didn't seem to provide any benefit otherwise (a Douglas evaluation did note that that a bad landing was less likely to result in the airplane bouncing over the barriers). On a single-engine airplane it significantly restricted the space available for a bomb bay if low-drag carriage of bombs was desired.

Nose landing gears could also be at risk of collapse following an inflight arrestment.

In any event, the next Douglas design, the BT2D, had a tail wheel. It was subsequently redesignated as the AD when the carrier-based bomber designation system was simplified to one mission, attack.

In part as a result of its preference for tail-wheeled landing gear, the Navy lagged the Air Force in adopting trainers with nose landing gears, trading off a somewhat higher accident rate for an earlier and more thorough indoctrination in the art of landing a taildragger.

For more on how the Navy transitioned its pilots to tail draggers after its changeover to trainers with tricycle landing gear, see