by Tommy H. Thomason

Sunday, September 2, 2012

Fitting In

Many of these posts are the result of questions from acquaintances or asked online. If the question is interesting, often the answer seems worthy of saving by this means.

In this case, the question was from Larry McCarley, who is working on a 1/48th model of the Skyhawk. He was having trouble with the width of the side consoles and the distance between them relative to the actual aircraft.

The answer was basic and similar to the problem of putting an exact scale reciprocating engine in the cowl of a plastic model: the actual thickness of the fuselage skin is far thinner than can be replicated in a plastic model and engines are closely cowled. In the case of the A4D, the fuselage skin was a relatively heavy 0.10" aluminum sheet.* In 1/48 scale, that's .002," or half the thickness of a sheet of 20-lb copier paper. Given that there was some insulation on the interior of the sidewalls (it's cold outside at 35,000 feet), the 1/48-scale sidewall would have to be literally paper thin if the width of the consoles and ejection seat are to be to scale. Good luck with that.
Larry reports that the actual interior width of the Hasegawa 1/48 A-4 kit between the sidewalls is about 35.6 scale inches, meaning that the width of the consoles and the ejection seat has to be reduced by a total of almost three scale inches, a bit less than 10%. (I'm surprised that it isn't more; I would have guessed that the wall thickness of a 1/48 scale kit was about 1/16 inch, meaning the interior width would have been a scale six inches narrower than the real thing.)

I suspect that this is the problem with aftermarket resin cockpits that require extensive grinding on the cockpit sidewalls to install and undersized ejection seats in some kits. You have to fudge or cheat the width of the interior components to get them in the width available. Hasegawa fudged in part by narrowing the forward console.

The A4D cockpit is particularly challenging in this regard. Heinemann was obsessed with minimizing the Skyhawk's weight and wider was heavier. As a result, the Douglas-designed ejection seat was just wide enough for the average pilot's bottom and the consoles (at the front) just wide enough for the installation of the standard-width control panel. (Douglas probably avoided having to replace its seat in the A4D with one from Martin-Baker simply because of the narrowness of the installation.)

*As one of several weight-saving Skyhawk innovations, Heinemann combined a flak-mitigation design with the basic airframe structure. The AD Skyraider had proved to be susceptible to relatively light antiaircraft damage in the early days of the Korean War. An external "armor" (deflector plate) kit was quickly developed that could be added over critical areas including the side of the cockpit.
In the A4D, the weight penalty of the thicker than structurally necessary skin was somewhat mitigated by the fact that it did not require the use of longitudinal stringers in that area, which also minimized the width of the fuselage.