FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1955
1955 - 0205.PDF
FLIGHT, 18 February 1955 205 SKYWARRIOR Designing the World's Heaviest Carrier-based Aircraft SINCE the end of World War II, the Douglas AircraftCompany have built up a considerable reputation forbeing producers of essentially sound and efficient air- craft. No other company in the world is in production with so many completely different types of aircraft, and yet Douglas have still found time and resources to enter the missile busi- ness on a vast scale. The development and production of aircraft for the U.S. Navyis the responsibility of the Company's division at El Segundo, and this division's products are particularly indicative of the type oflogical engineering which the company have found so successful. Under the direction of their renowned chief engineer, Ed Heine-mann, the El Segundo division has now made many thousands of carrier-based aircraft for the U.S. Navy and Marine Corps, themost notable being the Skyraider, Skyknight, Skyray, Skyhawk, and Skywarrior. The last-named machine is especially note-worthy, for it is easily the largest and heaviest aircraft ever planned for carrier operation. It represents the optimum American solu-tion to a singularly difficult specification, and some comments on the evolution of the design form the subject of this article. Theaccount is based upon papers prepared by various El Segundo engineers, notably Harry Nichols (project engineer on the type),and Messrs. Dill, Lamoree, Melching and Stringham. The conception of a really powerful carrier-based attack bombertook shape in the years following World War II. The U.S. Navy wanted a machine which, although a fully "navalized" aircraftcapable of being permanently based on a carrier, could carry a heavy load of all types of weapons to a distant target while havingsufficient performance to ensure that it would be no more vulner- able than corresponding land-based aircraft.Initial discussions between Douglas and the Navy Bureau of Aeronautics started in 1947. Some idea of the difficulty of formu-lating even the basic specification can be gathered from the fact that the Navy's weight estimates ranged from 62,000 lb up to200,000 lb, the latter machine approximating to a navalized B-47. Gradually, however, the Navy began to crystallize its ideas, and,as detailed studies progressed, the all-up weights were narrowed to between 100,000 and 130,000 lb.Even these weights were many times greater than those of any existing carrier-based aircraft, and it was quite apparent that amachine of this size would be too large for operation from any type of carrier with the exception of the then-projected U.S.S.United States. Ed Heinemann decided that if the new bomber were to be operated from carriers other than a mydiical giant shipnot then built, the weight would have to be cut down by at least 30 per cent. The wisdom of this belief was emphasized by thefact that, one year after Douglas started actual design, United States was cancelled by Congress (but was later reinstated asForrestal, launched in December 1954 and followed by nine sister-ships). On page 207 appears a composite three-view drawing of some of the more widely differing forms which the aircraft assumed during its early days. The basic conception was a machine powered by a pair of large turbojets and supported by a slightiy swept wing mounted in the high or mid position. Anything approaching a freezing of the design was, however, prevented by the fluidity ot the Navy requirements. One of the most constantly changing factors was the geometry of the weapons bay, which had to be tailored exacdy to fit themany highly secret atomic and other stores which were coming into use at that period (1948-9); some of these weapons were longand slim, some were short and fat and others had unusual pro- jections or tail assemblies. Another variable concerned the pro-vision of defensive armament. This was expected to be a single radar-directed barbette carrying a pair of 20 mm guns, mountedat the extreme tail-end of the fuselage. In some versions of the design, however, no armament at all was specified. The growdi factor was found to be roughly 6.4, i.e., for everypound saved in the initial design, the overall reduction in weight produced by the correspondingly lighter structure, smaller wingarea, lower power requirement, etc., was 6.4 lb. Applying this factor to the basic project, it was calculated that elimination of thetail turret would reduce the final maximum weight by no less than 12,500 lbj making possible a much smaller aircraft employingengines already well developed (this machine is the smallest of those shown in the composite drawing). But eventually the designwas standardized with the tail armament, and the engines chosen were afterburning variants of the Westinghouse J40, which wasthen considered to be the future standard turbojet for the U.S. Navy. The design was given the Navy designation A3D, follow-ing the AD Skyraider and the unsuccessful A2D Skyshark. Having settled the basic form of the aircraft, the next step wasto work out the aerodynamics. During die late 1940s, the design of any aircraft capable of flying well at a Mach number much inexcess of 0.8 was, as we in Britain know to our cost, sufficient to occupy the time of a large staff for a number of years. Thedifficulties facing the El Segundo team, who were attempting to combine such performance with the requirements of carrier opera-tion in a machine with a span approaching 100ft, can perhaps be appreciated. The wing of the Skywarrior had to be a direct compromisebetween the conflicting requirements of high and low speed, carrier stowage and efficient cruising at high altitude. The aspectratio chosen was 6.75; this value is higher than average in the U.S. Navy but less than that employed by U.S. Air Force machinesdesigned for similar purposes. Originally, the figure was placed slighdy higher, but the value was brought down owing to aero-dynamic pitch-up at high speeds and to the problem of flutter which, of course, largely controls wing weight (the flutter problemis referred to later). The thickness /chord ratio was fixed at 10 per cent at the rootcentre-line and 8.25 per cent at the tip. The sweep angle was chosen as 36 deg at the quarter-chord line, since wind-tunnel andflight data available at the time that the wing was finally settled indicated that this value would give satisfactory low-speed charac-teristics as well as low drag and good control at high speeds. The Douglas Company recently stated diat, if the Skywarrior werebeing designed today, the sweep angle would not differ greatly and would certainly not be more than 40 deg. Dihedral was setat zero, which again was a compromise between high- and low- speed requirements. This factor is of paramount importance indetermining the low-speed behaviour of swept-wing aircraft, and, if the Skywarrior were to be redesigned today on the basis offlight experience, Douglas would choose a dihedral angle of — 1 deg (i.e., 1 deg anhedral). As the composite general-arrangement drawing shows, therewas no dogmatic acceptance of any particular form of engine
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
