Douglas A-26 Invader Proves "Hottest" Attack Bomber

First-hand examination of craft and observance of its performance during action-packed training mission impress Aviation correspondent, who finds ship's salient design. structure and flight qualities fully warrant AAF's enthusiasm.

New design features giving exceptionally high speed and unusual maneuverability, together with unmatched ruggedness and hitting power, make the Douglas A-26 Invader what Army Air Force officers call the world's outstanding medium- and low-level attack bomber.

Study of its structural details and participation in a bombing training mission by this correspondent bear out AAF contentions that the A-26 is a weapon of such versatility as to open new tactical concepts.

A two-engine mid-wing craft of all-metal construction, the Invader has a two-spar full-cantilever NACA laminar flow wing of 70' span. New type Douglas-designed electrically-operated flaps operate by first extending straight aft farther than conventional flaps, then hinging downward, with a small deflector between the wing and flap directing the airflow to the top side of flaps, resulting in increased drag.

Spars are built up of unspliced spar caps with integral end fittings. Use of these caps necessitated new rolling processes by the aluminum mill. High-speed automatic machining processes split the rolled billet diagonally, then cut cap to shape.

Chordwise stiffeners and heavy skin between spars permit wing deflection without wrinkling of the skin, thus preserving the laminar flow. Large areas of wing and nacelle skin are 3/8" or 5/8" dural plate to give deflection protection from angular machine gun fire, a feature which has proven a vital factor in the craft's ability to take heavy punishment but still complete missions and return to base.

Engine mounts supporting the two 2,000-hp R-2800 Pratt & Whitney Double Wasp engines and 3-blade constant-speed Hamilton Standard propellers are of unusual design, one which helped avoid a welding bottleneck in production and which makes for simplified maintenance. Elimination of conventional welded tubular members was accomplished by using a large metal spinning in the forward part and stainless steel aft part, tied together by six identical forgings running from the engine to the nacelle. The six engine mount attachments tie to the fore part of the forgings; bolts for quickly removing the entire power plant installation attach the aft end of forgings and engine mount to the nacelle. All plumbing and wiring is run out next to this engine mount skin, giving maintenance men easier entrance and plenty of work room by way of an access door set in the firewall.

Complete power plant changes may be made in about an hour, and installations are interchangeable between right and left sides. Engine cowling was designed for ease of maintenance, with the upper and lower halves each removable with a sparkplug wrench by loosening of two quick fasteners for each section. Smaller panels in the mount and nacelle are also quickly removable, and mechanics can sit inside the nacelle to work on the accessories.

The nearly-square fuselage is semimonocoque, designed to facilitate both production and maintenance. Well protected tunnels, for example, are built into each side to carry electric, hydraulic, instrument, heat, and vent lines. In the fuselage, as in the wing, large areas of skin are 3/8" or 5/8" dural. This is, of course, in addition to regular armor plate for the crew of two or three.

An outstanding feature of the A-26 fuselage is its all-purpose nose, with which the craft can quickly be equipped for special-type missions right on the production line (at El Segundo, CA, or Tulsa, OK) without having to go to a modification center. For straight medium bombing a bombardier's nose compartment may be attached.

A new bubble-type canopy gives greatly improved visibility, and the cockpit is well laid out for pilot efficiency and convenience. A single lever on the control quadrant serves to lock both throttles in closed position, and elevators, rudder, and ailerons in center position, thus making it unnecessary for ground crews to insert the usual wedges. Since the throttles cannot be opened until the locking lever is moved, taking off with locked controls is impossible.

Invader's flying qualities were shown in a training bombing mission at the Florence (SC) Army Air Field, commanded by Col Arthur I Ennis. This base is one of four of the First Air Force’s 56th Combat Crew Training Wing's eight bases which are devoted to training crews on A-26s.

All instructors are "returnees", veterans of European, Mediterranean, or South Pacific theaters who have completed at least one tour of duty in Douglas A-20s, North American B-25s or Martin B-26s.

The mission, on which Aviation's correspondent flew with Capt Douglas Dean, was typical of the 56th Wing's operations, simulating actual conditions insofar as possible, from the pre-flight briefing to the "post mortem" interrogation by veteran intelligence officers.

Every step followed a rigid schedule, including takeoffs at 20-sec intervals. Because of the A-26's unusual climbing ability, less than normal time was required to get the 36 participating planes — two flights of 18 craft each — in formation and on course in a climb steep enough to use the altimeter as a rate of climb indicator.

Evasive action against theoretical anti-aircraft fire was taken by the entire group as it moved toward IP (Initial Point) at speeds heretofore unequaled by medium bombers. While actual figures may not be revealed, it can be said the bombing run was in excess of 300 mph. "Enemy" fighters diving out of the sun were able to make but one ineffective pass at the formation.

Bombing was coordinated by two bombardiers — one in the lead plane of each flight — and at their signals every bomb landed within the specified target at the specified second. With bombs gone, the entire formation made a quick break-away which brought speed up near fighter-plane rates.

Effectiveness of the flaps and general handling qualities of the Invader were clearly shown on return to the base, when Capt Dean brought his craft in to a perfect landing at just under 100 mph in a moderate crosswind and with three other planes on the runway ahead. Having four planes on the runway at one time is standard practice with the 56th for, as one pilot put it, "when we have airplanes to get in the air or back on the ramp we don't fool around".

This article was originally published in the "Flying Equipment" column of the April, 1945, issue of Aviation magazine, vol 44, no 4, pp 175-176, 251, 255.
The original article includes 3 photos.
Photos credited as Official AAF photos.

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