S

HOOTING down one of these four-engined American

bombers is like taking a fortified position ― it is a task

for ordnance; the heavier the better!" Fieldmarschall

Schperrle, Nazi air bigwig, back-handedly paid the B-17 her

greatest compliment when he made this statement. He was,

according to the Swedish aviation publication Flygning,

arguing for heavier guns on future interceptor aircraft.

Indications are that, he will get it, but whether anything less

than a field gun will be effective against the B-17's

miraculous structure is a question.

The B-17 can take it. Event after event prove that this four-

engined production air cruiser can absorb punishment that

could split a corvette and possibly send a destroyer to the

bottom.

The Fortresses' toughness just didn't happen. It was

engineered into B-17s long before the first one was more than

a military idea. When even American air strategists thought

four-engined planes were impractical, the Fortress' structural

ancestor, a single-engined mailplane called the Boeing

Monomail, flew five passengers and 750 lbs of cargo at a

cruising speed of 140 mph on a 575 hp air cooled engine. In

an era where wooden wings and fabric covering were still

good conservative engineering, a smooth-skinned, flush-

riveted semi-monocoque airplane was an unheard-of

innovation. Conservative operators despised the craft, and

conservative legislators wanted to know what was wrong with

biplanes for flying the US Mail.

Nevertheless, the Monomail proved that it could fly faster,

farther and with greater loads. Its rigid, stressed-skin structure

could carry its load with less weight invested in structure and

with less maintenance grief than the conventional airplane.

The Boeing Monomail begat two offspring; one was

destined to be popular and famous in its own right, the other

to quietly revolutionize military aviation. The popular child

was the Boeing 247 twin-engined all metal transport. For the

pilot, here was a ship that had two engines for top

performance, and a power reserve for good flying on one

engine. To the operator, here was an airplane with a sturdy

airframe that would need little or no maintenance for its entire

lifetime.

The military offspring was another twin-engined low-wing

monoplane not quite as pretty, but more revolutionary in its

field. Its maximum speed with full military load was 186

mph, and it went by contemporary combat planes as though

the fighters were parked. This Boeing Death Angel marked

the doom of many reactionary ideas in design. It kissed

farewell to the biplane as a military entity, it doomed the fixed

landing gear, and started a world-wide design competition for

better ships, tougher structures and higher cruising speeds.

There is a lot of history between the B-9 and the B-17

including the decision that a proper defensive airplane for the

nation must be one that can reach into the middle of either

ocean and drop enough weight to sink a battleship. It must

have enough stamina to take any beating defensive aircraft

can hand out in order to reach the bomb release line. The

Fortress has this stamina ― it has proved itself more times

than has ever been recorded for public observation. Like the

predecessor, the Fortress is a semi-monocoque structure,

one in which the skin or outer shell, reinforced by a widely

separated supporting structure, carries the weight. Compare

this with the skeleton structure used a decade or so back,

and still prevalent in light airplanes. This frame, usually

made of welded steel tubing, is faired off with wooden or

metal spacers, and covered with doped fabric. In non-

combat aircraft, this is fine, but in a military plane, it is

unsatisfactory, for if a major or even a supporting member is

blown away, the entire structure will collapse.

The secret of the Fortress' structural strength is

decentralization of stress. No single part of a Fortress

carries more than a just proportion of the total load, so there

seems to be no Achilles heel. To knock a Fortress down, one

must kill three engines, fire the fuel tanks or blow off the

entire tail or entire wing. This is admitted, even by the

Luftwaffe experts.

The evidence supporting it seems to be their willingness

to surrender speed and performance to carry enough fire

power to down a Fortress. Look at the planes they send

against them. Fw-190s armed with four 20-mm cannon,

special interceptor versions of the Junkers Ju-88, with four

20-mm cannon in the nose and 13-mm machine guns in the

top and bottom turrets. Special "souped up" versions of the

Dornier 217 have attacked them with compound attack,

using 88-mm rockets and a new type 30-mm cannon.

Goebbel may mouth, and the critics of the old Boeing

may hunt for new epithets, but the enemy still pays her the

greatest compliment― heavier ordnance ― big guns to

storm a Fortress.

And the Fortress will stand the assault,

This article was originally published in the February, 1944,

issue of Air News magazine, vol 6, no 1, pp 24-25.

The original was printed on 9½ by 12¾ inch paper. The

pages were reduced to print on letter-size paper.

Photos credited to Signal Corps, USAAF.