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Stratojet
The B-47 Stratojet became an essential component of the U.S. Air Force’s Strategic Air Command (SAC) during the 1950s and early 1960s, both as a nuclear bomber and a reconnaissance aircraft. Designed to meet a 1944 requirement, the first XB-47 prototype flew in December 1947, performing far beyond its competitors. It incorporated many advanced features for the time, including swept wings, jet engines in underwing pods, fuselage mounted main landing gear and automated systems that reduced the standard crew size to three.
In May 1951 the B-47 began replacing the propeller-driven B-29s and B-50s in SAC’s medium bomber units. While it could carry about the same bomb tonnage as the aircraft it replaced, the B-47’s top speed was more than 200 mph faster.
The Stratojet saw numerous configurations studied – with plenty of diversions taken and missteps made along the way.
Models 450-30-10 and 450-31-10
As explained by Scott Lowther in his book Boeing B-47 Stratojet & B-52 Stratofortress Origins and Evolution, Models 450-30-10 and 450-31-10 from February 1950 were part of a series of medium bomber potential growth studies ranging from Model 450-25-10 through 450-64-10. The studies included both turbojet and turboprop variations on the B-47 theme, mixing and matching then-known powerplants in a wide range of configurations.
These Boeing designs followed the publication of a 1949 RAND Corporation study which concluded that turboprop-equipped bombers were the best way to successfully penetrate deep into Soviet airspace. As often happens, a single report gained prominence for a moment and caused not only a stir of interest but a change in spending priorities.
Models 450-30-10 and 450-31-10 fitted a standard B-47B configuration with four T40 turboprops. The 450-30-10 tried something new with the location of the engines; instead of hanging below the wings in podded nacelles, here the Allison T40-A-8s were mounted above and ahead of the wings in long cylindrical nacelles that extended well past the trailing edge. The exhaust vented through two nozzles at the top of the nacelles just aft of the leading edges of the wings. Access to the engines for maintenance and replacement should have been fairly convenient given their location ahead of the wings.
The Model 450-31-10 used a similar podded nacelle layout to that of the 450-9-3, looking much the same except for one difference. That difference, which the Model 450-30-10 shared, was a lack of contra-rotating propellers. Instead, both designs featured pointed and seemingly somewhat bulbous propeller hubs with four surprisingly small diameter (11ft) propellers. What these propellers lacked in number and diameter they made up for in speed – the tip speeds were meant to easily exceed the speed of sound.
B-47 with four XF-84H Thunderscreech’s T40 engines
It should be noted that this engine was mated to supersonic propellers on the XF-84H ‘Thunderscreech’. The name was well chosen; with a single T40 and a three-bladed supersonic propeller it achieved dubious fame as being possibly the loudest aircraft ever built. While sitting motionless on the ground with the engine idling, shockwaves could be seen radiating away from the aircraft for a distance of some hundreds of feet. Nausea, headaches and seizures were reported among ground crew unfortunate enough to be anywhere near it.
The idea of an aircraft fitted with four of these engines boggles the imagination; not only would it have turned the brains of ground crew into silly putty, low altitude overflights of foreign territory would likely have been met with charges of crimes against humanity. It seems fairly certain that the structure and skin of the B-47 would have suffered badly under the assault of sonic booms constantly raining down onto it from the tips of the propellers.
Boeing B-47 Stratojet & B-52 Stratofortress Origins and Evolution is published by Mortons Books and is available to order here.
Photo credit: U.S. Air Force
