Because early jet engines could not provide enough power the lack of adequate thrust at takeoff was a constant problem for the B-47 Stratojet.
The Boeing B-47 was the US’ first swept-wing multiengine bomber. It represented a milestone in aviation history and a revolution in aircraft design. Every large jet aircraft today is a descendant of the B-47.
An innovation pioneered on the B-47 was the concept of placing the engines in pods (nacelles) suspended under the wings. A pod containing two General Electric J-35 engines (GE J-47 engines for all production models) hung from each wing inboard, and a single engine hung farther out.
As explained by Scott Lowther in his book Boeing B-47 Stratojet & B-52 Stratofortress Origins and Evolution, because early jet engines could not provide enough power the lack of adequate thrust at takeoff was a constant problem for the B-47; the use of the ‘collar’ full of 33 JATO units was an expensive and logistically complex solution. So the All American Engineering Company proposed a solution of their own: replace the rockets with a jet-propelled ‘pusher’ aircraft. All American was a small aeronautical firm that specialized in landing gear, arrestor cable and launch systems, and some unusual projects such as a system enabling aircraft in flight to snatch up packages or people on the ground.
They were not in the aircraft manufacturing business, which might explain the rather bizarre B-47 `pusher’ project.
The pusher, apparently nicknamed ‘donkey’, was little more than two turbojets, a cockpit, a long nose which would mechanically link to the main aircraft and the wings and landing gear needed to recover the vehicle. It would be a lightweight vehicle carrying little fuel and with no need for a pressurized cockpit and anything more than the most basic navigation equipment. The available documentation on this concept, a popular magazine article and a patent, have contradictory depictions of the craft so the diagrams here are somewhat provisional, as is the scale of the craft. No hard data regarding weights, dimensions and performance are currently available.
All American filed the patent in 1956, by which time the B-47 was starting to head off the public stage. It might be thought of as simply an odd little concept from a small and now nearly forgotten company, an idea of little relevance or importance — especially or since the B-47 was only crudely sketched in to the patent diagrams. But earlier in 1956 a much more famous aeronautical company, Goodyear Aircraft Corporation, had filed a patent for a somewhat similar concept. The Goodyear concept would have been not of only a more substantial aircraft but was also explicitly designed to boost the B-47. The All American ‘donkey’ could have pushed any number of large jet aircraft as long as they’d had the required modifications, but the Goodyear design was specifically tailored to carry a B-47 on its back.
Not only would the Goodyear design have saved weight for the B-47 by providing takeoff thrust and lift, it would also have allowed the B-47 to save weight by deleting the landing gear. One might be forgiven for wondering how happy the B-47 crews would have been at having to rely on a post-mission rendezvous with a flying undercarriage.
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