Saturday, April 8, 2017

Designing B-47 Maneuvers

The B-47 was the first swept-wing bomber. Boeing aerodynamicist Robert (Bob) Montgomery stopped by Pease AFB and briefed emerging maneuvers possible with the B-47.
B-47 Stratojet & Pease AFB
The wing entered the jet age in June 1955 when it received the first all-jet bomber: the B-47 Stratojet. The wing moved its people and equipment to Pease AFB, N. H., in August 1958. There, it continued to function as an integral part of Strategic Air Command.

I have no idea what was said, but it is fun to watch the B-47 do barrel-rolls, half-cuban eight, and Immelman loops in this video.
I have watched that video several times over the last 30 years and still burst with pride at our capacity to engineer and willingness to try some crazy stuff.  The first time was at the Boeing Employee Flying Association old chalet at Boeing Field - someone had a 16mm copy - probably mid 80s.  Youtube is such a great resource!

It was only when I came across the clip from the Peace AFB newspaper did it occur to be that (my Father-in-Law) Bob had played a role in designing the maneuvers when he first joined Boeing to work on the B-47. Of course, not once did I ever talk with him about these maneuvers (not knowing his contributions), to which he would have had so much insight. May he rest in peace, and revel from his prime, when he visited Pease.

These maneuvers were designed for "toss bombing" nuclear ordinance, but were found to create too much fatigue on the airframe to be widely practiced.
You may recall Tex Johnston did a famous barrel roll.
I heard Tex talk about this (and the invention of the mach meter), how it was such an easy maneuver. Well, watch the video of the B-47 and you will agree.

On swept wings (stop the presses):
In May 1945, the von Kármán mission of the Army Air Forces inspected the secret German aeronautics laboratory near Braunschweig. On von Kármán's team was the eminent chief of the technical staff at Boeing, George S. Schairer. He had heard about the controversial swept-wing theory of R. T. Jones at Langley, but seeing models of swept-wing aircraft and extensive supersonic wind-tunnel data generated by the Germans, the concept was decisively confirmed. He wired his home office: "Stop the bomber design", and changed the design of the B-47 wing.

Analysis work by Boeing engineer Vic Ganzer suggested an optimum sweepback angle of about 35 degrees.[6] Boeing's aeronautical engineers modified their Model 432 design to include swept wings and tail, resulting in the "Model 448", which was presented to the USAAF in September 1945. The Model 448 retained its four TG-180 jet engines in its forward fuselage, with two more TG-180s in the rear fuselage. The flush-mounted air intakes for the rear engines were inadequate, while the USAAF disliked the installation of engines within the fuselage, considering it a fire hazard.

The engines were moved out to streamlined pods (pylon mounted) under the wings, leading to the next iteration, the Model 450, which featured two TG-180s in a twin pod mounted on a pylon about a third of the way outboard on each wing, plus another engine at each wingtip. The Army Air Force liked this new configuration, and so Boeing's team of engineers continued to refine it, with the outer engines being moved further inboard, to about 3/4 of the wingspan. The thin wings provided no room into which wheels could be retracted, so a "bicycle landing gear" was chosen, with the two main gear assemblies arranged in a tandem configuration and outrigger struts fitted to the inboard engine pods. As the landing gear arrangement made rotation (i.e., lifting the nose during takeoff) impossible, the landing gear was designed so that the aircraft rested on the ground at the proper angle for takeoff.
Drag chute
The XB-47A Stratojet bomber, an icon of aerospace history, returned to Edwards Air Force Base (2016)

Stay tuned!

Peter Lemme

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Peter Lemme has been a leader in avionics engineering for 35 years. He offers independent consulting services largely focused on avionics and L, Ku, and Ka band satellite communications to aircraft. Peter chairs the SAE-ITC AEEC Ku/Ka-band satcom subcommittee, developing ARINC 791 and 792 characteristics and contributes to the Network Infrastructure and Interfaces (NIS) subcommittee developing Project Paper 848, standard for Secure Broadband IP Air/Ground Interface.
Peter was Boeing avionics supervisor for 767 and 747-400 data link recording, data link reporting, and satellite communications. He was an FAA designated engineering representative (DER) for ACARS, satellite communications, DFDAU, DFDR, ACMS and printers. Peter was lead engineer for Thrust Management System (757, 767, 747-400), also supervisor for satellite communications for 777, and was manager of terminal-area projects (GLS, MLS, enhanced vision).
An instrument-rated private pilot, single engine land and sea, Peter has enjoyed perspectives from both operating and designing airplanes. Hundreds of hours of flight test analysis and thousands of hours in simulators have given him an appreciation for the many aspects that drive aviation; whether tandem complexity, policy, human, or technical; and the difficulties and challenges to achieving success.

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