The origin of the B-47 actually goes back to 1943 when the Army put out a proposal for a jet powered bomber/reconnaissance aircraft. Jets were still in their very early stages in 1943 but the Army was looking a few years down the road.
Boeing’s initial design used a conventional straight wing and would have looked a lot like a B-29 with jet engines. Except by then it was 1945 and we had discovered the German (of course) research on swept wings. I’m actually surprised it took us until 1945 to figure this out. We’d already seen German ME-262s with swept wings that were 100 mph faster than anything we had.
Boeing went back to the drawing board. No, really, they used drawing boards in those days. They redesigned their prototype to incorporate our knew aerodynamic knowledge. Now the tricky part, where do we stick the engines?
The British liked to bury the engines in the wing root. This certainly made for a clean looking design. I think the De Havilland Comet is still one of the best looking jets ever built. It just looks right.
The problems with burying the engines are three-fold. Maybe more than that but I can only think of three right now:
1. The wing has to be fairly thick to make room for the engines.
2. It’s hard to get at the engines to work on them.
3. That’s not really where you want them to be if one catches on fire or goes explody.
The Boeing engineers decided that slinging the engines on pylons under the wing was the way to go. This let them build a nice thin wing and made the engines much easier to get at. If an engine threw a turbine blade, well at least it’s out there and not in here. As an added bonus, it’s much easier to “up engine” the aircraft later on.
To this day that’s how we build ‘em. Almost every large jet has the engines mounted on under wing pylons. Smaller jets tend to mount them back at the tail, because there’s just not enough room under the wing.
This makes the B-47 the archetype for most modern jets.
The end result was a groundbreaking aircraft. Imagine how futuristic the B-47 must have looked when it was first rolled out. I was going to say it looked like Star Trek, except Star Trek was 20 years away in 1947. The initial test pilot wasn’t even sure it would actually fly.
It didn’t just look like a modern jet, it pioneered some features still found on modern jets like a yaw damper and anti-skid brakes. The yaw damper was a necessity to fix the “dutch roll” inherent in swept wing aircraft. The anti-skid brakes were needed to stop an aircraft with such high approach and landing speeds.
The first B-47 units became operation in 1953. Strategic Air Command wanted jet bombers and it wanted them now! Demand was so high that additional production was contracted to Lockheed and Douglas. Probably a good trivia question there: “Who built the B-47?” “Boeing!” “And???????”
There was a steep learning curve involved in the transition from props to jets. Not just for aircrew but training, maintenance and operations. We were literally writing the book back in the late 40s and early 50s. Loss rates were high in both the fighter and bomber communities.
I can’t even wrap my brain around the loss rates at the time. For example, the month of October 1955 saw five B-47s lost to training accidents. Today we’d ground the entire fleet for something like that, but it was just the “cost of doing business” back in the day. Out of 2,032 Stratojets produced, 203 were lost. A full ten percent of the fleet. Yikes!
Most pilot accounts of the B-47 describe it as not being particularly difficult to fly, just unforgiving. Once at speed, handling was reported to be “fighter like”. The takeoff and landing phases of flight were very critical however.
Takeoff roll could be very lengthy, especially at high gross weights. Takeoff was augmented by water-alcohol injection. We used a similar system on the B-52.
In true Wile E. Coyote fashion, they also used 18 ATO (Assisted Takeoff) rockets at high gross weights. The movie Strategic Air Command has some good footage of a B-47 takeoff with rockets. Note that these are sometimes called JATO or RATO units but the B-47 flight manual uses the term ATO.
I don’t know if there was any way to reject a rocket assisted takeoff. It would seem to me that once the rockets are lit you’re going whether you want to or not.
Loss of an outboard engine on takeoff was apparently rather “sporty” and required the correct rudder input be made immediately. Loss of an outboard engine causes the plane to yaw (pivot) into the dead engine. In a plane with swept wings, this will cause the wing with the dead engine to lose lift (and the other wing to gain lift).
So now it also wants to roll into the dead engine. All this is happening at low speed, close to the ground. The further you let it go, the worse it gets. If not corrected early you would have a B-47 cartwheeling off the end of the runway (it happened more than once).
One B-47 pilot described an engine failure on takeoff:
“we were headed across the boondocks in an uncomfortably skewed condition, gaining neither airspeed nor altitude”
Approach speeds were high and landing distances were long. Thrust reversers had not been invented yet. The B-47 was a very aerodynamically “clean” aircraft and I don’t think it had air brakes or ground spoilers. For descent the rear landing gear could be extended to act as a speed brake.
The early jet engines took a long time to spool up, sometimes taking twenty seconds to reach full power from idle. This made a go-around particularly sporty. The B-47 actually used a small “approach chute” in the traffic pattern to allow the engines to be kept spooled up at a higher power setting. A much larger drag chute was used for full stop landings. Typical approach speed would be around 150 knots with touchdown around 135.
Some articles will point out that by 1954 the B-47 had the best safety record per 100,000 flying hours of any military jet. That’s damning with faint praise, however. We lost a lot of jets in 1954.
The Stratojet, as it was called, had incredible performance for the day but it had its share of quirks. At high indicated airspeeds the ailerons would cause the thin wings to warp and “aileron reversal” would set in. Turn the yoke to the right and the plane would bank left.
Go faster yet and the air loads would become so great that the ailerons would be unmovable even with hydraulic boost. The only way to restore lateral control would be to slow down. This was later fixed in the B-52 by using spoilers for roll control.
Another danger was the “coffin corner” at high altitudes. At some cruise altitudes and weights, the B-47 could get into a regime where only a few knots separated a high-speed stall from a low-speed stall. This didn’t leave much room for error. In contrast, a modern 757 has 50-60 knots of buffer at cruise altitude.
The three man crew had a very high workload on missions that might last as long as 24 hours. The copilot doubled as a gunner, and the poor navigator had no relief at all. The copilot’s ejection seat could actually swivel so that he could face rearwards to operate the guns. The small cockpit was very cramped, and while the crew could unstrap and move around there wasn’t much room.
One B-47 pilot described the missions as “tedious”, “demanding” and “grueling”.
One oddity was the tandem seating for the two pilots under a fighter-type canopy. The canopy could be opened on the ground for ventilation. With the pilots sitting under a greenhouse and the navigator down in “the hole” I can imagine that nobody was ever really comfortable. Either the pilots would be hot or the navigator would be freezing. Visibility was excellent, but I’m glad Boeing switched to an airline type cockpit with the B-52.
Additional “observers” could be seated in the walkway next to the crew. Doesn’t look very comfy to me. The only person I’ve ever met who flew on a B-47 had to bail out from that position.
Even worse was the RB-47, which crammed two or sometimes three Electronic Warfare Officers into a “pod” or “capsule” which was stashed in the bomb bay. Note that some sources claim four “Crows” or "Ravens" were carried but every picture of an RB-47 crew I’ve been able to find shows six total crew members.
The Ravens had downward firing ejection seats but i don’t believe any were ever used successfully. Rather than using a hatch that could be jettisoned, the seat was supposed to cut through the floor of the capsule. I think the Acme corporation may have had a hand in its design.
The RBs were the only Stratojets to see anything approaching combat. They frequently overflew the Soviet Union, mapping the routes that bombers would have flown to attack their targets. The RB-47s were often chased by and sometimes fired on by MiGs.
I’m sure we’d have been just peachy with Soviet bombers overflying our territory, but that’s just how we rolled back then.
On two occasions, however, the Soviets shot down RB-47s in international airspace. Not cool.
One was lost without a trace. The other was shot down by a MiG-19 over the Barents Sea. The Copilot and Navigator survived and were taken prisoner by the Soviets. They were ultimately released after seven months of captivity and high level negotiations between the two governments.
That’s right. Quiet diplomacy rather than macho chest-thumping got them returned. I think there’s a lesson there.
While it technically could carry conventional bombs, the B-47 was primarily a nuclear bomber. It never saw actual combat. I don’t know how much, if any, conventional warfare training B-47 crews did.
There’s no shortage of B-47 videos out there on youtube. This one is pretty typical of Air Force training videos from that era.
The main problem with the B-47 was lack of range. All the fuel was carried in the fuselage, although you will sometimes see them with two large drop tanks under the wings.
It either needed to be forward deployed or extensively air refueled to reach targets in the Soviet Union. Air refueling behind the KC-97s of the day must have been pretty sporty. The propeller driven tanker would by flying at full speed and the B-47 would have been close to stall speed.
During the Cold War B-47s were frequently deployed to bases around the world to put them closer to their Soviet targets.
By the mid 1950s it was obvious that newer Russian aircraft and missiles were going to make the high altitude regime untenable for SAC’s bombers. The solution was a switch to low level tactics.
Minor problem: the early nuclear weapons, however, were not designed for low level delivery. No problem, we’ll just “toss” the bomb.
Toss bombing was accomplished by a mechanical computer known as the Low Altitude Bombing System or LABS.
The B-47 would approach the target at low altitude and high speed. Prior to the target, a 2.5 G pull up would be initiated. Somewhere on the way up, the LABS computer would release the weapon. The bomber would continue over the top and then roll right-side up.
This is sometimes incorrectly described as an “Immelman” maneuver (for the German WWI ace who invented it).
It was actually a “Half Cuban 8” because the B-47 ended the maneuver in a dive rather than level flight. The bomber would be as slow as 85 knots and in a stall buffet as it came over the top.
We never did this in the B-52 because newer nuclear weapons come down on parachutes and can be dropped from a few hundred feet. I did try the LABS maneuver in the simulator once just to see if it could do it (it could).
All of this was tough on the airframes and we started pulling the wings off B-47s in the late 1950s. After several losses the B-47 fleet required extensive modification (at great cost) to strengthen the wing attach points.
Amazingly after building over 2000 of these aircraft, we started retiring them in 1963. Strategic Air Command parked its last B-47 in 1966. This means we were sending planes that were less than ten years old to the boneyard!
Why were they retired so early? Several reasons. By the mid 1960s, having US nuclear bombers deployed on their soil was becoming less popular with our allies. There wasn’t nearly enough tanker support to make up the difference. With the B-52 and long range ballistic missiles coming into the inventory, Secretary of Defense MacNamara decided to retire the B-47 fleet. Most of the B-47 crews transitioned to the B-52 or B-58.
The Navy kept a few on for electronic warfare testing until 1977.
We even loaned one to Canada to use as a test-bed for the Avro Arrow’s Orenda engine. Reportedly it was a nightmare to fly with the extra engine stuck back by the tail. Probably another trivia question there: “Who else flew the B-47?”
The last flight of a B-47 took place in 1986 when one was partially restored and flown from the naval weapons test center at China Lake to Castle AFB. Castle has long since been closed, but I believe the museum is still there.