Convair B-58 Hustler Engine-Out Takeoffs
“Power is nothing without control.” For decades, this has been the slogan used by tire manufacturer Pirelli to emphasize the importance of safely harnessing the performance potential of some of the fastest cars in the world. And it’s a concept that has always been a primary concern of aerospace engineers when designing the fastest aircraft in the world.
One such aircraft with an extreme amount of both speed and power put its engineers to task when they were faced with the very nonstandard requirement of taking off with only three of the four engines operating in the event an emergency evacuation became necessary.
The B-58 was capable of blistering performance. It could achieve a 17,400 feet per minute rate of climb and had a service ceiling of 63,400 feet. The speeds and altitudes that it achieved were so extreme, engineers designed capsules to protect the crew members in the event they needed to eject.
The B-58 flew in a challenging political environment, as well. Deep within the Cold War, top military officials acknowledged that strategic bombers might occasionally need to evacuate an airfield or be ferried from one base to another with inoperative engines. This presented an interesting challenge.
When faced with the requirement of taking off with inoperative engines, Convair’s engineers had to take a number of factors into account. Aircraft weight, runway length, and other factors were key. But as the engines were wing-mounted with the potential to generate great amounts of asymmetric thrust, controllability was paramount.
Just as a rowboat with only one oar will pull to one side and refuse to travel in a straight line, an aircraft with more thrust on one side than the other will present controllability issues. Control is most difficult at lower speeds, when comparatively little air is flowing over the vertical stabilizer and rudder. As speed increases, rudder effectiveness increases correspondingly, making it easier to harness the asymmetric thrust and extreme yaw.
During the B-58’s development and testing, Convair engineers calculated the minimum airspeeds necessary to maintain control during takeoff with inoperative engines. Taking both rudder effectiveness and nose wheel effectiveness into account, they compiled a performance chart and included it in the Emergency Procedures section of the flight manual. This chart listed minimum airspeeds for the aircraft with the nose wheel on the ground as well as with the nose wheel raised to the takeoff attitude. Below the listed airspeeds, pilots would have to supplement rudder input with nose wheel steering to maintain directional control.
Interestingly, the engineers included data for takeoff with two inoperative engines, as well. They included this data despite specifying elsewhere in the manual that “Takeoff with two engines inoperative is not recommended.” As expected, the speeds required to maintain control in this situation were extraordinarily high.
The engine-out takeoff speeds spanned quite a range. With three engines set to maximum afterburner and one inboard engine operating but unable to utilize the afterburner, Convair determined the pilot could maintain directional control at speeds as little as 70 knots. This is little more than the takeoff speed of a small Cessna.
Conversely, with two engines inoperative on one side and maximum afterburner used on the remaining two engines, the jet required 211 knots to maintain directional control during takeoff. This extreme speed would have subject the tires to similarly extreme forces and temperature, creating a relatively high likelihood of failure. It’s a safe bet crews proactively requested fire and emergency equipment to stand by during such takeoffs.
InteThe available flight manual excerpts do not include runway distance requirements for such unconventional takeoffs, but considering the jet required nearly 8,000 feet of runway at heavier weights, takeoffs with inoperative engines – even at lighter weights – must have required the vast majority of the 12,000-foot runways that were commonly found at air bases of the era.
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