Dash 80- page 3 | History | Air & Space Magazine
Current Issue
September 2014 magazine cover
Subscribe

Save 47% off the cover price!

Dash 80

The story of the prototype 707.

Air & Space Magazine | Subscribe

(Continued from page 2)

There were also problems with the design of Dash 80’s tail.  All three test pilots had been aware of them from the start of the test flights, and apparently they were noticeable to others as well.  However, they were not great enough to prevent Johnston from doing a seemingly impromptu barrel roll in front of 200,000 spectators.  Then, for anyone who had missed it, he rolled Dash 80 again.  In fact, Johnston’s famous rolls were a sort of pointed rebuttal.  “I’d heard that Douglas was telling people our prototype was an unstable airplane,” Johnston says, “and I believe that when you fly for a company, you sell the product by demonstrating what it can do.”

The International Air Transport Association was meeting in Seattle, and airline executives from all over the world were scheduled to be at Lake Washington for the Gold Cup hydroplane races.  “I knew we had to do something to impress ‘em,” Johnston recalls.

Earlier, when Allen had asked him to fly over the race course, Johnston decided he would impress ‘em by rolling Dash 80.  Copilot Gannett had gotten an inkling of what was coming several hours earlier, when Johnston flew the airplane through a couple of rolls during a test flight.  Allen, however, had no idea.  When he looked up and saw his company’s biggest investment on its back, he looked like a clinical example of apoplexy, according to people seated near him.  Everyone loved the stunt, but Allen never got over it.  He fired Johnston at least a thousand times before they met the next morning and cooler heads prevailed.  Nonetheless, the infamous maneuver was a forbidden subject in Allen’s presence for many years.  At his retirement dinner in 1980, he was given a huge photograph taken from one of Dash 80’s windows while the airplane was upside down.  He left it behind.

The stunt may have impressed airline executives, but it didn’t cure the problems in Dash 80’s tail fin, which had both a bad case of flutter and persistent Dutch roll.

Flutter is a vibration in the airframe that is induced at high speed in response to aerodynamic forces.  It usually arises on an extremity, and, if left unchecked, it can intensify until it breaks up the strongest airframe.  Dutch roll—so called because of its resemblance to the rolling side-to-side gait of ice-skating Dutchmen—occurs in all airplanes, but is harder to check in those with swept wings.  As the airplane yaws from side to side, one wing advances and develops additional lift, causing the airplane to roll to the opposite side, which results in a combined rolling and yawing motion.  If this motion continues, it creates a cycle of alternating, increasing yaw angles that can result in uncontrollable roll.

Dash 80’s original tail fin was short, compared with the fin of the B-52, and not much of a yaw inhibitor.  Its size, coupled with the lack of a power boost for the rudder, may have contributed to its tendency to flutter.  “Flutter…it was a black science then,” Dix Loesch says.  “When the flutter guys started talking to their bosses, everybody else just sort of looked at the ceiling.”

Johnston hunted for flutter in Dash 80 early on, and he found it near maximum speed, where it can be expected.  Even though the flight engineer’s instrument panel was shaking so hard the mounting bolts broke, Johnston coolly reported, “We’re experiencing an appreciable vibration up here.”  Later, however, Loesch encountered flutter during normal climb.

“I did the normal things to fight it—leveled out, throttled back.  They didn’t work.  I thought the airplane was going to shake itself to pieces.  All of a sudden the rudder froze, and the flutter stopped.”  A minor structural failure saved the day—a balance weight had broken loose and jammed the rudder.

Whatever it was that caused Dash 80 to shake, rattle, and roll, Boeing discovered that changing the fin’s internal balance weights, increasing its size, and adding an electronic yaw damper and a hydraulically boosted rudder control ended the problems with flutter, yaw, and Dutch roll.

Late in 1955, orders started trickling in, then flowing.  Douglas’ DC-8 orders were not far behind.  By the end of 1959, 100 707s had rolled off the production line at Renton, and the first of several hundred KC-135s had been delivered to the Strategic Air Command.  Dash 80’s career as a prototype and dealer demo was finished, but Boeing was not yet ready to put it out to pasture.

Comment on this Story

comments powered by Disqus