TALES FROM THE VAULT: the "Pogo Stick." I have the honor of being a Life Member of the Institute of Electrical and Electronics Engineers (by virtue of being 65 years old and a member for 35 years). The Life Members newsletter has a section titled "Tales from the Vault" of anecdotes from member's experiences. Here's one from the December 2009 issue (not on line yet) on the development of the Convair XFY-1, the first vertical takeoff aircraft.

When I worked at Convair's Dynamics Test Lab in the 1950s, we were flight testing a novel new combat support aircraft nicknamed the "Pogo Stick." So far as I know, it was the very first vertical takeoff and landing aircraft, other than helicopters. It had delta wings and large contra-rotating props on its nose, driven by u turbine engine. For safety, Flight Test had us inst all accelerometers on the turbine bearing cases and the case of the reduction gear transmission, which drove the props. That way, the test pilot would receive advance warning of a bearing was getting noisy and about to seize while he was hovering tail-down. If that catastrophe were imminent, a row of red lights on his instrument panel was supposed to light up, giving him time to touch down. Or, so went the theory.

There was one small problem. When I climbed aboard the aircraft to check the calibration of the instrumentation. I found someone had gotten tired of seeing the lights constantly flickering (due to the exremely noisy environment in this experimental craft) and had cranked the channel gains to zero. Problem solved. Right! When I informed the Flight Test Department that they had been flying this highly experimental craft without their safety net, so to speak, the chief test pilot was not a happy camper.

There were other problems. They had provided the pilot with an ejection seat. This seat swiveled forward when the craft was hovering vertically, so he was at least able to sit much as one sits in a recliner chair, not upright, but not flat on his back either. Flight Test wanted to see how much actual safety this arrangement provided in case the pilot had to eject at a very low altitude, so they arranged a test. With the craft resting on the tarmac, and the seat in the appropriate position, they fired the 75 mm shell attached to the seat, propelling it at prodigious velocity in a low arc. The seat and its occupant (an anthropomorphic test dummy). landed perhaps 250 feet away, still traveling at high velocity. The parachute, which was supposed to have deployed by this time, dragged uselessly behind, partially opened at best. Needless to say, the dummy suffered a cruel fate indeed. The chief test pilot, who was of course watching intently, merely walked away, muttering. Rumor had it he went directly to executive row and negotiated a much larger bonus for his services.

At long last came the day of the big flight-the first transition from vertical hovering to horizontal flight supported by the delta wings. The Marine Corp's Osprey performs a similar maneuver. All of us were gathered beside Lindbergh Field watching expectantly. The pilot hovered about 20 feet up for a few minutes, gunned it, and the craft thrillingly shot straight up several hundred feet, then performed a beautiful arc into horizontal flight. There was much cheering among the observers. After a triumphal tour around San Diego Bay, Pogo Stick returned, roared down the length of the field, and then performed a perfect upward arc. It came to rest, hanging on the huge props as planned. There was only one small problem: It was about 500 feet up.

Now, this might not seem like such a problem. What's the big deal? All the pilot had to do was back down to a touch down, right? Well, as we know, conventional aircraft control surfaces assume the slipstream is going to flow from front to back over the rudder and elevators. When Pogo Stick hovered, this flow was supplied by the propwash. What happens when the craft is traveling backwards fast enough that the propwash is overcome? Answer: The effect of the controls is reversed. Still no problem, you say? All he had to do was back down slowly, just as he had done on dozens of practice sessions while hovering 20 feet off the ground. But imagine what it is like to visually judge your sink rate from 500 feet. You can't.

So, while we watched breathlessly, the pilot began his descent. Suddenly, the craft began oscillating wildly. The controls had reversed and the pilot had now become part of a positive feedback loop. He quickly realized his situation, gunned the engine , and roared upward, saving himself from certain doom. However, he now found himself about 1,000 feet up! This was not going at all well. I honestly don't know how he did it, but he spent the better part of an hour slowly, slowly, easing himself out of the sky. The landing was not a thing of beauty, but the aircraft and pilot survived. The Pogo Stick was never flown again.

Thomas l. Kirkpalrick, LM
Half Moon Bay,CA

Some engineering details of the aircraft can be found here, and here is a short video of an RC "Pogo Stick."

This one is of personal interest to me, as it dates to my early interest in flying - and eventually a career in science and engineering.