In a Pegasus glider, beginning the airtow. Accelerating down the runway one is quite preoccupied keeping in position behind the tow plane; mustn't get too high and put the tuggie's life in danger! etc etc.
At about 300' or so cast a quick glance at the ASI. Which read zero. As I looked again the needle began to circle the dial, indicating ever increasing airspeed, until it reached the stop! 280 knots or so, well above VNE, anyhow, don't recall without going out to look what the top reading was, but thats where it stayed! while the tug kept on climbing at the same old rate.
ASI obviously lying. And I knew what I had forgotten to do; when parking the glider overnight, in case of rain, we tape up the various apertures. No harm done, carried on up to 3,000' or so, and did a couple of stalls just to see how it felt, listen to the wind noise, and spent the next half hour soaring.
Coming home again, my approach and landing were of an unusually high standard!
No harm done, then. Unlike the famous story of a glider that went wave flying over Scotland. Overnight he had taped everything he could think of, and forgot to remove the little stickies over the vent on the water ballast tanks.....did you know gliders carry water ballast to increase performance?
(We tell onlookers that we use the H2O for fuel....)
Anyhow, all went well, until after spending a couple of hours at 20,000 feet or so over the Cairngorns, the expensive fibreglass glider was on downwind at Deeside, when there was a hideous crunching noise. The wings had imploded. No longer the perfect airfoil, more like a couple of planks attached to the fuselage.
Of course, you know why. The ground level air pressure remaining in the water ballast tanks had seeped out from under the sticky tape while in the climb. And on descent, with the increased outside pressure, the tape firmly clamped back in place.
Rule one if even something is making a horrible noise, if its still flying, keep on aviating and sort it out later! The glider landed safely. The insurance paid for a new set of wings, decent chaps, those underwriters.