Ok Centaurus - here is the Vampire story.
Back in the 50s we didn’t know too much about compressibility and shock waves. I converted from Mustangs to single seat Mk30 Vampires which had been re-engined with Nenes which needed increased airflow over the original Derwents. Two scoops above the engine were fitted. Flight testing did not explore the high Mach corner of the envelope and three RAAF pilots were lost leading to the aircraft’s Mach tuck being seriously examined.
We used to take the aircraft to compressibility with some apprehension as the ‘shake, rattle and roll’ and inconsistent elevator effectiveness was quite startling. Years later as a TP at BD I was to find a similar edge of the flight envelope with the Vulcan.
‘Black Jack’ Walker was a very experienced WW2 RAAF pilot who was given the responsibility for factory production flight testing following some intense coaching by De Havilland’s pilots at Hatfield. His description of his exploratory flights is an extract from his book “Black Jack”.
“By early '49 the first Australian Vampire was beginning to take shape and I was taking more than an academic interest in its progress. In fact it was not ready for its first flight till late June of the same year. We had very little trouble with that first Vampire. Its Mach number was limited to Point Seven Five and I had only ever taken it to near Point Eight which I thought was sufficient margin. This could have been, in hindsight, the cause of a problem.
After we had delivered half a dozen to the Air Force and they appeared to be functioning quite well from the station at Williamtown, two Vampires, after flying in formation at altitude near Newcastle, went into the ground in an almost vertical dive. Apparently they had never even looked like recovering. So De Havilland, to whom the matter had been referred, told me, "You, Mr Test Pilot, had better take the next Vampire up and see what happened to those two aeroplanes."
Well do I remember that flight. I knew it must have something to do with compressibility. I took it up to well over forty thousand feet and put it into a very steep dive, as steep as I dared, with not too much power, about three-quarters, because if anything was going to happen I wanted it to happen fairly quickly. I soon found out. Once the aeroplane went over Mach Point Eight, the nose got heavier and heavier and the aeroplane kept on endeavouring to go past the vertical and the controls were largely ineffective. So I closed the throttle and put on the dive brakes immediately and this would have been somewhere around twenty-seven thousand feet. The aeroplane obviously had to be got out of a very sticky situation. As it got into the lower, denser atmosphere the dive brakes started to slow it up. I was even thinking of throwing the undercarriage out, which would probably have destroyed the fairings, but -- anything to slow it up. Otherwise I would not come back with any answers.
Fortunately, as I descended to twenty-thousand feet I could feel the controls slowly becoming a little more effective and I was able to lift the nose up from almost vertical to an attitude where the Mach number was slowly decaying and recovery was becoming possible. We eventually came out of that dive at about thirteen thousand feet and though it was a fairly cool day, I was dripping with perspiration. It was pretty close and as the characteristics were so different to the English Vampire at high Mach numbers, it seemed to me it must have something to do with those wretched Elephant's Ears on the upper surface of the fuselage.
As it happened, the design team came to the same conclusion -- we tended to generally agree -- and they quickly did a switch around and took the auxiliary intakes from off the top of the fuselage and placed them on the bottom of the fuselage. This redesign took several days but our production rate was not that high and a few days later they said, "All right, check it out and try again."
On this occasion I still wasn't taking any chances and I took it up to as far over forty-thousand feet as I could reach comfortably and this time put it into a dive of about seventy-odd degrees with a bit of power on. I was ready for it this time. If it kept on ducking its nose down when it hit high Mach numbers, I intended to haul out of it as quickly as I could. But imagine my relief when, instead of ducking its nose down, once I reached Point Eight the nose began to rise. This was 1951 and Point Eight Four was high. Today aeroplanes cruise at that rate. We still had much to learn but that solved that problem with the Vampire and thereafter they all had their auxiliary intakes underneath the cowl, in spite of the fact that on a grass aerodrome the engine could suck in tufts and dust.”