I tend to side with Neil here I'm afraid. Not from the position of a DC anorak, but from someone who has spoken to those people that have been mentioned (the problem solvers) and from the point of view of someone who has done considerable testing work in racing cars and spoken to those who race and test, right up to F1.
Whereas Leo may well have suggested and then attcahed sand bags, it was DC, during the debrief, that explained the problem he was encountering, perhaps not in full engineering terms, but still describing what it was he was feeling, seeing and sensing, that could allow Leo, or Ken to suggest/try solutions.
As an example, one Michael Schumacher is very highly respected as an F1 driver, he is touted as "THE" test driver, yet when I interviewed him in 1996, he did not know it was the airflow UNDER the aerofoils that sucked the car down on to the track, he thought it was the air traveling over the top that deflected the car down! (He asked to shoot that bit again so as not to appear "a bit of a prat"!!). Yet his feedback from the cockpit allows his team to suggest and make adjusments. As is clear, he may not do it with the correct knowledge, or engineering terminology, but he DOES describe it accurately.
DC would know the difference between a "normal" run, and one where abnormal things had occurred. His description of the August '56 'flight' was; " she was bouncing about, then, for a few seconds, smooth, and no banging about, just engine noise. The BANG, followed by all theat vibration and bouncing". Even if Leo hadn't witnessed this from the middle of the course, it's not hard to see that even though DC hadn't realised he had flown, it's pretty obvious that is what he is describing, and next time it happened he knew it too, to the point where it was a thrw away comment, in the bar, ours afterwards. The juggling act of reducing hydrodynamic drag, by using aerdynamic lift, is a very very fine one, but one K7 managed most of the time, I suspect there may have been many many "flight of the Bluebird", sadly, just one very large one!
Steve Holter, UK and France, and sometimes reality....................