David Cook and The Shadow.


While exploring the "Australian Hang Gliding History" site, I came across the "David Cook Aviator" section.  I learned that David had built and flown a Volmer Jensen VJ-23.  I have always been interested to know how well this aircraft flew, and what I found was very interesting.  I also found that David had added a small engine to the VJ-23, and had flown it across the English Channel, a remarkable feat that was formally recognised.  All of this was leading David to build a more serious aircraft, with more horsepower, enclosed cockpit and built for the job as a microlight, safe and easy to fly.  As I went through the general design concepts I found a strong relationship with tried and true aircraft design, and not surprisingly a few of the wrinkles to squeeze out some extra performance, eg., swept forward wing, no dihedral, the wing plan view vaguely reminiscent of a Cessna 172 layout,  all good practice, all very commendable.  Then I was to discover in the text that it did not have a definable stall, that it tended just to mush without losing stability on any axis, didn't spin, and it achieved all of this at speeds at or below 25 miles per hour, and when the stick was pushed forward it immediately regained normal flight.  My curiosity was now aroused way above normal, and I just had to find out what airfoil David had used.  I made some guess's and expected an airfoil section that would be commonly used at speeds below 100mph.  I thought perhaps a Clark Y or a Naca 4411.  I was wrong.  I was amazed to find that David had developed the airfoil himself, following some study to airfoil reference books.  In a piece that he had written for a magazine, he inferred he developed a fairly normal 30% forward section of the airfoil, and then just drew a straight line from the top surface to the trailing edge, and similar treatment on the bottom surface.  I have seen something like this before with Benson B-7 and B-8 Gyrocopter rotor blades.  I found in the photos within the website a picture of several "Shadows", a side view of the airfoil where the wing connects to the centre section of the structure.  I compared this shape with dozens of others and found it to be most like  helicopter rotor blade airfoils.  To me this is an astounding finding. The shape of David's airfoil is unique in its use in a fixed wing aircraft.  That it was untested in a wind tunnel, and simply built onto the aircraft and flown is remarkable.  I conclude that it is the case sometimes, that some people, and David is one of them, have an instinctive genius when they know something is right.  His aircraft, with its amazing airfoil, has a most enviable record, in that there has never been a fatality, although 450 examples have been built and flown, many of them with low time amateur pilots. 

David's Shadow is a most remarkable aircraft.    

John W. Dickenson.