Recollections and Conclusions of Bluebird K7 and the Water Speed Record Attempt
Ken Wheeler- 10th October 2006
This talk was given as a tribute to Ken Norris, the Designer of Bluebird K7
It is almost 40 years to the day when members of the female staff were sent around the houses in the vicinity of the Norris Brothers offices in Burrell Road, Haywards Heath to post letters saying that Mr. Donald Campbell was having a new engine fitted to his hydroplane BLUEBIRD K7 in the large wooden shed adjacent to our offices, that on certain evenings during the week the engine would need to be fired up to half power in order to check that all was well before the vessel left Haywards Heath to be shipped to Coniston Water for an attempt to raise the water speed record above its present level. BLUEBIRD which was some 13 years old in 1966 had originally been fitted with a Metro-Vick Beryl turbo-jet delivering around 3500 pounds of thrust and was now being modified to accept a Bristol Orpheus jet giving 5000 pounds of thrust at full power.
Additionally, she was to be fitted with a larger tail fin made from the rudder of a Folland Gnat. The Gnat with a time expired airframe provided an Orpheus engine and was cannibalised in the yard of the Norris buildings. BLUEBIRD was also to incorporate a new feature; a braking system. At a meeting with Donald Campbell in October Ken Norris, John Stollery from Imperial College, myself and one other, whose name I cannot remember, discussed ways of braking the speed of the boat once it has passed through the measured kilometre on its first run and as it went around Coniston Water’s Peel Island sited at the southern end of the course before refuelling and traversing the measured kilometre in the opposite (northerly direction) for its second run; the average of the two speeds through the measured kilometre in each direction recorded by the official timekeepers would determine the speed for the record. The solution took the form of a water brake mounted on the transom. After looking at several complicated ideas one of us, I can’t remember who, said that as the density of water was some 814 times that of air a cylindrical rod lowered under power into the water could supply an enormous braking force and it was determined by the proverbial “back of the envelope” calculations that a rod 2 inches diameter penetrating 6 inches below the free surface of the water would suffice subject to the detail design of an integral hydraulic jack of adequate strength.
The overall BLUEBIRD K7 (1967) project was undertaken on the assumption that there was no money; Campbell certainly had none and we would procure the materials and equipment if possible without charge. Man-hours with the exception of Ken Norris and myself were charged to Mr. Campbell’s account on the assumption that some day in the future it would be paid. Personnel from the Company were co-opted onto the project from other paid work as and when the need arose. The engineers were Ken Norris as Principal, Tony James as Project Manager, Ted Ravenhill and myself. Workshop staff included Leo Villa who was Campbell’s mechanic and fitters Bill Izatt, Peter Pateman and Maurice Parfit. Outside support came from Bristol Engines, Imperial College and others. To keep costs down I, whose normal function was General Manager of Norris Brothers R & D, was charged with maintaining a critical path network schedule updated on a daily basis and to design the water brake. For outside services and parts we submitted orders with a note inviting the suppliers to provide without charge for the publicity they may receive; a device which was quite successful. Items provided free usually meant someone collecting them and as I in the eyes of some had the least to do, got the job.
BLUEBIRD and other hydroplanes can be considered to be in one of three states. As a displacement vessel, as a hydro plane or airborne (out of the water.) An important factor is that the independent vectors for the air and water freestreams are not always parallel.
For BLUEBIRD in common with other hydroplanes with forward sponsons relied on the aerodynamic pitch up being countered by the weight moment and engine thrust forcing the nose down. Conventionally, the pitching moment, weight and thrust moments are measured about the transom eliminating the rear shoe reaction from the calculations. The vessel in reality reacts about its centre of mass in all planes of pitch, roll, yaw and heave. For BLUEBIRD’s configuration the centre of pressure about which the aerodynamic forces react is forward of the centre of mass such that for a free body (i.e. out of the water) the pitching moment about the centre of mass will cause the vessel will rotate counter-clockwise when viewed with the nose to the right hand side of the centre of mass.
It is important to note that pitching moment is expressed as a function of the angle of attack of the vessel relative to the air freestream and not the water freestream. BLUEBIRD K7 was a conventional 3 pointer in the plan position on its 3 planing shoes. Vessels of this format invariably “flipped over” about the transom if the pitching moment exceeded the restoring weight moment. A free body diagram established from the scarce data available showed that the reaction on the forward shoes is affected by the all up weight (AUW) which is the fully fuelled vessel and pilot, the shoe drag and the thrust moment; the fuel tank was located about the centre of mass to allow fuel depletion to have little effect of the longitudinal trim.
Typically, BLUEBIRD’S forward planing shoes were immersed to a depth dependent on the square of the velocity through the water this being just over 0.1 of an inch at 294 mph. The spring rate of the shoe was extremely high. This stiffness meant that for considerable changes in the value of the front shoe reactions the shoe immersion depth changed little and the vessel followed the contour of the free surface of the water.
BLUEBIRD K7 gained 7 successive speed records from 202.32 mph on Ullswater in July 1955 to 276.33 mph on Lake Dubleyung, USA in December 1964. On January 4th 1967 on Coniston Water the Orpheus powered BLUEBIRD K7 (1976) in its final build completed its first run travelling south through the measured kilometre without incident at an average speed of 329 mph using the water brake to slow down before turning to refuel and return through the course. For some inexplicable reason he started his return run without waiting to refuel and without waiting for the water, which was grossly disturbed by the enormous kinetic energy dissipated by the water brake to die down in spite of the protestations of the experienced Leo Villa who could sense danger; as this was an unplanned event Ken Norris was on his way back to Sussex at this time. What happened during the last fatal run was filmed by the media from the shore. BLUEBIRD left the water at speed at a low trajectory rising to some 28 feet above the water rotating backwards and rolling slightly to port before coming down almost vertically into the lake, cart-wheeling forward and sinking.
I have been asked over many years to give a talk on K7, which inevitably would mean discussing the cause of the crash. I didn’t know the reason and I had no intention of saying anything in deference to and during the lifetime of Ken Norris who last discussed the matter with me some 12 years ago. I now feel free to give a talk and the conclusions regarding the crash are mine alone produced from an intensive period of research and calculation using data and comment provided by others including Ken Norris and Leo Villa.
Considerations arising for a post incident investigation suggested that a computer model was inappropriate due to the shortage of hard data of sufficient calibre and the expense of such an exercise and I decided that a simple first order study using the methods and knowledge available in 1970 be used. The first step was to determine the value at which the pitching moment about the transom as a function of the angle of attack to the air freestream at 294 mph matched the restoring weight moment which was the AUW less ½ tank of fuel; the engine having cut out provided no thrust moment. The pitching moment was further enhanced by engine failure increasing the frontal drag from the intakes producing an additional up moment. The values for the pitching moment were derived from the wind tunnel results at 250 mph, which was the highest speed ever tested. The value of angle of attack to the air freestream when pitching and weight moments are equal is 4.5 degrees. Graphical data shows that BLUEBIRD at 1.05 seconds after the engine cut-out left the water at an angle of 3 degrees and where the starboard sponson was already about 12 inches above the free surface of the water; the other two shoes were still in the water. I believe the sponson lifted due to the vertical fin applying a rolling moment aided by the port shoe flow straightener as the vessel rolled to port about its centre of mass under conditions where the restoring moment was low. Because of the 3-point shoe configuration the vessel subtends an angle of attack to the free airstream of 1.8 degrees. At the same time the swell in the water due to the water brake disturbance made worst by the returning waves from the shore of this relatively narrow waterway produced an angle of 3 degrees in the water freestream which increased the angle of attack to the airstream to 4.8 degrees thus reducing the restoring moment margin to zero. At this point the vessel left the water as an un-powered projectile with its centre of mass travelling forward at an angle of 3 degrees to the horizon with the aerodynamic moment about the centre of mass causing the vessel to rotate backwards followed by the subsequent crash.