A guest post by Ken Thomas, Rocket Maker
My daughter Rachel and I have been building and flying model rockets for almost 15 years – all thanks to National Museums Scotland. In the late 1990s they ran ‘Rockets to Go’ workshops at the National Museum of Flight. It was amazing! You built a model rocket – mainly from cardboard and paper – learning about aerodynamics, stability and rocket propulsion. Then, in the afternoon, you flew the model using a supplied solid rocket motor. Ours achieved a very stable flight approaching 1,000 feet in altitude. We were hooked! We are now members of the United Kingdom Rocketry Association (UKRA) and the Scottish Aeronautics and Rocketry Association (SARA).
We’ve just returned from the 2012 International Rocket Week run by John Bonsor, our good friend and mentor, who ran those original workshops. There were 54 participants with a total of 139 flights and a maximum altitude of 9,000 feet. It was a truly international event with visitors from Australia, Turkey and Libya, as well as from all over the UK. It is also very much a family event, with 11 junior flyers this year. They are a great crowd – very friendly, enthusiastic and with a wealth of experience and novel ideas.
From the basics of 15 years ago I’ve progressed to, among other things, scale modelling. I won this year’s scale contest with a 1/16th scale model of the Museum’s Black Knight rocket.
I was very taken with the rocket when the new Connect gallery first opened. Over the past two years I’ve been planning a flying scale replica of the Black Knight. After taking many photos – I do appreciate the Museum’s open policy on photography – I started working on the scaling. There are scant dimensional details available and, following a request to the Museum, curator Julie Orford very kindly supplied dimensions of the fins – one of the most complex areas of the rocket.
I then spent some time learning a computer aided design program to help with the scale design. I also modelled the rocket in SpaceCad, which allows you to check centre of gravity, centre of pressure and the resulting stability of your design.
A 1/36th scale prototype followed to check dimensions, choice of finish and to see whether or not it would fly! The real Black Knight had gimballing rocket motors with hydraulic swivels controlled by an autopilot system with gyros to achieve stability and directional control. This is the reason the fins are relatively small – they only needed to be effective at low speed as the rocket left the launch pad, after which the vectored thrust would take over. Such control is very difficult to achieve in a model, so I was reliant on fins only, but the prototype flew well.
I decided to use Flair Aluclad as the covering material. This is real aluminium, 70 micron, adhesive-backed foil and would produce a realistic finish to the model. Then there was another visit to the Museum to compare the model with the real thing and fine tune the dimensions and fine detail.
I decided to use 56mm diameter tube, giving a scale of 1:16.25 with a total length of 714mm.
I made a trial motor / fin section to check the finish and decide where the panel lines and base bleed holes should be. On the real Black Knight, these holes were cut in the skirt to reduce base drag. They built a 5′ test vehicle (about twice as big as my model) which was flown on solid motors to test the theory. Eight 6″ holes produced a significant improvement in performance.
Then work started on the final model. The ‘rivets’ were applied individually by hand using a home-made tool.
The nose section was quite difficult to produce. I used a modified balsa transition with a piece of standard 25mm tube topped off by a handmade nose cone.
The nose and pods were airbrushed before the aluminium parts were added. These last bits were applied on the Sunday morning – the last day of International Rocket Week – and the rocket had its maiden flight that afternoon.
The model was powered by an Estes ‘D’ solid rocket motor, producing a total impulse of 20Ns and an altitude of around 150 metres.
Recovery was by parachute – an expulsion charge in the motor blows off the nose section and deploys the parachute, allowing for a safe, low-speed landing with no damage to the model.
The Museum’s BK02 never flew – it was used for structural tests – which is probably a good thing as we are able to see and appreciate such a well preserved example of this important British rocket. My model may not be perfect – there’s always a trade-off of time versus quality. However, the main intention was to produce a model which actually flew. So, finally, after more than 50 years, the Black Knight BK02 has taken to the skies.
Film courtesy of Mitch Hamilton.
Photos by Ken and Rachel Thomas.
Black Knight details from A Vertical Empire: The History of the UK Rocket and Space Programme, 1950-1971 by C.N. Hill.