Making the F1 hovercraft number 1244

Building New (photo's & notes) Mirage Rotax F1

New entries added at end - latest entry 16th June 2001

Towards the end of my time racing hovercraft 1127 in Juniors and then F3 I found that I was on full throttle most of the time and felt that a more demanding drive would be nice, where I would have to use throttle control..........

In formula one configuration "our" Mirage race number 11 will be powered by a Rotax 253 for lift and a Rotax 809 for thrust. The 809 is still in restricted supply from Rotax and so far (05/05/01) only three engines are known to have been imported into the UK. The reason for the restriction being something to do with Snowmobile racing and this particular engine being state of the art.

	04/05/01 I can only get home for weekends infrequently so have to do work on the new machine as I can. Two weeks ago we (Ken, Dad and I) made various smaller parts such as nose cones, flow straighteners etc. In the meantime Ken has manufactured all the clever bits such as bearing blocks, lift engine frame etc. This is the mould for the one piece top section looking from the front, the circular object is the underside of the lift fan duct which is built in. The top part will be the cockpit. Today we started laying up the hull by waxing the new mould, again and again and again......
.....and again. This photo of the moulds that will make up the underside of the craft, the planing surface, was taken between coats 5 and 6.
	The colour scheme is two tone blue and yellow, this shot was taken shortly after the masking tape had been removed (with the blue gell coat still tacky). When ready, the yellow gell coat was put on, painting over the join line.
This is Ken putting the finishing touches to the front floor section. Two layers of 2oz matting and re-inforcement to the vulnerable areas. The batons strengthen the area at risk in a "plough in" or nose dive on landing. By the evening of the 4th we had laid up the main components of the hull, to be left over night in the moulds. 05/05/01 The shots below are of the top section as removed from the mould, ready for final trimming. Now turned the right way up of course.

	This shot is of the thrust duct area. The square cut out in the lower bell housing is to accommodate the drive pulley. The lower thrust duct area had to be truncated to allow for the air holes underneath and the arrangements for fixing the lower rudder mounting. The craft being wider in the cockpit area enabled the whole engine and duct assemblies to be mounted lower.
The top section was then loosely returned to the mould for fitting out with emergency buoyancy foam blocks and re-inforcement of the duct top section mounting points which are under the expanded foam. The top part of the duct will be bolted into place, for ease of repair. The yellow colour of the main body of the hull is due to the resin for the chopped strand being coloured to give some depth to the yellow at the front of the craft. The blue gell for the remainder of the top section being opaque, remains blue. The nylon rope securing of the buoyancy blocks looks simple, but is very durable. My original craft 695 now many years old had the styrene held in place the same way and is still doing the job.
	Team Eagle at work!! The front and rear sections of the floor, were prepared with centres for the air holes pre-drilled and the nylon line that serves as the lower mount for the skirts, being threaded in The bottom, planing sections were then clamped into place and the floor glassed in to give a flat smooth bottom to the craft. see below. There are 60 air holes and therefore skirts that need to be fitted. At this point the edges of the craft are still free waiting fitment of the aluminium strip to which the top sections of the skirt will be fixed. To finish off the day the lift engine was bolted to its frame and brackets made for the pulse pump and electrics.

By the end of the second day the hull was pretty much complete, requiring fitting of the duct and seat, which we made during the hull lay up when the right colour was mixed. 06/05/01 Sunday morning was spent fitting the flow straighteners, UK race regulations stipulate that the straighteners should not be more than 12 inches apart at the circumference. This gives protection to people falling into the largish duct, as well as the benefits to the air flow.

"The Office" The inspection hatch is to enable access to the steering gear and fuel lines. 2 and a half days to this point. The shiny strip around the edge of the craft is the aluminium strip riveted into place that will be used to clip on the skirts. The fixing also joins the top and bottom mouldings together. As seen here the hull weighs 180 pounds. Not light, but it needs to be fairly strong because of the horsepower and also the craft is fairly big. Even so the power to weight ratio will be approaching 1000 horsepower per tonne.
19th May 2001 OK Ken, where did you say the exhausts had to go? If you are wondering where the stays for taking the thrust of the fan frame are, there aren't any! For reasons of safety, ease of exhaust run and good engineering, stays that act in tension (as opposed to compression for forward mounted stays) are sited between the duct and the duct shroud, terminating at the back duct mount and are hidden away...very smooth!

	The fuel tank holds 19 litres and fills the under seat area leaving little space for the steering and electronics for the thrust engine. The bearing block was specially designed and made by K & M Products. The Polychain is mega expensive compared to the cost of a Polybelt. The radiator is from a Mini. A guard for the rotating shaft has yet to be made/fitted.
All these shots are of the same craft but the camera (on automatic) sometimes gets the colour balance wrong. The picture at right is about correct. No rev counter, just a temp gauge for the thrust engine. Both engines will run below peak revs when blade angle finally adjusted, so engine speed will not be an issue. Exhausts and skirts left to make and final fitting of detail items. The electrics and fuel lines are installed and the fan guards just need final modification to fit. The seat area and steering are complete. 28th May 2001 The craft seems almost complete, but it is amazing how much time tidying up detail items takes. I have taken a weeks holiday to study for exams but will really have to spend most time with Ken finishing the craft off if we are to test it before the first race meeting..
	1st June 2001 Initial running of the engines and a brief and gentle run up and down Hougham airstrip in the dusk just to get the initial feel for the craft. 2nd June 2001 Finished and cleaned up. Shots were taken on our driveway. The exhausts look the "bees knees". Each are exactly the same length and volume. The shot below is of the K & M Products manufactured bearing assembly with the pedestal for the top pulley of the polychain drive. The lower pulley is the serrated bit in this photo. The shot was taken from the rear between the rudder and a flow straightener. The horizontal ally bars are for the radiator mounts.

3rd June 2001 We hired the Tattershall race track for the day (with Richard Eaton who has a sister craft to Team Eagles), to do final tests. It floats! A brief flotation test and then a practice start on water - it when straight over the hump the moment the engines were lit up! a lot different to my early FJ days with craft 695 which only had 30 bhp and required a real technique to get away cleanly after stopping on water.
	First race meeting less than 7 days away. The lift engine area needs some attention and I am not sure that the blade setup is ideal. The old six blade arrangement is no longer available and we were obliged to use the replacement five narrow blade setup which seems to me to not have the same skirt pressure characteristics. The lift engine is running a bit slow so perhaps just some fine tuning is required. The race numbers and decals are being made and will be fitted Friday or Saturday at the race meeting.

Penton Lake (Near Heathrow Airport) 9th June 2001

The craft was inspected and certified by scrutineers of the HCGB Jonathan Spedding and John Rees. A log book for the craft was issued with the number 1244 giving us clearance to race.

The craft seems quick to drive and early indications are that it will be competitive. There are two very minor design problems that we have to work on.

1) The type and number of lift blades.

2) The radiator design.

For further details see the Penton Lake 2001 race report..