Spring 2005 modifications - Part 2
Replacing the seat
With the narrower tank I could now build a narrower seat.
The first seat (shown here) was wide enough to cover the original plastic fuel tank, and so was too high, too wide and too short. I wanted a longer lower narrower seat, which would suit the new fuel tank and run from the engine to the front of the cockpit, to help brace the floor.
The previous seat was also pretty uncomfortable, as it had 90 degree corners - and after a race my thighs really knew about it.
As the tank would only occupy half of the volume underneath the seat, I thought the front half could be filled with polystyrene buoyancy foam, which would either add to the existing buoyancy or could replace some of the foam in the plenum chambers, which would then allow better air flow to the skirt.
The new seat was again made from a sheet of 3mm aluminium, folded into an upturned U, but this time I used 2-stage 45 degree folds to give a bevelled edge at the top - much more comfortable to sit on! The folding was done on the manual folding machine in work. That 3mm aluminium really is tough! It took two of us to lift the folding handle.
Once the folding was complete I cut out some lightening holes in the sides using a hole saw and beat the edges of the holes over to give some added strength, using a short length of aluminium scaffold pole and a plywood support, with even larger holes underneath. I was a little disappointed in the result, as beating the edges tended to warp the entire sides of the seat, but another session on the folding machine returned it to its former glory.
The seat was then screwed to a couple of lengths of aluminium angle running from the engine to the front of the cockpit floor. The new seat was a lot narrower than the old one, so the old holes in the floor from the previous seat mountings needed to be welded up. As the seat is going to take a lot of wear from my backside I didn't think it would be worth painting, so I left it in bare aluminium.
The large void underneath the new seat could now be filled with slabs of expanded polystyrene. But as this was near the petrol tank I thought it was worth finding out whether petrol and polystyrene react at all. Well, the picture (left) shows what happens when you pour a little petrol onto a slab of foam - the polystyrene turns into goo very quickly. So I made up a block of foam to fit underneath the seat and wrapped it in a thick polythene bag to protect it from any spilt petrol.
Replacing the steering control
The steering had been the one big thing that let me down at the Black Ditch races last year so I really needed to improve things. It originally used a pair of bicycle brake cables - one pulled the rudders left and the other pulled them right. The main problem was that a double pull system like this requires some exact geometry - the distance from the pivot point of the rudder to the cable attachment point needs to be exactly the same as the distance from the steering pivot to the steering cable attachment point, otherwise the tension in the system will vary with steering angle. It also needs the cable outers to be anchored down properly - and one wasn't which meant the steering went slack half way through a race.
The new system was to be based on a Morse cable, which could push as well as pull, and so only a single cable was required. I bought a 10ft Morse cable from K&M and fitted it inside the left plenum chamber, so that it emerged through the deck at the rear, and through the cockpit side near the handle bars at the front. The cable ends are finished with an M5 threaded rod so I added a length of aluminium tubing to extend it by around 100mm. The ends were then joined to the steering mechanism and rudder bar with ball joints, and I made a couple of brackets to hold the Morse cable sleeve in place.
The new steering worked well at the next race meeting at Jakes Place in April (see below), although being a novice I did tend to swing the handlebars from lock to lock wildly, when a more gentle steering input was needed.
All it needed now was a bit of lettering on the deck panels. A couple from the hovercraft club just happen to run a sign making business in Aylesbury called SignWizzard and they made me up a set of self adhesive vinyl letters on a backing sheet. The lettering (in Alba font) is supposed to look like bent pipes, which ties in with the way the craft was built.
When the lettering arrived it put the hovercraft paint work to shame - the side deck panels had never really had enough paint applied. As I had to remove the left side panel to fit the steering cable I thought I might as well get both deck panels off and give them another coat. This is where the space frame design with removable panels really works well! In a couple of minutes I had removed around one hundred M6 screws (using a cordless drill and Allen bit) and the deck panels could be rubbed down and painted. A couple of days later when the paint had had a chance to harden I polished it up and applied the lettering. Mmmm sexy!
Jakes Place - April 2005
After a lot of late nights in the garage it was all ready to go to the Hovercraft Club's second race meeting of the year, which would be at Jakes Place near Hinckley in the Midlands.
Everything was looking good mechanically, but I still didn't have a craft registration book, to prove that it had gone through its major scrutineering inspection. It wasn't a problem though as on the Saturday morning, Reg Turnbull had a chat with Jon Spedding (who had previously scrutineered the craft at Black Ditch) and I showed him the modifications that I had made to the rear duct-guarding and the extra propshaft cover which he had requested back then.
The practise and racing went well on the Saturday, although I was suffering from a lack of power, especially on the uphill stretch. Going down the hill was another matter. I don't know what speed I got up to but it felt very fast for a newcomer like me, and at the bottom of the hill the race circuit turned to the left - so if you couldn't turn in time you'd end up in the trees. And I was being overtaken on the downhill stretch !!!
But the main thing was that I had the opportunity to really fly the thing, and get the hang of turning early, and going round the corners sideways. I managed to finish both my Novice races, and I even won the second one (OK, so I was the only F3 Novice competing).
At one point I noticed that the drive belt had slid backwards on the lower pulley (which only had a flange on the front edge) and had been rubbing its way into the bottom of the duct. I needed to keep an eye on that.
Sunday was much the same as Saturday. Another practise session and another two finishes. The practise session went well, until I was coming back into the paddock, took the corner wrong and ended up stopped on the wrong part of the course. Another craft came round the corner and although the driver tried to avoid hitting me he slammed into the rear side of my craft quite hard. I stopped the engine and had a look round, but everybody seemed happy so we all carried on back to the paddock to inspect the damage in more detail. Mine now had a bit of a bend to the side of the duct guard, and his had a bend in the deck. Fortunately neither was serious.
Monday was a very different story. I went out on the practise session, got across the pond and the engine suddenly spluttered and wouldn't go above 7,000 rpm. Then it died completely and wouldn't start at all. This was bad news. I wondered whether I had forgotten to add 2-stroke oil to the fuel mix. Had it partially seized? I got trailered back to the paddock and Tony Broad loaned me a compression tester. The rear cylinder was showing plenty but the front cylinder was showing zero. Nick Long and I took the head off the engine, to find the front piston had a distinct lack of aluminium on one edge. Further inspection showed that a circlip (from the end of the gudgeon pin) had embedded itself in the side of the piston. I won't ever re-use a circlip again! Nick measured the bore and was surprised to find that I had standard (un-rebored) barrels - which meant that I was very unlikely to find anyone with a spare.
That was the end of the racing for me that weekend, but it had been a great weekend anyway. I had been keen to prove that the new tank was big enough to last an entire race - with a bit to spare, and it did! And the steering worked well, and I had got the hang of driving the craft properly (kind of). Now all I needed to do was to rebuild the engine with new pistons and NEW CIRCLIPS.
Fortunately, once I got home I was able to clean up the barrels. Although there was a large lump of aluminium stuck to the cylinder wall, it came off with a bit of careful scraping and acid. The cylinders were not damaged - just a very slight score, which wasn't going to worry me so I bought a set of new pistons (plus small end bearings and those all-important new circlips - total cost: around £100) and put it all back together again.
I took the machine into work on the Friday before the Gang Warily race and gave a short demonstration to colleagues. This went well until the nuts holding the rear exhaust flange to the engine came loose. I tightened it up and everything seeemed OK
Thanks to colleague Dave Butler for taking the pics above.
Gang Warily May 2005
The following day at Gang Warily, the morning practise session went well, although the rear exhaust came loose again - changing the engine note. This time I used a spring washer on each stud and an extra nut to lock it all in place. The drive belt was still moving on the pulleys and I noticed how much had been worn off the edge of the belt. It should have been a 2 inch wide belt, but it was now down to only around 1.5 inches!
I decided to leave it, and change it for the spare after the first race... During the first lap of the first race I suffered a strange low fequency vibration above 9,000 rpm - something which I had never come across before. This persisted for a lap and then suddenly I lost all drive and the engine revs went off the scale (over 12,000rpm). I pulled the engine cut off to stop it revving its nuts off. Clearly the vibration had been the drive belt skipping on the pulley, and it was now hanging loose, but it hadn't snapped, or damaged the fan. I came back on the recovery trailer.
The upper and lower pulleys were clearly not quite parallel, causing the belt to edge backwards. Back in the paddock I shimmed the lower bearings blocks up by 1mm to make them more parallel (or give it a slight forward taper if anything).
Mechanically, things went well for the next 3 races. I did suffer a severe bruising to the right arm and ribs when I was hit in the side by a Novice F2 craft, as I was leaving the water exit area. I won't name the driver but she did have fun in the catch netting that weekend.
Poor Paula Broad (Tony's wife, and no, it wasn't her who hit me) must have suffered the same type of accident as me - but she broke 5 ribs and punctured a lung and ended up in Southampton hospital for a few days. Ouch, what an accident to suffer in your very first novice race!
Novices is a bit of a Demolition Derby. Around ten novices, with different engine powers, charging round the course with too much competitive drive and not enough skill. But then we are there to learn...
While getting ready for one race I had serious problems. The engine started and I drove through the paddock, but the engine then wouldn't rev, then died and wouldn't restart. I sat in the paddock desparate to think of what might have gone wrong. Everything looked OK and it felt like there was plenty of compression on both cylinders... Then I remembered that I had left the electrics switched on for ages earlier - maybe the fuel and water pumps had run the battery down ??? I switched the electrics off, and on again and watched the powervalve servo as it reset itself. It moved much slower than normal. I switched the electrics off and tried starting it again. This time it revved fine - powered by its own alternator, but without the drain of having to charge the battery. So while the engine was still running I switched the electrics back on and let it recharge the battery for a couple of minutes. Then off I went to the race, and I didn't have any more electrical problems.
On the last race on Sunday I heard the engine note change again and it woudn't go over 8,000 rpm. I had now learnt that any change in the sound the craft makes is generally a bad thing, so as it was nearly the end of the race and I had completed enough laps for it to count as another race my novice requirement of 15 races I came into the paddock a little early. It turned out that both exhaust pipes had cracked around the tight bend near the engine. One of them was pretty severe. I could have got them welded up that evening, but as the family was going on holiday just two days later we called it a day and went home. It had been a good weekend overall - I got to know more people in the club, and caught up with old friends.
While I am getting plenty of lift from the fan (maybe too much) the thrust is well below what is needed. I currently have a 12-blade hub, with 8 blades. I chose a 12-blade hub because it allows 3,4,6,8,9,10, or 12 blades, and with 4ZR blades they fill the width of the 900mm duct. Anyway, as I had nothing to do, I had a walk around the paddock to see what other people were using. Nobody else was running with 8 blades. Most had 6 blades, some had 4, and one craft had 3, but nobody had 8 except me. Looks like I need to try 6 blades, and pitch them up a little.
The exhaust pipes which cracked were almost exactly as removed from the original TZR bikes, so had only ever been a temporary measure. Keith Oakley had told me that they probably wouldn't last a season, when he saw the craft at Black Ditch last year - how right he was! Anyway, this seemed to be the right time to think about having a go at hydroformed exhausts.
Here are a few pictures I grabbed at Gang Warily 2005. Both Tony and Nick have the same engine as me, but they are both qualified F3 drivers.
Tony Broad in his F3 #143 going around the catch netting
Nick Long in his F3 with shaft drive to the lift fan, after the first corner.
Me just after the finish line. That hole in the rear right corner segment probably doesn't help...