I decided to fit full cockpit sides as the weather is now cold (and to stop Matt complaining about getting wet!). I bent up a frame using some 1/2" aluminium tubing from an old frame tent (the aluminium is impossible to bend unless you heat it first). I used 2mm thick acrylic sheeting to cover the frame - it is
hinged at the top and opens like a gull wing door. At present I just used a bungee cord to hold it up but I will need to get some sort of latch or gas strut mechanism. The sides make the hover much quieter than it was inside - most of the noise now seems to come from the engine through the lower part of the rear panel.
I also changed the twist throttle for a plastic bicycle brake lever fitted to the front on the control stick (I fitted a second short section on tube to the rear of the control stick (for the hand grip) above the brake lever to allow the brake lever to have a wider range of travel than normal. I also bought proper length cable for the throttle (although it is much stiffer than the open cable I had).
14th Feb 2005
Fitted a vent to the battery compartment in the nose - I used part of a plastic cavity brick vent which had a water trap and drain built in. Repaired skirt rip properly. I also re-hung the skirt at the nose on both sides - it was attached further up the hull than it should have been (it's now about 50mm lower at the nose). I re-balanced the prop using two Stanley knife blades embedded in wood as the balance edges (rolling on a metal tube through the prop. I balanced it by adding longer studs to the hub and fitting extra nuts as weights to these studs. It is balanced to better than 5grams now. Practiced in flat field next to house until I could drive through small gaps reliably. Fitted return cable to trim wing using a bike inner/outer.
Disassembled variator as it was very sticky to operate. I discovered that the bronze bushes had worn on the stainless shaft and allowed the pulley halves to twist. I machined new, longer bushes and re-fitted the variator. The aluminium pulleys halve were also pretty worn - aluminium isn't a good material for a V belt pulleys!
Fitted extra idler pulleys under seat to prevent long fan belt slapping (plans use PVC tubes but they wear out quickly and end up being pulled through the drive system). I used plastic belt rollers from a lawn tractor cutter deck - problem now fixed!
fitted speed control lever from an old lawn tractor in place of handbrake for lift control - much easier to use!
Replaced trim wing control wires with a push/pull cable system - much smoother to operate. Also replaced rudder cables with 2mm stainless cables - should last forever!
I decided to re-weigh the UH18 as I had it off the trailer anyway. I used 650Kg digital platform scales and lowered the craft onto them at the balance point - the final weight was 349Kg. The design weight is 341Kg (750lbs). My craft weight included about 15 litres of fuel and the usual box of tools/spares and the paddle so I'm just about dead on! It's obvious why it performs well as this isn't much more than a lot of integrated two seaters!
After destroying the thrust duct when trailering the Scout (see hover diary 2006) I decided to try to re-join the five sections again.
I made a new 5ft diameter double disk former from sterling board and fitted it to the prop hub.
I then assembled four of the sections by pulling the joints together using cables ties punched through holes in the duct sections. I also used wood screws through the duct into the former in a couple of places to pull the sections into place. I used epoxy with some flock filler in the joints themselves with a layer of bi-axial woven on both inner and outer surfaces.
Three of the four joints went together well with very small joint gaps (see above pic).
It actually fitted the curvature of the former almost perfectly. I glassed the exposed sections of the joints and left the last section of duct off for now. I will trim the last section to compensate for the filled gaps in the other joints and hopefully get a good round duct again (the last section was sawn off at the roadside so it has a clean cut edge)!
Fitted the last duct section into place. I had to cut about 5mm from the end of the last section to get a good fit. I used an external curved former (along with cable ties "stitches") to pull the last section into the internal former. Once I re-fitted the thrust stand braces it became very rigid again.
I used a length of ply bolted to the prop hub to check the duct for roundness before attaching the support struts/ It looks to be better than 1.5mm - not bad considering it's made from five broken sections!
I finished the internal joints using lightweight (1oz?) woven to smooth the duct wall as much as possible.
Finished duct repair.
The final result looks pretty good even though I say so myself!
I had to cut a small amount (about 2mm) off each prop blade as the duct has ended up very slightly smaller than it was before.
Tested UH18 in field - discovered lift fan was well out of balance - the vibration was pretty bad. Re-balanced fan and ran around field for an hour or so. The craft hits about 35mph from a standing start going uphill (about 10 degree slope) - see videos. I need to treat the inner cabin walls as they are showing signs of black mould - the craft has been sitting outside uncovered since March this year. I will use Glycol (otherwise known as anti freeze!). It seems to work OK as a wood preservative - even when applied to painted wood - it soaks through most paints.
I've gotten tired of having to re-balance the lift fan - it goes out of balance very easily, probably because it is sitting at an angle and one side is always exposed to trapped moisture. I used the 12 blade Hasconwing hub originally used on the Scout and installed 9 4Z blades in it ( 3 sets of three). I only had to cut an inch or so from each blade - it's a big fan!. A quick test on the trailer shows full lift at 1700rpm - I will check it out in the field. I I suspect that there may be too much lift which will result in excessive spray on water. I've set the blade pitch to 25degrees at present but it can be reduced to 20 easily.
Tested new lift fan setup in field. At low variator settings the lift is very similar to the wood fan. At higher settings there is a lot more lift. I found I didn't need the variator set to more than about 2 or 3 to start off on full hover (the variator control has a scale from 1 to 7). Too much lift may generate spray on water so I'll need to check it out. the fans seems quieter than the wood one until you get to the higher speeds - the type of noise is different but the actual volume sounds about the same.
Tested new lift fan on water (see diary). It performed OK - there is definitely more lift available, it was much easier to maneuver on pebbly beaches. There was no significant increase in spray when getting over hump so overall it seems to be successful.
Carried out noise tests in field - it was a nice still evening. The UH18 reads 80dBa at 25 metres. The highest reading is from directly behind the craft - not surprising as the exhaust and prop face backwards. The craft makes a low frequency helicopter type chopping noise which may be why the reading is so low (lower frequencies are reduced in amplitude by the "A" scale to compensate for their lower "annoyance" factor.
After some heavy use at the Loch Fyne Hoverin, one of the the rear idler pulley bearings had partially seized. After a squirt of release oil and some gentle rotation it unstuck enough to let us use it on a final cruise on the Loch. I trailered the craft home and replaced the bearings on all of the idlers at the same time. It's surprising how much noise a rumbly bearing makes at full speed - the cockpit is much quieter than before - the front idlers are just under the dash in the seat box.
After a very hard winter, the UH18 paintwork was in need of some major repair. I stripped most of the old paint (wasn't hard as half of it was falling off anyway!) and re painted the hull. I also replaced the lower plastic screen as it had gone cloudy green. Replaced the outer curved screens as they were both cracked (6 years isn't bad not bad for indoor-only plastic!). Apart from that, no other maintenance or fixing was needed