[Steve Holland Posts: 1646 Status: Offline]

Those orange size stones are lift killers, try for smoother if possible although it's sometimes unavoidable.

[Nick Flint Posts: 5067 Status: Offline]

Great to hear Al!

[Al Posts: 1008 Status: Offline WWW]

I’ve just got back from having a play out on the loch, hover running great now, so it must have been the lift belt slipping.  Only issue we had today was getting stuck on the beach, as the pebbles were about 2” to 3” in diameter, from memory that is the worst size as they let lots of air escape from the cushion

[Al Posts: 1008 Status: Offline WWW]

I've checked the skirt all over and no visible damage.  I've painted a layer of glue on the contact area of the skirt in the hope it will help protect the skirt against wear.

[Al Posts: 1008 Status: Offline WWW]

I've ordered a digital spring balance / luggage scales, as they'll probably be more accurate than my 100kg spring balance on such a low tension of 5 to 6lbs.  Un likely I'll be getting out on the hover until at least the end of next week, as working and have stuff already planned for a couple of days.  At least the scales will be here before then, so can double belt tensions are correct.
 

[Steve Holland Posts: 1646 Status: Offline]

The original surveyor uses approximately 9.5hp for lift on a 9 blade fan at 25 degrees. Your belt should easily handle that. The most common reason for belts turning over is wear combined with an overtightened belt. I would stick to the manufacturer advised tension where possible.

[Al Posts: 1008 Status: Offline WWW]

Becky said last time we were out, she could smell something.  Becky was sat further back than me. "It wasn't me that she could smell, honest"   I thought we had the roof up the last time we went out, but Becky said the roof was definitely down the last time out.  My memory isn't what it used to be     So perhaps the lift belt was slipping a bit.


The yellow Surveyor I had, the lift fan used to eat belts within a few hours of use.  When building the original drive for Kermit, I spoke to Bryan Phillips about it & he suggested that I fit two belts to the lift fan, as recommended on the Geoduck.  This was why originally there were twin belts driving the lift fan.  From memory it was a nightmare to fit the four idler pulleys in such a tight space.  He tried to sell me the carbon drive system, but the cost was out of my budget, especially with P&P from the USA & import duties etc.


 
 

[Ronnie L Posts: 530 Status: Offline]

The Tensioner pulley bearings are new and there are spares ones in the spare parts box.
I wondered if there might be corrosion on the pulley to belt surfaces with the craft standing…..although it’s been inside all the time.
The lift belt isn’t very old, and as Al said there is a a new one cable tied in, so it’s easy to get to.
So that’s easy to change if needed.


When I bought the craft the propeller drive belt would slip quite often.
It was something you couldn’t miss the engine revs would rise when under power.
I changed the drive belt tensioner to jack bolts………solved. Never did it again.
I baffled by this

[Steve Holland Posts: 1646 Status: Offline]

Your lift belt situation is something I was chatting to John about when he was designing the 'glass cockpit ' for my vanguard. John added an input from a hall sensor on the prop so that the speed can be monitored although you can use software linking engine speed to prop/fan speed to provide a warning which imo would be useful to have.

[Al Posts: 1008 Status: Offline WWW]

I've replaced the belt with the new one that was cable tied to the frame.  I've also ordered a new set of belts to keep onboard



I've just put spring balance scale about half way between the driven pulley & idler, at 5lbs pull the belt moves about 1/2"  looking in the plans written instructions , that should be about the correct tension.


Both idler pulleys are free and smooth running.


One difference between the first time out and the other two times, is that the first time I had the hood folded away and the last two I had the roof up, but I don't think that should make much difference

[John Robertson Posts: 5272 Status: Offline WWW]

Not so sure that is the issue.  The belt turning over can be caused by low tension OR an overload (its  mule drive so there is a rotating force all of the time trying the straighten the belt).  The width reduction is perfectly normal - that's how V belts wear (the contact shoulders are still the same surface area so there is no performance degradation (the limit is when the tension cords (top edge of belt) reduce in width and the belt loses strength - i.e. needs tensioning more often)  OR it bottoms out in the pulley groove.  Obviously if there is damage to the shoulder surfaces then I'd swap it but it should be good down to around 9.5mm width.
If its' been slipping badly enough to reduce lift then its' probably overheated and needs changed.  I'm surprised you couldn't smell/hear it as the amount of heat in a slipping belt is usually catastrophic.  The engine would have been over-revving also as the load would be lower.
Also worth checking is that the idler pulleys aren't sticky or jammed - that would overheat the belt, losing tension.  And the driver/driven pulley grooves are clean.
Measure the tension properly - 'feels OK' isn't enough.

[Al Posts: 1008 Status: Offline WWW]

I haven't finished checking the skirt yet, as on shift and hasn't stopped raining the past two days, but I do think that I may have found the problem


I checked the lift fan belt tension and it felt OK from the rear drive pulley end down to the idler pulleys, but I couldn't see into the lift fan area very well because of the covers over the rear end.  So this morning as the rain had stopped, I removed the middle cover to get a better look at the lift fan.  The lift fan belt is very worn and has twisted on the pulley, so I'm thinking the lift fan belt is probably slipping so not giving me the full lift.  The spare belt that is cable tied to the frame is 12.59mm at the widest part of the taper and the current belt is 10.51mm at its widest point.

[John Robertson Posts: 5272 Status: Offline WWW]

This isn't complicated.  Its a working craft so it isn't anything subtle or obscure.  It's either skirt damage OR lift transmission issues.

Check the skirt (a one minute job which you should be doing every 2nd trip anyway).  Pull the skirt out and up so the inner section is tight & flat up against the plough plane (side & rear) and the contact area will be at the outside hull edge so very easily checked without any crawling around.  If you want to crawl then hold as said and look under - you can see all of the inner skirt section (apart from an inch or so at the inner attach).  You can pull the entire side/rear up using awning clips and bungees if you want.

Damage to the inner skirt should be very obvious - however, that isn't going to reduce the lift performance as its feeding the cushion anyway - its' only external/contact line damage that will result in lost cushion volume).  Internal/contact.surface line damage usually results in a 'scooper'  which dramatically increases drag and is very obvious during operation.

I'm assuming that you've already checked for skirt external surface damage?

As to the cause  - either operator error or trailer.  There isn't anything else. 

When coming ashore, as Ron says, unless you 'hover-know' the surface very well, you need to get the speed down to <10mph by using the brake (do NOT reduce power below full lift - see below).  That allows you to release the brake and increase power a metre or so from the shoreline allowing you to  traverse a leaky surface without increasing speed (the higher power also gives much more control).    The other reason for bleeding speed is that the surface you are moving onto may have lower leakage than the water so the craft can suddenly accelerate - not good!  Watching your video of leaving the shore made me wince!  The craft was clearly not hovering properly yet you still carried on onto the water despite the banging and thumping going on - I doubt anyone would do that with any other vehicle?  You'd have stopped and investigated surely?  You are very likely to damage the skirt and hull operating without full lift (again - see my comments below).

Unless you are absolutely sure the trailer doesn't have any hidden potential snag points you should load/unload when you are outside of the craft so you can keep an eye on the skirt (look for wrinkles indicating snags).  If using an electric winch extreme care is needed as there is no feedback - it just keeps pulling until something breaks and it doesn't take much for even a small 1ton winch to rip a skirt.  If you can push the craft sideways a bit and returns to the centre (or 'bounce it up and down) then it usually indicates the skirt isn't snagged on something.  The throttle will be above full lift RPM during load/unload due to losses caused by  the surface transitions (tailgate, etc.).  For unloading you shouldn't be able to push the craft completely  off the trailer as it will be trying to climb back on again.  Push it off until the rear flat bit of the hull floor is above the surface.  Drop the power a bit until the rear settles on the surface (the front should still be on hover) - then pull the trailer out from under the craft (it's a good idea to leave the winch attached (or a rope) to prevent the craft wandering off while you move the trailer).

And to reinforce what I said early - if the craft is moving then it should ALWAYS be at or above full lift RPM.

And, lastly the lift transmission as a cause.  Very unlikely but it could be a badly slipping drive belt, loose drive or driven pulley or a damaged fan (again, very quick and easy to check all of them).

[Al Posts: 1008 Status: Offline WWW]

It probably is something I'm doing wrong.  I'll get to the bottom of it, either adjust how I'm piloting it or if there is something that has happened to the skirt.  It was fine the first time out and at over 30 mph up and down the loch, so if something has happened to the skirt it's since I've had it.  I was impressed with how well it flew the first time out and how quickly it gets over the hump.


On the latest video, I can be seen to touch the brake and the front starts to dip, can also hear the RPM pick up as I apply more throttle and my foot is off of the brake, but the brake pedal can be seen to go downwards again.  That maybe due to the front curtain being pushed up, so making the pedal rope go tighter giving the impression the brake is opening, but in fact the whole curtain has moved inwards and upwards.   


I'm busy again at work, because of staff shortages, but I'm looking at possibly booking a hotel or cottage for a few days on Loch Fyne in the next few weeks, so hopefully get John to go out with me and he can put me right if I'm doing something wrong.  I also need to see if / when John would be available and also weather favourable.  July is probably out though due to the extra shifts I'm booked to do.  In the meantime, I'm going to renew the glue along the contact area of the skirt and check the skirt for any rips etc.


I'm pretty sure it's poor piloting skills 

[Ronnie L Posts: 530 Status: Offline]

Al
Now you must excuse me if I’m being thick …….but…..
You said at 25.4 mph and 3000rpm you touched the brake and it ploughed in.
When you touch the brake going fast, you collapse the front section of the cushion and the nose dives and things slow down very quickly.
It’s the brake, that is what is supposed to happen.
When you release the brake the nose bobs up again.
That is what always happens.
I imagine that’s what happens on all Sevs.


I was watching the video of you taking Karen for a ride as we bought Kermit from you.
When coming onto the beach you didn’t use the brake at all to reduce speed.
You reduced and increased power so the rear dropped and lifted to reduce your speed.


Just an observation.


Please let me know your thoughts.
I feel a bit upset really that you aren’t getting on with Kermit, when after all the mods and recalculating by Ian on the transmission ratios. It doesn’t seem to be right for you.
I remember one trip, as we arrived on a beach, John said “ it doesn’t want to be much worse than that”
During that crossing it was rough but I didn’t feel threatened at all.
Don’t know what’s going on.