The duct moved when it was loaded on the trailer. Not much just a mm or so but the fan only has 3mm to play with both sides. I need to re fabricate the engine mounting steel. The holes allowed me to move the engine to get it centred. Problem is under load the engine moves to its preferred position which is not my preferred position. Pain in the backside.
The duct needs lifting so it stops contacting the hull. Contact with the hull creates vibration, vibration is the enemy of hovercraft. Vibration at specific harmonics destroys hovercraft. Nuts come off and bolts come undone bolts snap, all sorts of weird things happen.
It does seem to work, the hover height could do with lifting. Another painful adjustment that requires the skirts taken off lowered re attached. So the lower skirt attachment will need lowering as well. Far easier to write than to do.
I will fix the engine mount first, then the duct and go for a ride before fiddling with the skirt. Give me a week to get the repairs done.
Alright, fixed and almost ready to fly. I had to move the front engine mounting points 3 inches rearward and 2 inches higher. Not quite as easy as it sounds. A trip to my local Bunnings, where I have brought so much stuff over the last 5 years they gave me a trade card. I got a wooden sleeper to make the mount. I could have just got a longer m10 bolt and done it that way. However, I thought it through and the bolt would more than likely bend over time. So I went with the wooden mount with a m10 embedded.
I had to figure out how to stop the engine wonder. I got a flat steel bar and put the m10 holes precisely where they needed to be so it can’t move. I put it on top of the existing steel bar and bolted it back together 4 times before I stopped the rub in the bottom left hand side of the duct. I also put the m10 x 15 tap through the engine mounting points they looked a little worse for wear. I put in longer s/s bolts to hold the engine firm.
I fired it up and we have wind again, lots of wind. 50hp with 9blade 5z with a 860mm duct makes vast quantities of air.
It is now to hot to go in the Sun to finish the seat mounting maybe later. Temp gauge says it 35 degrees already, it is 10 am. Going to be a hot one.
To beat the heat, I go inside and have a shower cool off put clean clothes on and go back out. I sometimes go through 4 sets a day it is the only way to work as being soaked in sweat is uncomfortable and dangerous around electricity. Water or sweat on epoxy is not good either.
There has been some discussion about epoxy and its quick pot life.
I get plenty of working time by using a slow hardener and more importantly small batches. I use the pumps to get the perfect mix and use 5-10 pumps of each the resin and hardener. I always use a 50mm brush as they are cheap and jut the right size for doing taped edges. Epoxy doesn’t burn your skin the same way polyester does it is far easier to mix quickly with the pumps (West system)
Also I have used the product Megapoxy and had good results. Both the thickened epoxy for gluing and the thinner stuff for fibreglass. On this build I used West Systems Epoxy. I so love the mixing pumps makes glassing so much easier for both big and small jobs. But you pay for convenience.
The Rhino had its first water outing today. The throttle cable is not long enough so it revved slightly above idle, it lifted off and tried to move with just this small amount of throttle. I couldn’t tell you the rpms as I have no rev counter. I took this to mean it was going to work. I took it out over the water and it felt ok. Dragging the rear end it felt like. I moved the fuel tank to the front and the seat behind and tried it again. It leapt off the beach into the water and accelerated like no hovercraft I have ever owned including the White Knight Lightweight Viper cruiser. Wow does it blow the hair back. I knew it would be fast but it is another level of fast, very exciting. The fan moved again into the duct and that was the end of the test. Now I have to find another way to fix the engine mount but that is a small detail. It works people it really works, honks along too.
I went to the trimmer after the successful test run to get a quote to make it look as good as it goes. All with out adding to much weight and killing the performance. So next week the Rhino is going for a makeover to make it really special. I was worried it might not work well enough to get to the rally, I did keep that quiet as no one likes a pessimist.
It is coming to the rally, it does work very well.
The Black Rhino has been named, her name is Tempest. As of this morning it is now registered in WA as a boat. This now means I can take it out for a proper test. I hope to do this this week. I need to make sure I wasn’t dreaming last time I tried it out.
I have made a few modifications to the engine frame, fingers crossed I got all the Gremlins out.
I got it out on Tuesday. It was a little rougher and winder than last time. I pushed on anyways. It seemed sluggish and slow to start with, until I found the other half of the throttle. Cable was a little long as it had stretched so I wasn’t getting anywhere near full power. When I got it, yes it worked again. It was not the fast beast I remember from last time though, ok but not great. I found the hull slapping on the top of waves. I almost got chucked going sideways as the cushion let go and the hull meet the water. The issue as I see it is the hover height is to low. I did put the attach points higher than I ever have. Oops, I’ll move it lower and see what happens. Plenty of power from the engine happy with its output. The engine frame moved just so slightly again so it needs a rethink somewhere. Tempest is at the trimmers getting the interior done and a cover made.
So more to do not to much time to get it done either.
It was painful but I lowered the bottom skirt attachment points. It wasn’t as easy as relocating a few screws unfortunately. The lower hull is carbon fibre into foam panels. Screws will not hold up to punishment and I will punish it. So I used sika flex marine adhesive (swear by the stuff sticks to anything and gives a flexible join). I glued aluminium stripping to the hull then screwed the attach points to the aluminium. Job done, not quite. The rear skirts were way to high. This is what happens when you do not use plans. I covered the drilled air feed holes with a piece of ply. Then redrilled the feed holes 50mm lower. I then reattached the rear skirts. I also moved the front skirts lower. Now as I said in a previous post how did this craft work at all with all the skirts uneven?
The engine frame, I drilled another piece of steel and bolted it as another bracing piece. Seems to be holding for now. I will just add bits until it doesn’t fail. No point starting heavy and reducing weight easier to build it to where it has to be to work, but only just. Better not to be an engineer as an engineer will tell you most things we do are impossible on our hovercraft. So I’ll clean her up and get her out on the weekend to see if it is fixed and the gremlins beaten.
Life is to busy at times, this is one of those times. I have not had a chance to get Tempest out on the water. My days keep getting hijacked. Next chance to get it out will be Thursday next week it seems. After that no chance until the following week. I really hope I have time to make it work before April 5. This is the deadline and the day we leave for Moe. Not long to go and I am feeling the pressure. I had a wonderful purple patch there for awhile, I got a lot done. My hope is next post should be a cruise report, fingers crossed.
I got Tempest out for a test flight this morning. A little windy but otherwise ok for testing. Water reasonably flat. It went pretty well today, no engine movement I can see. The extra frame work I installed yesterday seems to have done the trick. I took Tempest for a long ride around the Canning river. Still seems a little heavy in the rear like it drags its bum. Being a smaller craft than my usual fare I am not used to the balance issues such a small light craft throw up. I am still having trouble with the thumb throttle that is a little broken and causes no end of grief, also the throttle cable is to short. I’ll get a new throttle cable and fix the problem and if that’s the worst Gremlin I have left then he shall be easy to slay.
I hope to have time enough to get it just right in 4 weeks time. I doubt all the issues will be sorted by then but it will be good enough. My aim is to show anyone can put together a hovercraft with minimal skills. This becomes obvious when you see it in person, I have left the warts for all to see.
Stuart Herring just happened to be in town for a meeting so popped down to the river for a first glimpse of the Black Rhino. So tell us what did you think, without giving to much away please?
Sounds Biblical, Stuart Herring (4x Viper) called for an emergency cruise. He is busy until after the rally so Today was the day to go. So we went. To the Swan river for a jaunt and to test the Black Rhino on a longer cruise. A quick trip around deep water point, a cable tie replaced. Oh and I fell out on the land, rookie mistake I let the cushion off a little to much. I wasn’t moving very fast so only pride damaged. I have never flown a small craft like the rhino before. The Vipers I have are wide and don’t ever flip up.
So out to the main river we kept to 20-22 knots and just cruised on a very calm Swan river. Tempest sounds like a pack of bees humming along. A growing personality for sure. We turned for home just south of Point Walter. I pushed a little harder on the way back 25-27 knots. The engine cut out at one point. The Rhino came to a beautiful halt with no nasty plough and ejection. Very Pleased with that. It would not however get up on water and the back skirts would not drain. So a little Gremlin still to fish out. Got it to the bank and emptied the skirts and off to the boat ramp without further incident.
The craft performed well couldn’t get the grin off my face. I still need to adjust the lift part of the duct but she’s a goer just making it better until the 5th of April when we begin the road trip East.
The Tempest is epic, and fun to fly. ;D
Well the weather here has been horrible for the last week or so. I finally got Tempest out today to test my latest modifications.
I moved the front skirt segments down as they were higher than the sides. She still worked as she was but Stuart did say he saw light under the front skirts on our run. This could mean heaps of lift in the front which it has. However the gap below the skirts should be the same all the way around not just the front. I also moved the battery to the front for balance. I mounted the seat on a hydraulic pedestal and fixed the fuel tank into place.
Now it hovers very well and leaves not a wake above planning speed, just as it should be.
I keep blowing rectifiers for some reason, but that doesn’t stop her working at all. The battery is more than enough to start her all day. I’ll look into this one for an easy fix if not fix it after our trip.
So I recon I am 85% there, the last 15% is not possible in the two weeks we have before we leave so, I have decided to keep it at this level as it works well but not as well as it could with more time. Any more fiddling could result in making it worse.
I have no Tacho so tuning the fan is overly hard so I’ll go with 37.5 degrees on 50hp Rotax with a 9 blade 5z. I am sure it would be better at 39 odd degrees but that requires lots of time to get just right. I just don’t have it any more.
So for the next two weeks when there is time I will spruce it up. Then apply some more safety guarding (a little minimal at present). Finishing the trailer to carry it over would be a good idea as well.
Getting real close to go time, tempest is a working prototype and ready to go as is.
Now when you get to see the black Rhino realise she was started on the 23rd of December 2014. So she might not be as pretty as she could be. I lost my measuring tape along the way so a lot of Tempest is eyeball measured. This means she isn’t straight everywhere. There are bolts all over the engine frame, this made mock up easier and required less welding. Point is anyone seeing it will believe, quite rightly that they could build one like that. After the rally depending on the reaction I’ll take her further and finish the Black Rhino to 100% and straight and pretty. For now Tempest is a prototype and a one off build.
I was approached at the servo by a bloke asking if he could buy it then and there. Didn’t even ask the price! He was driving a Ferrari at the time. I had to decline his offer. I explained She is going to Melbourne for the 2015 Hover rally. I hope this is an indication that Tempest is a desirable toy to have