View Full Version : Balance or pressure??

hovercad - n/a
26-Aug-06, 03:45 PM
Hello All,

Well if its not one thing its another.

To cut a long story short.

Sorted out the thrust probs knew the craft required new skirt when I got it.

So made a new skirt.

Took for a spin.Briefly

Back of the craft is high up but the front was very low with my son in it.(Dont think he understands the world get further back.)

When it was me in it he said it looked like all the other craft he's seen.

If I sit any further back i'll be on the duct.

Anyone know a simple test??.

Thought about balancing on a tube until the crafts balanced.

Find the center line then see if this coresponds to the position of the driver.

If not I suspect pressure is the problem.(The rear has smaller holes than the front.Intergrated craft.)

Any clues or is it just trialand error?



AuburnUniversityTeam - n/a
26-Aug-06, 05:12 PM
Your integrated craft will change with the driver; so depending on the location and weight of the rider will determine how the craft will pitch. Now there are ways to fix this for lighter drivers. You could use sand bags or bags of water placed in specific spots on the craft. This will help determine where you need to move or place weights when riding. There are some crafts that have a system that will pump fuel/or water to the front or rear of the craft to balance them during flight. You could do this as well but could be pricy.

Simplest solution trial and error; also you could move your gas tank to a different location as well. (If possible)

Hope this helps out or gives you an idea to fix your problem.


hovercad - n/a
27-Aug-06, 08:47 AM
Hello Kyle,

Thanks for the reply,

One of the things I intended to do was to move the petrol tank further back along side the engine.

Balast etc is out as the craft is being used for racing.

Think a bit of the problem is that the original engine was a TZR when the craft was built and is now using an ec44 driving through a flexi coupling so the engine weight is further forward.

Willhave to experimant a bit


Derek Sweetman - n/a
27-Aug-06, 10:19 AM
Hello Craig,

We met at Claydon when you were in the paddock alongside Duncan, yes a new skirt was necessary!

What is the weight difference between you and your son?

The EC44 and TZR250 are similar power.

The further forward the engine the nearer to the centre of lift it is which would make it more sensitive to the driver position.

But has plough-in been a problem with you in the craft?

The splitter plate could be made adjustable to allow for different payloads and conditions.

You could add an elevator to adjust the trim.

As you know the driver normally moves back and forward as well as left and right to trim the craft in a race situation.

My brother attached a water carrier to adjust the trim for his son, but the splitter plate adjustment really made it more contollable as it got rid of the excess lift!

Balencing on a pole is useful to do when positioning an engine.

Small feed holes at the rear and larger at the front is normal for an integrated craft.

Kind regards


darwin - n/a
27-Aug-06, 10:56 AM
Hi Craig

you say a new skirt what type of segmemts have you got open or pressure segments also your duct size and fan speed tzr runs at 10,000 what speed does a EC44 run at also your ratio would help?

I think a was teaching your son at claydon on bob's craft.


hovercad - n/a
27-Aug-06, 12:49 PM
Hello Derek and Geoff,

Yes the skirt did need replacing.Which is done.

I hadnt intended going out until next year as I didnt have an engine.Thanks to ebay and a few beers engine turned up so was a rush to get ready for Claydon.Just too eager to have a go.

New skirt fitted.

14 rear Chip(open) rest pressure.

Replaced like for like.

Splitter plate is variable.Have added an adjustable splitter clearnce plate as the gap was very large.

There is a weight difference between me and my son.

Problem dont think he's grasped the driving postion idea.

I sat as far back as possible when I had a go.Video camera next time I go out to see whats going on.

The EC44 runs max 7000 (according to the manual.)Im running at about 6000.Ratio about 1.89 i think.840 mm duct

Flow starightners removed at the moment as they were for the TZR that runs the opposite way than the Robin.

Unfortunately the field I was using has now been taken over by football pithces and they say i will chew up all the grass.Wasnt going to argue as I dont want to upset the natives.

So it looks like im not going to be able to test until Blackditch.

Im glad im having the problems as im learning a lot more than if I had just got a craft ready to run.


hovercad - n/a
27-Aug-06, 06:57 PM
Well here I am again.

Moved the petrol tank to sit next to the engine.

Tested with no one in.

Front lifted.

Tried with me in it sitting close to the engine.Front lifted up.

Couldnt open up fully in the back garden and only had about 2 ft before hitting the trailer.

As im the heavyest driver dont think the kids will have a problem.Wellmaybe the youngest will get him to wear lead weights. http://hovercraft.org.uk/images/icons/smiley_icons/icon_smile.gif

If only I could test on some open land.

Well Blackditch will see if alls ok.

Maybe i wont be the slowest.


darwin - n/a
27-Aug-06, 07:57 PM
Hi Craig

Have looked at your fan speed i can't see a problem when i've put craft together i've not had a gap larger than 10mm between the fan and the spilter plate with one craft that had lift problems the trailing edge of the fan was behind the duct cut out that turned out to be a large problem also some people swear by pressure segments i've never used them.If you've got any of the old segments try taking out the pressure bit and replace some of the front ones just to test weather the pressure bit is holding tomuch air in the hull.

Good luck let us know how you get on.


hovercad - n/a
27-Aug-06, 09:45 PM
Hello Geoff,

The craft is alot better than Claydon.

wrong flow straighteners removed increased thrust and lift.

New sirt has increased lift so much now get vertigo its so much higher than before.Think it would get around claydon without sc**ping on the ground.Unlike last time.

Feels like a completely different craft.

Reliant more on driving skill than before.

That may be the let down.

Have about 5mm gap with splitter plate down.Have made the leading edge adjustable in case I have to pitch the blades more.

So more lift,more thrust.

Tank repositioned.

Have to learn the right driving position.