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erbus - n/a
27-May-06, 08:32 PM
can anyone help?



went out for the first time ever today after spending months refurbing the craft... it went ok, apart from the steering linkage coming adrift and some blowing from a group of skirt segments.



It appeared as if air was blowing out (from all the spray) from about 4 or 5 segments. they are fixed at the bottom with a tyrap and a platic strip all round the hull at the top.



should the segment be tight against the hull or should there be a given amount of play?



any help most welcome on setting up the segments. it should have 8 in clearance but was very poor on short lumpy grass leading to the shore.



have attached a photo showing place of use.



thanks in advance

Nickinoue - n/a
28-May-06, 09:31 PM
Is most of the spray coming from the back?,

Do you have chipbag (closed segments)at the back or a drag flap even both?

From what i know the skirt should be up to the hull as tight as possible, i have built a modified challenger and one of the biggest mods was to get the skirt to actually fit the hover's planing surfaces tight which i did my shortening the skirt attach tabs and having short cable ties. It should increase the skirt pressure and therefore make the digging in the water less (i have a feeling im gunna be corrected on that)creating less spray.

Its alwase worth having a go both ways if you have the time?

If you have no chipbags that could be the problem, but if it its a restored craft i would think that it was originally designed to have them at a guess!

Regards

Nick

erbus - n/a
28-May-06, 10:13 PM
nick,

thanks for all of that.

the spray seems to be mainly on the forward quarter on one side, i didnt notice the back as i had more pressing matters trying to steer! (the wife however said the spray only seemed about the front)



it has a drag flap fitted, what do you mean by a chip bag?

sorry new to this so not familiar with all the terms.



i had all the segments off and they all appeared identical, they all appear bag like with 3 sides if i remember.



also when putting the skirt back together i noticed only a few segments were tight on the hull the majority are loose ... maybe this is the problem?



thanks again

dave

Iceman - n/a
28-May-06, 10:47 PM
Hi



The tightness of the skirt on the hull is not too critical if your skirt does not have inner bags. The pressure of the skirt will NOT be effected by the fit of the skirt against the hull.



What is more critical is the contact point, that is the point at which the skirt touches the ground at full lift. If this point is in the wrong place it will effect handling.



A chipbag is a rear seggy with a built in drag flap to stop the skirt scooping up water.



If the spray is isolated to one area, I would think those seggys are damaged or worn. If there is alot of spray and the craft hovers level then it might be a case of too much lift. Try backing off the throttle when the spray appears, you won't lose too much speed and it will reduce noise and fuel consumption to.



I hope this helps?

Sean Atterbury - n/a
29-May-06, 05:07 AM
Nick, I also have the modified challenger and you are 100% on the money with making the skirt fit tight against the hull, it realy did'nt hover very well with them plapping around like it did hey?



I also agree with you on the skirt being worn or not at equal length to the others as from the pic it looks like just the front four on the left by the driver are shorter, or maybe too tight against the hull and the others are loose.



Just one of the little things in life that keep us all tinkering with the craft to make them better. http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif



I did notice that the grass looks long, my craft also struggles in long thick grass and I am shure that is y the ride down was not smooth and the craft struggled just a little.

erbus - n/a
29-May-06, 07:38 AM
thanks for all the help there.



i will check segments all all mounted the same length and tighten them all close to the hull, at least that way all are the same....



thank you

dave

Sean Atterbury - n/a
29-May-06, 07:46 AM
Let us know what happens. http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif

andycollins - n/a
29-May-06, 02:31 PM
Hi Dave,



A chip bag is a variation on the standard open segment. The modification is to improve the segments performance at the rear of the craft. An extra flap of fabric is sewn into the segment to prevent water rushing in when the craft is not on full cushion over water.



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erbus - n/a
11-Jun-06, 06:56 PM
Tried again today with all the segments tight against the hull. Although I snapped a tyrap and lost 2 forward quarter segs on my way out it was still blowing really badly from the opposite side. The lift was scarily poor on the sea with the front segs hardly inflating. I could not get it to plane either. In a previous reply a mention was made the segs could be worn (they are not ripped but are probably at least 15 yrs old)when you say worn what are the signs that indicate worn? does the neoprene separate from the backing material?



any suggestions as to what else i could check or do would be most welcome as i'm at a loss now and really dont want to call my mate up in the rnli when i'm foundering....



thanks

dave

Nickinoue - n/a
11-Jun-06, 09:36 PM
what size holes do you have at the front?

Is there any obsicles in the way of the holes or that disturb the airflow in the air ducts?

It is quite hard to think of a reason for that http://hovercraft.org.uk/images/icons/smiley_icons/icon_redface.gif .

When it means by worn out it means when the neoprene nylon is just thin i think. I have an old skirt some one once have me and i would say that is WORN.

Regards

Nick

erbus - n/a
11-Jun-06, 10:05 PM
nick the holes from the plenum appear to be the same size all round from what i can remember ... talking of worn i had another look at the probelm area earlier and the end of the segment that contacts the ground is frayed, do the segments shorten as they wear? maybe the whole lot is simply worn short?



thanks

dave

Nickinoue - n/a
11-Jun-06, 10:35 PM
If the frayes are severe then its a stong indicator that they have been shortened, its is hard to tell without comparing a brand new one but comparing front skirt and back, aslong as they are the same, would be a good place to start.

If the holes have already been drilled by the manufacturer that size i wouldnt worry about that but in my craft the hole size increases as you go toward the front of the craft. goes from 32 odd at the back to a 72 at the front. The back is only used to blow up the chipbags so no need for anymore air and as it is direcly after the fan pressure tends to be more.

If the holes have already been drilled i would not advise re-drillign them.

It must be infuriating seeing as it is a less major part of the craft but neverlesless essential!

Nick

erbus - n/a
12-Jun-06, 06:05 AM
thanks nick - if i get time i will try and check hole size, the craft is an old dragonfly made by ghl, it does make sense that the holes should get larger toward the front. another couple of questions...



i noticed someone offering to make segment skirts on ebay do you or anybody know if these are ok? are there any other people how make complete skirts? also found original segment last night so i can now compare to those fitted and can use as a template to get more made.



what is the best grade of material for say use over stoney ground?



thanks

dave

erbus - n/a
12-Jun-06, 04:31 PM
had a closer look this evening.... the holes from the plenum are 75mm at the front and back. Took off one of segs at the side where its blowing, compered to the unused spare it is identical. maybe i'm just missing something fundamental when i have reattached the skirt. any ideas most welcome. the lift is very poor even on relatively flat ground with a lot of blowing from the front quarter. i will check all the segs when i get time but the few in the prob area i looked at were ok.



dave

erbus - n/a
12-Jun-06, 04:58 PM
another thing that crossed my mind, should each segment be fitted centrally over each hole in the plenum?

hover t - n/a
12-Jun-06, 07:59 PM
HiDave

Each hole feeds one bag.

The easy way (I have found) to check the bag ground contact point is to lift the hull up on blocks to its hover height on a flat surface and adjust all the tips to just touch the ground around the craft.

What pitch is your fan set to? I was just thinking if its set at a low pitch you may have loads of lift ,but hardly any thrust,(I may be wrong)

To find the pitch of the blades measure from the center line of the fan hub(where the two parts join together)to the bottom of the leading edge of the blade eg 22mm =30 deg 31mm=40 deg 38mm=50deg

I reckon its worth a look.



Hope this helps



Trev B

erbus - n/a
12-Jun-06, 09:32 PM
Checked the blade from the join of the 2 hub halves to centre of the leading edge is 28mm (multiwing). The engine is a cuyuna 440 and has been very reliable so far, it revs (max) about 6500 -7000 with the eht at 1200 which according to manufacturer is about max best pwr for both figs. Is it likely the angle could be wrong?



ref the holes, i will align each bag to a hole when i lift it off the ground. does it matter then if a small gap say 5mm or so is between each bag, whats more important aligning centrally to each hole or making sure the bags overlap all round?



another thing i read was to use 2 tyraps (1 per bag to each common p-clip) instead of 1 - does this make a difference?



thanks for all the help

dave

hover t - n/a
12-Jun-06, 10:30 PM
Hi Dave

I think 28mm is around 36.25deg

If your engine revs out the fan may not be consuming all the engines bhp 1mm can make a big difference



If your bags have the air feed hole dead center a small gap at the top between bags would be ok, as the preasure blows into the bags they seal against each other .



Yes use 2 tyraps per p clip , if you use 1 to hold on 2bags every time one bag snags two come off.



are you at kyle of Lochalsh?



Hope you get your probs sorted



Trev B

erbus - n/a
13-Jun-06, 07:52 AM
thanks trev, the engine doen't appear to be over revving in fact it seems to be working up to the manufacturers max pwr figures for revs and temp. live withing a couple of miles of kyle yes.

dave