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Sean Atterbury - n/a
9-Feb-07, 07:34 AM
The craft has been running well till this last trip to the damb.



We went for 10 days to the damb for a short break, spent some bucks getting the craft ready and was not disappointed.



Besides the belt comming of due to a loose nut, no damage luckily but a mission to get some help to tow me back, craft floated well too.



On the third last day I took my nephew for a spin, with the new rudders the craft does nice dounuts and we had great fun, the water was a little restless but the craft just lapped it up and we were flying, I felt good and opened her up. We then passed some friends of mine and them being in a speed boat wanted to see how fast we were going, so 180 and back to chase, we got up to speed in no time and got into there wake, I backed off just a little to negotiate the wave, as we crested it we lost all lift and ploughed in heavy, I felt the loss and gunned it but it did'nt help, SMACK and the sound of ripping fibreglass.



Riped the stearing out, the one whole side folded up and several pickets came loose.



I got to land streight away, and found a hole broken out of the bottom of the hull, in the middle, funny enough. Two blades had cracks down neer the tips for about 5cm and damage to the duct where they hit.



SO THERE AND THEN, DECIDED..



LIFT, NEED LIFT.



I want to put a seperate lift engine and fan in the front.



What HP engin and what fan do I need, I have a 503 thrust with 850mm duct.



Any sugestions, donations and revolations welcome. (in other words, you got any c**p that could help that you do not want any more, send it, TO ME)

hovmart - n/a
9-Feb-07, 09:15 AM
best cure is to slow down

sixpackpert - n/a
9-Feb-07, 09:34 AM
best cure is to slow down




Where's the fun in that??? http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif

Sean Atterbury - n/a
9-Feb-07, 09:53 AM
agreed

Russ Pullen - n/a
9-Feb-07, 11:12 AM
<table border="0" align="center" width="90%" cellpadding="3" cellspacing="1"><tr><td class="SmallText">hovmart wrote on Fri, 09 February 2007 10&#58;15</td></tr><tr><td class="quote">
best cure is to slow down




Where's the fun in that??? http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif
</td></tr></table>





More to the point, wheres the fun in mending it? http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif

hovmart - n/a
9-Feb-07, 12:09 PM
if you need to race a speed boat, buy one it will be faster

sixpackpert - n/a
9-Feb-07, 01:31 PM
<table border="0" align="center" width="90%" cellpadding="3" cellspacing="1"><tr><td class="SmallText">Sixpack Pert wrote on Fri, 09 February 2007 10&#58;34</td></tr><tr><td class="quote">
<table border="0" align="center" width="90%" cellpadding="3" cellspacing="1"><tr><td class="SmallText">hovmart wrote on Fri, 09 February 2007 10&#58;15</td></tr><tr><td class="quote">
best cure is to slow down




Where's the fun in that??? http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif
</td></tr></table>





More to the point, wheres the fun in mending it? http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif
</td></tr></table>



Was a way of life for me Russ. Race, crunch, mend. Race, crunch, mend... http://hovercraft.org.uk/images/icons/smiley_icons/icon_lol.gif http://hovercraft.org.uk/images/icons/smiley_icons/icon_lol.gif http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif

hovmart - n/a
9-Feb-07, 01:37 PM
100 GPS is a good way of telling how fast you are going and it works up the beach were you will be faster than the speed boat

Russ Pullen - n/a
9-Feb-07, 02:00 PM
<table border="0" align="center" width="90%" cellpadding="3" cellspacing="1"><tr><td class="SmallText">Russ wrote on Fri, 09 February 2007 12&#58;12</td></tr><tr><td class="quote">
<table border="0" align="center" width="90%" cellpadding="3" cellspacing="1"><tr><td class="SmallText">Sixpack Pert wrote on Fri, 09 February 2007 10&#58;34</td></tr><tr><td class="quote">
<table border="0" align="center" width="90%" cellpadding="3" cellspacing="1"><tr><td class="SmallText">hovmart wrote on Fri, 09 February 2007 10&#58;15</td></tr><tr><td class="quote">
best cure is to slow down




Where's the fun in that??? http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif
</td></tr></table>





More to the point, wheres the fun in mending it? http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif
</td></tr></table>



Was a way of life for me Russ. Race, crunch, mend. Race, crunch, mend... http://hovercraft.org.uk/images/icons/smiley_icons/icon_lol.gif http://hovercraft.org.uk/images/icons/smiley_icons/icon_lol.gif http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif
</td></tr></table>



You're not trying hard enough then...



it should read



Race, crunch, exit left, ouch mend... Race, crunch, exit front, ouch mend... Race, crunch, exit right, ouch mend... Race, crunch, exit (how the hell did THAT happen), ouch mend...



Repeat ad infinitum.... http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif

jon_curtis - n/a
9-Feb-07, 02:54 PM
your lucky you didnt hurt your self or your nephew! but we know your not one for any kinda sense when it comes to saftey atters!



your craft is based on a challenger is it not? when these plough in they do it properly!



adding a seperate lift engine will help, but its gona cost you a lot of money, and to be honest, your craft aint really worth it, for the benifit it will get (my opinion only). a plough in should not have cracked your thrust fan??? its goes to show your craft is not very rigid!



there are more than a few things you can do to the skirt design for a start to limit plough in, i was in hospital after a very nasty plough in and will have problems with me knees for the rest of my life, hence why i am now building a BIG craft, with seats that will be less prone to plough!



with regards the skirt design if its straight out of the constructors guide, the skirt will be a load of pants, and plough in will be expected! i have 4 different types of skirt segement on my challenger based craft now, the most important being high pressure segments on the front, these have dramatically increased the resistance to plough, and modifiying the entire skirt design so its not so baggy with the rear of the bags tight against the hull will also help!



also look at your intergrated setup, close tip clearances and the minimum splitter plate distance you can get away with, (taking into account blade movement) will help!

Sean Atterbury - n/a
12-Feb-07, 04:43 AM
Looks like in general a new craft is in order, My craft is not one of the safest and it still puzzles me how the fan hit the duct, as well as the hole in the middle of the hull, unless that was a vacume area and thus sucked it out, not sure.



I like the SEV, not that keen in the prop though, I have never liked the fan spinning around at that speed and with the prop, well jest gets me nervious. http://hovercraft.org.uk/images/icons/smiley_icons/icon_confused.gif



I do however like the construction of it though and the simplicity of the craft in general and the fact that it will make a great all round craft that I can go fishing with as well as cruising, seems that there are no other craft around to race against, cruising is fast enough.



I am a little worried about the skirt, we have unfriendly terrein here and thus the finger skirt is better, but seeing that I do use the craft on water must of the time, the little that it has to go off perfect conditions is rare and the bag as Don said is easier to make, just glue it all together. I will however get it stiched as the guy who made mine is in tent making business and will do a neater better job.



Well, seems I got some thinking to do, I think that for now, will just mend the craft and get the new blades, in the event we decide to go away, there is no point in having the craft and not using it. It can still work a bit longer.



Has anyone got a patern to modify those front skirts of mine?



Thanks http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif

hovmart - n/a
12-Feb-07, 07:35 AM
may be go a bit slower, they tend not to plough in at the bottom end of the speed range, still thats a learning curve

Nickinoue - n/a
12-Feb-07, 07:28 PM
Hi Sean, Glad to hear u thinking of safety.

If you built the craft from the constructors guide if it is an old edition (like mine-1984) it does not include pages on pressure seggies or chipbags. It was quite a surprise when people said to me "ur craft aint gunna work well without skirt improvements" as at the time i had no idea it would be that much of a problem. Luckily i obtained the missing pages *Attached below.

Good luck

Nick

Ian Brooks - n/a
13-Feb-07, 01:57 AM
Hi



The SevTec would be a good choice for your type of operation, in reckon.



The prop/fan is a matter of choice - you can fit a fan if you choose. A well designed propeller and a well designed ducted fan will be comparable in performance



It is a misconception to think that the prop is in some way less safe than a fan... Considering the propeller in my craft - it runs at 50% of the manufacturers recomended maximum blade load. Compare this to a multiwing fan blade, which at 168m/s is running well in excess of the manufacturers recomended maximum - something like 160% (I don't have the exact numbers with me) of blade load. The prop has been qualified for aviation use, I have formal test reports for overspeed, low cycle fatigue, high cycle fatigue, flutter, endurance, foreign body damage, etc for my prop. All very professional.



In addition, look to the failure database - multiwing fans fail very commonly. There a very few prop failures recorded in the CAA failure database.



My point is that you can choose a prop or a fan according to your preferance, but the data does suggest that the propeller is more reliable than the fan.



Ian

Sean Atterbury - n/a
14-Feb-07, 09:33 AM
Thanks for the skirt file, am at another shop so will mail i t to my place, and look at it there.



The prop fan debate, I like the prop but do not like the changing ratio thing, I have just got a good supplier for the fan and belt and to have to look for new one's all over again is more work that I did'nt enjoy in the beginning and do not want to do again. and how funny will a Sev look with a duct and fan at the back hey?



Will sleep on it a bit and make the change to the skirt, then see how ve get on.



Thanks for all the replies.

Russ Pullen - n/a
14-Feb-07, 10:28 AM
- multiwing fans fail very commonly. Ian




You have my interest Ian!



Can you quantify that more exactly? Tho we use Hascons now, we've never had any 'failures' with multiwings, other than those due to external causes (stones/rope ( http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif ) /collision etc.



Russ

Ian Brooks - n/a
14-Feb-07, 11:36 AM
My statement is anecdotal really, and I shouldn't have been specific regarding multi-wing, as I am sure that the evidence relates to a variety of manufacturers.



I'm also sure that you are right when you say that most failures are due to external causes, with foriegn objects being one, and tip/duct collisions being another. Having said that, we should consider that these are 'likely' events in hovercraft use, and in a perfect world the fan/prop will have sufficient design margin (safety factor) to withstand them. In the same way, for an aeroplane, a birdstrike (bird sucked into the engine) is a likely event and an aero engine has to be tested to show that it is able to survive it.



If we were trying to certify our craft to the aerospace authorities, we would certainly have to simulate and survive a blade strike, or otherwise prove that it could not happen.



Having looked at the stress levels, compared to the manufacturers allowable levels, it is clear that many fan installations have much less design margin than equivelent propeller installations, therefore they will be more prone to failure due to some other factor that "triggers" the failure. If we were running more slowly, then an blade would be more likely to have enough reserve design margin to survive the addition stress of the tip strike.



As I'm sure you guessed, I am bringing an Aerospace Engineers perspective to this one, and I could go on. These are some of the factors that influenced my decision to select a microlight propeller in preferance to a rraditional fan for my craft - as an example they have tested it for a "typical" foriegn object (a spark plug) ingestion at full speed - which it survived in one piece although it was damaged badly.



So thats the background to my statement...



Ian

hovmart - n/a
14-Feb-07, 11:45 AM
i know of may damaged props that sucked stones of the strip on take of or landing, if hovercraft hovered at 2000 feet the fans would last a lot longer

Jeremy - n/a
14-Feb-07, 06:45 PM
I've been flying for close on thirty years now. In that time I cannot ever recall a prop failure. I've personally had gloves go through through the prop (twice!), a helmet visor go through (once) and a large crow hit the prop at take off (once). None of these even marked the prop, although small stones have caused a number of leading edge chips over the years.



A microlight prop operates at full power just a few inches above the ground at take off, so frequently sucks in stones, bits of grass, twigs etc. A hovercraft prop is much better protected from such debris, both from being higher up and from the fact that it'll have some sort of guard to keep out the really big stuff.



The only time I've ever had a prop badly damaged was when operating very low over water. I can't say more, but Tony's seen the damage(!). The wooden prop looked as if very large mice had been at it, with approximately 20 to 30% of the leading edge eaten away by high speed water damage, not surprising really, as it had experienced solid water thrown into it at a reasonably high power setting. Even then it all stayed together, despite having big splits down the prop that were just glued back together with a bit of araldite.



You get to see it on telly in September, I think.



Jeremy

jon_curtis - n/a
14-Feb-07, 07:01 PM
i agree regards props and fans arent designed for the operational environment hovercraft put them thru.



going back to the skirt design, and nick hope you havent made your skirt yet, even tho those pages do give you some more info regards the pressure segement design, the pressure flap don't do anything unless the skirt tags are very short and the rear of the segment is tight against the hull. a looped back bit at the end of the flap, an inch or so upwards which will be pushed against the planning surface and give a better pressure segement seal helps

the bagyness of the constructors skirt, i.e. the long bottom tags are its major downfall. you can get away with bringing the contact point in a tiny bit too, it made my craft more stabile for some reason.

Nickinoue - n/a
14-Feb-07, 07:09 PM
Thanks jon,

No i havent made them yet http://hovercraft.org.uk/images/icons/smiley_icons/icon_redface.gif .

I have however redesigned them further so they seal the hull much much better ill take the looping back into serious concideration. By the way, how do you design skirts on Pro Engineer, it has been baffling me for weeks? you can do lofting through different profile shapes and i know you can set coorinate shape connection?

Thanks

Nick

jon_curtis - n/a
14-Feb-07, 09:42 PM
its fairly pants with fabric, closest you can get is with some clever use of the sheet metal package.

a bag skirt is really easy to generate, you can edge rip joints and create a flat pattern. fiddle with the y factor to get no bend allowance!

segments would be hard to model accurately, but never really tried. create datum curves in multiple planes and extrude surfaces to them? or use the sheet metal thingy and shell solids.

Sean Atterbury - n/a
15-Feb-07, 08:36 AM
Well, some intersting points made, I have heard from people that used to fly that the prop does form a little tornado under it that sucks stuff into it, another reason for the ducted fan as there is a lot of loose stuff where the craft is operated.



The water damage sounds bad and would like to see a pic of the damage. http://hovercraft.org.uk/images/icons/smiley_icons/icon_eek.gif



Skirts, I learnt very early on that the craft workes better if the skirts are tight against the hull and so to fiddle the inner flap should be good enough, only time will tell.



Will check in and let you know how I get on.

Sean Atterbury - n/a
9-Mar-07, 04:07 AM
Right, I decided to have a look at the craft last night and determine how much it'l cost to fix, my biggest worry was the stearing console.



However, the damage is not that bad, I held the console in with pop-rivetts and they just pulled out and broke the fibreglass in a few places, quick fix there.



The same thing happened where the hull and deck come together and that too is a quicky.



the duct can be mended but the damage is so little that I am just going to ignore that.



The bottom of the craft has a hole in it about 20 X 20 and that I will just glass over, filled it with foam at the damb and will just sand down the edges to get the new stuff to stick.



The back of the craft is the worst, all around the back corner for about six pockets the edging that the scirts are attached to is off, that will have to be remade of something, I am thinking of using the mold that I still have to maybe make that part over again and then just bond that to the deck, am thinking that this is the best way to go.



Well only got till the 28th so must hurry, want to fix the front skirts too before then, not much time. http://hovercraft.org.uk/images/icons/smiley_icons/icon_confused.gif