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RE: 25cc for lift, 40cc for thrust... - 2/27/2004 11:52 AM   
wossname



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From: Midlands, UNITED KINGDOM
Status: offline 		I have spent the last year or so trying to perfect my hovercraft designs.

Some quick tips:

Length : Width ratio - best between and 3:2 and 4:3 (IMHO)
Weight - a contentious issue, light is good but tends to get thrown around a lot, heavier is more stable, you get a better ground seal but can be slow.
My electric craft hull weighs about 1.4 kilos unladen, the rubber skirt (by far the hardest part of the build) brings it to about 1.6 kilos. Then there's batteries, esc, motor, radio etc. All in weight about 3.5 kilos. Quite substantial for a 600x460mm plan.

Made it out of 6mm plywood and a hot glue gun for the joints. I'm using a RS545 motor and a 228mm (9inch) prop for both lift and thrust.

Low center of gravity is important.

Should be finished this weekend hopefully.

< Message edited by wossname -- 2/27/2004 8:53:02 AM >


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RE: RE: FOR SALE - 2/29/2004 8:56 PM   
Crazy Bird


 

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From: Herent, BELGIUM
Status: offline 		Hi,
I'm busy with my hovercraft.
I'm using a .35 os for lift for the moment.
And it works, but I just want him to go higher.
It's just that the surface has to be extremely flat.
Are there ways to get him higher?

Thanks.

I'll try to get some pics of it and post them.

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RE: FOR SALE - 3/2/2004 4:22 PM   
aljsk8


 

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From: wigan, UNITED KINGDOM
Status: offline 		I NEED HELP

IM BUILDING A R/C HOVERCRAFT
PLANS ARE FOR A VACUUM FORMED SHELL
RIP STOP NYLON SKIRT

I HAVE A TINY E.S.C
1 SERVO
RX
2 400 SIZE MOTORS
1000MAH 9.6V BATT PACK

TOTAL WEIGHT CALCULATED - MAX - 1000g

IVE MADE A CARD MODEL
WHICH WORKS WELL ON LAMINATE FLOOR
BUT NOT OUTSIDE

I DONT KNOW IF ITS THE CRAP SKIRT IVE MADE
OR THAT 400 MOTORS AND 5 INCH PROPS ARNT GOOD ENOUGH
IM GONNA KEEP TRYING WITH CARD MODELS TILL I GET IT RIGHT
ID LOVE TO SEE THE UNDERSIDE SOME OF THE KITS LIKE THE KINETICS SK5
OR THE COMMANDO THATS ON THE QUICKTECH HOBBY SITE

WHAT MOTORS DO THEY USE?

PLZ HELP

ALEX

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RE: Hovercraft - 3/2/2004 6:22 PM   
aljsk8


 

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From: wigan, UNITED KINGDOM
Status: offline 		DO U HAVE ANY PICS OF THE UNDESIDE?

WHAT MOTORS DOES IT USE?

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RE: RE: FOR SALE - 3/2/2004 9:33 PM   
tegwin



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From: malvern, UNITED KINGDOM
Status: offline 		Try using three or four blade props and lower RPM so less batteries.

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RE: FOR SALE - 3/2/2004 10:14 PM   
Hover Mal



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From: Basingstoke, UNITED KINGDOM
Status: offline 		RE IVE MADE A CARD MODEL WHICH WORKS WELL ON LAMINATE FLOOR BUT NOT OUTSIDE

I have a couple of questions for you Alex, what kind of skirt (bag, segment or C) and do you run both motors from the same battery pack and if so how are they wired?

At a guess I would say you have problems with the skirt (laminate floor is a very nice smooth, low friction, flat surface). If you haven't already, take a look at Hovercraftmodels.com, it may help.

If you are using a C skirt then I can help more, I have a bit of experience resulting in a single motor electric hovercraft that works (est 30mph) on most surfaces including grass. I had similar problems, working well on kitchen floor but very bad on car park until I improved the skirt.

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RE: RE: FOR SALE - 3/2/2004 11:22 PM   
struts


 

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From: Rye, East Sussex , UNITED KINGDOM
Status: offline 		have a look at www. modelhovercraft-tech.com this guy has been building model and full size for years, and if anybody knows about skirt design its him. check his site.

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RE: FOR SALE - 3/5/2004 2:38 PM   
aljsk8


 

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From: wigan, UNITED KINGDOM
Status: offline 		both motors are run from a 9.6v 1000mah AA batt pack

they are wired in paralell
lift fan is direct from the battery via a switch
thrust fan is through the speed controler

ive tried about 4 card models
all about 14x8"

i get different things happening

2 main probs are - skirt gets pushed out to the side because of weight
with skirt mounted more underneth the craft wobbles around everywhere

ive looked at ALL the websites

nothing gives cross sections through or views from under

both lift and trust are 400 motors
with 5/6" 2 blade props

the thing goes rapid if i hold the battery up off it

the whole thing weighs about 800g

im using binbags for test skirts - a bag skirt

not sure what a c skirt is???

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RE: FOR SALE - 3/5/2004 9:49 PM   
Hover Mal



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From: Basingstoke, UNITED KINGDOM
Status: offline 		Motors in parallel should be OK .. 9.6v each (in series it would be 4.8v I think).

If this works there should be a pic here of Bag skirt/C skirt
[image][/image]

There are plans on some sites of bag skirt models, not sure if they show skirt patterns but worth a look (I'm a C skirt person so can t really much more sorry).

Can you post a picture of your skirt.

Not sure if I got the image thing working, so there may or may not be a pic of my hovercraft here.
[image][/image]

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RE: FOR SALE - 3/7/2004 9:15 PM   
struts


 

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From: Rye, East Sussex , UNITED KINGDOM
Status: offline 		A skirt for any hovercraft to function properly has to be designed around the inner and outer skirt fix points and includes the all up weight and mean and max skirt areas to be calculated , there are 3 well known skirt types:Bag skirt ( C skirt )
bag and Finger skirt
Finger skirt
Forget c skirts, the correct names are above., all other skirt types pale into history including the jupe skirt,another type of skirt.
Let me give you guys out there some advice, if you are trying to design or build a model hovercraft you have to know all of the criteria for design.
A model hovercraft behaves exactly as its full size counterpart.
one more thing! unless you are able to seal ripstop nylon, ie coat it with a rubber solution, you will lose valuable air from your cushion,as ripstop is permeable.
Have a look at www. modelhovercraft-tech.com

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RE: 25cc for lift, 40cc for thrust... - 3/7/2004 9:24 PM   
struts


 

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From: Rye, East Sussex , UNITED KINGDOM
Status: offline 		have a look at post 110.

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RE: FOR SALE - 3/7/2004 9:25 PM   
struts


 

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From: Rye, East Sussex , UNITED KINGDOM
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RE: hovercraft go - 3/7/2004 9:30 PM   
struts


 

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From: Rye, East Sussex , UNITED KINGDOM
Status: offline 		You say you are using a .40/6.5cc glow , can you tell me your models dimensions.? Read post 110.

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RE: RE: FOR SALE - 3/7/2004 9:34 PM   
struts


 

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From: Rye, East Sussex , UNITED KINGDOM
Status: offline 		Is the gemini acv able to fly over grass ?. and have a look at www.modelhovercraft-tech.com

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RE: 25cc for lift, 40cc for thrust... - 3/7/2004 9:41 PM   
struts


 

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From: Rye, East Sussex , UNITED KINGDOM
Status: offline 		Your 25cc mc cullough is good enough for lift and thrust, with forced air cooling, your model dimensions should be around 120cmx60cm.
You do not need a bigger engine,but if you use it , it will only provide extra power to get you out of trouble should you need tp. checkout www.modelhovercraft-tech.com.

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RE: FOR SALE - 3/7/2004 11:54 PM   
Hover Mal



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From: Basingstoke, UNITED KINGDOM
Status: offline 		Struts, instead of telling us we don't know enough, perhaps you could solve aljsk8's or provide some useful/constructive advice/suggestions?

BTW.
A bag skirt is very different to a 'C' skrt the 'C' skirt is much more efficient and effective as it provides a much better plenum (cushion of air). See diagram below (seen before but now with labels ). The explanation is far too long for here involving aerodynamics and Bernoulli. The bag skirt is very popular and can work well.

This post is not meant as an attack in any way, more a request for more open minds. Experimentation is a very powerful tool .

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RE: RE: FOR SALE - 3/8/2004 12:12 AM   
rcrd


 

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Status: offline 		Hi - I've been having a play with the movie at http://www.onyabike2in1.co.uk/100_0135.mov and cut out the best bit to make a smaller file of the Gemini in action on grass. The movie belongs to the guys at onyabike2in1 not me. The smaller file is at http://homepage.ntlworld.com/rcl276/2in1geminimovie.mov for now, though I wont be leaving it there forever.

Richard

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RE: FOR SALE - 3/9/2004 1:39 AM   
struts


 

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From: Rye, East Sussex , UNITED KINGDOM
Status: offline 		Im not saying you dont know enough ,Im merely trying to give you some advice and point you in the right direction,based on years of experience with full size design, and 14 years of model design from the drawing board up so I am sorry if I have offended you guys, but my advice is sound and could give you the answers you need, incidently Mal, the 'C' skirt may give you max cushion, but not max stability nor stabilised centre of pressure.! The answer to your problems lies in a properly designed skirt.
I do have to say that in all the skirts I have designed the most efficient is the Finger, but is easily displaced by grass, the bag skirt is excellent for higher speeds , and a bag/finger combination gives increased hoverheight and flexability, Imsorry Mal but the 'C' in my opinion is regalated to history , but then you go with what you like, and I would never use a 'C'.
So I will open my big mouth,and take your advice and try to help.

(1)To begin with ,decide on the size of your hovercraft both length and beam, in fact let the beam be slightly over half the length.
(2) calculate the AuW.
(3) calculate the cushion area.
(4)decide on the hoverheight.
I hope this helps to begin with.

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RE: FOR SALE - 3/9/2004 3:41 PM   
Hover Mal



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From: Basingstoke, UNITED KINGDOM
Status: offline 		No offense taken Strut, I was just correcting your claim that a 'C' skirt was a bag skirt.
I'm not sure I would agree about a bag skirt providing max stability and stabilised centre of pressure because of Bernoulli, but its good that people do different types of skirt, then we can compare.

How well does your bag skirt work on grass? Usually the are not so good but with the power of 22cc engine I guess it should work. 'C' skirts are really, really bad on water (surprised you didn't mention that bit ).

People work in different ways, some research every fact about actual hovercraft and use the exact details, other (like myself) use the basic concept and develop/experiment. After all how did Sir Christopher Cockerel do it . But the most useful part is discussion/sharing of ideas and findings.

Btw, at the weekend I saw a model with a bristle skirt (bit like a carpet) and it worked really well.

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RE: hovercraft go - 3/9/2004 4:58 PM   
kf01


 

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Status: offline 		The hovercraft is approximately 72cm long and 37cm wide.

After seeing the designs for the bag type skirt i think i might have to make some modifications to the hull to allow that type of skirt to be used. Should the air be directed in to the skirt and from there to the under side of the hull or can it be directed under th ehull and from there inflate the skirt?

Hopefully some pics are attached.

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RE: hovercraft go - 3/10/2004 3:49 AM   
struts


 

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From: Rye, East Sussex , UNITED KINGDOM
Status: offline 		there are two types of flow entry and they are full flow and no flow, the full flow feeds all of the lift air into the skirt and then into the cushion.
The no flow feeds the air in to the loop skirt via scoops at the tios of the blades.Direct the air into the skirt and thence into the cushion, your hull length beam ratio is ok ,now all you have to do is sort out the skirt.start by deciding the hoverheight.

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RE: FOR SALE - 3/10/2004 4:48 AM   
struts


 

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From: Rye, East Sussex , UNITED KINGDOM
Status: offline 		Hiya Mal !
Please dont confuse brute force with proven designs, I use my skirts suitable for the terrain they will be running on , and do not depend upon the size of the engine, and as for the bag skirt performance over grass ,well I have to say that from day one Ive had no problems, my skirts inflate to the correct pressure and according to skirt tailoring,and I use finger , bag and finger and bag skirts, infact turbulant and laminar flow play a vital role in the craft skirt performance, and I also use compartmenting in my skirt designs, just as the fullsize craft do, and skirt shift. Sir Christopher Cockerall was a geat man and inventer, but all of the hard work has been done by him , we have just refined the design, and aerodymas and bernis theorom are also subservient at this stage , the work has been done. 50 years on our approach to hovercraft should be the same as for aircraft, the experimenting is done the calculations have been proven, it just needs for us to build a hovercraft. my intakes are designed properly, the hoverheights are correct and the angle of the skirts in relation to the hull are also correct,my c of g's are bang on, and the craft reach speeds of 40 to 50 mph and fly in windy conditions without being flipped over, and a video to prove it, model hovercraft have arrived if you like to say that , we dont have to grope around in the dark anymore, the info is there the technology is there.Btw my model hovercraft is the only model hovercraft to fly across the goodwin sands 5 miles out in the English channel. Hovercraft design technology has , up untill now being out of reach, but not any more,and we dont have to design a complete new craft ,just build a model of the fullsize job.I have a complete library of all of the acv's that I would like to build, a lifes work! and to booth my own fullsize hovercraft . You would be surprised at some of the mouldings I have in my workshop. So if you guys need some help ,or if you think I can help you just post it. I will try!.

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RE: FOR SALE - 3/10/2004 3:45 PM   
Hover Mal



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From: Basingstoke, UNITED KINGDOM
Status: offline 		Hi Struts,

I get the impression you are not a fan of innovation or experimentation, or perhaps you just think that your craft can not be bettered?

Proven design and not just brute force .. hmm so are you confident you could produce a single motor electric model with a bag skirt that would beat mine in areas of speed and agility on concrete/tarmac and grass? (Speed 700 motor, 10 cell 12v battery). It would be very interesting to compare bag and C skirt and different craft design with same motor and power. Are you up to the challenge?

Btw I dont think my craft is the best, its different.

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RE: FOR SALE - 3/11/2004 1:49 AM   
struts


 

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From: Rye, East Sussex , UNITED KINGDOM
Status: offline 		Sorry Mal
Ive not come on here to better anyone , nor am I interested in electric hovercraft, nor do I think that my craft is better then anyone elses,these are your words not mine, ( did I say that I could or would build an electric hovercraft )sorry Mal the last electric acv I played around with was about 15 yrs ago and I have no wish to do so again, so Im not interested in your challenge,sorry to disappoint you.
Regarding innovation and experimentation, Sir Christopher did it all back in 1959, so I dont need to experiment nor innovate, nor did I come on here to bandy words with you, Ive come on here to help, but it seems that it is not needed.

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RE: RE: hovercraft go - 3/11/2004 1:59 AM   
tegwin



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From: malvern, UNITED KINGDOM
Status: offline 		I must argue against what you are saying "struts" christopher cockeral may have invented somethign truley amazing in 1959, but technology has advanced somewhat since his day. This new technology needs people like "hover mal" to embrase it and use inovative ideas to create the hovercraft of 2004 instead of relying on ancient methods.

One of the reasons that there are so few full size hovercraft in service is the simple reason that people refused to introduce new ideas.

I dont mean to insult anyone, but this had to be said

No hard feelings

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