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lazza - n/a
15-Mar-06, 10:43 PM
What are some of the ways people use for measuring static thrust ? I was going to tie a rope to the rear of the craft with some hanging scales mounted in line and then tie the other end to a wall/post/towbar etc but i'm finding it differecult to locate some appropriate scales , let alone some that will go up to 200 - 400 pounds. So what are some alternative ways please.



And the process i briefly explained above what is the "correct" name for those types of scales ? i call them spring or hanging scales but thats obviously not right cause i cant find them under that name hehe.

nickyd - n/a
15-Mar-06, 11:30 PM
Hi Lazza,



The scales you were thinking of using are called a spring balance. If you pop that into google then you should be able to find something.



I have used that method to measure my thrust before, it does get a bit windy for the person doing the reading! I think the balance I used was used to weigh meat but i'm not sure.....



Nick

Sean Atterbury - n/a
16-Mar-06, 04:52 AM
What I did that worked was, take a piece of wide marsking tape and stick it over the slide area where the guage runs, then do your test and OH by the way, take up the slack first, when when you feel the first resistance then only give it plenty.



I found that this works realy well and you can do it over and over, just replace the marsking tape each time.



So, the wife can keep her hear doooo. http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif



Hope this helps, if it sounds Idiotic, Ignor it.

tonybroad - n/a
16-Mar-06, 07:38 AM
i use the spring balance method but another is to position a set of bathroom scales on a wall and push against it -



don't pay too much attention to the actual reading but use it as a comparison i.e. higher or lower than the last time



a quick approximate conversion is 100 Newtons for every 10Kg on the scales



100 Newtons = 22 lbs thrust(approx) if you want to convert



hope that helps



Tony

jar2 - n/a
16-Mar-06, 09:24 AM
One other I would like to add is to make sure that there isn't a wall or other vertical surface close behind the craft. I found that the thrust air hitting a wall showed a higher reading and also generated turbulance. The best thing I found to tie to was a rugby post in the middle of a big pitch!

Nickinoue - n/a
16-Mar-06, 12:12 PM
Why not use some fairly low range newton meters available from a hardware, school suppliers and hook it up to a block and tackl in reverse so a small movement produces a big movement of the end connected to the spring balance, the force is alot less. This means an acurate reading would be taken using cheap available balances. Just a thought. The more bloacks and tackles you use the less force will be put on the the spring balance but the further it will pull. Also remember that the more you use the more friction so it will be less accurate.



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Nick

lazza - n/a
17-Mar-06, 08:56 PM
Thanks , i may end up going with a idea like that yet because i'm un able to find a siutable spring balance so far and my bathroom scales are digital ones that turn off if not pushed within 10 seconds, so either way i will have to find something. I'll keep looking

Nick Long - n/a
17-Mar-06, 09:06 PM
In theory pulleys and ropes could be used to put the spring balance where the driver can see it, or at least out of the air blast. But when I tried it the friction in the pulleys was too great. It might work with very high spec ball bearing ones, but its probably just another source of error you can do without.



I use the ropes set up in a Y to back of the craft to keep it from turning. What you then have to do is to use the rudder(s) to keep the whole assembly in the right direction. You will find though that the steering works backwards. http://hovercraft.org.uk/images/icons/smiley_icons/icon_eek.gif



Nick

lazza - n/a
18-Mar-06, 08:24 PM
Must be some mind reading going on there Nick, i was just about to ask that exact question when i seen your post. http://hovercraft.org.uk/images/icons/smiley_icons/icon_razz.gif

lazza - n/a
20-Mar-06, 05:27 PM
I'm still struggling to find some form of suitable spring balance or similar locally that is cheap enough for the one or two time usuage that it will get, but what i did come across over the net that im curious on some opinions is, this site here http://members.aol.com/riccnakk/hydlc.html (members.aol.com/riccnakk/hydlc.html) its a way to test static thrust using stuff i have availible at work. Do you think its a idea that could be used for measuring hovercraft thrust ? and the bar he has along the top of the wheel cylinder, if that was extra long would that effect the outcome of the reading the longer it got ?



cheers lazza

www.hovercraft.geek.nz

Hovertrekker - n/a
20-Mar-06, 07:24 PM
Larry,

What you want is some industrial hanging scales. A quick "google image" search will turn up a bunch. Here's an example



http://images.google.com/imgres?imgurl=http://www.davco.bc.c (images.google.com/imgres?imgurl=www.davco.bc.ca/images/khs-a.JPG&imgrefurl=www.davco.bc.ca/mechanicalhangingdialscales.html&h=640&w=480&sz=53&tbnid=42r-Q1MsIIltjM:&tbnh=135&tbnw=101&hl=en&start=84&prev=/images%3Fq%3Dhanging%2Bscales%26start%3D80%26svnum %3D10%26hl%3Den%26lr%3D%26rls%3DGGLR,GGLR:2005-39,GGLR:en%26sa%3DN) a/images/khs-a.JPG&imgrefurl=http://www.davco.bc.ca/mech anicalhangingdialscales.html&h=640&w=480&sz=53&a mp;a mp;tbnid=42r-Q1MsIIltjM:&tbnh=135&tbnw=101&hl=en &start=84&prev=/images%3Fq%3Dhanging%2Bscales%26star t%3D80%26svnum%3D10%26hl%3Den%26lr%3D%26rls%3DGGLR ,GGLR:2005 -39,GGLR:en%26sa%3DN



http://www.davco.bc.ca/images/khs-a.JPG



Not cheap though - about $150 USD.

Here's a shot of a Neoteric getting tested for static thrust

http://photos.neoterichovercraft.com/photos/rescue/main/testbig.jpg

lazza - n/a
20-Mar-06, 11:34 PM
yeah thats the sort of thing i have been looking for. I was just hoping (and struggling) to find something a bit cheaper considering it will only get used once or twice, hence why i was curious about that hydraulic set up on that link i posted.

Ian Brooks - n/a
21-Mar-06, 06:28 PM
Yep - the hydraulic set-up will work. To get the force, take the area of the piston (less the piston rod if ther is one) in sq inches and multiply by the pressure in psi, to get the force in lbf.



Actually - it would be cleaner to use a pnuematic ram and pressure gauge if you can get one.



Ian

sixpackpert - n/a
22-Mar-06, 06:03 PM
Used to work in the weighing industry, so try this, will be dead accurate and should be cheap. Sold quite a few of these systems and they are dead good.



Best thing I can think of is to ring a scale calibration and sales company and ask to hire a load cell and an indicator. An S-Type load cell would be the best as you can screw eye-lets to each end of it to attach your rope to. Make sure you have a rough idea of how much thrust you have so that you can get an appropriately rated load cell (they're usually rated in kg 50, 100, 200, 350, 500 etc etc). The load cell would have to be wired to measure in tension NOT compression but that's no problem, just a case of swapping two wires around in the plug that goes into the weighing indicator. Most indicators have a peak hold function on them, this means that they will show the highest value attained.



The joy of a weighing indicator is that if the wire from the load cell is long enough you can have it in the craft with you!



Here's a link to the type of load cell I am thinking of.



http://www.vishay.com/test-measurements/transducers/s-type/ (www.vishay.com/test-measurements/transducers/s-type/)



A whole load cell and indicator system doesn't cost much to buy so hiring one shouldn't be that expensive.