Page 1 of 2 12 LastLast
Results 1 to 8 of 16

Thread: Intergrated design help please

  1. #1
    Less than 10 posts so far!
    Join Date
    Sep 2009
    Posts
    7

    Question Intergrated design help please

    Ok so here in the states (at least in north carolina) we have to complete a senior research project to graduate high school, i am now a junior. I have chosen a racing hovercraft build.
    My basic design is a 10'6"x6'6" craft although if i could get away with something a bit smaller that would be good too (by good i mean cheaper). I've calculated that for an integrated system i need 5095cfm for lift alone. If this has to be 33% and the other 66% is thrust then i need a total of 15,285cfm from my fan to power my lift and thrust. And since i plan on using a 40hp 8000rpm engine i would need at least 1700ft/s tip speed on the fan.
    My dad owns a industrial supply warehouse where they sell fans. I have found a 4 blade 15,300cfm fan but it doesnt show the tip speed. What i dont really understand is that it uses a 1hp electric motor run on a pulley system that powers the fan. If a 1hp motor can provide the 15285cfm that i need than why is it everything i find says i need at least a 22hp engine? would a 1hp engine not suffice if it can move 15,300cfm? please answer this question for me.

    My Build: I am using 2" rigid foam insulation for my core covered in fiberglass (6oz?) for structural integrity and a section of steel towards the back to support the engine and fan weight. I have not decided on an engine or fan yet but i have a 500cc 1972 suzuki motorcycle engine that im debating on using. Since i'm on an extreme budget i cannot afford to order rubber coated nylon for my skirt so i am using heavy duty pocho sewn together with vinyl shower curtain for my skirt (segmented). I am using a handlebar steering sytem with a twist grip throttle and tandem style seating for the driver +1 passenger.

    Please give me any helpful advice as it is grately appreciated and i wont have to go back and change anything since i havent started the build yet.

    By the way it would be awesome if i could use this build for the occasional race

    I really like this concept
    http://www.originalwonders.com/wp-co...rcraft-web.jpg

    But i think attaching the skirt and providing enough clearance would be a true pain so i plan on sticking with the traditional hovercraft body style

    All constructive critism is appreciated

    Thanks! =]

  2. #2
    Extremely active > 250 posts!
    Join Date
    Mar 2009
    Posts
    283

    Default Re: Intergrated design help please

    dont use the fan from your dads DIY shop. it will breakup chucking bits of nylon all over the place. me thinks you have your sums wrong if you think a 1hp fan will do the job.

    http://www.multi-wing.com/zseries/index.htm

    4 z or 5 z depending on the size of the duct.

    i think it would be a good idea for you to buy a copy of the hovercraft constructors guide, which will show you a simple hovercraft design, that will fly around a lake.
    Jon

  3. #3
    Less than 10 posts so far!
    Join Date
    Sep 2009
    Posts
    7

    Default Re: Intergrated design help please

    How much are the z series impellers?

    And by the way it is not a "DIY" shop. It is a business that import industrial steel blade fans 48" in diameter to cool machines in factories. they are electric and belt driven by a 1 hp motor and outputs 15,300cfm. an 800 lbs hover only needs 5095cfm for lift alone. this is 33% the other 66% plus that 33% for lift = 15,285cfm.
    If you misread it is an industrial steel bladed fan and outputs 15,300cfm.
    Meeting and surpassing the requirements. And finally this is not a project to build a "cruise around the lake craft" it is for a fully operational 40mph race craft. Hence i do not need the simple plans. I'm and engineering major and have fully calculated the mathematics and designs for the craft.
    my only question was that since this fan outputs 15,300cfm on a 1hp motor, why would i need anything larger? i only need 15,285cfm the lift and thrust the craft.

  4. #4
    Extremely active > 250 posts! Club Member firth5731's Avatar
    Join Date
    Mar 2009
    Posts
    343

    Default Re: Intergrated design help please

    sounds like you already know everthing
    infamy ,infamy, they`ve all got it infamy

  5. #5
    Less than 10 posts so far!
    Join Date
    Sep 2009
    Posts
    7

    Default Re: Intergrated design help please

    No i just dont get why a 1hp motor and this fan can provide 15,300cfm but when my hovercraft only needs 15,285cfm i need a 40hp engine. Im sure theres some logic behind it, i just want to know it

  6. #6
    Forum God > 400 posts Club Member
    Join Date
    Mar 2009
    Posts
    978

    Default Re: Intergrated design help please

    You haven't mentioned cushion pressure in your calculations so far. Taking your 800lbs weight (including payload) on a craft 10.5ft*6.5 ft = 68 sq ft (ignoring skirt toe-in) that would give a cushion pressure of 11.7lbs/sqft. According to my faded 30 year old copy of the design handbook you need a flow rate (in cu ft/min) of 60*3.5*craft length * sqrt(cushion pressure) which would be 7500 cuft/min. So you need to find a fan that delivers 7500cfm at (at least) 11.7lbs/sqft cushion pressure. - in fact at a higher pressure because of the losses you'll get in the duct between the fan and cushion.
    I can't comment on your industrial fans but you do need to look at the flow rate it will deliver at a given pressure. Most craft of this size use between 5 & 25bhp for lift - racers tend towards the high end of that range. Most integrated craft allocate around 20-30% of their fan area for lift.
    Personally I'd be a bit nervous about a steel fan because of the damage it might do in the event of a failure but you'd need to check with the Hoverclub of America what their rules are on that.
    Good luck with your project.
    Keith
    Last edited by Keith Oakley; 10-Sep-09 at 07:21 PM.

  7. #7
    Less than 10 posts so far!
    Join Date
    Sep 2009
    Posts
    7

    Default Re: Intergrated design help please

    Here is the link to one of the fans my father sells

    http://www.globalindustrial.com/gcs/...web#gridAnchor

    As you can see the 48" diameter steel blade fan uses a 1hp motor and provides 15,200 cfm. as you mentioned i only need "you need to find a fan that delivers 7500cfm at (at least)" This fan provides that with only 1hp. Im just trying to figure out how 1hp provides twice of what i need and yet everything ive found say that i need a 20hp engine.

  8. #8
    Forum God > 400 posts Club Member
    Join Date
    Mar 2009
    Posts
    978

    Default Re: Intergrated design help please

    The technical specs your looking at are presumably at no back pressure. You need to know what flow rate they will deliver at (for example) 11.7lbs sqft back pressure. Thats at least part of your conundrum. I'm sure more fan techy folk will be along to explain.
    Keith

Similar Threads

  1. New engine design
    By Paul Fitz - n/a in forum General Forum
    Replies: 2
    Last Post: 21-Dec-07, 02:17 PM
  2. Intergrated Duct Construction
    By Sean Atterbury - n/a in forum General Forum
    Replies: 2
    Last Post: 28-Jul-06, 08:56 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •