# Air-power? Need a number cruncher! ;-)

**URL:** <https://community.cartalk.com/t/air-power-need-a-number-cruncher/10323>\
**Category:** The Show\
**Created:** [February 7, 2008, 7:04am UTC](https://community.cartalk.com/t/air-power-need-a-number-cruncher/10323 "2008-02-07T07:04:49Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![meanjoe75fan](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/meanjoe75fan/32/552_2.png) [@meanjoe75fan](https://community.cartalk.com/u/meanjoe75fan)\
**Post date:** [February 7, 2008, 7:04am UTC](https://community.cartalk.com/t/air-power-need-a-number-cruncher/10323/1 "2008-02-07T07:04:49Z")

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Ok, this isn’t strictly automotive (well, I guess it IS in the most literal sense!) Basicaly, I like to bicycle: I don’t like hills. I decided to devise a system that could get me, the bike, engine and cargo (call it 275#) up a 400’-long, 8% hill at 15 mph with me helping. Crunching the numbers, I need 0.88hp (0.66kw) output for 227 sec (0.047 kw hr–or 0.063 hp hr, if such a thing exists).  
  
  
  
 Two questions:  
  
 1. Would a 4.5 gal pressure vessel at 200 psi give sufficient range for a pneumatic engine?  
  
 2. My (electric 115v) cut-off wheel puts out 1kw/1.3 hp. Does this mean a air tool is just about right (hope, hope)?

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**Author:** ![B.L.E](https://avatars.discourse-cdn.com/v4/letter/b/848f3c/32.png) [@B.L.E](https://community.cartalk.com/u/B.L.E)\
**Post date:** [February 7, 2008, 1:05pm UTC](https://community.cartalk.com/t/air-power-need-a-number-cruncher/10323/2 "2008-02-07T13:05:32Z")

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Why don’t you just use lithium ion batteries and an electric motor? Just buy a DeWalt Lithium rechargable saw and rig it up to power your bike. It would probably be cheaper and lighter than the air tank idea.

When riding a bike, I find that I acheive the fastest moving average by attacking uphills with everything I got and coasting on the downhills while recovering for the next uphill.

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**Author:** ![Opera\_House](https://avatars.discourse-cdn.com/v4/letter/o/9dc877/32.png) [@Opera\_House](https://community.cartalk.com/u/Opera_House)\
**Post date:** [February 8, 2008, 3:03pm UTC](https://community.cartalk.com/t/air-power-need-a-number-cruncher/10323/3 "2008-02-08T15:03:56Z")

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Air tools have high hp/weight, but quite inefficient. you are better off with electric assist and downhill you can recharge. You had better have some electronics knowledge to understand new DC Transformer technology used in the hybrid electric cars.

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**Author:** ![Seraph](https://avatars.discourse-cdn.com/v4/letter/s/5f8ce5/32.png) [@Seraph](https://community.cartalk.com/u/Seraph)\
**Post date:** [February 8, 2008, 6:04pm UTC](https://community.cartalk.com/t/air-power-need-a-number-cruncher/10323/4 "2008-02-08T18:04:49Z")

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I think the answer to #1 is “No”.

The energy in a pressure vessel can be roughly calculated by Volume_Pressure  
The volume of your tank is ~17000 cm^3  
The pressure drop is 200 psi which is 14 Megadynes/cm^3  
Multiply the two together and get ~2.4_10^11 ergs  
Apply 1 J = 10^7 ergs to get 23800 J  
Apply 1 kWhr = 360000 J to get 0.0065 kWhr

0.0065 kWhr is a lot less then you say you need.

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**Author:** ![Troubleshooter](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/troubleshooter/32/36_2.png) [@Troubleshooter](https://community.cartalk.com/u/Troubleshooter)\
**Post date:** [February 10, 2008, 4:20am UTC](https://community.cartalk.com/t/air-power-need-a-number-cruncher/10323/5 "2008-02-10T04:20:29Z")

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Get off and walk the bike up the hill.