Coldpower using R134a vs. R12?

Discussion in 'Propulsion' started by prfesser, Nov 22, 2019.

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  1. Nov 22, 2019 #1

    prfesser

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    Been wondering...the old Coldpower motors used R12 refrigerant which is of course highly restricted and is to be phased out by 2021. The most common replacement seems to be R134a, which has nearly the same boiling point and presumably very similar vapor pressure at room temperature. Is there a reason why 134a couldn't be used in Coldpower motors? Anyone actually done it?

    Best -- Terry
     
  2. Nov 22, 2019 #2

    SDramstad

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    Not legal to intentionally vent R134a. It has no affect on the ozone layer but is a major greenhouse gas.
     
  3. Nov 22, 2019 #3

    jderimig

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    Propane is an R12 substitute for AC anyways.
     
  4. Nov 22, 2019 #4

    cerving

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    You can also use "canned air", difluoroethane... it's much less flammable than propane, with a similar vapor pressure. If you actually have one of the Vashon motors, the little straw on the cans should go right in the valve.
     
  5. Nov 23, 2019 #5

    prfesser

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    I don't have a Vashon motor, in fact I've never seen them except in pictures. Just wondering how difficult it would be to make and fly such a motor. Now that electronic deployment is widely available and quite inexpensive there would be no need for the delay/ejection arrangement used way-back-when (which was rather makeshift from what I've heard).
     
  6. Nov 24, 2019 #6

    cerving

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    It probably wouldn't be hard to make something up, the easiest way to take care of the filling would be to have it filled through the nozzle plug like the Estes Coldpower motors (vs the rubber fill valve on the original Vashon motors). Maybe drill a very small hole through the top of the tank for venting... like a hybrid, you'd launch immediately after filling. The tank could be made of just about anything non-porous, it only has to be able to handle the 70 psi vapor pressure.

    Yes, I've thought about this... I really liked my Vashon rockets when I was a kid.
     
  7. Nov 24, 2019 #7

    Cape Byron

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  8. Nov 25, 2019 #8

    prfesser

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    I wonder what kind of motor might be contrived from a 16 oz beer can (12 oz too, but 16 oz is the same diameter and longer), or one of the big 24 or 32 oz ones. Certainly they could take the pressure and are extremely lightweight. I know I've seen something about a rocket motor and a coke can, but I don't remember where.
     
  9. Nov 25, 2019 #9

    cerving

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    The Vashon motors were aluminum, probably about .025". The 8 oz motor was a C9, the 4 oz motor was a B9. The nozzle throat was 1/8". I think any motor with more than 8 oz would need a larger orifice, or it wouldn't get off the ground. One of those skinny beverage cans might make a good substitute... especially the 8 oz size.
     
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  10. Nov 25, 2019 #10

    Charles_McG

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    Beer cans are spec’d at 90psig max.
     
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  11. Nov 25, 2019 #11

    Alan15578

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    I've been wanting to post something like "Beer loft Revisited". I did this in MR at NARAM 24. Rick Gaff got a photo in Sport Rocketry by calling it a dual egglofter. The key there was a 7 oz. can of PBR, which was a perfect fit inside BT-70. They were sold in 8 packs, but they were not available for long. Today , well for several months, we have had 8 oz. cans of Budweiser, and related brews, sold in 12 packs. I've only seen them at Walmart, but beer distribution is ridiculous, especially in Iowa. They will not fit in BT-70, but today with LMR we could actually fly dual beer loft with a G motor from a small field.

    And yes I have a cold Power rocket but I have not flown it since the good propellant went away.
     
  12. Nov 25, 2019 #12

    AlphaHybrids

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    Where I live there is a dearth of breweries. And with the breweries many of the have small can lines or single crowler canning stations. That might be a good source for a can.

    Edward
     
  13. Nov 25, 2019 #13

    Charles_McG

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    I use 12oz sleek cans. They are 58mm OD. So they’d fit in BT80.

    I’d take a close look at the vapor pressure v temperature curve of your proposed propellants/refrigerants. 90psig might not be a lot of margin - you might have to keep the motors in the same cooler as the cider for afters.

    From a bit of searching, it looks like a beer can would only be good up to about 80F for diflouroethane.
     
    Last edited: Nov 25, 2019
  14. Nov 25, 2019 #14

    djs

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    I wouldn't trust @Charles_McG's knowledge here. I've used a few of his cans, and they have very low ISP (even when they come in a 4 pack cluster). To be honest, the thrust to weight ratio from them is very crappy. With one, I don't even get very far off the couch.
     
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  15. Nov 25, 2019 #15

    Wallace

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    I've personally pumped up a soda bottle to 120psi with a burst disk in the lid and set it in the sun for a couple days. Worked/held just fine. Part of a non-pyro system I've been toying with off and on for more than a year. It definitely has potential, just needs refining (witch means attention/time spent) that my lack of focus has not yet allowed. How high does the pressure in a 20 oz. Bottle of Coke left on your dash in the sun on a 90 degree day get? Do you happen to know the rated pressure for a plastic bottle vs a can? And what is the allowed safety margin?
     
  16. Nov 25, 2019 #16

    Wallace

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  17. Nov 25, 2019 #17

    Wallace

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    20191125_145018.jpg what about something along these lines?
     
  18. Nov 25, 2019 #18

    Wallace

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    20191125_145340.jpg 20191125_145350.jpg Granted, that's a 16 oz vs. 12 oz. can, but they seem to be much heavier/stronger..
     
  19. Nov 25, 2019 #19

    Wallace

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    Guess I',
    m gonna have to make a sacrifice in the name of science and go buy some 16 ouncers..
     
  20. Nov 25, 2019 #20

    Wallace

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    20191125_150042.jpg I have a bunch of these saved also due to not only the apparent strenght but the much more friendly aspect ratio..
     

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