Vashon Cold Propellant Rocket Motor

All I remember from my teenage brain was that it involved some sort of wax paper disk.

Koen

I think there was a little chamber in the front of the motor... it was connected to the main propellant chamber through a fitting containing a little stack of porous disks which could be lengthened or shortened to change the delay time. When the motor was filled with propellant (Freon-12), the front chamber would become pressurized with vapor, and a diaphragm/piston on the front would be pushed forward, engaging a clamp to hold the nose section on. (I think the clamp was a dished piece of spring steel, shaped so that when its middle was pressed forward, tabs around its rim would extend sideways and press against the I.D. of the forward airframe.)

Once the propellant had been released during thrust, the pressure trapped in the forward chamber would take some seconds to bleed off through the "calibrated leak" provided by the stack of porous disks... eventually, the pressure would fall enough that the clamp would release the forward airframe and allow it to separate. (I don't think there was any specific "ejection" per se.)

I never flew one; the above is what I remember from reading the catalog many years ago.

-dave w

just remember if you get caught flying one its a $10,000 fine :-)

I w> >

implemented

R134a? should work just fine...

-dave w

David - Your description is accurate for the original Vashon design. There was no active ejection for the parachute, the upper body tube, actually a paper body tube taped to a short section of aluminum tube for the retention clamp to grip, would simply fall away, and the parachute would "fall" out.

Estes later redesigned the system. The engine was inserted into a full length paper tube rocket, much like a normal model rocket. A spring loaded piston tube that slip fit between the body tube and the motor was inserted into the front of the rocket. The motor used a thrust ring glued to the rear of the motor since the piston needed forward clearance. The retention mechanism was now a rubber bladder in the front section of the motor that protruded through several round holes in the side of the aluminum motor tube. The bladder was inflated when the engine was filled with Freon. The bleed mechanism was internal to the motor and not accessible, probably a small hole, so the delay was no longer adjustable by changing the number of paper disks. When the bladder was inflated, it gripped the piston, and when deflated, the spring loaded piston ejected the parachute.

Although I had both, I never flew the Vashon rockets. I did fly the Estes version. They were fun, but the performance didn't compare well to regular model rocket motors.

I still have a couple of each of the Vashon and Estes motors, and the original instructions for each (but no Freon-12). If anyone wants to see more detail, I can scan and email the instructions that have detailed drawings of each system.

It's interesting to note the early use of a piston and a rear motor mounted thrust ring in the Estes system!

TomF

implemented

R134a should most likely work just about as well - the vapor pressures are nearly identical at ordinary ambient temperatures. (It might be possible to fill the system from cans of the "non ozone depleting freeze spray" from Radio Shack.)

-dave w

I think the regulations changed recently to require the new refridgerants handling to be the same as all the others. Watch for increased prices and yes the $10,000 fine.

Dennis

But note that R134A also does nasty things to the ozone layer, and there is discussion of banning it too (it's not nearly as bad R12, which is why it has replaced R12).

fetchen:

I would like to see some scans of the estes system if possible...... you can email them to the email on this post.... 1mb limit so you may need to zip anything you seen,,,

After I made this post I found some resources online that had diagrams, pics and even descriptions of the Vashon version...

thanks to all who replied...

What got me to thinking about the vashon and estes parachute ejection assemblies was a thought that they might somehow be adpated for use as a passive ejection system for hybrid rockets....no pyrotechnics....what do you engineering types think? use some of the nitrous to do either the vashon or estes ejection method?

I was thinking of combining the two ideas....for example the original vashon method squeezed up against the parachute tube and just feel off....how about some kina combo device that squeezes and whe the pressure is released then the estes method is activated, ie a spring is released? the best of both worlds...

shockie B)

Still illegal, though.

You may be thinking of R22, which has a nonzero Ozone Depletion Potential rating, but much less than R12: it's still popular for air conditioning and similar equipment, but is scheduled to be phased out for new equipment after 2010; although it can be used to service previously constructed equipment until 2020. R134a is one of the non-ozone-depleting "long term alternative" refrigerants... even the ones which don't deplete ozone at all are still considered to be "greenhouse gases".

I'm not sure what the EPA thinks of those circuit cooler" cans that Radio Shack still sells for testinng electronics... these days they contain R134a instead of R12.

-dave w

Rats. So the stuff we use now sucks too?

It is a $10'000 fine for individuals and for companies its $100'000, it does not matter if its a CFC, HFC, HCFC, They are classing greenhouse gasses (134A) in the same catergory as ozone depleting substances.

Remember to follow the MONEY!! The EPA has become a self supporting agency. Its fines and fees support itself. As the ozone depleters (12,22,502,ect.) run out or companies fase them out the fees and taxes on new and recycled refridgerants will continue to dwindle. Example R-12 was well over $50 a pound and is now coming down because there is no demand. So now the EPA is making very little off of it. So if we now include the new safe refridgerants we now have a funding source for who knows how long.

Dennis

carbon-containing fuel...)

There's a mix of isopropane and butane that has the same pressure curve as R-12 (and even the same heat capacity per mass) - I think it's about 80/20 isopropane.

Some fly-by-night repair shops were actually using it in older car air conditioners a while back - generally without the customer's knowledge. It works great until there's a leak under the hood, then it's 'To the moon, Alice!' Several of these guys are doing time in various places...

Of course, as noted elsewhere in this thread, hydrocarbons are also greenhouse gases. Never mind that the major component of greenhouse gas in the atmosphere is water vapor, which accounts for somewhere around 95-98% of the greenhouse effect, and is pretty much non-negotiable on a planet that's

Never happen. EPA is too good at guilt-tripping politicians. No congresscritter wants to risk some opponent/reporter asking him why he voted to "Weaken Environmental Protections". They've sure, for a relatively recent agency, carved out an entrenched power niche.

-dave w

I wasn't thinking of R22, I was thinking that R134 had a non-zero ODP. But you're right, it doesn't.

Yeah, the EPA specifically lists hydrocarbon blends as "not acceptable as alternatives for CFC refrigerants" in most applications... and the compressor manufacturers are singing the same tune. I think it's being driven by the liability lawyers as much as anything: if you fill your air conditioner with propane (similar boiling point to R22) and it leaks and you have a propane fire, they want it to be damn clear that it wasn't _their_ idea.

-dave w

R-134a is also used as propellant in asthma inhalers. It has zero ozone depleting potential since it is a hydrofluorocarbon (HFC). All "big" molecules have substantial infrared cross-sections. The fact that R-134a is a 'greenhouse' gas, while true, is not particularly noteworthy - most gases you use or come into contact with are 'greenhouse' gases, this includes the ones you are exhaling (i.e. CO2 and H2O, sometimes CH4), N2O, etc. The famed combustion chemist Sidney Benson has a few remarks about global warming toward the last half of this paper that warrant reading:

Brad Hitch