Something that floated through my mind today... Can you...

[K'Tesh]

Ok... So, getting your HPR certificates depend on whether or not you can build a rocket that can survive a launch with a HPR motor (and know the rules for launching such a rocket). What about this... Can you cert on a water rocket?

If you can produce enough NS to replicate a the required HPR motor, pass the test(s), and can safely launch, and recover it in a safe and reusable manner, is there anything that prevents you from using DiHydrogen Monoxide as your propellent? OK, so I know I'm technically violating the propellent rules, but is a fairly safe fuel (barring certain rivers and lakes and their propensity to catch fire), and is required by all lifeforms we are aware of.

 

[tim cubbedge]

Dude you gotta get out of China!

 

[ttabbal]

I don't think water rockets violate the DIY propellant rules.

One of the certification rules is that you have to use a certified motor. I don't know of any water motors that have been tested and certified by NAR/TRA, so I don't think you can.

So the next question is, if they did certify one, could you use it? I don't know on that one.

 

[cerving]

As far as certing on a water rocket, my guess is no. It's technically not a model rocket or a high-powered rocket, no matter how big it is.

RocSim will do water rocket sims, so you should be able to answer the question of whether or not a water rocket motor is high-power (> 160 n-s total impulse) with a bit of fiddling. Apogee did a newsletter on water rockets ( https://www.apogeerockets.com/education/downloads/Newsletter219.pdf ) and had an impulse chart of a 2-liter rocket; it turns out that it equates to about a full D, like a D300 (yes, you read that right... it fires for about .07 secs.). If you stacked eight of these you "might" get to the HPR range, I'd be willing to bet that it doesn't scale linearly, though. There's some interesting stuff on uswaterrockets.com, but it looks like most of it is several years old at least. The highest altitude that they managed to get was about 2,000', and that was with a really big rocket with just below the bursting pressure of the bottles.

 

[Nytrunner]

Never underestimate the power of soda bottles wrapped in glass-fiber reinforced packing tape B)

I'm interested in the staging mechanism of that guy that did the 3-bottlestack cluster staged to one bottlestack.

 

[mccordmw]

As far as certing on a water rocket, my guess is no. It's technically not a model rocket or a high-powered rocket, no matter how big it is.

RocSim will do water rocket sims, so you should be able to answer the question of whether or not a water rocket motor is high-power (> 160 n-s total impulse) with a bit of fiddling. Apogee did a newsletter on water rockets ( https://www.apogeerockets.com/education/downloads/Newsletter219.pdf ) and had an impulse chart of a 2-liter rocket; it turns out that it equates to about a full D, like a D300 (yes, you read that right... it fires for about .07 secs.). If you stacked eight of these you "might" get to the HPR range, I'd be willing to bet that it doesn't scale linearly, though. There's some interesting stuff on uswaterrockets.com, but it looks like most of it is several years old at least. The highest altitude that they managed to get was about 2,000', and that was with a really big rocket with just below the bursting pressure of the bottles.

If you think that's impressive, you should see the Air Burst air rockets? I bring those to launches. It blows all its thrust in fractions of a millisecond and launches a rocket >1000'. I can't begin to guess the rating on that membrane burst thrust. Two red membranes burst at about 120 psi. Sounds like a Rifle blast and the rocket disappears. :-D
Kids love it.

 

[FredA]

Commercial motors are required for certs on the basis that they are a known and consistent impulse.
Without TMT (and the NAR, CAR equivalents) testing your propulsion is "unknown" and therefore harder to prove you met the impulse required for the cert level.

One could argue that you could use altimeter data to extract the motor performance, but that's too much effort for the certifying entity.

 

[qquake2k]

Imagine the air pressure needed to push the water out at HPR thrust.

 

[REK]

Motors only certified by NAR and TRA are allowed to be used for certification flights. Sorry, but it wont work.


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[ttabbal]

For the sake of argument, say there were a certified water/air motor (would that make it a hybrid?)...

Is there any reason you wouldn't be able to use it to certify?

 

[cerving]

Imagine the air pressure needed to push the water out at HPR thrust.

A 2L water rocket has 300 n average thrust, that looks HPR to me. Of course, you blink and you miss it...

 

[rstaff3]

Average thrust may make it HPR, but you can't cert with a >80ns G either. 'Burn' time's are very short. I may have to see what the high pressure large ones from Air Command are rated at(?)

 

[Steve Shannon]

For the sake of argument, say there were a certified water/air motor (would that make it a hybrid?)...

Is there any reason you wouldn't be able to use it to certify?

At least for now, the only oxidizer allowed in a hybrid motor is nitrous oxide.
However, the reason for certification is laid out in NFPA 1127 in order to pave the way for people to use rocket motors as defined by NFPA 1127. There's no such need for water rockets.
Several years ago NAR worked on a safety code for water rockets. I've not heard of it in a long time though.


Steve Shannon

 

[dhbarr]

At least for now, the only oxidizer allowed in a hybrid motor is nitrous oxide.
However, the reason for certification is laid out in NFPA 1127 in order to pave the way for people to use rocket motors as defined by NFPA 1127. There's no such need for water rockets.
Several years ago NAR worked on a safety code for water rockets. I've not heard of it in a long time though.

What subsection is that for NOS? I'm genuinely curious why that's okay but a solidox liqfuel wouldn't be kosher.

 

[Steve Shannon]

What subsection is that for NOS? I'm genuinely curious why that's okay but a solidox liqfuel wouldn't be kosher.

5.2.1. With the exception of nitrous-oxide hybrid rocket motors, liquid rocket motors are prohibited at Tripoli Research Launches. BOD approval may be given for very well documented liquid motor projects.

 

[dhbarr]

5.2.1. With the exception of nitrous-oxide hybrid rocket motors, liquid rocket motors are prohibited at Tripoli Research Launches. BOD approval may be given for very well documented liquid motor projects.

Thank you, that's a useful fact for me to tuck away.

I'm assuming HT's GOX initiation & Contrail's tribrid alcomotor didn't run afoul?

 

[Steve Shannon]

Thank you, that's a useful fact for me to tuck away.

I'm assuming HT's GOX initiation & Contrail's tribrid alcomotor didn't run afoul?

As I recall, the Tribrids were done after asking for board permission. That was before my time on the board, but I remember at least one company got approval for a tribrid.

There's nothing in the rules as far as I know against GOX. The text I pasted earlier is about Liquid Motors. An earlier in the code definition of Hybrid Motors says this:
3.2.2.5. Hybrid Rocket Motor. A rocket motor in which the fuel exists in a different physical state (solid or gaseous) than the oxidizer and that derives its force or thrust from the combination thereof.

Steve


Steve Shannon

 

[Rocketjunkie]

Ok... So, getting your HPR certificates depend on whether or not you can build a rocket that can survive a launch with a HPR motor (and know the rules for launching such a rocket). What about this... Can you cert on a water rocket?

I don't think there are any commercial certified water rocket motors (Commercial, certified are in the rules.)

 

[REK]

For the sake of argument, say there were a certified water/air motor (would that make it a hybrid?)...

Is there any reason you wouldn't be able to use it to certify?

If its certified by NAR and TRA you should be able to use it for certification.


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[Steve Shannon]

A 2L water rocket has 300 n average thrust, that looks HPR to me. Of course, you blink and you miss it...

The average thrust can be used to classify a motor as a motor that requires HPR certification to use. So can other factors. However, in order to be used to certify, it must have the appropriate impulse.


Steve Shannon