Don't Debate This, Too

[drew]

Fantastic work Mike.

[SpaceManMat]

I’m not sure I’d feel safe behind that board for a 900psi test.

[RainierWolfcastle]

I’m not sure I’d feel safe behind that board for a 900psi test.

At those pressures it depends a lot on if all air has been bled from the system. I've seen a ~5kg fitting shot across a workshop by under 2000psi that would have likely killed anyone in its path due to trapped air not correctly being bled. I've also been hit in the chest by a hose and fitting that failed at 6000psi, luckily since the system was well bled it didn't have a great deal of energy. Pneumatic systems at 100psi can be much more dangerous than hydraulic systems at ten times the pressure.

Water is more compressable (is that a word?) than most hydraulic fluids so care does need to be taken at higher pressures, but with light weight material casing and care taken to bleed the system the danger from failure is minimal and likely to be stopped by reasonably light weight barricades.


Besides all that, incredibly cool project! Loving what you are doing with it and the skills you have in working with these materials really shows.

[drew]

I’m not sure I’d feel safe behind that board for a 900psi test.

At those pressures it depends a lot on if all air has been bled from the system. I've seen a ~5kg fitting shot across a workshop by under 2000psi that would have likely killed anyone in its path due to trapped air not correctly being bled. I've also been hit in the chest by a hose and fitting that failed at 6000psi, luckily since the system was well bled it didn't have a great deal of energy. Pneumatic systems at 100psi can be much more dangerous than hydraulic systems at ten times the pressure.

Water is more compressable (is that a word?) than most hydraulic fluids so care does need to be taken at higher pressures, but with light weight material casing and care taken to bleed the system the danger from failure is minimal and likely to be stopped by reasonably light weight barricades.


Besides all that, incredibly cool project! Loving what you are doing with it and the skills you have in working with these materials really shows.

Guys, guys, guys... I think you're ignoring one critical thing. Mike did this testing in America; that's ballistic plywood!

[SpaceManMat]

I’m not sure I’d feel safe behind that board for a 900psi test.

At those pressures it depends a lot on if all air has been bled from the system. I've seen a ~5kg fitting shot across a workshop by under 2000psi that would have likely killed anyone in its path due to trapped air not correctly being bled. I've also been hit in the chest by a hose and fitting that failed at 6000psi, luckily since the system was well bled it didn't have a great deal of energy. Pneumatic systems at 100psi can be much more dangerous than hydraulic systems at ten times the pressure.

Water is more compressable (is that a word?) than most hydraulic fluids so care does need to be taken at higher pressures, but with light weight material casing and care taken to bleed the system the danger from failure is minimal and likely to be stopped by reasonably light weight barricades.


Besides all that, incredibly cool project! Loving what you are doing with it and the skills you have in working with these materials really shows.

Guys, guys, guys... I think you're ignoring one critical thing. Mike did this testing in America; that's ballistic plywood!

LOL, how could I have overlooked that.

[RGClark]

Impressive amount of work you put into this.
How much do you expect your mass ratios to be for the two stages using carbon fiber casing? What do you expect the altitude to be?

Bob Clark

[Oldboy]

Towels would have helped with dissipation of energetic event .
"Shine on Mike you crazy diamond" and keep posting.

[Viking]

Towels ....

Wise words...

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Even the ISS knows how mind-bogglingly important a towel is...

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[drew]

How much do you expect your mass ratios to be for the two stages using carbon fiber casing? What do you expect the altitude to be?

It's a single stage project Bob.

[RGClark]

Ok. Thought it was two stages from the image of the two pressure vessels side by side.

Bob Clark

[Passaretti]

Hi Guys,

I've been going at it non-stop, 7 days a week for the past ... I lost track.

Since attending my first BALLS event, my goal has been, and forever will be, to "be ready yesterday". Meaning, drive onto the playa with the rocket truly 100% done and ready to fly. It's easier said than done in general, not to mention with complex projects being flown 3,000 miles from where you live. Hence the radio silence over the past few months. However, I think I am 99% there!

I was extremely diligent about weighing all parts of the rocket, updating the sim and constantly monitoring the dynamic stability margin throughout the entire build process. In a nutshell, the rocket came in a few pounds underweight. Namely in the aft which helped the CG pull forward and meant less ballast needed in the tip. I still have some very fine tuning to do, and will put the lead ballast in last (approx. 1-2lbs), but this is the most current simulation outputs. RASAero is predicting about 10% less in terms of max. altitude, which from experience, seems reasonable.

Way too much to catch up on in one post, so I'll post a few photos to show my progress and then plan on catching up after BALLS. Thank you for your interest in feedback on this project. I'm scheduled to hit the road later this week!

100% built from scratch: Rocket/Launch Controller/Tower

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K-Type Thermocoupler / 1Hz Logger for the NC Tip

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[Passaretti]

Impressive amount of work you put into this.
How much do you expect your mass ratios to be for the two stages using carbon fiber casing? What do you expect the altitude to be?

Bob Clark

Thank you! Wait until I post the other 90% of the build photos! Just ask Drew

As Drew said, this is a single stage.

My best guess is 100-110k ft AGL IF everything goes well. Being this is the first motor case I've ever made, and the aggressive nature of the motor, I have to expect there is a good chance it will not make it past 3.5 seconds...

Regarding mass ratios though, an interesting point themselves - As built, at the moment this is where I am:

41.2 lbs - Rocket - measured weight as it sits right now, missing a few minor items, but call it about 99%.
19.89 lbs - Propellant - stated weight of propellant per ThrustCurve.org

Propellant Mass / Initial Mass of Vehicle = 19.89 / 41.2 = 0.48276

So a propellant mass fraction of about 48%. Note: This includes 1.5 lbs of lead ballast to keep my dynamic stability between 1.5-2 calibers which is where I am comfortable.

Compared to DDT (2012) which was about 41.3% (19.89 / 48.1 lbs)

[SpaceManMat]

really nice build. Will sure be interesting to see how this goes. All the best.

[drew]

Regarding mass ratios though, an interesting point themselves - As built, at the moment this is where I am:

41.2 lbs - Rocket - measured weight as it sits right now, missing a few minor items, but call it about 99%.
19.89 lbs - Propellant - stated weight of propellant per ThrustCurve.org

Propellant Mass / Initial Mass of Vehicle = 19.89 / 41.2 = 0.48276

So a propellant mass fraction of about 48%. Note: This includes 1.5 lbs of lead ballast to keep my dynamic stability between 1.5-2 calibers which is where I am comfortable.

Compared to DDT (2012) which was about 41.3% (19.89 / 48.1 lbs)

This is one of the most important take aways from this project for mine. Propellant mass fraction for orbital vehicles according to Wikipedia "... are typically around 0.8 to 0.9." For example the Space Shuttle (full stack) had a propellant mass fraction of 0.8. The fact that you've improved your propellant mass fraction by 6.7% has effectively delivered a doubling in simulated max altitude is borderline RIDICULOUS imho. It also provides further evidence that the well worn adage of "build light for speed, build for optimal mass if you're looking for altitude" in HPR is a bit of a misnomer. Sure, in theory it makes sense from a physics perspective. But in application the relatively inefficient propellant mass fractions of our rocket motors due to their over-engineered aluminium casings effectively deems that we should be building as light as possible whilst keeping dynamic stability in check if we're looking to optimise altitude. You've taken it one step further and replaced the aluminium casing with cf, which has caused your sims to go TO DA MOON!!! And I'm sure if you didn't have the 1.5 lbs of lead ballast you'd go even higher (assuming your vehicle stayed stable, which, well, is quite an assumption!)

Kinda reminds me of Chris Attebery's Insanity Plea M2245 build over on TRF. Someone asked and according to Chris his rocket is 1 lb over optimum mass according to his analysis in RASaero II. That's a sub minimum diameter rocket that consists of 4 fins directly attached to the case and a upper AV Bay + recovery + nose cone that including fins weighs 3 pounds. I mean look at the thing.


So let that sink in. According to Chris "The fins, nose cone, electronics and recovery system weigh just under 3 pounds." Let's call that 1,350 grams. Previously he mentioned his fins are 100 grams each, so his "forward of motor" mass is ~950 grams or ~2 pounds. And according to RASaero II he's 1 pound over optimum mass. He'd need to eliminate 50% of his non-fin dry mass to make the rocket weight optimised which would most likely make the vehicle unstable from a dynamic stability perspective.

TLDR; less mass in a MD rocket = more altitude, at least in the commercial/hobby space we're playing in. And if I'm being honest given the fact that propellant mass fraction plays an important role in the rocket equation I'd go as far as to say a high propellant mass fraction is critical for getting higher regardless.