This blog covers the day to day progress of water rocket development by the Air Command Water Rockets team. It is also a facility for people to provide feedback and ask questions.

Wednesday, February 15, 2012

Shadow flies to 947 and 1017 feet

I’ve updated our main website with the launch report from this Sunday. The Shadow had a perfect first flight at 330psi. It reached 947 feet, deployed it’s parachute at apogee and gently landed in the grass. On the second flight at 360psi the parachute failed to deploy, and the rocket crashed heavily. Although the camera was destroyed, the altimeter still recorded the flight. The altimeter read out 1017 feet.

The update includes photos, video and the altimeter data as well as additional performance info. It also discusses what we suspect went wrong with the deployment mechanism.

The rocket is not a total loss though, and most of it can be reused or repaired. In fact repairs have already begun to see if we can get the Shadow to at least repeat the last flight without damage. :)


jan said...

hi George,
The rocket reached 1000 feet - a milestone. Congratulations!
About the crash : I guess it was the acceleration that caused the nose-cone to get stuck. It was pushed on the rocket with a forces 55x its weight.
Ever though about putting the nose-cone free on the rocket but secure it mechanical and release it with a servo? Just an idea.

Anonymous said...

It's cool! It is possible to learn engine volmue, diameter of a nozzle, gross weight and water weight?

George Katz said...

@Jan Thanks Jan, the deployment reliability is one of the things we are going to revisit. We are currently exploring a system that is physically locked so the nosecone doesn't separate on burnout, but instead of the piston we use a pilot chute to pull the main out.

Rocket capacity is 5.8L, nozzle is 19mm and the rocket dry on the pad weights 1370 grams. The amount of water depends on the launch pressure, but for these two flights we used 1.3L.

Rodrigo said...

Impressive fligths!
I wish the best in the rebuilding!

Unknown said...

Congratulations on your personal record. Unfortunatly that the rocket crashed, but It's actualy a beautiful sight to see it coming down so fast and hear the whistle.
Hope there's not to much (invisible) damage.


rstaff said...

Excellent report George. You build such cool stuff!

rstaff said...

George, out of curiosity, could you plug all the data for the Shadow's 2nd flight into a calculator (such as ) and then post or send me the resulting thrust curve? I'd love to know the 'pyro' motor equivalent. There are a couple of inputs that I couldn't find on your site and I'm sure you'd know them off the top of your head. TIA!

George Katz said...

Hi Dick,

Here are the parameters for Clifford's simulator for this rocket:
Rocket volume: 5.8 (litres)
Water volume: 1.3 (litres)
Pressure: 360p (in Kpa, append 'b' for bars, 'p' for PSI)
Nozzle size: 19 (millimeters)
Nozzle loss factor: 0.16
Bottle diameter: 61 (millimeters)
Coefficient of Drag: 0.3
Dry mass: 1370 (grams)
Initial speed (for second stage): 0 (metres/second)
Launch tube length: 300* (see below for explanation) (millimetres)
Launch tube diameter: 0 (millimetres, zero means same as nozzle)
Water density: 1 (kg/litre)

*Note that there seems to be an issue with the launch tube simulation part of the sim. If I use the actual length of the launch tube (1500mm) then the predictions are way too generous. If I reduce the length of the launch tube in the sim to 300mm then the results are more realistic. Changing the length of the launch tube changes the shape of the thrust curve. (Dean Wheeler's simulator generates the correct results with the normal launch tube length but does not create a thrust curve)

The other thing the thrust curve does not show is the tail off after the water runs out and high pressure air is still producing some thrust. This is know as the air pulse.
Here is an example of a thrust curve (test#4) from Clifford's simulator overlayed over a measured thrust curve showing the difference.

Here is what a typical thrust curve looks like:

Even though the simulator may be calculating the correct final performance this may not be reflected in the thrust curve. Regarding the air-pulse the introduction on Clifford's simulator says: "Now including Bruce Berggren's air pulse formula! The air pulse is taken as an instantaneous impulse, so the acceleration curves don't show it, but the velocity curve takes a jump upwards on burnout."

I think a very rough approximation for the thrust produced during the air pulse for the purposes of working out the total impulse is perhaps 1/3 the thrust of the final water phase thrust running for approximately 60% of the length of the water phase.

I'd be keen to hear how that translates to a pyro equivalent.

rstaff said...

For a WAG at the motor class, I entered your info in Clifford's simulator to get a curve. I generated a WRASP file and appended the air burst per your description. I then re-entered the curve to get a new WRASP file. The latter was a big source of error. I come up with a 100G674 (25% G). The program I used to get the data from the curve (via made me enter a motor description and I just entered junk. If interested the following can be edited an run thru a simulator:

G674 61 'motor length' P 'prop wt' 'total wt' ACShaddow
0.0020 704.321
0.01 695.679
0.011 1326.543
0.05 1006.79
0.077 881.481
0.078 306.79
0.147 302.469
0.149 0.0

George Katz said...

Cool, thanks for that Dick. I'll have to try the motor file in a simulator to see how the results compare. Now if we could only buy a real G674 :)

Luciano said...

Hola George, realmente ha sido espectacular el vuelo del cohete, un vuelo totalmente limpio y veo que prácticamente no gira lo que dice que es muy estable. Se lo que se siente cuando no abre el paracaídas :-) cuando veía el vídeo parecía que era a mi que me estaba pasando.Suerte en la reconstrucción.
Felicitaciones y 10 puntos!
Un abrazo desde Uruguay.

MariusD said...

Hi George,
Congrats for this achievement! Well done! I was looking for such a great result.
The rocket turned out heavier that I expected, almost 1.4kg. Can you make it lighter?
In contrast with above question, can you consider a pyro ejection system? I don't know because of battery involved.

Unknown said...

Hey George,

The Shadow was absolutely incredible, i had imagined it would move fast and go high but not quite such as it did.

Real shame about the crash on the second flight :( I hope all the best in its rebuild for you though :)

Regards Doug

George Katz said...

@Luciano: Yes, you get that sinking feeling when it has been a couple of seconds past when the parachute should have deployed but you're always hopeful all the way to the ground :)

@MariusD: Yes the rocket is actually quite heavy when you consider it is only 5.8L. From what I recall the payload section and nosecone weighed in at around 350 grams or so. Something we'll try to address with the next version. The two PVC bulkheads are also quite heavy, and could be made lighter. On this rocket we are focusing on strength rather than weight. The tube can also be made lighter, there is a lot of epoxy on it.

@Doug: Hi Doug, the speed was interesting for us as well, it really came off the pad like a gun shot and it sounded like one as well. You can't really hear the deep pop in the video. The high speed also makes it hard to track with the camera.

Todd said...

Congratulations George, 1000 ft+ is truly an amazing effort .... Im sure the shadow will be rebuilt and breaking the 1000ft again in no time

well done !! :)


George Katz said...

Thanks Todd :)

Anonymous said...

Hey George!

AMAZING your Shadow! I was affraid to your launch and wanted to see how your shadow will works. But its awesome...great!!!
Buts its very sad that the second flight wasn´t was allready a flop :D
I hope that you will repair it and make more such great videos.
Well done George!

If it comes warmer a bit I will test my "Berlin 1°". You will hear soon.

greetings from the cold cold Germany (the hole last week -22°C brrrr....)

George Katz said...

Thanks Felix :)

-22C is way too cold! I look forward to seeing your "Berlin 1°" rocket. When do you expect to launch it?

Anonymous said...

good mornig George,

I hope that I can test in in one or two weeks if the weather is fine. Later than the first April 2012 is a competition between me and one friend of me. So there is allready some time to prepare and correct may some difficulties. :) But could I wait so long?? I didn´t think so :P

I look forward!!


Unknown said...

Why hasn't there been any updates for ages?