Видео

We haven't needed to replace it yet. I'd say we've cut perhaps 10 linear meters with it so far and it still looks fine.

Some paint may rub off during staging.

Cheers! :)

Does that mean that as the pressure drops, since you are letting some of the air out early, that there is less pressure to accelerate the rest of the water that is still left in the rocket? There have been a couple of proposed nozzles where the geometry of the nozzle changes when the water runs out. That way you get the best of both worlds. One of them was a simple insert that drops away at the end of the water phase.

Yes this is correct. I think from the tests we did the booster segment increases about 1-2mm in circumference so let's say 0.5mm in diameter. The sustainer will also increase slightly , perhaps 0.3mm? There is about 1-2mm clearance for the sustainer between the booster segments. So yes a squeeze when pressurised and under acceleration which is good, and by the time of staging we should be back to the right clearance. The ring does have a little bit of flex under those loads so I am hoping we should be OK.

This is a really good question, and it was one of the options we explored when designing it. When you have a look at the geometry of that setup and where the sustainer fins extend to, there wouldn't have been enough clearance for the fins over the entire range of possible positions of the fins. The size of the sustainer fins is fixed as the sustainer is already built. In order to get the full clearance you would have had to offset the the hexagon away from each of the booster segments. We compromised a little and the hexagon isn't a true hexagon three of the sides are shorter than the other 3.

@@AirCommandRockets Ah right, I forgot that it's not a true hexagon. (I had to watch the video in two part). Thanks for your answer!

Cheers, thanks for the tip.

Cheers! Yup it's been a few years since we've flown it. Fun times :)

Yes, the loads on this ring are enormous. I hope even as is it is now that it is strong enough. You have a 2m long lever (the portion of the sustainer above the ring) trying to force it's way sideways during acceleration especially if the rocket has any kind of angle of attack which it will have. With the acceleration ~50G just before staging imagine the amount of force on that lever if say the rocket has a AOA of just 5 degrees and air speed of 360km/h pushing on that. Saving a few grams here isn't significant in terms of performance as the booster produces about 1 ton of peak thrust. The weight forward on the rocket also helps keep the rocket stable. Another way to look at it, sit on a bullet train and stick a 2m piece of wood out the window and angle it at 5 degrees from the direction of travel. Now hang on to it while the train gets up to 360km/h in about 1.1 seconds.

Thanks Luc! I hope we get more than one flight out of it. Actually I'd be happy with even one flight. :)

Thank you for following along. :)

Cheers!

Thanks! ... not long now until the launch so I am panicking a little bit, there is still so much to do.

The current plan is around 10th August or so.

😮😮

It's definitely been useful in getting things lined up and sized correctly.

No, the edge will stay as is. In the whole scheme of things this makes very little difference on the booster. If it was on the sustainer than we would probably streamline it.

@@AirCommandRockets Understood. Great job as usual though.

Agree 100%!

Cheers :)

Not sure, you can always try the web archive/wayback machine to access it.

The files are available here: www.thingiverse.com/thing:5502347

@@AirCommandRockets Thank you!

I am not sure I quite understand your question. The second stage IS in the middle between the boosters. Water rockets by their nature are more efficient when they are long and thin. The second stage is almost 3 meters long. When the booster accelerates at 50G trying to make sure that long and skinny second stage doesn't just tip over is not that simple. So the booster is designed to hold the second stage vertical during that acceleration. The rocket will have some AoA on the way up and the force on the second stage will be great trying to rip it sideways. We need to have the whole staging mechanism half way up the booster rather than at the bottom to make sure the whole rocket is stable. (moving the center of gravity further up).

@@AirCommandRockets Thanks for quick reply and sorry for the unlucky wording of my question. You’ve understood it well though and answered it clearly. I do appreciate it. I get the thinking behind the layout much better. I was very astounded about the length to diameter ratio of the second stage. And it seems that weight ratio between stages is a bit unusual as well. I would have expected numbers between 4 and 5. Depending on the specific impulse and empty to full weight ratio of each stage it might get outside of this interval, but I thought I saw you using some calculating tools for conceptualizing this numbers for your design. I wasn’t entirely sure if the design was a compromise between the calculations and meaningful building and operating effort of your launching set up. Thanks again, and sorry for my challenging English - I'm not native in it.

Thank you! :)

For the full 2 stage stack. With water ~20Kg and ~9.5Kg dry +/- 0.5Kg. We should have much more accurate weight estimate for the booster fairly soon. The booster weight is not that critical 100 grams here or there doesn't matter much. The peak thrust is around 1 ton. What is more important is weight distribution on the booster to make sure it remain stable throughout the entire flight with and without the sustainer.

Cheers! Thank you for following along :)

Cheers! :)

Cheers! :)

A lot of the techniques we use are just things we are familiar with or that we've seen others do. Sometimes we are limited by the tools we have as well. (We'd love to try vacuum forming for example) We do spend quite a bit of time thinking how we go about constructing something and figuring out what tools or jigs we'll need to make specifically that part. Often we are limited by the materials we have on hand. That's a part of the fun challenge. But in reality a lot of it is just guesswork with a calibrated eyeball. :)

Thanks. We're pushing really hard to get everything wrapped up and ready for launch. I think there are 67 days left before launch and a huge amount of work still to be done. But having fun doing it.

Awesome craftsmanship. I wish my composites work looked that nice. Best of luck finishing this project, I'll be watching along.

I don't think the two hobbies are all that different. Simple rockets are easy to build. A lot rocket parts over the last few years are now 3D printed with various materials. That makes rockets much easier to build. I am sure that at the high performance end of model airplane design you would be pushing materials to their limits the same way rocketeers push materials to their limits at the upper end of the rocketry hobby.

Yup, it would be nice to have some of this stuff manufactured. But like you said the price is an issue.

And making the video of it adds another big complication!

Thanks for following along :)

2524? I know we've been a bit slow ... we better get cracking on that ... :)

Wow, Hi Daan, good to hear from you, it has been quite a few years! Ha ha yup we are still here making water rockets. It would be good to see you back in the hobby. :)

When the project is finished, all the design files will be released. In the meantime we detail the whole build process in this Horizon series. ruclips.net/p/PL-zcDPSotX7pQ490T-lMMBW_i7fbfD8UH