I’ve been taking my 3d printed rocket boat to the next level through scaling it up and adding more engines!
With the success of my micro hydroplanes, the natural succession was to do more testing. Here’s my video.
Firstly I scaled up the boat on CAD and got to work printing out all the parts I needed. This boat is twice the size of the previous boats I was playing around with last month which should help with stability when going over small ripples and waves at high speeds. This didn’t take too long as I’ve now got three printers to speed up big print projects. I assembled the pieces and painted them with paint and then spray sealant which would make it waterproof
I wanted to start small-ish and work upwards, combining motors with higher and higher powers until either the boat destroys itself or we find another limiting factor. These engines are all black powder engines that work through burning a propellent which flings loads of hot gas out the back at extremely quick speeds. The resulting reaction forces the boat in the other direction. To make the motors easy to swap out and combine into clusters of engines, I made this modular design of engine adaptor where you can slide them in and out of the back of the boat.
I wasn’t really sure if it was such a great idea to combine so many motors as I’ve found in the past lighting them all simultaneously is not always too reliable. To try to get a reliable connection I soldered all the igniters up to one feed and then ran an experiment
Based on the poor result of that test, I decided to use fewer but higher power motors to get a similar amount of thrust from five of these small motors, which was a shame because they looked pretty cool.
Test Run 1 – with 1x Estes D motor
So what benchmark speed could we get with the first rocket motor? The track was a couple of lengths of guttering filled with water. To accurately measure the velocity of the boat, I stuck up these reference squares and pointed a high speed camera at them. I could then calculate the speed by watching it back and seeing how long it took for the boat to clear them. At the end I piled some snow to catch the boat, which was a terrible idea!
On that first run the boat got up to an eye watering 10.638m/s or 23.796mph so it was time for more rocket engines. Firstly though, when watching the video back in my workshop, I’d noticed the boat was jumping along quite a lot. This was probably caused by a negative angle of attack of the boat so I adjusted the sponson angle to raise the nose up a bit. It would be interesting to see what effect this had.
Test Run – with 2x Estes D motors
Now to double the power with two D size engines. At first I failed to ignite both motors at the same time!
Test 3 – attempt 2 at 2x Estes motors.
This run showed I had improved the speed of the boat but at the cost of stability. I found the nose up angle of attack resulted in the craft trying to take off as air got under the nose. It basically started to do a Donald Campbell
Test 4 – attempt 3 at 2x Estes motors
I adjusted the sponsons again, just a little, to reduce the angle of attack of these contact points. Rerunning the 2x D motor test didn’t go to plan though, as, yet again, the dual rocket motor setup failed to light. I managed to fix the damage.
Test 5 – with 1x Cesaroni Pro29 F motor
Undeterred, I really wanted to know what would happen by doubling the thrust again with an F motor with 14.5kg of peak thrust. I adjusted the sponson angle yet again in an effort to point the nose down – go too far though and I’d get the bouncing I experienced in the first test, and perhaps high speed submarine-ing, which is what happened with my smaller rocket boats in my previous video. As expected, it didn’t end well.
I’d learned lots of useful things about behavioural changes with sponson angles, and this will be important for future hydroplane builds and, specifically, with making sure they don’t fly! It seems the hydroplane goldilocks zone only gets narrower and more perilous as speed increases, so perhaps there is a limit to how fast a boat will go. We’ve reached a barrier with this boat, but I it’s a barrier I intend to break going forward.