Water Rocket Car MkXI – The Green Hornet

A lot of work has gone into reworking the rear of the rocket car and reducing weight as much as possible. The modifications include
– New rear chassis of the car
– Low friction (Lighter) rear wheels
– Rear wheels much further back from the nozzle – reduce thrust steering
– New Rear fin design – larger wing surface
– New nozzle alignment guide
– New electronics bay

The following parts were also modified to reduce weight
– Chassis
– Nosecone
– Rear wheels
– Rear Fins
– Electronics bay
– Rear Alignment guide

As this will probably be the last major change to this chassis before we build a new one, we also gave it a nice paint-job and christened it “The Green Hornet”

Rear of the Car
The Rear section of the chassis was replaced with a new design that was lighter, had the wheels much further behind the nozzle, allowed for the new 45 degree wing design as well as a space to try a new additional nozzle / air amplifier (not pictured yet). The rear section is only glued to the front section of the chassis with wood glue. It is extremely strong, as we found out when pulling off the older rear section of chassis which was also glued on.

Rear of the Car

Rear of the Car

The rear wheels have had the rubber removed to both lighten the rear wheels and reduce friction with the road. The theory is to minimize the force required to straighten the car, ie: move the rear of the car back into alignment with the front of the car. We are trying to make it behave more like a rocket than a car as per our previous down-force rear wing design which tried to reduce thrust streering by maximizing rear grip. Testing will tell if this configuration will work or not.

The nozzle alignment guide has been lightened but still ensures the nozzle points directly out the back of the car.

Rear Fins
The new rear fins are made of corrugated plastic to reduce weight. A set was made from thin plywood first but they were to heavy and too flexible, the corrugated plastic ones with the corrugations running from the centre to the tip were actually stronger and lighter. A 45 degree piece of wood was glued to the fin using PL Premium. The wood is screwed to the chassis to secure the fins.

Rear 45 degree Fins

Front of the Car
Changes here include a new electronics bay setup with a flip top section that opens up to allow access to the servo and steering rod connections. The on/off switch has also been moved to a better location now protected within the nosecone.

New Electronics Bay & R/C Steering

The nosecone has also been lightened and of course painted green :) A hoel to access the on/off switch


Nose Cone

Chassis Weight Reduction
The new chassis is 1.40m long but a lot lighter than the previous chassis.The jigsaw and hole saw were put to good use to lighten the chassis as much as practical while still retaining its strength. Being painted white, it is easy to see the holes cut out of the chassis. Triangles were used where possible for cross-members to retain strength.

Chassis in white

Front Alignment Guide
The front alignment guide between the first and second bottle was left as is. This is the section where the rocket itself is imparting most of the force to propel the rocket car forward, without it the rocket will shoot off and leave the car where it is. So it was thought to best leave this with a larger surface area rather than reduce it.

More Pics of the Car

View from the front

View from the Rear

Rear Wheels - No rubber

Weight Saving
The car pictured above weighs in at 2.560kg which, while considerably more than a water rocket, is far below the previous version of the car which weighed in at 4.5kg. This weight reduction should improve both the maximum speed of the car as well as the distance traveled .. hopefully.

Additional Work
The new “additional nozzle / air amplifier” will be a second nozzle behind the main nozzle. The idea is to try to push in some of the surrounding air into the exhaust plume using a difference in air pressure between the exhaust plume and the air rushing past the rocket car. This will sit in the area, behind the main nozzle and in between the rear fins. It will be removable so we can test the car with it and without it.

We also need to strap the bottles down to the chassis and do a hydrostatic test to make sure we have allowed enough space for the bottles to expand under pressure with the new alignment guide.

We need to modify the launcher to increase the length of the hose from the launcher to the female gardena connector, this is due to the extra length added to the car and the nozzle now being further away from the rear wheels

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This entry was posted on Thursday, May 20th, 2010 at 2:57 am and is filed under Development. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.


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