Aerodynamic testing at the Purbeck School Science Fair

tl:dr – Make LEGO models and test them in our Scale Wind Tunnel, test and improve!

At the recent Purbeck School Community Science Fair, I was fortunate enough to be running a Scale Wind Tunnel manufactured by Clive Evans at Scale Engineering.

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Quote in wired magazine about making your own wind tunnel. 

These are truly magnificent pieces of engineering, and we were very lucky to be able to use one for the day.

Our version had been outfitted with a Lego studded test bed, which allows for the rapid testing and prototyping of Lego models.   As you can see from the picture above, the tunnel is a finely-engineered beast.

 

On the left of the tunnel is a laminar air intake, which forces the air through a honeycombed aluminium structure to reduce the turbulence.  Once through this, the diameter of the tunnel reduces sharply, increasing the airspeed through the test bed.

The LEGO bed is attached to two load sensors as can be seen below.  One senses movement in the vertical direction, which indicates a Lift force in Newtons, and the other senses the Drag generated by the model in Newtons.  The machine outputs the readings to two digital 7-segment LED displays, and are accurate to 0.01 of a Newton.   The air exits via the exhaust side, and is driven by a mains-powered air conditioning fan.  This is adjustable up to 18m/s at top speed, so the tunnel can really push the limits of most lego models.

It is very hard to directly visualise the airflows without some seriously dense smoke (which would set off alarms, asthma), but we have cotton thread on a wand that can be used to directly visualise the airflow over a model by tracing it around the outside of the model.

After the initial setup in the school library, I opened up my Big Box o Lego (TM), featuring many classic LEGO pieces from the golden era of 1980s space lego, and infused with Dexter’s more contemporary LEGO star wars pieces.  We even took my younger son’s duplo airplane as seen above.

The basic procedure was outlined:

(1) Build a model, get it tested in the wind tunnel

(2) Record the Drag and Lift Values from the tunnel

(3) Refine your design, retest.

(4) Repeat.

We had an incredible variety of models made, from the austere and efficient to the beautifully sculpted and adjustable masterpieces.  Over 45 different models were made and refined over the course of the day, involving multiple rounds of testing.

The best models of the day tended to have the best Lift to Drag ratio, the best being 1.09N Lift,  0.38N Drag. We discussed how you could make them more efficient, including using flat pieces to reduce drag around the studs, removing unnecessary fandangles and gizmos.

The crowd that gathered was equal parts boys and girls, as well as equal part child and adult.  LEGO is a great leveller, and many families had to pull away their participants in order to see the amazing things on offer elsewhere in the Science Fair.

This close-up shows the control unit, with readouts as well as the test bed.  Models to be tested are also lined up on the bottom.  That's me twiddling knobs.
This close-up shows the control unit, with readouts as well as the test bed. Models to be tested are also lined up on the bottom. That’s me twiddling knobs.
This was a particularly sassy model, with adjustable angle of attack for the wings.  The builder decided that inverting the wings would reduce drag.  He was right!
This was a particularly sassy model, with adjustable angle of attack for the wings. The builder decided that inverting the wings would reduce drag. He was right!
I was constantly surprised at the amazing variety of designs that people were able to make out of my limited pool of LEGO.
I was constantly surprised at the amazing variety of designs that people were able to make out of my limited pool of LEGO.
Two different solutions to aerospace design: reduce the surface friction, or go for maximum lift
Two different solutions to aerospace design: reduce the surface friction, or go for maximum lift
The fan running at 70% power.  This was, of course, off limits to members of the public in the rare case of a 'testing to destruction' event.
The fan running at 70% power. This was, of course, off limits to members of the public in the rare case of a ‘testing to destruction’ event.
This gives an idea of the beautiful engineering that went into the creating of this incredible wind tunnel.
This gives an idea of the beautiful engineering that went into the creating of this incredible wind tunnel. Thanks to Clive Evans for the loan of the wind tunnel.
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