We have lots of experience from last year and the results at the National competition.  We should be able to put our knowledge to use and get back to Nationals.

After some designs and the launch on October 21, we have decided to focus on BT-80 body tubes. They are inexpensive and parts are easily acquired. It gives us plenty of space for an egg, parachutes and electronics. The BT-70 last year was too small and we could not protect the egg sufficiently.

Here are some early fin designs. We should decide on either 3 or 4 fins. This has a  impact on the launch tower.

In the past, we have had problems getting the fins straight on the body.  We should build a fin fixing gig.  See http://www.vatsaas.org/rtv/construction/finjig.aspx for a design.
 

Here are four possible fin designs.  A trapezoid fin design seems to be the least likely to break when landing. The important issue is to make the fin large enough to keep the center of pressure low.

We are planning to use thin plywood for the fins.  1/16th plywood should be strong enough without too much weight. We may also try 3/32nd basswood.

Fins should also have more than a straight cutout from fin material.  They should have a more complex airfoil profile. There is a good discussion on fin design at http://www.apogeerockets.com/technical_publication_16.asp.

One final piece of advice, the grain of the wood needs to be parallel with the leading edge of the fin.

Based on last year's experience, the fins should have a tab that goes through the body and is glued to the engine tube.

The engine tube must extend past the end centering ring so you can tape the engine to the tube. The end centering ring should be flush with the end of the body to reduce the drag.  You could also add a cone to eliminate more drag.

The top centering ring should extend a little below the top of the engine tube so you can insert a pin (or something) as an engine block. The engine tube should be no longer than the longest possible engine.

Our rocket needs to go exactly to an altitude of 850 feet.  It is hard to get that altitude consistently using just a ballistic apogee. We are considering ways to control the ascent to 850 feet.  We will use an engine that would get us above 850 feet, but retard the ascent as we approach 850 feet.

One initial thought was to use the release of a CO2 cartridge to retard the ascent. We could release the gas as we needed it, based on feedback from an altimeter.  We decided to test the force of a CO2 cartridge.  Here is a video of the force on our rocket scale.  After some discussion about the weight of the cartridge and the valve, we decided this would be an unlikely solution to the problem.

Our next idea was to use some form of air brakes.  These flaps can be extended as the rocket approaches 850 feet.  Here are some design pictures of the flaps retracted and then extended.

While we are designing this complicated rocket, one of our teams could use a simple rocket kit as a base for their rocket, much like the use of a Fat Boy last year. Some starting kits from Estes...

• X Prize Canadian Arrow (http://www.estesrockets.com/products.php?number=2188)
  (BT80 150g)

• Executioner (http://www.estesrockets.com/products.php?number=1951)
  (BT80 230g)

• Big Daddy (http://www.estesrockets.com/products.php?number=2162)
  (BT100 150g)

Here are some links to users of a Big Daddy...

• http://www.rocketreviews.com/reviews/kits/est_big_daddy.html

• http://shepody.physics.iastate.edu/lajoie/model_rockets.htm