EZI-65 Max Altitude Build

Getting the max altitude can be quite the challenge. Running a quick sim on that in WRasp32 with a Cd of 0.3 shows 4900 ft with a optimum weight of 28.4 oz. At a Cd 0.4, the optimum mass goes up to 31.7 oz, but the peak altitude drops to about 4100 ft. Weight and drag reduction is definitely the two primary goals. I would keep the boattail, but drop all metal as patelldp suggested.

The Battle of the Rockets used to have a G and H motor altitude contests where some part of the rocket had to be a minimum of 54mm dia. Shippensburg University was able to get over 7000 ft on a G motor. It was a very light rocket made of carbon fiber IIRC and shaped similar to an inverted bowling pin. Slippery and light is the key.

Good luck.

The first fin is epoxied in using about 2 grams of Aeropoxy structural.



I also epoxied in the stiffy tube into the avionics bay.



As the tail cone is moving the CG towards the rear, I'm keeping the metal parts in the avionics bay to put a little more weight forward.

I have reached a nose cone dilemma.

The stock "blunt" nose cone is 8.25 ounces. The "pointier" nose cone I ordered for it is 10.65 ounces.

I'm thinking of going back to the stock nose cone and saving the 2.4 ounce penalty of the pointier nose cone. Anyone think the pointier nose cone would be more aerodynamic to make up for the weight penalty?

Here are pictures of it with both nose cones.




Thoughts?

Subsonic, or super? If sub then the blunt is aerodynamically superior as well as lighter. If super then, I think, the pointy is aerodynamically superior, but I won't hazard a guess as to the trade-off. Run sims.

jqavins said:

Subsonic, or super? If sub then the blunt is aerodynamically superior as well as lighter. If super then, I think, the pointy is aerodynamically superior, but I won't hazard a guess as to the trade-off. Run sims.

Click to expand...

Thanks for the info - it will definitely be subsonic as we are limited to a CTI I242 motor. I'll stick with the lighter blunter cone.

Fillet time! I made nice small fillets to keep it light. One pump of West epoxy, one pump of West 206 slow hardener, and one heaping spoon each of colloidal silica and high density filler was enough to do all three at once. I also put a really thin layer of straight epoxy on the back centering ring to seal it - not necessary, but i had some extra.

Blue tape is really easy to apply and pull up before it cures. Tonight I'll sand it smooth and then use a little bindo spot putty to make sure it has a perfectly smooth radius.

After sanding tomorrow, it should be ready to start shooting primer. I'll also cut the G10 sled and start getting the avionics bay wired.

So far, the assembled rocket (without Kevlar shock cords or parachute) only weighs 3.38 pounds.