Tuesday, September 10, 2019

How much power do you really need?

The Geezer TARC flyoff is this weekend, and I am busy going over my final calculations before the event, making sure I have the proper descent rates with my chosen parachutes. I am also following a lot of activity over on the Contest Rockets group, where the discussions are focussing on the NRC, NAR's relatively new competition format. This got me to thinking about egg lofting and wondering if it would be possible to apply competition techniques to this year's TARC, given the relatively simple payload and design constraints. My two Geezer TARC models fly on E impulse, but could you get a single egg and altimeter to 800 feet with a D motor? A quick glance at the NAR records shows altitudes of over 600 meters (1968 feet) for this impulse class, so yes, it should be doable - if I was top of the line contest rocketeer, which I ain't.

But I did get inspired enough to fire up OpenRocket to see if I could come up with a workable design using off-the-shelf parts. Wonder of wonders, I found it surprisingly easy to do so. Meet Eggsperimental!

A visual rendering of Eggsperimental (Click to enlarge).
Eggsperimental is a BT-50 based, D12 powered model that meets all the TARC requirements. It consists of a light weight Apogee clear plastic egg capsule with padding for the egg and a Firefly altimeter in the shoulder, a long piece of BT-50 body tube, an engine hook, three balsa fins, and 2 Apogee 3D printed rail guides (which I have decided to replace with an Apogee egglofter fly away rail guide to reduce drag even more). Weighing just 146 grams with a D12-7 motor, it only requires a 12" Mylar parachute to bring it safely back to earth. OpenRocket says this puppy should break 1000 feet, which gives me plenty of margin for additional weight (i.e., nice paint job).

Apogee egg capsule and padding (Click to enlarge).
Eggsperimental in the OpenRocket design screen (Click to enlarge).
So what are the pro's and cons of this design?


  • Very economical
  • Standard model rocket construction techniques - assembles like an Estes Alpha!
  • Easy to construct, finish, and paint
  • Uses a relatively cheap black powder motor that can be bought locally


  • Not very robust - may not survive many flights (but easy to build copies)
  • Would have to come up with a way to add weight to lower altitude (body tube segment glued to egg capsule capable of holding sand, clay, or bb's - not hard to do)
  • Fly away rail guides may malfunction (I've seen this happen)

I'm planning to construct one soon, but won't have it by Geezer TARC. However, I should have it built and ready to fly by the time the teams start practicing. If it works, it'll make the other rockets look like big pigs.

I kinda like that thought..


  1. Why such a long body? Fin size reduction?

    1. Because TARC rules specify the rocket must be at least 25.6 inches long. No way around that.