Rocket Planning, First Steps

I’m building Ryan a rocket from scratch. The first step was to decide on an engine since the size and weight of the rocket would need to be built around that.

D12-5, I Choose You!

I chose the Estes D12-5 rocket engines and bought 3 of them from Amazon.

I chose the D engines as a compromise between price and power as well as for convenience. The first letter of the rocket engine name describes how powerful it is. E is more powerful than D which is more powerful than C. C engines cost about $3.00 per engine, D engines are just under $5.00 each and E engines are almost $10 each. $10 per launch seemed too expensive and the fact the D engine supposedly fits nicely inside a piece of PVC pipe sealed the deal.

The next step was to figure out the parameters I had to use to build the rocket. I didn’t want to build a cool rocket and have it only launch 10 feet off the ground.

How High Can I Fly?

I found a fantastic site with all the formulas I needed to calculate how high my rocket would go. My physics skills are rusty, but I can still plug-and-chug formulas like nobody’s business.

I put all the formulas into a spreadsheet which you can download here. You need to enter 6 fields, and it should tell you how high your rocket will go. The fields you’ll need are

  • The Mass of Your Rocket in Kg
  • The Mass of Your Motor in Kg
  • The Mass of the Motor Propellant
  • The Diameter of your Rocket in cm
  • Your Motor Impulse In Newtons*s^2
  • Your Motor Thrust in Newtons

Before you panic since you don’t know those values, they’re pretty easy to look up. A chart on the same site lists the blue italicized values above for Estes motors – other companies provide this information too. Your motor’s thrust (the red bold value) is the first number in its name, eg, the 12 in D12-5.

The two remaining values are the ones I was looking for. Essentially I end up with three unknowns. My rocket’s mass and diameter, and how high it will fly. By playing with the two inputs I can see what the effect will be on the height.

Fun Vs. Safety

Raygun Retro Rocket
Raygun Retro Rocket

I stumbled across the NAR Model Rocket Safety Code while looking up engine info and realized that rule number 1 conflicts with my plan:

Materials. I will use only lightweight, non-metal parts for the nose, body, and fins of my rocket.

I want to build a retro rocket similar to the one picture at left. I am considering using thin aluminum sheets and pop-rivets, both of which are metal, of course.

I guess silver spraypaint would get a similar look but I am kind of hoping that I can build a rocket sturdy enough that the kids can play with it as a toy when it’s not being launched. I’m not convinced that I can accomplish that with cardboard and plastic.

Now, off to the hardware store!

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2 Responses to Rocket Planning, First Steps

  1. AnnaMarie says:

    And to think, I’ve been saving all my Have-Michael-Help-Me-With-This projects because I thought you were way too busy with work! Glad you’re finding some fun time. If this is what you consider fun. :) Just kidding. Ryan will love it.

  2. Pingback: Ryan’s Rocket — Implementation, Phase One |

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