Apex Rocket engine

Building and testing a solid fuel rocket engine 

Background

Playing around making gun-powder and rocketfuel from scratch I also started designing rocketbodies out of empty craft-paper tubes but I never quite got around to actually designing a working engine. This need to change! Here I’ll log the progress in building a re-usable solid-propellant rocket engine capable of lifting a 1 kg ish rocket to a couple houndred meters.

The motor (I call it the Apex 1) will be heavily based on the A-200 designed by Richard Nakka over at http://www.nakka-rocketry.net/engine1.html only with a few modifications to casing dimensions and some minor tweaks on the nozzle.

Goals

  • Design and build a solid fuel rocket engine running on KNSU propellant.
  • Testfire and logg thrust-data.
  • Use the developed engine to launch a rocket containing a handfull of sensors.

Nozzle

The Nozzle is machined out of a general purpuse mild steel bar (C1018)  and polished. A groove for an O-ring is machined inn, and four mounting holes 90 degrees apart for standard M4 screws are drilled and tapped (importan to take note of the screw material in regards to maximum shear stress). 

Testrigg

A testrigg for testing the thrustprofile of the rocket is made from an aluminium load-cell incorporating a wheat-stone bridge circuit. The output of the load-cell is hooked up to a HX711 Chip that takes care og signal amplification and analog to digital conversion.  The output can then be connected through an arduino for logging data on a computer. I will be using the LabView software from National Instruments to process and logg incomming data.

 

Notes:

– Make Labview program with adjustable sample frequency.

Calculating max chamber pressure:

In order to get an Idea of what our combustion chamber ie. the actual Rocket engine should be able to withstand in terms of pressure we need to figure out the chamber pessure that will develop in our motor.

when calculating this I came accross alot of variables that needed to be sorted out. Some of them includes:

  1.  FUEL: Propellant parameters (burnrate, density etc.).
  2. NOZZLE: Design parameters. connecting flow-rate to pressure.  

Chamber pressure is dependent on fuel used and nozzle-design.
therefore it makes totally sense to further investigate matematical equations for these parameters.  

In designing the engine we have some preset conditions:

  • Fuel -> KNSU 
  • Casing diameter 32mm – this makes nozzle ratio calculations another constraint.

Important resources for further development:

Stress inflicted on casing and components

When the maximum chamber pressure is found we can get going and calculate nessesary strenght of the engine components so that we hopefully don’t get an unschedueld rapid dissasembly ie. explosion upon launching

Complete component-list of MJOLNIR MK. I Rocket engine:

  • CASING.
  • NOZZLE.
  • BULKHEAD.
  • Connecting bolts.