OZ1SEJ
Educator
- Joined
- Jun 20, 2016
- Messages
- 13
- Reaction score
- 1
I'm writing a model rocket flight simulator, and I've just finished a module that reads and parses .eng thrust files from e.g. thrustcurve.org.
It suddenly occurred to me that the .eng file format (https://www.thrustcurve.org/raspformat.shtml) only contains "total weight" (i.e. before firing) and "propellant weight", which, on the page I just linked to, is defined as "the weight of all consumables in the motor".
This is horrible in itself, because it makes it impossible to know how much propellant is in the engine, thus rendering it equally impossible to calculate the specific impulse.
The problem doesn't stop there, though. If for instance I look at the Estes A8-3 engine, the data sheet (https://nar.org/SandT/pdf/Estes/A8.pdf) reads
Initial mass 16.7 g
Mass after firing 10.2 g
-which should give a value of 6.5 g for the data file (https://www.thrustcurve.org/simfilesearch.jsp?id=1251). However, in the data file, it says 3.3 g, which the data sheet states as the mass of propellant!
Conclusion:
1. The data definition for .eng files is insufficient for simulating accurately the flight of a rocket, since is it not possible to extract propellant mass from total mass,
2. This definition isn't adhered to in at least one case. How many others might there be?
What is one to do in this situation?
It suddenly occurred to me that the .eng file format (https://www.thrustcurve.org/raspformat.shtml) only contains "total weight" (i.e. before firing) and "propellant weight", which, on the page I just linked to, is defined as "the weight of all consumables in the motor".
This is horrible in itself, because it makes it impossible to know how much propellant is in the engine, thus rendering it equally impossible to calculate the specific impulse.
The problem doesn't stop there, though. If for instance I look at the Estes A8-3 engine, the data sheet (https://nar.org/SandT/pdf/Estes/A8.pdf) reads
Initial mass 16.7 g
Mass after firing 10.2 g
-which should give a value of 6.5 g for the data file (https://www.thrustcurve.org/simfilesearch.jsp?id=1251). However, in the data file, it says 3.3 g, which the data sheet states as the mass of propellant!
Conclusion:
1. The data definition for .eng files is insufficient for simulating accurately the flight of a rocket, since is it not possible to extract propellant mass from total mass,
2. This definition isn't adhered to in at least one case. How many others might there be?
What is one to do in this situation?