Firstly, sorry for any silly mistakes or improper use of this website - this is my first time using it!
I am trying to use Excel to model the flight of the Apollo 11 Saturn V rocket using the real values from the mission evaluation report. However, I can't seem to get the right acceleration. It is always too low. My initial acceleration at t=0.1s is 2.06 m/s^2 while the values in the evaluation report show the acceleration to be close to 10 m/s^2. My final goal is to calculate the acceleration at the S-IC OECO event (at t=161s). My spreadsheet showed 28m/s^2 while the real value is 39m/s^2. Obviously I have done something terribly wrong since the difference between the values is quite large, but I've been looking over my spreadsheet for days now and I just can't find my problem.
What should the columns be?
This is what I have so far:
- Range time (s) - in increments of 0.1s down the column
- Mass (kg) - the mass at that time calculated by previous mass - mass flow rate*0.1s
- g (m/s^2) - the acceleration due to gravity at that altitude
- Weight (N) - mass*g
- Thrust (N) - the thrust at that time using real values from the graphs in the evaluation report
- Drag (N) - using the drag equation and estimated coefficients
- Total force (N) - weight + thrust + drag
- Acceleration (m/s^2) - using F=ma so I did total force/mass
- Velocity (m/s) - previous velocity + acceleration*0.1s
- Altitude (m) - previous altitude + velocity*0.1s
I've taken into account changing thrust, mass flow rate, acceleration due to gravity and drag as well.
The values in the report are given as 'inertial acceleration' but I haven't learnt this yet (still in high school). So is inertial acceleration different to the acceleration I have calculated using F=ma? Have I misused Newton's second law? Was I wrong to consider the weight of the propellants in this case?
I'll appreciate any and all helpful feedback and I can provide more information if needed. Thank you so much! :)