Teaching Fysics and Phaith thru Rocketry
The heavens declare the glory of God;
and the firmament sheweth his handywork.
Psa 19:1
All to the glory of God – Soli Deo Gloria
Rocket Science (Astronautical Engineering)
Physics
F = ma
F = 0.5rV2CdA
Science can answer the “what” questions – “What is the force resulting from an acceleration acting on a mass?”
Science cannot answer the “why” questions
- “Why does a force equal the mass of an object times its acceleration?”
- “Why does gravity exist?”
Science cannot answer the “who” questions – “Who designed the forces of the universe so simply modeled with F = ma?”
What are the forces acting on a rocket?
- Thrust – engine (f = ma)
- Weight – gravity (f = ma, a = 9.8m/s2)
- Drag – air friction (0.5rV2CdA)
- Lift – fin stability (CG ahead of CP)
A safe rule of thumb for thrust/weight ratio is 2/1.
A rocket will reach terminal velocity in a few seconds due to drag forces.
Therefore, a rocket will cease acceleration approx at engine burn-out for common model rocket engines.
Chemistry
CH4 + 2O2 à CO2 + 2H2O
Science can answer the “what” questions – “What is the most efficient fuel/oxidizer mixture?”
Science cannot answer the “why” questions
- “Why do fuel and oxidizers burn (exothermic) when ignited?”
- “Why is oxygen diatomic?”
- “Why do the laws of thermodynamics govern the universe?”
Science cannot answer the “who” questions – “Who designed the elements to react the way they do?”
Combustion, the chemistry of rocket engines, is a macro subset of physics.
Combustion of methane is the most basic hydrocarbon equation.
Combustion of other hydrocarbons have similar stochiometric equations.
Black powder is a common fuel that has its own oxidizer.
Sugar can be burned with an oxidizer of KNO3, NaNO3, or LiNO3.
Electronics
E = IR
Science can answer the “what” questions – “What is the current thru a one ohm resistance with a potential of 12V?”
Science cannot answer the “why” questions – “Why do flowing
electrons cause heat (ignition)?”
Science cannot answer the “who” questions – “Who designed atoms so that electrons would flow thru metals?”
An ignitor follows the equation E = IR for engine ignition. Igniters are typically 1W.
An ignitor may be tested with a small current (mA) for circuit continuity (no-fire).
An Estes standard model rocket igniter has a large current (~12A peak) for engine ignition (all-fire).
The battery chosen must be able to deliver such a current surge for about 30ms.
A fully charged, 12V, 7aH, SLA battery is a good, reliable choice for obtaining all-fire current.
Wire length decreases voltage available at the igniter (E = IR).
Air-start circuitry usually requires a 9V battery. A separate battery for the ignitor is recommended.
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