# I on my rocket engine thrust equation

• Monomethylhydrazine
In summary, the user believes that their calculations show a different thrust than originally calculated, due to a difference in the NASA equations used.
Monomethylhydrazine
I have been working on a rocket engine and I have cad models and everything and I am getting ready to build it. Then, I was running over the numbers one more time and I realized that the thrust I was getting was completely different from what I should have been getting.
The big problem is the NASA equations. It uses the variables Ttotal and Ptotal. NASA states, "pt is the total pressure in the combustion chamber, Tt is the total temperature in the combustion chamber." However, when I plug in 300 psi and 5742 degrees fahrenheit and the exhaust values for each variable as given by NASA's isentropic equations, I get a thrust of 735 pounds, whereas the first time I ran the numbers I got 32 pounds of thrust.

Here is my data, most of it was from a formula. The top ten rows are all givens. I got that information from https://risacher.org/rocket/eqns.html as I am building a gasoline-GOX engine.

What it is Value Unit
Combustion pressure (Pc) 300 PSI
Mixture Ratio 2.5 n/a
Flame Temp 5742 Fahrenheit
ISP 261 Seconds
GOX Density 0.083 lb/ft^3
Gas Density 44.5 lb/ft^3
Nozzle Throat Cross Sectional Area 0.00173611 ft^2
Gas constant (R) 65 ftlb/lb
Gamma (heat ratio) 1.2
gc (gravitation) 32 ft/second/second
Tt (temperature of gasses at nozzle throat) 5637.618 Fahrenheit
Tc (temperature of cumbustion flame) 6202 Rankine
Pt (gas pressure at nozzle throat) 169.2 PSI
Me (mach number of gasses at exit) 2.55
Area Exhaust/Area throat 3.65
Temperature Exhuast/Temperature combustion 0.606
Thrust 31.84104294 Pounds
Mass flow rate 0.0009229501076 pounds per second
Exhaust velocity 1380.669321 ft/second
Temperature Exhuast 3479.652 Fahrenheit
Exhaust pressure 24.4297 psiAs you might imagine, I would really appreciate someone going over and double checking my numbers. Thank you so much!

@Monomethylhydrazine -- Please start a Private Conversation with me to discuss several issues (click on my username and select Start a Conversation):
• What is your educational background and experience with high-energy projects, and rocketry in particular?
• Have you looked into your local rocketry clubs for help on your project?
• Why did you choose your particular username? It does not bode well...

## 1. What is the rocket engine thrust equation?

The rocket engine thrust equation, also known as the Tsiolkovsky rocket equation, is a mathematical formula that calculates the amount of thrust produced by a rocket engine based on its exhaust velocity and mass flow rate.

## 2. How is the rocket engine thrust equation derived?

The rocket engine thrust equation is derived from Newton's second law of motion, which states that force is equal to mass times acceleration. In the case of a rocket, the force is the thrust produced by the engine, and the acceleration is the exhaust velocity.

## 3. What factors affect the rocket engine thrust?

The rocket engine thrust is affected by the exhaust velocity and the mass flow rate of the propellant. The higher the exhaust velocity and the greater the mass flow rate, the greater the thrust produced by the engine.

## 4. How is the rocket engine thrust equation used in rocket design?

The rocket engine thrust equation is used in rocket design to determine the amount of thrust needed to overcome the weight of the rocket and any external forces, such as air resistance, during launch. It is also used to optimize the design of the rocket engine for maximum thrust.

## 5. Are there any limitations to the rocket engine thrust equation?

The rocket engine thrust equation assumes ideal conditions, such as constant exhaust velocity and no external forces acting on the rocket. In reality, there are many factors that can affect the performance of a rocket engine, so the equation may not always accurately predict the actual thrust produced.

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