MatthewMachinist
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- Oct 3, 2015
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Hello,
I am building my first rocket and I am using some calculators so check performance before I start actual testing, the results of my inital calculations tell me that this little rocket is going to fly to 6000 feet!
Could anyone help me by checking to see if I have made an error. When I say "if I have made an error" I really mean where I have made an error.
I have made my rocket from aluminum tube, it has the following specifications-
Weight 190 grams or 0.41lb excluding propellant
Rocket o.d. 0.875 or 22.22mm
Now my plan is use the i.d. of the aluminum tube as the motor, my plan is to simply partition the tube with a machined plug.
So my motor will have -
Motor diameter 19.1mm (751 thou)
Nozzle diameter 3.7mm or .145
Core diameter 0.205 or 5.2mm
With a single grain 3 inches long
So I punched these values into a fantastic calculator I found called the Bates Grain Burn Rate Simulator
This motor will have -
Propellant weight 0.0793lb (36 grams)
Burn time 0.4234 seconds
Initial thrust 15.4964 pounds force
Total impulse 10.54 pounds force
So I took this data and punched it into another calculator -
https://www.unm.edu/~tbeach/flashstuff/RocketAltitudeFixedSize.html
But first I needed to convert total impluse to newton seconds,
So I divide the total impluse by the burn time and get 24.89 pounds force second
I then multiply it by 4.44822 to get 110.7 newtons
Which gives me 6027 feet. I suspect I haven't converted the total impulse correctly?
For my first rocket I am actually aiming for the 5 to 700 foot range.
I am building my first rocket and I am using some calculators so check performance before I start actual testing, the results of my inital calculations tell me that this little rocket is going to fly to 6000 feet!
Could anyone help me by checking to see if I have made an error. When I say "if I have made an error" I really mean where I have made an error.
I have made my rocket from aluminum tube, it has the following specifications-
Weight 190 grams or 0.41lb excluding propellant
Rocket o.d. 0.875 or 22.22mm
Now my plan is use the i.d. of the aluminum tube as the motor, my plan is to simply partition the tube with a machined plug.
So my motor will have -
Motor diameter 19.1mm (751 thou)
Nozzle diameter 3.7mm or .145
Core diameter 0.205 or 5.2mm
With a single grain 3 inches long
So I punched these values into a fantastic calculator I found called the Bates Grain Burn Rate Simulator
This motor will have -
Propellant weight 0.0793lb (36 grams)
Burn time 0.4234 seconds
Initial thrust 15.4964 pounds force
Total impulse 10.54 pounds force
So I took this data and punched it into another calculator -
https://www.unm.edu/~tbeach/flashstuff/RocketAltitudeFixedSize.html
But first I needed to convert total impluse to newton seconds,
So I divide the total impluse by the burn time and get 24.89 pounds force second
I then multiply it by 4.44822 to get 110.7 newtons
Which gives me 6027 feet. I suspect I haven't converted the total impulse correctly?
For my first rocket I am actually aiming for the 5 to 700 foot range.