Model Rocket - Thrust to weight ratio

[Th3bozz]

Hello Everyone, Anyone

 

I have recently built a model Rocket (Q-Modelling Nike-X) and I am interested in finding out how many Newtons of thrust I would need to launch it.

 

The total weight without the motor at present is 330grams, is there a simple equation I can use to work out the above.

 

Also could someone please explain g = 9.81 m s-2

It's the -2 (per second per second) I can't get my head around???

 

kind regards

 

Th3bozz

[insane_alien]

good questions.

 

g is the gravitational field stregnth of the earth. and as such it is an acceleration. 9.81 metres per second per second means that every second an object in freefall will gain 9.81 ms^-2

 

example:

time(s) velocity(ms^-1)

0 0

1 9.81

2 19.62

3 29.43

 

etc. etc. until it hits the ground.

 

now for your rocket. with a mass of 330grams.

 

to get it off the ground you will need to give it an acceleration greater than 9.81 ms^-2.

we can use F=ma for this. and to use the mass we must turn it into kilograms(divide by 1000) and we have the acceleration we need to at least match(9.81)

so we get F=0.33*9.81 this give a force of 3.24N any engine that can provide a higher thrust than that will lift the rocket.

 

you are getting the concepts of mass(kg) and weight(N) mixed up. mass is constant and is essentialy the amount of stuff that is there.we measure this in kilograms.

 

weight is the force acting upon the mass due to gravity and we measure this in newtons.

[Th3bozz]

Just to say a BIG BIG thank you for the Reply, after down loading pages of Info I still couldn't figure it out. You've made it so Easy to understand.

 

I look forward to presenting some other problems shortly

 

kind regards

 

 

Th3Bozz

[insane_alien]

i made something sound easy? man thats a first.

[swansont]

i made something sound easy? man thats a first.

 

 

And it's rocket science, no less.

[Rocket Man]

i would roughly double/triple the force to reach equilibrium, most model rocket engines have a thrust curve made to get the rocket up to enough speed to have the drag stabilise the flight, not enough and the rocket could fall off the launch rod before it hits a stable speed... not pretty...

"pages and pages of info" sounds like you'd have the center of drag-center of gravity right, (i did a course on rocketry and an unstable rocket is plain scary)

but make sure you balance it, i've forgotten more than once.

just out of interest, what brand of engine are you using?