Power question.

[The Visionary]

I am wondering if there is some type of formula for figuring out how big an engine I am going to need. I don't think that rocksim is going to help as this is a 100% recycled rocket I am making for the EMRR challange. My problem is that it is going to be PRETTY heavy.

 

[ben]

weigh it in ounces. Times that by 5 and that wil be how much thrust you need for a 5:1 thrust ratio.

Ben

 

[The Visionary]

Now I just have to go buy a scale... LOL. Any sugestions?

 

[LaneKG]

I divide the average thrust of the motor in newtons by 22 to give the weight in pounds I can lift with a five to one thrust ratio. 22 newtons = 4.94579675 pounds and 4.94579675 / 5 = 0.98915935 which is close enough to a pound for me.

Greg

 

[ben]

Originally posted by The Visionary
Now I just have to go buy a scale... LOL. Any sugestions?

I would get a pre-weighed container and hold that in one hand and hold the rocket in the other. the estimate. Get one that is 1lb f possible.

Ben

 

[uncle_vanya]

Originally posted by The Visionary
I am wondering if there is some type of formula for figuring out how big an engine I am going to need. I don't think that rocksim is going to help as this is a 100% recycled rocket I am making for the EMRR challange. My problem is that it is going to be PRETTY heavy.

I do a lot of scratch building and use RockSIM. My materials are often found and they do not fit the Materials Database always. Essentially if you measure the dimensions and weigh the parts or even get close you'll be ok.

 

[blackjack2564]

I'm a cheapie, I still go to the post office and use their "free" digitalscale. All PO's have them in the lobby which is usually open till midnite. Sometimes I do get strange looks ,though. Especially when weighing 8ft 4in diam rockets like a competitor 4.

 

[The Visionary]

Originally posted by blackjack2564
I'm a cheapie, I still go to the post office and use their "free" digitalscale. All PO's have them in the lobby which is usually open till midnite. Sometimes I do get strange looks ,though. Especially when weighing 8ft 4in diam rockets like a competitor 4.

Oh my God... LOL... I bet you do...

With that said, LOL, I am going to go tomorrow. LOL

I needed a good laugh.

Thanx

Trust me when I say I am a cheapie too.

I will have to say that you guys definately use your heads.

 

[blackjack2564]

Glad to see that your joining the "going postal'' crowd! Kinda adds new meaning to an old phrase, doesn't it?

 

[The Visionary]

I went today at lunch. LOL. I got a few heads to turn putting my garbage on the scales. LOL. I am going to put it in rocksin tonight and see how big I am going to have to go to make it stable.

Thanks Blackjack for the idea.

Tim

 

[The Visionary]

Now that I have the weight, how do I calculate the CG for rocksim?

 

[heada]

Measure it? Tie a string around the object (or the rocket) and measure where you place the string when it is balanced. This is the CG for that object (or rocket)

Rocket Science....its not just for breakfast anymore!

-Aaron

 

[Pantherjon]

Or balance it on your finger(if it's small enough-which I doubt)..But yeah, tie a loop of string around the BT and move it til when you hold the string the rocket is parallel to the ground..TADA, there's your CG And do it in 'flight' setup with motor, wadding, etc...

 

[The Visionary]

Originally posted by heada
Measure it? Tie a string around the object (or the rocket) and measure where you place the string when it is balanced. This is the CG for that object (or rocket)

Some how I figured ya'll were going to say that. LOL

I guess I was trying to make rocket science out of it. LOL

Thanks fellas

 

[The Visionary]

Now does the 5 to 1 ratio include the engine weight or not?

 

[LaneKG]

I divide the thrust by lift-off weight which includes the weight of the motor. This article is interesting. It recommends a 10 to 1 ratio on windy days.

Greg