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1. ## just how fast?

does anyone know how many mph these things are going? iam launching fairly light e engine rockets n they look fast. iam think if it goes 1200ft with a 3second burn then it really must be flying. cmon someone, give me a good answer!

2. How heavy are they, and what diameter? E engine rockets can definitely get to several hundred miles per hour.

3. its a bt-50 tube with a fairly pointed nose. built with ca n wrapped with monokote so fairly light. sorry i dont have specifics but if it goes at least 1200 n 3 seconds then its really got to be moving faster than i realized!

4. 347.7 mph

5. Originally Posted by Rocket_Man
does anyone know how many mph these things are going? iam launching fairly light e engine rockets n they look fast. iam think if it goes 1200ft with a 3second burn then it really must be flying. cmon someone, give me a good answer!
You can get an average speed with simple math.
An Estes E9-4 Burns for 2.8 seconds and coasts for 4 seconds. If the rocket travels 1200 ft in 6.8 seconds...

1200/6.8 = 176.47 feet per second
176.47 fps * 0.6818 = 120 Miles per hour (average)

But what about the top speed? The rocket starts at 0 mph on the pad accelerates to it's top speed and then slows back down to 0 mph at 1200 feet. It's easy to find top speed with simulation software like OpenRocket.

OpenRocket simulates that an Estes Guardian on an E9-6 flies almost 1900 ft in about 9 seconds and hits a top speed of 325 MPH.

6. Here's the old standby from Estes, Technical Report 10.

http://www.oldrocketplans.com/pubs/E...R-10/TR-10.pdf

Even though it only has charts up through D12, there are equations in the back that you can use to work with just about any size rocket or motor available, though you have to make two big assumptions:

1. Constant thrust -- Of course, motors don't have constant thrust. These equations can only approximate the motors' effect.

2. Subsonic speeds -- Different equations need to be used once the rocket starts flying at 80-90% of Mach.

You also have to have some way of getting the hyperbolic trig functions to solve these equations. Fortunately most programming languages have a math package that has these functions.

Still, just using the charts will give you a good idea of how a rocket behaves, and you can extrapolate what difference an E9 motor (@28ns) would make over a D12 motor (@17ns).

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