56 replies to this topic

[italteen3]

LadyKate I really loved that tail! Hopefully I can pull that off with a 1" comet, softer lift, and a longer length. Did you mill the comp for 12 hours like Bleser recomends?(minus the FeTi of course)

Anyone happen to have video of a Shimizu Silver Wave 50/50 ratio by any chance?

Creepin you dont happen to have that vid in mpeg, avi, or mov format do you?

Edited by italteen3, 11 October 2005 - 10:13 PM.

[sasman]

I havent made a fountain yet...but when you see a nice one like that you think i gotta make one of them...and the terminology "chuffing " is what i would describe.I also remember a nice fountain you made with i think was Blue microstars ...that also got a " ohh thats pretty from my GF "..


Keep up the good work...

Also you have tempted me with that Ebay item...But the price is going up and up...& i can see you have bidded for the item..If the formulas were more modern i would make a Bid for sure...

[TzaRocket]

I didn't know were to post this so I will here:


A few fireworks from my piro night in the mountains:

[MDH]

I think my stuff is pretty professional.

My shells reach twelve seconds of flight time before exploding, but I am using VERY expensive to produce lift.

Once I can find a program that converts MPEGII to a format exportable in windows movie maker I will show you guys some of my work.

[paul]

Errrrrm... No shell should fly 12 seconds and then explode Not even the famous 48" shell got 12 seconds from lift to apogee...

Edited by paul, 05 August 2007 - 08:46 AM.

[marble]

12 seconds, what is that... rocket assisted?

[Arthur Brown]

Is there a simple formula for time/height etc?

[marble]

Depends on the exit velocity, i imagine it would be over 200fps

[Anders Greenman]

There's a formula, but it is only for calculating height based on the time it takes for something to fall down. It's not very accurate too, but it works ok if the objects is not very non-aerodynamic.

X=T2*G/2

X= altitude
T= time in seconds taken to fall from maximum altitude
G= acceleration due to gravity (9.8 m/s/s)

[cooperman435]

given that a falling object (and also a rising object) are unlikely to reach terminal velocity from the heights shells will get to, aerodynamics wouldn't make any noticeable difference anyway?

There is a formula Ive seen somewhere that enables you to calculate knowing the time from launch to landing of an object its height. If I remember its based on knowing gravatational pull slowing an object down the accelerating it towards earth.

as any object rising will have the same force slowing it down going up that it will have pulling it down then the mass of an object will have little impact on the hang time as it will counter balance from going up to coming down.

[MDH]

It was a 2" salute with a weight on it.

And it was indeed in the air for twelve seconds.

I thought the shell was dud when I heard the report and saw the cloud of smoke floating the sky far over my house (Funny because it was pointing away).

[BrightStar]

given that a falling object (and also a rising object) are unlikely to reach terminal velocity from the heights shells will get to, aerodynamics wouldn't make any noticeable difference anyway?

The aerodynamics (or at least the drag) make a big difference to the shell flight. Here's my latest model of a 4" shell (that doesn't burst) fired straight upwards. The x-axis is time in seconds.



This has broadly matches my own experiments and data tables from various literature. The shell is launched at about 5 times its free fall terminal velocity, so the air drag on it at first is very much greater than its weight. If the shell doesn't burst, it does indeed approach terminal velocity on the way back down.

To put this into perspective, if you launched the same shell at the same speed without any air resistance, it would take 12s to reach an apogee of 2450ft, as apposed to the 3.5s to reach 400ft with air resistance.

The action of air resistance gives rise to some very helpful effects:

Due to the 'damping action' on the motion, for a given shell, the time of flight is broadly constant over a fairly wide range of lift energies; the height is more sensitive. This means that you can experiment with quite a wide variation in lift powder quantities to 'dial in' the height', and the 3.5s fuse timing remains broadly the same.

This might also partly explain why there is such a variation in the reported 'ideal' amount of lift to use.

Edited by BrightStar, 06 August 2007 - 02:53 PM.