My son and I have been toying with a launch idea, but I figured someone must have considered it long before us. A thorough search of the internet yielded nothing, so I'm opening up here for dialog.
Here is the hypothetical setup: Take 20 feet of 1.5" PVC and mount it vertical as a launch tube. Cover each end in lightweight mylar from a balloon. Make a rocket that is exactly the same diameter as the ID of the launch tube (e.g. 1.25") and equip it with spring loaded fins. Place the rocket and a remote ignitor in the bottom of the tube, before securing the bottom mylar. Then pull a vacuum on the launch tube and turn a valve to close it off. Stand back and light up the ignitor.
When the engine lights up it will pop the bottom mylar, thus breaking the vacuum. Air will enter the bottom of the tube at 500mph giving the rocket lift, while the engine thrust will also push it up with zero drag, until it hits the top mylar, punches through, and hits solid air at 21 feet, but going XXX mph. I think, freakishly faster than a normal launch.
This is based on a the same concept as a ping pong cannon we built in our garage, but a ping pong ball is obviously more conducive to air "thrust". Here is a video of the ping pong experiments. The ball gets going 400-500 mph when it exits the tube, enough to go through a coke can. only using a vacuum in a ten foot tube.
[video=vimeo;127385173]https://vimeo.com/127385173[/video]
If we could get this to work with a model rocket what would the equation look like for the benefit? It seems to me we'd get increased thrust newtons from the air coming in and we'd have decreased drag for the first 20 feet.
thoughts?
Here is the hypothetical setup: Take 20 feet of 1.5" PVC and mount it vertical as a launch tube. Cover each end in lightweight mylar from a balloon. Make a rocket that is exactly the same diameter as the ID of the launch tube (e.g. 1.25") and equip it with spring loaded fins. Place the rocket and a remote ignitor in the bottom of the tube, before securing the bottom mylar. Then pull a vacuum on the launch tube and turn a valve to close it off. Stand back and light up the ignitor.
When the engine lights up it will pop the bottom mylar, thus breaking the vacuum. Air will enter the bottom of the tube at 500mph giving the rocket lift, while the engine thrust will also push it up with zero drag, until it hits the top mylar, punches through, and hits solid air at 21 feet, but going XXX mph. I think, freakishly faster than a normal launch.
This is based on a the same concept as a ping pong cannon we built in our garage, but a ping pong ball is obviously more conducive to air "thrust". Here is a video of the ping pong experiments. The ball gets going 400-500 mph when it exits the tube, enough to go through a coke can. only using a vacuum in a ten foot tube.
[video=vimeo;127385173]https://vimeo.com/127385173[/video]
If we could get this to work with a model rocket what would the equation look like for the benefit? It seems to me we'd get increased thrust newtons from the air coming in and we'd have decreased drag for the first 20 feet.
thoughts?