Last weekend I did the first test of a ram-rocket that I built, but unfortunately a bulkhead blew at about ten feet causing the rocket to smash into the ground. After this experience I've decided that building an airframe for an experimental motor is an inefficient way to go about the process because it takes a long time to get a full-blown launch vehicle together. Has anybody tried tube launching a rocket?
What I'm envisioning is attaching a simple set of fins to the nozzle end of a motor for spin-stabilization, and launching the entire thing (possibly with a small charge in the tube to get everything going nice and fast) straight into the air.
Concerns:
What goes up must come down--no recovery system
In the instant that the motor leaves the tube but before it spin stabilizes will it shoot off course?
Difficult to explain to the police that the rocket launcher in my truck isn't intended for malicious purposes ;)
Anyway, there are some drawbacks to the method but it's almost the only way to test a ram-rocket motor without doing a full flight. If anybody's ever tried it let me know.
Tube-Launched Rocket
Moderator: Mike Everman
Rocket stability
For a rocket to be statically stable it needs to be moving at about 30 fps for the fins to do their duty of stabilizing the rocket. I have read (but may be wrong) that spin stabilization only works while under power. In order to get spin going you can either put a slight cant to the motor tubes so that the motor thrust is off-center. Another method is to put a slight angle to one of the fins (or a angled tab at the bottom of one of the fins) The greater the angle, the higher the rate of spin.
For recovery, I would suggest that you invest in an altimeter. Perfect Flight makes a very good one called MAWD (Mini Altimeter With Deployment) It has a barometric sensor in it to tell when it has reached apogee and will deploy a recovery device (parachute). It has the ability to do something called dual deployment as well (deploy a drogue at apogee and main at set altitude)
You're not too far away (I'm in Indy) so I can let you use my electronics if you'd like. I have multiple altimeters and even a GPS transmitter so if the rocket goes too high, we can track it via GPS. We also have a waiver to 8,000 feet once a month with an L motor limit (1150 pounds of thrust)
-Aaron
For recovery, I would suggest that you invest in an altimeter. Perfect Flight makes a very good one called MAWD (Mini Altimeter With Deployment) It has a barometric sensor in it to tell when it has reached apogee and will deploy a recovery device (parachute). It has the ability to do something called dual deployment as well (deploy a drogue at apogee and main at set altitude)
You're not too far away (I'm in Indy) so I can let you use my electronics if you'd like. I have multiple altimeters and even a GPS transmitter so if the rocket goes too high, we can track it via GPS. We also have a waiver to 8,000 feet once a month with an L motor limit (1150 pounds of thrust)
-Aaron
rocket spin
In doing a little looking about using spin to stabilize a rocket, I came across this tidbit:
Roll/spinning is often discussed as a means to enhance the stability of sport rockets. People have tried various methods, including canting the fins and adding spin tabs. While I have no guidance on just how effective these methods are (does it matter? spinning rockets do look pretty cool), I spotted some information regarding the impact spinning has on altitude performance. Steve Ainsworth has written several articles on roll control for Extreme Rocketry (he also has a guidebook, which is also available through them). In his article Roll Control (Issue 54, May-June 2006), he notes that "As far as altitude is concerned, for a fin guided rocket, roll is bad news squared." He further explains that fin drag is proportional to the roll rate squared. He also referred to one study where a roll rate of ~20 rev/sec induced drag equivalent to ~20% of the installed motor impulse!
-Aaron
Roll/spinning is often discussed as a means to enhance the stability of sport rockets. People have tried various methods, including canting the fins and adding spin tabs. While I have no guidance on just how effective these methods are (does it matter? spinning rockets do look pretty cool), I spotted some information regarding the impact spinning has on altitude performance. Steve Ainsworth has written several articles on roll control for Extreme Rocketry (he also has a guidebook, which is also available through them). In his article Roll Control (Issue 54, May-June 2006), he notes that "As far as altitude is concerned, for a fin guided rocket, roll is bad news squared." He further explains that fin drag is proportional to the roll rate squared. He also referred to one study where a roll rate of ~20 rev/sec induced drag equivalent to ~20% of the installed motor impulse!
-Aaron