Piston launchers are used in some national or international model
rocket competitions. They seem to be used more often with low total
impulse rockets, </= C, I think. I don't know the largest impulse that
has been tried.
Descriptions here:
https://www.apogeerockets.com/education/downloads/Newsletter374.pdf
https://www.apogeerockets.com/education/downloads/Newsletter428.pdf
Naturally, when scaling up, at some point, different materials would
be required.
This project took a completely different approach:
https://www.apogeerockets.com/education/downloads/Newsletter468.pdf
On 7/11/18, Ray Rocket <dmarc-noreply@xxxxxxxxxxxxx> wrote:
I notice "easier to just add more fuel" is quite often the most effective
solution with rocketry. Seems we should have Sea Dragons flying by now...
On Wednesday, July 11, 2018 9:18 AM, Henry Spencer
<hspencer@xxxxxxxxxxxxx> wrote:
On Wed, 11 Jul 2018, Ray Rocket wrote:
The initial rocket exhaust could be put to better use if it pressurized a
tube/gun launcher rather than just roaring out the nozzle.
Folding fins or a sabot would be required if fins were deemed necessary.
It seems this would be ideal for smaller rockets, why isn't it used?
One problem is, if that exhaust is brought to a halt, or doesn't get
moving very fast in the first place, it's *hot*. This is hard on the tube
and the base of the rocket, which are now exposed to conditions resembling
those in the nozzle throat. Attempts to do something about this tend to
move quickly in the direction of a separate ejection charge generating
cooler gas, followed by main-engine ignition after ejection; there are
ICBM systems which do exactly that.
It has been done for some small rockets, I believe, but it's not as easy
as it looks, and it's not clear that it's really worth the trouble.
The classic rocket takeoff *looks* wasteful and inefficient, but it
doesn't last long, and improving on it usually turns out to be much harder
than just giving the rocket a bit more fuel to get through it.
Henry
