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Lentamental

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I remember reading a good 7 years ago, about a launch pad that someone mounted a slingshot on. The idea was that the rocket sat in the cradle of the slingshot, which was being held back by a thread, which was directed under the nozzle, so that when it ignites, it burns the thread, and is launched substantially higher. This could help with many problems. Heavy rockets could use lower thrust motors, and on windy days it can help get much higher velocities by the time it leaves the rod.
I have searched the forum to the absolute best of my ability, and came up with nothing, but do you know of anyone else doing this?
also, does anyone know if this would be allowed in a competition, or at TARC?
I can see it as being an easy way to adjust altitude, more accurately than simply adjusting ballast, by changing the stretch length.
 

Micromeister

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No such a thing is specifically forbidden in all NAR competition.
rule 5.5 Momentum: A launcher must not impart to the model any velocity or change of momentum except that caused by the model rocket Motor(s) contained in the model.

To be honest I think such a launcher would be more of a headache the a help. with many more problem causing areas then helpful ones.
 

rokitflite

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I have had a similar Idea within the realm of helping a heavy model get started... I had sketched out something that would slide over the launch rod. Not enough "umph" to fling it off the rod itself, but to make the model weigh substantially less on the pad... A sort of counter weight.
 

kjohnson

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Yeah there was an article about it in Sprocketry a while back (I think it was Sprocketry anyhow). As John said, you wouldn't be able to use it in NAR contests, but TARC doesn't have anything specifically disallowing it in the rules.

If you're just looking for a little extra oompf off the pad for sport models that used to fly great on the C5, it's a cool idea.

kj
 

Quixote

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Set up and successfully flew a Centuri Nike Smoke from 6 feet of Estes C Rail, several feet of Surgical rubber as a sling shot, and igniting a B6-4 motor using a 50 Uf electrolytic capacitor, mercury switch and a flash bulb / Sure Shot wick back in 1975.

Can't remember how the model was held down pre-flight, but once released the rubber sling flung it into the air , leaving the C rail at sufficient speed to be stable. The flash bulb flashed about 10 feet above the rail, the motor lit up and off she went. Only did this once though, have never even thought about a repeat. Wish I had photos.
 

shreadvector

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Yeah there was an article about it in Sprocketry a while back (I think it was Sprocketry anyhow). As John said, you wouldn't be able to use it in NAR contests, but TARC doesn't have anything specifically disallowing it in the rules.

If you're just looking for a little extra oompf off the pad for sport models that used to fly great on the C5, it's a cool idea.

kj
From the TARC rules:

"They must be powered only by commercially-made model rocket motors that have 62.5 grams or less of propellant each and are listed on the TARC Certified Engine List posted on the TARC website and provided in the TARC Handbook."
 

Lentamental

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Alright the "powered only by..." makes it seem not allowed... Still a very fun concept that I wish there was more of. I still may make a launcher like that for launching heavier stuff or on windy days, even if I can't use it for TARC.
 

MarkII

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Alright the "powered only by..." makes it seem not allowed... Still a very fun concept that I wish there was more of. I still may make a launcher like that for launching heavier stuff or on windy days, even if I can't use it for TARC.
Nothing wrong with using such a device for sport launching, though, assuming that you could make it work and avoid any problems. That slingshot catapult-to-airstart that Quixote described sounds absolutely too cool. I can't believe that you only did one launch with that setup, Qui. I'd love to see something along those lines created to launch an Estes Outlander or a Semroc Mars Lander, or some other "just a bit too heavy for the available motors" model. :D

MarkII
 

kjohnson

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Alright the "powered only by..." makes it seem not allowed... Still a very fun concept that I wish there was more of. I still may make a launcher like that for launching heavier stuff or on windy days, even if I can't use it for TARC.
Don't take our word for it, the best answer to that would be Trip Barber.

kj
 

MarkII

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Don't take our word for it, the best answer to that would be Trip Barber.

kj
For what is and what is not allowed in NAR competition in the US, the final answer is actually here. Consult with your PB lawyer for further information.

MarkII
 

Quixote

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Mark, cannot remember why I didn't repeat the experiment, must have just moved on to other things, did a few multiple staged flights with the Capacitor/Mercury Switch combo, I think I still have a switch or two laying around, if I can find some surgical rubber may have to try the sling shot again. With the new rails and buttons will likely be even easier.

Garth Illerbrun
CAR S04 TRA 817L2
 

shockie

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This technique was developed way back in 1962 or so by Paul C. Hans. He useda rubber band powered launch sling to help accelerate a model rocket into the air. The rocket exhaust burned through a burn string .......Paul told me that the NAR ban on launchers imparting velocity to a model was specifically written due to his rubber band launching technique.

Now what might be cool is using this technique to lob a rocket into an air start....... or perhaps have a launcher that works like the air rocket launcher....it would lob an airstarted rocket into the air to say 1000 ft where by timer or whatever the engine was ignited....


Terry Dean
 

JStarStar

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Piston launchers do something similar to this, except the impulse popping the rocket off the end of the piston is supplied by the motor propellant (and thus legal).
 

terryg

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I can see the point of not allowing this type of assist. I have had enough engines that chuffed for a couple of seconds before fully igniting to make me a bit wary of it! It would be a cool thing to try when I am launching by myself and could run from a potential land shark without endangering spectators.
 

CoyoteNumber2

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I think there was a university student group that did something like this at Plaster City not long ago, except they were using some sort of magnetic ramp or something similar.
 

MarkII

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The only kind of "ban" by NAR that I can find for this type of launcher is Rule 5.5 in the Pink Book pertaining to its use in competition. There is certainly no mention of it in the Model Rocket Safety Code (or in the High Power Rocket S. C. or in the Radio Controlled Rocket Glider S. C.), which is the only other set of "rules" that NAR specifies for model rocketry. I hope that this doesn't become another "rockets that eject their motors are not legal" type of "rule" that doesn't actually exist.

I certainly don't have any problem with it; I think that it could be an interesting type of launch when it is used in conjunction with airstarting engines. Regarding terryg's concerns, the same sort of risk is involved with any complex rocket that employs airstarts to give it sufficient boost, and for that matter, with any rocket that employs clustered motors. Such risks are usually deemed acceptable if the rocket passes RSO inspection, safe launch distances and launch angles are observed and everyone who is present at the site is alerted to the impending heads-up launch.

MarkII
 
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