#### ScrapDaddy

##### Well-Known Member

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In 1927, modern rocketry was born, when Robert Goddard launched his Nell into the stratosphere(not really more like 100 feet or somthing around that) his rocket was sopposed to prove the pedulum rocket fallacy, which Mark graciously explained in greatly simpiflyed terms why this wouldn't work

"In plain (and simplified) terms, the pendulum theory assumes that gravity will always pull the weighted aft end of the rocket down toward the ground. This will bring the motor back up to a vertical orientation and insure that its line of thrust is perpendicular to the ground (so that the rocket goes straight up). The problem is that if the rocket motor's thrust is powerful enough to lift the rocket up against gravity and launch it into the air, then it is also strong enough to overcome the supposed stabilizing effect of gravity. Also, even if the rocket motor remains in an absolutely vertical orientation, its line of thrust will vary a little bit from perpendicular to the ground. That variance (or misalignment) will cause the thrust to "push" the rocket over. Since the thrust is stronger than the pull of gravity, it can easily overcome any pendulum effect and will keep forcing (torquing) the entire rocket over and turning the line of flight away from vertical until the rocket's trajectory eventually intersects the ground.

The rocket needs some other stabilizing mechanism because the pull of gravity will never be sufficient to keep the rocket aligned vertically in relation to the ground."

As us modern rocketeers know the Nell did not achivemrnt stability during it's flight proving the theory false,but strangly enough 83 years later Jim Flis shock the world(not really this stuff is right up his alley) by creating a stable sport scale model of the Nell, now the question is how did he do it? We all know the basic criteria for stability is CG in front of the CP...... Hopefuly at the end of this ten day period Jim will be willing to share how the stability is achived in his model...... If not I'll google it......... And Jim, if you see this tread please don't respond until 4/7/10..... However if you wish you can tell the TRFers I they are right or wrong

"In plain (and simplified) terms, the pendulum theory assumes that gravity will always pull the weighted aft end of the rocket down toward the ground. This will bring the motor back up to a vertical orientation and insure that its line of thrust is perpendicular to the ground (so that the rocket goes straight up). The problem is that if the rocket motor's thrust is powerful enough to lift the rocket up against gravity and launch it into the air, then it is also strong enough to overcome the supposed stabilizing effect of gravity. Also, even if the rocket motor remains in an absolutely vertical orientation, its line of thrust will vary a little bit from perpendicular to the ground. That variance (or misalignment) will cause the thrust to "push" the rocket over. Since the thrust is stronger than the pull of gravity, it can easily overcome any pendulum effect and will keep forcing (torquing) the entire rocket over and turning the line of flight away from vertical until the rocket's trajectory eventually intersects the ground.

The rocket needs some other stabilizing mechanism because the pull of gravity will never be sufficient to keep the rocket aligned vertically in relation to the ground."

As us modern rocketeers know the Nell did not achivemrnt stability during it's flight proving the theory false,but strangly enough 83 years later Jim Flis shock the world(not really this stuff is right up his alley) by creating a stable sport scale model of the Nell, now the question is how did he do it? We all know the basic criteria for stability is CG in front of the CP...... Hopefuly at the end of this ten day period Jim will be willing to share how the stability is achived in his model...... If not I'll google it......... And Jim, if you see this tread please don't respond until 4/7/10..... However if you wish you can tell the TRFers I they are right or wrong

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