posted 04-05-2006 07:33 PM               

By that time gimbaling was perfected, no stabilization fins were needed. Look at the Atlas, Thor-Delta and Titans too.

On von Braun's early rockets, more so on the Redstone than the V-2, he used the inside fin surfaces to direct the thrust. But when the man behind the Atlas (who no one remembers, unfortunately) came up with the thrust vectoring concept for his rocket, everything changed and fins were no longer needed. Von Braun and others followed.

posted 04-05-2006 07:41 PM               

The fairings are required, as the outboard F-1 engines, and especially their gimbal acutators, extend beyond the diameter of the S-1C stage.

The fins do add additional stability. Remember that the S-1C flight was a predetermined guidance program, it did not adjust for outside forces. It merely placed the vehicle close to a pre-programmed location so later guidance could refine the trajectory. The fins helped stabilize this first stage flight.

posted 04-05-2006 07:51 PM               

quote:

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Originally posted by spacecraft films:
One does not add additional weight for "show" when one is surmounting the problems of boosting a useful payload to the moon.

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Is it possible the fins were not required but they chose to use them partly because they did provide stability and partly for "show"? Or is it a total rumor that can be thrown out?

posted 04-05-2006 08:13 PM               

Additionally, the longer Saturn V with its tremendously massive first stage has a lower CG and longer moment arm then the shuttle, Titan, Atlas etc. The continuous application of fin stabilization reduced the amount of gimbaling required to correct flight path anomalies (put simply, it made the control system work a little less harder).

posted 04-06-2006 09:59 AM               

1. The fins were not needed in normal flight, but did slow down loss of control in certain failure cases, giving the abort system more time.

2. The fins were pure superstition and did nothing useful whatsoever; we tried to talk Marshall into removing them, and would have tried again if Saturn V production had continued.

As mentioned above, all the Saturns had closed-loop control, actively controlling the pointing direction rather than relying on the fins to stabilize it. As far as I know, none of them were aerodynamically stable at any time.

posted 04-06-2006 12:04 PM               

One of the distinctive features of the Saturn launch vehicle was the presence of four engine fairings and fins at the base of the S-IC and mounted on the exterior of the thrust structure. The fins added considerable stability to the vehicle, and were fabricated from titanium to withstand the 1100C heat from the engine exhaust.

posted 04-06-2006 12:41 PM               

By using the fins there would be no need for stabilization augmentation (some form of vernier thrusters). In this way you carry the weight of the fins but that is offset by the weight you would have to carry for fuel and systems.

posted 04-07-2006 09:46 PM               

Many rockets today don't have fins, however, for manned spaceflight — in most cases fins had a definite advantage. Von Braun goes on to explain:

Since the flight path, usually into orbit, is predetermined, and thus ideally suited to programed changes in gain setting, it might appear that there should be no need for fins. The problem of manned spaceflight, however, lies in the area of emergency provisions... or more specifically, abort procedures.

Suppose a large launch vehicle such as Saturn V has a serious autopilot failure at the most critical part of its ascent through the atmosphere — the high-stagnation-pressure period when the speeding rocket bucks the most severe aerodynamic forces. A failure in a swivel actuator may throw one of the five F-1 booster engines into a hard-over deflection, while an additional electrical failure may prevent the other engines from counteracting the unwanted turning motion.

In such a case, if high inherent aerodynamic instability assisted in rapidly increasing the angle of attack, structural overload might break up the rocket before the astronauts in the Apollo Command Module, triggering their escape rocket, could put a safe distance between themselves and the ensuing fireball in the sky.

It is in this area of crew safety that fins come in handy. In Saturn IB and V the booster fins are not used to provide perfect aerodynamic stability under all conditions — that would take fins of excessive size. But the fins reduce the aerodynamic instability enough to make sure that the astronauts can safely abort, no matter what technical trouble may afflict their space vehicle.

Our aim is to reduce the "turning rate, the rotational speed at which the aerodynamically unstable Saturn, when stricken by an autopilot failure, would turn into an angle of attack at which its structure would be bound to fail.

posted 05-06-2016 07:06 PM               

quote:

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Originally posted by Ken Havekotte:
Von Braun goes on to explain...

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