Stabilizers on Saturn V

[sevenperforce]

The F-1 engines on the Saturn V had a pretty significant gimbal range. Were the tail fins on the first stage really necessary? Did they provide active or passive guidance?

[Tullius]

A quick Google search provides the answer:

Quote

"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...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...In Saturn V...the fins reduce the aerodynamic instability enough to make sure that the astronauts can safely abort" Von Braun in Popular Science, Sept 1964, page 68 (http://books.google.com/books?id=MiYDAAAAMBAJ&lpg=PP1&pg=PA68#v=onepage&q&f=false)

(found on https://forum.nasaspaceflight.com/index.php?PHPSESSID=mmgc4g1h792727issbo6823647&topic=36103.msg1290770#msg1290770)

And the article itself contains even more interesting details (absolutely worth a read, even if you are not a rocket scientist).

[DerekL1963]

1 hour ago, sevenperforce said:

The F-1 engines on the Saturn V had a pretty significant gimbal range. Were the tail fins on the first stage really necessary? Did they provide active or passive guidance?

Gimbaling leads to cosine losses...  passive stabilization helps avoid these losses.  Passive stabilization also helps with overall vehicle stability which in turn makes aborts safer.

Dr. Von Braun's words the matter:

https://books.google.com/books?id=MiYDAAAAMBAJ&lpg=PA185&ots=Cw7tIvaYUk&dq=Since the flight path--usually into orbit--is predetermined%2C and thus ideally suited to programed changes in ga in setting%2C it might appear that there should be no need for fins.&pg=PA185#v=onepage&q&f=false

Edit:  Ninja'ed by Tullius...

Edited July 4, 2017 by DerekL1963

[sevenperforce]

Well that makes it very straightforward!

[Bill Phil]

No, they weren't. Had they built more Saturn Vs, the stabilizers would have been removed, and it's likely that crews would have launched on the soon-to-be space shuttle, had the STS proposal in its original incarnation been approved.