Fins on the Saturn Rockets

[llanitedave]

I've often wondered about the fins that were attached to the base of the Saturn rockets.  The fins were pretty large on the Saturn 1 series, and a bit minimalist on Saturn V.  They seemed more stylistic than functional. (I'm sure they really weren't) They seem a bit anachronistic.  The Atlas and Titan did not have fins, neither did the Jupiter.  I'm wondering what pupose they surved.  They added weight and drag, but how did they increase stability?  Was the gimble rate on the engines too low to keep the rockets controlled?  How much greater payload could have been launched without them, if they could have been dispensed with?

[the_other_Doug]

I've always heard that the Saturn V fins were designed to stabilize the stack during some engine-out situations.  My impression was more that they would give the crew more time to abort than they were to keep them from needing to abort.  I want to say that they were designed to keep the stack upright during early engine-out situations so that, as the Saturn fell back to the pad, the CSM and the LES still pointed upwards for a clear abort path.

Being on the first stage, the Saturn fins were at the bottom of the staged rocket equation, where extra weight doesn't hurt your total performance as much as extra upper-stage weight can, but we need some of our actual engineers around here to answer the second part of the question with any authority...

-Doug  (With my shield, not yet upon it)

[NovaSilisko]

IIRC the planned second batch of Saturn Vs would have lacked the fins, as flight data showed they didn't do as much as predicted.

[the_other_Doug]

Would've looked strange without the fins... but I guess that has more to do with what you grew up with, so to speak.  I was used to that majestic beast having those stubby little fins (in scale to the rest of the bird, anyway).  The TVC obviously kept the stack pointed true with or without the fins, though, so if it ever became absolutely necessary to lose their weight, the S-ICs that flew could probably have been retrofitted to remove them.

The fins on the first Saturn I boosters always looked *way* too big, though (as far as aesthetics are concerned, anyway).  Especially with the S-IV stage being so much slimmer, at 18 feet in diameter, as opposed to the 21.5-foot-diameter S-I.  It looked like the thrust section/fin mount of a huge rocket, the first stage tankage of a medium-sized rocket and the second stage of a small rocket.  Granted, none of the stages were small, but the look of it was that it started oversized and ended sorta puny.

I always thought it was a shame, BTW (totally off-topic) that the S-IV stage was never used for much beyond checkout flights and the Pegasus satellites.  It was a nifty stage, and the first to cluster more than two hydrolox engines.  It may not have taken Apollo to orbit, but it did pave the way for further hydrolox engine and clustering development.

Was there ever any real thought of using the S-IV with other main stages?  I wonder what a Titan-III type main stage with an S-IV on top could have accomplished?  (I should probably just search the topics, I bet there are half a dozen threads about other uses for the S-IV in here somewhere.)  If they hadn't gone through the process of developing the S-IV stage, I dunno how confident the Marshall guys would have been just jumping directly into developing the S-II and S-IVB stages.

Sorry for the drift -- we return you now to your regularly scheduled topic. 

-Doug  (With my shield, not yet upon it)

[deaville]

Of course the Saturns had fins. How else would the scale models of the rocket be kept upright without something to slot into the supports on the base? 

[tonya]

Ariane 4 used to fly both with and without fins, depending on the booster configuration.  In silhouette, both rockets had quite similarly shaped base stages.

[jtrame]

Of course the Saturns had fins. How else would the scale models of the rocket be kept upright without something to slot into the supports on the base? 

Obviously to help us model rocketeers build stable models!

[Bob Shaw]

Ever seen a Saturn of any shape close up? NONE of those fins were exactly 'small'! Them birds wos BIG!!!

[edkyle99]

The fins on the first Saturn I boosters always looked *way* too big, though (as far as aesthetics are concerned, anyway).  Especially with the S-IV stage being so much slimmer, at 18 feet in diameter, as opposed to the 21.5-foot-diameter S-I.  It looked like the thrust section/fin mount of a huge rocket, the first stage tankage of a medium-sized rocket and the second stage of a small rocket.  Granted, none of the stages were small, but the look of it was that it started oversized and ended sorta puny.

The fins provided stability for Apollo spacecraft during planned crewed flight abort modes - and yes, Saturn I Block II was originally developed to perform early manned Apollo missions (later cancelled in favor of Saturn IB).  On the Block II Saturn I vehicles, they were big because the rocket used a small second stage and was relatively short.  Plans called for taller follow on Saturns with bigger second stages (with S-IV moved up to become a third stage) that would likely not have to use the fins.  Note also that Saturn I "stood" on its fins, so part of the fin structure was required for that purpose.

 - Ed Kyle

[Dmitry_V_home]

Gentlemen, we won't forget that some time on the Saturn-1 rocket was supposed to send DynaSoar rocket glider to space. As his wing created the big destabilizing moment, on the rocket it was necessary to use large stabilizers.

[kevin-rf]

Gentlemen, we won't forget that some time on the Saturn-1 rocket was supposed to send DynaSoar rocket glider to space. As his wing created the big destabilizing moment, on the rocket it was necessary to use large stabilizers.

Huh? I always thought DynaSoar was baselined on various generations of Titans through out it's evolution. Did it have a Saturn period?

[joema]

...
The fins provided stability for Apollo spacecraft during planned crewed flight abort modes...

This was discussed by Von Braun himself in Sept 1964 Popular Science, page 68:

http://books.google.com/books?id=MiYDAAAAMBAJ&lpg=PP1&pg=PA68#v=onepage&q&f=false

"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"

[Dmitry_V_home]

Huh? I always thought DynaSoar was baselined on various generations of Titans through out it's evolution. Did it have a Saturn period?

http://www.astronautix.com/craft/dynasoar.htm

[llanitedave]

...
The fins provided stability for Apollo spacecraft during planned crewed flight abort modes...

This was discussed by Von Braun himself in Sept 1964 Popular Science, page 68:

http://books.google.com/books?id=MiYDAAAAMBAJ&lpg=PP1&pg=PA68#v=onepage&q&f=false

"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"

I'd say that's pretty much straight from the horse's mouth!

[kevin-rf]

Huh? I always thought DynaSoar was baselined on various generations of Titans through out it's evolution. Did it have a Saturn period?

http://www.astronautix.com/craft/dynasoar.htm

Only two references to the Saturn I are made in that.

The Titan was base lined in June 1959, Airdrops B-52, Titan I for suborbital tests, and Titan C (which was never built).
In November 1960, the Titan II replaced the Titan I for suborbital flights.
In September 1961, the Titan C evolved from an all liquid booster to the Titan IIIC with solids for orbital flights and Transtage for deorbit.
In December 1961, the suborbital tests on the Titan II where deleted.
It stayed pretty solid on the Titan III after that point.

So where does the Saturn I fit in according to the article?
In March of 1961 

USAF Dyna-Soar System Project Office personnel visited NASA headquarters for review of technical and management programs.

The report was delivered in April.

Those are the only two mentions. Based on the article, it was looked at as an option as part of a one month study. The Saturn report was never acted on in the time line.

[truckmen]

Does anyone have the actual dimensions of the Saturn V fins?

[rocketguy101]

Does anyone have the actual dimensions of the Saturn V fins?

http://www.accur8.com/SaturnV_Fin.html

if you're wondering about the source, read about John Pursley
http://www.accur8.com/About_Me.html

[JoeFromRIUSA]

I wonder how the S-IV would have been as a fourth state on a Saturn 5? Re theotherDoug's earlier post

[Michel Van]

on Dyna Soar and Big fin Titan

they were needed to counter balance the Dynamics's soar wing on top of Titan during launch and max-Q
why the Titan IIIC do not picture with fins for Dyna soar launch  is mystery for me

is any date on weight of Saturn V Fins ?
i'm interested payload gain on Saturn V were fins are removed.

[Proponent]

is any date on weight of Saturn V Fins ?
i'm interested payload gain on Saturn V were fins are removed.

Page 17 of the PDF attached to this post specifies 2054 lb for "nonmoveable aerodynamic control surfaces" on the S-IC stage.

I suspect that removing them might have increased payload by a couple of hundred pounds: first stages aren't terribly weight sensitive, since the weight is not carried very far.  Removing the fins would have lowered drag a bit too, but I doubt the effect would have been large.