Saturn V Stability

[Dugway]

I have 3D printed a 1/50 scale Saturn V and now I'm modeling it in Rocksim to calculate how much nose weight will be needed to make it stable. When I look at the Rocksim file provided by Apogee for their 1/70 scale Saturn V, I see that they have taken the profile of the F-1 fairings and created fins that are basically 2 dimensional outlines of a 3 dimensional object. If I do the same thing on my model, I end up needing 2 lbs. of nose weight to get at least 1 caliber of stability on the motor combinations that I'm interested in. Fine.

On the other hand, if I create pods containing conical nosecones and use them as the fairings, I end up needing 3 lbs. of nose weight to get the same stability. Does it makes sense that half a cone imparts less stability than a fin of the same cross section? How does Apogee get away with doing it that way, is the Saturn V short/fat enough to benefit from base drag? Is there something else I could be missing?

 

[David Schwantz]

I have the same Saturn V. Flies on AT 2050 ST. I have lots of lead up front. If you 'd like I can remove CSM and weigh that part for you. Good luck with yours.

 

[Dugway]

I guess the question is, how did you decide how much nose weight to use? The model on thingiverse doesn't come with fins so that part will vary wildly between builds. I found an accurate fin model and then scaled it up as much as I dared. It looks quite a bit different than yours and is also mounted closer to the aft of the fairings.

 

[David Schwantz]

Did you not get the Rock sim file that Dave posted? That is what I used for starters. I enlarged the fins a bit for stability, should have gone a bit more than I did. next one will have larger fins. On first flight, at burn out, she did a half roll kind of thing. So I added more weight so on second flight she did not. Love to see pics of yours.

 

[lakeroadster]

I have 3D printed a 1/50 scale Saturn V and now I'm modeling it in Rocksim to calculate how much nose weight will be needed to make it stable. When I look at the Rocksim file provided by Apogee for their 1/70 scale Saturn V, I see that they have taken the profile of the F-1 fairings and created fins that are basically 2 dimensional outlines of a 3 dimensional object. If I do the same thing on my model, I end up needing 2 lbs. of nose weight to get at least 1 caliber of stability on the motor combinations that I'm interested in. Fine.

On the other hand, if I create pods containing conical nosecones and use them as the fairings, I end up needing 3 lbs. of nose weight to get the same stability. Does it makes sense that half a cone imparts less stability than a fin of the same cross section? How does Apogee get away with doing it that way, is the Saturn V short/fat enough to benefit from base drag? Is there something else I could be missing?

Old thread... but for the sake of anybody else building a Saturn V....

I'm in the final throws of completing my scratch build 4 stage Saturn V, and am reviewing the Apogee 1/70th Rocksim just to get a feel for what a good caliber of stability is for a Saturn V model. More on my build here.

I pulled up the 1/70th scale Rocksim file posted here on the Apogee Components website. I used Open Rocket to view the file. The Rocksim is a crude simulation with nearly no detail whatsoever.

Per the simulation there is 3.25 ounces (92 grams) of nose weight in the Command Module:

• The stability of the Apogee Components Saturn V without any motors is 0.816 calibers,
• The stability of the Apogee Components Saturn V with a G79-14 motor is 0.35 calibers,
• The Apogee Components Saturn V falls within the base hack recommended 10:1 max length to diameter ratio. The stability of the Apogee Components Saturn V rocket with a G79-14 motor and the base drag hack applied is 2.36 calibers.

 

[Daddyisabar]

Darn Saturn V's. So thick, resulting in a lot of drag and likes to act like a sail in just a tiny bit of wind. I've seen the mighty Apogee Sat 5 on a G80 in good conditions. Barely stable and under powered in my opinion, but a nice slow, NASA style liftoff so sought after by the scale crowd. It was much better on an H125, it just loves to soak up thrust on the initial take off for some reason. Then I saw it go on an H in a 5 to 7 mph wind, but dude had to launch that day, impatient and waited for the lull. At a 45 degree flight angle it went sideways as much as up. Right over our heads. Super cool and a good pucker factor too!