Whats better 3 or 4 fins

[boomtube]

With me it isn’t so much “What is better” as it is “What looks better”.
When I am developing a design of my own there comes a time when I look at the overall appearance of the rocket and I make a judgment call as to how many fins this particular rocket needs to look its best.
This is all subjective for the most part but I can usually explain my decision if asked.

I recently built a rocket based on one of the small “Quaker Oats” containers. About 4” dia. and about 8” long. I chose to use the fins from Semrocs’ “Little Joe” kit and four such fins just looked inadequate on such a stubby rocket so I went with six.
Would the rocket have flown well with only four? Perhaps, but it truly looked silly with those four tiny fins spaced so far apart on that 4” dia tube.

 

[qquake2k]

I prefer three fins because I'm lazy. Three fins require less slots to cut and less effort to attach.

 

[ClayD]

I like 4 fin rockets, can make the fins smaller.

Always thought 3 fin kits were a mfg preferred thing, less parts to mfg, less slots to cut etc.

Kenny

yep, depending on the "shape" of a fin, the velocity, material properties, and altitude 4 fins can have less drag than the equal surface area of a 3 fin rocket. if the surface area, or span increases on a 3 fin rocket to a point to make the area adequate, 4 fins can be more efficient as it can eliminate drag from flutter and higher fin deflection.

a good point to this is the SPACE LOFT. https://www.space.com/3368-aerospace-return-flight-progress.html

"There were no fins that fell off. The vehicle actually remained structurally intact throughout the entire flight...down to the ground," Larson said. The rocket's less than adequate spin rate, he added, meant that the rocket could not correct for thrust-induced moments typical for a fixed-fin vehicle nosing to higher altitudes and reaching higher speeds.

The SpaceLoft XL's return to flight will feature a fourth tail fin and an increased spin rate, Larson said. The four fins are larger in size and shaped differently in response to the mishap findings from the first flight.

It does talk about increasing the fin size, in responce to handeling larger deviations of stability. BUT, is proof to the point that sometimes engineering actually requires 4 fins.

Here is the most beautifull powerpoint ive ever seen!
https://tripolimn.org/files/Nose Cone & Fin Optimization January 2011.pdf

 

[jadebox]

ok, how about 2 fins?

the cp changes dramatically (for the worse) with two fins.

is it possible to build a stable 2 fin rocket?

Yes ... here are a couple of examples:

• Two Fins, No Kidding
• TwoFin

-- Roger

 

[Derek]

Yes ... here are a couple of examples:

• Two Fins, No Kidding
• TwoFin

-- Roger

interesting. thanks Roger!

 

[Nathan]

Real rockets have zero fins

 

[Derek]

true, but real rockets also have active stabilization.

I think my next project might be in this area.