Whats better 3 or 4 fins

[RDE]

I am building a large mpr so i have a very important question whats better 3 or 4 fins?

 

[paul.nortness]

Depends on what you are trying to do and what you like.

Generally speaking, 3 fins provides less drag

 

[Handeman]

Depends. What are you designing it for? High performance would need low drag so 3 would be better. If you need the CP low on the rocket for stability, then 4 fins will work better.

 

[Green Jello]

3 is deFINitely easier to get to look nice and aligned.

 

[rocketgeek101]

If your design has a low stability margin 4 fins might be better then 3. Also 4 fins are easier to align properly then 3 fins. I say go for what ever you think is best...

 

[RDE]

Thanks guys for replying .....

 

[Gary Byrum]

Nobody makes an easy answer for you here. 3 fins can be as efficient as 4 depending in your build. When I design a model, I run it through my head if 4 outweighs 3, 5 or 8 fins. I just have to look at my design and make a decision. It has to look aesthetically appealing as well as stable. I'm a little gifted in that I can look at a design and know it's stable. OK, time for all you disbelievers to tap that note.

 

[fyrwrxz]

Nobody makes an easy answer for you here. 3 fins can be as efficient as 4 depending in your build. When I design a model, I run it through my head if 4 outweighs 3, 5 or 8 fins. I just have to look at my design and make a decision. It has to look aesthetically appealing as well as stable. I'm a little gifted in that I can look at a design and know it's stable. OK, time for all you disbelievers to tap that note.

you do this long enough and it's like a machinst can tell just by looking the different between .003 and .005 shim stock. Trained eyeballs. No argument here, buddy! Oth-you have to pay your dues and see a LOT of rockets. Sometimes-it's what's inside the counts (Hallmark Moment Reminder...) Just 'cuz it has fins don't mean it drives like a Cadillac. Old school, that is....

 

[RocketflierVB]

3 is better then 4. That is only 3 fins to glue up and 6 fillets to make instead of 8.

 

[SacEsq]

This is a long-debated subject and you will get a variety of answers and opinions. Next up for discussion ... is it an engine or a motor?

 

[qquake2k]

Do you have a Rocksim or Open Rocket file? Or a sketch of the design?

 

[qquake2k]

Next up for discussion ... is it an engine or a motor?

:lol:

 

[JPVegh]

4 fins is best.
It's a motor not an engine.
Wood glue is better than epoxy.

Hmmm, are there any other rocketry controversies we can stir up?

 

[Green Jello]

Also 4 fins are easier to align properly then 3 fins.

I could not disagree with this any more.

 

[Getmore]

I like 3 fins for my rockets its one less fin that I have to make. 4 fin rockets can look cool and fly just as good. I like some speed in my rockets I quess that is why i go with 3 fins and a tail cone.

 

[Daddyisabar]

I've been likin' two big fins way up at the front of the rocket, with the motors up front too. Makes 'em look like airplanes, but the fellers tell me that is bad rocket science and that it would be much better to put 3 or 4 fins and the motor at the hind end of the rocket.

 

[Handeman]

Nobody makes an easy answer for you here. 3 fins can be as efficient as 4 depending in your build. When I design a model, I run it through my head if 4 outweighs 3, 5 or 8 fins. I just have to look at my design and make a decision. It has to look aesthetically appealing as well as stable. I'm a little gifted in that I can look at a design and know it's stable. OK, time for all you disbelievers to tap that note.

Permanent RSO duty for you! :y:

 

[qquake2k]

I could not disagree with this any more.

I agree with your disagreement.

 

[rocketgeek101]

I could not disagree with this any more.

Why? I have always found aligning four fins to be easier to do then aligning three (but then again I don't use a jig -- I just eyeball them).

 

[cerving]

Three fins will have less drag than four, all other things being equal. It's going to be less tolerant of misalignment, however, so if you're not using through-tube fins and/or a jig you need to be a little more careful to get it right.

 

[neond7]

From my experience, my most stable rocket is a 4f (LOC Doorknob). My most squirrely is a 3f LOC IV blue tube clone - at the last launch, the RSO commented "Its got a wiggly butt!!" since it shimmied around a bit right after motor burnout. I added nose weight, but it still shimmies. Turns out its not a CG/CP relationship stability issue, the stupid fins are crooked!!

 

[RDE]

I have Open Rocket and my dad helped me to design the fins, so far I am leaning to build three fins. I am building my rocket with G - Cesseroni and I try also to build dual deployment. Any suggestions? I am trying to enter competition, so the hight, look (style) and the flight.

 

[qquake2k]

I am building a large mpr so i have a very important question whats better 3 or 4 fins?

I have Open Rocket and my dad helped me to design the fins, so far I am leaning to build three fins. I am building my rocket with G - Cesseroni and I try also to build dual deployment. Any suggestions? I am trying to enter competition, so the hight, look (style) and the flight.

You're building a large MPR dual deploy to fly on a G? Seems like overkill to me. Can you post the Open Rocket file?

 

[qquake2k]

I'm sorry, but the more I think about this the less sense it makes to me. If it was a minimum diameter on a G, I could see flying it dual deploy. But when you say "large MPR", that makes me think of 2.6" or 3" body tubes. My first dual deploy was 2.6" Blue Tube, and I flew it on an I. You have to remember, dual deploy will add a lot of weight with the av-bay and electronics, two chutes and harnesses, etc.

 

[Derek]

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?

 

[Daddyisabar]

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?

Read the Apogee Newsletter #220. Two finned rockets are dynamically unstable and will quickly cause the rocket to go unstable. Maybe curved fins will work?

Lots of nose weight and power will help with stability, as will opposed canted motors getting what I call some good "flame fin action." That combo will make an oddroc airplane rocket, basically a 2 finned rocket, fly like a 3 or 4FNC model rocket.

 

[Derek]

Read the Apogee Newsletter #220. Two finned rockets are dynamically unstable and will quickly cause the rocket to go unstable. Maybe curved fins will work?

Lots of nose weight and power will help with stability, as will opposed canted motors getting what I call some good "flame fin action." That combo will make an oddroc airplane rocket, basically a 2 finned rocket, fly like a 3 or 4FNC model rocket.

that article is interesting. when I tried a 2 fin rocket in openrocket with the fins 180 degrees apart, the cp ends up in the nose cone. what I didn't do was try reducing the angle between them. doing so does move the cp back into the tail, but now it is asymmetric.

the curved fin approach seems like it would be more draggy than 3 fins, which would defeat the purpose imo.

thanks for point me to that article.

 

[Green Jello]

Why? I have always found aligning four fins to be easier to do then aligning three (but then again I don't use a jig -- I just eyeball them).

Because the human eye can't tell if three fins aren't spaced EXACTLY 120 degrees apart, where it sure as hell can see if you mess up a cross pattern.

 

[soxfan121]

well it really depends on what your goals for the rocket are. if you are looking for height 3 fins (less drag, less stability) with a large root chord and smaller or zero tip chord (triangular) with a high angle. but if you are looking for a straight slower (not by that much) you should go with 4 fins, more drag but more stability.

 

[KenRico]

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