How many fins

[xenon]

I have seen rockets with 3 fins and some with 4. Which is better? Wouldn't 4 create more drag or is installation easier when you use 4?

[Batkiter]

I have seen rockets with 3 fins and some with 4. Which is better? Wouldn't 4 create more drag or is installation easier when you use 4?

Hi Xenon!

That is a question of the proportions of your rocket.

The number and size of Fins depend on the relationship of the length of the rocket and the centroid of the individual surface components. Depending upon size and weight the relationship between emphasis and pressure point becomes more favorable or more unfavorable. Most favorably is the relationship of the surfaces to each other, if the emphasis 1 to 1.5 calibers before the pressure point lies. The rocket must be so designed that this relationship of the surfaces to the emphasis corresponds.

Regards Batkiter

[da-water]

it's better to use 3 fins bigger than 4 fins smaller to reduce drag..

[xenon]

Thanks for the explanation but wouldn't the drag be dependent on the area of the fins and not the number. If two rockets were built and one had 3 fins and another had 4 (both have the same total fin surface area). Wouldnt the drag be the same?

[da-water]

yes, it would, but (now it's REALLY hard to explain so i could say something that has no meaning... )
each fin "cuts" the air ("the top side")... it increases drag... 3 fins are less than 4fins so there are less "top sides" that "cut" the air and it means that there is less drag...

did you understand??? :P

[dwrrule]

I have seen rockets with 3 fins and some with 4. Which is better? Wouldn't 4 create more drag or is installation easier when you use 4?

Hi Xenon!

That is a question of the proportions of your rocket.

The number and size of Fins depend on the relationship of the length of the rocket and the centroid of the individual surface components. Depending upon size and weight the relationship between emphasis and pressure point becomes more favorable or more unfavorable. Most favorably is the relationship of the surfaces to each other, if the emphasis 1 to 1.5 calibers before the pressure point lies. The rocket must be so designed that this relationship of the surfaces to the emphasis corresponds.

Regards Batkiter

Your right Batkiter i like your "answer"

[Tim Chen]

yes, it would, but (now it's REALLY hard to explain so i could say something that has no meaning... )
each fin "cuts" the air ("the top side")... it increases drag... 3 fins are less than 4fins so there are less "top sides" that "cut" the air and it means that there is less drag...

did you understand??? :P

Do you mean it all depends on the frontal area of the fins? If you calculate the area of the front edges of the fins then you would know?

One thing I can say is that it is much easier to get 4 fins aligned properly because you can use anything with 90 degree angles (common) to hold them in place while you glue them on. With 3 fins I have to make something that holds them at 120 degrees (not common) and aligned. That's hard to do!

[da-water]

That's hard to do!

not too much..
i "created " a system to glue fins that is very easy and useful... i could explain you how to do it easier.. just let me make some photos

[Aquafire]

That's hard to do!

not too much..
i "created " a system to glue fins that is very easy and useful... i could explain you how to do it easier.. just let me make some photos

I am very interested in a system for fin aligning too! Thank you!

[Tim Chen]

That's hard to do!

not too much..
i "created " a system to glue fins that is very easy and useful... i could explain you how to do it easier.. just let me make some photos

Sounds good to me too!

Thanks!