How easily to large rockets roll?

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Neilw

Simulates with KSP
Joined
Aug 19, 2014
Messages
81
Reaction score
0
Hello,

Like most of the questions I end up asking, this one originated from a debate with a colleague. The question is, if we have a long and heavy rocket with stability around 1.5-1.7, how much will the rocket's tendency to roll be affected if it has 4 or 3 fins?

Thanks
 
The number of fins doesn't effect the roll rate. What determine the roll rate is the alignment of the fins. If the fins are aligned to be parallel to the central roll axis of the rocket there should be no roll. If they are canted (all in the same direction) then they act as a propeller in reverse and the roll rate will be proportional to the airspeed and the aerodynamic slip of the airflow over the fins.

https://www.apogeerockets.com/downloads/Newsletter228.pdf

https://www.backyard-ballistics.com/pdfs/backyard_ballistics_plan_4.pdf

Bob
 
What Bob said is gospel, but don't forget you can induce spin by not having a symmetrical airfoil. Almost anything is better than blunt square edges.
 
If any of my Rockets roll it means I screwed up putting the fins on and I scrap the Rocket or launch it up into my woods to hang from a tree.
I can't tolerate anything less than perfection when it comes to fin alignment.
 
If any of my Rockets roll it means I screwed up putting the fins on and I scrap the Rocket or launch it up into my woods to hang from a tree.
I can't tolerate anything less than perfection when it comes to fin alignment.

I would have the best decorated trees in town - and no flyable rockets if I held myself to that criteria. :grin:
 
If any of my Rockets roll it means I screwed up putting the fins on and I scrap the Rocket or launch it up into my woods to hang from a tree.
I can't tolerate anything less than perfection when it comes to fin alignment.
Your standards are higher than most, but most of us we still manage to occasionally decorate the forest with our better rockets...........:facepalm:

Bob
 
The argument actually arose when one guy I know said that rockets acquire a little bit of roll when they correct from an angle of attack. He brought out some fancy maths which apparently proved that fewer fins meant more roll acquired on correction. Maybe these values are just negligible?
 
If any of my Rockets roll it means I screwed up putting the fins on and I scrap the Rocket or launch it up into my woods to hang from a tree.
I can't tolerate anything less than perfection when it comes to fin alignment.

When that happens instead of launching them into the trees tell me and I will take them none of my rockets are even close to that standard. :p
 
Back
Top