Effect of Bent Fins on Flight?

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Nov 11, 2015
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I'm in the process of building an Estes Ventris for the first time. After gluing the first fin on, I learned the drawback of those otherwise-wonderful "laser-cut fins"... my fins are bent. Not to extremes, but bent enough to bother me. I've read that there are ways to reduce the bend, but with one bent fin already glued, and a lack of patience on my end... I'm proceeding as normal.

I understand any fin that is not aligned perfectly will cause unwanted forces on the rocket. And while I am sticking a G80-7T in it once it's done, I'm sure the TTW fin mounting and relatively large surface area to attach the fin to the BT will be able to take the additional forces. But how much, in practice, have bent fins on your rockets caused issues? I'd think that they'd have an inadvertent benefit of spin-stabilizing the rocket at the expense of speed and altitude... which I already have more than enough of with a G80... :cool:
it depends on the nature of the bend, if when looking from either end the fins look like this ( or this), then the answer is not much. on the other hand if they more closely resemble fan blades...then you'll get roll/spin, how much depends on whether all the fins are bent the same way/amount or if some are bent in the opposite direction.
Here is the worst set of warped fins I have. First and last set of fins I made from laminated cardboard. :eyeroll:

Here's one - bowed and twisted

And another bowed and twisted

Here's an(underpowered) flight on a C6-5 where you can see it kind of wiggles it's way up - but still fun nonetheless.

I've had the same thing happen to me. Everyone thinks I designed it to spin.

My Estes Ventris has one slightly warped fin. On its first flight, it was a straight boost on a G76. There may have been some rotation, but on a motor like that it is hard to notice!

I have a Darkstar Jr with a slightly misaligned fin (still not sure how that happened), it does tend to yaw just slightly on launch but otherwise flies straight.
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That's why in my old age I'm only interested in G10 fiberglass fins. Stiffer is better (that's what she said )
You might get some corkscrewing, depending on how warped they are. I've gotten warped fins in PSII kits too; wet them and put something heavy and flat on them for a few days and they'll straighten out.