Fin Alignmemt - After the Fact

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Hospital_Rocket

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Read all the posts.

Checked my math

Rubbed my lucky bunny foot

Followed all the appropriate directions

And still managed to get one TTW fin about 5 degrees out of whack. :mad:

So, what to do?

Would you grind away the fillets, recenter the fin, or just live with it?

It is stilll perpendicular to the airflow, it just looks a little weird.

Any thoughts?
 

powderburner

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probably should tear it out, trim up the slot as best you can, and put the next fin in a bit better
that angle sounds like the fin is quite a bit out of line(?) and should be fixed-----or else you could build a bunker next to your launch pad

(BTW, how can it be perpendicular to the airflow and still be 5 degrees off? and I assume you mean 'in line with' the airflow and not literally 'perpendicular to' it?)
 

kkooch

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Here is a simple fin jig that has served me well over the years. It uses a small C clamp to fasten a reference angle to the plate. The plate is a piece of aluminum with a laminated cad drawing showing fin locations at 120 degrees apart (or you could draw one up with other required divisions).

To use simply slide the fin up against the angle, place the body tube on the alum. mandrel and then slide the fin up to the body. Then hit with some ca to set.

For contest work, my fins are simply rounded at the leading edge with 1/4" of the trailing edge sanded to a knife point. This leaves a nice flat center section to reference on the angle.

For the purist, a full blown tear drop foil could be sanded in. The angle on the fin jig though would need to be sheaved to accomodate the foil. I prefer to use flat fin stock though to ensure alignment is dead on and repeatable, fin to fin.

Kevin K.
 

llickteig1

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Kevin,

Your jig idea is simple and effective. I have struggled with something that the 4-H kids can use to get dead-on fin placement and alignment. You have done it and I'm going to borrow your idea.

I think the hardest part will be finding something for the angle piece that is a true 90 degree angle and can be clamped properly. I can't tell from the photo, what do you use?

Thanks for the great tip, --Lance.
 

Hospital_Rocket

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Originally posted by jcrocket
I'm assuming (because a ttw would have a slot parallel with the tube) the 5 degrees is it leaning over? Considering it would probably fly fine with 3 fins, I'd leave it.

Yeah, it leans to one side. I was mostly wondering if it would be safe to fly. It's my Sudden Rush CP3K so I'm going to go in and fix it. I just can't see my L2 certification bird with a cockeyed fin.

AAAAAARRRRRRGH!

:mad:
 

kkooch

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Originally posted by llickteig1
Kevin,

"Your jig idea is simple and effective. I have struggled with something that the 4-H kids can use to get dead-on fin placement and alignment. You have done it and I'm going to borrow your idea."

Actually, all the credit goes to teammate Ross Hironaka...

"I think the hardest part will be finding something for the angle piece that is a true 90 degree angle and can be clamped properly. I can't tell from the photo, what do you use?"

Precision ground steel angle plate (see plain angle plates on this site). The 3"x 3" x 3" goes for $8.

https://cme-tools.com/surfaceplates2003.html

Enjoy.

Kevin Kuczek
 
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