getting fins truly perpendicular?

I'm putting together an LOC kit. Yes, the body tube is pre slotted with fins TTW, but is it enough to just eyeball the fins as close as possible to perpendicular?

Should I attempt to use some sort of jig?

See this thread for ideas:

https://www.rocketryforum.com/showthread.php?t=6115

Greg

M31 said:

I'm putting together an LOC kit. Yes, the body tube is pre slotted with fins TTW, but is it enough to just eyeball the fins as close as possible to perpendicular?

Should I attempt to use some sort of jig?

Click to expand...

I often use the Fin Guide Tool from PayloadBay.com:


It prints a template you can glue to a piece of cardboard or foam board. Cut out the circle for the body tube and slots for the fins. It then slides over the rocket's body tube and fins to help align them and hold them into place while the glue dries.

As an example, please see:


-- Roger

thanks guys

The Fin Guide Tool is a great idea, use it.

M31 said:

I'm putting together an LOC kit. Yes, the body tube is pre slotted with fins TTW, but is it enough to just eyeball the fins as close as possible to perpendicular?

Should I attempt to use some sort of jig?

Click to expand...

One last thing ...

It is indeed "good enough" to eyeball the fin alignment, especially with TTW. The rocket will fly fine. Getting alignment with the axis of the BT is much more important and the fin slots take care of that for you.

On 3 fin rockets, being off by a small amount is usually visually imperceptible. On 4 fin rockets, getting a perfect cross can be hard to eyeball. My daughter built a Harpoon for her 4H rocket this year (darn thing has 12 fins), and had to tear the fins off twice before it was right. She's no rookie and it made her mad they were off a little. Gladly, she was willing to try again.

If you're a perfectionist, use a jig. If not, don't worry, that LOC rocket will still fly great.

--Lance.

I have always eyeballed mine. The way I figure it- if I look at it and they look like they are off a little bit, then I correct them. If they don't look like they are off then who would know if they are off or not? Maybe they are perfect.

Eyeballing always works for me. Even my L3 Ultimate Wildman was eyeballed, and it's flown on one N and three Ms.

I have used both the Estes Fin Guide as well as the one from Info-Central. The print it out/glue it on carboard/cut out the slots seems to be the better choice.

OTOH, the Estes tool is instant gratification. No work required to get it up and running. Mostly I use the Estes to mark body and motor tubes for cutting. Be advised that the scale while accurately marked doesn't necessarily yield accurate lengths due to the pencil's pointiness or lack thereof and or the placement of the pencil sleeve. There's a bit of trial and error involved. Mine is about a 1/16 of an inch short.

I use this method. I cut the profile out of cardboard, slide it on the BT, the through wall method, keeps you longitudinaly alligned, and this keeps your fins perpendicular, (you have to keep the alignment jig at the same distance from the end of the BT, or it may alter the angle a skoach...

i know this works, because i can set my rocket on a template and they "almost" always align.

Eyeball. Occasionally I recheck them with a printed fin guide. Once the epoxy fillets have set you have to live with what you have.

bradycros said:

The Fin Guide Tool is a great idea, use it.

Click to expand...

Now that's a good idea.

If the assembly job is good enough to make you happy, then it is just fine. If you are worried about impacting flight performance, your fins will have to be significantly (visually obvious) out of whack before it will make much difference (rounding the fin leading edge and feathering the trailing edge will make FAR more difference in flight performance). You can do 99 percent of your sport model assembly by using the old Mark 1 eyeball.

If you are entering a model in a scale competition, you better have them dead-on straight, square, true, and all the rest. It's tool time.

ClayD said:

I use this method. I cut the profile out of cardboard, slide it on the BT, the through wall method, keeps you longitudinaly alligned, and this keeps your fins perpendicular....

Click to expand...

The approach Clay is showing is a great one, and pretty simple to do. You can also use foamboard for your assembly tool, which has the small advantage of being a little softer and 'squishier' compared to cardboard. If you cut the assembly tool exactly to the needed fin thickness and span, the foamboard will hold the fins a bit more snugly (I think) and can still be wiggled off the dried fins later.

Rocketman248 said:

Eyeballing always works for me. Even my L3 Ultimate Wildman was eyeballed, and it's flown on one N and three Ms.

Click to expand...

Yup ,works for me !

Actually ,I do both.Eyeball and have several jigs I made.

oint::roll:

bill2654 said:

oint::roll:

Click to expand...

You new it was comming sooner or later

Paul T

I had pictured you diffrently in my minds eye!

Sodmeister, you need to stop glueing on 2 fins at a time......

XrayLizard said:

Sodmeister, you need to stop glueing on 2 fins at a time......

Click to expand...

Great for my paranoia.I can see people comming at me from all around

OK sorry.Back on topic !

Paul T

These are what I use, even on slotted airframes.

https://www.rocketryforum.com/showthread.php?t=9694

https://www.rocketryforum.com/showthread.php?t=9859

Once I get the time and inclination to resume work on "Loop Quantum Crapien" ( an Endeavour inspired Darkstar looking L3 build), here's the latest plan, but nothing original.

I'll share... Values in ( )'s are sizes I'm using. (1/2" birch ply)

Cut the centering rings into hexagons big enough so the opposing sides are bigger than the ID of the tube they fit in (8") https://www.wikihow.com/Draw-a-Hexagon

Run the hexagons(X4) through a table saw with dado blade (3/16" wide [LQC fin width] ) from point to/through center. (3/16~1/4" deep). The hexagon shape keeps the part nice and flat on the fence .

Once done (in my case 4, front fin set and back fin set), Cut the OD of the centering rings out and then the OD of the motor mount out (via router/jasper jig).

The rest is up to ya'll. Align the centering rings correctly and drop the fins in or build the motor mount with fins on and slide it into the back of the rocket. ( I'll be doing a hybrid of the latter).

This not only aligns the fins (3 per set) but locks them in as well.

I guess you'd need a more-complex-o-gon for a 4 fin set.:wink:

-SB

fin guide tool

I learned it from the "spinal tap" build photos. And i think apogee news letter did a write up on it.
(my first few hpr builds were just like most the new guys, who scrounged from the internet.) So, i obviously cant take credit....
i am too lazy to invest in the time and money others spend aligning them.

Thanks, glad it worked for you. It is very easy to get good alignment, and if you have multiple sets of fins, you can use the wildman darkstar method for the subsequent sets of fins. (go look at wildmanrocketry.com - darkstar instructions.pdf)

Best part is I always have something laying around to cut up and do that with, i have learned paper ream box tops are great, because, i can set it flat on the table, and leave the rocket verticle.

(that fincan in my pictures hit 1531 FPS, and it was quite a strait flight, on a day many were weathercocking .. (nice and gusty kansas day...))

Dollar Tree (I think that's the right name) stores have foam board sheets for ... you guessed it ... a dollar each. They work well for making fin guides like the ones discussed in this thread.

For larger rockets, I've used pieces of 4'x8' sheet foam insulation bought from a home improvement store.

-- Roger