Aligning Fins

[dg1]

I started my 24 mm Patriot build last night. Got the MMT installed, marked the BT for the four fins and LL, sanded the fins and was going to start installing them and then just said hmm...

On non-TTW type construction, on rockets who's fins trailing edge is forward of the aft end of the BT, how do you make sure that the fins are perpendicular to the BT and that opposing fins are 180 degrees apart with out the Estes fin dohicky jig?

When I was a kid I just eyeballed the postion of the fin relative to perpendicular (with sometimes less than spectacular results). I was hoping to be a little more precise than that now. I did just eyeball them for my latest Red Max...

I was thinking of clamping scrap balsa to the fins to make the trailing edge overhang the end of the BT and then aligning them like I normally do with a straight edge. Any easier tricks? What about 3 FNC rockets?

 

[GregGleason]

Study and find out what works best for you, now. I say "now", because it will change as experience and circumstances dictate.

Take a look at this thread, and look at what many experienced flyers have done to address the challenge of fin alignment.

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

Greg

 

[Scotty Dog]

Like the above thread,there are all kinds of tricks and what ever works for you. I will thro in my 2cents to show you a jig I mad,cuz I got tired of holding a straight edge and aligning the fin and dropping things and so on. I like it cuz it works also on rockets where the fins are aft of the aft end I can ajust the guide in or out. OH-YA on this rocket I used a motor spacer tube and glued the straight piece of balsa on across the center of it. Made lines on the outside of this and aligned those lines on the lines on the main tube.I also like to make a mark on the inside of the aft end on the center line of where the fin goes so I can see it after the other lines get glue all over them. All in all it works for me and YES you still are using the ole EYEBALL to some point.:wink:

 

[dg1]

Thanks for the thread reference.

I knew this had to have been discussed around these parts.

 

[RocketManDan]

There's a lot of fin jigs on the market. Find one that suits your build needs. Apogee has one called the Guillotine

https://www.apogeerockets.com/Rocketry_Videos/Rocketry_Video_74.asp

well made. It's $85 but there was some time put into the designing it and its made of some very good materials. I'm thinking about buying one.

 

[Wayco]

There's a lot of fin jigs on the market. Find one that suits your build needs. Apogee has one called the Guillotine

https://www.apogeerockets.com/Rocketry_Videos/Rocketry_Video_74.asp

well made. It's $85 but there was some time put into the designing it and its made of some very good materials. I'm thinking about buying one.

I was just thinking about posting that link up Dan, but you beat me to it!
I've also had good luck with the Estes fin jig:
https://www.hobbylinc.com/htm/est/est302227.htm
I use it for my smaller Estes and similar models.
I watched the video on the Guillotine, and like it's design too, but the price is a little high for me.

 

[RocketManDan]

Like the above thread,there are all kinds of tricks and what ever works for you. I will thro in my 2cents to show you a jig I mad,cuz I got tired of holding a straight edge and aligning the fin and dropping things and so on. I like it cuz it works also on rockets where the fins are aft of the aft end I can ajust the guide in or out. OH-YA on this rocket I used a motor spacer tube and glued the straight piece of balsa on across the center of it. Made lines on the outside of this and aligned those lines on the lines on the main tube.I also like to make a mark on the inside of the aft end on the center line of where the fin goes so I can see it after the other lines get glue all over them. All in all it works for me and YES you still are using the ole EYEBALL to some point.:wink:

I like it Scotty...pretty clever thinking on your part.

 

[RocketManDan]

I was just thinking about posting that link up Dan, but you beat me to it!
I've also had good luck with the Estes fin jig:
https://www.hobbylinc.com/htm/est/est302227.htm
I use it for my smaller Estes and similar models.
I watched the video on the Guillotine, and like it's design too, but the price is a little high for me.

I agree the price is a little high, but you have to admit it is a really cool jig...

Scotty Dog has a cool idea with his jig and I suppose the ESTES jig for the money isn't too bad...

 

[atxcple]

and I suppose the ESTES jig for the money isn't too bad.

..

i like this one as i have used it all the way up to a couple 29mm Loc kits The WEASLE, LEGACY, and LIL NUKE

 

[bjphoenix]

How do you know if the fins are aligned or not? If you can see visually that they are not aligned then you would say that they are not aligned. If they look aligned to you then who is to say if they are or are not.

If you can see that they aren't aligned after the rocket is finished, then you should be able to see if they are aligned during construction. Put the fin on and look at it until it looks to be aligned, then let it dry.

If you want something better than this, if you aren't good at aligning visually, or if you want to know that the fins are aligned better than what you can see, then make some templates. I've seen photos on here of rockets with fin templates made out of a flat piece of cardboard. Cut a hole in the middle and cut slots for 3 or 4 fins. Slide it down the tube and over your fins to hold them in alignment while the glue dries.

I just align mine by looking at them until they look right, but then I'm building low power and mid power models. The hardest alignment is on rockets with 4 fins, because it is real easy to tell if one fin is aligned with the fin on the opposite side of the airframe.

 

[RocketManDan]

How do you know if the fins are aligned or not? If you can see visually that they are not aligned then you would say that they are not aligned. If they look aligned to you then who is to say if they are or are not.

If you can see that they aren't aligned after the rocket is finished, then you should be able to see if they are aligned during construction. Put the fin on and look at it until it looks to be aligned, then let it dry.

If you want something better than this, if you aren't good at aligning visually, or if you want to know that the fins are aligned better than what you can see, then make some templates. I've seen photos on here of rockets with fin templates made out of a flat piece of cardboard. Cut a hole in the middle and cut slots for 3 or 4 fins. Slide it down the tube and over your fins to hold them in alignment while the glue dries.

I just align mine by looking at them until they look right, but then I'm building low power and mid power models. The hardest alignment is on rockets with 4 fins, because it is real easy to tell if one fin is aligned with the fin on the opposite side of the airframe.

You make some valid points. Also making through the wall fins would solve the problem I would think?

 

[Micromeister]

Alignment is a tricky thing. Having the fins perfectly aligned on the long axis is paramount for best performance, while being a degree or two off absoluetly 90° or 120° apart has very little effect.
Most fin alignment guides sort of take fin thickness into account. Estes plastic fin alignment guide offsets the vertical guides for 3/32" and 1/8" fin thicknesses but doesn't do much for other material thicknesses. Centering the fin thickness on our marked lines can be tricky.
Personally I don't even try anymore. I built a fin aligment jig with changable shims the match the tickness of whatever fin thickness i'm working with so alignment is almost automatic as I lay the fin on the mounting table. Sure the attachement points and extended lines still have to be made but that's what we have other tools for.
Whatever method you choose remember that fin alignment doesn't have to, nor will it ever be "perfect". We're flying Model Rockets so it really doesn't have to be....If one fin is off a little we'll observe a spin on the way up. it won't really harm the flight path and would only cost a tiny bit in achived alititude. and unless your really pickey and looking down the model head on most won't ever notice.

 

[dg1]

Well, after looking at all the available "fixtures", :wink: I used the Mk. CDXII Bio-Optical Fin Alignment Device for the Patriot. Though the precision of the BOFAD is not up to current specs (new optical correction lens retrofit needed) I believe that it was adequate for this project.

Thanks for all the input. I'll probably buy or build something in the future based on the recommendations, but I was itching to put this puppy together and couldn't wait.

 

[Scotty Dog]

Well, after looking at all the available "fixtures", :wink: I used the Mk. CDXII Bio-Optical Fin Alignment Device for the Patriot. Though the precision of the BOFAD is not up to current specs (new optical correction lens retrofit needed) I believe that it was adequate for this project.

Thanks for all the input. I'll probably buy or build something in the future based on the recommendations, but I was itching to put this puppy together and couldn't wait.

So, the "EYES" have it.Good choice.

 

[UrbanKnight]

How do you know if the fins are aligned or not? If you can see visually that they are not aligned then you would say that they are not aligned. If they look aligned to you then who is to say if they are or are not.

If you can see that they aren't aligned after the rocket is finished, then you should be able to see if they are aligned during construction. Put the fin on and look at it until it looks to be aligned, then let it dry.

If you want something better than this, if you aren't good at aligning visually, or if you want to know that the fins are aligned better than what you can see, then make some templates. I've seen photos on here of rockets with fin templates made out of a flat piece of cardboard. Cut a hole in the middle and cut slots for 3 or 4 fins. Slide it down the tube and over your fins to hold them in alignment while the glue dries.

I just align mine by looking at them until they look right, but then I'm building low power and mid power models. The hardest alignment is on rockets with 4 fins, because it is real easy to tell if one fin is aligned with the fin on the opposite side of the airframe.

With a 3FNC rocket, of you lay it on its side on a table, the one fin sticking up will be tilted one way or the other if the fins aren't perpendicular. The reason this can't be checked while building is because resting it on the other 2 fins will cause them to start shifting out of place. Also, you wouldn't be able to tell exactly which fin is off, as it might not be the one sticking up.

As for alignment lengthwise, when I used square or rounded fins, I just aligned one edge along the line I drew. With airfoiled fins, I align the tips, and they will be as accurate as my sanding was... which is "enough" for a piece of wood and plastic I'm going to shoot hundreds of feet into the sky.

 

[MarkII]

I use this online tool to create a fin guide that I print out and then glue down onto a piece of foam core. Then I carefully cut out the center circle and the slits for the fins. I cut the circle slightly smaller than the tube diameter, and then use a piece of sandpaper wrapped around a large dowel to sand the edges of the hole right to the printed line to get a precise fit. I tack my fins on and then slip the guide over them to keep them aligned and straight while the glue dries. It's simple and effective.

 

[GDJ]

I use this online tool to create a fin guide that I print out and then glue down onto a piece of foam core. Then I carefully cut out the center circle and the slits for the fins. I cut the circle slightly smaller than the tube diameter, and then use a piece of sandpaper wrapped around a large dowel to sand the edges of the hole right to the printed line to get a precise fit. I tack my fins on and then slip the guide over them to keep them aligned and straight while the glue dries. It's simple and effective.

I just checked this out. Pretty slick! I likes it!

 

[UrbanKnight]

I use this online tool to create a fin guide that I print out and then glue down onto a piece of foam core. Then I carefully cut out the center circle and the slits for the fins. I cut the circle slightly smaller than the tube diameter, and then use a piece of sandpaper wrapped around a large dowel to sand the edges of the hole right to the printed line to get a precise fit. I tack my fins on and then slip the guide over them to keep them aligned and straight while the glue dries. It's simple and effective.

I did pretty much the same thing, except I just used a compass, a protractor, and a ruler to find and mark the foam core. This link will be very helpful. Thanks!

 

[RodRocket]

The Estes jig needs to be mounted to something flat to keep it from flexing. I have quit using mine until I can get it secured to something as I have been having trouble getting fins aligned with it. And may change my gluing method with the jig. Maybe try to get everything aligned dry and then set the fins with spots of thin CA.

Right now I use the eye method and a light application of glue so it sets a bit quicker. Just enough glue to hold in place and get aligned. After that dries, I go back and do the fillets.

The tube marking guides and ruler that Estes has work great and I use those all the time. Just need to tinker with the fin jig to make it work better.

 

[RocketManDan]

I just checked this out. Pretty slick! I likes it!

It is pretty cool, but what if you have a rocket with a 3" diameter and a 5" fin span? You would need a pretty large piece of paper or just upscale it.

I also noticed when I print the fin wraps at 100% it seems to come up short?

 

[BABAR]

One trick for longitudinal alignment

Assuming your marking lines are straight, cut a 1/16" x 1/16" balsa strip the length of the fin. Glue this along one edge of the marking line. Allow to dry.

Because this is small and light, easy to get this perfectly lined up.

Butt your fin against this and you get arrow straight alignment and an extra strong joint.

 

[MarkII]

It is pretty cool, but what if you have a rocket with a 3" diameter and a 5" fin span? You would need a pretty large piece of paper or just upscale it.

I also noticed when I print the fin wraps at 100% it seems to come up short?

I haven't tried it with anything that large yet. But when you print out a template that is larger than one sheet of paper, you can print it out over several sheets. Then just piece them together when you go to glue them down. The site also has a tool to create a different style of fin alignment device that might be easier to use with larger rockets.

The fin wrappers are only as accurate as the dimensions that you input. If the first one comes out being too short, then bump up the diameter a little bit and try again. Repeat until it comes out right. Save that document somewhere convenient so that you can look up the setting (it's printed on the page) and won't have to go through the process again the next time that you want to create a wrapper for that tube. I need to do this from time to time. Also, the tool will adjust the document format so that it can fit the whole pattern onto one page, but this might be a larger sheet of paper than your printer can handle. If you create a wrapper for a larger tube, then it would be a good idea to click on Document Properties in the File menu to verify the generated document's page size. If your printer outputs to 8.5" by 11" paper, and the site creates a fin wrapper sized for 11" by 17" paper, then things can get complicated.

 

[UrbanKnight]

One trick for longitudinal alignment

Assuming your marking lines are straight, cut a 1/16" x 1/16" balsa strip the length of the fin. Glue this along one edge of the marking line. Allow to dry.

Because this is small and light, easy to get this perfectly lined up.

Butt your fin against this and you get arrow straight alignment and an extra strong joint.

What if your fins are airfoiled?

 

[BABAR]

You shouldn't have any airfoiling at the rootof the fin where it attaches to the body tube, just on the lead and trailing edges, and some people will round or otherwise shape the lateral edge

 

[UrbanKnight]

You shouldn't have any airfoiling at the rootof the fin where it attaches to the body tube, just on the lead and trailing edges, and some people will round or otherwise shape the lateral edge

I understand that, but if you airfoil the trailing edge and round the leading edge, that makes a teardrop profile for the root and tip edges. Or am I not understanding you correctly?

 

[Woody's Workshop]

Root edge is the edge mounting to the body tube.
Leading edge is the edge pointing forward into the launch.
Trailing edge is the edge pointing back at the launch pad at launch.
As for the apogee expensive jig, I have aluminum angle on hand, and it seams to be an easy clone to make per your size rockets that intend to use it on.
I just may make one.
Also thinking about cloning the Estes one in a larger size with different shaped verticle supports to fit different fin shapes.
But that will be upcoming this winter as the fires stoked in the wood shop!

 

[MarkII]

I understand what UrbanKnight is talking about because I sand airfoils into fins myself from time to time. The root edge isn't airfoiled itself, but it takes on a teardrop profile following the airfoiling of the leading and trailing edges. Therefore it no longer has straight sides along its length. Gluing on a guide strip of wood along the length of the root edge becomes ineffective because of this. A foam core alignment guide like the one that I described earlier can still be used, though. You just may need to adjust the fit of the slots a little bit. Prior to cutting them out, place the root edge on the guide and align it as you would want the fin to be on the rocket, and then trace around the root edge. You may not need to duplicate the root edge profile in the slot that you will eventually cut out, but the tracing may give you an indication of where you can make some adjustment to fit the actual shape of the fin a little bit better.

 

[Marc_G]

The Estes jig needs to be mounted to something flat to keep it from flexing. I have quit using mine until I can get it secured to something as I have been having trouble getting fins aligned with it. And may change my gluing method with the jig. Maybe try to get everything aligned dry and then set the fins with spots of thin CA.

Right now I use the eye method and a light application of glue so it sets a bit quicker. Just enough glue to hold in place and get aligned. After that dries, I go back and do the fillets.

The tube marking guides and ruler that Estes has work great and I use those all the time. Just need to tinker with the fin jig to make it work better.

I haven't had trouble with the jig flexing, but I have had loads of trouble with the little tubes they give you (13mm, 18mm) etc. jiggling around making it hard to ensure the rocket is straight. Even after following the directions and using tape/label shims to tighten them up there's more play than I like.

I think I fixed this, though. I bought a big old bolt, 1/2" diameter, and used it in place of the 13mm tube. I got an appropriate nut and tightened 'er down. The bolt is now exactly 90 degrees to the flat surface and 100% stable. I wrapped a little masking tape around the bolt and either a BT-5 or the 18mm tube fit securely with almost no wiggle.

Marc

 

[BABAR]

What if your fins are airfoiled?

I see your point (pun intended). As MarkII notes, if you have a perfectly airfoiled fin (continuous curvature from lead edge to trail edge) you will not have any perfectly flat surface to line up against the balsa edge. As a sport flyer, my fins are never that perfectly tapered, so in my case I'd say about 90 plus percent of the the edge is flat, so it works for me. As a compromise, you could sand a curve along the lead, trail, and outside (non-body tube, non-fin side) of the balsa strip, and cut a length a bit shorter than the fin so you don't mess up the airfoil at the root edge as much. For competition flying however I am guessing the added weight and the drag would be prohibitive in any even.

Terminology question.

Root edge is the part attached to the body tube.
Lead Edge is part toward the nose.
Trail Edge is part toward the tail.

Is there an accepted name for the "other" edge, I guess I'd call it the lateral edge (the edge opposite the root?)

 

[UrbanKnight]

That makes sense, BABAR. Come to think of it, I doubt my tapers go all the way to the front either, even if I'm trying.

OpenRocket calls the edge opposite the root the "tip", but I have no idea if it's an official term or not.