Fin aerofoil

[Iya2]

Hello all I'm starting to get into Mid and Hi powered rocketry. I'm trying to airfoil my fins but I'm having trouble finding a precise and repeatable method for sanding them. Looking for any literature or information on procedures. What methods do you use to aerofoil?

 

[SolarYellow]

There's an Apogee newsletter showing the use of jigs.

 

[David_Stack]

In addition to the Apogee newsletter resource mentioned by SolarYellow, a search of the forum here using terms like "fin bevel" will pull up numerous threads with various members offering their contributions on how they do it.

One Example:

https://www.rocketryforum.com/threads/questions-on-beveling-a-plywood-fin.176413/
and a link to one of John Coker's 'how to's from that same thread':

http://www.jcrocket.com/finbevels.shtml

 

[SolarYellow]

Just pointing out that "beveling" is a very different and much easier process than generating an accurate, consistent, repeatable/repeating airfoil profile.

For HPR, methods can get more advanced and resemble model aircraft composite construction. CNC router profiling of foam or wood or hot wire cutting foam cores which are then laminated with fiberglass or carbon fiber. John Coker has done the CNC thing. I plan to do both CNC and hot wire in the future, but haven't actually done it yet.

 

[watheyak]

CNC router profiling of foam or wood or hot wire cutting foam cores which are then laminated with fiberglass or carbon fiber.

Got any examples of this?

 

[SolarYellow]

Got any examples of this?

https://www.jcrocket.com/aerobee.shtml#fins
https://www.rocketryforum.com/threads/fin-airfoiling-jig.136139/#post-1618857

 

[Tobes]

Just pointing out that "beveling" is a very different and much easier process than generating an accurate, consistent, repeatable/repeating airfoil profile.

For HPR, methods can get more advanced and resemble model aircraft composite construction. CNC router profiling of foam or wood or hot wire cutting foam cores which are then laminated with fiberglass or carbon fiber. John Coker has done the CNC thing. I plan to do both CNC and hot wire in the future, but haven't actually done it yet.

I definitely don’t think anyone should be presenting foam core fins as an acceptable method. I think John’s example may be the lone example of this technique that’s actually flown. (Did it?)

Hot wire foam doesn’t have the required strength as a composite core in this application, and is absolutely unsuitable for high power rocketry. I find it odd that @SolarYellow presented like a professed expert on the matter, and presenting it as a common practice.

Bad info that could lead to expensive and dangerous mistakes.

 

[SolarYellow]

I assumed the reader would design their composite construction appropriately, including selection of foam and design of the layup. You can make the layup like an HLG wing, or you can make it as strong as it needs to be with as many layers of glass/carbon/aramid as required over whatever density/strength of foam is required. There is no question in my mind that a foam core fin can be made Mach capable if required.

 

[kalsow]

I definitely don’t think anyone should be presenting foam core fins as an acceptable method. I think John’s example may be the lone example of this technique that’s actually flown. (Did it?)

Hot wire foam doesn’t have the required strength as a composite core in this application, and is absolutely unsuitable for high power rocketry. I find it odd that @SolarYellow presented like a professed expert on the matter, and presenting it as a common practice.

Bad info that could lead to expensive and dangerous mistakes.

Huh?? My L3 rocket was a ~1/3 scale Honest John. Fins had foam cores cut with a hot wire. They were covered with carbon fiber and glass and then tip-to-tipped. They've survived just fine, even a hard landing where the main did not deploy.

 

[justforfun]

This is the finished product, hot wire, etc.

Roy

 

[ghostfather]

If you have OpenScad (free parametric CAD software), and a 3D printer, you can make your own sanding jigs for beveling fins. Using this file, you can set your fin thickness, and angle of bevel, print it, glue some sandpaper in it, add some elbow grease, and Bob's your uncle.

 

[Seatechnerd83]

I definitely don’t think anyone should be presenting foam core fins as an acceptable method. I think John’s example may be the lone example of this technique that’s actually flown. (Did it?)

Hot wire foam doesn’t have the required strength as a composite core in this application, and is absolutely unsuitable for high power rocketry. I find it odd that @SolarYellow presented like a professed expert on the matter, and presenting it as a common practice.

Bad info that could lead to expensive and dangerous mistakes.

happens all the time. If you need a big rocket and fins that dont weigh 20Lb each, you get foam core fins and laminate them with fiberglass. This is very good info if you're not worried about fin flutter. If you need to protect from fin flutter, your rocket likely is not big enough to warrant needing foam cored fins anyways. Either way it's very strong as others have pointed out and a very viable solution to a very common problem.

 

[David Schwantz]

OMG Bill, that HoJo is super nice. Why have I not seen it flown yet? If you don't have room in car to haul it, just leave Bob at home

 

[David Schwantz]

As far as making fins airfoiled, I use my belt sander. I like to do each side one at a time and then go onto the next. You can get them pretty close .

 

[Seatechnerd83]

As far as making fins airfoiled, I use my belt sander. I like to do each side one at a time and then go onto the next. You can get them pretty close .

i use a pneumatic rotary sander because I dont own a belt sander, but It works just about the same, I haven't really done anything that requires a perfect airfoil so it's worked fine enough.