Sanding

[christian]

Yah, so I'm sort of a beginner at making rockets and about to start making my rocket.

I want to sand my rocket to make it aerodynamic. How do I do this? And which parts of the rocket do I sand?

Thank you

 

[Pem Tech]

Christian,
Welcome aboard!

Chiefly you will focus on the fins for lessening aerodynamic drag. The simplest approach is to round the leading and trailing edges of the fins. The next step is to sand and seal the balsa, if this is what you are using. You can search the forum for a frightening array of sanding sealers, tips and tricks, but the Ole' Stand-by is ELmers Fill N' Finish. Sand the leading and trailing edges of the fin, lightly sand the flat surfaces of the fin (I use 230 Grit Norton paper) then start with the sanding sealer. Start with a light coat on both sides of the fin to prevent warping, allow to dry and sand. Repeat, and repeat and repeat till they are smooth enough for your tastes. Then paint or shoot with primer and sand some more!


Hope this helps....

 

[hcmbanjo]

Layne,
I second everything you said - except:
We should clarify that Fill N' Finish is no longer available under that name.
It's now Elmer's Carpenter's Wood Filler.
Christian, you might have trouble finding it under the old name, some places may still have some of the older stuff.
Be sure you buy the regular filler, it comes in a white tub with a blue and orange lid. There'll be a small 10-144 number on the lower right side of the lid. Stay away from the Stainable Filler, under the latest formulation it's very hard to sand.

 

[Marlin523]

Another great way to get more aerodynamic is to forget the Elmer's stuff and paper the fins. It's cleaner, makes the fins stronger, and finishes great. This is assuming you aren't doing high power stuff.

 

[Pem Tech]

Layne,
I second everything you said - except:
We should clarify that Fill N' Finish is no longer available under that name.
It's now Elmer's Carpenter's Wood Filler.
Christian, you might have trouble finding it under the old name, some places may still have some of the older stuff.
Be sure you buy the regular filler, it comes in a white tub with a blue and orange lid. There'll be a small 10-144 number on the lower right side of the lid. Stay away from the Stainable Filler, under the latest formulation it's very hard to sand.

Oye....
Didn't even catch that, am used to the "Old Ways".
:bangpan:
Thanks for the correction.


Marlin has a good point as well. My personal experience with papering fins is limited but it does work well. The only problem I had was getting clean transitions on the leading and trailing edges between the paper and balsa. Always end up with fuzzy edges.
:bangbang:

Marlin can you give us a pointer or three?

 

[Marlin523]

I recommend watching the video from Tim Van Milligan. I supplied the link below. I sand the fins as usual making certain I have smooth surfaces. If you don't do this, you will see irregularities through the paper. Next I cut paper about an inch larger than the fin using the fin as a template. Next I use only enough white glue to cover one side of the fin, smooth it out with your finger (have a paper towel handy) When you have clean fingers, lay the paper on the fin and burnish it with your thumb. I don't lay the fin down while doing this to prevent it from getting "bruised" on the other side. Burnish from the center out to the edges. If you get wrinkles, you used too much glue. Burnish around the edges of the fin to make certain you have adhesion all the way to the edge. I then repeat for the other side and when finished use my thumb nail to crease the paper on both sides. Again, this ensures adhesion at the edges. Then, put the fin in a thick book and place weight on it so the fin dries flat. I don't touch it until the next day! To cut the excess the next day, start at the middle of one edge with the point of your knife and cut backwards using the fin to guide the blade just as you would a ruler to guide your cutting the balsa. Turn it around and do the other half the same way. Obviously this is repeated for all fin edges. Don't worry if your cuts aren't perfect because you can finish by using a sanding block and very fine sandpaper to clean it up. Once finished you can use thin CA glue to "seal" the edges. I don't do this because it's very easy to mess up the paper with the glue. When you put primer on the rocket, it seals anyway. It's a great technic - no mess, no mixing filler, no sanding the filler, and no repeats necessary. The papered fin will be stronger than any sealed fin without any significant weight. Hope this helps - let me know!


https://www.apogeerockets.com/Rocketry_Videos/Rocketry_Video_16.asp