Fin design and material needed

[Wei Chun]

Can I know what fin design ( better in templates) is the best for a basic 1.5L water rocket and what is the material needed? This is because I am joining a competition at the end of the month and I need some advice.-Help will be greatly appreciated!!!

[bugwubber]

What kind of nozzle, bottles etc will.be used? Thin straight (rectangles) or slightly tapered airfoils are best. Do you know what design of launcher is being used? How big will depend on whether your rocket will be long smooth and thin or wide short etc. Are you allowed to scuff/sand the pressure bottle? That will help glue adhere. Epoxy, low temp hotmelt applied to the fins, then stuck on the bottle, or polyurethane glues work great. Payloadbay.com has some tools for printing out a fin guide to help with spacing.

[Wei Chun]

The rocket is just a normal 1.5 L Bottle (Nozzle is not allowed)The launcher is just a simple one with a PVC pipe stuck up the bottle to provide air into the bottle and a release chamber.Yes, I am allowed to sand the paper.Is the fin material using PVC board or plastic board of folder keeping documents better?

[bugwubber]

Personally I'd use balsa, sanded to an airfoil, then glue thin paper on the surfaces of the fins to reinforce the balsa. Other materials are corrigated plastic, credit cards, and thin plywood.

[brett74]

Is balsa wood lighter than plastic from a three ring binder?

[bugwubber]

Balsa can vary from the density of foam to hardwood. Plastic binders vary as well but are usually not very stiff. Floppy fins are bad.

Balsa has the advantage of being shapeable.

I wouldn't use balsa on a rocket I want to launch a bunch of times. But for a competition rocket? Definitely.

[Wei Chun]

But isn't balsa a quite heavy material?

[bugwubber]

I think you'd be challenged to find lighter material that can be shaped into slight airfoil.

Maybe you only have the denser wood available locally?

Here's more than enough material weighing in at 9 grams:

tmp_24377-20150519_074522-88729488.jpg (2.24 MiB) Viewed 82 times

[Wei Chun]

9 gram? Oh yeah. that will be it.Thanks for the help.By the way can i know is there any other way to form the nose cone except the top of the plastic bottle applied with half of the ping-pong ball that is good?

[bugwubber]

I use a bench grinder to.grind and melt the nozzle into an ogive shape. Just takes a little filler to get smooth.

[Wei Chun]

So I just take a bottle and cut of the drinking part and shrink it down to that point using the bench grinder. Wouldn't it be impossible as the bottle is already wide and if you grind it, it will become wider?Any video for example?

[Wei Chun]

Oh wait...now I get it about the grinding part after some research..But still any video for an example?

[bugwubber]

I can try to come up with a video, I use a whole bottle, nothing cut off, just start grinding on the threads while rotating

[Wei Chun]

Thanks for but my competition is next week ,would it be possible for you?

[bugwubber]

Sure I needed another nosecone anyway.

[youtube][/youtube]

This is the first step. Then filler and sanding to shape.