necessary reinforcement

I am having trouble deciding whether I should Tip to tip fiberglass the fins on my 7.5" Nike Smoke or drill holes in the sides of the fin slots and inject fillets. I feel that injecting fillets will be easier since I already have the epoxy for it and plenty of syringes(dad being a doctor). The fins are 1/4" thick 12 ply baltic birch and are very solid. My other option is to leave out internal fillets and instead form only external fillets using aeropoxy mixed with milled glass.

Also, both aft centering rings are glued into the BT so i cannot access the interior from the rear end.

Alot of that will depend on what size the motor mount is, and what size motors you are going to use.

I would suggest 1 layer of 6oz. on the fins before you mount them just to protect from nick & dings.

Inject the internals & regular external with colloidal silica [West 406] or milled glass.

They will be rock solid. 12 ply birch is really nice stuff & plenty strong for this UNLESS you plan something Xtreme like a N-10,000 you will be mint.

If going nuts...definitely a layer T-T.


PS
Ya know it helps alot to mention what the tubes are made of and size MM or largest motor you intend to fly.

The highest average impulse motor I am going to use is an M3100. The mmt is 75mm.

Could I just coat the fins in epoxy to protect them?I have bondo laminating resin from Home depot that I could use for that but If gluing on fiberglass is necessary then I do have some.

Aris said:

I am having trouble deciding whether I should Tip to tip fiberglass the fins on my 7.5" Nike Smoke or drill holes in the sides of the fin slots and inject fillets. I feel that injecting fillets will be easier since I already have the epoxy for it and plenty of syringes(dad being a doctor). The fins are 1/4" thick 12 ply baltic birch and are very solid. My other option is to leave out internal fillets and instead form only external fillets using aeropoxy mixed with milled glass.

Also, both aft centering rings are glued into the BT so i cannot access the interior from the rear end.

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I agree with Jim, I'd go ahead and put 1 layer of 6 oz on the fins. My 5.5 inch has one layer of 6 oz, it seems to have added significant strength, and it definitely protects from dings.


Whatcha gonna fly it on? :grin:



Braden

UPscaler said:

I agree with Jim, I'd go ahead and put 1 layer of 6 oz on the fins. My 5.5 inch has one layer of 6 oz, it seems to have added significant strength, and it definitely protects from dings.


Whatcha gonna fly it on? :grin:



Braden

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Well in march I am gonna drag race Jack garibaldi's 7.5" nike smoke on some L motor (L850,1150,1395....idk yet) and will probably just do single deploy for the first flight since it will only go to 8k feet where I can still spot it in the sky. Plus Lucerne Dry Lake bed is just a great, flat, large site so I wont easily lose it.

I also saw that you added the glass after you glued on the fins. If I do add glass instead of just coating the fin with epoxy, I will do so before I glue in the fins.

Also, just to be sure why will coating the fins in epoxy not be a good idea? I have never done that before.

Why not do both internals and glassing?

Alex

I would fiberglass the fins. 1/4th inch is strong, but it is not fiberglass and is still quite vulnerable on landing. If it lands funny, and you get a snapped fin, fixing it is going to be harder than either of these options. Only fiberglassing will prevent this.

The only fiberglass I have is this. It seems pretty heavy duty but I am not sure since I have not done much fiberglassing before.
https://www.acehardware.com/product...&origkw=fiberglass+cloth&searchId=54757958604

here are a few pics I took of my idea on how I would glass the fins. Please comment because I am not sure If this is right.

second pic

third one...

On my 5.5" polecat nike smoke, I did not glass the fins. The rocket came in hot from 8000 feet on its 5th flight (K700 motor) and the fins are unscathed. I still have them and plan on using them for another rocket. The rest of the rocket except for half of the altimeter was destroyed Based on that, are these fins really that susceptible to dings?

I can't speak to dings, never seen that in wood. But stains, dirt, water damage, etc... Epoxy alone could prevent that, with paint. But my concern is them actually snapping on recovery. If this were a smaller rocket I would say just go wood... but this is a 7 inch, I presume level 3 rocket. They land very hard. And like I said there are scenarios where a cracked fin would be very hard to repair without cutting into the rocket. Devils advocate says that a Nike smoke will be less likely to land on a fin because of how they are placed.

New Ocean said:

I can't speak to dings, never seen that in wood. But stains, dirt, water damage, etc... Epoxy alone could prevent that, with paint. But my concern is them actually snapping on recovery. If this were a smaller rocket I would say just go wood... but this is a 7 inch, I presume level 3 rocket. They land very hard. And like I said there are scenarios where a cracked fin would be very hard to repair without cutting into the rocket. Devils advocate says that a Nike smoke will be less likely to land on a fin because of how they are placed.

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I am not going to let this one come down hard. It will be under a 12 foot chute which should yield 15 f/s based on the burnout weight of a 6 grain M.

Also stains, water damage, and dirt marks never were a problem with my 5.5" nike. The weather at the launch site is always so dry.

Well then the best would be for you to fly it without fiberglass and let us know if it works!

New Ocean said:

Well then the best would be for you to fly it without fiberglass and let us know if it works!

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Well, I just fiber glassed one side of one of the fins. I used blue tape to cover the bevels and the fin tang so that the fiberglass would only stick to the main portion of the fin. I then covered the fin in a layer of wax paper and placed some objects with a large surface area to press down on the wax paper/fin. I put the fin along with a large lamp that generates quite a bit of heat under a clear container and sealed the sides somewhat. I waited for it to to be slightly sticky but not sticky enough to adhere to anything other than the original are that was not covered with tape (exposed), and removed the blue tape by carefully sliding it out from the edges of the cloth. Finally I waited for it to dry (sets in 2hours) and used a power sander with 100 grit to cut off the edges of the fiberglass that had hardened and also to smooth out the rest of the glass.

In my opinion, the end result was wonderful. The glass has be sanded so it doesn't even feel that it is there. The edges turned out perfect too.

Welcome to the wonderful world of fiberglass laminating!

I repeated the precess for 3 more sides of fins and this time let the wax paper stay on top of the fiberglass for longer. The end result was a close to perfectly smooth finish on the fiberglass.

This will provide an extra margin of strength for the fins on recovery. Worth it imho considering the money you put into large kits.