TTW Fin Reinforcement

Hello. I know that I've posted stuff on TRF before, but once I got into college, I got out of the hobby. Now, I'm a few years older and hopefully a little wiser, so I'm trying to come back to rocketry in my spare time. So, hopefully I will begin building my first major mid-power rocket, a Madcow DX3 (not super DX3), before too long, and I have a question about the TTW fin mounts. It seems like many of the EMRR reviews and build threads I read show rockets that end up overweight and tail heavy, and all these rockets use epoxy. Since the DX3 is cardboard tubing and wooden fins, can I just use wood glue instead of epoxy? I thought I might try cutting out an extra, modified centering ring that was notches in it, as well as cutting notches in the fin tabs; the notches in the fin tabs would mate with the notches in the centering ring, allowing the parts to interlock and allowing any bending forces on the fins to be transformed into compressive forces in the special centering ring. Anyone heard of doing this before (I normally use the forum search feature, but I didn't really know what to search for)? Do you think that it would work?

Absolutely wood glue would work. Most of us tend to over build anyway.

Wood glue is both cheaper and stronger then epoxy in some scenarios (wood-wood, wood-paper) it is great to work with when building any HPR or MPR. Personally, I use epoxy just because it doesn't take long to cure.
Posts in a previous thread show that the final weight from both an epoxy built rocket and a wood glue built rocket aer about the same.
What it comes down to is just a matter of personal preference.

Use the wood glue. I wouldn't bother with the extra CR. Just more weight without a significant amount of extra strength.

Just remember woodglue ( Elemers, Titebond ect, Shrinks as it dries. So check that it does not pull your fins when doing fillets.

jim fustini said:

Just remember woodglue ( Elemers, Titebond ect, Shrinks as it dries. So check that it does not pull your fins when doing fillets.

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Do you know of any ways to prevent this "pulling," and if it occurs, what would I need to do to fix it?

Also, I am going to use fillets inside and outside the airframe, and I am considering using epoxy for the outer fillets as it looks nice when applied correctly.

GrossApproximator said:

Also, I am going to use fillets inside and outside the airframe, and I am considering using epoxy for the outer fillets as it looks nice when applied correctly.

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I think that is a good plan. Also I think if you do TTW fins, especially if you extend them to the motor mount tube, they are a lot stronger and the fillets are not so critical to strength. With TTW fins there are ways to fillet the inside and then the outside fillets can be made with whatever material you can work with the easiest.

Definitely go with epoxy for the external fillets, if you have the means, west system or proline epoxy with colloidal silica makes a super strong and super light fillets, very simple to sand. Put masking tape on the airframe and fins you are filleting and apply the fillets, then remove the tape, check out the Extreme Darkstar instructions at Wildmanrocketry.com





Braden

UPscaler said:

Definitely go with epoxy for the external fillets, if you have the means, west system or proline epoxy with colloidal silica makes a super strong and super light fillets, very simple to sand. Put masking tape on the airframe and fins you are filleting and apply the fillets, then remove the tape, check out the Extreme Darkstar instructions at Wildmanrocketry.com
Braden

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Cool. Can I buy the stuff in small quantities? I've looked at West Systems stuff before and I've only seen it sold in large containers, although I imagine it must be sold in smaller containers too. I don't want to spend $50 just on glue.

One more thing. The Madcow DX3 comes with a kevlar cord and a nylon cord that are tied together. I like to glue my tubular nylon cord right to the motor mount, and I've read that kevlar can cut non-kevlar cords. I've never attached nylon to kevlar cords. Will the Madcow 2-cord system work well?

GrossApproximator said:

Do you know of any ways to prevent this "pulling," and if it occurs, what would I need to do to fix it?

Also, I am going to use fillets inside and outside the airframe, and I am considering using epoxy for the outer fillets as it looks nice when applied correctly.

Click to expand...

If your fin slots in the airframe are a tight fit, I would not worry about the woodglue pulling the fins. If they are a loose fit you use a piece of wood or aluminum right angle with a slot cut to fit the fin .To hold it 90 deg. to the air frame. This is one way I hold my fins until they set up. I also have fin fixtures for various rockets. Model ,Mid and HPR. I have seen many photos of different fixtures right here on TRF.

In the past, I used super glue to tack the fins in place after I aligned them. For instance, I would apply super glue to the joint between the fin and the fin slot. I planned on doing that again since I don't have a nice fin alignment fixture.

GrossApproximator said:

In the past, I used super glue to tack the fins in place after I aligned them. For instance, I would apply super glue to the joint between the fin and the fin slot. I planned on doing that again since I don't have a nice fin alignment fixture.

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OK So your going to CA ,woodglue and epoxy. What ever works for you.

GrossApproximator said:

I thought I might try cutting out an extra, modified centering ring that was notches in it, as well as cutting notches in the fin tabs; the notches in the fin tabs would mate with the notches in the centering ring, allowing the parts to interlock and allowing any bending forces on the fins to be transformed into compressive forces in the special centering ring.

Click to expand...

I'm new to rocketry, but I think that this would be a really cool mod to the centering rings. I don't think that you need to add any additional rings around the fins. I think that the two CRs could articulate with the front and rear end of the fin tabs.

It might be a little tricky getting everything lined up, so dry fit, dry fit, dry fit. You might check out Aerotechs fin attachment for some ideas.

Che said:

I'm new to rocketry, but I think that this would be a really cool mod to the centering rings. I don't think that you need to add any additional rings around the fins. I think that the two CRs could articulate with the front and rear end of the fin tabs.

It might be a little tricky getting everything lined up, so dry fit, dry fit, dry fit. You might check out Aerotechs fin attachment for some ideas.

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Let us know how it works out. I think it may make the anchor point of the fins less flexible and you could end up with more broken fins from landings then you would with just the BT and MMT being the attachment points. It will be interesting to find out if there really is a difference.

This setup makes for rock-solid fin cans, and it's quite light. Using the bamboo skewers from the kitchen reduces the amount of epoxy used, and the foam makes any movement impossible. I do it cheap, too. Skewers from the grocery, five min. epoxy, and foam from a can. Haven't busted one yet!