first wildman style fillets

I am building my first fiberglass kit and am doing Wildman style fillets. Traditionally I have made the aft centering ring and motor retainer the last two structural steps of any build, so this is a significant change.

Before I would do six point fillets for through wall fins, but two of those would be difficult if not impossible to inject. Do people simply skip #3 and #4 and make four fillets per fin?



I purchased some of the chopped carbon fiber too. Does one normally chop further, or use as it came? Is that used alone, or along with another filler like the colloidal silica?

Yes,I did the upper I ternal fillets on my super DX3 which was my first hpr rocket and have now realized that it only added weight where I didn't want it without asking much strength. You really only need to do fillets at the mmt to fin joint on the inside and fin to body tube one the outside. It has been said they the later isn't even necessary as external fillets are more for looks then strength.

For all the Wildman kits i have built, I have injected epoxy & in all instances I was able to fill all internal fillets with one injection. Ses some of Crazy Jim's build threads. And no, you don't need to cut the chopped carbon fiber any more than it is (at least if it's the stuff you get from Wildman)

Here is what I do... unless the airframe is exceeding long or upper fins are blocked by centering rings....

I do what you've done in the past, leave the aft centering ring loose so after fin expoxy sets remove the aft ring and I can inject large amounts of expoxy down tube for fillet 3,4,5,6. I use a long rod/stick to spreadout and flip rocket around so fillet expoxy can set before moving to next fin. You must mask off motor mount, fin gaps, etc to keep expoxy in place.

I drill and inject only when access to internal fillets is blocked to far, like a 4" or large darkstars, X-Celerators, Broken Arrows

I think doing fillets 1,2,3,4,5 and 6 are needed on all builds... any weakness can cause a failure under liftoff or touch down stress.

Hah, I forgot my main question! Do you try to epoxy the root of the fin well, or simply tack it on and let the fillets do the work?

watermelonman said:

Hah, I forgot my main question! Do you try to epoxy the root of the fin well, or simply tack it on and let the fillets do the work?

Click to expand...

I alway epoxy the fin on well with the double dip technique.

conman13 said:

I alway epoxy the fin on well with the double dip technique.

Click to expand...

Do you still need to inject internal fillets with this?

Watermellon.......


Just follow the Wildman instructions or the sticky at top go high power for DS 3in.
They are really the same.
99% of all your questions, pertaining to any aspect of building fiberglass rockets is right there.

Forget 3&4, they just add weight...they were popular with cardboard kits and even needed in some, not with glass.

Don't make the common newbie mistake of overbuilding & overthinking this stuff.

Injecting internal is stupid simple & eliminates all the difficulties of the past... that's why we do it that way.LOL
We build huge 12in rockets weighing 275lbs the same way & it hasn't failed yet.

SCrocketfan said:

Do you still need to inject internal fillets with this?

Click to expand...

I came up with "double dipping" to simplify smaller builds where injecting is not needed. Mini's.... Lights and Sports. 29mm motor mounts.
Those will handle I's with DD gluing.
For High Powered builds over H's you tack fins on and inject. 54mm tubes and up... as in Jr's , 54 airframes with 38 motor mounts. That's how I define the limit, generally speaking. There are exceptions as always.


Edit: Please remember these are my techniques/recommendations, there are many, many other ways to do this & most of them will get the job done.
Many find these ways [mine] are just far more easier and work as well any any other.

I am by no means saying my methods are "the only way to do it". Over time you will probably find yourself picking up this technique from one & that from another, till you find what suits your style of building the best.
Have fun & good luck!

blackjack2564 said:

I came up with "double dipping" to simplify smaller builds where injecting is not needed. Mini's.... Lights and Sports. 29mm motor mounts.
Those will handle I's with DD gluing.
For High Powered builds over H's you tack fins on and inject. 54mm tubes and up... as in Jr's , 54 airframes with 38 motor mounts. That's how I define the limit, generally speaking. There are exceptions as always.


Edit: Please remember these are my techniques/recommendations, there are many, many other ways to do this & most of them will get the job done.
Many find these ways [mine] are just far more easier and work as well any any other.

I am by no means saying my methods are "the only way to do it". Over time you will probably find yourself picking up this technique from one & that from another, till you find what suits your style of building the best.
Have fun & good luck!

Click to expand...

Thanks. I saw you used double dip on a Vindicator Jr (happens to be what I'm prepping to build), but since I'll probably fly J530s and J150s in mine eventually (and definitely I540s) I may try injecting fillets after all. If (3) and (4) fillets don't need to be added I'll probably build my Darkstar 3" the same way with injected fillets. I just want to be sure the 54/38 and 75/54 frames of the two rockets can handle the full range of motors.

blackjack2564 said:

Watermellon.......


Just follow the Wildman instructions or the sticky at top go high power for DS 3in.
They are really the same.
99% of all your questions, pertaining to any aspect of building fiberglass rockets is right there.

Forget 3&4, they just add weight...they were popular with cardboard kits and even needed in some, not with glass.

Don't make the common newbie mistake of overbuilding & overthinking this stuff.

Injecting internal is stupid simple & eliminates all the difficulties of the past... that's why we do it that way.LOL
We build huge 12in rockets weighing 275lbs the same way & it hasn't failed yet.

Click to expand...

Hah, I love overthinking and making rookie mistakes! But more seriously, I am mostly following those directions. I do get a little nervous working with new materials and techniques, so I like to check in and see what has worked well for others around here. Heck I even did that when getting back into rockets with an Aerotech kit! I will start to get comfortable working with fiberglass, though, and then probably be low on questions again for a while.

I think 3 & 4 is just a recipe for adding back-end weight that serves little purpose. I use a slightly longer motor tube with at least 3 centering rings. Can leave the last ring off and inject with a withdrawing silicone tube swaged to a syringe. Or let the epoxy dribble on down. Drilling the holes Wildman style works absolutely fine too. Done some rockets that way. Kurt

While we're on this subject, what's the best epoxy to use for injecting? In the past I've used cheapo hobby grade 30min and it worked just fine. I've tried Proline 4500 and it worked but made a horrible black mess all over the tube wherever I touched it. This last time, I used too thin of an epoxy and it leaked pretty badly - not only out the opposite fin slots (which I expected) but also around the fore centering ring and ended up affixing my shock cord to the inside of my motor tube! I don't want to make that mistake again so please recommend a product.

Kevin

I like West System with some chopped carbon fiber.

kruland said:

While we're on this subject, what's the best epoxy to use for injecting? In the past I've used cheapo hobby grade 30min and it worked just fine. I've tried Proline 4500 and it worked but made a horrible black mess all over the tube wherever I touched it. This last time, I used too thin of an epoxy and it leaked pretty badly - not only out the opposite fin slots (which I expected) but also around the fore centering ring and ended up affixing my shock cord to the inside of my motor tube! I don't want to make that mistake again so please recommend a product.

Kevin

Click to expand...

I have decided on West with chopped CF, but I am still unsure on whether I should add 406 colloidal silica or another filler. West pure is so thin that I think CF may be too chunky to serve as filler by itself. Anyone else?

Don't use colloidal silica for internal fillets. Use chopped carbon fiber. Carbon fiber adds strength. Colloidal silica is only a filler.

Oh, to be clear I meant both. There would be a little silica for consistency and then the CF for the rebar filler. West runs like CA!

Of course I have not tried the CF yet, maybe it impacts consistency more than I thought.

I gave these a shot last night. Wow does that work well! Appearance and feel, at least so far, I can confirm their strength later. It is all in the set up. Once prepared properly, it is super easy.

To answer my own questions, I did epoxy with plain filler on fin roots the night before. For injected fillets themselves, I used chopped carbon alone without any other filler. It is much more malleable than it looked sitting still in the jar.