# Finishing options.... Will this be trouble?

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#### Trenman

##### Well-Known Member
Ok I am building and flying a 98mm mongoose in a L2 capacity as I have little time/ interest (at the moment of course) for a L3. I am flying it on a 75mm motor. Rocksim is projecting minimum 10k feet at Mach 1.7+ depending on which motor I use. I am wrapping the fins tip to tip in 2x2 twill cf (2 or 3 layers of 5.9oz/ fin depending on how much thicker this makes things). I want to finish this rocket as I find finished cf to be a thing of beauty. I am thinking a few light coats of a slightly metallic copper orange from mid fin up to
the avBay tapering the edges to be translucent so one can see the twill underneath. I think this combined with an aeropoxy finish (6 coats with coats 4-6 nearly completely sanded down for gloss and finished with finesse-it) will make this rocket look amazing. I will taper-cure the rocket to ensure that it is heat resistant.

Question: am I kidding myself? Even with high temp resistance, will my rocket bubble up under the heat and forces?

I know there was a thread on this topic 2 weeks ago but I didn't find it to be conclusive. Thanks!!

#### Brent

##### Well-Known Member
Do you fly with a local club? Personally I think a carbon fiber Mongoose is a little bit of a waste for just a level 2 cert project. How long have you been level one?

#### Trenman

##### Well-Known Member
So much negativity on this forum.

My question was not "do you think a mongoose is a waste?"

And yes I fly with a club. And my motormount is removable allowing 98mm motors should I choose to one day. I doubt I will because when I'm ready for L3 I'll build a new bird.

Why!? Because this is just a damned hobby and I find pleasure in this.

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#### Trenman

##### Well-Known Member
And what exactly is wrong with being "JUST a level 2"? Is that a shortcoming of some sort!? I believe one must reach L2 before reaching L3, at least last time I checked. Perhaps I enjoy challenges: milling custom bulkheads from solid Al, wrapping my OWN CF and airbrushing a beautiful paint scheme instead of settling with something easier just to name a few features of which I am quite proud.

#### Handeman

##### Well-Known Member
TRF Supporter
I don't think the paint will be a waste, even if it does burn off. If you're like me, no matter how good it looks, there will always be something you wish you did different. If it burns off, that's your chance to fix those things.

I'm expecting lots and lots of pics.

#### Trenman

##### Well-Known Member
Believe me I can't wait to post my finished product.

Handeman: If it does burn, won't it create a hard permanent layer of crap on the surface or would one be able to sand through that?

#### Handeman

##### Well-Known Member
TRF Supporter
I've never had a rocket burn the finish, yet But I saw the new paint on one that was burned pretty bad and it was great. It was repainted by an autobody shop so I know there wasn't any structural work done. I would assume that sanding through the burned layers should be pretty straight forward.

#### troj

##### Wielder Of the Skillet Of Harsh Discipline, Potent
Why!? Because this is just a damned hobby and I find pleasure in this.
That, to me, is the whole point of the hobby.

What one person builds or flies may not trip the trigger of someone else. No biggie -- build and fly what makes you happy!

Now, in answer to your question, I don't think you'll be at high Mach numbers long enough to get any real burning, and even if you do, it'll be on the leading edges of the fins and on the nosecone.

All that said... Remember that composites do degrade under UV light. However, in your case, you're building a 98mm capable rocket, and it sounds like you plan on flying it on motors up through L. I don't think it's going to be an issue.

-Kevin

#### Trenman

##### Well-Known Member
Thanks for the advice and support. I think I'll go ahead and paint it up!!

That, to me, is the whole point of the hobby.

What one person builds or flies may not trip the trigger of someone else. No biggie -- build and fly what makes you happy!

Now, in answer to your question, I don't think you'll be at high Mach numbers long enough to get any real burning, and even if you do, it'll be on the leading edges of the fins and on the nosecone.

All that said... Remember that composites do degrade under UV light. However, in your case, you're building a 98mm capable rocket, and it sounds like you plan on flying it on motors up through L. I don't think it's going to be an issue.

-Kevin

#### COrocket

##### Well-Known Member
Trenman,

I like your idea of using a 98-75MM adapter in your mongoose. If you cant use a large motor for reasons such as waiver, recovery area size, or L2 limits, then why not use a 75MM motor? Instead of using a 1,2 or 3 grain 98MM motor, u can fly on a 2,4, or 6 grain 75MM motor respectively. For comparable power, 75 motors are less expensive, and help out the CG/CP relationship by not concentrating mass in the rear of the rocket. Then a Mongoose 98 allows for a sweet 4" motor if you get a L3. Some say that a 75 motor defeats the purpose of a 98 minimum diameter, but for smaller motors not seeking maximum altitude, i don't see a disadvantage.

#### bobkrech

##### Well-Known Member
Ok I am building and flying a 98mm mongoose in a L2 capacity as I have little time/ interest (at the moment of course) for a L3. I am flying it on a 75mm motor. Rocksim is projecting minimum 10k feet at Mach 1.7+ depending on which motor I use. I am wrapping the fins tip to tip in 2x2 twill cf (2 or 3 layers of 5.9oz/ fin depending on how much thicker this makes things). I want to finish this rocket as I find finished cf to be a thing of beauty. I am thinking a few light coats of a slightly metallic copper orange from mid fin up to
the avBay tapering the edges to be translucent so one can see the twill underneath. I think this combined with an aeropoxy finish (6 coats with coats 4-6 nearly completely sanded down for gloss and finished with finesse-it) will make this rocket look amazing. I will taper-cure the rocket to ensure that it is heat resistant.

Question: am I kidding myself? Even with high temp resistance, will my rocket bubble up under the heat and forces?

I know there was a thread on this topic 2 weeks ago but I didn't find it to be conclusive. Thanks!!
Bubbling is highly dependent on the type of epoxy you use, how you cure it, how you finish it, how you layup your composite and the Mach number of the flight. You probaly won't get bubbling below Mach 2.

A phenolic or epoxy phenolic resin can be cured at hgh temperatures. High temperature curing will get rid of any volitile species in the resin, and some resins are cured at 175C (350 F). Some bisphenol resins I have worked with will not bubble until after several hours at 350 C (660 F).

If you don't cure your epoxy, the water made and trapped in most epoxies during curing can boil and cause bubbling. Additionally, in consumer epoxies that are thinned by solvents, the solvent can come out during aeroheating.

Bob

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#### Trenman

##### Well-Known Member
THANK YOU! That was my reasoning behind the whole thing. Maximum versatility!!
Trenman,

I like your idea of using a 98-75MM adapter in your mongoose. If you cant use a large motor for reasons such as waiver, recovery area size, or L2 limits, then why not use a 75MM motor? Instead of using a 1,2 or 3 grain 98MM motor, u can fly on a 2,4, or 6 grain 75MM motor respectively. For comparable power, 75 motors are less expensive, and help out the CG/CP relationship by not concentrating mass in the rear of the rocket. Then a Mongoose 98 allows for a sweet 4" motor if you get a L3. Some say that a 75 motor defeats the purpose of a 98 minimum diameter, but for smaller motors not seeking maximum altitude, i don't see a disadvantage.

#### Trenman

##### Well-Known Member
ahh very interesting info thank you. I believe I should be fine! I'm not looking for any records, I just want to fly my rocket once a month and have fun with the boys. I just wanted to make sure a killer paintjob would be safe

Bubbling is highly dependent on the type of epoxy you use, how you cure it, how you finish it, how you layup your composite and the Mach number of the flight. You probaly won't get bubbling below Mach 2.

A phenolic or epoxy phenolic resin can be cured at hgh temperatures. High temperature curing will get rid of any volitile species in the resin, and some resins are cured at 175C (350 F). Some bisphenol resins I have worked with will not bubble until after several hours at 350 C (660 F).

If you don't cure your epoxy, the water made and trapped in most epoxies during curing can boil and cause bubbling. Additionally, in consumer epoxies that are thinned by solvents, the solvent can come out during aeroheating.

Bob

#### rfjustin

##### Well-Known Member
I think this combined with an aeropoxy finish (6 coats with coats 4-6 nearly completely sanded down for gloss and finished with finesse-it) will make this rocket look amazing.
I can vouch that if you get the CF layups on "cleanly" and then do multiple Aeropoxy filler coats, you will have a slick looking bird.

If you have never done a CF fin-to-fin layup before make sure the Mongoose 98 is NOT your first attempt. Buy a cost effective LOC kit, and give if CF fin-to-fin for practice. You will quickly figure out what do to and what not to do.

Aeropoxy is great stuff for filler work, but do keep in mind that it remains very tacky to the touch for quite some time. Post curing the fin can (~180 degrees) will eliminate any tackiness of the Aeropoxy.

Justin

#### ben_ullman

##### Well-Known Member
I can vouch that if you get the CF layups on "cleanly" and then do multiple Aeropoxy filler coats, you will have a slick looking bird.

If you have never done a CF fin-to-fin layup before make sure the Mongoose 98 is NOT your first attempt. Buy a cost effective LOC kit, and give if CF fin-to-fin for practice. You will quickly figure out what do to and what not to do.

Aeropoxy is great stuff for filler work, but do keep in mind that it remains very tacky to the touch for quite some time. Post curing the fin can (~180 degrees) will eliminate any tackiness of the Aeropoxy.

Justin
Justin you are 100% correct. I fiberglassed some 7.5" Bt's using aeropoxy. It was like my 3rd time doing glassing and my first with aeropoxy. I had no idea how tacky the sh!t would be!! I let the tubes sit in my shed for one spring and summer and when I got back to them in the fall you could still feel a tiny grab. Not a glass smooth finish.