Phiberglass Phillet Phollies

The Rocketry Forum

Help Support The Rocketry Forum:

Hospital_Rocket

Well-Known Member
Joined
Dec 25, 2003
Messages
4,009
Reaction score
1
Actually I got a few questions for you fiberglass wizards


1, If you are doing fiberglass layup to strengthen a fin joint, do you do a regular epoxy fillet underneath?

2. There is a posted reference to orienting the weave crossways to the joint. Can someone clarify this?

3. How far do you extend the fiberglass onto the fin and onto the body?

4. PML states QT is not good for fiberglass construction. Would this apply to a fillet?

5. Would filling the epoxy paste with milled fiberglass be just as good for subsonic flight on fin joints?

Thanx
 

jetra2

Well-Known Member
Joined
Jan 25, 2009
Messages
2,795
Reaction score
2
Originally posted by Hospital_Rocket
1, If you are doing fiberglass layup to strengthen a fin jouint, do you do a regular epoxy fillet underneath?
Are you talking about just laying a strip of fiberglass in the fin root/body joint? If so, I recommend laying the fiberglass down first with the thin epoxy, then going back over it later with the regular epoxy fillet. It seems to work better that way.

On most of my rockets, instead of taking the hassle of cutting that little strip of fiberglass, I'll just cut a big piece, and after of done the fillets (see "Making Easy Epoxy Fillets" thread in this forum), I'll lay down the glass and brush the epoxy over it all. I think that this adds strength by using the fiberglass to create, in my mind, a solid piece, joined by the epoxy/glass matrix.


2. There is a posted reference to orienting the weave crossways to the joint. Can someone clarify this?
I haven't heard anything about this, but I don't think it makes much sense on most fiberglass cloths because it is most always already woven together, with glass fibers going up-down and left-right. It probably wouldn't do anything 'cept make a mess.

3. How far do you extend the fiberglass onto the fin and onto the body?
See the second half of my answer to #1.

4. PML sez QT is not good for fiberglass construction. Would this apply to a fillet?
I've never used QT, but the reason fiberglass and epoxy makes rockets stronger is because it penetrates the material, locking it all together in it's matrix. QT is basically a plastic tube, IIRC, which would mean it is pretty impenetrable to epoxy, making it not worth your time to glass it, since it'll likely peel off anyways!

5. Would filling the epoxy paste with milled fiberglass be just as good for subsonic flight on fin joints?
I don't quite understand what you are getting at here.

I hope I was able to help you. Remember, this is jsut stuff I've learned in my experiences with hobby-shop epoxies and fiberglass.

Fiberglass is fun, but it is also a PITA...:p

Jason
 

lalligood

Well-Known Member
Joined
Jan 21, 2009
Messages
1,985
Reaction score
0
Originally posted by Hospital_Rocket
Actually I got a few questions for you fiberglass wizards

5. Would filling the epoxy paste with milled fiberglass be just as good for subsonic flight on fin joints?
I'm no fiberglassing wizard--in fact, i have yet to fiberglass anything! But I can help you with this question...

Milled fiberglass greatly thickens & strengthens epoxy, especially for fillets (which is what I've used it for)! Mix your epoxy to the proper ratio & then add the milled fiber until it's the consistency fo ketchup (it'll be a little grainy though). If using it for fillets, make sure that you get the fillets how you want them to look before the epoxy cures because you will have created considerable extra work if you have to sand them to shape afterwards :(

Subsonic, supersonic, it doesn't matter... I like it because it does add considerable strength with little extra weight (if any at all) & helps me to get some great looking fillets.

HTH,
 

DumasBro2

Well-Known Member
Joined
Jan 26, 2009
Messages
311
Reaction score
0
I usually use 4 or 6 oz. glass to attach the fins to the motor tube. In rockets with little clearance between the motor tube and the airframe milled glass works great. I try to do all my fillets on the inside to keep a sharp edge between the fin and the air frame on the exterior. If I have filling to do along the root edge of the fin I'll use fairing filler along with the milled glass to thicken the epoxy and make sanding a little more manageable.


Steve
 
Top