What weight fiberglass for fin strengthening ?

[wbyman]

What weight fiberglass do you guys use to make the fins stronger on d-g motor rockets ?

 

[TheAviator]

Personally, I don't. That being said, if I, theoretically, were going to add fiberglass, I would go with one layer of .6-.75 oz. Fiberglass in such small sizes is never necessary, use either label paper over balsa or just aircraft ply. If your fins are popping off, fiberglass isn't the answer; have someone check your glue technique and/or your recovery systems.

 

[cjl]

Typically none. In the vast majority of cases, D-G powered rockets do not need any fin reinforcement.

If it is needed, a single layer of 0.6-0.75oz would be perfectly adequate. Why do you want to use fiberglass for a D-G powered rocket though?

 

[ScrapDaddy]

Personally, I don't. That being said, if I, theoretically, were going to add fiberglass, I would go with one layer of .6-.75 oz. Fiberglass in such small sizes is never necessary, use either label paper over balsa or just aircraft ply. If your fins are popping off, fiberglass isn't the answer; have someone check your glue technique and/or your recovery systems.

Aircraft ply? Well the in between of ply and balsa is Basswood, much easier to finish because of the tight grain configuration.

 

[Handeman]

What weight fiberglass do you guys use to make the fins stronger on d-g motor rockets ?

I've never fiberglassed a fin for a D-G size rocket. Actually I've never fiberglassed fins for H or I sized rockets either.

I have used some fiberglass to repair a broken or cracked fin on F-I size rockets but haven't needed it for D & E size.

 

[MarkII]

Typically none. In the vast majority of cases, D-G powered rockets do not need any fin reinforcement.

If it is needed, a single layer of 0.6-0.75oz would be perfectly adequate. Why do you want to use fiberglass for a D-G powered rocket though?

After all of the discussion about fiberglassing on another thread in the last couple of days, I realized that one of my dormant projects could probably benefit from tip-to-tip fiberglassing of the fins, and it is in that range, at least partly. It's more in the F to H (possibly I), range. I was building an upscaled Estes Super Flea that was based on 2.34" diameter tubing. If you don't quite recall what the Super Flea looked like, see here. Note the long swept fins. For my upscale, I made them out of 1/4" basswood, which worked fine and wasn't at all heavy. Because I was also making the rocket with an interchangeable motor mount, the fins were surface-mounted.

Yeah, I know.

I thought that bonding them with Aeropoxy and giving them really good fillets would be sufficient, but I found out otherwise when I accidentally backed into the partially-completed model (I had it standing on the floor behind me, along with a whole bunch of other stuff) with my desk chair in the workshop awhile ago. Two fins broke off, taking chunks of the airframe with them. Sure enough, the bond was much stronger than the parts that were bonded, but that wasn't good enough in this case. A tip-to-tip veil of lightweight FG would seem to be indicated here, even though this is basically a mid-powered rocket. I plan on starting the build over from scratch with new components, because there are a few additional things that I want to execute better on it this time around as well. It will be my first experience with fiberglassing a fin can, but I think I know what I will need to do. Just in case, though, any tips?

Mark K.

 

[Handeman]

Two fins broke off, taking chunks of the airframe with them. Sure enough, the bond was much stronger than the parts that were bonded, but that wasn't good enough in this case. A tip-to-tip veil of lightweight FG would seem to be indicated here, ...
Mark K.

I would suggest that taking parts of the body tube with the fins is an indication that tip to tip was NOT needed. Tip to tip is good if you are going near or over Mach and need to prevent destructive fin flutter, but for joint strength, is sounds like you already achieved what you need. Or maybe you need to stop testing the structural integrity of the rockets with your desk chair! :bangpan:

 

[cjl]

Tip to tip would improve the bond strength, and could definitely improve survivability. For that, I'd be tempted to go with balsa (to save weight) and then do a single 1-2oz or so layer of glass. That should end up no heavier than the basswood was, but significantly more durable. It might not hold up if you really wanted to push the speed, but for reasonable sport flights (< mach 0.8 or so), you would be fine. It would also strengthen the bond and help prevent issues such as you had when you knocked the fins off.

As for tips? Use a slow, thin epoxy, and take your time. Also, wear gloves. Aside from that, the best way to learn is to do - tip to tip (especially on smallish rockets with light fiberglass) is somewhat of an art, and you need to do it to figure out what works best.

 

[MarkII]

I had my concerns about the fin attachment right from the start, well before the accident. On the real Super Flea, the fin bond isn't much of a concern; it's a BT-5 sized rocket with very low mass. When you look at it proportionally, the strength to weight ratio of the original Mini Brute is phenomenal. No matter how hard it landed, the fins could never experience enough stress to break off. It could be a whole different story with my upscale, though. The fins are 2.125" wide by 5.375" long by 0.25" thick parallelograms and there are four of them. I am worried about cracked fillets, etc. when it touches down, even after a slow descent. The tips of the fins make great levers, if you know what I mean.

I just pulled out the remains of my first build, and looked it over for the first time in months. The two remaining fins are more solidly attached than I remembered. Perhaps tip to tip is not necessary; maybe just a patch on each side of the fins on top of the existing fillets will work. (If I do the build all over again, I would put them on before adding fillets, of course.) I haven't decided yet if I can reattach the other fins securely without having the brand-new never flown rocket look all nasty and patched up. Oh well, I have options to consider. Thanks for your input.

Mark K.

View attachment Estes Superior Flea-18mm cluster.rkt

 

[dedleytedley]

What weight fiberglass do you guys use to make the fins stronger on d-g motor rockets ?

I use "Fibatape" fiberglas wall repair tape for fin strengthening for midpower. It's not as strong as glass cloth as it's an open weave and I usually coat it with several layers of white glue. It also requires filling to get a smooth surface. Depending on the fin span/size I don't generally cover the whole fin. It's a lot of work to do it right but I think the results are worth it as I can pick up my rockets by the fin and give them a good shake with no ill effects. Paper laminating as suggested will be easier and probably all you'll need. Ted

 

[Micromeister]

The answer to your question for D-G motor levels is NONE. use paper laminate, other woods or even light ply (as a laminate) instead of fibreglass. Overbuilding is the bane of the hobby and MUST BE stopped. Build for your flights NOT expecting a crash. Paying attention to your recovery system and motor selection will eliminate broken fins and other damage.

 

[GregGleason]

I use 6 oz fiberglass or carbon fiber for big area fins, but that's just me.

Greg

 

[GregGleason]

Let me clarify something. Where I launch, there is an "opportunity" for the rocket to land on concrete (it's at an airport).

There is a big difference in what a fiberglassed fin looks like after it hits concrete vis a vis plain balsa. I have experienced both scenarios for some scratch builds that I fly (2.60" OD airframes).

I do it to minimize repair, so there is a rational rationale.

For most fields though, you probably don't need it for those motor sizes.

Greg