Tip to Tip Fiberglass / Carbon Fins

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martymonsta
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Tip to Tip Fiberglass / Carbon Fins

Postby martymonsta » Wed Apr 08, 2015 11:16 pm

So I'd seen the Tip to tip fin construction method mentioned repeatedly in various build threads, photos of before and after but very little on how to actually do it. So over the weekend I figured that I would try to work it out, in preparation for some projects that I'm planning that will need it, I mean how had could it be.

So I started with the Drag Queen Kit that I got for Thunda but never got built and subsequently flown due to a certain dust storm on the Friday night. This has blue tube airframe and 1.6mm (1/16") G10 fins. So I started by roughing up all the components with sandpaper, then tracking on the fins with 5 minute Araldite and then mixed some 105/205 West systems (yes its that cold in Gippsland VIC) and added some 403 filler and added fillets smoothed out with some small plastic conduit.
Image

At this stage I was pretty happy with how it was going. I cut out appropriately shaped pieces of 175gsm FG cloth, wet down the areas of body tube and fins that required it and... that is where it started to turn into a ripe mess. and then it got worse. I didn't take photos because it has nothing to do with How To and a lot to do with what not to do. Fortunately I sanding attachment for my angle grinder which with some work has salvaged something from the mess that with a stack more sanding by hand will be flyable, however I would recommend that no one do what I did.
Image

What went wrong? Lack of Peel Ply, Lack of Patience, Lack of any idea what I was supposed to be doing. In the past when I have fiberglassed something (like patching a surfboard) I wet down the area, wet the glass to be applied and then lay the wet glass over the area and then worked any small air bubbles out with a brush, I tried to do this but it didn't work the way that I wanted it to.

So after making a mess I went looking for a better way it do it, and I found this


Is this the way you do Tip to tip? Is there a better way again to do it? So did he go all the way to the Tip itself or stop at the bevel, it was hard to tell? Does doing tip to tip like this have any risk of de-laminating on high speed flights and what can be done to prevent de-lamination? Strips along the leading edge etc. and if so how do you blend them in without leaving an obvious joint? Where do you get peel ply? I have seen Vac bagging done on fin cans but what when it isn't a separate fin can, how do you go sealing the bag/air frame? Any other question that I might have over looked?

Any input would be greatly appreciated. Thanks
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Re: Tip to Tip Fiberglass / Carbon Fins

Postby OverTheTop » Thu Apr 09, 2015 7:28 am

never got built and subsequently flown due to a certain dust storm on the Friday night

That was a mongrel of a dust storm. Trashed several dozen gazebos around the camp and flight line, including two of ours.

Do you really need tip-tip? My Orange Revolution flew to Mach1.8 without tip-tip. No sign of fin movement. I have been thinking about the performance of f/g and cf around the fillet joint for a while which is why I made OR without tip-tip, to prove that is isn't necessarily necessary (provided the forces and damping are otherwise adequately handled).

Are your fins mounted on the surface of the tube or glued into slots in the airframe?
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Re: Tip to Tip Fiberglass / Carbon Fins

Postby drew » Thu Apr 09, 2015 12:03 pm

Is this the way you do Tip to tip?


I've used tfish's 1/3, 2/3, full technique before with success. Some people think it's not as strong as 3 full layers but the AeroPac 100' team wrote this in their project report (page 25):

The progressive layering provided several benefits: It kept the fins thin at the leading edges, varied the fin cross section thickness to reduce vibration, and strengthened the fin/body joint. This asymmetric fin planform substantially reduces the susceptibility of the fin to flutter.

So did he go all the way to the Tip itself or stop at the bevel


Without rewatching the video I'd say yes, he went all the way. In the past every tip to tip I've done I've covered the bevel.

Does doing tip to tip like this have any risk of de-laminating on high speed flights and what can be done to prevent de-lamination?


I doubt the Drag Queen airframe will ever see speeds much above Mach 1 so I think your concerns regarding delamination aren't an issue with this vehicle, even when using West System. I can't recall exactly which video (it may even be the one you linked) tfish speaks to this issue but he states (iirc) that no vac bagged tip to tip layups like the one he's doing in the video can easily withstand Mach 2-2.5 speeds. He speaks from experience of course.

Strips along the leading edge etc. and if so how do you blend them in without leaving an obvious joint?


You can run a coating of high temp epoxy on the leading edge but unless you're approaching Mach 3 I reckon you're just making unnecessary work for yourself. As for blending them, sanding mate, a lot of sanding. :/

Where do you get peel ply?


The place you got your fiberglass from? Otherwise you can order it online. The teflon coated stuff that tfish uses is available from skyshop (skyshop.com.au) but there's a significant "Australia tax" on the cost.

I have seen Vac bagging done on fin cans but what when it isn't a separate fin can, how do you go sealing the bag/air frame?


I'd completely ignore vac bagging for now, first build up experience with doing layups without bagging. I've yet to go down this path and I've successfully flown up to Mach 2.2. Further if you do want to go down the vac bag path I'd also recommend getting rid of the West Systems and picking up some Araldite 3600 instead.
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Re: Tip to Tip Fiberglass / Carbon Fins

Postby b-h » Thu Apr 09, 2015 9:08 pm

What went wrong? Lack of Peel Ply, Lack of Patience, Lack of any idea what I was supposed to be doing. In the past when I have fiberglassed something (like patching a surfboard) I wet down the area, wet the glass to be applied and then lay the wet glass over the area and then worked any small air bubbles out with a brush, I tried to do this but it didn't work the way that I wanted it to.




Some fiberglass mat has a binder on the glass soluble to polyester resins and not epoxy. Using epoxy on that type of mat is awkward, I'm not sure about the mat you used but I'm sure some of the other guys here could elaborate a little more.
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Re: Tip to Tip Fiberglass / Carbon Fins

Postby martymonsta » Thu Apr 09, 2015 10:49 pm

drew wrote:I doubt the Drag Queen airframe will ever see speeds much above Mach 1


OverTheTop wrote:Do you really need tip-tip? My Orange Revolution flew to Mach 1.8 without tip-tip.


Quite correct the Drag Queen kit has been flown by both Blake and Simon and doesn't need tip to tip, however since I had the kit and wanted to try tip to tip on a rocket before I attempt it on a rocket that does need it, I thought that it would be a good opportunity to do this.

Thanks Drew for the rest of the info. That AreoPac 100k document really is great, I had a read through the rest of the fin construction section and it is really insightful.

b-h wrote:Some fiberglass mat has a binder on the glass soluble to polyester resins and not epoxy. Using epoxy on that type of mat is awkward, I'm not sure about the mat you used but I'm sure some of the other guys here could elaborate a little more.
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Re: Tip to Tip Fiberglass / Carbon Fins

Postby martymonsta » Fri Apr 10, 2015 7:23 pm

b-h wrote:Some fiberglass mat has a binder on the glass soluble to polyester resins and not epoxy. Using epoxy on that type of mat is awkward, I'm not sure about the mat you used but I'm sure some of the other guys here could elaborate a little more.


My internet connection played up and removed my reply, which was,

That's an interesting point. I'm not sure if that is the case with the mat that I used, I couldn't find anything in the manufactures material however they only mention using their resin, so it could be the case. i'll have to look into it further.
Many years ago the great British explorer George Mallory, who was to die on Mount Everest, was asked why did he want to climb it. He said, "Because it is there."
Well, space is there, and we're going to climb it

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Re: Tip to Tip Fiberglass / Carbon Fins

Postby Kryten » Sat Apr 11, 2015 9:26 am

b-h wrote:
What went wrong? Lack of Peel Ply, Lack of Patience, Lack of any idea what I was supposed to be doing. In the past when I have fiberglassed something (like patching a surfboard) I wet down the area, wet the glass to be applied and then lay the wet glass over the area and then worked any small air bubbles out with a brush, I tried to do this but it didn't work the way that I wanted it to.




Some fiberglass mat has a binder on the glass soluble to polyester resins and not epoxy. Using epoxy on that type of mat is awkward, I'm not sure about the mat you used but I'm sure some of the other guys here could elaborate a little more.

Yep!
The binder is PVA. It's used to hold chopped strand mat together. Woven mat doesn't need a binder
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Re: Tip to Tip Fiberglass / Carbon Fins

Postby martymonsta » Sat Apr 11, 2015 11:49 am

Kryten wrote:The binder is PVA. It's used to hold chopped strand mat together. Woven mat doesn't need a binder


Thanks Kryten. I used woven mat not chopped, so that should be ok.

I think most of my issus came from wetting down the fiberglass mat before applying it to the fin.
Many years ago the great British explorer George Mallory, who was to die on Mount Everest, was asked why did he want to climb it. He said, "Because it is there."
Well, space is there, and we're going to climb it

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Re: Tip to Tip Fiberglass / Carbon Fins

Postby jase » Sun Apr 12, 2015 11:19 am

Coat the surface with resin first, then drape the cloth over it and 'pat' with a brush or 'roll' with a high density foam roller the cloth. The resin will hold the cloth (not completely but sufficently) in place and you'll have a good idea about how much more resin you'll need to completely wet out the cloth.

Then apply the peel ply using the same technique.

Although unless you are going to re-coat the cloth with more cloth, or enjoy sanding, then no need to use peel ply. If you want a nice shinny surface finish without having to sand, use mylar or a thick plastic over the top of the wetted out cloth.

Dont rush it till you are use to it, I'd advise that you start out with a slow cure hardener until you build experience/confidence.

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Re: Tip to Tip Fiberglass / Carbon Fins

Postby cryoscum » Sun Apr 12, 2015 12:54 pm

All good advice, Marty!
Vacbagging adds a new layer of complexity to it all, so I would also not suggest to mess around with that yet. It's a b!stard and I'm only now really getting the hang of it myself. I would also suggest you stick with woven cloth and either Araldite or FGI epoxies. PM me for more details if you need them.

Well done, however, on giving it a go! It is the kind of spirit that makes successful flyers! Keep of ticking, matey!
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Re: Tip to Tip Fiberglass / Carbon Fins

Postby A5tr0 An0n » Sun Apr 19, 2015 5:58 am

Just seeing this thread now so I thought I would give my opinion.

Is this the way you do Tip to tip?


The method used by Aeropac is not as strong, they basically have one full layer of tip-2-tip. For there flight more wasn't needed though. When I do layers of cloth I step them out but each layer goes from some point on one fin all the way to the other. Simply putting a layer of cloth only on one fin (not covering the airframe/fillet etc) is not tip-2-tip; if you want thicker fins then that is a different story. My thought is thicker fins reduce the chance of flutter and tip-to-tip reduces the chance of the fin being pulled off. A bit of both, maybe. My basic point is when talking tip-2-tip there are better ways but it all depends on what is really needed for your flight profile. Honestly most people do tip-to-tip when it isn't even needed and overkill it when it is needed.

So did he go all the way to the Tip itself or stop at the bevel


I have gone up to the start of the bevel and all the way to the edge. I feel for faster flights on bigger rockets going up to the bevel start or even lower is superior. Why? Less heating. The heat caused from the friction through the atmosphere can cause the epoxy resin to soften, weaken, or even liquify. The then "calm breeze," will pull the fibers loose and delmaninate them. I think either route you will want to take steps to prevent the fibers from delaminating if the flight vehicle and flight profile call for this. Some flights do not need anything others you can use high temp epoxy, ablative, metal leading edges.

Does doing tip to tip like this have any risk of de-laminating on high speed flights and what can be done to prevent de-lamination?


Yes. In a basic sense it depends of the dimensions of the rocket and the Mach number. As aforementioned, this is the reason I no longer bring the cloth all the way to the edge of the fin. Also as I said you can cover the leading edges/cloth with high temp epoxy, metal, or ablative.


Where do you get peel ply?

If you like I can provide all my composites sources, however none of them are in Aus.

I have seen Vac bagging done on fin cans but what when it isn't a separate fin can, how do you go sealing the bag/air frame?


First vacuum bagging is uber ;) Second I do not think the learning curve is that great. To answer your question, you put the entire vehicle in the bag or you seal aft and fore of the fins. I seal the bags with sealant tape made for that very purpose. If you want to go the vacuum bagging route then do it right. That is my commentary.


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