Gt-R - A 29mm MD Rocket - Build Thread - MIA

qquake2k said:

It looks fast even in the RockSim rendering!

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Thanks!

RAHagen said:

Wow! Those look great! Thanks again for going through the trouble of making these! I'll make sure to get a camera pointed at the top of the rail so I can try and get it on camera.

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If you fly this with us, make sure we get the GoPro setup for this flight. 30 fps from 15 ft away should show the working nicely.

Cl(VII) said:

If you fly this with us, make sure we get the GoPro setup for this flight. 30 fps from 15 ft away should show the working nicely.

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And please send me the pics!

I will send the short and long set, you pick which works. That's what beta testers are for...

Here is the short set, on the tube with the long set in the background and next to an orange set of 38mm guides:

wfcook said:

And please send me the pics!

I will send the short and long set, you pick which works. That's what beta testers are for...

Here is the short set, on the tube with the long set in the background and next to an orange set of 38mm guides:

View attachment 257592 View attachment 257593

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Awesome! I plan to work my way up the motor scale with the rocket so hopefully I'll be able to run the guides through their paces.

I'm thinking that the two lengths will both work fine. The one thing that would give the longer one an advantage in my opinion is in high acceleration situations where a little more friction could help them stay in place or maybe in a long skinny rocket where there is a lot more leverage to pull on them.

wfcook said:

And please send me the pics!

I will send the short and long set, you pick which works. That's what beta testers are for...

Here is the short set, on the tube with the long set in the background and next to an orange set of 38mm guides:

View attachment 257592 View attachment 257593

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Provided I time the photo burst correctly (30 fps is a 1 sec burst). Sometimes a motor comes to pressure slowly or chugs and I get 30 pad shots.

Regardless, I'll share anything worth sharing.

Okay I thought it was probably time to update the thread.

I got my fly-away rail guides from Wfcook! They look amazing and are very well built. Can't wait to try them out!

Other than that, I finally got around to reinforcing the fiberglass plate I made for the fins, and the result was much less than I anticipated. Even with six more layers of glass the boards was still quite flexible. On a rocket going slower than this one I'd probably go ahead and use it but since this rocket is going well over mach 1.5 I thought I should redo the board. The only issue I can see as a reason is that I might have squeezed too much epoxy out of the matrix using the press. This next plate will not be put under the press so hopefully this one will be a little stronger.

This rocket has taken a lot longer than I anticipated to build. Hopefully I can get it finished up within the next 2 or so weeks...

If my grandfathers press was working I'd prove to you that the press has nothing to do with the weakness of the laminate. Removing as much epoxy is the key to a lighter stronger laminate. If it is still flexible then it is something else. Do not forgot that it takes 7 days for the epoxy to reach full strength. I dont know what temperature you can ramp up the US Composite's epoxy to, but a post cure should make it stronger. You should contact them and ask to what temperature you can bake the laminate.

SinfulDarkLord said:

If my grandfathers press was working I'd prove to you that the press has nothing to do with the weakness of the laminate. Removing as much epoxy is the key to a lighter stronger laminate. If it is still flexible then it is something else. Do not forgot that it takes 7 days for the epoxy to reach full strength. I dont know what temperature you can ramp up the US Composite's epoxy to, but a post cure should make it stronger. You should contact them and ask to what temperature you can bake the laminate.

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This board has been finished for nearly a week. I also cut a fin out of it and post cured the fin at 175 for a couple of hours, and then proceeded to veil the entire thing in another layer of epoxy. It's stronger but still flexible. The only thing I know of that left for me to conclude is that the glass doesn't have enough epoxy in it.
I'm just not sure that this amount of flexibly in a fin is not normal (see picture)

I got the layup on another smaller board finished yesterday, it's still curing but my first impression is that this one will come out a lot better. If not in strength then in the cleanliness of the layup. I guess we'll see in a day or so.

Forgot to attach the photo...

Why didn't you use carbon fiber cloth instead of glass? It lighter and much stiffer than glass. 45 mil of CF cloth would be plenty stiff and wouldn't cost much more.

I suppose that if the pressure is too high you could deform the carbon fibers and reduce the strength, but I don't know what that pressure is.

If you vacuum bagged the plate and pumped out all the air, you get 14.7 psi pressure. Vacuum bagging produces good composites, so unless there's a reason your not telling, I don't see any reason to apply a load greater than 15 psi for small plates. For a 1 ft square plate that's 144 square inches x 15 psi = 2160 pounds ~ 1 ton per square foot. ACP-Composites has a 200 ton 5'x10' hot press which if use to capacity can apply 55 psi but I don't know what pressure they actually use.

Bob

bobkrech said:

Why didn't you use carbon fiber cloth instead of glass? It lighter and much stiffer than glass. 45 mil of CF cloth would be plenty stiff and wouldn't cost much more.

I suppose that if the pressure is too high you could deform the carbon fibers and reduce the strength, but I don't know what that pressure is.

If you vacuum bagged the plate and pumped out all the air, you get 14.7 psi pressure. Vacuum bagging produces good composites, so unless there's a reason your not telling, I don't see any reason to apply a load greater than 15 psi for small plates. For a 1 ft square plate that's 144 square inches x 15 psi = 2160 pounds ~ 1 ton per square foot. ACP-Composites has a 200 ton 5'x10' hot press which if use to capacity can apply 55 psi but I don't know what pressure they actually use.

Bob

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So if I'm reading this right, you don't believe the pressure is too much? I'm pretty much shooting in the dark on this stuff. This is my first attempt at making fiberglass board so I'm just going with what other people say. The problem is I seem to be getting differing opinions.

I guess a question I should have asked earlier is whether a 1/16" fiberglass plate should be flexible at all?

.063 glass is not going to be all that stiff. We routinely do parts in the autoclave at 100psi so unless you have a serious press you didn't apply to much pressure. The uscomposites is a pretty basic resin system and should work fine. Like Bob suggested carbon is a better choice for fins.

Okay so after a little thought I've decided that I'm going to do a little more testing with the original board. I had a conversation with my dad and we both think that the fins will be much less likely to flex when the root chord is glued to a tube. Because of this I'm going to attach a fin to a scrap tube and see how flexible the fin is.

Sadly I don't have the money to spend the cost of CF on this small of a rocket so I'm gonna have to stick with FG.

Well I've got some good news!
I was talking with SinfulDarkLord and he's decided to give some of his carbon fiber for the layup of some new fins! I'm extremely grateful and looking forward to working with carbon fiber. I've been reading from other threads about the layup of CF, but as before, this will be my first attempt at working with carbon fiber plates so all advice is welcomed!

RAHagen said:

I was talking with SinfulDarkLord and he's decided to give some of his carbon fiber for the layup of some new fins! I'm extremely grateful and looking forward to working with carbon fiber.

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Sold your soul to the devil for some carbon fiber. Typical rocketeer.

wfcook said:

Sold your soul to the devil for some carbon fiber. Typical rocketeer.

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Lol your funny man.

Okay! I got some carbon fiber, but not exactly how I first thought I'd get it...

Turns out a friend of my dad's who built his own airplane a while ago had a ton of CF laying around that he wasn't using. He gave me at least two to three yards of it! Even though its not really wide enough to use for body tubes, I've got enough to last a long time!

Finished my first CF layup.

I cut out five layers, alternating between straight and cut at 45 degrees, and two sheets of peel-ply.



After I had finished with the layup I put a good amount of pressure on it using my press.



One thing that caught my eye before putting it in the press however was when I laid the peel ply down on the board, a ton of bubbles started appearing in between the weave of the CF. The more I tried to get them out the more that seemed to show up. My first guess was that it was just air from other layers coming to the surface but I started getting worried when so many started showing up.



Is this normal for a CF layup? I though I wet out the layers fairly well (I put epoxy on it till the cloth was shiny and then added a little more), but since this is my first attempt at using CF I might be wrong.

Those are just little pinholes that form. If you didnt use a press I'd be concerned about it, but with the press it should get rid of that.

I've found that Peel ply isn't the best for making plates. Ive had it suck out too much epoxy leaving dry spots anti require sanding to make the plate smooth. For these reasons I switched to using mylar that will leave a very smooth surface and no pinholes.

conman13 said:

I've found that Peel ply isn't the best for making plates. Ive had it suck out too much epoxy leaving dry spots anti require sanding to make the plate smooth. For these reasons I switched to using mylar that will leave a very smooth surface and no pinholes.

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Yeah sadly I didn't have any Mylar on hand. I also had seen another post suggesting the use of peel ply to prevent pin holes.

I guess I'll see how it turns out. If the plate doesn't turn out well I can just make another. I only made just enough to make the fins this time I hardly used any cloth.

The Carbon Fiber came out great! The peel ply gave me a bit of a scare because it made the board look filled with pin holes, but once I pulled it off it came out nearly perfect. It also came out to .067" which is exactly the size I need. It's also a ton stiffer than the FG board and it isn't even completely cured.

RAHagen said:

The Carbon Fiber came out great! The peel ply gave me a bit of a scare because it made the board look filled with pin holes, but once I pulled it off it came out nearly perfect. It also came out to .067" which is exactly the size I need. It's also a ton stiffer than the FG board and it isn't even completely cured.

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That looks awesome, you must have a heavy weight cloth to achieve a 0.067" thick laminate after compressing it. Good work RAHagen.

3k PW cure thickness is ~.008

8 plies of 3kPW ~.064

flynfrog said:

3k PW cure thickness is ~.008

8 plies of 3kPW ~.064

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The thing is I only used five layers. The nearest I've found is 9oz but as far as I can tell it's only made in unidirectional cloth.

The guy who I got it from apparently got it for free from a junk store, and they apparently got it from a manufacturer (of what I'm not entirely sure). Maybe it was a custom weave or something. It's definitely cut weird. It was a really long roll but only 12" wide.

RAHagen said:

The thing is I only used five layers. The nearest I've found is 9oz but as far as I can tell it's only made in unidirectional cloth.

The guy who I got it from apparently got it for free from a junk store, and they apparently got it from a manufacturer (of what I'm not entirely sure). Maybe it was a custom weave or something. It's definitely cut weird. It was a really long roll but only 12" wide.

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6k PW is around ~.016 Cured Ply thickness

flynfrog said:

6k PW is around ~.016 Cured Ply thickness

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Oh okay, then that's probably it!
Either way, it's nice stuff!

Took another look at the plate today. The epoxy on the edges was still pretty flexible so I put it back between the plates and put around 25 pounds of weight on it to keep it from bending while it cures. This stuff is awesome! The FG plate I made doesn't even come close to being as strong. I also weighed it and the entire board is only ~50 grams.

Got the fins cut out today. All three together weight around 13.8 grams, and are around .067" thick. I'm debating whether or not I should heat treat them. Also I'm considering painting them with a veil layer of epoxy to give them a nice smooth finish since I used peel ply and the get rid of a couple pin holes. I'm not really sure it's worth it though.

Any throughs are appreciated.

RAHagen said:

Got the fins cut out today. All three together weight around 13.8 grams, and are around .067" thick. I'm debating whether or not I should heat treat them. Also I'm considering painting them with a veil layer of epoxy to give them a nice smooth finish since I used peel ply and the get rid of a couple pin holes. I'm not really sure it's worth it though.

Any throughs are appreciated.

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sand them a bit until they are pretty smooth, a clear coat will fill pretty much all of the pin holes depending on their size.