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

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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I am assuming you mean post cure? Not sure what resin you used but not all epoxy systems benefit from a postcure. If you have a low temp system and take it past its tg with your fins unsupported they can warp. Most room temp cure epoxies need a pretty specific ramp and hold cycle to properly post cure them.

See the cure data for this system to get and idea
https://www.ptm-w.com/dynamicdata/data/docs/pt2620 bulletin.pdf

This is the text described in the techincal data sheet from the 635 resin from US Composites.

Physical properties shown are based upon the following cure schedule: 24 Hours at 77F + 2 Hours at 250F

Will try to post a link to the data sheet information. The file is on my OneDrive storage.

Hopefully this works

https://onedrive.live.com/redir?resid=8CAC86B7ACFEA30B!1982&authkey=!AK-xUzW8rrQzG8M&ithint=file,pdf

SinfulDarkLord said:

This is the text described in the techincal data sheet from the 635 resin from US Composites.

Physical properties shown are based upon the following cure schedule: 24 Hours at 77F + 2 Hours at 250F

Will try to post a link to the data sheet information. The file is on my OneDrive storage.

Click to expand...

Thanks, so if I'm reading that right, it says to post cure the fins at 250°? I know that when I post cured the FG fins, I only heated them to 170.

The fins are already really strong so I still might decide to just glue them on the body tube and go.

Another question. What would you guys do with the texture left by the peel ply? Should I sand it off?

Sand it off..

RAHagen said:

Another question. What would you guys do with the texture left by the peel ply? Should I sand it off?

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What I do with the peel ply finish is to paint it twice with a thin coat of epoxy. Sand after the first coat. The painting step has to be done slowly or you generate a bunch of air bubbles. Two coats should fill the rough finish. i would heat treat at this point. Then, you should be able to sand them smooth without sanding into the carbon. You can stop here, clear coat, or wipe on a very very thin layer of epoxy.

Jim

conman13 said:

Sand it off..

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Agreed here, know your peel ply. The airtech easylease or econolease peel ply has silicone in it, which will be left on your part. The silicone will prevent glue from sticking to it.

You could also go with what Jim Jarvis said, by putting a few coats of epoxy and then sanding it smooth.

SinfulDarkLord said:

Agreed here, know your peel ply. The airtech easylease or econolease peel ply has silicone in it, which will be left on your part. The silicone will prevent glue from sticking to it.

You could also go with what Jim Jarvis said, by putting a few coats of epoxy and then sanding it smooth.

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Okay thanks. I thought about it a little more and I'll probably paint a thin veil layer on the fins and sand it smooth. I'm still trying to decide whether to post cure the fins but I'm leaning towards just gluing them to the body since they're already plenty strong.

Also I was looking over the sim a while ago and I think I could make a go for the G altitude record. If I remember correctly, it sims about 300 ft above the record!

Fins tacked on today.

Printed off the fin guides from payloadbay.com and stenciled them on to some cardboard.

I tacked the fins on with just enough five minute epoxy to keep them in position. Next I'll use either rocketpoxy or US composites w/ aerosil to make the fillets.

Tacked fins:

RAHagen said:

Tacked fins:

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I hope you gave the tube a good sanding before tacking on those fins. Remember that the superlease/econolease has a silicone coating that stays on your laminate and will prevent glue from bonding to it.

I forgot you gave the tube a coat of epoxy, my bad lol.

Just finished the fillets!



I decided to go with dyed RocketPoxy as my fillet material just because the I was feeling too lazy to add aerosil to the US composites (I took an ACT this morning ).



Rocket with the AV-bay in comparison to 29/40-120 casing:

Talked with SinfulDarkLord about the FG nose cone he's making me, and it turns out that due to multiple reasons it won't be done any time soon. Because of this, I've decided to go ahead and make a balsa NC for GtR until the FG one is done. I should be able to stop and get a block of balsa today and try to get it turned on Saturday.

Didn't get around to turning the NC today... I did however update the paint scheme for GtR. I got some vinyl decal paper for home printers and I'm gonna see if I can get them scaled and printed out.

Finally got some time to work on the rocket.

I was able to get the Nose cone turned and coated in epoxy. I'm still trying to figure out how I'm going to mount the nose weight now that it's not hollow fiberglass. I'm thinking I might try to slightly hollow the center out and fill the hole with epoxy but I'm not sure if I'll be able to get the amount of weight I'll need. I'm trying to find a way around using metal around my electronics to keep interference to an absolute minimum. I'm going to be trusting the tracker a lot for finding this rocket.

I also got the shock cord glued to the coupler and the coupler glued to the lower body tube, and just for peace of mind, I laid a small piece of Carbon fiber down on the shock cord while the glue was curing.

Nose come is dried. I still need to do a little sanding to get a little better shape and a couple other things but the last part to this rocket is coming together!

Here is a photo of the NC dry fit on the rocket.

Okay I've run into a problem that I should have noticed a LONG time ago. The nose weight required to make this rocket stable is an extremely large amount of mass. Like around 200+ grams... I kinda didn't put any thought into the density of objects while I was designing this rocket so I just kept adding weight till it was stable. Bad idea. I'm trying to get around using metal as a nose weight because I plan to have the tracker's antenna stick up into the NC but sadly it's looking like I might not be able to get around it. The only other option I can think of is making a mold and forming the NC out of solid fiberglass resin, and even then I'm not entirely sure it will be enough.

Please, I would appreciate any suggestions and ideas you guys have. Thanks.

Make it longer.

grouch said:

Make it longer.

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+1

grouch said:

Make it longer.

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conman13 said:

+1

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Thanks guys, that's probably what i'll end up doing. I went back and did the sims with the extra 8" tubing I had left over, and doing that will help in two different ways. For one, the extra length allows me to not worry about having to insert the tracker antenna into the nose cone leaving it completely open for NC weight. It also, as I "conveniently" forgot about, adds more leverage allowing me to use "less" weight. I'll still have to use a lot but it did help. So far with three .25"x.25"x9.25" lead rods the nose weight is 343 grams, and the stability worst case scenario is .76 calibers. I'm pretty sure that i'll be able to fit it all in the NC, but I really should have watched the amount of weight I was adding to the NC...

Okay so I did some messing around with the Rocksim file today and side to the fact that I am completely confused with the mass override feature, I think it might actually be a better idea to leave the extra section of tubing off the rocket... It seems that adding an extra section of tubing somehow makes the weight of the motor more influential on the position of the CG and makes the design require MORE weight.
For now all I know is the weight and mass override features are messing with my head so I'm going to hold off adding nose weight till I get the motor for the rocket. Then I can physically determine the CG and find out exactly how weight I need.

RAHagen said:

Okay so I did some messing around with the Rocksim file today and side to the fact that I am completely confused with the mass override feature, I think it might actually be a better idea to leave the extra section of tubing off the rocket... It seems that adding an extra section of tubing somehow makes the weight of the motor more influential on the position of the CG and makes the design require MORE weight.
For now all I know is the weight and mass override features are messing with my head so I'm going to hold off adding nose weight till I get the motor for the rocket. Then I can physically determine the CG and find out exactly how weight I need.

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Post the file and I can sim it for you. It doesn't make any sense that more tubing would increase the need for nose weight.

conman13 said:

Post the file and I can sim it for you. It doesn't make any sense that more tubing would increase the need for nose weight.

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+1, get a second set of eyes in it

Okay here is the file: View attachment Supersonic G v1.2.rkt

Thanks for taking a look at it. I'm not entirely sure but I'm thinking that without the extra section of tubing on the rocket, the motor is slightly balanced around the CG making the weight of the motor cancel it's self out. With the extra tubing the CG is moved forwards past the motor and the motor has more of an influence on the CG since the weight is all on one side. The mass override feature in Rocksim is driving me crazy though so I might be completely wrong but that is what I got.

By the way, the extra section of tubing I have is 8 inches long. I don't think it saved to the sim file.

Okay so I found the issue with the weights in rocksim. Even with those improvements though I still had to add 120 grams to the NC. The problem was that I had just before hand melted down and added 350 grams of lead and poured it into into the cone... So yeah. Oops.

After I figured that out I promptly started drilling the lead out when the bit grabbed and ripped the shoulder completely off.

So finally, I gave in and bought a conical FG nose cone from apogee components. It's shorter and a different shape than what I wanted but it should work fine for my purposes. I just want to see this rocket fly soon.

Shock cords are glued in! Last step before painting is to add the nose weight to the new cone.

I really need to remember to attach photos...

Please excuse the picture quality.


My other photo doesn't seem to want to upload. it keeps giving me an error. I'll try later and see if it works then.

Gt-R is officially flight worthy! Yesterday I was able to finish the recovery system and add the nose weight making this rocket finally done side to paint. I hope to get it painted and decaled in time for the launch I'm attending on July 11th.

Got the primer on the rocket yesterday. painting it tomorrow, then decals after that.