Mach-Mobile 38

While at my friends house, I spotted some shipping tubes and awkwardly asked that I could have them, they didn't look anything special, just plain, fuzzy, cardboard shipping tubes. I took them home and began experimenting with sizes, trying on nose cones and getting a feel for how big they were. I tried an AT 38/480 and BINGO! It fit like a glove.
So, here we go: a 38mm minimum diameter rocket.
I have several goals for this rocket:

1. Be strong enough to fly on a large I motor
2. Be light enough to fly on an F motor
3. Have a nice, smooth finish
4. Have the capabilities to use dual deployment

Components:

Tubes: I will peel down the tubes till they are just paper "skins" and wrap them in 2 wraps of 6oz glass. Peel Ply over that. Tubes are 20in each.

Fins: 1/8in Plywood, with one layer of 6oz glass on each side

Nose Cone: Either a LOC 1.5in or a PML Utherane 1.5in.

Altimeter bay: I'll scratch build one.


Anyway, I have to go to work now....








Alex

A PML will be heavy (it's solid urethane). Get a Shockwave 7:1 Von Karmann.

Glassed the upper tube. It turned out horribly. I wrapped it in 2 layers of 6oz and put a layer of peel ply over that. I started getting bubbles when I put the peel ply on, I had no way to get rid of these so i moved them over to the end of the tube and hoped to save at least a 10in section. The remaining 9.5in section isnt pretty, It has rough spots, small bubbles and a nasty peel ply seam. Oh well, I might just buy another peice of 38mm tube and glass that.
Feel free to laugh at my attempt.








This'll take a lot of sanding.

:sigh: Hopefully the main tube will be more successful.

Alex

Yep, that sucks. I'm not sure what the problem was, but here's a few thoughts. One thing about peel ply is that is that it won't do uneven surfaces very well. That shouldn't be a problem on tubes unless they are rough to start with.

To apply peel ply, you start at one end and wet it out as you go. If you try to go too fast (like wrap it on the tube and then try to wet it out), that won't work.

Another problem I've encountered with peel ply is that if you try to cure the layup at more than about 100F, large bubbles will develop, and the imperfections that result are hard to repair. i have no idea why this happens. Your tube looks like this in a couple of places, but I don't know if you used an oven or not. if you did, let it green up first before you apply much heat.

The peel ply seam can be a bit of a pain. One problem is that the threads can get caught in the epoxy. I remove the peel ply slowly while the epoxy is still on the soft side. The threads can be pulled out. The other thing
I do is use a very sharp knife (exacto with new blade) to literally shave off the excess epoxy at this seam. You'll find that you can shave off quite a bit without getting into the fiberglass.

I also wonder if your layup ended up being too dry. The cardboard tubes are going to soak up a bunch of epoxy. You might have done the layup and then after you were done, the epoxy continued to soak into the tube drying out your fiberglass. I put a wrap of carbon on a larger cardboard tube a few months back, and i started by wetting out the cardboard tube. It was amazing how much epoxy had to be added before it stopped soaking up the epoxy.

Jim

JimJarvis50 said:

Yep, that sucks. I'm not sure what the problem was, but here's a few thoughts. One thing about peel ply is that is that it won't do uneven surfaces very well. That shouldn't be a problem on tubes unless they are rough to start with.

Click to expand...

I'm guessing that that was my problem. The tube was very rough when I started glassing.

To apply peel ply, you start at one end and wet it out as you go. If you try to go too fast (like wrap it on the tube and then try to wet it out), that won't work.

Click to expand...

Yep. Did that.

Another problem I've encountered with peel ply is that if you try to cure the layup at more than about 100F, large bubbles will develop, and the imperfections that result are hard to repair. i have no idea why this happens. Your tube looks like this in a couple of places, but I don't know if you used an oven or not. if you did, let it green up first before you apply much heat.

Click to expand...

No. Didnt use a heater, the tubes were cured at about 72 degrees.

The peel ply seam can be a bit of a pain. One problem is that the threads can get caught in the epoxy. I remove the peel ply slowly while the epoxy is still on the soft side. The threads can be pulled out. The other thing
I do is use a very sharp knife (exacto with new blade) to literally shave off the excess epoxy at this seam. You'll find that you can shave off quite a bit without getting into the fiberglass.

Click to expand...

Thanks for the tip! You might have just saved me a while of sanding.

I also wonder if your layup ended up being too dry. The cardboard tubes are going to soak up a bunch of epoxy. You might have done the layup and then after you were done, the epoxy continued to soak into the tube drying out your fiberglass. I put a wrap of carbon on a larger cardboard tube a few months back, and i started by wetting out the cardboard tube. It was amazing how much epoxy had to be added before it stopped soaking up the epoxy.

Click to expand...

Yeah, those tubes are like sponges I used most of my epoxy just getting the tubes saturated.

____________________________________________________________

I just did the main tube.

NO PROBLEMS!!! (or at least, none that I can tell)

Pictures to follow.

You should try this stuff: https://www.aircraftspruce.com/catalog/cmpages/vb7025.php
It's Teflon coated peel ply. It doesn't stick to the surface of the tube like Dacron does after the tube has cured. It leaves a nice finish. And it isn't much more expensive than Dacron peel ply.

I use it on carbon tubes.

Tominator 2 said:

You should try this stuff: .

Click to expand...

I just did. I like it a lot more then Peel ply, Smoother finish and says down better the peel ply. However, It doesnt wet out so it's hard to tell what spots are dry in the tube.

The second tube is better then the first but still not good. I didnt use enough epoxy and the tube is riddled with pin holes. Nothing a little bondo cant fix...
The seam is also prominent in the tube, I needed to use more epoxy here too. Oh well, this is a learning experience.










Alex

Openrocket file.

View attachment MAch 38.ork

An H400 Vmax might be a good choice.

______________________________

Now onto the topic of dual deploy. I've only got a JR Cert so that means that I cant handle BP. I would need to fly it under another adults name for it to pass the RSO. (anyone in UROC willing to help???) If that doesnt work out, 4K isnt that high. Tracking powder and reflective mylar would help track it.

Alex

I cut 3 fins out of 1/8in glassed plywood. 6oz glass on both sides. Very light and stiff.



Alex

Got a lot of work done.
Fins are now attached. I made up a fin alignment jig from payload bay.
Pretty simple process.



Imagine all fins like this. I couldnt upload the other photos of the fin attachment.

Alex

I did chopped carbon fiber fillets. DONT WORRY! THESE WILL LOOK OKAY IN THE END!
I mixed up some chopped carbon fiber with a bit of Proline laminating resin. I drained the extra epoxy out and smeared the paste onto the fin, It was very thick and couldn't run easily. I was left with very solid, very ugly fillets.




The next step was to do something about the smoothness of the fillets. I wrapped sand paper around a 1in dowel and started sanding. Next, I applied a coat of bondo over the fillets and smoothed them out with the same 1in dowel. After that, I sanded those down untill they had a nice smooth transition between the tube and the fin. I still need to fine sand them before I primer.







Well, they're smoother then they look.

Also, the fin can is ROCK SOLID. I'd be comfortable putting this thing up on some big I motors.


Alex

One trick i use to get nice fillets is to mask off the areas you don't want get epoxy on. and then once the epoxy gets tacky, peel it off.

Works very well!!

-Tom

I did that with one set of fillets. The Carbon fiber had a HUGE lip where the carbon fiber raised up. Took forever to sand.

Alex

Well, I filled the pin-holes in the tube with bondo and primered the tube with rustoleum 2x grey primer.


Here she is!



Fillets turned out nicely, I'm happy with them.




For the paint, I'm thinking bright orange with Monokote Chrome trim.

Any other Ideas for the paint?

What do you guys think so far?

Alex

Two coats of Rustoleum 2x "real orange" gets you this result.


The orange color isn't the best but I can live with it.


I'm really pleased with how these fillets turned out. To think that they went from that carbon fiber mess a few posts back to this is cool. I worked hard and long for these fillets and I'm glad I did. Those 3 hrs of sanding and filling really payed off.




Probably need another coat to even it out.

Now, on to the Monokote Trim.

Alex

Added some Monokote strips along the separation point. I like the look.






Next up: altimeter bay


Alex

Aksrockets said:

Added some Monokote strips along the separation point. I like the look.

Next up: altimeter bay

Alex

Click to expand...

That really does jazz it up, doesn't it?

Forgot to mention:
Price for this rocket so far $6 (not including paint)

Alex

qquake2k said:

That really does jazz it up, doesn't it?

Click to expand...

Yeah! Plus, It'll be more visible at high altitudes.

Alex

Aksrockets said:

Forgot to mention:
Price for this rocket so far $6 (not including paint)

Alex

Click to expand...

Wow, what a bargain!

Aksrockets said:

Forgot to mention:
Price for this rocket so far $6 (not including paint)

Alex

Click to expand...

I'll give you 7.00 for it & throw in a can of paint! Lol

blackjack2564 said:

I'll give you 7.00 for it & throw in a can of paint! Lol

Click to expand...

I would want to STEAL from you.

gdjsky01 said:

Nice job!! :clap: :clap: :clap:

Let's not quibble... I'll give you $20! j/k

Click to expand...

Ah, but you havnt seen it with the Decals yet....







Alex

Looks good, Alex! What size 38 mm motor are you going to use and what altitude and speed are you expecting? Are using dual deploy?

aerostadt said:

Looks good, Alex! What size 38 mm motor are you going to use and what altitude and speed are you expecting? Are using dual deploy?

Click to expand...

Depends, If someone is crazy enough to let me borrow their CTI 3 grain, I'll probably put 'er up on a H565 Vmax. She'll hit mach 1.46 (ish) and coast up to about 4500 feet. If not, I might just buy a 3G. At sport launches I might just fly her on Fs (1600ft) and Gs (2500 ft).

I hope to rip those cute little stickers off of there!!!!

Dual Deploy: I would LOVE to use dual deploy but I cant because I only have a JR L1. If someone from UROC were willing to help by setting up the altimeter and putting their name on the card then I could fly DD.

I'm fine not flying DD, 4500 isnt TO high (ive flown higher @ Hellfire). Mylar, a streamer and tracking powder would help in finding it.

Alex

If it makes it to hellfire, you're welcome to borrow my 38mm CTI case, assuming of course I havn't CATO'ed it before then.

I dunno, your cases and VMaxs don't get along very well...

Alex

I do have a poor history!... Ah, who cares.

Hurry up and get your fake ID so you can really let 'er scream in an I540 :dark: