Mach-Mobile 38

[Eat, sleep, and Fly]

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

That is a really bad idea... a 6xl can fit

 

[Aksrockets]

Finally got and painted my LOC nosecone. It was a bit heavier and sturdier then I expected. It'll work well.
I primered it with 2x primer and gave it a coat of orange.
I'm pretty pleased with how this turned out.




I'm still debating on whether or not to turn the top section into a camera bay or to build a dual deployment type thing.

Alex

 

[Aksrockets]

Wrote a blog post about this little guy...
https://aksrockets.blogspot.com/2012/06/machmobile38.html

Just over a month away from flying time!

Alex

 

[Aksrockets]

Only a few days before I lose this thing.
My shock cord just arrived in the mail. I ordered 100ft of 1/8in #750 Kevlar. I think it's about the right size for the job. I was thinking on using about 10ft. More? Less? Just give up?
It only just occurred to me that I have not thought on how to mount this in the rocket. I have several ideas:

1. Run a metal rod through the BT horizontally (through one wall across to the other.) This would be epoxied in and I would loop the shock cord around this.
Pros: Sturdy shock cord attachment, relatively easy placement
Cons: Ruins the paint job. Imperfections increase drag.

2. Use a glorified "estes SC mount". I would use the 3 fold estes method and epoxy the cord into the tube, then use one layer of fiberglass to strengthen the attachment.
Pros: No drag, I keep my rocket's appearance tidy.
Cons: Somewhat lower strength, more difficult to attach.

Any other suggestions?

Alex

 

[dixontj93060]

It only just occurred to me that I have not thought on how to mount this in the rocket.

Wow that is tragic.

 

[grouch]

I would add a bulkhead with baffles drilled around a central welded eyelet. Epoxy the bulkhead into a short section of coupler and secure the coupler/bulkhead with 2/56 button head screws so that you could remove it for maintenance and cleaning. Nice looking rocket by the way, it looks like it will really scream.

 

[Aksrockets]

Well, how bout un update a few months later!
This flew in August at Hellfire but I never got around to updating the build thread. I guess it's better late then never.
Right now I am kicking myself for not following what you guys suggested.
For the shock cord I just epoxied the cord to the inside of the tube and put a layer of fiberglass over it. I though it seemed pretty sturdy....
Well, bought an H400Vmax from Joe at Giant Leap.
Got it all ready for flight. Had a 12in chute filled with tracking powder along with a mylar streamer.
Loaded it on the pads. It looked minuscule on the HPR pads out there.
The flight:
[YOUTUBE]QKoj58WYwN0[/YOUTUBE]
At apogee I noticed the booster was a little ways away from the mylar streamer and the tracking powder.
The booster hit the ground pretty hard. Destroyed 2 of the fins.


The Payload Section is just fine, just a few scratches.

Just an excuse to build another one!

Alex

 

[qquake2k]

That's not a rocket, it's a bullet! Great flight, too bad about the damage. Is it repairable? I'm assuming the shock cord separated? Did the shock cord break or did the mount fail? What did you use for the shock cord? Pretty cool launching from the Salt Flats. As long as your rocket is a dark color, it should be pretty easy to spot. It looks like snow!

 

[Aksrockets]

The mount failed. I used 750# kevlar.
The salt flats are fun!

Alex

 

[qquake2k]

The mount failed. I used 750# kevlar.
The salt flats are fun!

Alex

Do you know if it deployed early or late? And did the cord break, or did the epoxy fail?

 

[Aksrockets]

It tore out the inside wall of the paper tube. The cord was just fine I didnt see it when It deployed. It was pretty high up there.
I dont think it's reparable. It might make sense just to build a new booster.

Alex

 

[qquake2k]

It tore out the inside wall of the paper tube. The cord was just fine I didnt see it when It deployed. It was pretty high up there.
I dont think it's reparable. It might make sense just to build a new booster.

Alex

For some reason, I thought the body tube was carbon fiber.

 

[CarVac]

It was carbon fiber wrapped around paper, if I remember correctly.

I guess that's one disadvantage to that strategy...

 

[Aksrockets]

It was Fiberglass wrapped paper. Captain and Carvac, you might be thinking of my 29mm MD, which is all carbon fiber.
I'm suprised it broke my carbon fiber fillets.

Alex

 

[CarVac]

It looks like you had an adhesion failure on one side (probably the side in tension). Did you scuff the surface where you were bonding the fins on?

Since you used teflon-coated peel ply, it can actually leave release agent on the surface, thus making any further bonding to the surface much worse.

Dacron peel ply is really the only option for getting a good bond to the outer surface of a layup without sanding (or ideally, sandblasting), since it really tears up the surface when removed. In fact, you can feel the little cracked flecks of epoxy flinging everywhere when pulling it off.

 

[Highpowerrocketyahoo]

Put a epoxy glazed coupler with an eye bolt in the booster drill a few holes for motor ejection and your good to go. Also gives you a more reliable and accessible attachment point.

 

[Aksrockets]

A little late with that suggestion, but I'll keep it in mind for next time. :wink:

t looks like you had an adhesion failure on one side (probably the side in tension). Did you scuff the surface where you were bonding the fins on?

Since you used teflon-coated peel ply, it can actually leave release agent on the surface, thus making any further bonding to the surface much worse.

Dacron peel ply is really the only option for getting a good bond to the outer surface of a layup without sanding (or ideally, sandblasting), since it really tears up the surface when removed. In fact, you can feel the little cracked flecks of epoxy flinging everywhere when pulling it off.

No, although I didnt know that Teflon Peel Ply gave it a release film. The other fin's fillet just cracked. No adhesion problem there.

I can make a new one really easily.

Alex

 

[CarVac]

Yeah, we learned that (though didn't actually use that particular piece of knowledge at all) when making Bare Necessities.

The only issue with our use of Dacron is that we bought a big roll of Dacron from Aircraft Spruce, but it has persistent wrinkles in it. I don't have an iron (or an ironing board) to smooth it out, though, and that would have to be done to any peel ply we want to work with, and if it causes it to not be perfectly flat (stretched edges, etc) then it won't roll nicely on a tube. Luckily, one section of the roll doesn't have wrinkles, so we use that for critical surfaces (e.g. wrapping tubes).

 

[Aksrockets]

I have a good bit of Darcon too. As you said, it leaves a much rougher finish but is much better for bonding. I think I'll use that for areas that will be under very high stress and use teflon stuff for just about everything else. Teflon is much easier to use. It doesnt fray, leaves a smoother finish and is much easier to peel off.
Thanks for the tips!

Alex

 

[grouch]

Crap that thing took off!

 

[Aksrockets]

Crap that thing took off!

It sure did. I heard people making bets whether I'd get it back or not. Getting it back in several pieces was not specified. :wink:
The video doesn't do justice to show how fast this thing went.

Alex

 

[MasonH]

Just wait until my bad boy hops in the air on an H410 Alex...

 

[Aksrockets]

my

Sorry. Youre?

:wink:

 

[MasonH]

It is still mine at the moment, yes. MINE!!

 

[Aksrockets]

ITS........ ALIVE!!!!!!!!!!!!

 

[MasonH]

And it has competition.

 

[CarVac]

If I was in the rocket lab I would post a photo of Disappearing Act's smashed fincan...