Aurora 38mm MD rocket

there is a pretty much zero chance its tapered. But it could be warped. If it were me Id skip the mylar and use a real mold release. Elevated temp cure will buy you more tolerance to get your tube off. You could build a pulling apparatus but I could buy an awful lot of pre made tube

flynfrog said:

there is a pretty much zero chance its tapered. But it could be warped. If it were me Id skip the mylar and use a real mold release. Elevated temp cure will buy you more tolerance to get your tube off. You could build a pulling apparatus but I could buy an awful lot of pre made tube

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You have a point, given that a tapered aluminum tube would be...expensive probably. But my guess is that something is nonuniform about it.


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Well the tube is off!! Sort of....

I basically shoved my Loki 1200 case in to try to push it out and it got stuck about 7" down. I had to break the tube where the case ended. after the tube broke about 7" from the top the rest slid off no problem same with the broken piece on the motor case. so I now have a 7" piece and a 27" piece. Sadly i need 31" for the airframe but I can use the 7" piece for the payload tube and now I have an extra 38mm tube for another build or to give to someone Because the tube slid off just fine after it broke in 2 I am left to think that the tube keeps getting stuck because of friction. For now on I'm not going to roll full length tubes and will stay under 31". I will get pictures in a little bit.

27" tube



7"ish tube



basically the 7" tube will be cut down to 4" for the payload tube and I will use the 27" tube for another project further down the road.

That point where the motor tube got stuck...where was that on the mandrel? Because I am thinking the mandrel has some defect right around there...


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I was at the end of the mandrel. basically before I put my casing in to push it out there was about 7" of tube already off. When I broke the tube it broke at the end of the mandrel where I was then able to slide the rest of the tube off. So it is confusing and is why I was stuck thinking it must have been the friction. I will cut that end of the mandrel off just to be sure though.

I would measure the mandrel thoroughly and try to find the bad spot if there is one.

Put your eye at the end and look down the mandrel to see if you see any curvature or irregularities (foreshortening)

Also, get something VERY straight and lay it the length of the mandrel all around the circumference to see if there are any gaps that indicate depressions are bends.

I would try very hard to diagnose the problem before cutting anything.

Did the tube come off about the same amount this time as it did when it got stuck last time? If so, that kind of consistency is a big clue...

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If it's giving you that much trouble, just forget the aluminum and buy a full length phenolic coupler. Mine haven't failed me yet.

Alex

wfcook said:

I would measure the mandrel thoroughly and try to find the bad spot if there is one.

Put your eye at the end and look down the mandrel to see if you see any curvature or irregularities (foreshortening)

Also, get something VERY straight and lay it the length of the mandrel all around the circumference to see if there are any gaps that indicate depressions are bends.

I would try very hard to diagnose the problem before cutting anything.

Did the tube come off about the same amount this time as it did when it got stuck last time? If so, that kind of consistency is a big clue...

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Click to expand...

Ya I'm going to do a lot of investigating before I do anything. No this tube came off a lot more then the other tube.

Aksrockets said:

If it's giving you that much trouble, just forget the aluminum and buy a full length phenolic coupler. Mine haven't failed me yet.

Alex

Click to expand...

I may just resort to this.

I have been using Blue Tube coupler tubes for mandrels for the last year or so. Works perfectly. Check this out. https://www.aeroconsystems.com/tips/cloud_FG_tubes.htm

SDramstad said:

I have been using Blue Tube coupler tubes for mandrels for the last year or so. Works perfectly. Check this out. https://www.aeroconsystems.com/tips/cloud_FG_tubes.htm

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I'm never going back to blue tube couplers after David sent me a defective blue tube. They can also warp.

I would agree to phenolic, since they are cheap and would most likely be straight. The downside is the limit to the length of tubes you can make since phenolic is usually 3' or 4'. Unless you couple two together.

I'm all for aluminum and my purchases from Texas Towers have been all worth it.

Your choice I suppose and as long as it works out its all good.


Alexander Solis

TRA - Level 1
Mariah 54 - CTI RedLightning- I-100 - 6,345 Feet

So the coupler from madcow is a bit tight in the airframe and sanding won't get it down enough. Anyone have a lathe that they could cut this down on? I can pay you for it if you would like. PM me

Aksrockets said:

If it's giving you that much trouble, just forget the aluminum and buy a full length phenolic coupler. Mine haven't failed me yet.

Alex

Click to expand...

I have always used the PML coupler/airframe tubing, but the more recent tubes (2" to 4") have had too much curvature. I can't use them unless I "open them up" a bit. The one in the pic has a slice every six inches or so and then an axle down the middle to line everything up. As bad as it looks, it provided a nice tube.

Jim

Payload tube has the final coat of epoxy and will be sanded/trimmed tomorrow. The carbon plate is now done and all I have to do is trace and cut out fins.

conman13 said:

Payload tube has the final coat of epoxy and will be sanded/trimmed tomorrow. The carbon plate is now done and all I have to do is trace and cut out fins.

View attachment 247578

View attachment 247579

Click to expand...

Looking nice

Primativerocketry said:

Looking nice

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thanks!

Ok so I'm going way over what I thought at first for velocity. Now I'm going to mach 2.4ish on the J1000. Now should I do T2T? I'm thinking a layer of 6oz fiberglass. Suggestions?

conman13 said:

Ok so I'm going way over what I thought at first for velocity. Now I'm going to mach 2.4ish on the J1000. Now should I do T2T? I'm thinking a layer of 6oz fiberglass. Suggestions?

Click to expand...

Depends what epoxy you use to attach/fillet the fins and how thorough your prep work is. That said, t2t hurts nothing but your stability, which you have some to spare.

My 54mm Md bird went 2.4 mach with no T2T. If you do want to do a T2T it is not a bad idea but I'd use carbon over glass as the reason for T2T is to add stiffness and carbon is going to be much stiffer than glass.

I would check your fins against flutter speed calculator. Keep in mind a T2T is adding mass to the wrong end of the rocket.

Just_Keep_Flying said:

Depends what epoxy you use to attach/fillet the fins and how thorough your prep work is. That said, t2t hurts nothing but your stability, which you have some to spare.

Click to expand...

The only epoxy going on this rocket is JB Weld.

A little update.


Av bulk plates have been drilled out for the allthread and a space for the telemetrum a antenna.



Got the battery and switch for the sled. Now I just need to find out how to mount the Telemetrum as it doesn't fit on the pre drilled holes.


Allthread has been cut.




I ordered an 18" the mill parachute to use along with my cable cutter.

Is that the sled from etsy?

I've found that the mounting kit from apogee works really well. Fifty times better than my last mounting setup which included nylon washers and some metal screws.

RAHagen said:

Is that the sled from etsy?

I've found that the mounting kit from apogee works really well. Fifty times better than my last mounting setup which included nylon washers and some metal screws.

Click to expand...

Yes the sled is from Etsy. No I have great mounting hardware it;s that the holes on the altimeter don't match up with the holes on the sled. I have to see if I can drill my own when I get the telemetrum.

Ok so now that I'm on break I can actually get some stuff done So I was tracing out the fins on the carbon plate when I started thinking that the plate may be too thin. As My goal is to reach mach 2 and as of now it sims to mach 2.38 I figured I may as well add another layer of carbon to each side. I got some heavy carbon that is .02" thick and last night laminated the first side. It came out great! Tonight I am going to laminate the other side and will get some pictures of everything. The plate should come in at around .09". Yes, a little overkill but hey I have a bunch of wiggle room from mach 2.38 to mach 2.0. If all goes well I will be able to finish the plate on the 2nd after everything has had time to cure and then move on to cutting the fins out. I'm working on getting more mylar so I can start on the main body tube. Almost forgot! I got my Telemetrum a couple of weeks ago so the electronics are set! Andrew is going to see of designing a 38mm sled for it is a possibility. I also got my coupler back from Flynfrog who was nice enough to grind down my coupler for me so that it fits snug in the body tubes. Pictures soon to come

1 fin airfoiled 2 to go






Thickness is about .09"



The coupler Flynfrog ground down just enough to fit snug in the body tube.




The almost finished payload tube



What sucks about the kevlar is that it leaves small fluffies when cut



Where the coupler will be epoxied into the payload tube. I need to get the nosecone before I epoxy it in though.

Can't forget the aftermath!!!!!!



Large pile of carbon dust

Ok so I was going to get a regular 4:1 fiberglass ogive nosecone from performance hobbies, However after beveling the fins like I did they are a bit smaller and the 5:1 VK filament wound from performance hobbies will add weight to the nose bringing the stability up a bunch as well as decreasing my altitude and Mach #. I am now at 18000 and Mach 2.18. Which makes me more comfortable as I'm still over Mach 2, Because the fins are much smaller now the fins are no longer on the borderline of needing T2T, My altitude is also lower which is ideal

Looks great so far. Those fins came out mean looking and that carbon/kevlar tube is really nice as well.

What motor are you using?

T34zac said:

Looks great so far. Those fins came out mean looking and that carbon/kevlar tube is really nice as well.

What motor are you using?

Click to expand...

Thanks

It is designed to fly around the Loki 38mm 1200 motors. It will fly on a J1000 at LDRS.