A little hiccup while building..

[MikeyDSlagle]

Finally getting around to building my SS gift from last year. A Madcow Tembo. I am putting a 54MMT in it, airfoiling the fins and probably gonna stretch it with a Madcow payload kit. A few mods to the nose cone is always a gimme. Nothing really revolutionary in the way I build my rockets so I don't do build threads. I just had a little hiccup I thought I'd share.

When I start on my fin cans, I usually take the fin slots all the way to the end of the tube...aft end of course. So I can attach the fins to the MMT outside the BT, get good fillets and then glue the whole thing in place. Did so on this one. Got all the marks for my centering rings and glued the fore CR in place. I double check my measurements to make sure it is square. It is.

I use a number of methods to get my index marks where my fins will go. I put my glue down, slide the MMT in and slide the fins through their slots into the glue, check alignment and wait for it to set up. I have a little trouble getting the fins to cooperate with my template, I just think the template wasn't scaled properly when printed. So I make do.

So the fins set up and I remove my fin can assembly. When I go to put it back in, it doesn't fit. It binds on the BT. I turn it and it slides in. Hmmm. Three fins, three slots. Something is off. I get to measuring and squaring, looks like one of my fins is canted just a hair and another is off its index mark by about 1/8" to 3/16". Nothing major but enough to mess up my alignment. So I remove the two messed up fins. A little water brushed on and then an Xacto did the trick.

Now I cut out some guides to make sure I get the alignment right. Doing a dry fit and using tape I get the fins aligned on the MMT outside the BT this time. Go to slide it in, one fin is off by about 1/8".

NO WAY! I check and recheck. Sure enough, the slots in the body tube are wrong. Well one of them is. It is off by about 1/8", a little more actually. Grrr.

I simply didn't want to reslot the tube. I would have had a large gap that would have needed filled. I could have contacted Madcow, but it seemed such a small thing. So one of my fins is going to be cockeyed a bit.

So anyway...there it is. My hiccup. I guess I'll start checking all my slots first from here on out. Never had any issues with this before.

Mikey D

 

[mpitfield]

Great looking rocket.

That is mine in my signature "Udder Moch"

I converted it to dual deploy, with a StratoLogger 100 altimeter and ComSpec AT-2B tracker in the nosecone, and a Dog House Rocketry 1.5g charge-well/terminals on the nosecone bulkhead for apogee in combination with a Jolly Logic Chute Release for main. For my retainer I went with the GLR Bell retainer.

Originally it had a Tinder Rocketry Peregrine CO2 for apogee and a Archetype Rocketry Cable Cutter with an experimental deployment bag and drogue/pilot chute for main

For the design I decided to go all paint and had Mark at Stickershock do up some 3M masks then I did a white over black base Dupli-Color Acrylic Enamel cow pattern.

Looking forward to see what you do with yours.

 

[fyrfytr310]

So aggravating. Though I understand your battle choosing here. Sometimes it's just not with the hassle.

 

[The_Lone_Beagle]

NO WAY! I check and recheck. Sure enough, the slots in the body tube are wrong. Well one of them is. It is off by about 1/8", a little more actually. Grrr.
Mikey D

Wow! I never would have thought to check that.

Totally out of your control...that's got to be frustrating!

 

[MikeyDSlagle]

My Cowabunga went together smoothly. No problems at all. This one must have been done kitted up a Friday.

Add a little salt to the wound. The nose cone is extremely loose, even before I hacked off the end. Loose fitting NCs are nothing out of the ordinary but this one has LOTS of slop. Madcow NCs have ridges that can be sanded to adjust fit, even the ridges have slop. As in "3 wraps of tape" lots of slop. Even the OD of the NC is smaller than the OD of the BT. They got me good on this one. LOL.

No issues, I will use epoxy or some wild idea to make up for the slop. Not much to do about the OD except for lots of paint and sanding.

I'll get some pics of the build highlights as I go. And post em here for those interested.

Sim file of what I have in mind.

View attachment 307769

It will get a bay in the NC so the weights will change up front and I can shave some weight from the ballast. I am going to epoxy sand into the nose cone for the minimum weight I will need and have a way too add weight for the rare occasion I put in up on a J.

The sled in the coupler will also add some weight. Going in to this, I was building it for the 54mm beer can hardware, namely the I117FJ. But stretched, that seems unlikely. Sims showing borderline off the rail speed and a semi-ballistic missile flight path. I may try HED and leave out the coupler and payload tube. I'll burn that bridge when I get there.

Mikey D

 

[fyrfytr310]

I'll be pretty surprised if MadCow doesn't jump in and offer to make it right.

 

[MikeyDSlagle]

That'd be nice of em, but neither expected nor necessary. A discount off my next order would be awesome no doubt.

I'm looking at going with dual deployment all from the NC and leave out the payload section altogether. Just gotta come up with a way to do that.

 

[mpitfield]

That'd be nice of em, but neither expected nor necessary. A discount off my next order would be awesome no doubt.

I'm looking at going with dual deployment all from the NC and leave out the payload section altogether. Just gotta come up with a way to do that.

Great looking rocket.

That is mine in my signature "Udder Moch"

I converted it to dual deploy, with a StratoLogger 100 altimeter and ComSpec AT-2B tracker in the nosecone, and a Dog House Rocketry 1.5g charge-well/terminals on the nosecone bulkhead for apogee in combination with a Jolly Logic Chute Release for main. For my retainer I went with the GLR Bell retainer.

Originally it had a Tinder Rocketry Peregrine CO2 for apogee and a Archetype Rocketry Cable Cutter with an experimental deployment bag and drogue/pilot chute for main

For the design I decided to go all paint and had Mark at Stickershock do up some 3M masks then I did a white over black base Dupli-Color Acrylic Enamel cow pattern.

Looking forward to see what you do with yours.

:confused2: it works

 

[dhbarr]

Originally it had a Tinder Rocketry Peregrine CO2 for apogee and a Archetype Rocketry Cable Cutter

Moving from Arch/PrairieTwister to JLCR makes a lot of sense to me. Why the move away from peregrine toward charge cups? Pros/cons vs. cd3?

 

[MikeyDSlagle]

I don't have a JLCR and I can't make myself buy one just yet. Having a bay in the nose for apogee deployment is pretty easy and if I had a JLCR it'd be a no brainer. I would copy my bay in my Cowabunga.
I'm talking about full-on dual deployright there in the nose. I know it's doable and it has been done. A few ideas are rattling around in my head, hopefully a sensible one will fall out.
We'll see.

 

[OverTheTop]

I will be curious to see if it suffers from windmilling on the way down.

I have been pondering doing something like that deliberately, to reduce the amount of windmilling the rocket does during descent. The other way I was looking at was making one of the fins a bit longer than the others.

 

[mpitfield]

Moving from Arch/PrairieTwister to JLCR makes a lot of sense to me. Why the move away from peregrine toward charge cups? Pros/cons vs. cd3?

My intention was to use my Tembo as a test platform for many different deployment technologies and configurations, I even had an ARRD on it at one point.

Specific to the Tinder Rocketry Peregrine system, my personal feeling was that it works well if you are very careful however I wanted something a bit more forgiving. The one failure I had was that the denotation was too energetic and the CO2 cartridge hit the end cap assembly that contains the piercing pin with such force that it just stuck and slowly leaked, more like hissed out as it was still hissing on recovery. Luckily I had a engine back-up and all ended well.

Now to be completely fair, my failure was also my fault and not a fault of the product. I used dual e-matches for redundancy and also a bit too much BP, but very close to the recommended amount. This brings me back to why I stopped using it, you have to be very precise.

Not to be too critical however in hindsight I believe that the design contributed to the issue as well. This is due to the combined mass of the lift piston and CO2 cartridge. To illustrate this you need to compare Tinder's new Raptor design to their original Peregrine. If you compare the two you will note what I believe to be a significant difference. That is, with the new Raptor the puncture pin is the only component that moves (besides the spring).

My interpretation of this is that because it has less moving parts it has less failure modes. Also the moving parts have less mass, which I believe was a contributing factor specific to my failure.

Incidentally I am looking at the CD3 and Raptor for my L3 build. Comparing the two designs they are close but I prefer the new Raptor because I believe it is superior in that the exhaust BP gases and the CO2 instantly mix cooling the BP gases without the need for a nomex sleeve. The problem, according to the specs on the Raptor, is that it only supports CO2 cartridges from 20-85g, and I likely need somewhere around 14g including margin. So the CD3 16g is close enough but the 20g Raptor may be too much.

What I will need to better understand is the affect that too much CO2 would have, and is 20g really too much. I not then I will go with the Raptor.

One other thing that I would like to add about Tinder Rocketry. I had a conference call with Gene from Fruity Chutes who sold me the product and the owner of Tinder (can't recall his name now) at his request, to discuss my failure. He was a very open and decent guy to talk to. He really wanted to understand what I did, and how the product failed. To me I can clearly see that he has put a lot of thought into his new Raptor design, based on lessons learned. This is the type of manufacturer I like to align with.

 

[dhbarr]

One other thing that I would like to add about Tinder Rocketry. I had a conference call with Gene from Fruity Chutes who sold me the product and the owner of Tinder (can't recall his name now) at his request, to discuss my failure. He was a very open and decent guy to talk to. He really wanted to understand what I did, and how the product failed. To me I can clearly see that he has put a lot of thought into his new Raptor design, based on lessons learned. This is the type of manufacturer I like to align with.

Absolutely true; I got the Peregrine kit w/ the dual-54 plate that had a minor machining inconsistency vs. the 12g tubes. Cameron responded right away and fixed me up far over/above/beyond my expectations. I need to remember to get another 8g tube sometime.

Have I hijacked this thread enough yet? Back to your regularly scheduled programming....