Redshift- 38mm Minimum Diameter Rocket

[conman13]

Alright, now WITHOUT starting a war... I'd like opinions on shear pins. I've never used them before, and have never seen any evidence of a main prematurely deploying or starting to deploy. I like the simplicity of friction fit, but is there something else I should know?

Nate

On a rocket this size I say go friction fit. It works just fine.

 

[rms]

Alright, now WITHOUT starting a war... I'd like opinions on shear pins. I've never used them before, and have never seen any evidence of a main prematurely deploying or starting to deploy. I like the simplicity of friction fit, but is there something else I should know?

Nate

I like shear pins for another reason with regard to md rockets and small airframe areas to stuff the recovery components. Besides keeping the airframe from drag seperating the pins will hold the airframe together with the pressure of the packed recovery componets trying to push it apart. In my 38 mm LDRS project I'm using shear pins on apogee airframe separation joint for just this
reason.

Greg

 

[Onebadhawk]

Nate,,,
Do not forget one very important point.....
Every flight you do with this minimum D rocket at Great Meadows under our 5K waiver will create similar stresses,, --- how much separation tension occurs during the flight when you DON'T want it to separate.........

When you have a few flights with this rocket under your belt and all is jived out and working perfectly flight after flight,,,,,

and then you get to Potter ----- with a slightly higher waiver-----

Things are different.....

In other words,,,

Burnout from a midsized I load that won't make 5K will be very different from burnout from a load with 3 times that amount of impulse...........

Just be certain that you don't wind up with the rocket flying perfect and wonderful until it's flight that is most important to you............

Teddy

 

[RocketHunter]

Alright, now WITHOUT starting a war... I'd like opinions on shear pins. I've never used them before, and have never seen any evidence of a main prematurely deploying or starting to deploy. I like the simplicity of friction fit, but is there something else I should know?

Nate

I would strongly recommend some way of securing the NC other than friction fit. If your flying to 3K+ at radrocks you do not want your main coming out at appgee - if there's any wind you'll most likely end up in the trees somewhere (I popped my main at apogee in my BH38 once out of its dozen or so flights because I left off the shear pins that one time, and that caused it to drift off and get stuck in a tree 60' up until I got it down a few weeks later). Also, as someone already pointed out, having shear pins will hold everything in and allow you to pack your chute much tighter into a smaller space.

I find shear pins to be annoying and difficult to reinstall at the field, so I've been using a wrap or two of aluminum foil tape to hold the NC and main parchute in. It's much easier to attach and remove than shear pins, but it still shears very evenly right at the joint with consistent force (seems about roughly equal to 1-2 2-56 shear pins).

 

[nute]

I think I'm leaning towards using shearpins. The new cone is such a near-perfect fit with a tube as is, any tape, even 1/8 of a wrap is enough to create an issue. So, I figure I'll give them a try. Also, like Coleman said, an early main, especially at our field would be catastrophic.

Thanks for the help guys!

Nate

 

[wfcook]

I think I'm leaning towards using shearpins. The new cone is such a near-perfect fit with a tube as is, any tape, even 1/8 of a wrap is enough to create an issue. So, I figure I'll give them a try. Also, like Coleman said, an early main, especially at our field would be catastrophic.

Thanks for the help guys!

Nate

I think using shear pins for this is the right choice.

I like to glue a small piece of brass inside the hole where the sheer pins go and then use a steel screw to thread through a slightly-too-small hole in the brass the first time. After you do that, the brass is formed to take the nylon screw and putting the shear pins in there is very easy.

 

[rms]

I think using shear pins for this is the right choice.

I like to glue a small piece of brass inside the hole where the sheer pins go and then use a steel screw to thread through a slightly-too-small hole in the brass the first time. After you do that, the brass is formed to take the nylon screw and putting the shear pins in there is very easy.

I have always size shear pin holes to just push in the 2-56 screw with a very little force. I have never seen the advantage of having to thread the screws in?

Greg

 

[nute]

Wooo!

Stickershock Decal arrived today!!




Due to the size and shape of the lettering, I'm going to line up and apply it sooner rather than later so I can plan out hole patterns that won't interfere (much) with the decal and visa versa.
No way I'd rather spend a snow-day!

Nate

 

[nute]

And... Stickershock decal applied!

I love it!

I also drilled shear pin holes, but that's not quite as exciting is it...

Just got to do the other 2 sets of fillets, drill holes for rivets, and the battery is still on track to arrive Wednesday, so then I can finish the av-bay.

Then it's just a matter of ground testing and shock cord attachment. Oh and painting. I hate painting.


20150202_180938
Nate

 

[conman13]

That looks awesome. Nice job!

 

[RKeller]

what paint?

 

[codysmith]

No paint!

 

[nute]

LOL, don't worry, very little FG texture will be covered. Just a red nosecone (w/ silver tip) and yellow fin tips. No paint on the BT- that's all fg and vinyl

Nate

 

[nute]

Time for an update:

I got the second set of fillets done. They're pretty good. Not perfect, but pretty good.

Pics:

Again, they look better in real life than on the camera.


I also did ejection testing for the main. I used 2 2-56 shear pins in the NC, 15" parachute in a nomex blanket, and the SC. .3g was not enough- it barely moved anything. Then i reset and used .55 grams, which was a touch over-energetic. I'm planning to use .5 or .55g. The way I see it, it's better to put a little extra stress on the recovery system than to have the parachute not deploy. I'll upload videos once my dad returns with his phone.

I also painted the cone red. For the first time in a while, the first coat looks like it turned out perfect. I'm rather happy. This also looks better in person. I'll try to get better pics later.

 

[RocketHunter]

Time for an update:

I got the second set of fillets done. They're pretty good. Not perfect, but pretty good.

Pics:

View attachment 254337Again, they look better in real life than on the camera.


I also did ejection testing for the main. I used 2 2-56 shear pins in the NC, 15" parachute in a nomex blanket, and the SC. .3g was not enough- it barely moved anything. Then i reset and used .55 grams, which was a touch over-energetic. I'm planning to use .5 or .55g. The way I see it, it's better to put a little extra stress on the recovery system than to have the parachute not deploy. I'll upload videos once my dad returns with his phone.

I also painted the cone red. For the first time in a while, the first coat looks like it turned out perfect. I'm rather happy. This also looks better in person. I'll try to get better pics later.


View attachment 254339View attachment 254340

I would go with .55g. You're absolutely correct - there's less chance of damage from a slightly energetic main deployment than a failed main deployment. Plus, in my experience, it sometimes seems like a deployment that was perfect in ground testing was a bit weak in the actual flight due to a tighter packed main, temperature expansion, etc. It's just good to have a bit of insurance in your charge size.

 

[nute]

I would go with .55g. You're absolutely correct - there's less chance of damage from a slightly energetic main deployment than a failed main deployment. Plus, in my experience, it sometimes seems like a deployment that was perfect in ground testing was a bit weak in the actual flight due to a tighter packed main, temperature expansion, etc. It's just good to have a bit of insurance in your charge size.

Yup, better to be safe than sorry.


Here's a video of the ground tests:


[video=youtube;kDAiuBGWhwo]https://www.youtube.com/watch?v=kDAiuBGWhwo&feature=youtu.be[/video]

 

[conman13]

Yup, better to be safe than sorry.


Here's a video of the ground tests:


[video=youtube;kDAiuBGWhwo]https://www.youtube.com/watch?v=kDAiuBGWhwo&feature=youtu.be[/video]

Ya, .55g. looks perfect.

 

[rms]

I'm not trying to be argumentive but it seems odd that .3 does nothing and .55 blows everything and the resulting ejection charge moves the airframe as well? Sorry but it seems a significant difference for not a huge increase in black powder. Again just saying not trying to be argumentive.

Greg

 

[nute]

I'm not trying to be argumentive but it seems odd that .3 does nothing and .55 blows everything and the resulting ejection charge moves the airframe as well? Sorry but it seems a significant difference for not a huge increase in black powder. Again just saying not trying to be argumentive.

Greg

It surprised me a bit too. I think the shear pins may have made it look less powerful than it really was. There was no room for movement; it would have to fully shear the pins to move at all. That said, just listening to it, it sounds like the bp burns for more time than one would expect with the.3g. . A pfzzzz, rather than a pop. It was really so little powder, I think it's a real possibility that when I was packing the first charge, i could or should have been better compressed or contained it. It felt good, but then again it was my first time using those size charge holders, or that small an amount of bp. Also, something to consider, it was almost twice as much- only a "bit" more, but still double the charge. Those are just my thoughts. Thanks for the feedback.

Nate

 

[wfcook]

I'm not trying to be argumentive but it seems odd that .3 does nothing and .55 blows everything and the resulting ejection charge moves the airframe as well? Sorry but it seems a significant difference for not a huge increase in black powder. Again just saying not trying to be argumentive.

Greg

Well, that is an 83% increase in black powder. Seems significant...

 

[Onebadhawk]

Well, that is an 83% increase in black powder. Seems significant...

+1.............
It's almost twice the powder.......
Looked quite consistent to me,,,,,,,
and that's what you're lookin for.............

Teddy

 

[nute]

I'm working on the shock cord attachment point on the booster, and I've got a question about length. I have 19.5" of space from the back of the rocket to the aftmost extension of the coupler (charge canister). The attachment point is one of the CRs that came with the kit, with a notch filed in it. Conveniently, the thickness of the CR (38mm-29mm) is the same (and less when slightly filed down) is LESS than the difference from the inside of the BT wall to the outside of the charge canister. So, the charge canister can seat down inside of the shock cord attachment point, and thus it is not a limiting factor in motor length.

Here's a picture, not a good one, but maybe it'll help.



Anyway, that means that the limiting factors in motor length and ease of packing said long motors are the charge canister and the shock cord length. I should be able to have a short leader on the SC attachment point like in the picture, and then tie on a separate actual cord. So, how short can I go? does it make sense to use a longer one when I have the room with shorter motors, and then switch it out to a shorter cord when space is an issue? Is 7ft too short? 8?


Nate

 

[CarVac]

Why two shear pins? On something this small, one is good enough and you get bigger margins for your black powder.

 

[nute]

Why two shear pins? On something this small, one is good enough and you get bigger margins for your black powder.

I know this topic has been discussed quite a bit, but I just feel like 1 pin creates a pivot point that could jam the cone. It seems like an off-center force holding the nosecone back could cause problems. Maybe it's just me, and it is my first time using shear pins, but I feel better with 2+ pins positioned evenly around the diameter.

Nate

 

[maxvelocity]

In that case you should be using 3. 2 pins would create an axis for a pivot. One pin does work fine, I've used it multiple time on a 54mm min dia. I like to have a very nice fit at the joint which will eliminate the issue. This can be accomplished by smearing superglue evenly around the shoulder until you have a nice fit.

 

[nute]

I got the AV-bay wired. I'll put up pics tomorrow.

HUGE thanks to the wonderful Joe (JJSR) of the Radical Rocketeers, here in NJ, who sent me some parts I needed!! (cuz I failed at soldering...)

Nate

 

[nute]

Alright, I did pretty standard wiring in the av-bay- battery leads to conecter- one goes to the altimeter, other goes to the switch- wire goes from switch to altimeter.

Here are some pics. I had my dad help me do some soldering, I don't have a soldering station, or anything to hold pieces in place so I need about 4 hands to get it done, lol.

Here's a pic:


Even just the wires make it a tight fit in the av-bay, but it fits.

Nate

 

[nute]

Yesterday I got the shock cord mount epoxied in. I don't have any pictures because, well, its a black ring in a black tube- nothing particularly special...

So, construction is now officially done! All that's left is to paint the fin tips yellow. Yippee!

Nate

 

[DeadMonkey]

I know this topic has been discussed quite a bit, but I just feel like 1 pin creates a pivot point that could jam the cone. It seems like an off-center force holding the nosecone back could cause problems. Maybe it's just me, and it is my first time using shear pins, but I feel better with 2+ pins positioned evenly around the diameter.

Nate

So some personal experience by proxy.
Don't do 1 shear pin!!!11!1
It can bind up. I watched it happen on a fellow rocketeers min diam 38mm. I watched him put it all together (because I'm learning too and he uses cable cutters). It lawn darted, never to be seen again.
Telemetry states all the charges deployed but it just never slowed down and came in ballistic.

At the very least you want 2 pins at 180deg and this is still sketchy.
Personally I would go with 3 pins for a stable "tri-pod" configuration at 120deg. pins and BP are cheap. Rockets, not so much.

 

[nute]

Alright, how about a little update. Redshift is now officially 100% finished. WooHoo!

I masked for the yellow fin tips with 3M scotch blue tape, then sprayed grey primer, and then 2 lightish coats of Rusto yellow. Turned out pretty well, but I should have used white primer. Yellow over grey over black doesn't cover all that well...

Tada! It's not a great picture, I'll see if I can get a better one soon.



Shock cord attachment point:

I mounted it by measuring where the ring would sit, smeared epoxy about 1/4" inside of that. Then I placed the ring in the tube, and used a carefully marked coupler to push it into position. (and then quickly pulled it out!). It worked very very well.

I did some sanding for the coupler fit, and this thing is done. I've decided on a 15" chute for the first flight, but I'm guessing I'll decide to step it up to 18" for subsequent flights, especially those to mid-range altitudes with heavier motor cases. I'll also be using a 4X40 streamer for the drogue, which I'll be getting soon. If need be I'll use a smaller one though. Test packing the chute, nomex, and a tracker stand-in was all very easy, and with all the newfound room in the NC, I've get room to spare in the payload section.



And, the all important weight......

..........19.5oz ready to go, parachute and all! Not bad, I think. That's only about 3-4oz heavier than my Shape Shifter mini without the recovery gear.
First flight will be on Sunday with the previously planned G339N. I will be using Bill Cook's "Mayhem Rocketry" Fly Away Rail Guides. I have very high hopes, and a full flight report will be here Sunday or Monday. OR is saying about 2300ft, but I don't think It'll be quite that high. It'll be off the rail in .09s, traveling at 85mph, and pulling 50Gs :grin: I'm very eager to fly this thing.

Two question; Has anyone had any issues flying the RRC2+ in rather high acceleration flights? Any tips to ensure my charges don't disassemble themselves prematurely?

Nate