AGM Pike NextGen, First DD Build

[geof]

Well, I've finally done it. I bought a Missileworks RRC2-mini from a guy leaving the hobby, and I'm going to attempt my first DD build. Those of you who know me from past years on the forum--and those who don't--I'm going to need a lot of advice. So, here's the plan:

I got a 4in AGM Pike from Madcow, plus a 12in payload bay (basically, as an extender, not for payload), plus their removable e-bay kit. The plan is to build a stretch version, and modify the fins (since I don't like the aft fins). I also got a zillion #2-56 shear pins from McMaster-Carr, and I'll get rivets from some Taiwanese online store after measuring the best size. I'll get some wires, plugs and electronic stuff from Radio Shack or something, plus fiberglass/epoxy from my usual suppliers if I decide to use it and don't have enough laying around.

Here are some initial photos. 1. The Madcow pic. 2. My preliminary idea for modification, shape only--internal bits not all in openrocket yet. 3. The kit & extra parts. 4. Just for fun, a pic of the last rocket I built, a 6-fin 38mm scratch design.

The first decisions are a) 38 or 54, and b) fiberglass or not. I'm leaning pretty strongly toward 38 and "yes". The 38 motors are plenty powerful for a low & slow fan like me (plus I have only limited interest in trying for L2 and I don't own any 54mm tube). Probably fiberglass just because it's fun to do and I prefer durability over high performance. Try to argue me out if these if you want

Geof

 

[dshmel]

I have an AGM Pike 33 and stuck with the 38mm MMT. It flies great on I motors. I did not glass mine. However, it landed in Argonia while being pushed by a cross wind and hit a big clod of dirt. This put a big old dent in the bottom of the body tube between the fins. I may now go back and foam the inside of the fin can after I pull out the dent.

I also added an anti-zipper band to mine at the top of the body tube. It worked great.

The first decisions are a) 38 or 54, and b) fiberglass or not. I'm leaning pretty strongly toward 38 and "yes". The 38 motors are plenty powerful for a low & slow fan like me (plus I have only limited interest in trying for L2 and I don't own any 54mm tube). Probably fiberglass just because it's fun to do and I prefer durability over high performance. Try to argue me out if these if you want

Geof

 

[geof]

...I also added an anti-zipper band to mine at the top of the body tube. It worked great.

I don't know what that is. Is it a piece of coupler inside the top of the tube? If so, doesn't it provide an edge for the chute to get caught and prevent/discourage ejection?

 

[CarVac]

I don't know what that is. Is it a piece of coupler inside the top of the tube? If so, doesn't it provide an edge for the chute to get caught and prevent/discourage ejection?

They're on the outside. They can be metal or carbon fiber or fiberglass.

 

[Sailorbill]

They're on the outside. They can be metal or carbon fiber or fiberglass.

or Kevlar. I put a 2" X 2 wrap band on my L3 rocket.

My grandson got his L1 at Argonia with an AGM-33 Pike on a CTI I350 BB. It had a little trouble with the tubing below the bottom centering ring getting banged up. We will address this before his next launch. After receiving the the kit I bought for him I really wished I had opted for a 54MM version.


On the Pad.

Launch!

When we were building the rocket we converted the coupler into an AV Bay. At 8" long it was perfect. We added a LOC Stiffy Coupler to the Madcow coupler for added strength. It also made a step to mount one of the bulkplates and a step for the aft bulkplate/sled mount to reside.
The Av bay is secured to the upper airframe/payload bay with 3 #8-32 button head screws. There is one length of 1/4-20 threaded rod running through the center of the coupler. It is mounted solidly to the non removable bulkplate. The other bulk plate is secured buy a nut. There are u-bots on both bulkplates for recovery harness attachment.
I will try to post some pictures of the Av Bay I built for my LOC EZI-65 electronics version because it is nearly an copy of the one for the Pike.

 

[dshmel]

Mine consists of two guitar strings wrapped around the tube with epoxy, and then covered with a couple of layers of Kevlar salvaged from a BP vest. I then used Bondo to finish it off smooth and to a uniform thickness. Looks like part of the design.

They're on the outside. They can be metal or carbon fiber or fiberglass.

 

[geof]

I started with the removable ebay/sled last night. It says to use Loctite threadlocker on some of the threads. Should I use red (permanent) or blue (stubborn but removeable)?

The bulkhead on the forward end is supposed to to have the threadlocked bolts, and the aft end would have the removable bolts. I'm a little surprised at that because I would expect more "wiggling" under drogue than main and would therefore want things more reinforced at the aft end. I suppose it doesn't matter much?

One thing that is interesting about the ebay kit is that it doesn't contain all necessary parts. You need to cannibalize some parts from the rocket kit itself. It says that in the instructions, but it took me a while to notice it.

 

[geof]

Here's a question.

The photo shows the beginning of the ebay assembly. Note that there are nuts on both ends of the thing. The nuts on the right hand side are permanent. The instructions show two pairs of nuts on the left: one inside the bulkhead and one outside. I'm wondering why you want the ones on the inside. If they were gone, then when I tighten the nuts on the left outside, it clamps together the whole thing tightly against the coupler. If the left inside nuts are present, then I would need to position them just right or else the thing would not fit snugly in the coupler. Explain?

Geof

 

[geof]

Oops, another look at the instructions shows that there are no left inside nuts. Okay.

 

[geof]

The nylon standoffs go between the altimeter and the sled, right? (Not on top of the altimeter between the bolt head and the altimeter surface)

 

[Buckeye]

I think Madcow's instructions leave a bit to be desired. I didn't like the ebay design - especially the part about permanently glueing on one of the bulkheads - so I scratch built my own from Madcow parts to use in the Frenzy.

https://www.rocketryforum.com/showthread.php?30648-Frenzy-(base-model)-build&p=297739#post297739

The Pike is 4", like the Frenzy? Should be plenty beefy for an L2 cert if you want to go for it.

 

[geof]

Couldn't tell from your pictures whether the answer is yes or no. Yes, right?

My previous L2 attempt was pretty embarrassing: lawn dart due to failed motor ejection charge. So I am in no hurry to try again.

 

[Buckeye]

As to your first questions:

Go 54mm - though I did my 4" Frenzy L2 with a 38mm motor. Someday I will put a 54mm in there.

Glass not needed - The 1/4" fins are tough. The tube is a bit thin. Take precautions on the ends. I put a ring of stiffy coupler at the aft end and a good coating of thin epoxy on the shock cord end.

Standoffs go between altimeter and sled to leave an air gap under the pressure sensor. My Perfectflite MAWDs have the sensor on the bottom of the board.

 

[geof]

Next questions.

1. The black thing is the switch. My understanding is that it works like this: when an object (e.g., toothpick) presses the metal lever against the black case, the switch is off. To turn it on, remove the toothpick so that the lever springs outward. Thus, the toothpick would be vertical in this photo, and perpendicular (and through) the airframe wall. If so, then how do you insert the sled into the coupler? The toothpick wouldn't "fit" inside. You would have to remove the toothpick, thereby arming the system, then insert the sled, then re-insert the toothpick to turn it off, then put the black powder in while hoping the toothpick doesn't fall out. Sounds dangerous. What am I misunderstanding?

2. The white thing is the cup for the powder. Is it better to drill a hole at the base so the ignitor goes through the wall and into the base of the cup? Or simply bend the wire over the lip of the cup with the ignitor tip facing down into the cup? It seems like the first option would be better.

Thanks!

Geof

 

[Handeman]

Next questions.

1. The black thing is the switch. My understanding is that it works like this: when an object (e.g., toothpick) presses the metal lever against the black case, the switch is off. To turn it on, remove the toothpick so that the lever springs outward. Thus, the toothpick would be vertical in this photo, and perpendicular (and through) the airframe wall. If so, then how do you insert the sled into the coupler? The toothpick wouldn't "fit" inside. You would have to remove the toothpick, thereby arming the system, then insert the sled, then re-insert the toothpick to turn it off, then put the black powder in while hoping the toothpick doesn't fall out. Sounds dangerous. What am I misunderstanding?

2. The white thing is the cup for the powder. Is it better to drill a hole at the base so the ignitor goes through the wall and into the base of the cup? Or simply bend the wire over the lip of the cup with the ignitor tip facing down into the cup? It seems like the first option would be better.

Thanks!

Geof

You basically have it right. What I do is put terminal blocks on the outside of the end caps. You install the sled and put the "toothpick" (I used a finishing nail with a loop bent in the end to attach the Remove Before Flight ribbon to) This allows you to install the altimeter and seal up the av-bay, install the pin to turn if off and not have to worry about charges. You attach the ematches and charges later with the altimeter turned off.

 

[geof]

You basically have it right. What I do is put terminal blocks on the outside of the end caps. You install the sled and put the "toothpick" (I used a finishing nail with a loop bent in the end to attach the Remove Before Flight ribbon to) This allows you to install the altimeter and seal up the av-bay, install the pin to turn if off and not have to worry about charges. You attach the ematches and charges later with the altimeter turned off.

Holes in the base of the powder caps...preferred?

 

[Handeman]

Holes in the base of the powder caps...preferred?

I don't put hole in the powder cups. That's just a spot for the powder to leak out of and an extra hassle sealing up every flight. Just bend the ematch over the lip so the tip is in the powder, fill with dog barf and some masking tape over and around it to hold it all together.

 

[Sailorbill]

Holes in the base of the powder caps...preferred?

I use the cups aka PVC Pipe caps as holders for the short sections of pipe I use as charge holders. I use a screw to hold the cap to the bulkplate. I take a 1" long piece of pipe, fill the bottom 1/4" with epoxy resin an let it set up. I drill a small hole in the pipe just above the resin plug to pass my ematch wires through then I wrap electrical tape around it to seal it up. I measure the amount of BP I plan on using into the pipe ensuring the match head is buried in the BP. Next I fill the remainder with Estes Wadding to keep the BP around the Match and cover the whole thing with more electrical tape. I also mark the exposed pipe with the size of the charge in the pipe. Doing this allows me to make up multiple charges before the launch so I can shorten the time between flights.
Another thing I do is eliminate the terminal strips. I connect my match directly to the altimeter and seal the bulk head with a #8 or #10 well nut.

This is the aft bulk head of my latest AV bay. The cap is at the top and the well nut is at the bottom.

 

[geof]

Here are some photos of what I've done so far. In all of these, "AFT" is to the right.

If I just bend the igniter over the top, how big is the risk of failing to get the tip deep in the bottom in the powder? I've also been wondering about something else. The aft powder chamber will be pointing downwards, of course. It seems to me like stuffing it with dog barf would be "leaky" in the sense that the powder might fall/disperse itself throughout the barf and down to the tape. Is that a problem?



I guess I should mention that I haven't yet filled the holes that the wires pass through.

 

[Handeman]

Here are some photos of what I've done so far. In all of these, "AFT" is to the right.

If I just bend the igniter over the top, how big is the risk of failing to get the tip deep in the bottom in the powder? I've also been wondering about something else. The aft powder chamber will be pointing downwards, of course. It seems to me like stuffing it with dog barf would be "leaky" in the sense that the powder might fall/disperse itself throughout the barf and down to the tape. Is that a problem?


I guess I should mention that I haven't yet filled the holes that the wires pass through.

You don't have to get the tip of the ematch "deep into the powder", you only have to have it touching the powder.

The powder falling through the dog barf has never been a problem. If you pack it on top of the powder tight and then tape it so the tape doesn't break, the powder will stay in place. If you are worried about a high G flight, lay the match in a piece of duct tape, pour the powder over the tip and fold the tap around the match and powder. You can stuff that into the holder or let if lay loose in the BT. It will work. The only caution about using the duct tape, is to ground test that setup first. I've found that you need slightly less powder when it's packed into a holder with dog barf then just folded into duct tape. That is with FFFFg BP. I haven't tried any of the BP substitutes.

 

[geof]

Thanks for the advice, Handeman.

I got the wood for my revised aft fins, finalized the pattern, cut and match sanded them. I discovered one surprising fact in the process. My original design had a perfect match between the in-cut region of the forward fin and the leading triangle of the aft fin. In other words, the two pieces would fit together seamlessly. However, when I laid things out, this made the gap between the fins look uneven. The top half (iirc) of the gap "looked" wider than the bottom. Eventually, I figured it out: it was because the angles of the two sides of the triangle are not the same. So, I had to trim about 1/32 off the other edge to get a matching look. Thus, if you close the gap, it doesn't fit perfectly: there is a 1/32 gap remaining along one edge.

Of course, the aft fin tab had to be re-positioned correctly due to the decreased distance between the two sets of fins. Not a problem, there.

 

[geof]

Been glassing the tubes: 2 layers 6 oz. The most interesting part for me was that this was my first experience using peel ply. Generally, I like it--especially getting rid of the seam bump. I did have a few difficulties, however. First, there were some air pockets under the ply, which left small craters where the texture of the fiberglass remained. I'll need to fill those. Second, the peel ply was much harder to remove than it looks like in the videos! Overall, it was a success though. I did make one little mistake: I forgot to tape under the fin slots, so I need to sand some epoxy drips on the inside of the tube. No biggie. Here are a couple pix of peeling off the peel ply, and the finished product.

 

[geof]

Now I have a question...

Madcow gave me 17 feet of 0.5in shock cord webbing. But I'm building this DD. So, presumably, I'll use the entire amount for the main chute (which will be in the top compartment). My question is, how much additional length do I need to buy/find for the drogue?

While I'm at it, for the drogue shock cord, how far along it should I attach the chute?

Thanks!

 

[ksm2001]

Geof, Your AGM is coming along very nice!

Subscribed to your thread,op: mine is in the bag to build over the winter.

As for your question on the amount of shock cord to use for the drogue, use at least the same as the main, longer won't hurt. I'm thinking of using 20 -25ft for each section for DD. I've never used nylon webbing but would recommend using a Nomex shock cord protector sleeve to prevent the ejection charge from burning through the webbing. I'll be going with 1/4" or 3/8" kevlar instead of nylon.

 

[geof]

Geof, Your AGM is coming along very nice!

Subscribed to your thread,op: mine is in the bag to build over the winter.

As for your question on the amount of shock cord to use for the drogue, use at least the same as the main, longer won't hurt. I'm thinking of using 20 -25ft for each section for DD. I've never used nylon webbing but would recommend using a Nomex shock cord protector sleeve to prevent the ejection charge from burning through the webbing. I'll be going with 1/4" or 3/8" kevlar instead of nylon.

Thanks for the advice. What prevents the drogue from entangling in the main?

 

[ksm2001]

Thanks for the advice. What prevents the drogue from entangling in the main?

A properly packed chute and shock cord along with ground testing to make sure you have a good separation of the main should minimize the chances of entanglement.

 

[geof]

If the drogue is longer, then the drogue shock cord would seem to interfere with the main chute. If the main is longer, then the main shock cord would seem to interfere with the drogue chute, which would seem to be preferable. Regardless of deployment issues, I don't see what keeps the chutes apart even with ideal deployment.

 

[Handeman]

What I've done on my DD is about 12 - 15 feet of cord on the drogue side with the drogue chute attached about 18" from the upper section. This keeps the upper section above the fin can as it falls. On the main, I use 10 - 12 feet of cord and the main attached to the end of the cord. The nose cone is attached about 3' from the end. That is for a 4" diameter rocket that is about 90" tall.

The key is to have a drogue that is small enough to allow everything to fall quickly, but large enough to keep the upper section even with or above the lower fin can. That way the fin can can't fall through the main after it opens. I've seen many drogueless setups where the upper section comes down ballistic, dragging the fin can with it on a very long shock cord and when the main opens, the fin can lands on the main or is a near miss. If it lands on the main, everything falls and crashes. If it misses the main, it hits the end of it's long shock cord and puts a huge shock load on the recovery system. Most will stay together, but not all of them.

The secret to DD is ground testing. Get the right sized charges so you don't need extremely long shock cords and the problems they cause. Use a properly sized drogue so it lets everything drop quickly but keeps the section with the main chute above the rest of the rocket. That will give you a much better and safer controlled deployment.

 

[geof]

Making progress...

I epoxied the forward CR to the motor tube, attached the eyebolt and shock cord, and glued the assembly in the body tube. Unlike the instructions, I did not glue the aft ring before this step. I prefer to dry fit it with some tape tabs. Then it can be used to center the motor tube, but after things have dried it can be removed. This lets me put fillets inside the body, both on the motor tube and on the back side of the body tube.

Then I made a fin jig, using a design popular here on the forum. It's fantastic! I'll never revert to any other fin alignment method again. Not only is the alignment great, but it also removes any warping in the fin.

Then I started beveling the fins and tacking them in place using the fin jig.

Two pix here: a dry fit of some fins, and the rocket in the jig tacking on a fin.

 

[qquake2k]

Nice fin jig! I've used mine on dozens of rockets, and it hasn't let me down yet.