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PML AMRAAM 4" CPR build

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manixFan

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I got the switch in and it works, but I had to cut a hole in the centering ring. The slot the wires need to run through to allow the altimeter mount end cap to pass through the tube is very narrow and shallow. I used 24 gauge silicon coated wires - they just barely fit in the slot. I would not use wires any thicker than that or you won't be able to get the end cap in the tube. I will leave the hole open until the build is complete to ensure things work before I plug it up. I may just cover it with aluminum tape for launches so I can get back in there if anything goes wrong.
Keep in mind that the top of that centering ring will be exposed to the ejection charge. You don't want pressure and black powder residue getting into your AV bay. You might consider a small plate that you can screw down over that hole to seal it up.

The final product looks great! I really like the how the nose cone looks. Have a great flight!


Tony
 

mtnmanak

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Keep in mind that the top of that centering ring will be exposed to the ejection charge. You don't want pressure and black powder residue getting into your AV bay. You might consider a small plate that you can screw down over that hole to seal it up.

The final product looks great! I really like the how the nose cone looks. Have a great flight!


Tony
Great point, thanks!

I did ground test the ejection charges today and put a piece of aluminum tape over the hole. It held for the ground test, but I think you are right that it would be a good idea to use something more robust for the actual launch. One nice thing about the piston system is that it takes very little black powder. The main ejected forcefully with only 0.8g of FFFFg. That may be why the aluminum tape held with no issues.
 

jd2cylman

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I only use ematches passed thru the bulk plate to the altimeter. So I have a small hole drilled in the bulkplate for the wires. I only use a single piece of masking tape to cover the holes. Has held up to 7 gram charges with no leaks into the AV bays... YMMV. Just sayin.
 

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  • very lightly dust the inside of CPR tube to allow the o-rings on the CPR mounts to easily slide into the tube
Tony.
Having now done my ground testing for the ejection charges, I can very much recommend this advice from Tony. I forgot to do this when I first tried to put the altimeter mount into the CPR tube and I almost broke the altimeter plate in half first trying to wedge it in, then trying to pry it out. In the end, I had it stuck so badly in the CPR tube, I used a dowel to push it back out from the other end and broke one of the flanges off the charge well holder (didn't affect the performance of the system and can be replaced).

Second time, remembered to follow Tony's sage advice and the altimeter mount slid in and out like butter. I may not listen very well, but I at least try to not make the same mistake twice :)
 

manixFan

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I only use ematches passed thru the bulk plate to the altimeter. So I have a small hole drilled in the bulkplate for the wires. I only use a single piece of masking tape to cover the holes. Has held up to 7 gram charges with no leaks into the AV bays... YMMV. Just sayin.
I was talking about the big hole in the bulkhead he made to access the switch that he installed.


Tony
 

jd2cylman

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I was talking about the big hole in the bulkhead he made to access the switch that he installed.


Tony
Sorry, missed that pic while trying to catch up...
 

mtnmanak

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Ground Test video for main deployment charge. This was with 0.8g of FFFFg.

 

manixFan

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Ground Test video for main deployment charge. This was with 0.8g of FFFFg.

That looked very authoritative. Surprising how little BP it takes to get the job done.


Tony
 

mtnmanak

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That looked very authoritative. Surprising how little BP it takes to get the job done.


Tony
The piston system really doesn't need much, that's for sure. PML recommends not going lower than 0.8 g, but that definitely produced a lot of PSI.

I ground tested an Apogee Level 2 this weekend as well and the volume of the main chute tube was almost the same as the AMRAAM, but it required 1.4g to deploy, and that was not with much authority. Will probably use 1.5g for that bird this weekend.

I definitely saw, though, that you have to clean the QT out very well afterwards or the piston will get gummed up. A little talc lube is in order, especially since it will be cold this weekend and the QTs may shrink (even thought I cold fitted the pistons).
 

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Flew the AMRAAM this weekend at METRA. Flew the maiden flight on an I245 and the second flight on a J250.

Both flights turned out great - all systems worked perfectly. No wind that day, so go very nice recoveries close to the pad. Flew it with a Stratologger CF. That is a great altimeter for this bird - perfect size for the CPR 3000 kit and, with the custom sled from Rocketarium, it was a breeze to setup.

Got some decent video of the ascent, but didn't realize I had stuff all over the lens on my video camera, so it wasn't focusing on any of the descent portion. Later, just had camera problems completely, so didn't catch any of the J250.

Here is the video for the I245 I do have. Flew to just under 1000 feet with a peak velocity of about 200 MPH.

 

MoreCowbell

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A nice project and good thread--you received a lot of good input, and I am glad that you had successful flights. A few thoughts for you going forward:

1. The CPR system is not a bad way to learn the basics of dual deployment (I built my first DD project using a PML Sudden Rush), but it is far from being a really good system, as you learned. There are much better and simpler ways to construct an avbay, and to put a rocket together for dual deployment.
2. PML is very clear in their literature that QT is not suitable for flights approaching or exceeding Mach, so you want to be careful with motor selection and not push the rocket too fast. However, it is a good material for sport rockets that are not going to go very fast or very high.
3. Comments by others on the brittle rail guides are spot-on. My friend Jim Hinton could have used much stronger language in describing his experience with the 1515 guide and it's tendency to break. ;) You might want to try the conformal rail guides sold by Giant Leap--they work great, although they should be attached to the airframe with JB Weld, not the two-sided tape that comes with the guides.
4. The Shurter switches work very well. I suggest Missile Works as a source for them at $5 each.

Congratulations on a really nice build.

Mark
 

mtnmanak

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A nice project and good thread--you received a lot of good input, and I am glad that you had successful flights. A few thoughts for you going forward:

1. The CPR system is not a bad way to learn the basics of dual deployment (I built my first DD project using a PML Sudden Rush), but it is far from being a really good system, as you learned. There are much better and simpler ways to construct an avbay, and to put a rocket together for dual deployment.
2. PML is very clear in their literature that QT is not suitable for flights approaching or exceeding Mach, so you want to be careful with motor selection and not push the rocket too fast. However, it is a good material for sport rockets that are not going to go very fast or very high.
3. Comments by others on the brittle rail guides are spot-on. My friend Jim Hinton could have used much stronger language in describing his experience with the 1515 guide and it's tendency to break. ;) You might want to try the conformal rail guides sold by Giant Leap--they work great, although they should be attached to the airframe with JB Weld, not the two-sided tape that comes with the guides.
4. The Shurter switches work very well. I suggest Missile Works as a source for them at $5 each.

Congratulations on a really nice build.

Mark
Thanks Mark, all great advice, appreciate it!
 

mtnmanak

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Couple other things I would point out to people using the CPR system for the first time.

There are 3 rubber gaskets the system uses. PML recommends changing them after 2 flights. I think that is a little excessive, I have launched this a few times now and the gaskets seem fine. I will probably switch out after 4 or 5 instead of 2. However, the gaskets are super easy to lose. I keep forgetting to take them off and store them, so they fall off easily. I would recommend picking up some more gaskets for both wear out and loss.

As Tony noted earlier:

  • plug the e-match wire holes in the CPR altimeter mounts with sticky-tack or clay to prevent ejection gases from getting into the A/V bay
This is absolutely true. First flight, I did use some mounting putty, but not nearly enough. Some gasses did get into the altimeter compartment. Now, I put putty both on the charge well and inside the compartment where the charge wire enters.
 

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manixFan

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Couple other things I would point out to people using the CPR system for the first time.

There are 3 rubber gaskets the system uses. PML recommends changing them after 2 flights. I think that is a little excessive, I have launched this a few times now and the gaskets seem fine. I will probably switch out after 4 or 5 instead of 2. However, the gaskets are super easy to lose. I keep forgetting to take them off and store them, so they fall off easily. I would recommend picking up some more gaskets for both wear out and loss.

As Tony noted earlier:



This is absolutely true. First flight, I did use some mounting putty, but not nearly enough. Some gasses did get into the altimeter compartment. Now, I put putty both on the charge well and inside the compartment where the charge wire enters.
Good photos. I also put Estes wadding at the bottom of the charge holder to help prevent gasses from getting into the e-bay, and to keep the BP a bit higher in the charge well. I hadn't thought of filling the hole on the side, that's a good idea as well.


Tony
 

mtnmanak

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I have flown this bird now a number of times and it has been a wonderful flyer. Some really superb launches.

After the last launch, though, noticed the piston is cracked. I am confident I can repair it, but upon inspection of the piston, it feels very dry and brittle. Wondering if the black powder or baby powder has a tendency to do this to the piston and how susceptible it would be to happening again. Anyone else have this issue?

For context, I have been using 0.8g of FFFFg BP for the ejection charges, so I don't think those have been excessive, and the last launch landed in the mud, so I don't think the piston hit anything on the ground. Also, the crack is on an edge that faces away from the BP charge.

It could have impacted with some hardware (like a quick link) upon ejection, so will have to insure in the future that the hardware is tucked inside the cup formed by the piston.

Also, I am thinking about coating the inside of the pistons with a light coat of laminating epoxy. Should give them a bit more strength.
 

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Joshua Smith

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I have flown this bird now a number of times and it has been a wonderful flyer. Some really superb launches.

After the last launch, though, noticed the piston is cracked. I am confident I can repair it, but upon inspection of the piston, it feels very dry and brittle. Wondering if the black powder or baby powder has a tendency to do this to the piston and how susceptible it would be to happening again. Anyone else have this issue?

For context, I have been using 0.8g of FFFFg BP for the ejection charges, so I don't think those have been excessive, and the last launch landed in the mud, so I don't think the piston hit anything on the ground. Also, the crack is on an edge that faces away from the BP charge.

It could have impacted with some hardware (like a quick link) upon ejection, so will have to insure in the future that the hardware is tucked inside the cup formed by the piston.

Also, I am thinking about coating the inside of the pistons with a light coat of laminating epoxy. Should give them a bit more strength.
The interior "cup" epoxy would also make a nice ablative material, not unlike epoxying the hot end of a baffle. I also coated my baffles with high heat spray paint, cuz why not. I have a PML Striker with a piston, so based on ur experience, I think I'm also going to epoxy and spray the cup side on that too
 

MoreCowbell

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I have flown this bird now a number of times and it has been a wonderful flyer. Some really superb launches.

After the last launch, though, noticed the piston is cracked. I am confident I can repair it, but upon inspection of the piston, it feels very dry and brittle. Wondering if the black powder or baby powder has a tendency to do this to the piston and how susceptible it would be to happening again. Anyone else have this issue?

For context, I have been using 0.8g of FFFFg BP for the ejection charges, so I don't think those have been excessive, and the last launch landed in the mud, so I don't think the piston hit anything on the ground. Also, the crack is on an edge that faces away from the BP charge.

It could have impacted with some hardware (like a quick link) upon ejection, so will have to insure in the future that the hardware is tucked inside the cup formed by the piston.

Also, I am thinking about coating the inside of the pistons with a light coat of laminating epoxy. Should give them a bit more strength.

It appears to me that the crack is the result of the piston rebounding back when it hits the end of the piston strap, and impacting the airframe. IMO the piston straps provided by PML are far too short. And the nylon gets brittle from exposure to BP charges as well. I suggest converting to a kevlar piston strap that is long enough to stop the rebound effect. Your BP charges might be a bit too large as well.

Upon further view of your photo, the crack could also be a zipper from the piston strap. Again, a longer strap will alleviate this issue.
 

mtnmanak

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It appears to me that the crack is the result of the piston rebounding back when it hits the end of the piston strap, and impacting the airframe. IMO the piston straps provided by PML are far too short. And the nylon gets brittle from exposure to BP charges as well. I suggest converting to a kevlar piston strap that is long enough to stop the rebound effect. Your BP charges might be a bit too large as well.

Upon further view of your photo, the crack could also be a zipper from the piston strap. Again, a longer strap will alleviate this issue.
Thanks for the feedback, Mark, makes sense. It is really difficult to replace the piston strap now since it is epoxied to the side of the mounting tube. For future piston builds, though, will absolutely switch to a longer kevlar strap. Lesson learned on this one.

The interior "cup" epoxy would also make a nice ablative material, not unlike epoxying the hot end of a baffle. I also coated my baffles with high heat spray paint, cuz why not. I have a PML Striker with a piston, so based on ur experience, I think I'm also going to epoxy and spray the cup side on that too
I will post some pics once the repair is done and the interior epoxy layer is cured. High heat spray paint is a great idea, nice!
 

mtnmanak

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Repaired and sealed.

First, Tacked down the outside crack with some CA. Then filled the inside hole with quick cure epoxy. Once cured, spread a thin layer of Aeropoxy 6209 on the walls of the cup and let that cure. I also did the same to the other piston while I had epoxy mixed. I kept the pistons in the body tubes while they were curing to ensure the did not cure misshaped.

Once everything was cured, I sanded the outside down until smooth. Hard to tell from the picture, but the outside crack is so smooth now that if you close your eyes and run your finger over it, you can't tell the crack is there.

I think the bird is back in commission!
 

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Joshua Smith

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Repaired and sealed.

First, Tacked down the outside crack with some CA. Then filled the inside hole with quick cure epoxy. Once cured, spread a thin layer of Aeropoxy 6209 on the walls of the cup and let that cure. I also did the same to the other piston while I had epoxy mixed. I kept the pistons in the body tubes while they were curing to ensure the did not cure misshaped.

Once everything was cured, I sanded the outside down until smooth. Hard to tell from the picture, but the outside crack is so smooth now that if you close your eyes and run your finger over it, you can't tell the crack is there.

I think the bird is back in commission!
I have to say, I'm consistently impressed with how much progress you make in such short periods of time. I think my productivity is about 10% of yours
 

mtnmanak

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I have to say, I'm consistently impressed with how much progress you make in such short periods of time. I think my productivity is about 10% of yours
:)

I actually have 5 builds going on concurrently... (not counting this one, this was just a repair...)

3 x Wildman Darkstars - 2.6", 3", & 4" - all underway, got a build thread for it, but building faster than I can post, so will probably do a dump near the end of the week

A Sirius Interrogator G in the mid-power forum is in the final stages. Everything is primed and getting ready for paint and decals

In the wings, I have a LOC Saturn V (5 x 54mm Cluster) and a US Rockets Swarm (1 x75mm core with 12 x 29mm outboards cluster). Those builds have pseudo-started. I am glassing the body tubes and fins for both right now and will include that process in the build threads when I get them posted.

And my kids each have an ongoing LPR or MPR build going on right now, so it can get a bit crowded in the workshop!

Not sure how much longer working from home is going to last, but I am taking advantage of it ;)

The only thing slowing me down right now is traveling to launches on the weekends...
 

mtnmanak

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Honestly, one of the key pieces of the puzzle to moving fast is having a "hot" room. I have a spare bedroom I use for letting epoxy and paint cure and keep the heat in there up over 90 degrees. That vastly decreases the wait times on cures.
 

manixFan

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I've also glassed the inside of the pistons as a way of repairing them. You got pretty close when you applied the epoxy, adding a small square of fiberglass would help reinforce the area even more. The 'piston rebound' phenomenon happened to me as well and is one reason I eventually quit using them. But overall they really do work pretty well.


Tony
 

Jimmy Neutron

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I had a motor chuffing on the launchpad for 5 or 6 seconds resulting in a high speed ejection which ripped the side of the piston in my 54mm Amraam 2.
My solution was to cut the Aluminium reinforced end off a Pringles can and epoxy it into the piston.
Sorted!
 

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mtnmanak

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I've also glassed the inside of the pistons as a way of repairing them. You got pretty close when you applied the epoxy, adding a small square of fiberglass would help reinforce the area even more. The 'piston rebound' phenomenon happened to me as well and is one reason I eventually quit using them. But overall they really do work pretty well.


Tony
Tony - Great point on the additive. I used Aeropoxy 6209 "structural" epoxy to laminate the pistons, so didn't think additives or FG/would be necessary. When I use laminating epoxies like Aeropoxy 2032 or West Systems base mix, I add some crushed FG or CF.

Not sure where I currently stand on using piston eject and Quantum Tubing after this build. Both have their pro's, for sure, but also come with a bunch of "gotcha's". On the pro side, the pistons really do make the whole deployment process much easier, when they work properly, with a lot less black powder. And they tend to protect your laundry a lot more.

I had a motor chuffing on the launchpad for 5 or 6 seconds resulting in a high speed ejection which ripped the side of the piston in my 54mm Amraam 2.
My solution was to cut the Aluminium reinforced end off a Pringles can and epoxy it into the piston.
Sorted!
Nice!
 

Joshua Smith

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I had a motor chuffing on the launchpad for 5 or 6 seconds resulting in a high speed ejection which ripped the side of the piston in my 54mm Amraam 2.
My solution was to cut the Aluminium reinforced end off a Pringles can and epoxy it into the piston.
Sorted!
LOL, no joke, I have been saving the odd aluminum tube ends (from frozen juice concentrate tubes) and even a couple Pringles cans for some unforseen rocket purpose. Something just like this, or an all "junk" rocket, or even just a small tube launch (using one or more Pringles "mega" stack, extra long, cans).

I think I just see something lightweight, structurally sound, and perfectly round and think...hmm...how can I...? I imagine I'm not alone in this ;)
 
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