PML AMRAAM 4" CPR build

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Basically, as simple as this:

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I think most experienced flyers would have two suggestions: never use that type of screw-eye - it can easily pull open, and putting all the force on once side of the coupler can cause it to break - they are not very good at handling side loading.

So I would use either a welded eyebolt or an eye-nut, and put one on either side and make sure the shock load is evenly distributed.


Tony
 
Definitely - wasn't planning to use that particular eye-bolt, just had it sitting on my workbench and used it as an example. I have plenty of forged eye bolts and u-bolts. If I go with this concept, I will probably use a u-bolt.

I am good with the hardware, I am just trying to figure out if there is any reason this concept is not a good idea. I do get that all the pulling forces would be on the ring versus a strap anchored to the motor tube. Just wondering if a U-bolt and well epoxyed ring would be good enough. Maybe doubled up ring, as you mentioned earlier.

Probably will use a smaller hole in the middle too - maybe 29mm or 38mm

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I have stacks of coupler bulkheads. I am going to be away for the weekend, but when I get back, I will drill a 29mm hole in one and 38mm hole in another and see how stable they feel with a U-bolt.
 
Definitely - wasn't planning to use that particular eye-bolt, just had it sitting on my workbench and used it as an example. I have plenty of forged eye bolts and u-bolts. If I go with this concept, I will probably use a u-bolt.

I am good with the hardware, I am just trying to figure out if there is any reason this concept is not a good idea. I do get that all the pulling forces would be on the ring versus a strap anchored to the motor tube. Just wondering if a U-bolt and well epoxyed ring would be good enough. Maybe doubled up ring, as you mentioned earlier.

Probably will use a smaller hole in the middle too - maybe 29mm or 38mm

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Ok, great to hear, that eye bolt looks good, a large U-bolt would also work of course. In the past I have fiberglassed the inside of couplers that will see a structural load. It's a bit of challenge but you can use a balloon to hold the fiberglass in place while it cures. (Use canned or other source of compressed air to fill in place.)

Seems like you have a handle on everything, but never hurts to get a second opinion.


Tony
 
Seems like you have a handle on everything, but never hurts to get a second opinion.

Tony - Please keep the opinions coming!! That's why I am here - love it!

Fiberglass is an excellent idea for the coupler - I hadn't though of that, but want to give it a try. Love the balloon idea.

I think it would be a good idea for the bulkhead as well. I have a lot of carbon fiber and some aramid fabric. I have rolls of different weights, so may just laminate the ring with a nice heavy weight CF and then drill the center hole afterwards. I vacuum seal the laminate, so it is actually super quick and easy. Will laminate a couple bulkheads tonight before I leave so they will be fully cured by the end of the weekend. Then a few seconds on the belt sander to fine tune the fit to the laminated coupler.
 
Got two bulkheads laminated with CF and bagged. Will let them cure over the weekend and then glass the coupler.
 

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[*]if you fly in cold weather the piston will bind - the Quantum tube shrinks quite a bit; test fit by putting the tube into the refrigerator until it's cold and then check piston fit and sand if necessary
Tony.

i had one of these back in the late 90s. went to a winter launch and prepped in the cab of my truck. maiden flight.was going to fly it on an I300. got to the rso table.rso asked about it. from my truck to rso table the tubing shrunk enough to bind the coupler. would have been a disastrous flight.
 
i had one of these back in the late 90s. went to a winter launch and prepped in the cab of my truck. maiden flight.was going to fly it on an I300. got to the rso table.rso asked about it. from my truck to rso table the tubing shrunk enough to bind the coupler. would have been a disastrous flight.

I think if I ever build another one of these, I will have them substitute the QTs for phenolic and glass them myself. For that matter, I will most likely do that for any PML kit in the future. Seems like there are just too many limitations to QT. Unfortunately, I am too far into this build to turn back now. Will take Tony's advice and leave the pistons/tubes in the freezer for a while and sand. PML does recommend a similar procedure in the FAQ.
 
Hi Folks;

For what it's worth, I've used the stock rigs on the PML pistons every time without failure. As an example, my first 4" AMRAAM met it's untimely demise due to a premature activation of the recovery system. It was launched on a K550, and the altimeter fired about the time the burn ended. It shredded quite dramatically as you might imagine. The chutes were totally destroyed, but the D-ring strap joint was 100% I build the pistons pretty strong with fillets etc., but I would not be looking for a failure there. I use only the QT tubing these days. I take the precaution of keeping it shaded from direct sunlight. I've launched in a wide variety of temps and have had no issues. I have however seen other flyers who were not so fortunate and were sanding their pistons to launch on a cold day. This will be a matter of tolerances in the piston and airframe tubing. Every build needs to be approached as an independent project. My previous experiences with Quantum tubing may or may not hold on my next PML project. I am quite fond of their kits however.

Jim
 
Hi Folks;

For what it's worth, I've used the stock rigs on the PML pistons every time without failure. As an example, my first 4" AMRAAM met it's untimely demise due to a premature activation of the recovery system. It was launched on a K550, and the altimeter fired about the time the burn ended. It shredded quite dramatically as you might imagine. The chutes were totally destroyed, but the D-ring strap joint was 100% I build the pistons pretty strong with fillets etc., but I would not be looking for a failure there. I use only the QT tubing these days. I take the precaution of keeping it shaded from direct sunlight. I've launched in a wide variety of temps and have had no issues. I have however seen other flyers who were not so fortunate and were sanding their pistons to launch on a cold day. This will be a matter of tolerances in the piston and airframe tubing. Every build needs to be approached as an independent project. My previous experiences with Quantum tubing may or may not hold on my next PML project. I am quite fond of their kits however.

Jim

Hi Jim - Thanks for the experienced update on QTs. How well do they hold paint? Assume you sand first, but have tried using Adhesion Promoter? I use the Adhesion Promoter on nose cones, was wondering if it would work on QTs.

Any tips on finishing these tubes?
 
Hi Jim - Thanks for the experienced update on QTs. How well do they hold paint? Assume you sand first, but have tried using Adhesion Promoter? I use the Adhesion Promoter on nose cones, was wondering if it would work on QTs.

Any tips on finishing these tubes?
If you clean the tube as directed it holds paint pretty well, much better than regular plastic. I pretty much have always used Dupli-Color automotive paint. I have a nearly 20-year old Tiny Pterodactyl that still has its original paint after probably 30+ flights. It's definitely looking a little beat up but not any worse that a fiberglassed kit.

The thing that I loved about QT kits was how easily I could get a great looking rocket, unlike with regular phenolic with spiral or a hand laid fiberglass rocket. That ease of finishing really helped me get started in HPR since I could build a rocket pretty quickly and have it looking great. Now I can spend hours filling, sanding, priming, etc. and a rocket.


Tony
 
If you clean the tube as directed it holds paint pretty well, much better than regular plastic. I pretty much have always used Dupli-Color automotive paint. I have a nearly 20-year old Tiny Pterodactyl that still has its original paint after probably 30+ flights. It's definitely looking a little beat up but not any worse that a fiberglassed kit.

The thing that I loved about QT kits was how easily I could get a great looking rocket, unlike with regular phenolic with spiral or a hand laid fiberglass rocket. That ease of finishing really helped me get started in HPR since I could build a rocket pretty quickly and have it looking great. Now I can spend hours filling, sanding, priming, etc. and a rocket.


Tony

So, no sanding first? Just clean, prime and paint?
 
So, no sanding first? Just clean, prime and paint?
Sorry, I wet sanded with 400 grit, just enough to take the shine off. As suggested, a Scotch-brite pad would also work well. I also always washed the body with Dawn before sanding to get rid of any oils on the surface. I think the key is to 'take the shine off' to provide a better tooth for the paint to adhere to.


Tony
 
If you clean the tube as directed it holds paint pretty well, much better than regular plastic. I pretty much have always used Dupli-Color automotive paint. I have a nearly 20-year old Tiny Pterodactyl that still has its original paint after probably 30+ flights. It's definitely looking a little beat up but not any worse that a fiberglassed kit.

The thing that I loved about QT kits was how easily I could get a great looking rocket, unlike with regular phenolic with spiral or a hand laid fiberglass rocket. That ease of finishing really helped me get started in HPR since I could build a rocket pretty quickly and have it looking great. Now I can spend hours filling, sanding, priming, etc. and a rocket.


Tony
I have to second you Tony. There's nothing I hate more than filling spirals, cuz I also hate sanding. The QT tubes definitely aren't going to get you any altitude records, but I'll take the ease of finishing first, unless I actually have an overriding other requirement.

BTW, has anyone tried appliance paint? I have some white that I'm going to put probably on some Bull Pups. Ostensibly, seems like it would be perfect, tho will certainly show my surface flaws. I wonder if adds significant weight compared to other paints.

Josh
 
I also have a tendency toward the rockets that look like, or are scaled from, real missiles. I then tend to want to have different sizes of the same rocket, so Estes Bull Pup 12D, PML 2.1" Bull Puppy (probably won't do the 3' one tho (no guarantees on that if it goes on sale ;) ). Estes 13mm Honest John (which is a fantastic mini modroc, esp when painted olive drab), Estes Estes Honest John 24mm etc. Anyway, point is, I don't need performance out of those, I'd rather have the ease of finishing. BTW, I've always wanted to drill a hole down the nose cone, lined up with the launch lug so that the launch lug doesn't have to be offset from the body tube. Maybe I'll try that on a mini first. Sorry for the length of this diversion
 
I have to second you Tony. There's nothing I hate more than filling spirals, cuz I also hate sanding. The QT tubes definitely aren't going to get you any altitude records, but I'll take the ease of finishing first, unless I actually have an overriding other requirement.

BTW, has anyone tried appliance paint? I have some white that I'm going to put probably on some Bull Pups. Ostensibly, seems like it would be perfect, tho will certainly show my surface flaws. I wonder if adds significant weight compared to other paints.

Josh

Interesting question on the appliance paint, I have not tried it. It does seem like it would be formulated to be thick and, therefore, add weight. Serendipitously, I actually have an old refrigerator I am relocating to my workshop and was thinking about painting it. Maybe I will give it a try and see how that paint works.
 
Interesting question on the appliance paint, I have not tried it. It does seem like it would be formulated to be thick and, therefore, add weight. Serendipitously, I actually have an old refrigerator I am relocating to my workshop and was thinking about painting it. Maybe I will give it a try and see how that paint works.
Let us know if you do, I'll do the same. In theory it's just a super-high-gloss paint, but who knows
 
Hi Jim - Thanks for the experienced update on QTs. How well do they hold paint? Assume you sand first, but have tried using Adhesion Promoter? I use the Adhesion Promoter on nose cones, was wondering if it would work on QTs.

Any tips on finishing these tubes?
[/QUOTE
Hey Mtnmanak;

I would pretty much echo Joshua, manixFan and other intrepid rocketeers. I sand all of the QT and FG tubes before construction in all area where glue or paint adhesion is required. On the outside, I use a SKIL Octo vibratory sander, but I sand lightly and quickly. You want to cover the entire affected area, but it is only necessary to lightly etch it. One can achieve the same effect by hand sanding. Scotch Brite works pretty well for this. On the inside, I sand areas for glue joints with self adhesive sandpaper on a piece of PVC conduit or pipe.
I use a sandable white primer on all of my rockets prior to color coat. One or max two coats is generally great with QT tubing. Sand lightly between applications. Good time for wet sanding. That's about it. I have not found an adhesion promoter necessary on the tubing. The NC is the spot where I have actually experienced paint cracking and flaking due to impact and flexing. I hope this helps.

Jim
 
Let us know if you do, I'll do the same. In theory it's just a super-high-gloss paint, but who knows

Painted the refrigerator today with Krylon Appliance paint. The photos below of the white fridge are the "before" and the black "fridge" is the after.

Put on two coats of the paint. Worked great. Didn't seem to be any heavier or thicker than regular spray paint. Dries quick, ready to go in about two hours.

It says it is an epoxy paint, but I am not sure how that can be. True epoxy paint is like regular epoxy - needs a resin and hardener. All in one can doesn't seem like it could be real epoxy.

Can't make any comments on durability, but it covers fine, didn't drip and dried quick. so, even if it is fake epoxy, it still seems to be a viable alternative if you are looking for a gloss paint.
 

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I think if I ever build another one of these, I will have them substitute the QTs for phenolic and glass them myself. For that matter, I will most likely do that for any PML kit in the future. Seems like there are just too many limitations to QT. Unfortunately, I am too far into this build to turn back now. Will take Tony's advice and leave the pistons/tubes in the freezer for a while and sand. PML does recommend a similar procedure in the FAQ.

ive wondered how the qt would handle higher altidudes. iirc, it gets colder with altitude. so if a qt rocket was launched to say 35k feet, would the temp change be enought to effect the qt?
glassing phenolic is wise. another pml kit i bought was the 1/4 scale patriot. phenolic tubing. maiden flight in january in mid michigan. something caused it to not get near the altitude it was supposed to. i think the ec went off about 10 feet off the ground on its way back down.
the bt from fin can forward was in about 136 pieces.
anouther one cracked /chipped the bt on what i thought was a soft landing.
 
ive wondered how the qt would handle higher altidudes. iirc, it gets colder with altitude. so if a qt rocket was launched to say 35k feet, would the temp change be enought to effect the qt?
glassing phenolic is wise. another pml kit i bought was the 1/4 scale patriot. phenolic tubing. maiden flight in january in mid michigan. something caused it to not get near the altitude it was supposed to. i think the ec went off about 10 feet off the ground on its way back down.
the bt from fin can forward was in about 136 pieces.
anouther one cracked /chipped the bt on what i thought was a soft landing.

Having done a fair number of HALO (high altitude/low opening) parachute jumps in my younger days, I can confirm it is pretty darn cold up there. Generally, at 30,000 feet, it was about -20 F or below. at 35,000, you can expect the temps to be at least -30 F. Those temps would be considered the high end of the temp range at those altitudes.
 
Getting back on track here. Drilled a 29mm hole in one of the bulkheads I laminated and fitted a long U-Bolt to it. It is going to be long enough to also attach into the motor mount bulkhead below, so that should be more than enough structural stability and will still allow for a motor eject backup. Final picture is a dry fit of how it will be - there will be nuts and washers on both sides of the bulkhead when it is glued up.
 

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Couple points about the electronics for this build.

First, I highly recommend if you do this build you figure out your switch solution and install it before you install the CPR 3000 bay. The instructions have you install the bay first, then cut a hole for a slide switch and feed the wires through a little slot. I didn't think it through and followed the installation sequence in the instructions. Now it is exceedingly difficult to install the switch. Lesson learned for the future.

Also, unfortunately, the CoPilot 3 I had for this build is dead. In the test I did for the switch above, I tested the switch using a multimeter. The picture above of the switch connected to the altimeter with a battery in it never worked. I thought I was doing something wrong and had a number of emails with PML over the past week to try and figure it out. Looks like the altimeter was just dead out of the bag. Sending it back to PML for a replacement, but I am going to proceed with this build with a Stratologger CF. Rocketarium sells a sled specifically for the Stratologger CF to fit in the CPR 3000 system, so I ordered one of those and it is on the way.

The CPR system is slick, but it is extremely limiting on the altimeters you can fit. Very few out there that can work in this system.
 
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.
 

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Okay, things are just about done with this bird. Got the piston straps sewed and the plates glued into the pistons. I left enough of a strap loop on the shock cord side of the piston plates to snap a quick link into. I did put the D-rings on, in case I ever need them for some reason, but they will not be the primary connection.

At this point, the only things left to do are to install the electronics and recovery system. I won't do that until after painting, so plan to start priming and sanding over the next couple days and paint this weekend.
 

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Everything is painted, no decals, may add those later.

Cold fit the pistons today. Ground testing the deployment charges tomorrow. Maiden flight, next weekend!! (crossing fingers for the weather)

PXL_20201031_223602717.jpg
 
Should have posted this one instead :)

Just want to show how big this rocket is - I am 6'2" for reference!

I have bigger rockets, but was surprised how big this thing is for a quantum tube build.

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