Public Missiles - CPR 3000 {Component}

Public Missiles CPR 3000

Public Missiles - CPR 3000 {Component}

Contributed by Michael Wilkins

Manufacturer:

(Contributed - by Michael Wilkins - 01/14/04)

Brief:
The CPR3000 (Close Proximity Recovery) is a dual deployment system from Public Missiles, Ltd. (PML). The CPR system comes with all necessary parts to convert a rocket to dual deployment. Electronics are not included. This system can be purchased for most PML kits and should be purchased before your kit is built.

Construction:
In the CPR kit you get two sections of 38mm phenolic tubing, centering rings for the upper and lower airframes, piston assemblies, two machined aluminum couplers to screw the two airframes together, a small drogue chute, shock cords, and altimeter mounting hardware. There are a few other pieces but I am sure you get the picture.

With anything in kit form, there will be good things and bad things. The CPR system is no exception to this. The assembly instructions are in the usual PML fashion: easy to read with illustrations for visual needs. The components of the CPR fit together nicely and make for an easy transition into dual deployment for the inexperienced rocketeer. With those things being said on a positive note here is where the fun begins. The CPR system has a list of down sides to it. Most of them are if you intend to use the system in a rocket that will burn just about any K classed motor.

To start your initial investment in the CPR will set you back about $130. When you look at the drogue that is supplied, the first thought through your mind will be "I need to buy another chute". If you will be launching your rocket with K classed motors you will want to replace the phenolic tubing with a fiberglass tubing kit that can be purchased through Hawk Mountain. This is a must! Once you have spent another $50+ on better and stronger components you are close to having a decent system.

Along with the upgrades there need to be some assembly modifications. When the CPR is built per the given instructions you end up with a mid to high power rocket that has a very weak midsection. Under high stress during boost, the airframes can flex at the joint. When this happens the phenolic tubing supplied will break and the end result is not pretty. The problem is with the mounting depth of the lower CPR mount into the lower airframe. After the assembly is complete you are left with approximately one inch of shoulder to support the joining pieces between the airframe. The way to fix this is to move the lower assembly three inches into the lower airframe. The upper assembly needs to be built into a coupler tube then inserted into your upper airframe. This gives you three inches of support from your airframe and the coupler tube assembly and reduces flex in the two airframes during the boost phase of flight.

The mentioned replacement components and new mounting locations will save you a lot of time and money by not having to rebuild your rocket after the original components fail.

Summary:
The CPR3000 is a good product for the mid range flier that is wanting to start utilizing dual deployment however, I would not recommend this product for those of you who will be pushing your rockets to the limits. For what you will spend on the CPR kit and upgrades, I would suggest building your avionics bay from scratch.

Overall Rating: 2 out of 5

Comments:

J.M.D. (January 25, 2004)

Michael may indeed point out a flaw of the CPR3000 system but I think there is another fundamental flaw as well. The system is designed in such a way that the only thing holding back the BP residue from the electronics are the "O" rings on each end of the assembled CPR system (with the electronics in between). These rings are supposed to fit snug enough against the inner circumference of the phenolic housing device to prevent any blowby of the hot gases and residue. It doesn't work especially on the aft end firing the drogue chute charge. The very fact that the electronics portion 'slides' into the tube tells you something. My experience and countless others I have seen is that you get six to eight perfect flights and then the residue has so corroded the electronics that you begin to have major problems. Changing the O rings with each flight (like I did - after 3 is PML's recommendation, I think) and lightly cleaning with alcohol may help. I was lucky enough to not have destroyed my rocket when I started having problems. After returning the CoPilot to the manufacturer for refurbishing it ground tested ok but after 1 flight it exhibited ground testing of the same in fight problem I was having - both deployments at motor burn out or apogee. No mater how much I cleaned it - same thing. It is 'retired' now and I spent a lot of time retrofitting my AMRAAM, Patriot and MBBBX - all have flown perfectly many times since (AMRAAM on a K550)with a self contained electronics bay (and new electronics).

M.R.W. (February 5, 2004)

JMD, You are correct in regards to the O-rings. I had experienced the same problems with my altimeter. After the destruction of a kit it was brought to my attention by another rocketeer to what the problem was. I contacted PML about the issue of gasses getting around the o-rings. It will get inside of the barometric sensor causing it to fail. PML stated that this is not covered under warranty. I have since sent several emails to PML with my opinion of their customer support. To this day I have not received a reply.

J.C. (May 17, 2006)

I have also noted the problem with the blow-back of ejection gasses from the aft charge holder due to the design of the CPR3K system and devised a solution for the problem. PML furnishes a short piece of 38mm coupler tubing with the CPR3K to use in helping place the aluminum connectors on the 38mm tubing. After you've constructed the system, glue the coupler tube into the 38mm tubing while you use the mounted altimeter to help place the coupler tubing in the proper location, which should have the lip of the coupler tube rest against the charge holder of the altimeter mount. The urethane charge tube will now be located in the center of your coupler tube while the lip of the coupler tube resting against the charge holder will help seal the rest of the altimeter from the ejection charge.

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