Ejection Coupler Concept - Potential New Product

[Ravenex]

I recently posted a new build thread in the HPR category "Warp Test #1" Build Thread, and one very observant rocketeer asked about my recovery setup so I have decided to post my new recovery system here to get some feed back.

A little while back I met with my father to discuss formalizing and prototyping an ejection system he flown in a rocket he recently launched at LDRS. I have since designed a few versions of this idea both for deployment on opposite ends of an avionics bay and single ended deployment with a tender descender or cable cutter. The versions pictured are the two options I want to prototype for use in my 2” rocket with single end deployment. The upper design was may original design and would be lighter, more compact, less expensive, and also stronger due to the coupler on the left having a thicker ring near the end and the one on the right being reenforced by the airframe. The downside is that it has an additional reduction in ID which could be a problem particularly in a 2" rocket.


2 inch single sides deployment assembled.


2 inch single sides deployment separated.

The yellow tubes on both ends are the airframe, the drogue chute is in nose section on the left, the main is in the tube on the right. The system consists of an aluminum coupler set with shelves to support 2 loose fitting plates with the parachute tethers joining the two end through the plates. The ejection charge(s) are placed between the plates which are held apart by a loose fitting tube and the couplers are locked together with shear pins (I have four 1/16” pins shown in this setup). When the charges a fired the plates are pushed apart shearing the pins and separating the rocket, the parachute tethers then pull the plates out and the chutes come out as normal. The idea is to provide several benefits over other systems, which use a combination of products to address each of these issues.

1. The system provides a small fixed volume for ejection which makes the necessary charges smaller and easier to handle.
2. The plates will be forced against their shoulders, like a check valve, sealing of the parachute and avionics from the ejection blast.
3. The system provides a metal to metal machined interface for a better joint fit (a significant problem in my dad’s rocket that used couplers).
4. The metal to metal interface provide an ideal place for shear pins.
5. The metal couplers should be much more resistant to zippering. In larger diameters where the constriction isn’t as large an issue the wall can be even thicker.
6. The couplers will have a significant smooth rounded edge on the end which won’t cut shock cords like glass tubes can.

I would eventually like to develop and sell these for all common airframe sizes. I also designed a setup putting one of these on each sides of an avionics bay for a two ended deployment with a bulletproof av bay. Any and all thoughts and comments would be appreciated.

 

[dixontj93060]

I still don't quite understand the sequencing... Is it deploy drogue and main at apogee (i.e., central charge container as shown releases both containment areas), and then deploy main at altitude via tether (Tender Descender specified above)? If so, I assume the tether is held in the aft airframe so it can be controlled be the av-bay below the main compartment?

 

[CarVac]

Metal to metal sliding fits are susceptible to dents. That is my primary reservation with this.

How do you connect the shock cords between the plates? How do you protect the section that is inside the charge volume?

 

[GregGleason]

Hmmm...

My first question would be the aluminum coupler, as it may fall into a gray area of "body", a structural item, and DQ it from NAR. Some RSO's may let it fly and some may not.

1. Materials. I will use only lightweight, non-metal parts for the nose, body, and fins of my rocket.

But that aside.

I like aluminum for the cited reasons, and I love to use it in my rockets where it makes sense. But the down side of aluminum is that is that it can be bent quite easily when it is thin, so sometimes you need to have it thick to offset this propensity. Also, a chunk of machined aluminum can be quite pricey (I do some hobby milling of aluminum). A formed composite structure could be a cheaper alternative.

Other than that, I'm not sure if there are any real advantages. At least ones that would make me consider adopting the system.

I'm not saying that it doesn't work, I'm just not sure that I see any advantages that would work for me as a designer/flyer. At least at this time.

Greg

 

[BrAdam]

I like the idea. Av Bay in reverse?

I too, am not understanding the sequence of events compared to the diagram. Looks like there is room for two chutes? One on each end of the loose plates? Also, why not just eliminate the plates, wrap the chute in nomex and pressurize the entire compartment to shear the pins.

I think you could simplify production if you went to FG and bulk plates. The cost of machined aluminum parts for this application might be pretty high compared to FG. Should be strong enough for an ejection charge and also to allow for shear pin usage.

Where would the electronics go?

Does "loose fitting plates" mean that no matter their orientation within the tube, they could not jamb? The distances from opposite edges across the diameter is smaller than the tubes inside diameter? If not and you are expecting them to slide within the tube, that may lead to problems.

Think I am rambling...

 

[Ravenex]

Ok, so I'm going to try to answer some of the confusion about this idea. Firstly the pictures are of two possible versions that I'm still deciding between, both images show one version on top and the other on the bottom. As to the sequencing, this particular version is designed for a dual deploy with a tender decender or cable cutter, though to be honest I plan to use the tender decender a little differently than normal. The electronics are further down the rocket behind the many chute with the wires running up through the bulkhead to the charge between the plate. When the charge fires the pins shear and the rocket separates pulling the plates out on both tubes (the cord would simply go through both plates and into the body and nose tubes, with knots or the like causing them to pull on the plates). This would also pull the drogue and main out and the deployment would proceed as normal with the cable cutter or tender decender.

There are several goals for this design that I think make it a viable product. First, is to provide a reliable joint in the rocket without the play of a normal coupler/tube fit. Second, to provide a very small fixed volume with repeatable shear pin fit to allow for smaller precisely define ejection charge sizes. Third, to add an extra layer (possibly removing the need for others) of protection for the parachutes and the av-bay from the ejection blast. Fourth, to provide a strong smoother edge for the cord to prevent zippering and shearing of the cord and to remove the need for additional component for that purpose.

As to the worries about the metal interface being damaged and not smoothly sliding. This can be handled through the wall thickness and material selection as well as by careful design of the clearance tolerances and geometry, none of which is finalized. Also hardcoat anodizing will help prevent nicks and scratches that could cause issues. There will of course be very hard landing and crashes that may require replacing these components or cutting back a tube, but this is true of any existing coupling, my goal is to make this more durable so that happens less often.

In regards to cost, if this were to become a production product with reasonably sized runs the costs could be brought to a very reasonable level. Look at vendors like Aero Pack selling retainer systems which are just as much work for $40-70 where as a one of retainer may cost $300-$400 or more.

I would also like to again mention I have also designed a version for a more traditional configuration with aluminum end caps and bulkheads to a build a bulletproof av-bay and then use these couplers on either end for a two joint deployment.

I will investigate the possibility of making this out of fiberglass or carbon fiber possibly with metal inserts for the shear pins.