Chimera orders Plastic Rod for fuel reload

The Chimera project has ordered a batch of eight plastic rods, 500mm in length, and in different materials and thicknesss (30mm, 32mm and 35mm). We need a plastic material that is easy to drill clean holes in, and easy to machine. Acetal Resin is good for machining, but unheard of as a hybrid fuel rod. Why is this?

Other materials we have ordered include PVC, PE (polypropylene), HDPE (high density polyethylene) and UHMWPE (ultra high molecular weight polyethylene).

PVC and PE are used in SkyRipperSystems commercial Hybrid motors. HDPE has been used in hybrid design. UHMWPE might offers advantages of more material being ejected, and therefore higher thrust. Presumably, this is all to do with the density of the plastic. Some of these plastics may be very difficult to machine or drill. This is why Chimera will be doing some experiments.

First Materials for Chimera arrive in Post

Great excitement. The first materials for the Chimera bench test motor, B0, arrived in the post on Friday. The project team are now the proud owners of two 600mm lengths of 38mm 6082 alloy type T6 temper Aluminium motor tube (3.2mm walls) and two solid Aluminium rod lengths 1.5inch and 2inch round, for making the end enclosures. This material was found at low cost on eBay, and appears to be of really good quality.

Chimera buys Aluminium for B0 Case

Found some cheap aluminium tubing offcuts on ebay last night. The alloy is 6082, stronger than Pro38 cases, 1.5in 38.1mm OD (outside diameter) with 3.2mm walls. This is easily thick enough to withstand the required pressure, and with just under 32mm ID (inside diameter) it is likely we will be able to find a fitting plastic, or skim 32mm plastic rod. It was a good find, and so I went ahead and purchased. Also bought some solid rod for end closures. The eShop, Ringwood Precision Engineering do a range of stuff that is likely to be useful in the future. Even if this material is only used for some lathe/machining practice, it will be worthwhile.

The Hunt for Suppliers

I would welcome comments of the team on the following issue:

Everything about a hybrid motor can be made, but we cannot make anything unless we have materials. The main two materials needed are aluminum for the case and plastic for the reload. It is proving very hard to find the right sizes of materials. Why?

1. There are lots of people who will supply aluminum tubing, but very few in the right alloy, right temper, right outside diameter, and right wall thickness. And they will only make tubing to our size requirements if we buy hundreds of meters (literally).

2. There are lots of people who will supply various kinds of plastic rod or tubing, but not in the right diameter (to fit in the case exactly) and with the right wall thickness for the burn. And they will only make tubing to size if we buy hundreds of meters (literally).

I've found some suppliers that can supply small quantities, even having quite a range of sizes, but, as yet, no match - nothing fits exactly.

You see, while I think we make make values, end closures and much else, we cannot machine four feet of aluminum tube to a specific outside diameter, let alone an inside diameter. And I don't believe we can take plastic rod and reduce its thickness, nor can we drill the large hole in it for the gas to pass through. The plastic will likely buckle. Even if we did manage it, we don't want to have to do this for every reload we make. What we want, is a reliable source of the fuel, and then build the motor and values etc., to fit that.

So... as far as I can see the main Chimera challenge now is to get a reliable source of these two materials, in the right specifications, in the right sizes. It's a hunt for suppliers.

Any comments?

Nitrous is the only way to go

Lately, I've been reviewing some of the videos of so-called hybrid motors tested on YouTube, and most of them appear to be using oxygen directly, not nitrous oxide. It is very easy to build a test motor on oxygen for bench test, and really does not require any complex skills as far as I can see. And oxyogen is completely inpractical for an actual motor. Far too dangerous.

So, for Chimera projects we shall be focussing on nitrous oxide (otherwise known as laughing gas or NOS). This is not to be confused with NOX which is a generic term for any single nitrogen atom molecule oxide. NOS got its name from the company that first made nitrous oxide for boosting internal combustion engines.

Hybrid Design Manual

Just a short note to say that I've ordered a copy of the Hybrid Design Manual. This is only available from the legendary rocket supply shop in the USA, Aeroconsystems :

http://www.aeroconsystems.com/literature/HybridPSD_colburn.htm

The introduction to Hybrid Technology is written by Bill Colburn, the Co-Inventor of the Urbanski-Colburn Valve for simplified hybrid motor construction. Bill also designed, constructed and tested the first Hypergolic Hybrid Motor in June of 1951.

Bill also built the first N2O Hybrid motor using 2 inch tanks (laboratory demonstration tanks), the fore-runner of the consumer High Power Rocket Motors now supplied by both Aerotech and Hypertech. Bill wrote the first Hybrid Propulsion Manual aimed at the field of Experimental Rocketry. This re-written manual is included as part of the SORAC Hybrid Manual.

Material for Chimera B0

Chimera is in the process of selecting the material, and supplier, for the main motor tube. The type of aluminium alloy, as well as its wall thickness is important. The tube must withstand great pressure. The problem is complex, for ideally we would like to make a 38mm motor, to fit standard motor tubes and retainers. If the walls are, say, 2mm thick, then the inside diameter is 34mm. The problem is, such a size is very rare, or impossible, to find for the plastic rod for reload/fuel.