[shown actual size]

General Description

Together with the Spacemaster 600A, the Scorpion 600 is one of the most powerful Jetex motors ever built. It has an aluminum engine chamber, and is fitted with a nozzle cap assembly that can be disassembled in part. All in all, the design is quite excellent, and this motor has been very popular for larger freeflight models.

Unlike other models, the motor has a built-in mounting tube on the forward end, to permit easy attachment to a vehicle. The roller-spring clip assembly uses a double set of five leaf springs, one set on each side. These leaf springs appear identical to those used on PAA-Loader 150 engine. The motor clips, of which there are two, appear thus to be somewhat shortened versions of PAA-Loader motor clips, used in tandem.

The Scorpion 600 uses pellets with a conical depression on the "hot" end, to increase burn surface, chamber pressure, and thrust. A special coned washer ensures positive contact between the igniter wick and the pellet. Only one charge can be fitted, giving a thrust of 6 ounces [170 gm] for about 8-10 seconds.

Historical Notes

The Scorpion was introduced in Sep 1953 (Aeromodeller, p 517), and was later distributed in the US by Aristo-Craft Miniatures, and perhaps also by Peck Polymers.

Remarks

Shallow fins are produced around the motor chamber circumference, improving engine radiant cooling. The Scorpion uses propellant pellets that have a coned surface on the front face, with the gauze disc coned to fit. The purpose of the coned pellet end is to enlarge the burning area and increase thrust.

Construction of the motor was, in the words of Wilmot & Mansour, "a compromise between the earlier and latest methods of manufacture. The main case is turned from a special aluminium alloy complete with rings ["ribs," or "fins"], etc. The end cap is a stainless steel pressing and the sealing washer and flame shield are retained by the screwed jet and jet collar, which are made from mild steel."

The end cap is sealed with a duplication of the Jetmaster spring assembly. Two saddles tensioned with leaf springs are fitted, and these snap onto a special yoke pressing on the mounting end of the motor. The actual motor mounting consists of a thin-walled aluminium alloy tube, screwed to the end of the motor, which is a good press fit into another tube fitted into a balsa block which can be cemented in place on the model.

Suitable Model Aircraft

Performance Specifications

Data posted in green is from original factory packaging and instruction sheets
SI (metric) units provided in brackets
Data in red indicates extrapolated information, and must be regarded as approximate, at best

This is a laboratory thrust curve showing Jetex Scorpion 600 performance.
From Aeromodeller's extensive test report, Nov 1953.

Additional Illustrations

The Scorpion engine has a forward mounting tube, which fits over a post in the model.

Note that the aft-closure assembly, including the twin spring clips, cannot be completely disassembled. The nozzle portion of the closure, however, can be unscrewed from within.

This exploded view of a scorpion shows the several parts used in this more complex design. (Click image to see more detail)

This old ad, from American Telasco, shows the features of the Scorpion.

A handsome package from American Telasco. Engine by Wilmot, Mansour.