• The Psst 50 and Psst Double-50 motors, which used the same propellant but were produced by another manufacturer.
• Operational instructions for the Jetex Rocket 50-HT motor, which used hollow-cored fuel pellets of the same composition as the standard Jetex 50 pellets.

   (approx, actual size)

General Description

By far the most popular of all the motors, more Jetex 50s have been sold and flown than all the other models combined.  This design, introduced in May 1949, has evolved through several versions, all of which are detailed on this page.

What is common to all "50" size engines is the thrust chamber internal diameter of ~0.560 inch  (14.22 mm), to fit standard "50" size (0.5-in [12.7 mm] dia) propellant pellets.  All the 50 size Jetex engines produce substantially the same thrust, averaging on the order of 1/2 to 5/8 ounce [14.2-17.7 gm], peaking to 7/8 ounce [24.8 gm], or even higher, at the end of the run.  (In other respects, the Jetex 35 is very similar to the Jetex 50 Export and 50B models.)

Here is a differentiation summary; each motor is described in greater detail farther below on this page:

The "original standard Jetex 50" motor had a machined (turned) aluminum alloy case with "ribs," and a turned end cap assembly.  The "export model Jetex 50" and the Jetex 50B both used pressed cases.  Soon only the 50B model was made and sold, and the original models dropped.  The 50B has a slightly longer case, to increase the "free" combustion space to give better wick-ejection properties.

The 50 Hell-Cat is the "standard" size motor, "fitted with exhaust deflector ring to prevent damage to model through faulty end cap sealing" (according to contemporary sales literature).  Early models did not have this deflector ring.

The 50 HT ("High Thrust") model also holds two fuel pellets; for test runs or short flights you can use just a single pellet, which, of course, cuts thrust duration in half.  Fuel used in the standard and HT engines is almost the same; the only difference is that HT fuel has a 1/8-inch [3.2 mm] diameter hole through each pellet.  It is ignited so that the fuel burns throughout its entire length--not solely on the rear surface, as with the 50 Hellcat.

The 50 HT engine has a steel chamber in place of the aluminum tube of the original Hellcat 50 engine, and is beefed up in other ways as well.  Combinations of fuel may be used in the HT 50 engine.  For example, you can use one HT pellet to give potent initial thrust and get a model off the ground in a hurry, then in back of it put a Hellcat (standard Jetex 50) pellet, which will give greatly increased thrust duration and much reduced push.  There are many tricks used to modify the Jetex engine thrust to suit specific models and conditions.

Historical Notes

Jetex 50 was the third design introduced, in 1949, by Wilmot & Mansour.  It has also been produced in different configurations by Sebel (UK) and Powermax.

Early after its introduction, the Jetex 50 was somehow modified "for export," and subsequent (beginning about 1953) models were packed as Jetex "50B" motors.  The 50B version produced, according to Wilmot & Mansour, "25% additional thrust."

We are not yet clear on the other differences between these two models.

The current "50C" by Powermax looks to us almost identical to the "50B" of Sebel; again we are not certain their differences.

The 50 HT model was introduced early in 1963; it was announced in American Modeler magazine, Mar-Apr 1963, p 21.

During a period when Jetex 50 motors were at peak popularity, an American firm designed a variation, sold widely as the "Psst 50" and "Psst Double-50" motors.  These are reviewed separately, as they have very different configuration (but burn the same propellant).

In its current incarnations, the 50 is sold today in the models Jet-X 50C and 50Z, by Powermax.  Powermax Jet-X sales commenced in 1985.

Remarks

DO NOT confuse the 50 Hell-Cat (sometimes called the "50HC") with the very different 50 Rocket HT (a high-thrust version, with a different nozzle).  50 Rocket HT propellant pellets are perforated through their axis with a hole of about 1/8-in [3.2 mm] diameter.  They must not be used in the smaller nozzled 50B, Hell-Cat, or similar motors!

Specific operational instructions for the "Rocket HT" may be found on another page.

Each engine takes two fuel pellets; for test runs or short flights you can use just a single pellet, which, of course, cuts thrust duration in half.

The Powermax Jet-X 50Z was originally identical to the older Hell-Cat 50, with a larger nozzle diameter to accomodate the higher burn rate and chamber pressures.

Suitable Model Aircraft

Performance Specifications

Data posted in green is from original factory packaging and instruction sheets
Data in red indicates extrapolated information, and must be regarded as approximate, at best
SI (metric) units provided in brackets
Many weights and measures courtesy David Fritchman, Socorro, NM

2:  Has a much thicker and metal-reinforced sealing washer (not suitable for any other engine), and a nozzle exhaust cone that are said to increase the thrust by up to 25 percent.  Uses perforated "Z" propellant pellets, of which it can hold four.  Minimum flights require two pellets.  The motor is gold anodized.

Additional Illustrations

Jetex 50 (original issue)
This Wilmot Mansour original version of the Jetex 50 has a machined aluminum case and end cap, and shallow "ribs."  (Graphics courtesy Howard Metcalfe)

Jetex 50 Hellcat
Believed made by Sebel (UK); distributed by Aristo-Craft Miniatures, NY; all steel, with aluminum motor mount.  Single spring.  Note the forward end is hemispherically rounded.  A blow-by ring is tightly fitted over the chamber, and slid nearly to the aft end.  This blow-by ring was not present on some early Jetex 50 models, we think.

Jetex 50 Rocket HT 
Left: a very early Rocket HT kit by American Telasco.  Right:  Believed made by Sebel (UK); distributed by Aristo-Craft Miniatures, NY; all steel, with aluminum motor mount.

The "HT" designation represents "high thrust."  It has a rather high thrust of short duration.  Note twin closure springs to accommodate higher chamber pressure created by perforated-grain pellets.  Forward end of thrust chamber is generally flattened, with a central dome perforated with a small machine screw, washers, and nut.  The exact purpose of this screw is unknown.  Nozzle diameter is 1.5 mm, unlike the 50 Hellcat and others in the series, which have a 1.0 mm diameter nozzle.  Note also the absence of a blow-by ring, as found on the Hell-Cat.  If the chamber seal leaks, hot gas will reverse direction, perhaps into or onto the model.

When the Rocket HT was introduced, enthusiastic Jetex designers glowingly had this to say: 

“New vistas of design are opened up.  Competition model aircraft should show tremendous improvements in performance, attaining heights and flight-time averages heretofore impossible.  Space-type craft with stub wings for safe descent and landing will offer new thrills.  Scale ships such as the Lockheed F-104, and even the X-15, now are feasible fliers.  Scale Atlas, Thor, Titan and other full-scale boosters can be made to lift off their pads and climb to exciting heights, all in complete safety. Who really can say what ingenious modelers can do with a 500% increase in thrust?  What way-out designs will spring from the drawing boards?  With the 50-HT to stir things up we will not have to wait long to see.”

...

Jetex 50 HT (top) beside Jetex 50 Hell-Cat (bottom)
In these views the differences can be clearly seen, including the forward end shapes, with screw hole in the 50 HT.

...

Jetex 50 Hell-Cat (top, and right) beside an early Jet-X 50Z (bottom, and left).
Looking carefully, one can see the difference in shape of the nozzle closure stampings.  The Hell-Cat is believed made by Sebel (UK), while the Jet-X 50Z was made by Powermax more recently.  Otherwise, the engines appear identical, including the motor mount clips.  Although the packaging for this "50Z" engine is clearly marked, this engine appears to be identical to others currently sold as Jet-X "50C" motors.

Jetex 50C, exploded view, showing components.

1.  Motor case
2.  Exhaust deflector ring
3.  Solid fuel pellets
4.  Gauze disc
5.  Igniter wick
6.  Flame shield
7.  Cap sealing washer
8.  Wire clip
9.  End cap

.....

Jet-X 50C
Powermax motor, recent vintage.  This is a clean, sleek evolution from the original Wilmot Mansour Jetex 50 of 1949.

50Z
Powermax motor, recent vintage. Note the exhaust nozzle, which may add some coefficient of thrust to the design.  Exhaust nozzle cones like this are essential parts of larger rocket engines, where they frequently contribute an additional 150+% to the effective thrust.