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"Liquid-Propellant JATO Rocket"

Air Force - Navy Overhaul Instructions Handbook

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Liquid-Propellant JATO Rocket

Model YLR13-AJ-7 (Aerojet)
Air Force - Navy Overhaul Instructions Handbook


A quality reprint of the original Air Force Overhaul Instructions Handbook for the Aerojet YLR13-AJ-7 Assisted Takeoff (ATO) Rocket System.

A hard-to-find reference resource of special interest to rocket scientists, engineerings, technicians, aeronautics historians, aircraft enthusiasts and pilots.

According to the document:  “The Model YLR13-AJ-7 Rocket is utilized to assist in the takeoff of heavy aircraft, thereby increasing the takeoff payload capacities and cruising radii.  This bi-propellant, pressure-fed rocket provides a nominal 400-pound thrust for 60 seconds.”  This book “provides complete instructions for the overhaul and testing of the Model YLR13-AJ-7 Rocket.”


The very first rocket propulsion projects at Aerojet were closely tied into work that had been started at GALCIT (Guggenheim Aeronautical Laboratory, California Institute of Technology). 

These three historic photos from the author's collection are to show what the unit looks like;
these 3 photos are not in this book

Aerojet’s early ATO units were used to enhance the capabilities of the World War II piston engined and early jet aircraft.  Their first contract (in May 1942) was for a liquid-propellant assist take-off (ATO) unit, the 25AL-1000, which had been preceeded by a very similar unit designed and built at GALCIT.  These engines were installed and used on the Air Force A-20 light bomber, and made the world’s first liquid-propelled ATO takeoff in January 1943.

The Air Force then ordered a few Aerojet ATO units for test on the new XB-45 light jet bomber.  This new design was the XLR13-AJ-1 (also designated the X60ALD 4000), the first model of the rocket described in this book.

The rocket used a pressurized propellant feed system, a regeneratively-cooled motor, and an unusual tankage configuration. The oxidizer was red fuming nitric acid (RFNA).
Illustrations from the book, reduced in size and resolution



Successful flight tests and drops were made using large cargo chutes.  A follow-up program successfully used smaller chutes with an air-bag ground impact decelerator. 

The success of this program led directly into a contract for ATO units to fit the B-29 heavy bomber.  These would provide 16,000 lbf total thrust for a minimum of 40 seconds, using four externally-mounted, dropable, expendible units. 

The first version of the new design (XLR13-AJ-3) was a reusable ATO designed for flight tests and training, but the second version (YLR13-AJ-3) was designed as a low-cost expendible unit.  The –3 and later –5 designs used tankage consisting of three parallel, long, slim, horizontal tanks, supported by two aluminum strongbacks that would engage sets of 30-inch external bomb racks.  The fuel and oxidizer tanks were 10 and 12 inches (respectively) aluminum tubular extrusions which were subsequently nozed over at each end to mate with welded-on end fittings.  The central air flask was fabricated on modified forged dies for the ASME standard industrial nitrogen bottles—with two bottle forgings welded end to end.

The –3 unit used the regeneratively-cooled 4000 lbf thrust chamber from the –1 unit and most of its valves and controls. However, the -5 went even further with the “maximum producibility” concept by including an uncooled, ceramic-lined thrust chamber and nozzle.  This was the first known ceramic thrust chamber, and served as a basis for the subsequent F-84, BOMARC, and rocket sled motors.

Because the aircraft would be based in Alaska, a low temperature hypergolic fuel was mandatory.  It was learned the Air Force had stockpiles a large amount of xylidine produced for another purpose during WW II. Tests showed that a 65/35 mixture of xylidine and gasoline was hypergolic and had an accptable pour point at -50ºF, and that fuel was adopted for both the –3 and -5 programs.

The –3 units were fabricated, qualification tested, and flight tested in less than six months. One hundred and fifty of the –5 ATO units were produced, and at least two B-29 aircraft were outfitted with the four external bomb racks.  This system provided the B-29s with a payload/range capability that would allow them to reach any target in the USSR,and still return to friendly bases. Previously, many of these targets could only be reached on a one-way trip.

This is the Overhaul Instructions Handbook for the Aerojet YLR13-AJ-7 rocket system, which was the final production version of the design, dated 1 April 1951 (revised 13 June 1951), and originally a Classified Restricted defense document.

Table of Contents
  • Introduction
  • Scope of handbook
  • Purpose of equipment
  • Principal weights and dimensions
  • Overhaul instructions
  • Special tools
  • Preparation for overhaul
  • Disassembly
  • Overhaul of components
  • Tubing and fittings
  • Pressure tank
  • Fuel and oxidizer tanks
  • Pressure line relief valve
  • Pressure line regulator valve
  • Pressure line valve
  • Pressure line safety diaphragm
  • Pressure line check valves
  • Pressure line drain valves
  • Solenoid control valve
  • Hydraulic accumulator
  • Propellant tank fill boss assemblies
  • Pressure fill valve
  • Propellant tank vent valves
  • Propellant control valve
  • Mixture ratio orifice
  • Thrust chamber
  • Reassembly of the rocket
  • Filling and bleeding the hydraulic system
  • Inspection of the complete rocket
  • Test procedures
  • Regulator valve
  • Solenoid control valve test
  • Oxidizer tank proof test
  • Leak-testing the complete rocket

The book is particularly useful ideas for amateur rocket designers and experimenters.  It has 19 photos, engineering drawings, and schematics.  Lot of detailed info on valves the and liquid propellant plumbing and pressurization system.  21 pages, color cover, quality bound, 11" x 8-1/2" size.  $19.95

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