Make a Pulse Jet Engine, (Scanned From 1958 Plans)

 Making A Pulse Jet Engine
 It powers a scale model MiG 15 fighter at 85mph. This is a powerful jet unit and one which can be made by anyone with access to lathe and welding facilities.
Emil Brauner of Kladno in Czechoslovkia is a model maker who was forced by circumstance to make his own jet engine.

: Message from Karroo Oakey

WARNING  : This a Scan-Able and not an Instructable:

(I’ve had this book for about 25 years (published 1958) hoping for a lathe or access to one. Nada. I had already planned to scan this and put it on Instructables for somebodies benifit, when I stumbled on the “Make your own metal lathe” on Instructables. That mindblowing experience now has led me to the whole gammet of all the Gingery books so that now I am collecting aluminum like crazy. Since this book was published 10 years before I born I really don’t think that there can be anybody left who really cares about the copyrights anymore that is if they have not expired. Also I have not found any other plans for Pulse Jet Engines anywhere, so like any good reporter, reporting bad smut, I too will shout the legend from the rooftops --- THE PUBLIC HAS A RIGHT TO KNOW! ) If somebody does object I guess I'll have to pull it.

 
Scan cont :

First, how it works:  Petrol or White Spirit (cigarette lighter fuel) is induced to spray through a metering jet by a fast airflow into the nose cone.  The fuel/air mixture passes through flap valves and into the combustion chamber, where it is ignited.   Immediately after combustion  the  burning  gases  pass through the only exit, the tail pipe, and the resultant reaction provides thrust.    As this column of burnt air escapes, a depression occurs in the combustion chamber, and the flap valves which were closed under compression are now opened and a further supply of fuel/air drawn in.

So the cycle repeats itself in a series of pulses, each. one igniting itself with the heat of the tail pipe which rapidly achieves the state of red heat, as the frequency of explosions is in the region  of 200-300 cycles per second.

 

Because of the fire risk, and the possibility of personal danger, pulse jets are neither to be advised for free-flying  nor  are  they  tolerated for such a purpose in Great Britain. They are, however, insurable under a special scheme by the S.M.A.E. for control-line flying and a class exists for Jet Speed, usually flown at the National contests.   Current record is 133.3 m.p.h.

 

Making the Jet

All dimensions on the drawing are  in  millimetres,  and  for  the convenience of British constructors we provide a table of required equivalents.   Start with part 1. a brass turning which serves as an adapter for the compressed air or car tyre pump air supply during starting.  It is brazed at 37° to part 3, the carburettor, which is another brass turning tapped to receive the pilot jet and threaded at the rear end to fit part 6. The pilot jet, part 2, has a I mm. orifice.  It is advisable to make a set with .9 mm. and .95  mm.  alternative  jet  sizes  to determine best diameter for performance.  Fuel flows directly from the tank to the pilot jet, thence into the carburettor; and out at 70° - 80 ° through the two .8 mm. oblique holes.

 

The head — or cone, part 4, is a light metal turning threaded at the rear to fit the collar in the combustion chamber.  Care to adhere to the aerodynamic curve, and external relieving to give a wall thickness of 2 mm., will improve performance and save weight.  Note that a 3 mm. recess is needed to take part 6 at a later stage.  Part 5 is  a  simple  light  alloy  fairing  to blend the carburettor to the valve plate, part 6, and this latter item is turned from the solid in mild steel. There are ten valve holes, each 9mm. diameter and tapering down to the centre for maximum opening. The valve itself, part 7, is the heart of the jet, and as such is a most critical component.  .15 mm. spring steel sheet was used in the original jet; while an alternative, cold drawn sheet, is easier to stamp out and will last for up to 30 starts.  Mass production by means of a steel die and hard rubber blanking plate would be one answer to the valve replacement problem.  To limit the opening of the valve, part 8 is a backing plate from dural, and here again it is advisable to make alternatives with different curvature to test   for   optimum   performance. Part 9 is merely a standard metric thread  bolt  to  hold  the  valve assembly together. Part 6 is peened in place in the head, see detail at 12, and a light alloy nose fairing, 10, riveted as a cone before being "clicked" in place between shoulders.   All that remains is the tail pipe, of welded heat-resisting  or   stainless   steel, thickness  is  not  critical  between .015 in. and .025 in. made up in three stages to the dimensions in 11.  Weld a steel collar in the combustion chamber, and thread to suit the head.

 

 Now mount the unit by means of metal collars to a stout board and prepare for first tests. With fuel in the tank, and a car pump connected to the adapter, part I, start pumping with alternate long and short strokes, checking that fuel is drawn through to the carburettor. This done, use the Continental method of ignition by playing a blow-lamp across the jet orifice (not on the tail pipe) and providing  a  fuel/air  mixture  is passing through into the combustion  chamber,  a  start  is  soon effected. 
 

There is no such thing as a "misfire" in a pulse jet, either it is going or it is stopped.  If the jet appears to show no inclination to keep going, then one should try variations with (a) the pilot jet and (b) valve backing plate. A low tone indicates a rich mixture and a high note, or short, barking tone, a weak mixture.  Hot weather calls for a larger pilot jet. Extreme cold a small jet Having made your own unit, you will soon appreciate these symptoms and their cures.

 

(Ex - CHAPTER TWENTY-SIX :

Scanned from Model Aero Engine Encyclopedia 1959, 208 pages compiled by R.G.Moulton, published by Model aeronautical Press LTD. 38 Clarendon Road Watford, Herts Published by Bletchley Printers limited, Bletchley, Bucks. 1^st edition March 1958, Reprinted January 1959.)