From: ansis@iunet.ann-arbor.mi.us (ansis_upatnieks)
Subject: Re: Pulse Jet Home Brew
Organization: Innovative Concepts
Date: Sun, 4 Oct 1992 05:06:29 GMT

>                             17335 U.S. HWY. 31 North
>                             P.O. Box 297
>                             Westfield, Indiana 46074
>                             Phone 317-896-2561
>                             Fax   317-896-3788
>
To answer some questions,

    The Dyna-jet is just over twenty inches long, and about 2 1/2 inches
wide at the widest point.  Most of its length is a welded thin stainless
steel combustion tube.  The forward end is widened into the combustion
chamber.  The valve head is screwed onto the combustion chamber end of the
combustion tube.  It is constructed of machined aluminum.  The valve head
has a venturi air intake leading to ten intake holes to the combustion
chamber.  A thin flat spring steel valve shaped like a daisy covers the
ten intake holes with its "petals".  An assembly mounted to the venturi
intake supplies fuel to the engine and is also a starting device.  It has
a threaded end for a tire pump so that pressurized air can be applied
for starting.  A spark plug is mounted on the combustion chamber. Unleaded
automotive gasoline is recommended as the fuel (regular, not premium)
although I have heard the CL speed fliers use methanol with nitromethane,
MEK, and other fuels in various combinations.  
    To start the engine, pressurized air (at least 40 psi) is applied
to the threaded end of the fuel supply assembly while activating the
spark plug.  We used shop air and a model T ignition coil.  Usually,
the engine pops loudly a few times and then starts running continuously.
The spark plug can be turned off once the engine starts because 
combustion is self sustaining. The pressurized air supply is turned off
as soon as the engine starts.
    The way this works is, pressurized air applied at the intake draws
fuel at the venturi.  The pressurized fuel-air mixture forces the petals
of the valve to bend, allowing it to enter the combustion chamber where
it is lit by the spark plug.  Combustion increases the temperature and
pressure.  This pressure increase forces the valve petals to cover the 
intake holes, preventing reversed flow through the intake.  With the 
intake closed, the hot gas is blown out the exhaust.  Pressure inside
the combustion chamber decreases as combustion ends, but the momentum
of the fast exhaust flow keeps it moving.  This creates a vacuum in the
combustion chamber, opening the petal valves and drawing in another fuel-
air charge into the combustion chamber.  This is met by remnants of the
hot exhaust flow, which has now completely reversed in direction (the end
of the combustion tube is flared because the engine breathes both through
the intake and the exhaust).  Mixing of the hot exhaust remnants and the
fresh fuel-air mixture causes ignition, and the cycle repeats, completely
self sustained.  This cycle happens 220-240 times per second.  The frequency
is determined by the combustion tube length, combustion chamber volume, and
operating temperature.  The petal valve (the only moving part) acts only
as a one way check valve to prevent reverse thrust out the intake.  There
is no fuel pump (fuel is drawn into the engine at the low pressure throat
of the venturi) and the ignition is turned off once the engine starts.
There is also no throttle, with only two speeds: stop, and go like hell.
    Running the Dyna-jet is spectacular.  During starting, bright yellow
tongues of flame sometimes shoot out of the exhaust.  Once it starts,
a faint blue flame can be seen extending a few inches from the end of the
tailpipe.  It heats up to a bright red within a few seconds.  We never
static ran it longer than 10-15 seconds at a time for fear it would melt
down.  The instructions say not to static run it longer than 30 seconds, but
they have been run as long as two hours without cooling air flow (not 
recommended).  We also took some video looking down the tailpipe.  The
engine is completely straight and hollow, giving a clear view down the
entire combustor tube straight into the combustion chamber to the valve
face.  A bright blue-white flame can be seen inside the combustion chamber
Ear protection must be worn because it is incredibly loud.  We didn't
measure the noise level but 124-130 db is typical for a pulse-jet.  Combustion
tube temperature can be up to 1850 deg. F for pulse-jets.  The combustion
tube of the Dyna-jet develops a dark scale on its surface from the high
temperature, even though it is stainless steel.  I have heard of 316 stainless
steel and nickel alloys being used.
    There is no way one of these could be flown at your friendly neighborhood
flying field, or the field would be lost in a flash.  A deserted wasteland
far from nowhere would be ideal.  I would like to know where the CL speed
fliers do their flying and how they get away with it.  BTW, I am not
associated with any company that has anything to do with pulse-jets and the
above are my opinions and facts as I see them.