Shreckling - Details and Pictures page.
This motor was built by Andrew Germaney, with absolute precision as per Kurt Shrecklings book.
The only differences from the drawings are that I have opened up the 'flaps' in the combustion chamber to 3.3mm, to cool the rear end of the motor. This removed any hot spots completely, and the gas canister (motor case) can be touched at all speeds right up to the nozzle guide vane area at the very rear end.
The 'coil' type vaporizer tube seemed to give unstable vaporization on liquid fuel, so this was removed and commercial type 'J-shaped' vaporizer tubes were added instead, along with the now almost standard fuel ring with syringe needles to inject fuel. We have not tried this arrangement yet - should be a major improvement.
Thick oil is bad, It does not flow freely, and at high speed the bearings 'skate' on the oil instead of rolling causing flats to appear and this causes bearing failure. Too much oil flow causes similar problems. This is why bearings in commercial motors are loaded with springs to prevent 'skating'. Use thin oil like transmission fluid / 3 in1 / or synthetic two stroke oil thinned with paraffin or similar. In addition starting is easier with thin oil and the motor runs cooler.
It starts very easily using the following technique.
1. Turn on the propane bottle very slightly (we have not tried kerosene or paraffin yet) and listen for a very slight hiss of gas.
2. Using the hair dryer (runs on 12v dc now that the heater coils are removed) spin the motor up to a reasonable speed.
3. Take away the hair dryer.
4. Using a lighter or match or cooker sparker try to ignite the tail pipe. If it lights and flares you have too much gas. As the rotor speed decays, it will be possible to ignite the gas and the flame will 'pop' inside and will appear to have gone out. If you listen carefully you can hear the change in sound as burns inside, and a look in the rear will confirm that it is lit.
5. Use the hairdryer again and keep it spinning as fast as possible and then gradually turn up the gas. The motor will eventually 'overtake' the hairdryer, and this can be clearly heard. Do not Remove the hair dryer until this point or the motor will run hot and this heat is then very difficult to lose. Remove the blower now and keep accelerating the motor to safe idle speed, or 1 psi case pressure. Any slower and the motor may overheat. Faster = Cooler. Don't rev past 75,000 rpm!
6. Check that the oil is flowing! - Clear tubing and marks on the oil tank! Actually it needs to be restricted.
In the model plane (subject to testing) we will use the tried and tested option of a model car electronic transistorized speed controller, to control the Kavan electric fuel pump to pump paraffin or kerosene from a bag. This can be set to give max safe rpm with the pump running flat out by using a by pass or return (across the pump) and a needle valve in line. Safe idle and start settings can be set up using the transmitter 'computer' that is built in. The fuel bag is actually a urine bag as used by wheelchair types, which I am now unfortunately after a bike accident. I have lots of these as provided by the National Health System (now there IS a subject..), if you need some just mail me. They are perfect and I have 2 types, 750cc and 2000cc. Much cleaner and better and lighter than clunk tanks! and no air! makes full use of any available space too so more fuel.
OK a Couple of pics.....
This was before I worked out how to open the
combustion chamber flaps to cool the rear end - It is now black
all over at all speeds. This is at idle, less than 1 psi on the
gauge, on propane, but at 5 or 6 psi it is impossible to stay in
the room due to the incredible heat build up! This is actually my
office / bedroom. On shut down it gives a 'puff' of smoke (oil)
that fills the room.
Running at slow idle speed was the only way to take
this picture as the camera almost melted... Too hot to hold! The
engine just sits here whistling away on my desk.. It would run
all day like this except that the room becomes too hot to breath
in in about 2 minutes flat. Looks so quiet on the page! The
turbine wheel cannot be seen, due to the speed but the stationary
nozzle guide vanes can be seen glowing dull red and this is
normal.
Stopped! The mark on the (3 in 1oil)
oil tank is before the last run. This run blew all the paperwork
off my desk and all around the room. Will have to tidy up. The
Very low oil consumption actually increases bearing life! The
highest pressure that we run at in the bedroom is 5 psi on
Propane, and this is plenty!
Not running.... Compressor is made from
good quality plywood for those that do not know. This always
worries me, but so far no problems.
The hot end is now cold! Black paint on case lasts
forever. The stainless parts at the very rear got this 'brown'
before I worked out how to cool the rear properly. Must get
around to re-polishing them. Also visible in this shot is the
draw runners that allow the thrust to be measured by the cheap
and nasty fishing 'spring balance' seen in the foreground. And
yes the turbine blades do have excessive running clearance....
Seems to work great though!
Note oil stain on case pressure nipple, Needs a new
sealing washer...... Due to the lack of vibration and torque
reaction, the only mounting is the two wood screws that go
through the large black washers at the rear! Pull the motor
backwards and it comes off in your hand! This is quite safe as
the motor simply pushes forward.