Some time during the 1930s, a Romanian by the name of Henri-Marie Coanda observed something very interesting.
He spotted that when air (or any other gas) was flowing along a surface that curved away from the flow, the gas didn’t just carry on straight ahead but followed the curvature of the surface.
Or, to put it another way, a stream of fluid or gas will tend to hug a convex contour when directed at a tangent to that surface.
You can see the effect illustrated in this diagram.
Instead of blowing straight past the circular surface, the air will stick to its surface and bend through 90 degrees.
You can check this out for yourself by turning on a
tap, so that there's a steady but gentle continuous stream of water flowing. Now bring the back of a spoon into slight contact with the stream and you'll find that the water will no longer fall straight down but actually stick to the curve of the spoon.
My own experiments indicate that a single curved surface will deflect a flow of
room-temperature air by a maximum of about 90 degrees -- after which the flow detaches itself from the curve and once again travels at a tangent.
Although the Coanda effect doesn’t play a large roll in traditional pulsejet engines, an understanding that it exists and how it affects the flow of gas is something that all budding pulsejet designers should have.
Plans
This chapter of the book includes a number of plans for various engines, including the 55-lbs –thrust enhanced Lockwood Valveless engine that currently resides on my kart and which featured in the popular TV series Scrapheap Challenge.
Although based on similar designs, this particular version has a flared intake cone and slightly different combustion chamber
dimensions both of which help to assist in throttling and easy starting.
This engine should be built from material that is at least 0.7mm in thickness and, if weight isn’t too much of an issue, you might find it worthwhile going up to 1.2 or even 1.5mm material.
Although thicker material will cost and weigh more, and is harder to form, the result will be a more durable engine that is less likely to suffer from cracking.
This plan is included as a separate PDF file (55lbslh.pdf) and contains all the dimensions you need to build your own.
One detail often missing in other Lockwood plans you might find on the internet is how the fuel-injection system works.
I’ve experimented with two methods that work very well.
Both methods involve passing a tube cross-ways through the engine. This tube is cross-drilled with a number of small (1.5-2mm) holes through which fuel sprays into the engine.
In the first method, the tube is placed in the intake tube, as close as possible to the cone that joins that tube to the combustion chamber. If you’re using a tube here it can be made from plain steel rather than stainless because it gets plenty of cooling from the incoming airflow.
The second method involves running a much longer tube through the engine so that it passes through the cone connecting the intake tube to the combustion chamber. This tube is positioned as close as practical to the combustion chamber end of the cone and will be quite a bit longer than the one required for the first method.
In both cases, the tubes should be around 8mm in diameter and the cross-drilled holes should point towards the sides of the engine, not to the front or rear.
The fuel-tube, once installed, is fed with liquid propane which sprays out through the row of small cross-drilled holes and vaporizes into propane gas.
If you want to run this engine on a liquid fuel such as gasoline, methanol, jet A1 or diesel then you can install a second fuel tube running at right angles with the propane tube – so that the two tubes form an overlapping cross when viewed down the intake tube.
Because these liquid fuels are not as volatile as propane, you will need to start the engine using propane and then start the pump that delivers liquid fuel to the second fuel tube. The propane can then be turned off and the engine will run entirely on liquid fuel.
Amongst the other files on this disk you’ll find many plans of valved and valveless pulsejet engines, most of which are readily available on the Net from websites such as www.pulse-jets.com and others. I’ve included them on this disk only for your convenience.
Building a no-weld pulsejet
If you don’t have a lathe, welding equipment or other specialist metalworking equipment then you’ll be pleased to know that this disk also contains a full-length video that shows how you can build your own pulsejet using nothing more than regular hand-tools. There’s also another file which accompanies this video and that provides additional material in text and pictures.
This simple engine won’t produce a whole lot of thrust, but it’s a great way to get your hands on a real working engine for probably less than $20 in materials.
Other plans will be posted to my website as they become available. You should check the subscriber section regularly for updates using the ID and password that will have been supplied to you when you purchased this disk.