CONE TEMPLATES

To make the cone templates, I can use knowledge learnt from my study of maths to make a shape that effectively looks like a pizza slice with a bite out of it with corresponding radius' to the ones on my design.
I had to re-do one of the templates for the long exhaust length. It is 1058mm long and I didn't think to consider the limit on size imposed by the length of the sheet metal roller. By looking at a picture of Bruce Simpson's and his Pulsejet, I can see that his has a weld halfway up the exhaust where it has been made in two parts; I will overcome the problem with this same solution; by spitting the cone to be rolled in two halves. Although this will create more to weld.

I have thought about the way I can make the templates and I reckon I can just print the templates onto paper; this is much easier than drawing out full size templates through geometrical methods.  To do this I need to digitalise the designs I have worked out; the choice of software to do this is Google Sketchup and AutoCAD; being relatively familiar with both, I know it will be easier to print and work to a 1:1 scale from AutoCAD so that is what I will use. My printer prints in A3 so printing shouldn't be an issue.

I had originally done all the calculations by hand which has turned out to be a waste of time when I could've just done them on the computer to start with. I suppose they gave me something to double check the templates against so they are definitely right.

From reading Bruce Simpson's work on building a jet engine, I have found that he used a plasma cutter to cut out his metal pieces. I still believe my idea of using an angle grinder will be fine for the larger radius', but I may have problems with the tighter radius'; I may look into the possibility of using a smaller cutting disk; if these do not exist I may need to look at sourcing a plasma cutter. 

FINAL DESIGN

The 90deg bends and tube arrived:




By comparing the diameter of the 90deg bends I have sourced with those used in Bruce Simpson's design, I have calculated a scale factor of 73.1/76 (ratios of inside diameters) that each measurement can be multiplied by to create the design I am going to follow. Effectively mine is slightly smaller than the original design.

I imputed Bruce Simpson's design into AutoCAD and applied the scale factor; this is easier than doing all the calculations by hand and also provides me with a digital copy of the design.

(3)

From using the dimensions describing the 90.deg bends in the table above provided by the manufacturer and comparing it to Bruce Simpson's design, the difference in U-bend length is (73.1/76 *190pi/2 - 160pi/2 =) 35.7mm. As the 90deg. bends have a small straight section at each end that will need cutting off, I can just leave 35.7mm on on of the bends to fill this gap.

Bruce Simpson's design:

(19)

Here is the design I will follow with labels showing how I refer to the pieces throughout this project:

FUEL, FUEL DELIVERY SYSTEM, IGNITION

As part of the Lockwood-Hiller I will need to choose a fuel for it to run on and how I will provide this to the pulsejet.

Pulsejets seem to run on virtually any fuel, 'if it burns, you can probably run a pulse jet on it' (8.1).

Although they can run on virtually anything, propane seems to be the best option for me; with it's boiling point being so low, it can be supplied straight as a gas-propane pulsejets are 'one of the easiest to start' (1.2). It is also easy for me to source in compressed cylinders and doesn't require any sort of vaporizer or pump. 

To supply the fuel most people seem to use what is called a fuel rod to do this but an alternative is injecting the fuel down the intake through to the combustion camber. I'm going to opt for the fuel rod method as it's the one that's most documented and therefore familiar; however it will require more work.  This shouldn't effect the rest of the design so won't restrict any progress.

I also need to decide how to ignite the fuel-Bruce Simpson outlines how to use a spark plug (1.1), however, Colin Furze just ignites the gas using a blowtorch at the intake. I think I'm just going to use this method to keep construction simple for the time being.
The fuel delivery system will also need designing; although Bruce Simpson recommends 2 valves: one for idle and one for full throttle/finer adjustments (1.11), I just want my pulsejet to run so am just going to use a single one. If it runs I can always alter the delivery system in retrospect to improve performance.

U-BEND

I've decided that the deciding factor on the scale of my pulsejet will be determined by the 180deg bend I can source as this will be the only part of fixed size.  The U-bend needs to be constructed from Mild steel to assist with welding and needs to be as close the thickness to the 1.2 mm sheet steal acquired from school to make welding simpler and the rate of thermal expansion similar for all parts making the engine last longer.

I've found a website called jetex.co.uk (18) which sells custom exhaust parts/manderal bends in mild steel in a thickness of 1.5mm (close enough to 1.3mm of the sheet metal) in a diameter (3inches) relatively close to the one used for Bruce Simpsons design. They sell a 180° bend that I could use for my pulsejet. However, this has a radius of 120mm-from quickly inputting this into google sketchup I found this to be too tight which would mean the intake and exhaust would be too close; this worried me due to heat dissipation; as pulsejets gets very hot whilst functioning good ventilation would be important to avoid the steel prematurely melting. I have therefore settled on two 90° bends they sell which I could then weld together creating a larger radius. From looking at the theory behind pulsejets, I've found that the relative dimensions are quite important due to the resonance theory of wavelengths, therefore to maintain the overall length of the bend, I can increase it with a straight tube section connecting them. I can also use this technique to create adequate spacing between the intake and exhaust if necessary and shorten the tubing between the combustion chamber and the U bend.

I'm also going to order a straight section of tube; to practise welding circumferences on and because the lockwood hiller design I'm following has a stretch of pipe the same thickness as the U-bend; this will save me rolling it.

Here is a diagram of how the pieces' sizes are supposedly meant to be related from the theory of resonance. Note 'supposedly'-no-one seems to 100% understand how these work.

(7.2)

FRENCHGEEK

I've had another look at the blog Frenchgeek (follows a guy doing an almost identical project to mine). This account of first hand research should help me prevent any problems he faced before they occur.

Cause for concern:
This guy did a 22 week welding course before embarking on building his pulsejet; i have neither the time nor money to do this and really have no longer than around 3 weeks before I NEED to start building my jet.If worst comes to the worst I'll have to find someone else to weld for me although I would like to do it all myself.
I am going to need to create a schedule for the construction of my artefact not only to help manage my time efficiently but to help make decisions on whether I will need to source any extra help to finish on time.