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)