Lockwood Hiller pulse jet rules of thumb?

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Lockwood Hiller pulse jet rules of thumb?

Post by Thingamajig » Sat Nov 17, 2018 1:24 am

Hello everyone, I'm working on my first build i've gathered up some parts to use, but they are of slightly different dimensions that what is called for in the plans that i've been going off of and i have not been able to find any information as to how i could accurately adjust the dimensions. I've read a lot of posts in this forum with people having problems with this same build and members have told them they're dimensions are off in one way or another, but i haven't been able to find a way to tell how... The plan i've been going off of is attached below.

I think i've managed to figure out some of these rules of thumb but i wanted to run them by someone who has a clue (because I certainly do not)

1 - Combustion chamber length should be 1.5 times the diameter
2 - Intake pipe should be 4 times the length diameter
3 - The volume of the combustion chamber should be 5 times the volume of the intake pipe
4 - The volume of the exhaust piping should be roughly 4.5 times the volume of the combustion chamber
5 - The last i'm not very sure of but i believe there is some kind of relationship with the length of the exhaust pipe and its average diameter.

I'm taking a long shot at #5 but i can't see how they came to this 92.3mm, and the average diameter seems to be the most likely, i just don't know how to calculate that figure.

I've managed to find a piece of schedule 10 304 stainless pipe approx 15" long for the combustion chamber. If rule 1 is actually somewhat correct ill need to add an extra half inch onto it.

I've also found two 3" 90's (haven't taken an exact ID measurement)
The 90's have been grooved for victaulic piping so there is a slight indentation on the insides that runs the inner circumference. From what i have read on the forum this would make them no good for my exhaust piping, but i figured i'd double check before i chopped the grooves out of them. For all i know they are the wrong diameter for my combustion chamber.

Am i on the right track with any of the parts that i've found or should i just throw it back in the scrap bin and just fabricate everything from scratch? Or would pyrojoes Caliber scaling method work for this type of engine? It appeared that the method was for valved models with a linear flow, but i just have no idea.

Thanks for any help you can provide! I'll be sure to update you guys on how my build goes and post a video of it running!
Valveless pulse jet.pdf
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Re: Lockwood Hiller pulse jet rules of thumb?

Post by metiz » Tue Nov 20, 2018 11:33 pm


It might be a good idea to use Pyro's recipe for beginners for your first engine (it's for valveless engines). That lockwood engine is pretty crappy. For your first attempt, try making a linear engine. They are the most easy to do and easy to start. When you get bored of it, you can have it cut up in 5 minutes to make something different.

If you really want to go with that lockwood, make the bends smooth. Don't worry about the .5" of combustion chamber length. I think it will work fine for this engine. If you still have the option, go for this lockwood, it's much better download/file.php?id=11410&mode=view
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Re: Lockwood Hiller pulse jet rules of thumb?

Post by Thingamajig » Sun Dec 02, 2018 11:29 pm

So I've abandoned the Lockwood plan and went with pyrojoe's caliber method to scale my dimensions, just wondering if my rough, no to scale drawing looks like something that will run. All dimensions in inches, and not too scale obviously...

I guess I'm mostly concerned with the scaling method because I've gone so much larger then what most designs show and, the larger you go the further out the volumes will become. Double the pipe diameter, quadruple the volume right? Looking at my numbers I think my exhaust cone is a tad large and I'm worried about the pneumatic valving not working.

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Re: Lockwood Hiller pulse jet rules of thumb?

Post by Mike Everman » Tue Dec 04, 2018 4:54 pm

Holy Canoli. 26" tailpipe exit? Might I suggest you start with a smaller, known to run motor to get yer feet wet? There's a lot to it before jumping into something so dangerous.
Scaling is definitely screwy up in this range.
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