Please put your "I am new and need help" question here.

[Viv]

Hi Paul

Sorry I don;t normally follow this section to closely but popped in to see what was going on, I think your questions about acoustics are interesting but you have effectively outgrown the beginner section of the forum, it might be best if you started a new thread specifically about pulse jet theory and acoustics in one of the other sections, off topic if you want to cover valved and valveless designs may be the place to start.

That way you will attract more of the general forum population

Viv

[paul fellows]

I don't need to prove anything. But if you insist: hows 104 years of history. If acoustics were not the driving force don't you think that, in 104 years some-one would have noticed? There's also some very complex maths that can acurately predict pulse-jets to amazing precicion. Do you think this is just a weird coincidence?

Go check out the "Essential reading" topic to find some good information.

If you're still not convinced, set up your own experiments, document them and prove 104 years of history wrong

sorry
i was not trying to make you personaly the champion of a cause that is not of your choosing.

i was just looking for some one to explain to this idiot how sound passing through a gas (some times the wrong way? )is so important.

[paul fellows]

http://jetzilla.com/topic_003_01.html
GIVES AN EXPLANATION OF WHAT ACOUSTICS DO IN A PULSE JET

[HPSCL]

I'm going to design another pulsejet and was wondering if I'm calculating the length of the tailpipe, correctly? Should your measurement of the tailipe, be based on the Inside Diameter, or the Outside Diameter?

I based my last one, on the dimension of the Outside Diameter and it runs well, but I'm weird about not knowing if things are as precise as possible.

[metiz]

Hey Hpscl

They should be based on the inside of the pipe.

[HPSCL]

Thanks, metiz!

[Kool]

Is there a program which take account of the thickness of the steel, and so calculate the inside diameter on the templates?

[metiz]

Is there a program which take account of the thickness of the steel, and so calculate the inside diameter on the templates?

Not necessary. You can use "cone designer" to automatically create templates for you. If you want to compensate for wall thickness, simply add to the diameter you want your pipe to be. Say you need a pipe 50mm internal and you want to use 1mm steel: simply imput 52mm as the diameter. .5mm steel? 51mm diameter.

[PyroJoe]

Pulserate, cone designer software website:

http://www.pulserate.com/

[metiz]

The new version on that website comes with an extrafree "wait one extra second everyday you use this program without buying before you can use it" feature, wich becomes anoying realy fast. The rar attached to this post contains an older, wait-free (just click on the screen you get when you start the program) version. It has less features but will do the job just as well as the new version.

[Kool]

Thanks for the tip Metiz.

With Cone Layout I've also to wait for each day a second

[HPSCL]

I recently built another pulsejet and it has a 3" Diameter x 33" long TAILPIPE... "IF" it had been designed correctly, how much thrust should I expect to get, out of it?

I ask, because I've experimented with different types of injectors and also setting them at several different depths into the intake. The most I can seem to get out of the engine is just over 5 lbs. of thrust.

I've got the engine's stand set up on a "ghetto-style" test stand: Two 1/2" diameter pieces of PVC pipe, with a fish scale hooked to the end of my workbench. Perhaps a better setup, would show a little more on the scale... or perhaps my engine is just not that powerful?

[metiz]

Although it's a good runner I'm afraid it's not that powerfull. The engine is "under aspirated" as far as I can tell by eye. Things like an expansive tailpipe and a proper choke will also help of course. With a proper intake and tailpipe system that CC could potentially push about 15 pounds.

You can't determine (accurately) the thrust of a valveless pulse-jet with just the tailpipe dimensions.

[HPSCL]

Thanks, metiz!

I understand what you've stated, about the expansive tailpipe, but what do you mean by proper "choke"? Are you referring to a cone section, between the CC and tailpipe?

I only build these to make noise and it's louder than any other one that I've built. My wife can tolerate all the others, with no problem, but says that this one sounds as though I were running it in the middle of the house.

I've gone back to my original injector setup, shoved about halfway down the intake. It starts now, with no air... I guess I should just be happy that it runs and stop thinking about how to improve it. - Taking into consideration, your input about the lack of an expansive tailpipe and such.

Thanks again, especially for the quick reply.
Dave.

[paul fellows]

Viv I know you said “you don't need to know how the engine works to drive the bus!” but I am directing this question to you because in an earlier post you where 'debating' with Bruno about the importance of acoustic waves in the working of a pulse jet.
In his page on valveless pulse jets, under the section on acoustics Bruno included this statement.

“The changes of pressure and the changes of gas speed do not coincide. They follow the
same curve but are offset from each other. One trails (or leads) the other by a quarter of the
cycle. If the whole cycle is depicted as a circle – 360 degrees – the speed curve will be offset
from the pressure curve by 90 degrees.”

I think I have followed that.
So measuring at the valve /CC end of the pipe and measuring pressure will give a sine wave as the pressure changes ether side of normal atmospheric pressure.
And measuring at the open end pipe and measuring the speed of the gas will give an other sine wave, with its peak values coinciding with the zero pressure difference points.

My question is where dose the acoustic wave fit into this picture, my guess would be that it will be in phase with the pressure curve. is that right?
If not what is right?

A second question what is the scale of the acoustic wave effects, if it where possible to double the amount of acoustic energy at work in the jet would it make the jet work better?