JamJar size and vent-hole size...

[PulseDuuude]

A (hopefully) simple question for the jamjar enthusiasts....how does one scale the vent-hole to match the size of the jamjar you are using?

Mark wrote in this thread http://www.pulse-jets.com/phpbb2/viewto ... d37642af3e...

drill a 7/16ths or so hole in the center of a a pint sized Ball jar or Smuckers jelly jar

So...given a pint jar, vent-hole size=7/16ths...does the vent hole size scale directly with the size of jamjar you're using or is there another 'rule of thumb' to use?

[Mike Everman]

Yes, it's a specific size, "cut and try". An ear piercing whistle means it's too small, a building whoosh, oops, too big. ;-P

[Bruno Ogorelec]

This is another lesson in the simplicity of pulsejets. You don't even have to convert from avoirdupois to metric or vice versa. Measurements like "cut and try", "too small by half" and "oops, too big" work perfectly in all measurement systems.

The precision of our measurements closely parallels the precision of our understanding of what goes on in pulsejets, too, so the two coexist in perfect harmony.

OK, there are two and a half people out there who actually do seem to understand, but the rest of us just pretend and nod sagely.

Our experimental methods are also a bit different. One of our esteemed members determines the basic frequency of his pulsejets by singing into them until they start to resonate sympathetically.

A team I know of tried to determine thrust by having an engine blow into gardener's gloves and estimating how far away the gloves would fly. (the result was 'damned far'. It was a good engine.)

We often check the condition inside the engine by the eyeball method -- simply looking inside. As a result, most of us have asymmetrical facial hair. A part has been singed away.

Welcome to the weird and wonderful worlk of pulsating combustion. If you are slightly odd, you'll fit in perfectly.

[Mark]

That's about it, cut and try. In Florida, on a hot humid day outside you might even find it to be fail and fail. It's a mother to start or sustain one if it's humid especially.
In winter on a cool day, you can get away with a larger hole than would normally run.
My methanol whistling bottles suffer meltdowns in summer because it takes so long for the spent gases to escape, the heat destroys them, whereas on cooler days, they can be reshaped by squeezing/flexing them if dented or slightly collapsed from the vacuum that forms inside after the ejection of gases. You can use them over and over without damage.
With methanol and a cool day, the rocket reaction is over in a split second and it can be surpisingly loud.
The 1/5th rule of thumb is good but there are exceptions.
Mark

[PulseDuuude]

Aaargh! 'Cut and Try'!

Thank you all for replying...now I'm off to work on the T.L.A.R. method....

[Mike Everman]

Bruno, L O freakin L. Ha ha. Well put, the whole thing.

[hinote]

Bruno, L O freakin L. Ha ha. Well put, the whole thing.

yep--I liked it too!

signed,

1/2 Bill H.

[Bruno Ogorelec]

signed,
1/2 Bill H.

Ha-ha-ha... now, that's a good one!

[Mike Everman]

I don't get it...

[Bruno Ogorelec]

I don't get it...

Well, I wrote that "there are two and a half people out there who actually do seem to understand". Bill just counted himself as the half.

[Mike Everman]

Waitaminnit, I thought I was the half! <grn>

[Bruno Ogorelec]

Waitaminnit, I thought I was the half! <grn>

Ah, I thought you were also a member of the nodding classes. Sorry. Two and two halves then. Better?

[Mike Everman]

Ah, thanks! I'll attempt now to live up to the title by knowing half of what I say, or more precisely, saying not more than twice what I know! :-)