Interested ?

[Bruno Ogorelec]

I think that fuel flow as a limit is untenable, even if everyone had a perfect orifice, pressure is just flat out going to be different time to time, temp to temp, early in the run, late in the run. The only way to make that work is fuel mass flow, which is the single most difficult thing to do accurately and cheaply.
Combustor volume has the problem of "where does it start and end?"
Total volume is good, but can't rely on calculated value, as we (most of us, including me) are not manufacturing to tiny tolerance and small diameter changes make big volume changes.
Filling it with water and not spilling any whilst measuring how much seems to be the way to go. Let creativity thrive in all aspects of the motor!
I do think that thrust should be measured with and without ejectors, and that there be a class for each.

We do all measurements on the one and the same restrictor. We do them all in that shed next to your company workshop (where my shoes were set on fire the last time around) at about the same ambient temperature, from the same propane bottle. We empty the bottle from full, keep the record of measurements and count the best one as the benchmark for that engine. Whoever is displeased gets another shot. Let everyone make several measurements. Every competitors pays some sum, I don't know, 50 bucks, to you for your gas, bother etc. per measurement. We can also do other measurements, like sound etc.

[milisavljevic]

Pater Bruno,

What is this "we" business? As if you will be designing, much less building a pulsejet for this or any other competition.
As far back as 2003 (yes, records do exist), you have consistently opposed or subtly throttled any possibility of Forum members conducting a "pulsejet challenge". And now we are to believe you have had a change of heart. Give it a rest.

You know that your proposal is a non-starter. It was advanced, as "Chadly33" put it, to "open a can of worms". Which is quite predictably what happens each and every time someone resurrects this IDEA of a valveless pulsejet challenge.

Edit: Yes, Tufty, it was a "stick too sharp". Considered it removed. Besides, the baron has apparently read it himself.

...

"Chadly33" may clarify this point, but it appears that he wants to encourage a "rush" of new designs, and rather more importantly, red-hot screaming METAL pulsejets, done "on the cheap", than launch a globe-trotting officiated F1 race.

As it stands now, I am sure we will go right back to where we were, until someone else raises the idea and we start...

(over again)

"Chadly33" (or as James Irvine calls you, "Chadders"): Some of us here were already well along in our preparations to test a powerful, yet compact pulsejet; competition or no, I will work with them to give you at least one (competitor)!

And on that note, I strongly urge you to consider having total volume as the pivot, not combustor volume. There are sound technical reasons to avoid the complexities of "angels dancing on truncated cones". (as Mike briefly observed)

M.

[milisavljevic]

PS: With respect to ejectors (augmentors), I agree with Mike! Proper ejectors eat up a LOT of volume, thus the "official" thrust reading should be sans ejector(s); however, there is no reason not to read thrust for both cases.

Separate categories works for me.

Cheers,
M.

[Chadly33]

How about we go with different classes? 250, 500, 1000ml with and without augmentation ? I think if we keep the measurement to the CC only we will see exactly what difference the various exhaust and intake designs can do for these little engines !

[Bruno Ogorelec]

Pater Bruno,

What is this "we" business? As if you will be designing, much less building a pulsejet for this or any other competition.
As far back as 2003 (yes, records do exist), you have consistently opposed or subtly throttled any possibility of Forum members conducting a "pulsejet challenge". And now we are to believe you have had a change of heart. Give it a rest.

Jesus, man, watch it.

By 'we' I mean the community of pulsejet enthusiasts, such as it is, gathered around this forum. Surely I can lay some claim to be one of its members. Or do you propose to ban me from the right to do so?

To mention you other ridiculous notion, no, I have never in my life opposed any kind of competition among engine designs. I would be uncharacteristically daft to do so. There's nothing like competition to keep things progressing.

I have only proposed, just as I am doing now, that the competition be based on sensible criteria, like engine efficiency.

[tufty]

M, although I tend to agree with you regarding rules and spirit, one part of your comment was, I feel, deeply tasteless and unlikely to do anything other than further cement sides in the "rift". Although we may not all "get along" perfectly, life's been relatively peaceful here for a while - it's perhaps best not to go poking at sores with a sharp stick, if you catch my drift.

Back to the pulsejets, I also think a total volume restriction is the only one that makes sense (although, in a "dancing on the head of a pin" mood, I might ask whether you'd consider "end correction" as part of the volume or not :). Obviously, that then opens up all manner of issues regarding measurements and fuelling, I don't think there is any easy way to avoid having multiple "classes". If there's no central "judging point", there are not only the issues of ambient environmental issues to deal with, but also that of differences with fuel; even "propane" varies from place to place. I would suggest the following:

Total volume restriction to include volume of any augmentors / ejectors / add-on ramjets, plus the volume of the gaps between the jet and any such augmentors assuming a "straight line" from exit to entrance.
Any fuelling system you like, but the same system and fuel type to be used throughout.
Engines must sustain without external air or spark.

Scores for minimum and maximum sustainable thrust (throttleable range, in other words)
Scores for best TSFC where thrust > some multiple of engine weight (calculated assuming construction of a duplicate engine shell from some known material, ignoring fuelling systems and any struts / structural elements / "beefing up")

And, of course, the one *really* important measure:

Which one is the loudest?

Simon

[milisavljevic]

How about we go with different classes? 250, 500, 1000ml with and without augmentation?

Hello again!

Two points:

Many times over the past 5 years (possibly 6, or even 7 years) people have proposed a "valveless pulsejet challenge"; to date, the number of these challenges that survived beyond this (discussion) stage is exactly ZERO. That's right: 0.

Ever hopeful that this new challenge "will be the one", I will be frank with you and say that even if we are successful, the number of entrants will be small (and I'm not talking 'bout the size of the pulsejets here... ). Having multiple classes is just subdividing a small number into (even smaller numbers). Best stick with your first idea, and IF things work out well enough, you post a NEW challenge in another class. Multiple Independent Reentry Success Vehicles!

To quote Austin Powers: "Yeah, baby!"

My second point comes back to combustor volume vs. total volume. I can see that you will not be persuaded to give
up on using combustor volume, and I do appreciate that it appears to be an intuitive "winner"; however...(it is not).

There are many types of pulse combustor, and including the "pointy bits" usually found at one or both ends of those with cylindrical main sections (combustor "cans") unfairly penalises certain types, the "Chinese" in particular. In the Chinese, the tapering transition connecting combustor to tailpipe IS NOT part of the combustor in the proper sense. But similar looking transitions in Lockwood-Hiller style pulsejets ARE. And spherical and entirely conical combustors escape the issue entirely, except for the troubling question, "Where does the combustor end when there is only the long cone?" (eg., most, if not all of Larry Cottrill's "FWE" family of pulsejets). Total volume avoids "dancing angels".

Think about it...

Cheers!
M.

[milisavljevic]

Hello Simon,

[snip] ...perhaps best not to go poking at sores with a sharp stick, if you catch my drift.

Yes, you are right. I edited my post (above). FWIW, the wanker in question is not the innocent he pretends to be.

I also think a total volume restriction is the only one that makes sense (although, in a "dancing on the head of a pin" mood, I might ask whether you'd consider "end correction" as part of the volume or not).

You risk the baron's ire for being "unsensible". For the record: "No." I did not mean to include the end corrections.

I don't think there is any easy way to avoid having multiple "classes".

See my previous posting (above ...and apparently, a little further down within this one! ) wrt. this suggestion.

If there's no central "judging point", there are not only the issues of ambient environmental issues to deal with,
but also that of differences with fuel; even "propane" varies from place to place.

I work with builders literally all around the world; environmental and fuel factors can be corrected for. All that is needed is for each builder to provide adequate information; if necessary, I volunteer to help normalise the data.

Piece of cake.

Scores for minimum and maximum sustainable thrust (throttleable range, in other words)... [etc., etc.]

IMO, the number of entrants will be in inverse proportion to the number of scores/classes/categories. "KISS" applies.

And, of course, the one *really* important measure: Which one is the loudest?

AGREED!

Under my proposed rules, section [5] ..."noise ordinances excepted (more noise more fun)"

Cheers!
M.

[Bruno Ogorelec]

Hello Simon,

[snip] ...perhaps best not to go poking at sores with a sharp stick, if you catch my drift.

Yes, you are right. I edited my post (above). FWIW, the wanker in question is not the innocent he pretends to be.
Cheers!
M.

I have now edited my own. Maybe I shouldn't have, given the language aimed at me but OK; I'll live.

[milisavljevic]

and now for something completely different...

malodorous haiku (in three parts)

moldy strawberries
tossed in the thames (by fairies)
"floating rarities"

high street grocers tell
of the rains that fell and fell
dear god! what's that smell?

(musical interlude)

violins are playin'
and yet, it keeps on rainin'
dead skunk in the bin.

(the end)

...

misdirected wodehouse

jeeves: "just in with the sunday times, sir: 'pulsejets contravene section 69 of the public decency act'."
wooster: "what! what's this world coming to if every tom... why?"
jeeves: "apparently, they...ahem... apparently, they... that is, pulsejets, they both... 'suck and blow'."
wooster: "well! of course pulsejets suck and blo... now hang on!"

wooster: "you're having a go at me."
jeeves: "yes, sir."
wooster: "may one ask why?"
jeeves: "one may, sir."

wooster: (sigh) "why?"
jeeves: "form, sir. i had to mention pulsejets at least once in this posting. a feeble attempt, i know."
wooster: "indeed!"

(the end)

gunports closed

[PyroJoe]

There should be a total volume size that corresponds closely with the 250 mls class.
Then we could use the water fill technique.

Every ? months we could double the volume and have a new challenge for a new class size.

[Mike Everman]

Hayzoos, M., quit with anything that smacks of name calling! Keep the gunports closed, or I'll have to exercise my godlike powers.
And, Haiku? After inviting Mark to go elsewhere?

[Graham C. Williams]

HA Ha. Seen a few of these in my time.
M. You posses a dark humour.
I'd only add: Perhaps make the Peak Volume 1.5L +or- 0.05L (easy to measure with water and allows the less able constructors to have a go)
( I only know 2 or 3 people (maybe a few more) that can make these motors to the very high tolerances some small designs need!)
While we're about it, why not specify that the volume be measured with water, it removes the problem of augmenters etc. (someone’s going to ask about the meniscus, Ha)
Graham.

[milisavljevic]

Hello Mike,

And, Haiku? After inviting Mark to go elsewhere?

LOL. As you know, the Haiku was a honeypot designed to lure a singular individual into revealing his presence.
And we have seen just how successful it was!

Btw., Mike has never heard of "Jeeves and Wooster" (and by inference, PG Wodehouse).
Bog save us from illiterate engineers!

Bet he's heard of "AskJeeves.com" (now "Ask.com"). And no Mike, you would never, ever, ask Bertie Wooster!

As I explained by phone, the "invitation to depart" was intended to dispatch Mark before his "camper-in-arms"
Bruno could arrive and set up a squat on this thread. You have seen firsthand that no thread long survives the
unholy pairing of these two individuals. You do remember the last time you began a thread about mini-kenny?!

What's more worthy of note is how many people have offered suggestions wrt. rules, and then contrast this to
the number of people who have offered to meet the challenge with a pulsejet. So far, the last group has as its
members: "Chaddly33" (by default); me (working with you); and (I hope!) you, entering your potent pocket jet.

At best then, that's THREE. And only TWO in the sense of people NOT "Chaddly33". Speaking of "suck & blow"!



And there are so many talented and CREATIVE builders out there! Maybe, some of them are looking at this the
wrong way... thinking "I can't win, so why bother?" I say, winning isn't the point; the point is this CHALLENGE!
Don't think on the volume (be it combustor or total...) build to any volume LESS than the maximum, or simply
dust off a qualifying puslejet that you're especially proud of. And we've all seen some interesting designs here.

Believe it or not, I will NOT be entering to win. I will enter because I have a new pulsejet in the pipeline which
fits neatly into the challenge, and as long as it runs as expected (performance metrics), I will be happy with it.

If you're out there reading this, and are at least considering building a pulsejet for this challenge: PLEASE DO!

Cheerleading is such a drag; writing Haiku is so much more fun. Now, where are all those moldy strawberries?

Cheers!
M.

[milisavljevic]

Hello Graham,

M. You posses a dark humour.

Guilty as charged.

I'd only add: Perhaps make the Peak Volume 1.5L +or- 0.05L ...

That's fine by me. Much larger than the Chinese as drawn by Laird (1.18 liters), but makes it easier...so why not?

As I suggested in my post above, I don't think the "idea" is that builders should sweat the volume restriction, but
look at it as a "do not exceed". To (re)paraphrase the challenge..."Build (the loudest and) most powerful pulsejet
you can, without going (much) beyond this total volume, as measured by filling your pulsejet with water." Simple.

The little pulsejet that I'm working on now, with Mike, is about HALF the volume you've suggested, with a target
thrust of not less than 20 N (4.5 lbf). I'm not going to divert to a larger design just because the rules allow... Or?

(maybe I need a second engine, and a second builder too... now hang on!)

A second engine would eat into my time for Haiku... Decisions, decisions!

Cheers!
M.