42Labs/Cotrill FWE Hyperpulse MK I

[Eric]

Congratulations, thats freaking spectacular! :)

With the intake insert can you play around with the length to further tune it, and maybe try a full length chinese layout? :)

Eric

[Irvine.J]

This is how I made the "Double D" injector...
It really is excellent and quick to make. The difference in mixing and starting was instantly noticable. I could achieve max throttle range easily before it started to drop in frequency after peak thrust is reached. It didn't just flame out without warning like a straight tube would normally do. For 30 seconds of work, I will use it for almost all of linear pulsejets from now on. Make sure you file that centre bit to a "V" facing the flow.
Great stuff.

[Rossco]

Thanx again James, another great day of sweat and fumes.

I am witness to this event, and am without a doubt that we have cracked the 4.5 Lbs mark. Happy indeed.

The video that i should have! If only i had a camera handy for James' victory dance!

Theres still more to be had there!
Larry, we are starting to crack the code of that centre chaimber. Tuning is proving to be rather head screwing, but we are getting there.

As far as we have gone, it only needs a few changes to suit this tail.

Rossco

[larry cottrill]

Rossco -

Yes, I think the main problem right now is that the location of the choke cone is way too far forward, because of the lengthening of the engine as a whole. The location (and to some degree the size and angle) of this element is absolutely critical to getting optimum pressurization. The more you work with it to optimize it, the less it will resemble the classic Chinese and the closer it will resemble a Lady Anne re-scale.

In my opinion, there is nothing "magic" about the Chinese engine rear end. The designer found that performance was improved by expanding out from a straight tailpipe to heavy up the tail piston, and got some wave shaping in the bargain. That's about all there is to it, I think. Of course, others are welcome to challenge this. The classic Chinese is a very good engine - but it's not some "ultimate" performance standard. It's a good standard for comparison just because a lot of them have been built, and people are familiar with them. Same with the Lockwood, of course.

L Cottrill

[larry cottrill]

Larry, we are starting to crack the code of that centre chaimber. Tuning is proving to be rather head screwing, but we are getting there.

Rossco & James -

It would be easy to make too much of the middle/choke cone set as a "chamber". The real design goal is to position the choke cone optimally as a wave reflector, so that pressure swings at the front end are fully developed. That's why its exact position is an important element of tuning.

All that being said, of course it creates some extra volume in the middle of the engine, which can also help pressurization and Kadenacy action (which generally benefits from increases in volume). However, I still feel it is mostly a way to position the choke cone to reflect back part of the pressure wave into the chamber at the opportune moment. The effect of altrering the position (and size) of this little cone is huge.

L Cottrill

[Graham C. Williams]

However, I still feel it is mostly a way to position the choke cone to reflect back part of the pressure wave into the chamber at the opportune moment. The effect of altrering the position (and size) of this little cone is huge.

L Cottrill

Yes absolutely Larry.
The Nudis model shows that happening. The effect is to change the gas flow and push the CofCombustion back up the motor at a time when the gas flow would normally have moved combustion into the tailpipe. It's as if the whole motor is a lot longer than it is. As you appreciate the timing of this event is crucial.
The other important effect is much earlier in the cycle. A (relatively) massive shock is formed at the two constriction points. This induces a rapid and early induction event (and possibly early combustion initiation).

Graham.

[Irvine.J]

I have spent an accumulative many months building these prototypes, studying the different effects of small changes on the Lady Anne engines and NUDiS. I have experienced a massive learning curve in regards to both. In the last month I've probably spent atleast 4 hours a day in my own time tweaking, changing and studying data presented to me by Nudis, and for that Graham I applaud your work on the program. I will try to put this all into words as I've thought about it so much, I'll write what I can...

I had already ascertained by looking at the wave data that the choke cone was acting as a reflector, but I am confident that its direct and most important relationship is with the combustion chamber and inlet, not the overall length of the engine. Changing its angle or its position in the pipe without taking into account that the reflected wave has more distance to travel, changes in gas temp, reflected angles etc, I ascertained that small movements will actually stop the engine from breathing at all. As Graham stated the timing is CRUCIAL, and I would suggest that its position, angle, and distance from the CC should be tuned to the CC and the inlet far and above a change to the overall length of the engine. I believe this theory is supported by the HPX Mk I running so well even though it’s overall length is considerably greater then the Anne. Though, I spent many many sleepless nights having to tweak the center cylinder section to the right length and D to fully act in symbiosis with reflector/choke cone.

I could clearly see that the reflector was changing the peak of the pressure wave at every second interval on Nudis. From this I was uncertain if we were looking at the effect of the return wave or if the reflector cone was ever so slightly in need of further tuning or if that small depression in the second wave was a visual representation of the desired result. Is it possible this is what you were referring to when you said…
“A (relatively) massive shock is formed at the two constriction points. This induces a rapid and early induction event (and possibly early combustion initiation).â€

[James D]

Excellent work James, I look forward to seeing your future developments.

[larry cottrill]

This is how I made the "Double D" injector...
It really is excellent and quick to make. The difference in mixing and starting was instantly noticable. I could achieve max throttle range easily before it started to drop in frequency after peak thrust is reached. It didn't just flame out without warning like a straight tube would normally do. For 30 seconds of work, I will use it for almost all of linear pulsejets from now on. Make sure you file that centre bit to a "V" facing the flow.
Great stuff.

James -

Do you feel this works significantly better than the pinched lemniscate nozzle? On the surface, they would seem to accomplish about the same thing; I realize the lemniscate is more restrictive, of course, meaning more flow velocity and "back pressure".

Your design is very nice, but not as easy to make, esp. for beginners. If performance is markedly better, an item for the "advanced course", maybe ;-)

L Cottrill

[larry cottrill]

Excellent work James, I look forward to seeing your future developments.

Yes it is!

James I -

Sorry - I should have tried to understand better what you were doing before trying to critique it. Obviously, for a project like yours, the key is to get what works best - nothing short of that will do, and you have every right to do whatever it takes, no matter how radical it seems.

Since this is still based on the FWE chamber, do you want me to include it in the 'FWE Evolution' drawing, with you shown as the designer? I'd be happy to do that (I think it's historically accurate), but of course, that would reveal your dimensions, which you may not be ready to do yet. I only ask because I'm about ready to tack on the Lady Jane Grey engine that Vern just got running.

L Cottrill

[larry cottrill]

I had already ascertained by looking at the wave data that the choke cone was acting as a reflector, but I am confident that its direct and most important relationship is with the combustion chamber and inlet, not the overall length of the engine. Changing its angle or its position in the pipe without taking into account that the reflected wave has more distance to travel, changes in gas temp, reflected angles etc, I ascertained that small movements will actually stop the engine from breathing at all. As Graham stated the timing is CRUCIAL, and I would suggest that its position, angle, and distance from the CC should be tuned to the CC and the inlet far and above a change to the overall length of the engine.

That is all true. However, it implies (probably without intention) that the relationship between the combustion chamber and mid-section is sort of "independent" of the rest of the geometry. My point is that this cannot be so. The way the chamber behaves, and particularly its pressure rise after the evacuation of the blast mass, will itself be affected by the overall length (and other geometric factors). The only way this would not be true would be if something behind it totally isolated it from the tail end phenomena (some kind of "wave blocking"?) - or else the tail impedance was so incredibly high that the front end is simply oscillating on its own. Part of the reason you're getting the results you describe is that you have developed a geometry where I would think of the combustion chamber as "undersized" (like the Chinese and even some of the Thermojet variations). I am NOT saying this is "wrong" or anything - just that it naturally affects what you do to perfect the rest of the design. There is no part (or combination of parts) of a valveless pulsejet that operates without influence from the rest.

Larry I ran and experimented with different reflector cone lengths and D's before our private conversation, however the data I had deduced from those earlier experiments at the beginning of making the HPX showed that moving the reflector back did not coincide with induction and completely destroyed the resonance between combustion from the CC and the return cycle. Simply, the distance that the reflector cone put forward is not taking into account we have not moved or changed the CC or inlet pipe D's or gas temps and hence the speed of the wave through that long narrow section was markedly different. The induction time and speed at which the wave is moving is now not in sync due to changes in gas temps, wall temps and the timing throws huge drops in pressure as it’s out of sync with the breathing cycle. This was limitedly quantified by several nudis runs but real life is still very different again. In some test it didn't seem to breathe once or power was significantly reduced.

This is the part I didn't appreciate earlier. Of course, I was naturally not privy to much of this work as it went along.

I believe I can comfortably say without offending you Larry in any way as I believe we are very good friends…

But, of course.

The HPX definitely makes the engine far happier to accept small changes in fuel and air mix whilst using a single intake. There is also no comparison between the HPX's tail section and the Chinese.

We noticed the engine with the original intake was running hot, so I fixed it with careful considerations and changes which worked exactly as calculated. It's exactly tuned to specific lengths (and now we have the final tweak complete its showing even more power at the same length) and its volumes, angles, lengths and diameter do NOT resemble the classic Chinese at all, I just thought I should get that out there.

I will concede this point, having already admitted to jumping to conclusions too quickly.

Although, as it stands, its one hell of a good engine; it’s stable, powerful, and shorter then the -standard- Chinese. Correct me if I’m wrong, but I was under the impression that it was what we were after, a smaller, lighter and equally powerful competitor to the standard Chinese (as a benchmark) with all the throttling stability characteristics?
This was achieved without the final tweaks.

Exactly. What you MUST have is what works the best in terms of your project goals. It is entirely possible that the Lady Anne (and its re-scaled daughters) will only be fully suitable for simple applications where throttling is not a big issue (e.g. U-control sport model aircraft). However, I am not conceding this yet, just admitting that I accept it as a possibility.

Anyway the engine is up for further testing or verification for people with serious and accurate thrust test stands ... I would more then anything like it to be thought of as an alternative to the standard Chinese for a flight engine. Simply it’s shorter, lighter and equal and possibly a tad more powerful, (or possibly –decidedly- with the latest and final tweak) with equal stability and throttle control.

That seems to be a reasonable expectation. I really don't remember what claims are made about the Chinese in terms of throttleability, just always assumed it was pretty good because the engine is generally considered a successful design.

Larry for your commitment to me to see me succeed, helping me and filling my head with all kinds of information, for trusting me with your designs… I cannot thank you enough. Your help and insight over the past year have been extremely important to my intellectual development with all aspects of pulsejets and for that I will remain eternally grateful. Your openness and willingness to help are unsurpassed and it’s a true measure of a man’s character that you persevere with those who seek help and information. At risk of sounding too soppy, you are a very good man.

Thank you, James, all that is deeply appreciated. One should not be too quick to accept the title of "good", however:
"Why do you call me good?" Jesus answered. No one is good -- except God alone." - Luke 18:19 NIV

I think Graham is one of those rare people that, with gentleness, patience and courtesy, can show you how the "impossible" can be achieved quite reasonably once you become willing to change the way you think about it.

L Cottrill

[Vermin]

To all on this thread
Great stuff, and remember......if the mountain won't come to you.... then you must go to the mountain.

[Irvine.J]

Attached are some photo's of my first attempt with stainless. I do have a TIG now, but I simply can't go past the gasless mig, turns out I can weld stainless with it...awesome...
Anyway, this is the MK-II, small change in 1 spot from the original, I'll give it a test run tomorrow, but my thrust stand is completely destroyed now, so no readings as yet.

This is the part I didn't appreciate earlier. Of course, I was naturally not privy to much of this work as it went along.

Yeah sorry about not filling you in on all the details, I got the impression you were quite busy with a bunch of stuff and went with some gut feelings, and tried a variety of things very similar to your suggestions. I'll fill you in with an email the length of War and Peace about it shortly.

Thank you, James, all that is deeply appreciated. One should not be too quick to accept the title of "good", however:
"Why do you call me good?" Jesus answered. No one is good -- except God alone." - Luke 18:19 NIV

You know there is such a thing as too humble :-P

Well, as a first attempt I'm quite happy with this, I think i'll have it even nicer next time around, now I know what to expect with the stainless. In .5mm, brush finish, it weighs in at 450 grams. Will looks sweet with a polish... Nice.

[Rossco]

Hey James,
Very nice! Ill come over and help with the polishing, then we can turn it all black!

Ive just about got mine polished up now, so time to take some photos, stick the bigger tail on and set it up on a thrust stand.

I will draw up a couple of the thrust stands i keep talking about, and we shall get in and build one.

Good work there. That tig has to be better than we are getting atm.
Maybe we could talk to Al about a good place to start with learning the real way to use it.
You about still Al??? or anyone, we are (meaning me) making a right mess of tig welding. I have done a lot of oxy welding, so i thought that the tig would be the holy grale! I suck tho!

Rossco

[larry cottrill]

James, that is a beautiful piece of work. What's more impressive to me, though, is the "450 grams" part - well UNDER ONE POUND! This is exactly the kind of thing we're after. Well done, man!

Do you have any plan to experiment with liquid fueling?

L Cottrill