Mike's Build Log

Moderator: Mike Everman

Sebastian LFT
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Re: Mike's Build Log

Post by Sebastian LFT » Wed Apr 15, 2009 1:16 pm

Ahkinxe tentay nemukem kenchimokan!! (most excellent fire pulse horn!!)
You'll never know 'till you try it.

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Re: Mike's Build Log

Post by Kool » Wed Apr 15, 2009 1:30 pm

Wow, that one looks very amazing 8)
I am looking forward to the results
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Re: Mike's Build Log

Post by Mike Everman » Wed Apr 15, 2009 1:33 pm

Thanks, guys! Yeah, M., I'm trying to step up my build log detail. I've been inspired by Ash's build log, and some of the ones over at the GTBA.

If I finish it up this morning before work, I can hopefully make a test run this afternoon. Much to do before I leave, though.

Nick's got a site for us to run motors in the vicinity of Gloucestershire on Monday. Anyone that wants to come, please PM me and I'll send a google earth location.
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Re: Mike's Build Log

Post by Johansson » Wed Apr 15, 2009 4:29 pm

That is the best looking engine I´ve ever seen, it is almost a shame to run it. Some polishing and clear paint and it would make a nice bookshelf sculpture.

Just kidding, can´t wait to see how it runs! :D

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Re: Mike's Build Log

Post by Mike Everman » Wed Apr 15, 2009 5:27 pm

Thanks, Anders.
I got the fuel and spark plug on it. It's ready for test this afternoon. Couple of places the TIG guy couldn't get at, so I had to hamburger it with my torch. Still looks good though. I can't wait for running it either. 6 hours and counting...
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Re: Mike's Build Log

Post by Mike Everman » Thu Apr 16, 2009 5:00 am

She runs orange hot!
...but when I went out with 30 minutes available to run it before going to the UK, all I had were empty tanks! One was up to a couple runs, but I sure couldn't get it over fueled. You'll like this vid. I did not notice the clamp undoing itself!
Attachments
triple jumps off bench, first run.wmv
(1.88 MiB) Downloaded 4358 times
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Re: Mike's Build Log

Post by Mike Everman » Thu Apr 16, 2009 5:09 am

Run 2 with thrust gage, you can see it crest to 5.9 lb then plummet on low fuel. 270 Hz, exactly like it's 1/3 parent!
Video notes:
The color was not yellow like that to my eye. Something with my camera. It was orange all over. Still learning the settings on this thing.
Likewise the autofocus is screwy for the movie. don't know why, but I'm going to figure out how to switch it to manual at least.
Attachments
triple run2 with thrust gage, 270 hz, empty propane tank.wmv
(1.87 MiB) Downloaded 4355 times
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Re: Mike's Build Log

Post by Johansson » Thu Apr 16, 2009 5:35 am

Great work Mike!

It ran colder on the right exhaust in the last video, was it because the engine was tilted somewhat?

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Re: Mike's Build Log

Post by Irvine.J » Thu Apr 16, 2009 8:16 am

Absolutely wonderful Mike! Yes the far engine does seem to run a little cooler, I think its due to his near empty tanks more then anything though. Wasn't much coming out the exhausts yet so I will be surprised if he doesn't near double that 5.9 figure. Wonderful work Mike, she's an absolute beauty. Starts easy too!
If you can find something to give it a really dark (black sheet) background will help see those tail plumes easier, I think your on a winner.
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Congratulations, Mike!

Post by milisavljevic » Thu Apr 16, 2009 12:30 pm

.
:D Congratulations, Mike! :D
Mike Everman wrote:You can see it crest to 5.9 lb.
I phoned Mike yesterday afternoon, moments after he concluded the test runs of his 3x pocket jet.
When he first mentioned his thrust measurement (above), I was surprised: like many folks here, I
naively assumed that this beautiful piece of work would punch out 3x the thrust of the original jet.

Then I remembered that multiple branches scale down in the general pulsejet equation: a 3-in-1 is
not the same as 3 equal copies, and 10.5 lbf of thrust (46.5 N) was never in the cards for this unit.

I offered to suss it out and to report back my results. Later that evening I left Mike voice mail and
told him that the simplest interpretation of the 3x combustor would peg maximum thrust between
6.0-6.1 lbf (27 N). I also said my result was probably an underestimate and that I would look closer.

As of this writing, I stand by a range of 6.0-6.1 lbf as the most probable thrust ceiling; however, I
offer an alternative Cronje limited evaluation that raises the ceiling to between 6.7-6.9 lbf (30 N).

I hope that Mike is able to settle this while visiting with Graham and Nick.*

Mike Everman wrote:[It resonates at] 270 Hz, exactly like it's 1/3 parent!
As Mike will know from many previous conversations, this is no surprise. As the 3x pocket jet is a
near-perfect bidirectional trifurcation of his original pocket jet, the special Helmholtz equation for
pulsejets will yield the same resonance frequency. Thank you Mike, for being the one to validate it!


With respect to the observations of asymmetric heating in the combustor:

As far as the three pairs of intakes and exhausts go, they are not equals: the central pair services
ca. 25-30% more volume than either side pair and consequently develops more thrust. This is over
enforced by Cronje saturation of the side pairs (ie., decreasing combustor radius in the y-z plane).

This does not discount the stack effect stemming from the orientation of the pulsejet on its stand.


This is a foundation piece of work by Mike and in my mind a major contribution to the community.
Thanks Mike, and I wish you a safe, productive and enjoyable trip to ol' Blighty! Have a warm pint. :D

Cheers,
M.

*The higher thrust range is the more (technically) interesting result.
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Re: Mike's Build Log

Post by Mark » Thu Apr 16, 2009 12:53 pm

I wonder if you made an engine with say eight tubes, same single chamber and all, if it would tend to flip-flop/recognize the oval combustion chamber in a different light? That is, would it attempt to delegate one side/end to more intaking and the far side to exhausting rather than working as a straight cluster all going uniformly? Funny how that one exhaust decided to let the other two fire off more of the activity.
I think one thing about odd shapes like ovals is that the combustion can be more erratic or the variation in reflective surfaces allows for more variables than the typical confined symmetry of a cylinder. Neat stuff and happy Zamfiring. ha
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Re: Mike's Build Log

Post by larry cottrill » Thu Apr 16, 2009 1:14 pm

CONGRATULATIONS! Seems like I'm always "amazed" by something or other, but this is certainly a worthy beast to be amazed by.

M -
Very interesting observations about the layout, and its effects on flow distribution and power. I would have guessed that the overall behavior would bring about the same frequency (since Mike was very careful about the dimensions), but I would never have suspected such predominance of the center, in terms of flow and combustion action.

L Cottrill

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Re: Mike's Build Log

Post by PyroJoe » Thu Apr 16, 2009 1:31 pm

Great Work!
I would like to see this thing run on a full, peppy fresh tank. Man, what a engine. I have a hunch that the lower cylinder would glow more evenly if the motor were mounted more horizontal. Strange how the flame will migrate to the highest point in many engine CCs, not sure if thats is happening with this one but it looks it.
Joe

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Re: Mike's Build Log

Post by Mike Everman » Thu Apr 16, 2009 1:59 pm

Thanks all, guys!
Yeah, I think it's just convection. I need a better hold down method, but was in a hurry!
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Re: Mike's Build Log

Post by m1tch » Wed Aug 26, 2009 9:15 pm

Thats a really amazing build, just read this thread though from the beginning and its amazing to see the evolution! Well done mate!! Makes me want to try and make one lol

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