Mike's Build Log

Mark · Post by **Mark** » Wed Dec 12, 2007 6:24 am

[quote="Mike Everman"]Mark, it's 16.6 fluid oz. (30 cu.in.)

I just figured out the Dynajet's 20 fluid ounces is just a whisker over 36 cubic inches, about the size of a grapefruit off my tree or so. ha

Graham C. Williams · Post by **Graham C. Williams** » Thu Dec 13, 2007 12:58 am

Dear Mike.
3+ Lbs from that petit thing? I can only think you've got something right. (I know it's the culmination of a lot of work.) As the motor becomes more unsteady the internal momentum part of the Thrust equation will come to dominate.

Best Regards.
Graham.

Irvine.J · Post by **Irvine.J** » Thu Dec 13, 2007 1:04 am

Dear Graham,
Sorry I seem to be online same time as you, but this is a very interesting comment and heres why.

On the Raptor, when we were moving the fuel line in and out at 5mm at a time, we found right as the Double d approached the elbow of the intake, at about 10mm back from the weld, the engine seemed to "Cough" occasionally, maybe once every 5 seconds, however, it was when we were reading the max thrust values! We took it out to 15mm from the weld and it was back to its normal stable self, with a loss in maybe 0.15lbs or so, it was very little. I would say just from you comment and recalling that observation, co-incidence perhaps? Seems pretty good to me.

Graham C. Williams · Post by **Graham C. Williams** » Thu Dec 13, 2007 1:12 am

Dear James.
No problems mate. Interesting observation. Are you saying, nice steady running may not produce the most Thrust? If so I might agree.

Sleep well for me. Have a good day for you.
Seasons Greetings and Regards
Graham.

Graham C. Williams · Post by **Graham C. Williams** » Thu Dec 13, 2007 1:14 am

Hmm. I seem to be stuck on 455 posts.

Not a problem. I like the idea of only speaking when I've got something to say!!!

Graham.

Post by **Mike Everman** » Thu Dec 13, 2007 5:59 am

Graham,
thanks, and best to you and yours for the holidays!

Jutte · Post by **Jutte** » Thu Dec 13, 2007 9:25 am

Hi James,
Just a quick question about the Raptor 'Coughing'.
After the 'cough' was there a split second pause in the usual
pulsation of the engine and then back to normal ...or was it constant pulsation with the 'cough' just a split second increase of noise and thrust?
I think this might somehow be important to warrant a bit of further study-
perhaps the Raptor was trying/momentarily to achieve/lock onto a
high resonance state(?). Or perhaps something else entirely ( or not !)
So many questions and so little steel!!!

Post by **Mike Everman** » Sat Dec 15, 2007 3:38 pm

I think I've got to cut pocky and put the expansive tail on. I've got to have apples to apples on the combustor. Since the expansion needs to start somewhere in the u-bend, I managed to slice and flare a 90 as a start. Time to get rolling and welding!
I tested again and got 3 lb last night. Cold here (for Santa Barbara), so fuel pressure was low. I couldn't flame it out. This combustor sure can take a lot of fuel!
Here is also a low res video of starting and running again, just for the hell of it.

Eric · Post by **Eric** » Sat Dec 15, 2007 7:43 pm

Hhahahahahahaha.... Hope you were able to pack up before the cops got there

Eric

Post by **Mike Everman** » Sun Dec 16, 2007 2:04 am

I did seriously wonder if they were coming for me! ha ha

Post by **Mike Everman** » Sun Dec 16, 2007 5:05 am

Just finished the expando tail for pocky2, and burned the *&^"$# out of my hand trying to finish in a hurry.
I may have to run out to the shop right now! I can't wait to try it.

I was going to make a whole new one and leave this 3.3 lb combustor alone, but oh well, I'm feeling my oats, I guess!

Eric · Post by **Eric** » Sun Dec 16, 2007 5:35 am

Wow that tail expansion looks really fat. Cant wait to see how it runs.

Eric

Post by **Mike Everman** » Sun Dec 16, 2007 8:18 am

...or how it doesn't run. ;-)

I ran out to the shop to run it for a few minutes, as it's a bit late, but hey, if someone lives in a house by the airport, they're in for some random noise! No sirens this time. Again, very cold out for around here, so low fuel pressure.

On reflection, I see that I tried a far too aggressive expansion. I'll put one of the start attempt vids. Interesting stuff on the blowtorch. sometimes the torch jet would just hug the wall. cool, but dissapointing. I'll put a proper expansion on there and give it a go tomorrow.

My worst day pulse-jetting is still a good day!

Post by **Mike Everman** » Sun Dec 16, 2007 8:24 am

The first bit on this run sounded promising, but then it was mostly blowtorch city. I got some almost-starts with quickly cranking the fuel full when the tail torch advanced inside the tail. I had time for only one change of intake length, adding about an inch, which is this vid.

Irvine.J · Post by **Irvine.J** » Sun Dec 16, 2007 2:09 pm

Mike just a quick experiment before you go cutting, I would be interested to see what happens if you quickly formed a cylinder, about 3/4 or just under 3/4 D of the current D of that tailpipe, and slid it in as far and as solid a connection as you could make... maybe hold it with 4 wooden (or metal whatever) chocks just to hold it in place, at least it might give an initial indication if it was expansion D or angle that it might be having trouble with. What do you think of that? Might save some work down the track possibly? I used to have all kinds of fun doing that and if you let it out a few mm sometimes you would get the most whacky tailpipe flame...

Anyway, I love it, its a sweet little engine, the tinkering is always exciting

Goodluck and looking forward to more videos!

www.pulse-jets.com

Mike's Build Log

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pocky update

pocky gets it's expando tail