tripwire?

[satamax]

Hi everybody.

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I have modified the core i have in my head. One question, is it worth cutting the feed tube to burn tunel, and heat riser first piece after the burn tunel a bit below the ceiling of the burn tunel to make a kind of tripwire? May be just one of thoses?

Thanks a lot.

Max.

[peterberg]

Max,

A trip wire at the end of the tunnel won't be doing much good. At the start of it, just maybe. So you could make the opening in the feed part at the top a bit lower as compared to the tunnel height.

The parts of the J-tube you've drawn are a bit out of proportion, though. The best method I've come across is doing the measurement in the heart of the complete J-tube. So the feed is measured from the top down to halfway height of the tunnel. The tunnel from the heart of the feed to the middle of the riser, and the riser from halfway the height of the tunnel to the top. The proportions in downstream direction would be 1:2:4 for the length of feed, tunnel and riser using this method. Start with the tunnel length, preferably as short as possible and size the rest according to that.

Just a suggestion: try to make a ramp at the back of the heat riser while maintaining the same cross section area at the spot. Can be done with a mix of vermiculite and clay, the effect is eliminating a low pressure zone and a counter measure to the collection of ash there.

[satamax]

Hi Peter.

Thanks a lot for your reply. I thought i remembered you saying that at the end of the burn tunel it wasn't much good. But re reading through the whole thread got me lost. Well, i read it late, two days ago. If i understand well, you're saying that i could drop the height of the tube a little bit at the begining of the burn tunel, to create a bit of turbulence, with the P chanel droping a smidge below that. Those two creating may be a depression, sucking more fresh air at that spot.

About the dimensions, you're saying that the burn tunel should be longer than the feed tube?

I have, acording to your system of measurement

Feed tube, 39cm
burn tunel 40cm (that is if by the heart of the feed tube, you mean the middle?)
Heat riser, 89cm.

If your 1/2/4 is right i should aim for

20cm to the mid point feed tube, plus the 11cm at the bottom to finish the tube.
18cm for the burn tunel tube + the two wall thicknesses and reach to the mid point equaling 40cm.
160cm for the heat riser + 11cm from mid point to the bottom.

I always thought it was 2/1/4 or something like this. Burn tunel being the shortest part.

Because, if calculated by "tube lengh" i was not far. 50cm feed, 22cm burn tunel, 100cm heat riser.

I noticed the rocket i have in the workshop works far better since i have added the offcut of one of thoses tubes to the feed, making it longer.

Thanks again.

Max.

[peterberg]

Max,

The trip wire and the p-channel that close to each other won't work. I would say, use a trip wire implemented as said or a p-channel, not both. The last one would be the better option probably.

As for the dimensions: when the tunnel is measured from the heart (= middle) of the riser to the heart of the feed tube you'll get 40 cm. So, following that, you'll get 20 cm feed tube length from top to halfway down the tunnel. The riser should measure 80 cm from the top to halfway tunnel again. To resume: feed:tunnel:riser equals 20:40:80 cm using this method.

Correcting this for your parts arrangement that would be 31 cm for the feed, 18 cm for the tunnel and 91 cm for the riser. The tunnel piece is the shortest by far, that's correct. I do prefer the above method because it will eliminate the differences between several arrangements people could use.

[satamax]

Ok Peter. I got it. So P chanel it will be. But sorry, i'll stick to my measurements. Not that i don't trust you. But i've had short feed before, and find theses very anoying. Frankly, 31cm, top to botom is too short for me.