Another pulsejet kick from Sweden

erik · Post by **erik** » Tue Mar 09, 2010 10:54 am

I realise that i need to order the matterial today if i am going make the deadline.
I can order 0,2-0,25-0,3-0,4 mm of stainless springsteel.
I was thinking 0.3mm thick and 38mm wide.

erik · Post by **erik** » Tue Mar 09, 2010 11:18 pm

Because of the little time available i gambled and ordered the valves in 0.3mm stainless springsteel and hopefully it will work.
If someone think that it wont work or something like that it may still be possible to change the matterial if i call early tomorrow.

WebPilot · Post by **WebPilot** » Wed Mar 10, 2010 12:37 am

Maximum valve free length after the clamp plate?

erik · Post by **erik** » Wed Mar 10, 2010 1:01 am

36-37.5mm

Edit: The Solar PJ32 pulse-jet engine seems to use 0.010 in (0.254mm) reeds.
"The reed valves are
fabricated from 0.010 in.-thick blue-
tempered spring steel and bent
approximately 15°."
http://hv4all.com/pulsejet/ny/AIAA-2005-0228.pdf

WebPilot · Post by **WebPilot** » Wed Mar 10, 2010 1:17 am

Erik,

Check back here in an hour. It is presently, 01:20 UT

Have you picked a name for your machine?

Hmmm, this is not so good to read

Because of the high temperatures and impact forces experienced by the valves during operation, the valves tended to only last 10-15 min before requiring replacement.

WebPilot · Post by **WebPilot** » Wed Mar 10, 2010 2:34 am

Erik,

Check back here first thing in the morning (your time). It is presently, 02:42a UT

I'm going to need some more time to check my work and advance it further.

WebPilot · Post by **WebPilot** » Wed Mar 10, 2010 5:44 am

Erik,

I've computed for your pj (here, I have assumed NO tail flare, just a cylindrical straight-through section there)

total volume is 2721.93 in³ (44.604 ℓ)
total length is 78.82 in (2.002 m)
estimated (driving) resonant freq is 83.72 Hz ( ±5%)

From my spreadsheet I calculate for a 0.3mm thick, 38mm wide and 36 mm long valve a fundamental of 200.3 Hz.

I compute a dfr of 83.72/200.3 = 0.418 which is already close to 0.431 . You'll have to make the valve clamp plates a little less wide to lengthen the effective valve length, but ... according to my numbers ...

"Stay the course", Erik!

erik · Post by **erik** » Wed Mar 10, 2010 12:15 pm

Thank you, i am really glad that you could help of with the calculations. And i am also glad that my choice of matterial thickness wasnt that far off.
This evening i am planing to make the intake cone but i cant find any information how to calculate the dimensions.
How important is the dimensions of the intake?

Edit: I forgot to ask if you think i will need to limit valve travell and if so, how much?

Eric · Post by **Eric** » Wed Mar 10, 2010 6:12 pm

With the intake stack on, and no valves in place, the engine should also go into resonance with a tuning fork, oddly enough without the valves and at room temperature the engine will resonate at about the mid range of its operational frequency.