Another pulsejet kick from Sweden

[erik]

I was persuaded by Johansson and his team members to also build a jet powered kick and participate in the race.
The valveless Lockwood engine i build a few years ago wasn't good enough and i always wanted to build a big valved pulse-jet so the decision to build a valved engine wasn't that hard.
I started with Eric's pulse-jet calculator but then i also was inspired by some other designs, including a design Johansson made a few years ago.
Can someone please make a sanity check of the design to see if i messed something up.?
Here is a few pictures of the build so far, i started building for almost exactly one week ago.

[metiz]

well looking at your build quality alone I'd say this thing is going to scream! sweat build quality

[WebPilot]

Erik,

I am in with your valve grid assembly, or at the very least, "in serious like". Using plates, I guess for valves?

• What is your flow area ratio and
• what is the valve cantilevered natural frequency?

Nice friggin' work.

NOTE: Using my circular rule (below is from a prior post), I estimate a 6" exhaust diameter may possibly develop 110 lbf thrust. Is that enough to beat Joha ?

[metiz]

Webpilot: you sure love that scale don't you

[WebPilot]

 
 I find it has become quite a "handy" tool for me to have around. I'm so glad I spent the time to develop it.

[erik]

Thanks for you comments.

What is your flow area ratio?

I hope you can forgive me, but i have been away from pulse jets for a few years and haven't caught up with everything yet.
What dimensions do you need?

what is the valve cantilevered natural frequency?

I don't have the valves yet, but the piece of 0.1mm (0.004 in) brass in the same size have a frequency of around 45Hz when i record the sound.
The valves will be made of thicker steel so i believe they will have a much higher frequency.

I am planing the fuel system at the moment, If i am not wrong the rule of thumb is around 2.5 lbs fuel/lb thrust/hour and that give me around 275 lbs/h.
Gasoline weights around 6.073 lb/US gal with gives around 45gal/h.
Does it sounds like a good idea to use a few oil-burner nozzles with at total flow of over 45 gal/h, for example 6x 8gal/h nozzles?

[WebPilot]

Hi Erik,

I apologize for letting my curiosity get the better of me.

How did you "lock in" to this size of a valve grid? The pictures are great but I don't see how you can add to it if you need more inflow. Reduction is EZ PZ. Great work and we're gonna have to make it work.

I suppose you have enough room to alter the clamp length or width for each valve in order to adjust frequency, eh?

... I estimate a 6" exhaust diameter may possibly develop 110 lbf thrust. Is that enough to beat Joha ?

Absolutely incredible work on your part!

[Hydrazine]

Wow! Excellent work.

[PyroJoe]

No sanity check needed for that one, beautiful work!

[Johansson]

Hi erik!

As I´ve said before, great work! I hope that everything goes smoothly with the project since you are following a very tight schedual, the race is only three weeks from now so there is not much room for trouble shooting...

The drawings I sent erik were of an upgraded but never built version of my old 100 pounder, the "project thread" where the valve area and such are discussed is found here: viewtopic.php?f=2&t=1574&start=15&st=0&sk=t&sd=a

[Mike Everman]

Very nice build so far!

[erik]

Yesterday i did some work on the venturi section and i think it did come out pretty good.
Today i am going to start constructing the fuel system, i was thinking of using four 13.5gal/h and one 10gal/h oil-burner nozzles connected to two fuel pumps.
With 2x 13.5gal nozzles on one pump and 2x 13.5gal + 1x10gal on the other i could use one pump for idle and then start the other for full power, that would give me a total around 45gal/h with 5 bar fuel pressure .
I am planing to inject all the fuel in the intake before the reds, does that sounds like a viable option or is it better to inject half or even all the fuel directly into the CC ?

[erik]

This evening i made some parts for the fuel system , i am going to have two tubes with three nozzles on each one and not six nozzles on one tube.
Any comments?

Hi Erik,
I suppose you have enough room to alter the clamp length or width for each valve in order to adjust frequency, eh?

Yes i think i can alter the clamping dimensions if needed. Do you have any suggestions for what dimensions and thickness of the reds would be the best for this motor?
I attached a drawing of the valve-grid so you can see the dimensions.

[WebPilot]

Hallo Erik,

It really is a matter of what material thickness is available to you. I have written a very good Excel spreadsheet for predicting the frequencies for such cantilevered valve plates.

Can you recreate the Kadenacy effect in the tube w/o the valve grid attached?

Perhaps close/block off the valved end, inject the cc with some fuel, ignite it and make it go "bang" one time? Naturally, record the resulting noise with a cell or good vid cam to a .wav file.

[erik]

Thanks, i will try to do that,
My biggest concern for the moment is time because the race is in less then 3 weeks... (25-27 March)