Any Input?

[rogers236]

I just became interested in valveless pulsejets recently, and drew up an idea for one; I was wondering if anyone could give me their input or opinion as to whether it may work before I try to build it.
The first Image I drew up with proportional measurements, the second is (or was when I drew it) in proportion with x=.25in - exhaust pipe not drawn - because I can't find my metric rule.




Comments Please?

[Ghrey]

Just off hand ( in complete dimensions to work with and all, I just could be missing something on that score { yup I see now 2x I am blind } ), and having given Lots of time for others to post...

It looks compression challenged to me. Tuning the intake and exhaust against the damper of an open front, I just do not see a good out come.

It should be noted that I have been wrong many times in the past...

You seem to be attempting some sort of hybrid but from what I see it is neither fish nor fowl.

And again I say: It should be noted that I have been wrong many times in the past...

I do hate to discourage you from the pursuit of sound and fury, but better an honest response is my thought, and hope you continue.

All the best.

[Jutte]

OK - my 2 cents worth( not corrected for inflation plus to take with a grain of salt).Just concentrating on the intake 'spike' and inward/outward flow area for the moment.Messerschmit used something similiar ( note: as in "generally in the ball park similar if you really stretched your imagination sort of thing")-but it was enclosed + used entrapped vortices to control outward flow.There is also a similiar idea to what you are advocating in the'www.aardvark.co.nz' site under the heading 'coanda' - plus a little vid entitled "coanda 1" ,that sort of shows airflow around the internals of the unit.
Now -I am not saying it would work or not but heated gases tend to behave differently to the cold air as that was used in the vid.I think that you will get some sort of gas flow out the front until you get some forward speed ( but what do I know?).
That main thing that sticks out for me is the fueling arrangement - you probably might have to go through the middle of the 'spike'.
You can see how other famous Pulse Jet scientists did it in the famous " Valveless Pulsejet Engines 1.5-- a historical review of valveless pulsejet designs --by Bruno Ogorelec" available on this site for free ( just love that word "free" - my most favourite price).
Also you might have metal errosion problems where the main combustion chamber doubles as a chamber wall and intake/exhaust wall ( hot gases on both sides) - less probs if you go stainless steel.
That's just the front part - now you have to get the 'intake' and 'tailpipe' ratios sorted out- as in do you go for total intake length -or is it
intake internal volume- ratio to the tail pipe ( and does that include the combustion chamber volume as well) ?[more knowledgable folk here can answer that one for you far better than I can]
In the end - as I am a large hammer and hacksaw type of guy - just build it have a whole lot of fun and learning.
You could even have an adjustable 'spike' to test postioning - nah... just build it dude...

[Jutte]

Oops Sorry - it was the Argus chappies that bought the infamous V1 Buzz Bomb
into reality that had the entrapped vortices to control outward flow.
Messershmit used the 'spikey' thing.
School holidays here at the moment - so I fired up the quite pulse jet
for the kids to roast marshmellows in the exhaust - yummy!

[Viv]

Hi There

Nice work your on the right track heres Foa's original layout for his engine as detailed in his book, Bruno and I had a whole series of ideas based around aerodynamic valving like this in the old days, its a fun concept

Viv

[Ghrey]

Thats why that thing looked so familiar... and then again not so.

Has any one of these designs ever been made to work?

[Fred]

I too have just come to understand the valveless potential. I like Foa's design. was there ever any info printed on it?

after reading Bruno's pages on the valveless, and looking Messerschmitt's pulse-ram and looking at Foa's design, couldn't one surmise that Foa's could be used as a Pulse-Ram?

i used Beck's calculated to for valved engine, and then added Foa's idea to the front end, see attached:

200# pulse jet Model (1).pdf

200# Foa Valveless -Ram

(3.36 KiB) Downloaded 609 times

i have not built this yet, but would love some comments and critiques on the designs feasability before i try.

[metiz]

Hey Fred,

I can not comment on your intake design since I am not familiar with Foa's work. I can tell you that you can not use Eric's calculator for valveless engines. Valveless engines need a lot more confinement in the cc because of the pressure loss due to the intake.

Because of the "lack of power", the tailpipe will also need to be longer, and probably thinner. (thermojets have big cc's and can get away with a shorter tailpipe because of this, at the expense of fuel consumption).

Your engine will not work.

If you want to design a valveless engine, use Pyrojoe's "Recipe for beginners" topic on top of the vpj forum.

[Fred]

Thanks Metiz, for the info. I read Pyro Joes info, and will recalculate the CC and tailpipe accordingly.

One thing i noticed about his article is the taper from CC to tail pipe, he specifies a 20 degree angle is about optimum, but if you look at Messerchmitts design, it appears less than 20 degrees.

thanks again.

[metiz]

It all depens on the type of engine and the engine design itself. The 20 degrees is a safe bet, but it can vary. The choke cone angle on my M25 is 19.3 degrees and on the M40 it's 21.5.

[Fred]

thanks.

i was just re-reading Pyro Joes article and then looked at the Messerschmitt designs again.

looks like i made sum presumptions based on asthetics and not on acoustics.'

I'll change my design and repost later for critiquing again, hopefully i can up with a good enough design to experiment with.

I read on some other threads that the pulse jets don't work well at altitude? that the Argus only managed to get to 3 kilometers in elevation?

I am going to investigate the american Loon project to see what they were able to acheive.

[metiz]

traditional Valved engines don't like high speeds; the air flow messes up the air intake in each cycle and also makes it harder for the valves to close again. Don't know about height restrictions but like any air breathing engine there's a max altitude at wich point the air becomes too thin.

[Fred]

well my motives for this experiment are to power a glider i am working on. I like the simplicity of the pulsejet, especially the VPJ, and the weight. after i fine tune the engine design, i'll post the schematic of the design i am working on for the glider. my start elevation here is 5100' so i am hoping that a properly designed VPJ will get me to at least 10,000' to 12,000' to catch thermals.

But my first attempts will be on a go-kart to see if we can get enough thrust to achieve flight.

[Jutte]

I can remember somewhere on the forum that Eric had designed some sort of
thing (Valves or intake arrangement I can't remmember which) that allowed a Valved Pulse jet
not to be effected by high air speeds.

[metiz]

yeah, mount a cone in front of the intake, problem solved