New ramjet experiments

[Irvine.J]

Please read this all before commenting (as I know its not to "gugenheim" specification :D) I just left it this way to test BEFORE I cut it to specification just for a bit of FUN and sharing some info that might (who knows) be useful to some.

Ok guys so I've read the PDF and the available information on this website, and still scratched my head wondering if (as i'd really like to) I could contribute anything to the forum by experimenting my free time with different ramjet designs etc.

I decided to build a ramjet to more physically accurate dimentions, however, while i was putting it together, I decided to do a few random things just so I can experiment with certain factors of ramjet functions. Just to drag it out longer for experimental purposes.

Unfortunately in the nightrun It was running very well, but my cameraman forgot to record the long burn and me throttling it, i was practically out of gas and you can see fuel problems start to arise, Im getting my brothers camera so i'll record a prolonged burn in this state before I do any cutting.

For instance in the movie your about to see, the ramjet is smaller then the last, however I believe much louder.
NOTE
1-The exit nozzle is MUCH smaller then the intake, and it has a second (though very small) baffle toward the rear of the engine. All of these things were supposed to be removed and cut to the right size but I it left this way for a trial, the exit nozzle could easily be cut back and second baffle could easily be removed a bit later on to correct specifications. -Note the exit flame is much greater in length then that of the previous engine.-

2. I used the same fuel stinger as I suggested to the cheat only with slightly larger holes. I'd suggest to the cheat to NOT give it the centre hole and plug it completly, and just use 4 holes around the outside directed toward the flame holder.

3. Note the flame immediately after the exit nozzle is blue, but almost instantly becomes a yellow colour... I now believe this may have something to do with rust and the paint i left inside there :D Also because the design is not 100% accurate...however the escape velocity does seem to be VERY high.

4. You could only start it in this config with a sparkler laid inside it. Interestingly enough the sparks weren't traveling anywhere NEAR the speed they were out the exit nozzle when the gas was initiated. I took note of this before turning on the gas as its the only way I could get an idea of the gasses accelleration.

5. Note that the combustion seems to be held in the rear section of the engine on this ramjet, it doesn't seem to be getting past the second baffle.
I originally thought with enough gas it would breach past the second baffle, and up to the primary flameholder up front, hence creating an area of much higher pressure before discharge. I didn't originally intend this as the design, (which was to be a typical ramjet with no secondary "Baffle") but I thought I'd leave it in there and I'm very interested in whats going on inside this engine.

6. No matter how much I turned up the gas, till the point where my LPG tank was litterally steaming with cold condensation, i couldn't over gas it, it ate literally everything I gave it... which i thought was "Cool" or hot, or whatever. Heres a quick diagram of how it looks inside, I liked the idea of the flameholder as its cross section is very small, and quite aerodynamic, if you can get what I'm talking about. Be aware also that when putting my hand around the intake to feel for any airflow that might be escaping or being pushed back out the front I felt no flow (as i clipped my blower throttle to max) it seems to be eating it all?

Well still it was an interesting way to spend a few hours over the weekend whilst I wait for electrical parts for my aircraft, which is still progressing along nicely. Enjoy, any comments welcome, escpecially on point 5 why the combustion seems to be limiting itself to the back of the engine.
TURN YOUR SPEAKERS UP, as the camera pans around in the daytime run, you really hear the low resonant rumble! Atleast its a good NOISEMAKER!

I hope you atleast like my write up :D I'll cut it to specification size after a bit more experimenting.

Best regards to all
Mangy.

BOTH VIDEOS ON THIS PAGE.
http://mangyjet.freewebpage.org/rj.html
CLICK THE LITTLE PLAY BUTTON DOWN BOTTOM LEFT NOT THE BIG BOX!
I love the BOOM when it kicks in on the daytime run 1/2 way through

[thecheat]

hmm... I can't seem to get anything but a white page.... dang...

Anyways, good to know your ramjet works!

But, how long is your diffuser? is it anything as insanely long as mine?

Also, what's the Diameter of the CC? I don't know what your jet looks like (as I can't seem to even see the blasted movie...) so I'm just trying to get a mental picture...

PS: you should try coating the inside of the CC with saltpetre, it's supposed to turn the flame whitish, or get some calcium nitrate, turns the flame deep red (we've tried this, as, we have some) might give some cool effects, I know I'll try it!

[Irvine.J]

Try it now, the issue might have been i had the video's on "private".
Wierd when I click on the link I see the videos, give it a few seconds to load the boxes... anyone else have issues? I'm going to start cutting away the tailcone today or tomorrow, just be aware that the people who first built a ramjet for themselves would not have miraculously known everything about it, and would have experimented with longer tailcones, smaller nozzles etc etc... this is really all about seeing what would happen for myself.

[Irvine.J]

I'm thinking about making a circular spinning apparatus to test these engines on, and i have the parts i need to do so, however i'm stumped as to how to make the gas line free to spin around without eventually winding up tearing off. Any ideas, I'm thinking maybe the air compressor clip-joints as they can turn freely, but don't know if gas would be able to escape? Something like this?
I have heard of using a bicycle wheel as your spinner, but the gas line still remains the critical issue. My gas line from the rubber hose to the first metal joint spins on its own, but its under a little friction and don't think it would hold lone at 500rpm or something rediculous like that.

[jthompso]

Could you use the fuel tank as the counterweight so the whole apparatus spins? Of course then you'd have to come up with a way to control the fuel remotely which might be more complex.

[Irvine.J]

Infact sir thats not a bad idea. I could shorten the length of arm for the fuel counterweight to keep it balanced. However I do worry in that setup of the concequences of a critical failure... i think the words "flying" and "bomb" come to mind :D Good idea though i'll look into it. Possibly a burnsomatic blue tank might be appropriate. :D I'd just turn the fuel on max and burn the tank dry :D Who needs throttle! hehe. I can brake the hand drill arm easily with bolt that i can just turn already part of the hand drill.
Did the videos work for you sir?

Attached is my first attempt at using UFLOW1D. ITS A COMPLETE FAILURE AS ITS NOT WORKING saying "Cannot run" or something. I don't know what the initial pressures are or what the volocity in Mps are after entry into the CC. Lets just say that the blower is pushing into the inlet at 89 mps or 200mph initially. Does Uflow commonly work for ramjets too? if someone could take a look i'd appreciate it. What have I done wrong here?

[Mike Everman]

Hold on, what good is a fuel tank counterweight if you can't use the fuel, lest you go horribly out of balance?
Remember mv2/r is the centrifugal force on your counterweight and your motor. Put a few numbers in there and see what kind of forces you are dealing with. It would not be a trivial thing to pump fuel to the middle against that force, either...
Just 2 cents worth; I've done a bit of thinking on the subject. ;-)

[Irvine.J]

Thanks for the 2 cents mike, your comment on "It would not be a trivial thing to pump fuel to the middle against that force" has got me thinking. What if the tank was in the centre, standing upright, and rotating around? As if the tank and apparatus itself was spinning on 1 table. Do you know what I mean.? Imagine the Tank was right ontop of the centre of the bicycle axle, and the engine and counterweight were connected directly to the top of tank? This way the tank would be in the centre, and the gas would actually be helped to the ouside by its centrifugal force. (If it has much bearing on lpg) What you think?
The tank could also be lying down i suppose.

On second thought instead of deleting this I'll just add to it... I think its kind of silly to have a setup i can't throttle, so I might try the air compressor hose connectors with some high rpm motorcycle oil in there to it wont lock up... that could be seriously bad!

[tufty]

Imagine the Tank was right ontop of the centre of the bicycle axle, and the engine and counterweight were connected directly to the top of tank? This way the tank would be in the centre, and the gas would actually be helped to the ouside by its centrifugal force. (If it has much bearing on lpg) What you think?

This is an interesting question, and one which Mike only hints at the potential complexity of by saying he's "done a bit of thinking on the subject"

Assuming fuelling from the centre, one way or another, centrifugal force is going to have an effect, even on an initially pressurised fuel; as a result, as the jet speeds up it will be seeing more fuel pressure. The big question, of course, is "does this matter?" Personally, I would argue that it probably doesn't matter that much, but if you feel otherwise it would be a "relatively simple" matter to add a regulator of one sort or another at the point where you're fuelling the jet (as opposed to at the tank exit).

More important, IMO, is balancing the assembly, and failsafe devices. The slightest internal failure in the jet is likely to result in off-axis forces, and you'll need to be able to deal with those. And you need a way of shutting it down, fast; that means at least an instant fuel shutoff combined with massive braking on the wheel, I would probably consider the possibility of dumping something non-flammable into the engine as well (preferably doing all of this this automatically, especially in case of "axis failure")

Remember, to get, say, 360mph linear off something at the end of a 14" arm (28" is about the biggest bike wheel you're going to find):
1 mile = 63 360 inches
360 mph = 6 miles per minute = 6336 inches /sec
Circumference of 28" bicycle wheel = 2 * pi * 14 = 88 inches
So we need 6336 / 88 revolutions per second == 72 revolutions per second or 4,300 rpm.

This is all, of course, something like 10x out of spec for bicycle bearings; I'd scrap the idea of using a bicycle wheel, personally. Or, indeed, running a standard air fitting as the axle.

Nice videos, by the way.

Simon

[Irvine.J]

Ok well I just got back from working getting the air tube connector and spinning it as fast as I could with an electric motor designed for EXTREME rpm. I noticed even with the oil it still got really hot, way to fast and was emitting a hi-pitched noise. I really don't think in the end its going to work how I was envisioning it so it seems for now i'm gonna have a hard time rigging up any sort of thrust measuring device for it.

Excellent write up simon by the way.
Yes 4,300 rpm seems way off spec for anything i have lying around in my garage. THanks for your time taken to write the info you have I appreciate it alot.

I'm going to go off and scratch my head for a while and see if I can't come up with a slide and a spring scale that i can attach the jet to.
So far your comments have been most helpful :D

[Najm]

5. Note that the combustion seems to be held in the rear section of the engine on this ramjet, it doesn't seem to be getting past the second baffle.
I originally thought with enough gas it would breach past the second baffle, and up to the primary flameholder up front, hence creating an area of much higher pressure before discharge. I didn't originally intend this as the design, (which was to be a typical ramjet with no secondary "Baffle") but I thought I'd leave it in there and I'm very interested in whats going on inside this engine.

Are you providing it with fuel after the primary flameholder?
Try aspirating your ramjet, you are currently injecting fuel into it if I'm not much mistaken.
Also the ramjet's diffuser is not slowing the air down as much as it should, try using a higher ratio of intake area to combustion chamber area to slow down the air.
Maybe the rate of combustion is not faster than air velocity?

And in the night run video what are the blue flashes at the intake?


BTW How do the pulse-jet poeple measure their pulse-jet's thrust??

[Irvine.J]

Hmm, so i scratched my head and low and behold I'd been gazing at a spare tire for about 20 minutes + or - ...

Then it hit me, what about a car axle?! EUREKA! as us auzzies would say.
A car axle generally could handle 200mph for atleast a short time. If exceedingly well oiled, and completely cut away to remove almost all of the unecissary metal and tyre etc just leaving the "hub", much like cutting of the rear axle of an old car that was front wheel drive. Even so, you could cut either axle, as the hole left for the diff could be used to run the fuel up it. You could cut the axle to about 1/2 a foot, and weld it to a large base plate and anchor it to the ground...with the hub now in the correct position you could simply attach the "swing arm" if its well oiled and completely free it should spin with very little resistance, be solid as a rock too.

This would allow me to keep the propane tank well away also.
If you think this might just do the trick, I might start thinking about an appropriate gas system that can handle the turning motion. An rpm meter from your standard car should be sufficient (though i can easily aquire an electronic one) to work out what speed its travelling at a certain throttle setting, as Simon so nicely pointed out, RPM would be directly related to the speed the engine was travelling.
I believe this might be the answer, what do you guys think?

Najm wrote:

Are you providing it with fuel after the primary flameholder?
Try aspirating your ramjet, you are currently injecting fuel into it if I'm not much mistaken.
Also the ramjet's diffuser is not slowing the air down as much as it should, try using a higher ratio of intake area to combustion chamber area to slow down the air.
Maybe the rate of combustion is not faster than air velocity?
And in the night run video what are the blue flashes at the intake?
BTW How do the pulse-jet poeple measure their pulse-jet's thrust??

Hi najm, well the fuel stinger is slightly infront of the primary flameholder, and yes your correct its lpg under moderate pressure. (my holes are a little large then i would like as i broke my really fine drillbit by not paying attention.) I think the PFH (primary flame holder) should be slowing the air down enough, it might just be the small nozzle basically creates a pressure zone at the rear where the incoming air wont allow it any further foward? What do you think? The blue flashes I THINK are caused because I was running out of gas and might have been loosing pressure. I had to slowly keep increasing the gas as it had died once or twice... which basically meant that it was coming in and out of life... WAIT A MINUTE!!!

I noticed when starting the second ramjet I made, that big blue flash meant it was BOOMING into life, however there is also the possibility the gas was starting to combust in the primary or "intended" combustion zone at the primary flameholder, but I wasn't supplying enough gas to contine it combusting up there... your question just made me think of that... What do you think??? If this was true I can only IMAGINE the amount of volume/speed that exhaust would be coming out the back... I HOPE SO... but I bet one of the physicists will tell me its not going to happen :(

I really didn't think of that blue flame in regards to what a ramjet looks like when it starts...I will FOR SURE be running it again with a full tank and try and get that same effect and the combustion up there next to PFH.
Thanks for the question I hadn't thought of that, you the man! Way to go!

How do you measure its thrust??? I'm working on it! Lol!

[thecheat]

well, first, I think having a fuel tank as a counterballance would be a very bad idea... As fuel is used, well, that side gets lighter and... you get the point. Having the tank in the middle wouldn't be too bad, but, would the gas not be pulled out to the ramjet as it gets going faster?

However, my biggest thing is that, how are you going to get it started? obviously you can't be running around with it using the blower... so, can your ramjet take the stresses of being red hot and rotating at 200mph?

PS: I think you'd want to use a nice, long pole for this, as, it'd probably be easier if the pole isn't going 30,000 RPM... perhaps you could go and put the nearest ferris wheel on high...

[larry cottrill]

Number47 -

I have thought about using a car axle in exactly that way, except for your nice gas path up the center. I think your schematic shows exactly how to do it - the one missing piece being a sealed rotary link for the gas. There always has to be some point at which the gas goes from a stationary pipe into a spinning pipe, and that's a real bear to work out.

As for running it: Of course, all you need to start it is a mechanism to get it spinning fast enough. Easier said than done, but not too difficult with some flexible thinking and a good junkyard somewhere within easy reach. As to safety, I think the only thing that makes sense is a pit or cistern or something several feet deep, with all remote controls so you can be up on top out of the way of flying steel. Another thing is that the G forces are going to be pretty outstanding - you need GOOD anchoring to a really solid footing at the base, in case something does fly off and unbalance things. If that happens at high speed, you WILL NOT be able to react quickly enough to get things shut down before destruction begins to happen in earnest!

Anyway, just a couple of comments without any real detail thinking being invested.

L Cottrill

[tufty]

Yeah, what Larry said. Also, yes, make the arm longer and you make the RPMs less quite rapidly, double the length of teh arm and divide the rpm by six or so.

A car axle is a much better choice than a bike axle - for starters it's designed for much bigger stresses, and, more importantly, to only be mounted on one side.

I'd consider a stub axle assembly, preferably with disk brake intact, beefily welded onto a good steel plate, itself chemfixed into a good concrete base. In a pit. No idea how you go about feeding gas to the motor, personally I'd mount the tank in the centre, rotating. Of course that means you have no easy way of directly controlling flow, it would most likely be "full grease or nowt", which could be *ahem* "interesting". You might be able to rig something with rotating contacts, at least for cutoff - have a valve that only opens when there is current flowing, that way you can spin it up to a reasonable starting speed, flip the switch and have gas and spark start, then flip the switch again to kill the motor. as an added bonus, this would kill the motor if the hub failed, too.

Like Larry says, this is not very well thought out, but hey. Ideas...

Oh, and before you rip out your "secondary flameholder", it might be worth trying to run your engine "backwards" if you can rig the fuel feed that way. It looks like it's the wrong way around.

Simon