The Great Ramjet Challenge!!!

[Zippiot]

I'm happier than a tornado in a trailer park!!!!!!

Congratz, hook up the fish scale and get a video/pics up soon!!

I could never use anything but steel in my jet, my last jet (not the bomb the one that didn't blow up) ran red hot after about 5 seconds...I even melted an older version of it!

Funny how different flameholders and fuel setups affect stuff soooooo much in something that is essentially an metal pipe...

[Eric]

Time for the new and improved video. No 5 second teaser this time :)

Made some modifications to the design and runs sooo much better on low throttle. The engine is also 7" in diameter and 19" long with 4 fuel injectors. The one seems to need some adjusting.

The video the pulsejet starts off at low throttle, with nice big blue flames from the ramjet, and then the engine is turned up and the flame shortens and gets much more intense, more like a normal ramjet would run. The afterburner fuel tank was almost empty so I didnt have enough fuel to tip the tank and feed it liquid propane, but the flames get much much larger when you do.

With the naked eye you can make out more than the camera, it seems that there are shock diamonds in the exhaust.

I have a feeling the thrust will be pretty damn scary with a CD nozzle.

The videos posted in the valveless forum, im going to try to get some stills from the video and see if i can play with the contrast to bring out the diamonds.

Eric

[redneck]

wow you shut us down, we are all speachless. that is amazing dude, i think you blew everybody away cause nobody is posting right now. i just hope people arent loosing interest in this thread. i have modified my jet again, making the cc a total of 3.8 inches long, from the primary flame holder to the pressure baffle to the tail pipe intrance. my shop vac which produces 200 mph winds approx couldnt even put enough winds out to keep the flame blue, i would turn up the gas and have to move the vac closer and closer, until i finally had to just make the engine and vac touch. i got a great blue flame and a very large roar. i then turned the gas upside down ( by the way this is map gass i am running on this run) the roar got so loud it hurt my ears. this is no small feat as i am in the navy and work around the loudest jet the navy has all day every day. the light produced was blinding, literally i couldnt see for the light from the flame, it hurt my eyes, i was able to squint and see a large flame shooting many feet back. only problem is is it was all yellow. i need to get a faster blower or something. how do i get a better burn in my cc without increasing my intake velocity? for somereason this time i didnt get any thrust though. im confused? what did i do different to make 0 thrust? maybe i had a flase reading? though i really doubt it. maybe if i restrict my flame holder more, or should i open it up some? maybe bring my pressure baffle further back? i dunno. help?????

[redneck]

i noticed a kool thing about my engine, my pressure manifold works in an interesting manner, at low air speeds, the pressure manifold acts as the flame holder and the area between the flame holder and the pressure maifold act as a mixing chamber. Then as air speed increases i hear a loud backfire, flame shoots out the intake, then the flame front is at the flame holder instead of the pressure manifold. i think this happens because the flame holder is a sink strainer full of holes, alowing alot of air through, which is good for high spead opperation, and the pressure manifold has only 4 large ones, less than half its total area, which is good for low speed operation. i think that is kinda crazy and kool. useful even. i think a ram jet can benifit from having two flameholders.

now i am stuck, i dont understand why i am not getting any thrust, im getting alot of noise, but no thrust. it has to be because of my difusers.
i now have my cc perfect, my flame holder and pressure manifold perfect. and a pretty good fuel delivery system. im just afraid to make any cuts on my difusers until i know exactly what to do as i can no longer find these cones i made them out of. one wrong cut and i am screwed. by the way i am willing to pay somebody to make me a liquid fuel spray nozel for my jet that gets a good spray. mine kinda squirts and sprays. i used a #60 drill bit and counter sunk a flare into each of my 3 holes i drilled to get a better spray, but still not good enough. will some of yall please help me out with these problems??????

[Zippiot]

Show us a picture to better understand what the insides look like.

Thrust is a very hard thing to get from a subsonic ramjet, best thing to do is guess and check at the moment (maybe Eric Larry or J will publish a book!) hopefully this thread is making it easier for everyone to design a working subsonic rammy :)

I welded together, or BACK together!!! my ramjet and to my surpize...forgot to drill the new flameholder to fit the fuel tube.............

So cut open the jet or try to drill with a copper pipe and big piece of steel in the way?
obviously I need to cut open my jet again, I'll do it friday and try to devote a few hours to make it look "nice"

[Eric]

You could try shooting a hole through the intake to hit the flame holder :D

Might be more fun than cutting and rewelding.

Most of the problems is that at best the average leaf blower is providing just barely enough air for the engines to start producing enough thrust to move it forward. If you only use a leaf blower I think the best thing to do would be to nozzle the blower down as small as possible to get the highest air speed and use a much smaller ramjet, with an intake the size of the nozzle opening.

I have been thinking about getting an RC ducted fan engine and making a blown motor-ram jet contraption for a while.

Have the ducted fan provide enough thrust for takeoff and getting up to speed, and then kick in the ramjet and really go.

Eric

[redneck]

so im not the only one thinking of using an rc ducted fan. here is the thing about the ducting down the blower. i dont think it will matter so much, i think that a ram jet needs an amount of air moving at high speeds through a duct the same size as the difuser intrance. you could make the air moving through a staw go 800 mph but i dont think that would help as much as the amount going through a leaf blower at 200mph. i think you need to move alot of air at high speeds and leaf blowers only move small amounts at high speeds. i may be wrong though i dont think i am. actually i think a ram jet would run just fine is you could push air through it at 50 mph so long as it is under alot of compression. i think if you could find a way to compress the air to an extreem before entering the flame holder, it could run at very low speeds, and if that could happen, you wouldnt need a difuser in the front. maybe use the ducted fan as the difuser? have it side right infront of the flame holder. i think this is true only because the soul purpose of the intake difuser is to slow down fast moving air and compress it against the flameholder. this is why the larger the intake the faster the jet, it moves in more air, however it compresses more as well making for a larger difuser exit area and a larger jet. to remedy this at low speeds, i wonder what a reverse de lava nozzel would do? it should collect large amounts of air, speed it up to the neck of the nozzel then compress it up to the flame holder. it makes since to me, and what if we were to put augmentors around the blower to increas the amount of air going through, it will also slow it a bit but i dont think that matters cause you want it slow anyway when it reaches the flame holder. however i will try what you said and nozzel down my blower just to experiment, why not? we will see if that works......

[larry cottrill]

so im not the only one thinking of using an rc ducted fan.

I have been trying off-and-on for years to get people to try this. I wish somebody that has the money to spend would just do it!

Here is the thing about the ducting down the blower. i dont think it will matter so much, i think that a ram jet needs an amount of air moving at high speeds through a duct the same size as the difuser entrance. you could make the air moving through a staw go 800 mph but i dont think that would help as much as the amount going through a leaf blower at 200mph.

That's correct - but that's why Eric was talking about making the engine smaller, so the intake would fit the concentrated stream. 800 MPH through a straw has less power than 200 MPH from a leaf blower. However, nozzling down the leaf blower to half its starting diameter will have about the same power at practically four times the speed! However, the front end of your engine will need to be smaller. It is POINTLESS to feed a ramjet inlet with a stream that is narrower than the inlet - you will never get pressure gain from the diffuser. Take a careful look at the diffuser information Al Belli posted on this forum yesterday.

Actually i think a ram jet would run just fine if you could push air through it at 50 mph so long as it is under alot of compression. i think if you could find a way to compress the air to an extreme before entering the flame holder, it could run at very low speeds, and if that could happen, you wouldnt need a diffuser in the front. maybe use the ducted fan as the difuser? have it side right infront of the flame holder. i think this is true only because the soul purpose of the intake difuser is to slow down fast moving air and compress it against the flameholder.

Well, that's true, but remember that the point of a classic ramjet is to use fast air at normal pressure. Sure, a true ramjet can be made that will RUN at 50 MPH - the problem is that it won't develop enough pressure to bring up the thrust to overcome the engine and vehicle drag at that speed. Yes, a ducted fan could drive the flameholder directly - that's how those "jet" garage heaters work, but the thrust is minimal. A fan is a good way to get air up to speed, NOT a good way to get it up to pressure! That's why the diffuser is still a critical part in a "motorjet". Even the compressor on a big turbojet is followed up by a diffuser going into each chamber - that diffuser is what really makes it a "compressor"!

This is why the larger the intake the faster the jet, it moves in more air, however it compresses more as well making for a larger difuser exit area and a larger jet. to remedy this at low speeds, i wonder what a reverse de lava nozzel would do? it should collect large amounts of air, speed it up to the neck of the nozzel then compress it up to the flame holder.

Unfortunately, no. A reverse deLaval nozzle would be a venturi. The air would increase in speed up to the throat, but at the same time it DECREASES in pressure! The pressure at the throat of a venturi is quite low, which is why you can put a fuel tap there and you have a carburetor! Then, as the air travels beyond the throat, it slows down again and regains pressure - once it gets back to the inlet diameter, the pressure is back where you started. No free lunch here ...

In my opinion the right way to do a motorjet is to use a fan whose outlet area is identical to the slightly flared inlet of your ramjet diffuser, but connect it up to the inlet rim with a short "flow straighter" duct to kill the flow rotation.

L Cottrill

[larry cottrill]

I have been thinking about getting an RC ducted fan engine and making a blown motor-ram jet contraption for a while.

Have the ducted fan provide enough thrust for takeoff and getting up to speed, and then kick in the ramjet and really go.

That is EXACTLY what I wanted to do with Maggie Muggs. However, I no longer think the diffuser on that engine is anywhere near good enough to pull it off. But, that was what was originally in mind for the project.

I had thought of doing it like this: Rig the impeller from a 1HP leaf blower on a .60 cu.in. displacement 2-stroke engine and provide a carved balsa volute that would turn rearward as a duct, cooling the engine and providing a fairly high speed propulsive jet. Behind that, at a reasonable interval, position your ramjet so it takes in a large part of the air jet from in front of it. The outside of the rear-jetting duct would smoothly cut in (slightly) to allow real ram air to flow around and impinge on the ramjet intake, so it would automatically take over. The beauty of this setup is that you could start the ramjet as soon as the piston engine is running - so, it would even help a little for the takeoff run. Once the plane is up to speed, the piston engine would be starved out, and the ram air would sustain the ramjet in the normal way, though of course the piston engine and duct are admittedly interfering somewhat with the flow into the diffuser. Anyway, that's the theory I was working from ...

L Cottrill

[Zippiot]

Historically, the motorjets had either an axial or centrifugal flow compressor, not just a ducted fan. This would compress the air not just speed it up...
Once the air is compressed all you need is a flameholder and nozzle.
I think caproni made a motorjet

[leo]

and the ram air would sustain the ramjet in the normal way, though of course the piston engine and duct are admittedly interfering somewhat with the flow into the diffuser. Anyway, that's the theory I was working from ...

L Cottrill

Larry what about placing the propeller after the diffuser and in front of the flame holder inside the ramjet, if you get speed the propeller would increase the pressure from the diffuser even more, and also the propeller would get a reduced airspeed, avoiding the problems propellers have at high speeds.

[Zippiot]

Caproni motorjet

http://www.airbornegrafix.com/HistoricA ... gs/CC2.htm

[redneck]

my vids are up on you tube finally.... here is the link...
http://www.youtube.com/categories_portal?c=26
tell me what yall think :)

they are in the science and technologies listing then click search and type in jet, my engines are under rednecks jet engine

[Zippiot]

http://www.youtube.com/watch?v=o1ryftn_StA
the rest of the videos are on the right of the page, scroll down :)

from this vid looks like you are having flameholder problems, it blows out a bit easily

[redneck]

in this video my cc was too short, and i had a large washer in the rear of the tail pipe just as a way to play around with different configurations. the washer keep wanting to be the flame holder, aslo i have lots of flameouts because my fuel pressure keeps droping and the blower is too close for the pressure i have. most of these problems i have corrected, i have one last vid i need to post of this thing running like a champ. soon as i get the disc back from wally world i will post it.