Calculations... double checking with the pro's

[thecheat]

Ok, here's the night run! We got a nice, blue flame the whole time, a little orange in it... but overall, a pretty nice run!

PS: This thing was able to swallow just about everything we put on it. Gas was on full, and we were able to get the blower (high powered backpack blower) to about half to 3/4th throttle before it blew out. (that's what we did in the last half of the video, pushed the power until it stopped)

Unfortunately, I couldn't get the thing to get glowing red hot... only the flameholder would get red hot. Does it need more fuel? Or is 20 gauge overkill for this application?

http://s19.photobucket.com/albums/b154/ ... ghtrun.flv
http://media.putfile.com/ramjet1-nightrun

comments?

[Irvine.J]

CONGRADULATIONS!!!
Way to go on a job well done!
That was certainly VERY loud :D I noticed the nice blue exhaust yes, and good on you using a sparkler it makes life nice n easy for starting doesn't it :D.

Its interesting you say the flameholder was becoming red hot, I also noticed this when my fuel stinger was about a half or 1 inch too far in front of the flameholder. The other reason i would suggest it is fractionally too far foward is the blue escaping flames from the inlet, and the bright flameholder... but hell thats a massive engine, and looks like it running extremely well especially for your first runs, I'd say we both are just not getting the massive amounts of air we need.

It seems you are getting really good mixing... did you go with the stinger I mentioned?

I would like to commend you on your successful run, It looks good and sounds good too. Way to go the cheat, excellent work! Now we just have to come up with some way to test the thrust now don't we mate :D
Also your flame holder idea is escpecially good by the looks of it, nearly a perfect ratio. All round, if Einstien were here, he'd say "That kicked some ramjet @ss" :D Hehehe
Its been nice collaborating with you thus far and I'm really happy for you because you put so much work into it. I look foward to your next test runs!
Sooo... How are we going to gauge the thrust now???
Also, was that blower on full power?

[Zippiot]

I think I can help you with you flameout problem!

Mount (weld) a metal rob or bolt about 1 inch before the exhaust. It gets a bunch of heat exposure and turns red very quickly, if the jet flames out there is a much better chance that this red hot bolt will re-ignite it compared to the sheet metal. Also it allows for proper cooling of the shell to extend jet life.

I welded mine to the flameholder, it was some 1/4 inch steel rod and it went back to 1 inch before the exhaust nozzle. Once I mounted it i never had a flameout again, didnt have many to begin with but I can tell it helped.

Pretty blue flame, I run [ran] my jet of liquid fuels so there was never any blue...

[Irvine.J]

3/4 throttle...hmm. Did you give about 3/4 cm atleast from the blower nozzle to the inlet, you do need a small gap there so the airflow is even across the entire face of the diffuser.

That is a substantially large engine, If the gas was on full, maybe your stinger might need to let a weebit more gas through perhaps?
Concidering your blower seems much more powerful then mine, it might also be worthwhile playing with your fuel location, just experiment I'm sure you'll figure it out. Still, great work! I still think your flame holder is exceptional.

Zippiots idea is very good give that a go also.

[Najm]

Nice run.
My ramjets also didn't got red hot, only the exhuast nozzle showed signs of getting heated(on one side) and that was because the leaf blower was not in line with the ramjet's central axis.
As a rule the ramjet's body should not get red hot.

[Zippiot]

I know it never should, but getting my old modified maggie glowing was awsome...

Turns out WVO and white gas mixed can melt stainless...

[thecheat]

hey, thanks! I guess it preformed as it's supposed to, as all you say... (I really have no clue about this stuff, as, well... I've never run a ramjet before!)

First off, when the flame came out the diffuser, that was due to the blower not being centered on the inlet hole... the big burst of flame was when it missed the jet entirely...

About the blower, it's a substantially larger blower than your regular leafblower, as, it's a professional backpack blower. However, the tube is about an inch or so smaller in diameter! So, it's got a LOT of airspeed behind it. We held the blower inlet about half a foot away, so that wasn't a problem. Couldn't have gotten it closer if I wanted, my dad didn't want to melt the nozzle any!



Stinger, Yup, I used your idea Irvine, 1/4th inch copper tubing, four holes and a blocked off end! Hehe, I welded mine shut!

The flame I get out of there is... well... as good as I could hope for! I get the flames to extend about 1 1/2 ft from each hole...

Oh, and the ramjet, from the flameholder down is now a nice, even color, it all discolored very evenly! (those spots are where we tapped the jet with our fingers, after licking them of course... it sizzled nicely)
http://i19.photobucket.com/albums/b154/ ... 0043-1.jpg


Anyways, I'll be setting up a rig today for thrust measurements, dunno how it's going to look... but, AT LEAST I can unbolt this thing from the test stand!

PS: next time I run it, I'll shine my laser through it, which is why I designed it the way I did... I think It's quite literally the only seethru engine out there! (not counting Jamjars or straight PJ's, as, those don't produce any real thrust, only the bent kind do, which aren't seethru)

If you noticed, you could see me playing with the stinger in the last part of the first movie.

PPS: i'll probably spotweld some shortened TIG rods for the "heating elements"
PPPS: oh, and I was only able to get the flame behind the flameholder when the stinger was stuck through the middle of the flameholder... but, I liked it much better when the flameholder was nice and red... Do these things remind anyone of a readyheater?

[thecheat]

I picked up some scrap material that was laying around and built myself a test stand! Not very hard to do... considering I had those nice castor wheels just laying around... The platform rolls very nicely (I'll oil it though) and is pretty light, so, it shouldn't interfere too much. The steel cable is really just so I don't have a rope burn off, I'm not worried about it breaking a rope with thrust, just to clear that up... ;)



PS: I'm using a electric fishscale that goes up to 20lbs, what's nice is that it will keep the highest weight until you press the on button again. However, the blower WILL NOT be attached to the rig, so, I'll have to ADD the thrust produced by it. (remember, it's blowing against the forward momentum)

[Zippiot]

My experience tells me that, even though its the proper thing to do, the bloew doesn't make any measureable thrust.

My 5hp vacume set to blow with a nozzle on it made less than 1 pound...but the ramjet itself made over 8!

My point is, whatever number you get on that fishscale is by most 1 pound off of the jets actual thrust. Even 1 pound of thrust means that the engine is trying to move forward, any measureable number is a good thing dont be discouraged by something lower than what you expected!

[thecheat]

That's my thoughts on this really, if I can even get a measurable thrust, well, that means I'm successful! If my crude little dolly even moves, well, that's great! If it maxes out the scale (the electronic one, I found, is broken, I'll have to use the 4lb one...) that's time to get REALLY excited! Go celebrate by filling up the argon tank, maybe even upgrade it to a larger size!

PS: could I see a picture of the ramjet? I don't care if it's got holes and half of it is slag, just wanna compare mine to yours, you know, get an estimate for what mine should do... :D

[Zippiot]

I threw away the 8 pound thrust ramjet months ago...I am welding together another one at the moment and I'll gladly post pics of that. I also have the remains of maggie...with its little flamehodler all 1/2 melted and sticking out the exhaust (still ran for another minute without it surprizingly!)


I want to go get more welding wire (I HATE MIG WELDING) and some sheet metal to throw together a new design I'm workign on. SHould light around 200 mph and make buttloads of thrust, its tiny btw. Uses aspects of the lroin ramjet, I'll draw up a pic of the basic idea later.

[thecheat]

Hehe, I LOVE TIG WELDING! It's just so far above my experiences MIG welding. Very controllable, supprisingly easy to fill in holes... (I've got experience in that area you know...)

Oh, and during the test run I was dissapointed, no thrust was really noticed... I have a guess the blower pushed as much against the jet as the jet pushed forward, as, the jet should have blown backwards if it produced NO thrust.

We WERE able to get the blower to FULL throttle with no problem! the flame stayed lit! (the sparkplug came in handy...) Oh, and the flame gets a little bigger if you tip the propane bottle upside down... like nearly three feet of blue flame... Unfortunately we were one hand short, so we couldn't hold the stinger in the proper position AND tip the Propane tank. I also probably won't be able to run the jet until Wednesday...

But anyways, the best place for the stinger was right through the middle of the flameholder. All the flame was kept BEHIND it, and I think that position, the fuel jetting on the back of the flameholder, kept the jet lit better.

Anyways, I can't wait to light it up again and get that propane tank in the right position, that was ONE BIG FLAME!

[Irvine.J]

Hey the cheat its all looking very good mate.
I noticed you said you are holding the fuel stinger??? Probably not the best idea incase something goes wrong...like your blower stalls or something (which has happened to me.) What I suggest you do so you can effectively run this thing on your own, tip the tank etc, is drill a very small hole in the side of your inlet first, then drill the hole to the size of your fuel line. Then Kink your fuel line 90* or in an L . Measure it so it ends up exactly where you want it. Then if you have any silver solder just silver solder it into place. It should not ever get hot enough up there to melt it, which leaves you a free hand for the blower, the other for the tank on your own.
Works pretty good for me. Goodluck with your little test rig.

I found yesterday some standard weight scales, where if you take the bottom off, you can see the mechanism that the spring connects to. So if you put the scale itself in a vice side on, you can connect a small fishing trace wire from the mechanism to the engine or test stand. Hence it will pull on the mechanism, and give you a thrust reading of a semi accurate nature. For 10 bucks, thats not so bad. I looked at few spring pull scales the only ones i could find go to 20 kg or so, so reading small changes was going to be really difficult. And they were 30 dollars. GOODLUCK !
What are you going to call this engine?!

[Zippiot]

A way to check if ur ram is making forward thrust is to place it on a sliding platform (like your test stand). Use the blower to push air on it and make sure it rolls backwards, just to show that it wont take much to move the sled. Then try it again, but this time light the jet. If it moves towards the air source, you have thrust! You can either move the blower back and see if it picks up speed forwards (tricky to do but fun) or let it run all the way up to the blower. Try not to play with the fuel while doing the test, little flux's can mess with results.

I got mine on a skateboard to follow me up the driveway, it was so impressive considering how much it takes to do that. get an r/c plane and have it crawl up the driveway and tell me what % throttle you used, took my friends little 100 dollar r/c plane almost full throttle at first (then it nearly took off into my house, he had to catch it!)


Point is thrust is thrust, if it can move itself and any amount of weight it is a success, if it doesnt well at least it proves some theories of jet propulsion (ram operation). And if it cant do that....well hell I made a ram out of 2 SS cups what are you doing wrong? Not to sound mean, ask questions if you are having trouble [anyone trying to build a ram].

[Zippiot]

I do my best work early in the morning :)

I was bored and realizing that I wont be able to go to the hardware store tomorrow, I decided to build a paper mock-up of my next ramjet.

Its going to be tiny, a mere 7 inches long.

When I blow in it the air coming out the exhaust is considerably warmer than the air going in, actually it seems much much warmer than the room temp. That is your first clue a ramjet might work, the air out the exhaust is wamrer and slower moving than the air going up the intake. This means at one point there is a pressure change signifigant enough to change the temp a noticeable amount.


How did I change the pressure, well I used the standard 6 finger flameholder and a basic sub-sonic ramjet shape. But I threw in a curveball, a cone. Point of the cone starts with the intake, there is a 3/4 of an inch clearance between the cone and the shell. Cone extends back 3 inches with the intake, at the end of the cone there is 1/2 inch clearance between the shell and cone. This speeds up the airflow a bit and also compresses it, just a bit. Cones are not used on subsonics, I just want to try it for now. At the end of the cone there are 6 fingers connecting the cone to the shell, this is the flameholder. The cone and fingers alone actually seem to warm up the exhaust air, adding the intake shell increases this a bunch! The cone also acts as a baffle flameholder, this combined with the 6 fingers and slightly higher airspeed the pressure changes a bunch [for a subsonic ramjet]. Then a 3 inch combustion chamber and an exhaust cone that has a slightly higher area than the intake cone.
What I find most important is that no air bounces back at my face when I blow in it, if I were to feel any air hitting my face at this blower speed then at 200 mph tests the losses would be immense!

Well I should be able to make a run to the hardware store tuesday and might be able to do most of the work then also, we will see.

Cant find the camera in the dark I'll just post pics of the construction then a side by side of the metal and paper ramjets.