The Great Ramjet Challenge!!!

[Zippiot]

If I can get stainless sheet for 1/3 price would it be worth it to get 347? My old highschool engineering teacher wants me to demo this stuff for his class and has offered to buy materials through the school. I barely use any for the jets so far, my most recent jet used a 12x7 piece of 22 gauge.

I welded up the CC intake and exhaust, need to do some grinding. I had the most perfect bead going, and once I got all the way accross the exhaust I noticed I missed the joint by about 1mm...so it had to be ground down and re-welded :(

Next is to do the flameholder, then just to rig the fuel system and weld all the parts together. Almost done here are some pics of pre-welded intake exhaust and CC

[Eric]

1/3 the price... your kidding right? Why not go with titanium if hes payin lol :D

Eric

[Irvine.J]

Larry wrote:

I have tried to show in the other thread that building and testing big ramjets is practically hopeless for amateurs of limited means.

my brother came round last nigth and saw the big lance, the first thing he said was...
My brother - "...soooo... can I strap this to my roofrack and fang down the highway..."
Me - "Yes...Do you have a good lawyer?"

Anyway, I thought because of the size and fuel type diversity that may be encountered in challenge 1 (Though I suggest we ALL run propane, as its cheap and everyone can access it and not need other pumps etc) we could get around some of the issues by having several Ramjet Awards, within the challenge, catagories for instance like...

1 Most thrust Under 4" Diameter
2 Most thrust Open class
3 Best conventional operation (Throttling /airflow)
4 Best Aerospike operation (Throttling /airflow)
5 Best constructed
6 Most Unique / odd /"Coolest" looking
7 Best flameholder design.

Each entrant can win a maximum of 2 awards, hence everyone should be awarded with something and everyone finishes the day happy! I really think in any competition everyone should be acknoweldge for their attempt in some way. Each of these catagories will easily be selected by video and documentation of thrust etc, and I'd be willing to share my email address at the end, everyone give me your videos, and I can put a big long movie on youtube with everyones entries, and what award they have won.

If you all agree on the catagories above that would be sweet, feel free to suggest other catagories and we can change and modify them, though we should get them set in stone within the next 48 hours.

What do you guys think?

[Zippiot]

They sell in bulk to the school for special projects, and he told me it is 1/3 the sticker price for any reasonable metal.

If I felt like my jet was good enough for titanium I might go for it, for now just gonna get some sheets of stainless and a few pieces of barstock.

[Zippiot]

I think there should be another catagory:
First practical ramjet

The first person to build a flight motor, whether it be for rocket or plane (or helicopter etc...) use.

[Eric]

What about high speed ground vehicle with high power to weight ratio? :D

[Zippiot]

I assume the smile makes the statement a joke...a 200 mph r/c car? Besides a nitro tethered car that is a bullet!


I want to see how a rectangular ramjet stacks up to a cylindrical rj, my next project will be called "squishy"
Gotta finish this one first I guess...Without my bench grinder I dont know how I could live with my welds!!!!

[Irvine.J]

Hands up those intending to run liquid propane?

Question about liquid propane fueling... I have tipped my tank once or twice and though just wanted to check my fuel line was up to the job. My fuel tube stats of the 4kg tank are as follows, with a quarter turn valve.

Primus 8mm LPgas AS/NZS 1869/C WP2.6Mpa AGA6356

Is this up to the job? I am using no regulator, just straight off the tank, I assume thats its pretty safe aslong as one remembers to tilt it back before you get too much loss in pressure.

Heres a little pic of my modified minilance, I had a much better run today, with new gas nozzles, but decided to take out the nozzles cut off the front cone and make another one. I cut off the inlet, made it slightly smaller, flared it a touch, and have made the aerospike the distributor by sealing it with silver solder, and drilling 10 .65mm (or very close) holes, so I have good pressure but more importantly lots more flow. Came up looking pretty good, though I'm not sure about my flameholder design anymore.
I'll run it like this tomorrow.

I like the "First Practical Ramjet" award too, are you guys happy with the other catagories... I think we should keep it purely for flight engines though, rather then RC cars. I think for the First practical ramjet catagory should inlcude a simple good fuel setup, easily installed into a small plane, helicopter etc. What do you think?

Man I like this zincalum, you can weld it/blow torch it, and it still comes up looking purdy.

[thecheat]

I nominate that we need one for "most likely to explode" :D

besides that, sounds good!

However... I'm still having trouble with that original idea thing... and I can't seem to make any 3D program work like I want it to! "I just want to lengthen the blasted thing, extrude! no, LEGNTHEN... GAAAH!"

PS: could someone please explain again the process of air in terms of pressure and velocity as it travels through the jet? I need to make sure I've got this down so my crazy jets will atleast have some sort of theory behind them...

PPS: how might I go about making pinholes in a sheet of steel?

[larry cottrill]

PS: could someone please explain again the process of air in terms of pressure and velocity as it travels through the jet? I need to make sure I've got this down so my crazy jets will atleast have some sort of theory behind them...

Assuming sea level operation, the air enters the inlet at standard temperature and pressure but at high speed relative to the inlet face. As the air travels through the diffuser, its relative speed decreases while the static pressure and density rise above standard values. The pressure at the rear of the diffuser will be the highest internal pressure developed in the engine, and the velocity there approximates the flame propagation speed of the fuel/air mixture at that pressure. There is additional local slowing, along with turbulence and vortexing, in the small volume of air that flows through or around the flameholder structure. Combustion at and behind the flameholder is basically at constant pressure, with the thermal expansion of air causing increased velocity at significantly reduced density. In the nozzle section, the velocity increases while temperature, density and pressure decrease until standard pressure is reached at the nozzle exit (gas temperature is still very high, of course, and density is quite low).

An interesting detail is that, if we assume that fuel enters the engine from somewhere in front of it, total massflow (air+fuel) is the same at every station throughout the entire length of the engine. This has to be true, because (unlike inside a pulsejet) there is never any accumulation of mass anywhere, even momentarily. That massflow muliplied times the increase in gas velocity between inlet and nozzle exit gives the theoretical value of thrust obtained.

L Cottrill

[Irvine.J]

The cheat wrote:

PPS: how might I go about making pinholes in a sheet of steel?

I can't find the drillbits of less then 1 mm at a hardware shop, so I go to my local model shop that deals in model trains etc, they sell a variety of #20 through to #99 drillbits. They are extremely tiny, but kinda expensive, and I break mine all the time, go slow! About 8 us dollars will get u 4 of them. If theres a particular size i'm after I get 2 just incase.

So your having trouble with your 3D? If you use wings, and want to hollow your objects out use intrude, and select only the ends of the cylinder, for example. To make a hollow cone, make a cylinder, intrude the two ends, then, select your "point editor" so you see all the dots at the ends of the cylinder. Then only select the dots at one end of the cylinder and use "Scale Uniform" or "Scale radial Z" then you can simply move them on the Z axis or make them look however you want. Wings is really easy, just play around with it. Personally, I usually add an object like a cylinder, then always rotate it exactly 90*, you will see the angle of rotation on the top left of the screen, I always work in that axis. You can also measure in CM your object, if you click the point edit again, and select 2 points, it will tell you how many cm apart they are, the cylinder when you first add it is 2 cm long. Hope that helps. I'll make a quick vid of wings for you now...

[Eric]

Yea drilling the small holes, especially in stainless, is crazy, thats why i just pierce things with the plasma cutter.

If you have a sketch of the engine made up I could do a quick rendering in autocad or inventor.

Eric

[Zippiot]

I might be the worst mig welder on the planet........

I missed the joint by 2mm.....

I am so ashamed!!! Dont look at me!!!



Need to do some major grinding, but the bead that hit the mark is strong and smoothe. Jet should be all welded up tomorrow and fuel lines r coming wednesday. Then I need to start with my combined fuel system (can be filled with gaseous fuels or liqid fuels under pressure) and mount it all on a test stand.

We need to agree on a common measurement system, like lift this amount of weight and such. Maybe lever system with a common weight at the other end. The more it lifts it the ahrder it gets to lift, so the higher it egts the more thrust created.

Or maybe a pulley system

[Irvine.J]

I had a decent run this afternoon, but probably wont get a chance to night run it till tomorrow. I would like to say my flameholder design is kinda bodgey. 90% of the flame was behind the flameholder, but a small whisp of blue flames were coming from 1 of the sections. Gasflow was adequite. Also my flame was a bit yellowish, though inside was blue, I think the zincalum was burning off the zinc and aluminium, though I can't be sure yet.

Ok so I gave my engine the complete 100point saftey check. I noticed around the tailpipe were lots of tiny (really damn tiny, but lots of them) little balls of metal. There were also some areas that looked like minor corrosion, I can only assume its the zinc and aluminum burning off, hence why nice n blue inside but when reaching the exit diffuser where it gets really hot, the flames become yellowish, still lots of blue though. I also think my exit nozzle could be slightly shorter, and maybe fractionally smaller...hehehe.

I'm going re-design a flameholder... cripes.

[Irvine.J]

Well that confirms it, its a little darker now, and I can see lots of small particles smashing into the heat shield. Though the flame looks far more blue as it is more easily seen, infact it looks really good. The flameholder creeping is still giving me issues, but as a body design its working very well. I was going to add a 1.5 inch section like this to the tail, purely for experimental sake. Ainy comments on it, simply a straight section off the exit nozzle. Anyone else try this? I look foward to seeing how it goes, I can always cut it off later.

Something like this, then possibly with a divergent nozzle would be fun to try. We will see, i'll add the 1.5 inch tomorrow, and upload the video for you guys in about 3 hours. You will see the constant but slow eating away of the zinc/aluminum and smashing it into the heat shield, however the tailflame looks really good, a nice clear "bell" right in the centre.