Calculations... double checking with the pro's

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Irvine.J
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re: Calculations... double checking with the pro's

Post by Irvine.J » Tue Oct 10, 2006 11:13 pm

Mate yeah you can roll a cone out of a cylinder, Thats how I did mine. (One slice and some grinding, then cutting off the excess.) Cutting it 8 times is alot of work and potentially very irritating. Trick is with a cylinder to roll the cone you want with a bit extra top and bottom, then start cutting the bottom flat so the two side angles begin to look symmetrical. Problem is when you first start rolling the cylinder it looks all out of whack, but i promise if you carefully cut/grind it down, it will look like a perfect cone eventually.

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re: Calculations... double checking with the pro's

Post by El-Kablooey » Wed Oct 11, 2006 1:10 am

It's MUCH easier to roll a cone from sheet than to make one from a tube. There is no way I would make 8 (no, make that 16) cuts in a tube and then make 8 welds.

Google a program called Cone Layout 2.0.3. It's free, all you have to do is enter your dimensions. It will show you a 3d model, and a flat layout for your cone. It will also print the layout, if it's too big for one sheet it will print several sheets with guides for lining it all up and taping together.

thecheat
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re: Calculations... double checking with the pro's

Post by thecheat » Wed Oct 11, 2006 11:37 pm

hehe- you said it couldn't be done? it HAS! I made 16 cuts with a HACKSAW (yes, a hacksaw), bent 'em together, and somewhat welded it up.... right now I'm grinding them down so I can do some spot welds to patch the cone up. I'll get pictures in a sec... after some magic with switching from the wireless to the camera card adapter, then back.

PS: the welds are hideous, I know, BUT the cone turned out alright. Heh, 47, I hope you take a look, this is me just saying that I take back that your welds were ugly, they were rather pretty!
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Irvine.J
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re: Calculations... double checking with the pro's

Post by Irvine.J » Thu Oct 12, 2006 2:34 am

Hehehe, reminds me of something out "Alien ressurection". Lol mate your and my first ramjet are twins of the ugly ramjet family! Ahahaha not to worry mate, twas a good effort and I can see alot of hard work involved. Couple of quick tips to tidy it up a bit...
It doesn't matter if you leave the excess on the outside, it will just look crazy, however you need to smooth out the inside as much as you can. In this instance, you might need a rotary tool with a grinding attachment. They are very cheap these days (like $20 and have a long teather so you can move it around.) I use one to grind down one of the nozzles on my video, grind the inside flat/smooth as possible.
If you like, I can post a video of how i made my cones out a cylinder, though flat is probably the least amount of work, welding lots of cuts is very tiresome! Also, there is alot of excess there, I think you said you have a mig, if this is the case lower the wire speed to very low, by turning the inside knob as tight as you can get it. Nice job though, never say never! I bet you'll have this monster burninating in no time. Goodluck sir. Also, that blue paint is going to smoke you out real bad, so run it, let it burn off, then sand it off and go again... if your unlucky, the paint will burst into flames.... remember how mine was painted white with "Burninator" written on it... well, it burst into flames... so do it outside first ok :D I wasn't going to say that because i was embarressed I left it painted... but, better to be a curious newb then a flaming one eh? ROFL... goodluck

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re: Calculations... double checking with the pro's

Post by Najm » Thu Oct 12, 2006 2:10 pm

Making a cone from sheet metal is wayyyyyyyyyyy more easier. You have to weld only once and the walls of the cone are also smooth.... you don't have to grind them to make them smooth.

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re: Calculations... double checking with the pro's

Post by larry cottrill » Thu Oct 12, 2006 3:35 pm

Go to this article in jetZILLA online magazine:
http://www.jetZilla.com/Vol02Num01/jetZ ... #Article_2

This has examples of using Eric Beck's freely downloadable Pulsejet Calculator, including an example of calculating cones. All you need to input is the large ID, the small ID and the length. There is also a link in the article so you can download the Calculator, but my link may not be the latest version. It always gives accurate cone sheet dimensions (it does not draw them for you, however). You can download the latest version from his Website here:
http://www.geocities.com/erjabe007/

I make perfectly adequate cones by getting the layout with Eric's calculator, making a paper pattern, tracing it onto the sheet metal, cutting with an air-powered tool and then hand bending the sheet around a piece of water pipe (with just a little gentle hammering to finish the straight edges that come together).

L Cottrill

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re: Calculations... double checking with the pro's

Post by thecheat » Thu Oct 12, 2006 9:45 pm

glad you like it! heh, but anyways, I HAVE to grind the stuff off as I've got to do some re-welding, considering my first try (as you saw) is "holy" at best.

The inside will be ground down with the dremel (I think I'm going to have to buy some more bits...) after the welding is done.

The paint IS going to come off however, BUT, I'm not going to bother with it until I get to welding it. Hehe, maybe I'll christen it with kerosene... (Relax, I'm just kidding)

But, is the general consensus that I should make the intake 10 degrees (total angle) BUT atleast chop the 19cm legnth down to half that?

PS: do one of you think you could attach the Cone Layout 2.0.3. program to a post? my intrernet won't allow me to get the thing from the site.

PPS: oh, I used a wire welder on the cone, as far as I know it didn't have any argon... but it may have, I really don't know, it's not my welder, I know someone else who has a GREAT industrial MIG welder, but, I don't think I can set up an appointment for a while to use it. Another thing, the wirespeed... though I played with it, didn't seem to make a difference, I tried the lowest and highest with no real difference. BUT it WAS on minimum when I welded.
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re: Calculations... double checking with the pro's

Post by Irvine.J » Fri Oct 13, 2006 1:39 am

http://www.i-logic.com/conecalc.htm

Another cone calculating program for use with sheet metal. Though Erics Pj calculator is just brilliant.

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Re: re: Calculations... double checking with the pro's

Post by larry cottrill » Fri Oct 13, 2006 2:44 am

thecheat wrote:But, is the general consensus that I should make the intake 10 degrees (total angle) BUT atleast chop the 19cm legnth down to half that?
cheat -

We need to understand WHY the diffuser is designed the way it is.

There are two limits to the pressure gain you can get with your diffuser. The first limit is the ratio of outlet area to inlet area; this has been called the 'area ratio', though to be honest, I don't know if that actually is the accepted term. It relates to the 'pressure ratio', but the relationship is undoubtedly non-linear. The other is (gasp!) the inlet air velocity. Ideally, the diffuser's length (at the chosen included angle) is designed to closely match the lowest operating speed (the slowest ram air the engine can take and still run). What this means is that a "perfect" diffuser will exactly provide the maximum attainable pressure gain for a given speed. The higher the speed, the greater pressure gain we can actually attain.

Most blowers we can get our hands on will deliver a few hundred feet per second at most - not a very high speed, in ramjet terms. What this means is that you can build a diffuser with a 2:1 pressure ratio if you want, but it won't do what you expect - you'll have combustion somewhere up in the diffuser, instead of holding it back in the chamber! I don't know how to calculate it (though I could probably find out easily enough), but I doubt that a 200MPH inlet speed could handle anything more than a few percent better than 1:1. If you look at "classic textbook examples" of ramjets drawn in old college textbooks, the area ratios look like something on the order of 1.5:1 or so - and that's for an engine that's supposed to operate at at least Mach 0.5 !!! It takes a LOT of input velocity to achieve a high pressure ratio.

A "classic" supersonic ramjet, on the other hand, has a long, narrow conical diffuser with an area ratio of maybe 10:1 or some such! But look at what kind of velocity is going into it. The inlet can be so small because at that speed the massflow (air mass per second) is still HUGE. Incidentally, at that speed, ten degrees would be way too "blunt" a cone to avoid separation.

That's why I said to start with what you have and gradually cut back as you watch it run - if, at the best air speed you can deliver, it looks like combustion is happening a couple of inches up into the diffuser, cut say an inch off. This will reduce the pressure ratio, BUT it will also increase the air mass flow going in (because of enlarging the inlet). Just keep working with it like that until the combustion stays in the chamber behind your flameholder. At that point, your diffuser is just right for that engine, at that air speed. That's all there is to it.

For low to moderate airspeeds, ten degrees included angle should have no trouble at all delivering smooth air into the chamber, without separation from the diffuser wall. The angle could probably be quite a bit larger than that for fairly low speeds (electric leaf blower, etc.).

L Cottrill

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re: Calculations... double checking with the pro's

Post by thecheat » Fri Oct 13, 2006 3:58 pm

AH, now I feel a little better...

now to pound some of it into my brain.

first off, I just followed the steps they used in the "example" engine on the main page... which I guess was built for 800 fps... So, the inlet doesn't have to be AS small as intended... good.

My leaf blower is a 150mph one (I've got a 200mph backpack one, but I'd rather use the less expensive handheld one just in the case something gets screwed up) does that help any?

Second, with the ratio, for the slower you go, should the inlet hole be bigger than the nozzle or smaller? It may seem obvious, but, I'm just learning this stuff...

PS: 47, actually (no offence) but the cone generator seems more professional with the PJ calculator, Now, if only I could get my hands on that Cone layout program... I like how it shows the 3D models, that's helpful as it lets me see "oh, that DEFINATLY doesn't look right!"(the internet security is screwing up a bit and won't let me get to some of the sites that are fine, even with override passwords... which is really annoying, meaning I've got to wait a while until the replacement software comes in.
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re: Calculations... double checking with the pro's

Post by Irvine.J » Fri Oct 13, 2006 5:40 pm

Lol no offence? As if I'd be offended, it was just another suggestion... any info is good info. Also, you can increase the speed of the airflow out of you 150 Mph blower by making a long slender angled cone... i rolled some cardboard, glued it up with some electrical tape to keep it together, got a massive boost of airspeed/flow out of it. Infact I was very surprised (I think larry or eric suggested it) but it made a heck of a difference.
Fire this thing up! Eagerly awaiting.

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re: Calculations... double checking with the pro's

Post by thecheat » Sat Oct 14, 2006 6:42 pm

Ok, well, somehow I was able to get onto the cone layout program, so, I tried out a couple legnths (total angle as near to 10 degrees as possible) that would fit on the remaining section of empty propane bottle that I have. Got that done (total angle is probably around 11-12 degrees) cut it and shaped it. Now I just need to weld it, reweld the nozzle, weld and trim them as they go on and I'll be ready to light it! (propane and spark plug have yet to be added)

PS: the intake to nozzle dia is 1:1 at the moment.
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re: Calculations... double checking with the pro's

Post by thecheat » Tue Oct 17, 2006 3:19 pm

well, progress is stalled for around a week... as, my schedule is locked up and I'm going to be unable to weld for that time... Darn.

But, in the meantime, I still've gotta figure out a good way to distribute fuel flow (propane) Are there any reccomended ways of doing this?

Also, do you think you guys who have built a ramjet could share a few pictures of your fuel delivery system?

PS: also, I've been looking at buying a mig... So far I've found one welder that seems to be the way to go. It's called the "Hobart handler 140 MIG" I don't know if anyone has any experience with this welder, but, some general pointers in what to look for in a welder would be greatly appreciated! (any suggestions for a MIG that costs under $500, and can weld smaller than 20gauge metal and some decently thicker stuff would be great)

PPS: 47, what welder did you end up getting/how well does it work?
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re: Calculations... double checking with the pro's

Post by Irvine.J » Fri Oct 20, 2006 4:56 am

G'day thecheat...Please correct me if i'm wrong, but I'm visualising a little yellow guy who knaws peoples faces off :D If i've got the wrong visualisation let me know... otherwise...

Seriously:
I'd use a stinger like this possibly 1or 2 inchs infront of your flameholder initially. Heres a pic on how i'd do it initially with some copper brake line with a plug silver soldered in the end, 5 holes. Remember I'm no pro but i think this would work well. Make the holes very small aroun .60 /.70 max, as there is 5 you'll get a fair drop in pressure. Angle the holes on the side so it doesn't go straight out but points toward the flameholder.

Also, if you don't want to go to the trouble of welding in a sparkplug just yet, you can always fire it up by holding a propane torch at the back. You might find it just doesn't light or blows the torch out if you dont have enough gas initially, so be fairly liberal with the gas. If it gets going and starts to work, add your spark later.

Welder:
As for the mig, Mine cost 250AU bucks, new on ebay and is "Gasless". It works quite well, however it only has "Hi and Low" voltage settings. if I had the chance again i'd probably go for TIG welder. Simply its pretty easy to burn holes in thin stuff with it, and as far as i'm told TIGs are good at real thin stuff up to very big stuff. Might be a little more expensive though. Ebay is a good way to get yourself a good welder I suppose, the MIGS at the shop were 500 bucks, so I got it half the price i normally would from an ebay online store. For 500 US you might be able to get the TIG/MIG/Plasma combo, if its not US a tig or mig 500 should be MORE then enough.

If you couldn't tell I like your nick :D Goodluck!
When you make the video of it running, PLEASE put the burninator themsong to it, you can get it from here... It would fit your name here perfectly :D Again I might be visualising the wrong "Thecheat"
Peace. Has such a cool midi guitar riff in there... LOL
http://us.share.geocities.com/cyberludwig/trogdor.mp3
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re: Calculations... double checking with the pro's

Post by thecheat » Sun Oct 22, 2006 7:46 pm

hey thanks! in a rush... but thanks for the imput! Actually, I kinda wondered when you put the burninator on your ramjet! Yes, impressions are correct! hehe, perhaps I'll try to draw a trogdor...

as for the welder, as far as I know TIG's (which I first sought after) are about $200 USD above my price range... which happens to be right at $500.

actually, if you see anything that looks good, please post it, I'd love to get a TIG (meh if it isn't easy! I'll learn!) but unless I can find one in the pricerange, that'll be tough.

PS: thanks again for the imput, I'll go try to work something out!
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