Welding tips for mig

[Irvine.J]

Ok here are a couple of photo's I've taken of the final engine...
I have flared the intake and tailpipe the best I could, which isn't really that well at all. (Eek- dont be mad)
I have noticed, and I dont know how this happened the CC is about 1/4 inch longer then 7 inches, thought the tailpipe is the correct length, and the fuel input point is the 3 inches from the top where I think its supposed to be. Also due to the fact its all I had left to use, i had to use an intake pipe that is
3/4 inches wide
3.25 inches long at the top
2 inches (at the 106* angle leading into cc) Which is probably only 100 degrees.
The tail pipe is 1.25 inches wide and slightly flared and 18 inches long.
Overall length is 26.25 inches long. I didn't try using my blower yet!!! I also have a hair dryer with a modified noze piece which might do it. It did make a little gargling noise that made me go "hmm".
I will try the propane torch in the tailpipe with the hair dryer tomorrow for sure. Also, i've filled it with water again, and seriously that end cap is welded quite porly, so it might give me the chance to grind it off to 7 inches and re weld it with something a little better, it leaks a fair bit of water indeed. Atleast it looks nice, i'll make some quick mods and give it another go.

Larry I watched you video and listened to ALL you audio tapes. They are clear, concice and well thought out... a truely professional job! I am very impressed! Thanks so much for all your help, i'll get this beast roaring and make ya proud you can count on it!

[Eric]

Here is a tip, and it is going to sound very counter intuitive to some.

Drill a 1/4", or even a 1/8" hole in the middle of the combustion chamber cap where a spark plug would normally go. Position the torch so that it blows the flame into this little hole at an angle, with the tip of the torch itself off set from this hole so any pulses of air coming out this hole do not blow the torch out.

Now light the torch, turn on the fuel, and blow the air into the intake.

The torch will ignite things in the combustion chamber where they are supposed to ignite, and you will not have to hastle with trying to ligth the intake or tail and have the flame progress and settle back in the combustion chamber.

If you do this you should at very least get it to run on compressed air which will give you enough push to continue with the project. Likely, you will have it self sustaining in 10 minutes or less.

Eric

[Irvine.J]

Ok fellas, I drilled a small hole in the front with the burner like eric advised... I ground down and re welded the front off cc better then last time. I got the hair drier with modified cone and started testing...

I got a grumble, and turned the gas up, and as i'd let it down got a few really loud BANGS... I yelled "Cmon you bastard!!" Several times and got a few more loud bangs but still didn't run properly...
I looked at the plans and measured the overall length of my engine, the cc is now the correct 7 inches, yet my tail pipe is 19 inches -(total nearly 26 inches) I think it might be 1 or 2 inches too long, (should be 24.3) I'll cut it down in 1/4 inch sections tomorrow if you guys think it might do the trick. I must say when it went BANG it really was bloody loud!

Q--->Do i need to flare the tailpipe each time I cut a bit off, or should it be ok leaving it straight till i get the length right?

Heres the video, a couple of loud bangs and a grumble...thanks to my father on his day off for working the airflow!

[larry cottrill]

Usually I advise people that they're pushing too much air. However, from what little the video shows, this time it seems like maybe not quite enough! I also get that from your description above - you're getting bangs when you are winding down on the fuel, which to me says that you're finally getting an explosive mixture when everything's just running "at a trickle". In other words, by the time you lean the fuel down enough to bang, the QUANTITY of air and fuel making the bang isn't quite adequate to set up oscillation. At any rate, you are VERY close to having it running!

The straight pipe is so forgiving that I almost doubt that the length is your problem. Amusingly, I have found (on straight tailpipe engines) that when you're just an inch or two too long, the engine will start to run (self sustain) and then 'fade out' to extinction over a few seconds. If you get it to do that, another inch or two off will get you where you want to be!

The explanation for this phenomenon is simple: The cold engine is just close enough to "in tune" to run, but as it heats up the frequency increases slightly until resonance with the intake pipe is no longer possible. In other words, the cold length is barely adequate, but the hot-running length is not! (An engine heating up expands physically due to the metal's thermal expansion, but this is more than compensated for by the increase in wave speed as the internal gas temps go up, so the frequency rises - in effect, the engine is acoustically shortened as the temp goes up, even though it gets slightly longer physically.) On the other hand, the air in the intake pipe is heated very little over time.

I hope you have equipped yourself and your father with good hearing protection!

L Cottrill

[Irvine.J]

Damn thing! So close, yet so far! Its popping more frequently, grumbling louder... and goes bang bang bang... but just can't nail that all illusive RAGHGHGHGHGHGH! I've used the blower and hair dryer... and I know i'm close, I also took it down to 24.5 inches.
I yelled "Cmon you bastard!" a few times for emotional support, "Talking to my engine" so to speak, offered it a little love by saying things " START YA F-ING MONGREL!" and still, she just wont recipricate. I'm now of the oppinion my welds are just crap, and there overlaps might be too big. Damn shame, i'll try a little longer...but as of 2pm this arvo after spending a good 3/4 times at 10/15 minute intervals, i'm just nakered and dismayed. I will keep this engine, but will probably start again. I fired up my ramjet for a while and that made me happy again! Gawd i love that thing. Off to buy some parts for my aircraft... damn shame i couldn't make it work properly...next time!

[El-Kablooey]

You need more air, and more fuel. A source of compressed air would be a great help to you here. That engine will run, you just need to get the starting procedure down. Also make sure your fuel pipe will not wiggle, and is centered in the intake, ending just barely inside the intake flare.



P.S. There is never anything to gain from getting discouraged and giving up. There is no reason that engine would not run. It may not me perfect, but it should still be a great noisemaker.

[Irvine.J]

Ok So I tried again, similar bangs n gargles but not recipricating. What I've notice is that by changing the nozzles (I cut off a primus torch tip to screw on different size nozzles at will) I found the nozzles with the smaller apatures ie more pressure seem to have better results... perhaps its time for a "rosco" trial? The nozzle with the .7mm hole seemed to have greater girgling volume and banging then leaving a nozzle off with a 2mm hole? Rosco's...anyone... I haven't given up yet... just siting here taking a break n having a glass of wine for 20 mins.

[El-Kablooey]

OHHHHHHHHHHHHHHHHH!

There's your problem! You NEED to use a bigger tank, I doubt you'll ever have any luck with a torch valve and a 1lb tank.

[Irvine.J]

No no its a 4kg or so tank... I use the blowtorch at the end of the CC to light it up... Lol its a standard little BBQ tank LOL! No regulator just straight tank to engine... I just had a spare primus torch tip I cut off and silver soldered onto the end of a small copper pipe... here is a photo. I seriously think my intake pipe might just be too thin. I think that may be the cause of all of my propblems. And possibly a much larger intake flare. Dimensions are posted above. I dont have an air compressor, only a petrol blower and this crazy hair dryer.

[El-Kablooey]

Ok, my bad. That tank setup is fine.

On my FWE's, I have had great luck with a piece of 1/4" brake line (available at autozone for like $3.00). I don't use a nozzle at all, just the brake line with a clean cut.

[Irvine.J]

Ok i'm gonna make the flaring a little bigger right now,and just dick around with it for 10 mintues, give it another go... see you in a few minutes, thanks for the tip kablooey, I'll try the open line again.

[Irvine.J]

Oh well, I tried pretty hard today, and to no avail... perhaps tomorrow being a new day the physics of the universe will be slightly different and this thing might just work... I'll look for a little hand held compressor at the shop tomorrow as well....if all else fails... a really big sledgehammer.

[Mike Everman]

I don't think anyone answered this, but you will want to flare the tail whenever you change it. If a motor is finicky, it'll need it for sure. This is a small motor, so you should be good with a 3/16 brake line fuel stinger. Progressively pinch it down, after trying randomf valve settings and levels of air. You might squash it down to .25mm slit as a guess, though I'd start it at full dia. Try a rosscojector, too, if you don't think you're getting enough air from your drier, which may be true. That fuel feed you have now is rather largeish, and maybe a bit obstructive.
Leaks shouldn't matter too much, but too many and it'll only run at high throttle, and that means you'd need way more air to get it started at that level, like from a shop compressor. Fill it up with water after plugging the intake, and see if there are any major leaks and fix them. Ignore the ones that slowly form a drop.

Good luck!

[Eric]

With my advanced FWE I could unscrew the spark plug, with was a big plug that left a 5/8" hole in the front of the engine and it kept running just fine. As far as leaks are concerned that hole is one hell of a leak.

A hair dryer on high should provide enough air, especially if you put a nozzle on the dryer so that it blows faster in a more confined stream.

Try it with the straight fuel line first, no nozzles, no pinches at the tip of the line.

Give it fuel until the pops and bangs become more frequent, and experiment with positions that you blow the air in at.

Dont bother with a hand held compressor, its not going to give you enough flow.

[Irvine.J]

I found my "wagner brand" spray-painting gun... it pushes an absolute monstrous amount of air in controllable angles... I set up the gas and it went BANG a few times in quick succession and I started to play with the settings with the copper brake line... I hadn't been working for more then 45 seconds when the neighbours ran out saying "Is everyone ok I thought we heard shooting!!!" I Laughed real hard and said no no, its just a jet engine! They were like oh... bloody loud! With a couple of "fair dinkums" from some of the males around the neighbours house, I picked a real bad day (being fathers day) to get this sucker running, though I KNOW this beast will come to life tomorrow... can't wait. Scared the crap outta my neighbours though MUAHAHAH... I love this stuff...