'Smooth Lady' - Easiest-To-Build FWE Ever

[larry cottrill]

My latest FWE - Version IV, with the intake redesigned for ease of construction. This method works because of slightly tilting the chamber upward [a Lady with her nose in the air].

The engine has the advantage of a straight intake without the 'split tube' manipulations found in the Fo Mi Chin II and FWE III designs. Instead, the intake is simply formed from a length of 3/4-inch EMT, without flaring but with the front spout hammer-formed. The front end of the tailpipe is cut with a small extended tab, which is simply welded to the outside end of the intake to secure proper alignment (the front-end transverse cut is slightly sloped to butt up to the tilted chamber cone). Put the front dome on the cone in the usual manner. Then, the fully welded intake/tailpipe assembly is slipped into the cone, the whole thing is rested flat on the floor [the bottom of the chamber lines up in the same plane with the bottom of the tailpipe tube] and the cone tack welded in place. Finally, finish weld all around and form the tailpipe and intake flares as a final step.

I think I personally would mount this one with the intake underneath, for a really clean, streamlined look.

L Cottrill

[larry cottrill]

Here's the chamber cone sheet pattern for this one. For the dome, you can use either the classic pattern or the FMC II pattern [if you want the plug down low on the front].

L Cottrill

[Jmitchell]

Will the old "Svelt Lady" cone sheet work for this? I fabricated a cone for that, and never got around to building the rest of it, but want to build this one.

[larry cottrill]

Will the old "Svelt Lady" cone sheet work for this? I fabricated a cone for that, and never got around to building the rest of it, but want to build this one.

It is very close. You should be able to make it work with some filing, especially extending the oval slot forward a little. The only real problem area will be at the rear, where you will have a fair-sized gap to fill with weld at each side, as you go down under the intake tube [since you will be using a full tube, not just a half-shell that's wide at the base]. In other words, there will be more and more gap to bridge with weld as you work toward the rear of the chamber cone.

To get a picture of what you're up against, print out the cone sheet above on your computer at 218 or 219 percent [or whatever works with your particular printer], or print it out as is and use a copier to blow it up so that 20 squares = 20 cm [208 percent on a copier here at work], then cut it out carefully with scissors and wrap it tightly around the cone you already made, carefully lining up the big oval hole. You'll see immediately where adjustments need to be made, and where the problem areas will be.

It should not be difficult for a good weldor, but challenging for someone who needs practice at bridging gaps in thin material!

Good luck - I'd love to see you build it and get it running!

L Cottrill

[larry cottrill]

Here are the precise detail dimensions to use for the intake / tailpipe assembly. Note that the side welds between the intake pipe and tailpipe 'spade' will bridge between the two with a significant void between them; you MUST carry weld clear across the front of the spade as shown here to seal off these areas from the chamber!

Again, note that [if everything fits just right] when this assembly goes into the cone so that the small end of the cone butts into the front of the pipe, the bottom of the cone and the bottom of the tailpipe should rest flat on the same plane. If the alignment between the intake and tailpipe has been done with care, the cone will be practically self-aligning in the side-to-side direction when the main assemblies are put together.

L Cottrill

[larry cottrill]

This may seem obvious to those that are seasoned jet builders and/or experienced in reading drawings, but I thought beginners might need clarification of how the main assemblies [chamber and intake/tailpipe assembly] go together and get welded up so that the connection is fully sealed.

L Cottrill

[ed knesl]

It seems like a lot of welding. What do you see as the disadvantage to having the intake running paralell to but not touching until it bends into the chamber, like the Chinese or Logan or NRL?

Larry, I always like simlification and your design is that !

Ben's comment is understandable - reason for Larry's approach is
avoiding welding under such sharp angle betw. intake tube and the cone,
so it may be easier to go all way around.

Good design, Larry, I might put one together and that would be stainless.

Ed

[Jmitchell]

My first FWE was kind of like this, because I couldn't weld under the sharp angle, so I just welded the sides of the pipe to the CC.

[larry cottrill]

Larry, I always like simlification and your design is that !

Thank you. If I can figure out how to take it farther, I will ;-)

Ben's comment is understandable - reason for Larry's approach is
avoiding welding under such sharp angle betw. intake tube and the cone,
so it may be easier to go all way around.

That's right, but not the main reason. First and foremost, I want to get these so that the largest transverse section is a 2.5-inch diameter circle. The Sveldt Lady does that, but it's sort of an advanced smithing project, what with split tubes and all. This one greatly simplifies the intake building process, while still ensuring good alignment, if the intake/tailpipe assembly is carefully wrought. To bring it off within the shadow of that 2.5-inch disk, you have to move the tailpipe down by cocking the chamber. Neither the acoustics nor the flows will be troubled by that, and almost no scale model designed for the Dynajet will be greatly troubled by lowering [or raising, if mounted inverted] the tailpipe CL by 5/8 of an inch!

Good design, Larry, I might put one together and that would be stainless.

Thanks again! Man, how I would love to see one like that!

L Cottrill

[larry cottrill]

Well, I did it - and it's one of those times when I wish I had a digital camera so I could post a shot right away. What did I do? Why, cut my own chamber cone out of sheet metal, that's what!

That's something I honestly don't think I have ever done before in my life with steel. I've cut a few heat shields out of thin aluminum, using big scissors, of course - but this is the real stuff, a Smooth Lady chamber cone cut from a piece of 24 ga black stovepipe! I made a pattern by printing out the jpeg I posted above and blowing it up with a copier here at work, then transferring it onto an old manila folder and cutting out. I then scribed around the pattern with a small nail, scratching easily through the black coating onto the steel.

One of the things I did right was buy a PAIR of shears from Menards - one for right curves and one for left. Unless you're using some of the new transparent sheet metal (or have some way of perfectly marking both sides!) that's almost a must, in my poorly-educated opinion. My hands are not very strong, as I have never been much into manual labor, so at times I thought it was pretty tough going; and, there was some edge distortion, though that was taken out after the fact by very light hammering. Oddly, using the correct shear, I had no trouble at all making the curved cuts, even the inward curving cut that forms each side of the 'oval slot', even at the front end where the curve is really tight! I almost couldn't believe how well it worked (of course, it helps to have brand-new cutting edges on your tools!).

After cutting out the part, I gently hammered down the edges and hit all the edges with small flat and half round files, taking out little flaws and dressing down all the sharp edge on both sides for safe handling. The only significant error found when laying the pattern back down on the finished piece was that the large radius at the front end is about 1/16 inch farther out than intended (obviously a flaw in the material that allowed it to stretch in that direction during cutting ;-) The curve is exactly right, however, and since a couple of mm is pretty small compared to the wavelength this should run at, I guess I'll leave it. Otherwise, it looks awfully good, and weighs in at exactly 5.0 ounces!

The next thing will be the rolling, of course - this material is thin enough to roll easily, and already has a fair amount of curvature in the right direction (since it is, after all, cut from a piece of stovepipe). Holding the edge up to my Engineer's scale, it appears to be roughly 1/40 inch in diameter, which would be about 0.64 mm. That should be adequate for a small prototype chamber - it's not as thin as Fo Mi Chin! I have nothing fancy to do the rolling, and will just work it around a piece of 1-inch pipe by hand until it seems right.

If I can put this together successfully, it will be the first engine I've done where I will have made my own cones from scratch. The cones for my original FWE prototype were provided by Steve Bukowsky.

L Cottrill

[ed knesl]

OK, Larry,

From now on, no more paper engines - everything must me METAL.
That will teach you !!! :-)

Ed

Next time try air nibbler or 4in grinder with cut off wheel, in both cases
distortion will not be a problem.

[larry cottrill]

OK, Larry,

From now on, no more paper engines - everything must me METAL.
That will teach you !!!

Ha ha - fat chance. As I've said before, I think of ten times as much as I draw and draw ten times as much as I can build myself. The only thing doing my own cones does is make me less dependent on someone else - it doesn't save me any working time getting it done (well, OK, maybe it did save a little time, since such thin material is so easily worked).

Next time try air nibbler or 4in grinder with cut off wheel, in both cases distortion will not be a problem.

I'd like to have found a nibbler type device. I just didn't spend the time looking around to find anything like that. There's a Northern Tools outfit a few miles away - I should have taken a look there.

I did roll the cone myself last night. The only "tool" I could find that was solidly mounted was the 1-inch galvanized pipe that sticks up out of the floor of our horse barn (it has a freezeless hydrant at the top). Using my leather gloves, I neatly pulled the piece around the pipe, working out from the center gradually in both directions. This worked well for all but the side edges, where my hands didn't provide the needed leverage, so along those edges I had to resort to careful light hammering. The result seems wonderful - much better than I would ever have expected for a first effort. One disadvantage of my "vertical roll" is that it has the clunky hydrant at the top, so I had to "spring" the piece off the pipe from the side. But, it was easily brought back to shape by hand so that the rather short straight edges come together almost perfectly. And, the front and rear edges seem almost perfectly round, too. The 24 ga steel is really a nice material to work with - even a young kid could do it, with patience and good work gloves.

Now I have to make the front dome. That's a lot smaller, but it will be harder to cut AND harder to roll, because of the very blunt conical shape and almost no clearance at the "small end" (where the plug mount goes). I'll get it done, somehow. I'll probably start by drilling and filing the center hole, then shear cut the rest. I have the pattern cut out and ready to use.

It occurs to me that an awfully nice thing to do would be to go ahead and cut out sheet metal patterns, so more of these chambers could be easily made in the future. But, I'll probably never get around to it, of course. If I want production, it would make more sense to contact Viv and Luc and try to talk them into cutting them in stainless ;-)

L Cottrill

[larry cottrill]

Jmitchell, Ed K et al -

You or anyone else who actually wants to try to build this engine can join my Ten Dollar Jet Engines web log as a member, if you want to contribute. Of course, anyone can add their comments onto any post on the 'blog, but if I sign you on as a member, you can actually post articles that will appear under your own name, with a bold header. All I would need is for you to send me your email address, which I would need to sign you up as a member of the blog.

Blogger is free and it is extremely easy to use, with basically a WYSIWYG editor as the main tool for composing a post. They now have it set up so you can easily upload picture files, much like on this site. Posts can be edited after publication, though I would want that limited to needed corrections. As Ben has pointed out, articles should be pretty short, covering just a specific issue. You would only be expected to contribute something when you really feel you have something important to add - anything that would clarify a building technique or propose an alternative method, suggestions of useful tools, etc. What you write wouldn't need to be flattering, you can be critical of a design or detail, as long as you propose something that you think would work better. Anything that would help a beginner build this engine (and/or others in the future) would be welcome. I want the blog to mainly be a place for beginners to go to find out how to get started.

Please consider this offer and let me know if you'd like to participate in this way.

Have look at what's there now - more to come soon:
http://tendollarjets.blogspot.com/

L Cottrill

[ed knesl]

Now I have to make the front dome. That's a lot smaller, but it will be harder to cut AND harder to roll, because of the very blunt conical shape and almost no clearance at the "small end" (where the plug mount goes). I'll get it done, somehow. I'll probably start by drilling and filing the center hole, then shear cut the rest. I have the pattern cut out and ready to use.

It occurs to me that an awfully nice thing to do would be to go ahead and cut out sheet metal patterns, so more of these chambers could be easily made in the future. But, I'll probably never get around to it, of course. If I want production, it would make more sense to contact Viv and Luc and try to talk them into cutting them in stainless ;-)

L Cottrill

Larry,

I would drill small pilot hole in the middle, than cut the dome shape,
weld the dome, weld the dome to the chamber and last drill the hole
for spark plug and weld the plug threaded insert.
The reason is to prevent heat distortion of the dome if plug insert gets
welded to dome prior to chamber connection.
I would make the dome thicker, at least 20ga, thin stuff will crack
around the plug from vibrations.

I use thick paper patterns for cone shapes.

Ed

[larry cottrill]

Larry,

I would drill a small pilot hole in the middle, then cut the dome shape,
weld the dome, weld the dome to the chamber and last drill the hole
for spark plug and weld the plug threaded insert.
The reason is to prevent heat distortion of the dome if plug insert gets
welded to dome prior to chamber connection.

Actually, I had no problem with distortion when I did these before for my original FWE cones. That material was about 1 mm thick, however. See photos below.

I would make the dome thicker, at least 20ga, thin stuff will crack
around the plug from vibrations.

That is an excellent suggestion. The only catch is that the weld around the edge becomes a thick-to-thin weld, which is always somewhat touchy. But, I have done it plenty of times. This has to be a good weld: the force trying to "blow the lid off" is about 4 x the engine thrust in the classic FWE chamber.

L Cottrill