Monster Mash: 32-inch Folded Lockwood Dimensions

[larry cottrill]

All right, I finally decided to use UFLOW1D to work out a 32-inch long version of the Lock Reynst Monster(TM), presented only in basic schematic form before. This should be acoustically nearly identical to a traditional Lockwood, with volume ratios off only a little. It also turns out that a cylindrical intake should be perfectly acceptable with the tail cone inside, to provide for the characteristic Lockwood "reverse" cone intake. The size of the intake flare is just a guess, since the consensus is that UFLOW doesn't tell us much about that, anyway.

The engine was designed as a miniaturized straight Lockwood with slightly lengthened chamber, then broken at mid-chamber and folded back, and then the intake was stretched slightly to meet the L/3 point at the flare (with a small assumed end correction applied). Finally, the chamber was widened a little to get what I thought was a reasonable volume. This should either run or come really close to running. It is acoustically really good in UFLOW. The one effect that is not accounted for is that all the intake air will be pre-heated and some of the tailpipe air will be air-cooled by the intake. This could mean that the intake will need to be lengthened a little, so it wouldn't hurt to prototype it with a sliding shell, as mentioned earlier in another thread.

It is critical that the front end of the tailpipe cone be lined up with the front end of the intake tube as shown in the detail. Support for the tail cone is via four sheet webs, also shown (dimensions not critical). Each of the four intake ducts thus created should have a separate fuel pipe, which can be manifolded together well aft of the flare. Each pipe should be well centered in its duct segment; the exact depth of the fuel spout must be determined by experiment, but should end up being somewhere around the 3/4 point of the intake duct, as shown approximately in the detail.

Also shown in the detail: a slight flare can be applied to the front end of the tailpipe cone to try to get the balance of intake to tailpipe outflows closer to the traditional Lockwood pattern. It applies a slight pinch to the intake inflow, however, and should not be more than the small amount shown, 1 mm all around.

I would not expect a lot of power from this engine, because of the relatively small area at the front end of the tailpipe cone. Of course, like any other Lockwood, a lot of the thrust will be from the intake.

L Cottrill

[Viv]

So tell me Larry why is it you consider this to be a relative of the Lockwood and not an annular chinese derivative?

Viv

[larry cottrill]

Viv -

I first proposed this engine (in raw schematic form) in response to Mike's assertion that a Reynst-breathing engine and a Lockwood are basically the same thing, taking the front-end reflector into account:
http://www.pulse-jets.com/phpbb2/viewtopic.php?t=1613

Here is his very interesting original discussion of this subject:
http://www.pulse-jets.com/phpbb2/viewtopic.php?t=1410

Even the traditional Reynst Pot obeys the Hinote Criteria (L/3, L/5 and L/8 critical points), if you hold your mouth right when you look at it:
http://www.pulse-jets.com/phpbb2/viewtopic.php?t=1572

But specifically, the only things that make this more like a Lockwood than anything else all derive from the fine points in the details:
- This engine has the uniformly tapered tail cone
- The tail cone inlet (front end) area is very small
- The intake area is very large
- The intake area tapers from full size at the chamber to smaller at the throat of the flare
- There is significant chamber nozzling out through the intake
- Kadenacy breathing action will be dominated by the intake
- Intake velocities and massflows will be relatively high
- Tailpipe velocity will be quite low, though massflows will be fairly high
- Much of the tailpipe air mass will be more-or-less stalled in the cone for a significant part of the cycle
- A very large fraction of total developed thrust will be from the intake

Some of these traits will be similar to a Chinese; some not. Some will be like the FWE, some not. Some like a Reynst Pot; some not. It is only the flows that are essentially modified by the geometric details. The acoustics are practically the same.

Optically, there is almost no difference between a 40-foot long room and a 20-foot long room with a mirror for one of its end walls. It's when you design the air conditioning that you'd see the difference.

L Cottrill

[Viv]

No sorry old mate I will have to disagree with nearly all the Lockwood points as the major point is the intake and exhaust are on the same side of the combustion chamber so you have a phase shift in comparison to the Lockwood layout of intake one end and exhaust the other.

The acoustics are differant not practically the same I would say, comparing cone angles of intakes and node locking points or lack there off in the exhaust makes little differance, its just not a Lockwood any way you look at it.

Am I being a pain:-)

Viv

[larry cottrill]

Well, you're at least a very gentlemanly sort of pain.

No matter what is or isn't ... I bet it will still run.

L Cottrill

[hinote]

. It also turns out that a cylindrical intake should be perfectly acceptable with the tail cone inside, to provide for the characteristic Lockwood "reverse" cone intake.

Larry--just a thought:

I didn't calculate the percentage reduction in intake cross-section, due to the growing influence of the megaphone inside it. Just eyeballing it though--it looks like the meg is going to cause too much restriction near the entrance end of the intake.

It would make little difference in the performance of the motor if you shorten the meg and substitute a constant-diameter "throat" tube, in the area of the intake. That way you can control the consistency of the intake area.

FWIW

Bill Hinote
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

[larry cottrill]

I didn't calculate the percentage reduction in intake cross-section, due to the growing influence of the megaphone inside it. Just eyeballing it though--it looks like the meg is going to cause too much restriction near the entrance end of the intake.

Bill -

The decrease in area from inside to outside end of the intake is almost exactly what I had in UFLOW for a "normal", i.e. slightly tapered, intake tube. I had expected to need a slightly outward-expanding tube. Of course, this concentric geometry is inherently draggier than a simple conical tube, so it might be better to expand it, or use a narrower straight tube for that region of the tailpipe, as you suggest. I'll bet it will actually run as shown, however.

I think there is a lot of "Coanda effect" on these concentric or annular intake designs. I wonder what the effect of that really is - whether it reduces effective intake area, causes excessive braking of the ejected gas, etc. I think it might be an improvement to force separation somehow, with a "separator ring" around the tailpipe or something. This kind of thing was suggested for my Smooth Lady FWE; I just don't know what significance the effect really has.

L Cottrill

[hagent]

Hi Larry,

I hope you can make it to the Coaxial Club! It's pretty lonely here.

Did Ed Knesl ever post a movie of his running coaxial PJ?

I only found the photo of his design.

Also, you may want to try my fuel ring idea or version of it on your new design. It was not that hard to make and I think it was the most efficeint mixing of propane and air that I've seen. Also I used 8 4/40 screws to hold my exhaust tube and it seems to work great. I haven't tried real long runs but so far so good. I would be happy to share how I built the fuel ring.

I wish you the best of luck and can't wait to hear the RESONNNNNATION...

Cheers,

[Bruno Ogorelec]

Yes, Ed has been quiet for some time. We have not really heard much either about his coaxial engine or about his straight-pipe Chiense. I don't know which looks more interesting to me.

[Rossco]

Larry,
I find it extreemly interesting the flow of Hagen's engine.
It looks to me the shape of the CC! Your thoughts?
If Hagan is prepared to disclose some dim's of his engine??? how do they stack up to your theorys? (or visa-versa as it has turned out)

Yes Hagen, we would love to have a description of that fuel ring! Looks like a vortex mixer? Put it up in your thread tho. And any other info or observations that you care to share.

Rossco

[larry cottrill]

Larry,
I find it extremely interesting the flow of Hagen's engine.
It looks to me the shape of the CC! Your thoughts?
If Hagen is prepared to disclose some dim's of his engine??? how do they stack up to your theorys? (or visa-versa as it has turned out)

Of course, flows are affected (we could even say "tuned") by area proportions, volume proportions, contours, roughness, etc. Flow is pretty complex - for example, I would never have thought that the FWE would turn out to create such a "separation" between the very hot-running chamber and the (relatively) cool tailpipe.

As to theory, all I know is what I can see in UFLOW1D simulations. And, that's not much good if there's significant reliance on separation and turbulence in the real engine. You just have to assume that the basic flow pattern will emerge once you get things set up rightly. Flow of hot gases through complex shapes is just not simple. Of course, you already know that ...

L Cottrill