Reversi concept

[metiz]

This is the Reversi concept. the "straight" tailpipe is very short. the remaining tailpipe folds over itself twice and expands at the same time. it uses the available steel on both sides, meaning you need less of it making it lighter. The engine will also become significantly shorter while still keeping the tailpipe length required to keep a functioning pulse-jet, incorperate a expanded tail and since there is less surface area, any drag would also be reduced. the model posted here is just a concept, not to scale, not fully 3d and not even fully symetricall. It is just to make my idea clear. I can't yet create the complex surfaces that would make this model much easier to follow - you'll just have to use your imagination a bit.

would this CONCEPT work?

I've included the google sketchup model. it has the extension .doc rename to *.skp

[PyroJoe]

Interesting concept.
The first section of tailpipe looks a little short. On most linear styles the tail pipe is usually 2 to 3 Combustion Chamber lengths before it expands. In many thermo style jets the tail pipe is 3 or more CC lengths before the expansion.

It appears the further the gas is traveling away from the CC, pressure is being traded for mass velocity. What this translates to me is that bends are best kept close to the CC. As the velocity increases, mass flow will have more difficulty making sharp turns later in the tail. None that I recall made a hard 180 turn that far down the tail.

Many jets have been run with several large radius bends late in the tailpipe. Erics pulse jet stew heater was one. Sometimes we just don't know for certain until we try it.
Hope this helps,
Joe

[Mike Everman]

Two things:
The sharing of a wall is good from a weight standpoint, and bad because that material is not cooled. you may have to use a heat resistant material there.
Next, do the math on the areas you'll need. You'll see that it becomes a very narrow annular gap, especially on the outermost run.

Generally, annular designs have an uncomfortable amount of drag. Too much surface area for not enough cross-sectional area. In my opinion, the reduction in length is not worth all the effort, and will be low efficiency in the best case.

[metiz]

can the drag not be decreased by making a dent pattern in the walls like in a golfball?

[PyroJoe]

This one has a 180 bend nearly at the end of the tailpipe:

download/file.php?id=10622&t=1

Joe

[Jutte]

Another tricky thing to consider would be the loss of volume and the drag
of internal support struts.Not a knock back - but a contruction consideration kind of thing.
However in saying that - I built a spud cannon that had internal supports
and 180 degree flow change - it worked just great (apples through wooden doors etc).
The dimples could work , but dimples on one side would be draggy bumps on the other
side of the wall.Also flow directing 'stators' might work - but then you get flow drag/disruption
+ the whole pulse jet flow reversal thing + a more challenging build.However in saying that
sometimes the more simple solutions work the best.
The more mathematically inclinded could work out the correct etc ratios for tail pipe
contruction. This would help in intake ratios etc.
In the end just build it ...and enjoy the journey!

[metiz]

This is a scaled drawing for a integrated design. I intend on building this but I don't know yet where to put the intake. Putting it on the front dome with the elbow still intact so that the opening clears the exhaust stream can be done right?
the laird usually gets realy hot so this is a good test to see if the engine can take the heat
any suggestions or comments on this one?