"Fat Boy" 12/118 thrust engine

[racket]

Hi Mark

Vanes all "massaged"into shape and are a sliding fit to the bottom of the cuts .

Throats vary between 14.0 mm and 14.2 mm , close enough , only ~4% bigger than "design" :-)

But once I fitted the flametube end cap with its 12 evaporator holes over the loosely fitted 18 vanes it was pretty obvious I'll need to make a new end cap with 18 evaps positioned on a slightly larger radius in the end cap so that they don't interfere with the gas flow into the NGV passageways ...............LOL , that'll teach me not to make the flametube bits before completing the NGV .

With the "higher" angle on the vanes compared to previous "small" flow engines , their outer entrance tip are a good 8mm further out radially , ideally both the front and back walls of the NGV need to be ~18mm larger in diameter than what was planned/assumed/purchased ............we live and learn .

Cheers
John

[pitciblackscotland]

Hi John,
Bastard!! all that work you done on the flametube end cap thanks for the update will keep that in mind We all make stuff ups just like i did with the oil tank, mounting block for the A/B pump and other parts we just have to suck it in and fix it.

Cheers,
Mark.

[racket]

Hi Mark

LOL , just another "trophy" to hang on the wall :-)

I'd always be unhappy if I used it , especially if theres problems when I fire her up, better to spend an extra day making something I can have confidence in .

The reason I used only 12 evaps was the flow area of the evaps when using 1/2" tubing , when I go to 18 evaps the flow area is a bit high , I might need to have fairly deep D'ing to reduce flow , the heating surface is better with 18 evaps vs 12 , its a juggling act to get the right combination , I probably needed 7/16" tubing , but thats not available , so I'll make the 1/2" stuff work .

Cheers
John

[racket]

Hi Guys

Bit of work been done on the engine this week .

New 18 evaporator end wall for the flametube made, 2mm stainless


Inner rear wall of flametube , it joins the inner wall to the NGV wall, 1.2mm stainless


And I finally found a solution to the evaporator flow area vs evaporator heating surface ratio , unfortunately as a tube gets bigger in diameter its flow area increases much more rapidly than its wall area , and when the length of evaporator is fixed , a problem arises,..... but by producing a "waist" in the 1/2" OD evap tubing I reduce the ID from 11.7 mm down to ~9.5 mm , now I have my ~11% of total hole area ( inducer area) for the evaps whilst having 6 times inducer area for the heating surface, with my original 12 evap design the flow area was OK but the heating surface was down .

I simply removed the cutting disc from my copper pipe cutter and fitted a steel disc with a rounded edge, a few seconds work and theres a nice professional looking waist in the evap.


Cheers
John

[Johansson]

A very neat way of making a waist on the evap tubes!

How do one estimate the effective flow area on an evap tube with D-ing in a labyrinth fashion? I have four depressions in each tube on my JU-01 but no idea how it affects flow, it seems to work though so I am not overly concerned.

[racket]

Hi Anders

Having D'ing in the tube seems to make very little difference to flow .

Last weekend I made up a test rig consisting of a 4 ft-1.2 metre vertical length of 1" ID plastic tubing with a fitting on the bottom that attached to my 1/2" evaporators, I wanted to test the flow time difference between a plain evap and one with D'ing .

I fitted a plug over the outlet of the evap and filled the system with ~550 ml of water .

Using a stop watch and doing several tests of each evap to get an average time to empty the plastic tubing , I found the variations was minimal .

With a plain evap the time was 1.50 seconds , with D'ing it increased to 1.60 seconds .

I then fitted a bellmouthed bush of 8.7mm ID into the the plain evap and the time went up to 2.00 seconds , this was the point when I decided I had to change the flow rate of my evaps by reducing the flow area through the use of either a bush , which would have been a bugger to make and silver solder in place , or workout a way to reduce the ID of the evap by "waisting".

An hours work modifying my little copper pipe cutter solved the problem , nice quick and easy repeatability .

I've just about sorted out the flametube design now , so can cut the evaps to their correct lengths and do the waisting and D'ing on the rest of the 18 evaps .

Then its just a matter of getting some 1.2mm sheeting cut for the inner and outer flametube walls and start drilling the couple of hundred holes in them .

It won't be long and I'll be dragging out the TIG to spent a few days welding everthing together .

Cheers
John

[pitciblackscotland]

Hi John,
Ah!! nice work on those parts are you using 800 series stainless steel sheet for the evaporator end wall & Inner rear wall ?

Cheers,
Mark.

[racket]

Hi Mark

Nope , just 2 mm 304 stainless for the evaporator wall, and 1.2mm 304 for the inner rear wall , they'll both have plenty of "air blanket" cooling .

The 2mm stainless needs lotsa oxy torch for me to be able to "roll" the edge with a decent weight hammer , the 1.2mm can be cold formed

Got all the evaps finished yesterday , my hands are hurting today from all the hammer work .

Will need to make a trip next week to find some suitable silver solder to fix them into the end wall .

The mockup looks pretty good :-)

Cheers
John

[racket]

Hi Guys

Bit of an update , evaporators all silver soldered ( 45% silver content) into the flametube end wall using a rudimentary wooden jig to get the evaporators at a bit of an angle so that their outlet are closer to radially centered on the front wall .






Note that all evaporators are positioned the same with regards their D'ing , when looking through the evaps the clear spaces are like radial spokes in a wheel , with the D'ing facing the adjoining evaps D'ing





Cheers
John

[pitciblackscotland]

Hi John,
Good work there That's one job out of the way on with the next

Cheers,
Mark.

[racket]

Hi Mark

Yep, another down , will start getting the TIG sorted this week , time to start welding the NGV together

Cheers
John

[ripp]

Hello John,

any updates?

Cheers
Ralph

[racket]

Hi Ralph

Coming very soon :-)

I've been busy fixing my house during the cooler months here in Oz , now that the warmer weather has arrived ( 34 deg C today) , its time for me to head back to my workshop to play with turbines rather than paint brushes , hammer and nail .

Hopefully I'll get my TIG operational later this week and start making some progress with the remainder of the build.

Cheers
John

[racket]

Flametube bits ready to start welding together





Cheers
John

[Deleted]

Hi John

Looking good, real peace of art work :-)

All Best
Andy