"Fat Boy" 12/118 thrust engine

[racket]

Hi Anders .

Yep , its nice to finally have bits bolted together rather spread around the workshop .

Whilst I've been waiting for the O'ring I got to thinking about freepower wheels for the engine , up till now I've more or less felt I'd have to use a C30 4th stage wheel as the flow is ~50% more than our TV94 based engines, but maybe the "common" C20 4th stage wheel will work .............heres my "rational??" thinking on this .

The C20 engine flows ~3.6 lbs/sec which is the same as the 12/118 engine ............off to a good start here :-)

The C20 turns out 420 HP from its two freepower stages , one would assume an equal division of work between the two stages , so 210 HP for the C20 4th stage wheel .

Now the calcs for the 12/118 gives at least 250 HP , therefore I must have more "energy" available going into the turb stage than the C20 has going into its 4th stage .

More energy means more gas velocity , so I should be able to get the same mass flow through the same stage flow areas if a C20 4th stage NGV is used with the C20 4th stage wheel .

Up to now I've always wondered why the 4th stage C20 NGV appeared to have an "oversized" NGV flow area of ~14 sq inches when the wheel only has ~15 sq inches , but it appears as though the stage is proportioned more for cruise efficiency than 102% takeoff power , at takeoff theres could be considerable "inefficient" swirl in the wheels exhaust gases,.......... N2 is kept constant between takeoff and cruise regardless of N1 power setting.

From my reverse engineering of the C20 freepower stages it appears as though they only have a PR of less than 1.5 :1 across each stage , whereas I should have 1.7 :1 out of the 12/118 .

It would mean some increased blade loading on the C20 wheel compared to the bigger C30 , but as both wheel look almost identical other than the longer blading on the C30 ,which would increase tensile loading on the blade roots and hub, we might just get away with it .

Cheers
John

[Johansson]

That is interesting reasoning, it should apply to my JU-02 powered C20 freepower as well since our gas producers are similar in size. Since the C20 wheels are much more common it would be great if it works.

[racket]

Hi Anders

I might have to do some experimenting once the engine is working , even if only a static test with a freepower and NGV rigged up behind the engine to see if the gases can get through without the temps increasing too much .

Cheers
John

[smithy1]

John,
That engine is just "DIY Turbine Porn"...! Very nice indeed.

Do you have a 4th stage C20B wheel?? If not I can probably shoot one to you.

Cheers,
Smithy.

[racket]

Hi Smithy

She'll look good once on the test stand with ancillaries attached and ready to fire up.

Yep , got a couple of C20 wheels , thanks for the offer :-)

The silicone O'rings finally arrived late this afternoon so I can get into the final assembly tomorrow .

Cheers
John

[smithy1]

Mar 15, 2016 3:01:54 GMT -5 racket said:

Hi Smithy

She'll look good once on the test stand with ancillaries attached and ready to fire up.

Yep , got a couple of C20 wheels , thanks for the offer :-)

The silicone O'rings finally arrived late this afternoon so I can get into the final assembly tomorrow .

Cheers
John

Be sure to take a couple of pics prior to running please....at least before the petina happens..

Cheers,
Smithy.

[racket]

Hi Smithy

A few pics as requested

Fuel manifold along with start gas manifold mounted and ready for outer can to be fitted .


On the test stand with umbilicals to be fitted







Went and purchased a 12Volt car battery this afternoon, I want to be testing the starter before the weekend .

Cheers
John

[pitciblackscotland]

Hi John,
Well she almost ready for a start Will you have anyone with you on the first start up That's a fairly quick build of the fat boy engine About 13 months

Cheers,
Mark.

[Deleted]

Hi John
looking good
not long to go now
Did the guy get back to you for the gearbox?
cheers chris

[stoffe64]

Looking good as always John!....impressive build and fast too!

[racket]

Hi Guys

Thanks for the encouragement :-)

Chris , they never got back to me , so will rethink things once the engines running successfully .

Mark , don't worry , I'll get video ;-)

Fuel and LPG are now hooked up along with the T2 pickup , working on the P4t and "extra " P2 pickup , the current setup is plumbed to the LPG supply line to the start injectors so that I can monitor LPG start pressure , a dedicated P2 will be a better proposition .

Then only the lube supply and battery wiring to the starter .

So back to the shed and get things finished :-)

Cheers
John

[stoffe64]

Hi John!
Will you measure the engines rpm?....i did not see any such devices!
Cheers/Stephan!

[racket]

Hi Stepham

I've got a hand held tach that I'll use .

My main concern is attaining sufficient start rpm so I don't get a hung start , so on the starter coupling theres a couple of "flats" that are there for tightening the coupling to the starter, the coupling is spray painted matt black around the area of the flats , on one of the flats I've glued a reflective piece of tape ( ~1 cm X 1 cm ) so that I can do some starter rpm testing to see what can be obtained.

On the snout of the comp wheel, half is painted matt black and the other left the metal , and a crescent of reflective tape is glued onto the radial section of comp snout surrounding half the nut , this will hopefully provide sufficient reflection for the tach to produce engine running rpm.

I've done some experiments with tiny pieces of tape( 2mm X 10 mm) on a cylinder ( ~1 cm diameter) in the Dremel spinning at 30,000 rpm , with 3 tiny pieces 120 degrees apart I'm registering 90,000 rpm on the tach even when the tach is at quite an "unfriendly" angle to the tape .

Hopefully things will work OK , I only need to verify RPM vs P2 pressures up to full power of ~60,000 rpm , once thats done I'll use P2 as my guide .

Cheers
John

[madpatty]

Fire it up sir.

Everybody is waiting so keenly.

Cheers and all the best.

[stoffe64]

Mar 16, 2016 19:45:12 GMT -5 racket said:

Hi Stepham

I've got a hand held tach that I'll use .

My main concern is attaining sufficient start rpm so I don't get a hung start , so on the starter coupling theres a couple of "flats" that are there for tightening the coupling to the starter, the coupling is spray painted matt black around the area of the flats , on one of the flats I've glued a reflective piece of tape ( ~1 cm X 1 cm ) so that I can do some starter rpm testing to see what can be obtained.

On the snout of the comp wheel, half is painted matt black and the other left the metal , and a crescent of reflective tape is glued onto the radial section of comp snout surrounding half the nut , this will hopefully provide sufficient reflection for the tach to produce engine running rpm.

I've done some experiments with tiny pieces of tape( 2mm X 10 mm) on a cylinder ( ~1 cm diameter) in the Dremel spinning at 30,000 rpm , with 3 tiny pieces 120 degrees apart I'm registering 90,000 rpm on the tach even when the tach is at quite an "unfriendly" angle to the tape .

Hopefully things will work OK , I only need to verify RPM vs P2 pressures up to full power of ~60,000 rpm , once thats done I'll use P2 as my guide .

Cheers
John

Hello john
Then you must know what rpm you have at a certain pressure(p2)right? You calculate that With pressure and temps? To know what rpm you have?
Cheers /stephan