"Fat Boy" 12/118 thrust engine

[stoffe64]

Good luck John, i keep my fingers crossed for successful start next try
Cheers/stephan

[racket]

Hi Stephan

Yep , maybe next time , at least I know the starter is producing enough rpm now , and I've started designing up a diffuser exhaust for it to give me a bit more help in getting it to run.

Cheers
John

[smithy1]

Hi John,
I thought she was running there for a few seconds, if it wasn't over the hump, it was only a few rpm away from it....yep...a diffuser may just help.....

A bit too much "trimming" of the turbine wheel maybe?? Starter has plenty of power....engine sounds good too..!

Did you happen to take note of the P2 just prior to shutdown? Or was it too low to pick up on the gauge?

Cheers,
Smithy.

[racket]

Hi Smithy

After viewing the video a few more times I have to agree with you that I also feel it was actually running , I've got a feeling that the battery feeding the ancillories may have started to run down reducing power to the fuel pump which in turn reduced fuel a tad to below self sustain .

I'll do some testing of the battery under full power drawdown to check the fuel pressures to see if they start to drop .

Unfortunately the exducer needed that much trimming to cope with the mass flow from the "oversized" comp ..............I've just gotta make it work .

LOL.....Even though the P2 g/g was right in front of me, my eyes were glued to the TOT g/g so didn't check the P2 :-( ..........next time .

Cheers
John

[smithy1]

LOL..low voltage battery issue?...that's a thought. Yep, give your batteries a good charge and try again...it was running, I'm damn near sure of it..!

Was the EGT in a reasonable range before it started to drop rpm..!??

I've now resorted to running separate batteries, a pair of 4 cell 16,000mah Lipo's in parallel to run all the ancillaries, oil pump, gauges etc...and a single 10,000mah 6 cell for the main fuel pump, I'm also running a separate small 1800mah 4 cell for the C20B igniter....you'll see it next week..!

Cheers,
Smithy.

[racket]

Hi Smithy

I'll be looking forward to seeing all the improvements you've made :-)

Cheers
John

[racket]

Hi Smithy

Found the bastard

I charged up the ancillories battery to 13.2 Volts .

Set the throttle valve to 40 psi ,this should be more than enough fuel as the 10/98 engine only had a 20 psi setting prior to spoolup and that was enough for idle .

With oil pump activated it produced 70 psi at 1200 rpm , but fuel pressure dropped to 34 psi , and dropped further to 32 psi with ignition activated, with another 2 psi knocked off when the starter solenoid was activated , so a drop from 40 psi to 30 psi for the fuel and oilpump rpm down to 1080 rpm , before even starting to spoolup.

With everything turned on and running for 1 minute, oilpump rpm down to 850 and fuel pressure down to 19 psi .

After another minute , about the same time lapse as I aborted yesterdays test , oilpump rpm down to 733 , and fuel pump pressure down to 17 psi

Battery voltage after 2 minute termination was 12.3 Volts , oilpump still producing 70 psi at 720 rpm .

Oilpump appears to have plenty of "reserve" .

That fuel pressure drop, from 19 psi at 1 minute to 17 psi at 2 minutes could have been enough to move the "running" engine from self sustain back over to the wrong side of the hump .

Bigger battery and more fuel required me thinks

Cheers
John

[smithy1]

Ahh...that'll probably do it. Would it help to separate the battery running the fuel & ancillaries..? And another couple running the starter etc...

Just pinch the car battery for a few minutes mate...LOL..Linda won't notice.. ;-)

Cheers,
Smithy.

[racket]

Hi Smithy

I took my ancillories battery to the auto electrician and it checked out OK .

He suggested running the oilpump off one of the "starter pack" of batteries , which I've done .

Will do more fuel pump testing this arvo

Cheers
John

[racket]

Hi Smithy

Arvo test went well , I let everything run for 15 minutes just to be certain I can get a 5 minute run in .

Initially the oilpump was doing 1250 rpm at 72 psi on 25 C oil temp .

Fuel pump dump v/v set for 40 psi as on previous test , with ignition and starter solenoid activated .

After 15 minutes the oilpump was at 1225 rpm at 72 psi , basically nothing changed, the oilpump warmed up a bit to the touch but still not hot .

The fuel pump on the other hand dropped pressure to 30 psi after 10 minutes and down to 28 psi after 15 minutes, though this would probably be extended as both ignition and start solenoid would normally have been deactivated soon after spoolup.

The ancillories battery ended up at 11.9 Volts whilst the oilpump battery finished on 12.9 volts .

The second starter battery was hooked up to the "oilpump" battery and with the oilpump activated, the starter spun the engine up to 12,000 rpm, this was a tad better than previous rpm test results , so maybe the new starter brushes are running in .

There was a momentary drop in oil pressure to 45 psi when the starter was activated , but this won't be a problem .

All looking good for the next spoolup attempt

Cheers
John

[gtbph]

Hi John,

I hope the next start will be a success now the the battery problem is solved, but what are your thoughts about adding a water spray nozzle in front of the inlet? Could that help, theoretically? Or would it create more problems?

Good luck for the next attempt,
Alain

[racket]

Hi Alain

Yeh , I feel its getting closer , also I'm learning about this engines peculiarities with each spoolup attempt , they're all a bit different , but this one has some radical construction that makes it even harder to find what it wants, even though it doesn't have a jetnozzle or freepower downstream to produce back pressure and high temps like a normal engine does , this engine still requires pretty high temperatures to produce the required high gas speeds to produce enough energy to drive the comp wheel , its a fine balancing act, the exhaust gases exiting the turbine wheel will be going at nearly twice the normal speed , its "open" exhaust sounds a lot like a jet nozzle exhaust .............a strange beast .

No need for a water spray , it'd only exacerbate the restricted turbine wheel flow problems I have .

Cheers
john

[smithy1]

Apr 29, 2016 2:36:58 GMT -5 gtbph said:

Hi John,

I hope the next start will be a success now the the battery problem is solved, but what are your thoughts about adding a water spray nozzle in front of the inlet? Could that help, theoretically? Or would it create more problems?

Good luck for the next attempt,
Alain

Hi Alain,
I think John would like to get the engine running properly first before adding any "augmenation" devices...another worry for him at this stage is not what's needed. Water injection does indeed work but for our purposes it's just another problem to overcome.

Cheers,
Smithy.

[gtbph]

Thanks for your answers John and Smithy, it helps me understand these things better

[racket]

Hi Guys

Exhaust diffuser fitted.

I found an old cardboard template of an exhaust diffuser from the TV84 experiments of 2001 which was just about the right size , saved a bit of work making another one .

She's a bit of a rough rolling job but she'll do for a temporary exhaust , inlet dia ~108 mm , exhaust dia ~145 mm over a 300 mm length , a 1.8 :1 area ratio , with an ~6:1 length to radius ratio, it should recover at least 50% of the exhaust energy and hopefully keep temperatures down a bit .



Ready for another spoolup attempt





Cheers
John