"Fat Boy" 12/118 thrust engine

[racket]

Hi Guys

Mods finished and test stand remounted back onto the car trailer.

Spring balance "calibrated" , 20 X 1 liter units of water from a measuring jug added to a large bucket and weighed , the spring balance was within 1 kg of "exact" weight , close enough at 5% margin of error .

Just waiting for an "offsider" to visit and aid with the testing ...............Chris , she's waiting for you ;-)

Cheers
John

[Deleted]

Sept 15, 2019 20:57:50 GMT -5 racket said:

Hi Guys

Mods finished and test stand remounted back onto the car trailer.

Spring balance "calibrated" , 20 X 1 liter units of water from a measuring jug added to a large bucket and weighed , the spring balance was within 1 kg of "exact" weight , close enough at 5% margin of error .

Just waiting for an "offsider" to visit and aid with the testing ...............Chris , she's waiting for you ;-)

Cheers
John

Hi John 
thats good to hear
will bring along a go pro camera as well ,cant have too much footage ...lol 
do we need anything else?

Cheers Chris

[racket]

Hi Chris

Nope , we should be OK , just hope its not a total fire ban day when you're here , theres enough bushfires at present with these drought conditions without me starting another one :-(

I'll get a bit more fuel brew made up and recharge the 4 batteries and checkout the ancillories before you come .

Another pair of experienced eyes will be appreciated :-)

Cheers
John

[enginewhisperer]

let me know when you're going to test and I'll try to come up too

[racket]

Hi Andrew

Chris has pencilled in ~8-9 October

Cheers
John

[enginewhisperer]

ahhh those are work days for me! Will see what I can do

[racket]

Hi Guys

Well, an attempt to fire things up yesterday failed miserably , Chris and I had a nice cool damp morning with overcast skies and we were feeling "confident" of an enjoyable testrun.

The gas producer simply couldn't get past ~16,000 rpm , with flames exiting the freepower resulting in an overheat situation and a ruined wheel , half the blades cracked :-(

Autopsy report to follow .

Cheers
John

[turboron]

Bummer. Development always bits when you least expect it to be a problem.

Thanks, Ron

[racket]

Hi Ron

Yep , its never "easy" , leaves me feeling "gutted" afterwards, but after a nights sleep I'm ready to start the "fight" once again .

Currently doing static testing of the starter to check the RPM against earlier data and things are showing a reduction .

Tested with open jetpipe and 70 psi oil pressure , then nil oil pressure, then with 107mm jetnozzle and 70 psi oil and finally with just the freepower scroll fitted and 70 psi oil.

Batteries are getting recharged , so more tests this afternoon.

If RPM numbers are still low I'll heat the oil and repeat .....................then start doing some insitu fuel flow tests to check flows vs delivery pressures to see if something has blocked up in the past 4 months since the last very successful testrun with the jetnozzle fitted .

Lots to try, hopefully there'll be a "problem" that can be easily fixed

Cheers
John

[pitciblackscotland]

Hi John,
Sorry to hear this was looking forward to hear what results you got.

Cheers,
Mark.

[Johansson]

Sorry to hear that John, I know the hopeless feeling that comes just after an engine failure.

[racket]

Hi Anders

Yeh , not the best feeling , but heh , its part of the process of progress, just gotta put on my "big boy" pants and get back into it .

I've got a feeling that the problem is the Allison wheel design , that "flat" blade in the tip region at ~20 degrees , its OK when the wheel is spinning and the gas/wheel velocity triangle angles are "better", but for stalled conditions theres no "hook" to grab the gases and bring them into the wheel , I feel the gases want to just ricochet off it and create a lot of turbulence which ultimately puts excessive backpressure on the gas producer .

I'm looking at fitting a "wastegate" into the interstage duct , I've got a short length of 75mm stainless tube that I'll "blend" into the ductwork to "unload" the gas producer when the freepower is stalled , it'll need some sort of blanking off arrangement for when the freepower is spinning at >25% N2

The C20 wheel doesn't appear to be quite as bad as the C30 with its longer blading , its almost as though they simply increased the "flat" blade segment length, I'll continue to use the broken wheel in my testing ,to maintain a "datum point" , more static testing today , so better go and get the batteries on the chargers.

Will keep you posted on developments as they may be critical to your success as well :-)

Cheers
John

[Johansson]

Hi John,

That might very well be the case, looking forward to some hands on research from you on this. The upside is that every failure on these engines lead to some serious R&D which the whole community benefits from.

I must have made the jet guys here shitloads smarter from all of the trouble I´ve gone through with JU-01 and JU-02! *LOL*

Cheers!
/Anders

[racket]

Hi Anders

LOL ...........yep , we're a lot smarter for your "experiences" ;-)

Did some testing for battery voltage drop during a starter run up .................not good :-(

With freshly charged batteries at 26.4V , upon application of the starter it dropped to ~8V and slowly climbed back up to 11.1V by end of rotor acceleration to ~11,000 rpm .

Tried single 12V batteries and got up to ~7,000 rpm , with batteries at ~12.6V afterwards , but voltage dropped to ~7.2V on one and only 6.7V on the other as the starter neared completion of its runup.

Something ain't right :-(

Will get the battery pack checked by the local auto electrician to see whats going on , but it looks like new batteries might be needed.

Cheers
John

[turboron]

John, I recently added a automobile type voltmeter to my DIY gas turbine. I soon noticed that my fully charged battery decayed rapidly as the oil pump was running. The battery was approximately 3 years old with a lot of tests and recharges on it. It is of the deep cycle marine type. I replaced with a new battery and now the voltage is maintained.

Thanks, Ron