"Fat Boy" 12/118 thrust engine

[racket]

Hi Aaron

LOL, I hope so .

A few pics of things back together.

Ready for testing





Dead C30 4th stage wheel , one to hang on the workshop wall as a reminder of what not to do



Cheers
John

[azwood]

I noticed a hung start on mine Antill I put the wastgate on now it just starts . I put it down to added turbulence in the drive housing but when it's up and running gate closed no problem.guess I'm lucky it could start fine then turn to crap haha.

[pitciblackscotland]

Oct 21, 2019 20:04:23 GMT -5 racket said:

Hi Aaron

LOL, I hope so .

A few pics of things back together.

Ready for testing





Dead C30 4th stage wheel , one to hang on the workshop wall as a reminder of what not to do



Cheers
John

Hi John,
Bloody Hell that 3rd stage wheel is stuff you do have a spare one

Cheers,
Mark.

[smithy1]

John,
I may have a 4th stage C30/C47 wheel floating around.

Smithy.

[racket]

Hi Mark

Yep , she cracked roughly half the blades , no spare , so thinking of fitting a "common" 4th stage C20 wheel , just a case of sleeving the shroud to fit the smaller diameter wheel .

Cheers
John

[racket]

Hi Smithy

If you do , it'd be much appreciated :-)

I'll continue using the dead wheel until I'm certain of getting a "cool" start proceedure worked out .

What I'm very concerned about is us DIY'ers attempting to use the Allison wheels in a stalled configuration , the blade design has a virtually flade section at the tip without any "hook" to catch the gases when the wheel is stationary , the flat design is fine once the blade is rotating and the gas velocity triangle become "normal" , but with a stationary wheel those flat blade tip just want to ricochet the gases off them , the gases are at ~20 degrees, as is the blade tip in the opposite direction , I feel we might be asking a bit much in expecting the gases to smoothly turn through so many degrees without any blade curvature/"hook".

The richocet will produce a lot of turbulence which could be effectively reducing flow area and putting excessive backpressure on the gas producer until such time that the wheel RPM are high enough to produce acceptable velocity triangles .

I've ordered a butterfly valve www.ebay.com.au/itm/163575949690 which will remain open during start and until such times as necessary to keep temps under control , I'll need to "fiddle" with its operation mechanism , but thats the easy part.

I've been having a look at the video of the "jet nozzle " spoolup of some 4 months ago and noticed the spoolup was drawn out a bit more than normal , so the exhaust wastegate wouldn't have gone astray in that scenario either.

R and D throws up a lotta heartaches , I still remember all those ball bearing problems with the FM-1 engine , which a change back to "brass" on latter engines solved , hopefully the "wastegate" will do the same with this engine which has always been just on the edge of achievability .

Thanks again for all your help over the years :-)

Cheers
John

[smithy1]

Oct 21, 2019 23:42:44 GMT -5 racket said:

Hi Mark

Yep , she cracked roughly half the blades , no spare , so thinking of fitting a "common" 4th stage C20 wheel , just a case of sleeving the shroud to fit the smaller diameter wheel .

Cheers
John

I have a 4th stage C20 wheel too if that is preferred..?? Also a 3rd stage C20 wheel IIRC...

I'll have a fumble around in my "new shed".

Smithy.

[racket]

Hi Smithy

You must have had "fun" :-( packing up all your shed's bits and bobs for the move , the household stuff is quick , the shed stuff always takes twice as much effort , then theres having to set it all back up at the new place , thankfully no more moves for me , .............LOL, it'll be someone elses job one day to throw it all into a skip bin :-)

I've got a spare C20 4th stage wheel here if/when I need it , but I'll keep your offer in mind just in case ....................if you ever come across a 4th stage C28 wheel , they have the same OD dimensions as the C20 but a larger flow area , almost as large as the C30 ...........please secrete it away .

Currently looking at centrifugal clutches for possible options to enable the wheel to rotate whilst the vehicle is stationary to help with those gas velocity triangles , ..........more time at the keyboard today .

Cheers
John

[racket]

Hi Guys

Well , centrifugal clutches seem to be a non option, the size required to cope wirth the torque means the clutch will cost more than the engine :-(

Another "difficulty" is fitting a sprocket rather the usual V belts , because of the ball races supporting the "drum" , the sprocket size would be getting too large once allowances were made for securing screw heads to chain clearances .

Ah well , have to think of another solution :-)

Cheers
John

[lofi]

It's not impossible to make a clutch, and well within your tooling/ability. Garage54 on YouTube successfully ghetto-fabbed (and I mean really ghetto) one out of a brake drum and shoes for a Lada recently.

youtu.be/o6AF3LiMIts

Given some dimensions to work to, it's something I wouldn't mind having a go at myself and shopping over to you!

[racket]

LOL.......love the russians :-)

I had thought about making something , but its only another potentially long development job, something I don't want to start ................theres also some "special" needs due to the 6,000 rpm output speed , the commercial clutches only go to ~3,600 rpm as their cast drums need to be replaced with steel ones above those rpm , then my potentially very high torque figure at lowish rpm adds another layer of complexity .

The more I delve into this, the more a simple sprocket on the output shaft is looking better all the time.

Once I get the spoolup sorted with the wastegate I'll be better informed as to what might be needed in the way of transmission bits ...............I'm hopeful that once it is up to idle , things will settle down into a more conventional scenario ..............the fact that it appears as though theres some "surge" during my dry spoolup tests, with the P2 gauge needle bouncing around , but which has been rock steady in all my "live/wet" test runs in the past. gives me hope .

Things are just a tad marginal in lotsa areas with this engine , just gotta massage her gently to get the best from her :-)

Did a whole lot of fuel flow tests today to verify the fuel system is producing the same results as it did when I installed the 19G needles , I've also added a small needle valve in the delivery feed line to the engine so as to provide a finer control of the spoolup fuel to minimise any temperature spikes from just using the inline ball valve which has worked OK up till now .

Development grinds on slowly.

Cheers
John

[racket]

Hi Guys

Been doing some "design??" work today on the relationship between gas flows into the turbine wheel and the wheel blade inlet angles and its become a little clearer why the Allison engine has N2 speeds of between ~94% and 100% for virtually everything , whether for heli or turboprop use .

The downstream load is reduced by lowering the pitch , allowing the freepower to almost freewheel , the FADEC keeping N2 rpm within its design range for the power output required .....................LOL, its sorta becomes more of a "single shaft" engine .

I did some experimenting using a ballpoint pen moving towards the C20 wheel blade (which is similar to the C30 design) at the ~20 degree angle of my "NGV" , the pens ball impacted the blade at the tip and simply ricocheted off , so I tried it further down the blade , the same outcome occured until near mid blade length , at which point the blade had an angled "hook" which grabbed the pen ball and pulled it into the wheel.

The velocity triangles I drew up indicated I'd need near 20 - 22,000 rpm before the blade tips would start to "grab" the gases in any but the smallest amounts , ...........as I was only going to use ~25,000 rpm as a max, I need to rethink things a bit more .

I'm thinking maybe this engine needs to operate as a combined thrust and shaft horsepower engine at various rpm , at low speeds the bias will be towards thrust and as speed increases and freepower rpm rise , the wastegate closes and shaft horsepower takes over , a bit of juggling might be required to get a smooth transision , but if theres even 40% shaft power/torque available initially thats still ~ 100 HP .

More thinking required ..............there will be a solution :-)

Cheers
John

[smithy1]

Hi John,
I had a fumble around in my shed, l have 3 x 3rd stage C20 wheels and 2 x 4th stage C20 wheels on hand....no series 4 wheels at the moment, but that could change soon as we get quite a lot of C30/C40/C47 engines coming through the shop. Many of the customers ask for their time x wheels back, the rest are destroyed and disposed of. I need to get hold of the ones that will be disposed of before they're destroyed.

Smithy.

[racket]

Hi Guys

Some flow testing of the C30 wheel using the leafblower and cotton thread stuck onto the blades

youtu.be/1fQo5GnBLJU

Cheers
John

[turboron]

John, part of the fun of DIY gas turbines is finding "work-arounds" to test our ideas/units without the test stands of the OEMs. Very interesting test.

Thanks, Ron