100-150 Hp turboshaft thoughts

[monty]

Thomas,

You were indeed correct. The gears would not work, but not because of surface durability or bending. Those were marginal, but OK, at least for limited life at my power levels...<<150KW. The problem was critical speed. I was right smack in the middle of the critical speed range, and I did not actually have a hunting tooth design. Interestingly if I use common off the shelf modules, I run into a conundrum. I can increase the module, to get out of critical resonance, but then I have problems with pitch line velocity, or the gearset becomes too large for my taste. You have gone to one side of the solution space, I have gone to the other. The optimum module was about 1.3 or so, not off the shelf....so my $300 gearset becomes a $3000+ gearset....

I think I have a solution. I will have to compromise on the ratio and fan tip speed a bit. The quantity of prime numbers that add up to something close to the right ratio is limited without going much larger. Surface treatments are required, but only nitriding, induction hardening, and grinding/lapping...nothing terribly exotic. Rolling elements will not work on the planets in my design. We shall see. It's certainly better than what I had before.

Thanks again!

Monty

[racket]

Hi Monty

The TV94 bearing kit doesn't have the Thrust bearing as its normally riveted to the comp housing back wall plate , generally by the time a turbo needs its overhaul theres damage done to the backplate as well .

The TV91 bearing kits we sourced from China came with the thrust bearing as they were probably intended for minimal low cost bearing overhaul rather than turbo remanufacture where a new back wall would be fitted.

The TV 91-94 thrust bearing is an old design , but it is 360 degree and has better thrust handling capacity than some of the newer 270 degree units , a modern 360 degree setup where the thrust surfaces are in a single piece rather than separate ones would make mounting much easier .

Cheers
John

[CH3NO2]

Subscribed.
Great thread with lots of great info.

Good luck with your build Monty.

[monty]

Nov 11, 2018 8:24:14 GMT -5 CH3NO2 said:

Subscribed.
Great thread with lots of great info.

Good luck with your build Monty.

Glad you like it! Hope my stuff can inspire others the way you guys did me. I was designing a piston engine/fan but they just weren't happy with each other...

[monty]

Nov 10, 2018 20:48:15 GMT -5 racket said:

Hi Monty

The TV94 bearing kit doesn't have the Thrust bearing as its normally riveted to the comp housing back wall plate , generally by the time a turbo needs its overhaul theres damage done to the backplate as well .

The TV91 bearing kits we sourced from China came with the thrust bearing as they were probably intended for minimal low cost bearing overhaul rather than turbo remanufacture where a new back wall would be fitted.

The TV 91-94 thrust bearing is an old design , but it is 360 degree and has better thrust handling capacity than some of the newer 270 degree units , a modern 360 degree setup where the thrust surfaces are in a single piece rather than separate ones would make mounting much easier .

Cheers
John

Thanks John,

I've decided to go with the Holset 360 thrust bearing. Since I changed the gearset, everything else also changed. I think it will work better with my current plans.

Monty

[monty]

To placate "doubting Thomas"  (who was..and perhaps will still be proven correct!) I have battled with my gear train design software....There are no longer any warnings or problems, including resonance speeds.

My design now has a 13 tooth pinion, a 21 tooth planet, and a 55 tooth ring. There are 4 planets. The pinion is case hardened, the planets are nitrided, and the ring is heat treated. They are lapped together with generous backlash. The ring is undercut a bit to give the proper backlash and center distance. Everything changed accordingly. I'm still working on the fan design to be happy with all these changes, but it appears to be 13in diameter...

The good news is the diameter decreased.

Monty

[CH3NO2]

Nov 11, 2018 19:54:36 GMT -5 monty said:

Hi Monty,

I know the feeling.   I've been "contemplating" a similar topic as yours.
Maybe after I get my gt6041 turbine finished, tested and characterized I will be in this forum asking Professor John and everyone similar questions.   
Not for pairing a turbine to a ducted fan but for possibly mating a free power turbine to a liquid oxidizer pump in a full flow staged combustion rocket cycle.
It would be cheap and easy to fabricate a regulated blow down tank to meet the flow demand, and I may do this, but using a performance automotive turbine wheel to power a pump head would be much more challenging and satisfying.

Getting way ahead of myself.  So much to research, study, test and learn first.

Tony

[monty]

Nov 11, 2018 22:31:03 GMT -5 CH3NO2 said:

Nov 11, 2018 19:54:36 GMT -5 monty said:

Hi Monty,

I know the feeling.   I've been "contemplating" a similar topic as yours.
Maybe after I get my gt6041 turbine finished, tested and characterized I will be in this forum asking Professor John and everyone similar questions.   
Not for pairing a turbine to a ducted fan but for possibly mating a free power turbine to a liquid oxidizer pump in a full flow staged combustion rocket cycle.
It would be cheap and easy to fabricate a regulated blow down tank to meet the flow demand, and I may do this, but using a performance automotive turbine wheel to power a pump head would be much more challenging and satisfying.

Getting way ahead of myself.  So much to research, study, test and learn first.

Tony

Tony,

Did we meet at Oshkosh a few years ago? You're not into combined cycle rocket stuff...perchance??

Monty

[CH3NO2]

Hi Monty,

I dont believe we have met.
Never been to Oshkosh but yes, I have always been into rocket propulsion and propulsion chemistry. From solid propellants to liquid monopropellants and liquid bipropellant engines. More recently I got infected by the turbine bug when the idea came to me that gas turbines engines could be used to leverage rocket propulsion and the chemistry in a way that I haven't previously considered.
So this led me to the path of turbine engines as an extension of rocket propulsion and its chemistry.

Tony

[racket]

Hi Monty

Did you get around to measuring the exducer throat on your G Trim turb wheel ??

I'm in the process of sourcing one , but if you have a throat size could you please pass it on so I can get on with some calcs

Cheers
John

[monty]

John,

Kind of hard to measure exactly, but I get somewhere around +/-7.843 in^2 as my best guestimate.

Changing the gear ratio has required redesign of the entire fan. Unfortunately my nice, elegant blade retention scheme has become a 5 axis nightmare. Very hard to model correctly... I'm bogged down in all that at the moment. Also waiting on my Holset bearing parts to arrive.

Let me know what you come up with for the numbers!

Monty

[monty]

John,

I just went back and checked your previous post and you indicated around 8.6 in^2. I measured from the tip perpendicular to the adjacent blade. This forms a triangle of sorts-with some curvature to it. That is what I based my estimate on.

Is that how you made your measurements?

If I fudge to the large side....at best 8.76 in^2

Monty

[racket]

Hi Monty

I've measured standard F Trim wheel exducers and found ~7.85 sq ins of throat , your 8.76 sq ins ( fudged;-) ) is more than I have at present with this "mutilated" exducer , so should be plenty big enough .

Yep ,throat is from the tip/outflow edge across to the "side" of the adjoining blade , its ends up a sort of wedge shape with a cutoff point.

Thanks for the confirmation ...........this might just work :-)

Cheers
John

[racket]

Hi Monty

Forgot to ask you , whats the inducer tip height ??

Cheers
John

[monty]

John,

Inducer ht is 19mm.

Monty