100-150 Hp turboshaft thoughts

[monty]

John,

We shall soon know about the wheel...since I ordered it! Only difference I can see between that one and the X897 is the super back is slightly smaller on the X853 and the material is not 7075. My local kts distributor wanted about $800 for the X897.. I was considering the X895 also, but I figured the extended tips on the X853/97 had the potential for a higher pressure ratio, and the 7+7 would choke at a higher flow than the 8+8.

I am going to run through the cycle analysis this weekend. What do you think is reasonable for the turbine efficiency 75% TIT 1200F ?

I've been working on the design. Slogging through the details. Mostly gearbox/front cover, since I haven't got the compressor to measure yet.

Getting excited about making chips! Just have to slog through the details first.

Monty

[racket]

Hi Monty

I normally use 80% for the turbine, its a large wheel and with a NGV stator , 80% should be achievable .

That $800 is a very high price for your comp wheel , I purchased 2 of X858 wheels for $AU800 ~$US600 late last year.

Flow rates/choking is a complicated business , lotsa things can affect it , the 8+8 wheels will have less slip at higher tip speeds and probably be a better wheel for us, but without verifiable comp maps its a lot of guesstimates.

Cheers
John

[monty]

John,

I thought the price was a bit high, and getting info from the guy was like pulling teeth, which is why I ordered the one off Ebay. I couldn't find an 8+8 with extended tips and a 95mm inducer. There was one with a much larger nose and a 97mm inducer that I considered, but Euler says those seeking higher pressure ratios should favor the smaller inducer... There are a few with larger inducers and the 27mm nose that I could cut down to my own trim. I may do that eventually since they cost quite a bit less.

Monty

[monty]

John,

Trying to check my numbers.

What TIT are you guys using?

What are you seeing for DELTA T across the turbine?

Monty

[racket]

Hi Monty

900 C - 1173 K for the TIT

Temp drop across the turb stage will depend on pressure drop and turb efficiency , you're aiming for full expansion whereas we only have "3/4" expansion , theres static pressure exiting the turb exducer that then has expansion/temp drop through the jetnozzle or freepower stage , so can't give an answer to that one, its different for every engine.

Cheers
John

[turbotom]

After some time of absence from the forum I just returned to have a look and found that nice project of yours, Monty. Since I'm somewhat involved in ultralight turbine helicopters that utilize the Solar T-62T-32 and the availability situation of good engines grows more and more difficult, our team jointly decided to manufature a replacement that stays design-wise as close to the original Solar engine that at least the major sections would be interchangable (and hence could be used as spares). Over the years of repairing and maintaining T-62T-32's, I got to know their strong points and their shortcomings very well. In general, they are really sturdy little engines that could be somewhat less sensitive to heat-cycling (which results in heat shield / seal plate warpage). Whatsoever, I kept the strong points and tried to improve the weak ones (our prototype will tell...) and we're close to running the first unit (power head that is). I eliminated all the mechanical accessory drives to cut weight and bulk considerably and integrated a brushless starter generator into one of the planets. Simulations proved the suitability of that approach. I also designed new turbine and compressor wheels that should provide slightly more power than the T-32 and especially in case of the turbine, higher reliability (had to phase out several turbine wheels due to crack development in the scallops of the web between the blades on high-time engines and came across an exploded wheel as well, fortunately without severe outcome). If you're interested in more details, please feel free to have a look at our "Info Package": www.turbinemuseum.de/files/Neo200.zip .

All the best and enjoy your project,
Thomas

[monty]

Hi Thomas!

I have been admiring your work for some time. I'm glad someone is preventing that design from being orphaned. Things don't get surplussed like they used to. I suspect the newer versions of the T62 are never going to be that common. If I was smart, I'd just design a fan to work with your engine. With 200hp, a 20 inch fan would give impressive performance. The gearbox would need to have a ratio that gives 8000-10000 rpm on the output shaft. 6000 is a bit on the slow side, and things would start to be too big fan wise.

For some strange reason I have an urge to build this thing. After working with the gearbox and fan design for a bit I've settled on 13Krpm and a 15.5in fan. What I'm doing isn't something a sane propulsion engineer would do. They would just stick to a piston engine, or use a turbo-prop for the flight mach numbers I'm interested in, but both of those are heavy complex solutions. I expect the fan will be about 30% less efficient than a turbo-prop, and about 20% better than a pure turbojet. The nice thing about the fan: the engine plus 300lbs of fuel is the same wt as a 160hp piston aircraft engine. so there is some hope when the system is considered as a whole. Being able to buy the entire rotating assembly for the cost of cylinder assembly is a plus too! And if I can burn diesel...the fuel cost drops significantly. Even if I burn more, it doesn't cost much if any more to operate per hr.

Monty

[monty]

John,

Thanks for the numbers. The problem I'm up against- this engine arrangement is not common. I have Mattingly's book which is good, but written so specifically for commercial engine architectures that the software won't work for me...sadly, since I could do an entire parametric analysis of the engine aircraft system if it did. Allowing me to optimize bypass ratio. I have an older text by Hill, and Peterson that I like better. Much more general, but no software. I'm too impatient to write and debug a complete parametric analysis for my engine cycle. So I'm writing a spreadsheet instead. I'm specifying the fan pressure ratio, efficiency and mass flow. Thus power. I'm getting somewhere around 300hp consumed by the core compressor, leaving the turbine to generate around 450 hp or so. The exhaust of the fan and core are mixed which results in the expansion of the core being behind the fan which is variable because the nozzle area is variable. I'm forcing the work balance to equal, thus giving me the DeltaT and P that must occur across the turbine assuming 80% efficiency. Right now I'm getting unrealistic pressures after the turbine. My guess is I'm not accounting for the loss through the NGV properly. I've been treating the entire turbine stage as one black box with 80% efficiency.

Monty

[monty]

Good news, I was missing a set of parenthesis in one of the equations. Everything is reasonable now. So the main question is what PR is the turbine stage capable of with a choked NGV. Looking at a GT60 map, the 84 trim wheel is good for PR 3. If that is the case I can only get away with about 3.3 Core PR and still get 150 hp out. SL static thrust will be up around 400lbs with .413 TSFC. Fan power 150hp, Core comp 220, and turbine making the balance. The core helps a little with 30lbs of thrust. That's with a core flow of 2.4 lb/s and a 12.5 Bypass ratio. If I can get a bit more from the turbine, and get the comp PR closer to 4 the fuel flow drops a bit. At PR5 the core nozzle chokes at altitude, limiting performance, and the fuel burn really doesn't get much better over PR 4-4.5.

The numbers at higher altitudes are....interesting ;-)

[racket]

Hi Monty

I have a turb map for the TV91 turb wheel (106mm exducer) and it indicates a Corrected Flow of 90 lbs/min at a 2:1 PR with a 1.70A/R scroll and 85 lbs/min corrected with a 1.46 A/R, the Corrected flow "flat lines" after 2:1 as undoubtedly the scroll is running choked , unlike the GT6041 turb stage that has some extra flow after a 2:1 PR .

With most turbo comps it doesn't pay to run much past ~3.5 PR if looking for good fuel efficiency , the drop off of comp effic generally means wasting fuel beating the air to death at a higher PR.

Cheers
John

[monty]

John,

I had settled at about 3.5 PR on the compressor just based on the cycle calcs. looking at altitude and SL performance. You don't gain much with higher pressure ratio with this arrangement.  If I can only get a PR 2 for the turbine....that's going to hurt. Is the GT60 turbine that much better than the TV and Holeset?? The turbine map goes out to about 3.25 or so PR. Dimensions look about the same.

Turbine PR of 3 and it works...not sure if 2 will do it.

Monty

[racket]

Hi Monty

Those maps are only for corrected flow into the wheel , not what pressure ratio they can process

Cheers
John

[monty]

John,

My numbers say with a turbine PR of 2, then 2.4 lbs/s with a core PR of 2.4 will leave about 100 hp for the fan, with a fuel burn around 23 gal/hr. TSFC = .55

Monty

[monty]

John,

After sleeping on it, and thinking a bit. It seems the limiting factor on this whole thing is the turbine NGV and inducer. In order to get high stage loading it needs to be choked. The references I have say max of about M 1.1 assumed into the turbine inducer. So I need to figure out that flow rate and pick the compressor that matches.

The cycle analysis shows that I can't use a compressor PR over about 2.2 or so if I want to take any power off the shaft with this arrangement. The issue is the mixed flow behind the fan. I don't have the option of expanding below ambient (or in this case P2 behind the fan). If I do that I get more shaft power, but it just causes drag when considered as a system. I need to expand to about M .4-.6 behind the fan to get the best trade off. I've found the TV91 turbine map. If 90 lb/min is the limit, I can only get about 70 hp from this turbine with this arrangement. Not sure the larger exducer on the G trim will help me, and I probably don't need such a large diameter compressor, one of the 141 wheels might be better matched. Is there something I'm missing???

Monty

[racket]

Hi Monty

Does your calcs take into account the supercharging of the core engine by the fan ??

Cheers
John