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  #121  
Old 03-08-2019, 04:46 PM
Turbine Aeronautics Turbine Aeronautics is offline
 
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Location: Adelaide, South Australia
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Originally Posted by hgerhardt View Post
How do you intend to drive an alternator? Some sort of PTO shaft to drive a V-belt pulley? Or a spline drive PTO?
As Ross has indicated, a starter generator is a commonly used solution for power generation. That is our preference. However, whether we do this will depend on a more comprehensive rotor dynamic analysis that will be undertaken when the preliminary design of such a system is completed.

Our reduction gearbox will have the facility to incorporate a PTO for a gearbox mounted compact alternator if we need it.

Further development work will determine our final choice for power generation.

Dave
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  #122  
Old 03-08-2019, 04:52 PM
Turbine Aeronautics Turbine Aeronautics is offline
 
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Originally Posted by David Z View Post
Things like cabin heat will be worked out, I'm not too worried about no bleed air option, there are other ways to get the heat.
Those were our thoughts as well. We believe there are quite straightforward solutions to work around some of the features that we will not incorporate on our launch engine. Engine reliability, simplicity, efficiency and affordability - all important attributes and the focus of our development program.

Dave
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  #123  
Old 03-10-2019, 02:19 PM
breister breister is offline
 
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Location: Atlanta, GA
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Originally Posted by rocketman1988 View Post
...and you are basing that 1% on what?
On the basic notion that siphoning off a bit of bleed air would result in less net system loss than driving a compressor off the PTO and plumbing an entire HVAC system into the cockpit. A typical auto AC uses about 2hp, which would be 1% of 200hp.

Quote:
I would think that the engine manufacturer would have a pretty good idea of the bleed air losses. They have already stated that the engine is capable of more power, so the whole discussion may be moot.

My point is that it takes power to drive that ACM and that power comes from somewhere...TANSTAAFL...
Yep, nothing is "free" unless it was already being wasted. Obviously there are other ways to accomplish heat and AC. And, if it TRULY is an issue affecting "simplicity and reliability" of the engine I wouldn't have pushed it this far. However, bleed air has a been a standard feature of turbines for so long now that, pardon my saying so, it sounds like they are making excuses rather than just saying honestly that, "it's one more thing to test and we don't want to look into it right now until after we start delivering engines" - an answer I would have happily accepted. So, maybe it's a bit mean of me to keep pushing the point - they don't need to do anything, it's their company, and they can do whatever they bloody well want! That won't stop me from encouraging them to explore it sooner rather than later.

Honestly, I find it hard to imagine any answer simpler than bleed air. Maybe someone with a thermodynamics degree will explain to me that this type of turbine is fundamentally different and that it really is hard to do.
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  #124  
Old 03-10-2019, 02:21 PM
breister breister is offline
 
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Originally Posted by Turbine Aeronautics View Post
I guess the easy answer is that the cabin could be kept warm using the same type of system that all the RVs use now with the piston engines that are fitted. Our engine will have an oil cooler for the gearbox and also exhaust pipes. Those are two good sources of heat that do not detract from the performance of the engine or add complexity/cost (two features that we are trying to minimise to the greatest extent possible!).

Guys, please remember that even though we are incorporating some innovative technology into our engines, we won't sell any engines if they are not affordable. A bleed air source will reduce the fuel efficiency, add development cost, add complexity etc. For the sake of a heat muff around an exhaust pipe or hot air pickup at the back of the oil cooler (two simple and low cost/reliable options), we don't want to add big cost by making the engine itself more complicated.

Our philosophy is that we want to deliver an affordable, reliable and fuel efficient turbine engine to the market in order to make the technology as accessible as possible to as many folks as possible. We can up-feature later when we know that folks are prepared to pay an extra $X,000 for an engine.

Dave
A fair answer. You are busy, I'll promise to stop bugging you about it!
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  #125  
Old 03-10-2019, 03:02 PM
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rmartingt rmartingt is offline
 
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Quote:
Originally Posted by breister View Post
On the basic notion that siphoning off a bit of bleed air would result in less net system loss than driving a compressor off the PTO and plumbing an entire HVAC system into the cockpit. A typical auto AC uses about 2hp, which would be 1% of 200hp.



Yep, nothing is "free" unless it was already being wasted. Obviously there are other ways to accomplish heat and AC. And, if it TRULY is an issue affecting "simplicity and reliability" of the engine I wouldn't have pushed it this far. However, bleed air has a been a standard feature of turbines for so long now that, pardon my saying so, it sounds like they are making excuses rather than just saying honestly that, "it's one more thing to test and we don't want to look into it right now until after we start delivering engines" - an answer I would have happily accepted. So, maybe it's a bit mean of me to keep pushing the point - they don't need to do anything, it's their company, and they can do whatever they bloody well want! That won't stop me from encouraging them to explore it sooner rather than later.

Honestly, I find it hard to imagine any answer simpler than bleed air. Maybe someone with a thermodynamics degree will explain to me that this type of turbine is fundamentally different and that it really is hard to do.
I'm not a thermo guy, but I work with aircraft pressurization and bleed air systems (among other stuff) at my day job.

Tapping off bleed air for "other uses" still requires the at least following:
  • Ports and ducting from the compressor
  • A regulator valve
  • Controller for the regulator valve
  • Scheduling within the engine controller to handle the impact to engine performance
  • Analysis of the engine to ensure surge and temperature margins are maintained

And that's just getting the air out of the engine. If you want to use it for, say, pressurization, you'll need some kind of precooler, an air cycle machine, controls for all of that, etc.

In a light airplane (especially an unpressurized one) it very well may be lighter and simpler just to tap off the gearbox or use a bigger alternator and drive everything electrically.

It's not just about pure thermodynamic efficiency, but also system complexity and weight. I'm having a hard time seeing a 2-6 seat homebuilt ducting hot bleed air around for anti-ice and running a jet-style bleed-air-driven ECS.
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  #126  
Old 03-10-2019, 05:01 PM
Turbine Aeronautics Turbine Aeronautics is offline
 
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Originally Posted by breister View Post
A fair answer. You are busy, I'll promise to stop bugging you about it!
Thanks breister.

We figured that probably 99% of our 200hp/120hp market would simply be looking for a turbine alternative to their LyConti or Rotax. We did not envisage that their mission would change significantly simply by having a turbine installed. That is, probably most missions would still be below 10,000? with the occasional foray above that altitude.

We are designing our launch engine to operate comfortably at all altitudes up to 20,000 which will cater for those who occasionally exceed 10,000? or wish to cruise above 10,000?.

I suspect that there are minimal aircraft that our 200hp engine would go into that are pressurised, so heating is really the only issue to resolve and as I have indicated, there are very simple, low cost ways to address the heating issue that will not impact the engines simplicity, performance or our ability to make it as affordable as possible.

Our 300hp engine however, is likely to go into aircraft that may be pressurised. Also, those aircraft tend to be at the top end of the cost spectrum where the builder may be better able to afford an engine that is $10k more expensive but will have the bells and whistles.

For us, it has been a decision making process to determine what are essential, desirable and non-essential features for our engines, and then designing accordingly. If we have left off a feature that some consider essential, we will look at the trade off between satisfying the few (or many if that is the case) and the economics involved to do so. For now, based on feedback from customers and airframe manufacturers, bleed air on our 200hp/120hp engines is not an essential feature but is one that would adversely affect the purchase price (not a desirable feature for probably 99% of our potential customers).

Dave
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  #127  
Old 03-11-2019, 05:03 AM
Timberwolf Timberwolf is offline
 
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Not to throw this into left field, but do you have an outline of planned future engines? I imagine 300 hp is as high as you'll need to go to fill the gap until the pt6a-20 and the like are able to meet the market demand, but just curious. Looking down the road to what I want to build next
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  #128  
Old 03-11-2019, 08:08 AM
Canadian_JOY Canadian_JOY is offline
 
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Quote:
Originally Posted by Turbine Aeronautics View Post
Our engine will have an oil cooler for the gearbox and also exhaust pipes. Those are two good sources of heat that do not detract from the performance of the engine or add complexity/cost (two features that we are trying to minimise to the greatest extent possible!).
Dave
Dave - thank you for your reply. I would suggest that oil to air heat exchangers are woefully inadequate to heat an aircraft cabin in anything but the most benign environments. Pulling heat off the exhaust would be a better way to go, by far. As suggested by Ross Farnham, engineer this into the accessory package from the start. You don't want this to be an afterthought (like alternators have been an afterthought on many piston aircraft conversions).
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  #129  
Old 03-11-2019, 06:16 PM
Turbine Aeronautics Turbine Aeronautics is offline
 
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Quote:
Originally Posted by Timberwolf View Post
Not to throw this into left field, but do you have an outline of planned future engines? I imagine 300 hp is as high as you'll need to go to fill the gap until the pt6a-20 and the like are able to meet the market demand, but just curious. Looking down the road to what I want to build next
It is unlikely that we will go higher than 300hp as we are then getting into RR/Allison power ranges.

I suggest you start looking at aircraft that could use up to 300hp as that engine will likely follow reasonably soon after the 200hp. First things first though, we need to deliver a reliable 200hp engine.

Dave
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  #130  
Old 03-11-2019, 06:24 PM
Turbine Aeronautics Turbine Aeronautics is offline
 
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Quote:
Originally Posted by Canadian_JOY View Post
Dave - thank you for your reply. I would suggest that oil to air heat exchangers are woefully inadequate to heat an aircraft cabin in anything but the most benign environments. Pulling heat off the exhaust would be a better way to go, by far. As suggested by Ross Farnham, engineer this into the accessory package from the start. You don't want this to be an afterthought (like alternators have been an afterthought on many piston aircraft conversions).
Addressing this issue will be high on the list of priorities that we discuss with the developers of FWF packages. I'm fairly certain that the company we are in early discussions with will already have given this some thought.

Offering a turnkey FWF solution to new build and retrofit projects will be important, and that solution will need to address all options that may be sought by customers of our engines, including the heating options.

Dave
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