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03-04-2019, 11:44 AM
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Join Date: Dec 2006
Location: Atlanta, GA
Posts: 1,231
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Quote:
Originally Posted by rocketman1988
"... And then of course, if you just add a small bleed air port, you could add pressurization..."
I know it was kind of TIC but there is substantially more to the design of a reliable, safe pressurized airplane than "just adding a small bleed air port"...
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Not to mention weight. Shhh, we're having fun...
Seriously though, if someone comes through with the right engine, someone else will undoubtedly try pressurization. Probably not me, at least not in my current plane, and probably never as I'm getting old.
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03-04-2019, 11:54 AM
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Join Date: Dec 2006
Location: Atlanta, GA
Posts: 1,231
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Quote:
Originally Posted by Turbine Aeronautics
For your interest, our current predictions (subject to validation once the engine is running of course) at 20,000? give a maximum continuous cruise power of 138hp with a fuel flow of around 9.8 usg per hour at a 180ktas cruise state, ISA conditions.
We don?t intend to offer a bleed port initially. We figure that not a high % of our customers will be pressurising their aircraft. Indeed, we optimised the engine for 10,000? because we feel that not many will likely go much higher. We suspect that 18,000? will be many folks limit where cannula oxy can be used and pressurisation is not a necessity. 140hp or thereabouts is still a fairly useful power at 18,000?.
Dave
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Thanks Dave. Interesting, 138hp @ FL200 is less of a lapse rate than a normally aspirated piston for a 10,000' altitude difference, I would think you might start running into turbine over speed to get sufficient compression?
And yes, most of the fleet is not pressurized and old girlfriends won't want to wear the mask. I don't recall which air frame you are quoting, but my current air frame would scoot considerably faster than 180ktas on 140hp @ 18,000'. A twin Velocity, if their ad is to be believed, should be very close to 210IAS with that horsepower which would be over 335ktas @FL200. I think my math is wrong on that, using 3% / 1,000' increase in TAS for the same IAS? There is probably some penalty for prop inefficiency up higher I'm not including.
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03-04-2019, 01:29 PM
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Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,766
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Quote:
Originally Posted by breister
I started with this:
"However, our 200hp engine is being optimised for a 180hp cruise at 10,000'"
I guesstimated 150hp up to about 15,000', with normal lapse rate thereafter. As I said, my napkin math may be far off!
A turbine is not exactly like turbonormalized piston, but as you pointed out they are generally flat rated (due to heat in the hot section) up to some altitude and then lapse the same as a normally aspirated. TA is saying they still generate 180hp @ 10,000', so 150hp per engine @ 15,000' is not a bad guess, and incidentally is the same horsepower as two normally aspirated IO 360 200 hp motors @ 75% power. With two engines, that is 300hp@15k'; normal lapse should drop you down to ~65% power @ FL250. You are looking at less horsepower but also less induced drag as you get closer to L/D (max) so IAS should drop slightly but TAS should continue to increase a bit. The general formula usually applies until you approach high Mach numbers, when induced drag begins to rise despite low IAS.
Again the caveats - my recollections are 35 years old, and this ain't no Phantom! 
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138 isn't far off 150 if it will do it so your calc was pretty close. Plenty to prove at altitude as far as compressor surge margins, relights up there, turbine inlet temps etc.
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03-04-2019, 02:57 PM
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Join Date: Dec 2006
Location: Atlanta, GA
Posts: 1,231
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Quote:
Originally Posted by Turbine Aeronautics
We don?t intend to offer a bleed port initially.
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Almost forgot, the bleed port is not just about pressurization.
It's about free air conditioning and easy heating.
All you need is an inter-cooler, a water separator, and an expansion valve. Lightweight, can fit under almost any cowling.
BIG opportunity for a selling point, especially if you cobbled together a kit for people...
If you make it standard, but ship it capped, it would preclude needing a separate design.
Of course, you could probably charge a premium for the feature too. It's not drilling the hole that is expensive, it's knowing where to drill... 
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03-04-2019, 04:00 PM
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Join Date: Oct 2006
Location: Garden City, Tx
Posts: 5,145
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Quote:
Originally Posted by breister
Almost forgot, the bleed port is not just about pressurization.
It's about free air conditioning and easy heating.
All you need is an inter-cooler, a water separator, and an expansion valve. Lightweight, can fit under almost any cowling.
BIG opportunity for a selling point, especially if you cobbled together a kit for people...
If you make it standard, but ship it capped, it would preclude needing a separate design.
Of course, you could probably charge a premium for the feature too. It's not drilling the hole that is expensive, it's knowing where to drill... 
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That would be especially handy for people that are planning on cruising at high altitude to take advantage of the engines efficiency up there - and no longer have a source of cabin heat from an exhaust heat muff.
__________________
Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2020 dues paid 
N16GN flying 700 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, 430W
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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03-04-2019, 04:28 PM
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Join Date: Jun 2010
Location: Sunman, IN
Posts: 2,189
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...and
...and, as always, the devil is in the details.
What do you think happens when you start siphoning off bleed air?
Let me give you a hint:
TANSTAAFL
"There Ain't No Such Thing As A Free Lunch" 
__________________
Bob
Aerospace Engineer '88
RV-10
Structure - 90% Done
Cabin Top - Aaarrghhh...
EFII System 32 - Done
297 HP Barrett Hung
ShowPlanes Cowl with Skybolts Fitted - Beautiful
Wiring...
Dues+ Paid 2019,...Thanks DR+
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03-04-2019, 05:28 PM
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Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,766
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Quote:
Originally Posted by rocketman1988
...and, as always, the devil is in the details.
What do you think happens when you start siphoning off bleed air?
Let me give you a hint:
TANSTAAFL
"There Ain't No Such Thing As A Free Lunch" 
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Sometimes it's beneficial to bleed compressor air at altitude to stay out of the surge region. Cabin air volume requirements are generally pretty low compared to the core engine mass flow. It's intriguing to contemplate the possibilities for simple heat and a/c.
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03-04-2019, 07:59 PM
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Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,766
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Dave,
Is there some reason your engine design suffers less power loss with altitude than PWC engines? Some test data on these shows variously 37-47% loss in shp at 17,500 feet depending on model and TAS. You're saying only a 31% loss in power.
I understand the recuperator improves the SFC at the expense of a loss in hp.
Is the thermodynamic rating of your engine higher than 200 shp at sea level/ standard day conditions?
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03-05-2019, 12:40 AM
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Join Date: Aug 2018
Location: Adelaide, South Australia
Posts: 37
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Quote:
Originally Posted by rocketman1988
...and, as always, the devil is in the details.
What do you think happens when you start siphoning off bleed air?
Let me give you a hint:
TANSTAAFL
"There Ain't No Such Thing As A Free Lunch" 
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You are spot on there Bob!
We want to make this engine as affordable as possible which means that at least initially, some non-essential features such as bleed air which comes at a cost, will not be designed into the engine. Most of our customers will be operating below 10,000?, most of the time. It is for this large group that we need to make it affordable for.
If we subsequently offer an engine with a bleed port, that will come at at the expense of increased cost due to different turbomachinery, different architecture etc.
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03-05-2019, 12:42 AM
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Join Date: Aug 2018
Location: Adelaide, South Australia
Posts: 37
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Quote:
Originally Posted by rv6ejguy
Valid points however it's really best not to project TBOs before even a single example has gone that many hours running in the real world...
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I agree Ross. A large amount of testing will determine this parameter. We have our target, but real life testing will ultimately determine the recommended TBO.
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