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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 17 Mar 2021, 05:49 
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If the R8 has twin turbos then why can't the Raptor?


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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 17 Mar 2021, 06:47 
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Username Protected wrote:
If the R8 has twin turbos then why can't the Raptor?


The Veyron uses 10 radiators! See, the Raptor is on the right track!

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Last edited on 17 Mar 2021, 10:32, edited 1 time in total.

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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 17 Mar 2021, 07:43 
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Can someone explain the horizontal axis on those turbo charts? The units seem to be mass flow (lbs/min), but the way he is using them, it must involve inlet or outlet pressure. In a compound turbo, both turbos will run the same mass flow, but the way I understood what he was saying, one would run at “30” and the other “80”.


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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 17 Mar 2021, 09:18 
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Username Protected wrote:
Can someone explain the horizontal axis on those turbo charts? The units seem to be mass flow (lbs/min), but the way he is using them, it must involve inlet or outlet pressure. In a compound turbo, both turbos will run the same mass flow, but the way I understood what he was saying, one would run at “30” and the other “80”.


I can't help with the charts, but I too was wondering if a TDI engine in airplane applications runs at 80 inches of manifold pressure.


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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 17 Mar 2021, 13:42 
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Username Protected wrote:
Can someone explain the horizontal axis on those turbo charts? The units seem to be mass flow (lbs/min), but the way he is using them, it must involve inlet or outlet pressure. In a compound turbo, both turbos will run the same mass flow, but the way I understood what he was saying, one would run at “30” and the other “80”.


I had the same question and queried the maker of the video. He gave a good response that I'll copy below

Compound compressors are typically matched from the 2nd stage airflow first and then multiplying by the first stage pressure ratio (2.68 in this case) Using Boyle's Law, volume delivered by the 1st stage to the 2nd stage will be 1/2.68 (0.37) 0.37 X 80= 30. Note that Boyle's law assumes constant temperature during changes in pressure and in reality, we won't have that in a compound turbo system, which isn't a closed system either.

The video also ignores the fact that there is substantial temperature rise during compression and does not take into account any intercooling of the charge air which we'd certainly need to do to have a functional system.

The video is illustrative only (which I'm sorry, I didn't make clear) and is not about solid numbers for compressor matching for Raptor. My main purpose was to show that the equally sized compressors cannot work at 25,000 feet and the required pressure ratios. I tried to make that part clear by using the analogy of the 2 stage air compressor and showing photos of the size difference on actual compound turbo setups.

I also tried to explain why the turbines used here are too small and also greatly impacting performance. As a data point, my 2.2L Subaru uses a turbine wheel about 10mm larger than Raptor where Raptor should have something around 10mm larger than mine with almost 50% more displacement and around double the HP.

I think many people are confused when I use the term compressor mass flow. Compressors are rated by CORRECTED INLET flow- either CFM (volume) or mass of air (usually lbs./min).

Corrected meaning inlet pressure and temperature are taken into account and often specified on the compressor map. If the map was developed at or near sea level, that will be the correct inlet mass flow processed by the compressor down there.

Now move the compressor up to 25,000 feet where in the inlet pressure and density is about 1/3rd of SL conditions and compressor won't process the same mass of air as at SL at the same compressor rpm.

Up high, we need to intake a greater volume of less dense air and compress it back to near SL pressure to feed it to the 2nd stage compressor so it can then increase that pressure to the required value in the intake manifold to make rated power.

There are a myriad of other factors involved but a simple, short video can't cover all those things and that wasn't the intention of this one.

I'll try to touch on some other factors in subsequent videos on turbocharging and intercooling as this seems to be a popular topic.


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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 17 Mar 2021, 13:46 
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Username Protected wrote:
I can't help with the charts, but I too was wondering if a TDI engine in airplane applications runs at 80 inches of manifold pressure.


They do. The Austro E4 in a twin Diamond I fly shows engine power in "% load," but if you look up the manifold pressure in the engine mx manual description, it's shown as 38.57 psi (absolute), or 78.5" MAP. Many fly those engines at 85% power all day for their 1800 hour OH interval and the engines are sound. That's probably a power setting somewhere in the mid to high 60" MAP range.

I think you added 10" there, but the difference doesn't qualitatively change your point that it's a lot of boost and that the engine provides reliable service at a respectable maintenance interval.


The video that John posted is a lot to take in. The guy seems like one of those people who has proverbially forgotten more than most of us will ever know on the subject, except I doubt he's actually forgotten much- he's got a strong command of knowledge. He hits some, ummmm, esoteric but critical details.


edit: I didn't pay attention to the units

Last edited on 17 Mar 2021, 13:57, edited 1 time in total.

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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 17 Mar 2021, 13:50 
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Very possible I miscalculated. I just used the Google

Attachment:
Screen Shot 2021-03-17 at 10.47.58 AM.png


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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 17 Mar 2021, 13:57 
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Username Protected wrote:
Very possible I miscalculated. I just used the Google

Attachment:
Screen Shot 2021-03-17 at 10.47.58 AM.png

Oh- you know what, it was me ;)

I read your post too fast and read the numbers as inches and inches, not psi and inches of mercury.


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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 17 Mar 2021, 14:07 
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Username Protected wrote:
Oh- you know what, it was me ;)

I read your post too fast and read the numbers as inches and inches, not psi and inches of mercury.


Your point was still valid--compression ignition engines typically require (much) more manifold pressure to make power comparable to a spark ignition engine.

edit: and they don't explode in the first 10 hours.


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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 17 Mar 2021, 14:45 
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Username Protected wrote:
Can someone explain the horizontal axis on those turbo charts? The units seem to be mass flow (lbs/min), but the way he is using them, it must involve inlet or outlet pressure. In a compound turbo, both turbos will run the same mass flow, but the way I understood what he was saying, one would run at “30” and the other “80”.


I had the same question and queried the maker of the video. He gave a good response that I'll copy below

Compound compressors are typically matched from the 2nd stage airflow first and then multiplying by the first stage pressure ratio (2.68 in this case) Using Boyle's Law, volume delivered by the 1st stage to the 2nd stage will be 1/2.68 (0.37) 0.37 X 80= 30. Note that Boyle's law assumes constant temperature during changes in pressure and in reality, we won't have that in a compound turbo system, which isn't a closed system either.

The video also ignores the fact that there is substantial temperature rise during compression and does not take into account any intercooling of the charge air which we'd certainly need to do to have a functional system.

The video is illustrative only (which I'm sorry, I didn't make clear) and is not about solid numbers for compressor matching for Raptor. My main purpose was to show that the equally sized compressors cannot work at 25,000 feet and the required pressure ratios. I tried to make that part clear by using the analogy of the 2 stage air compressor and showing photos of the size difference on actual compound turbo setups.

I also tried to explain why the turbines used here are too small and also greatly impacting performance. As a data point, my 2.2L Subaru uses a turbine wheel about 10mm larger than Raptor where Raptor should have something around 10mm larger than mine with almost 50% more displacement and around double the HP.

I think many people are confused when I use the term compressor mass flow. Compressors are rated by CORRECTED INLET flow- either CFM (volume) or mass of air (usually lbs./min).

Corrected meaning inlet pressure and temperature are taken into account and often specified on the compressor map. If the map was developed at or near sea level, that will be the correct inlet mass flow processed by the compressor down there.

Now move the compressor up to 25,000 feet where in the inlet pressure and density is about 1/3rd of SL conditions and compressor won't process the same mass of air as at SL at the same compressor rpm.

Up high, we need to intake a greater volume of less dense air and compress it back to near SL pressure to feed it to the 2nd stage compressor so it can then increase that pressure to the required value in the intake manifold to make rated power.

There are a myriad of other factors involved but a simple, short video can't cover all those things and that wasn't the intention of this one.

I'll try to touch on some other factors in subsequent videos on turbocharging and intercooling as this seems to be a popular topic.


Neema,

Thanks for the comprehensive response!

Learn something new every day.

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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 17 Mar 2021, 15:23 
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Username Protected wrote:
Ross Farnham is the right guy to give that lecture. Not sure the the Raptor guy is taking note any time soon.

http://www.sdsefi.com/index.html

http://www.sdsefi.com/racetech.htm

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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 17 Mar 2021, 18:22 
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Neema, thanks for asking. What I understand from that explanation is that the mass-flow vs. compression ratio curves are done at a given pressure (sea level). To actually design the second stage compressor you need adjust the values you are reading on that curve to account for the higher intake pressure.

Based on the low efficiency regimes of operation, we should expect the Raptor intake air will get extremely hot as he takes it to higher altitudes. I wonder how effective Peter's intercooler is; I don't recall a pre/post temperature measurement evaluating the intercooler efficiency.


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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 18 Mar 2021, 19:59 
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Whatever, I didn’t see one polar graph.


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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 20 Mar 2021, 12:01 
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Username Protected wrote:
Whatever, I didn’t see one polar graph.


That is about as funny as a monkey falling off a limb after sniffing his self inflicted dirty finger. And for the same reason.

Pro tip - Every single one of those turbocharger efficiency and mass air flow graphs and maps are by definition "polars." Both log and linear.

https://en.wikipedia.org/wiki/Polar_coordinate_system

https://en.wikipedia.org/wiki/Log-polar_coordinates

In your defense... (and that of the upvoters) you did not indeed see "one polar graph."

You saw many. :hammer:


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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 20 Mar 2021, 12:24 
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Curious to see how long it takes to address and fix the turbo charger issue. That time is rapidly approaching.

1.) The bird is overweight. (addressable in the next build.)
2.) She is starved for power.
A.) Not enough air getting to the engine
B.) The compressed air is hot do to the incorrect turbo set up.
i.) Effects inlet air temperature
ii.) Degrades combustion efficiency.
iii.) Engine works harder to produce less power. Could be the root cause of the over heating issue.
3.) Address number 2 above and let's see what the polar looks like at this weight. Excessive induced drag due to excess weight becomes an increasingly small share of total drag as velocity increases... so should be a good indicator.
4.) Fix 1 above after working out 2 above... Then we will see what we really have.

I am still optimistic and for all of the same reasons.

Fly Raptor Fly. :thumbup: :cheers:


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