Why We Removed The Supercharger

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TimS
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Re: Why We Removed The Supercharger

Post by TimS »

Chris B wrote: Wed Jun 03, 2020 7:37 pm
TimS wrote: Wed Jun 03, 2020 2:14 pm I am pretty sure it was discussed previously, the FAT solution helps those who fly in the teens.
The scale of performance loss below ~5000' was unexpected, and AFAICT not discussed.

Touted benefits were not exclusively limited to >12,000'. Otherwise we would not have been interested. With only 2-seat oxygen, we rarely fly above 12,500'.
Did not state that in absolute terms. Just that if you do not fly in the teens, a super charger or a turbo generally do not pencil out for most cases.
A super charger works in many use cases; e.g. Wayne but not in all cases, e.g. you.

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Re: Why We Removed The Supercharger

Post by Antoine »

Thanks Wayne :)

Performance of SC planes should be massively better even at low altitudes because no DA40 can make 30 inches of MP after take-off.
The price to pay is higher SFC, a big increase in FF and maybe wear, but if an engine overheats, something is wrong.
The FAA would have denied the STC if this issue were not under control.
With all due respect for Chris' efforts and disappointment, I am leaning (pun!) towards issue(s) specific to N171CB - mag timing, baffling, fuel flow - Brock's thread is full of stories about such issues and fixes.
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Re: Why We Removed The Supercharger

Post by Rich »

Antoine wrote: Wed Jun 03, 2020 11:38 pm Thanks Wayne :)

Performance of SC planes should be massively better even at low altitudes because no DA40 can make 30 inches of MP after take-off.
The price to pay is higher SFC, a big increase in FF and maybe wear, but if an engine overheats, something is wrong.
The FAA would have denied the STC if this issue were not under control.
With all due respect for Chris' efforts and disappointment, I am leaning (pun!) towards issue(s) specific to N171CB - mag timing, baffling, fuel flow - Brock's thread is full of stories about such issues and fixes.
The detail overlooked here is that extra MAP boost is not free. It robs engine power to compress (and heat) the incoming air, and the compression system is not going to be 100% efficient (nothing is). That's why SL performance is not going to be improved and might easily be degraded. The improvement comes at the point where the parasitic HP draw (and other factors) is less than the gains obtained by the increased MAP.

The compressor is going to be working at max effort all the time. At lower altitudes, you're then pushing back at that work by having to use partial throttle to prevent over-boosting. In some planes, an automatic waste-gate will dump a bunch of that work overboard - nice compressed hot air wasted into the atmosphere.

There's also the extra heat factor. Boyle's law will tell you that by running an IAT of 130 deg F (589 deg Rankine) will reduce the number of air (ergo oxygen) molecules at any given pressure substantially.

Rate of climb percent is not properly assessed by percent absolute power lost. It's the percent of power lost in excess of power required to maintain level flight. A 27% reduction in ROC is probably a result of something like a 12-15% power loss.
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Chris B
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Re: Why We Removed The Supercharger

Post by Chris B »

Antoine wrote: Wed Jun 03, 2020 11:38 pm Performance of SC planes should be massively better even at low altitudes because no DA40 can make 30 inches of MP after take-off.
Hi Antoine -

For a normalized system this is just not supported by physics.

The supercharger *always* saps engine power, and *always* adds 60-80F to the intake. No free lunch. The question is where the benefits outweigh the costs. Hence Tim's earlier point that "if you do not fly in the teens, a super charger or a turbo generally do not pencil out."

[Edit: Rich hit 'submit' seconds before me. His explanation is more thorough!]

Antoine wrote: Wed Jun 03, 2020 11:38 pmI am leaning (pun!) towards issue(s) specific to N171CB - mag timing, baffling, fuel flow - Brock's thread is full of stories about such issues and fixes.
Why would this not be apparent - at all - in the comparison with Wayne's aircraft in the initial post?
Image

Here is a comparison of my normally aspirated aircraft with the flight Wayne references in his PIREP:
Image
Full-resolution: https://i.imgur.com/T2ESwIA.png

Related Savvy Analysis flight logs: Chris
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Chris B
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Re: Why We Removed The Supercharger

Post by Chris B »

waynemcc999 wrote: Wed Jun 03, 2020 10:08 pm per my PIREP (pg 4) over 116 flights these are the data recorded changes from pre-supercharged to supercharged:
-- Max CHT in Flight up 7 degF (385 to 392)
-- Max CHT in Cruise unchanged at 374
The 2x improvement in CHT spread (32 => 17) suggests that the pre-supercharged configuration would have been up to 15F cooler with the baffle improvements FAT implemented during Wayne's installation.

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Re: Why We Removed The Supercharger

Post by Rich »

Chris B wrote: Thu Jun 04, 2020 1:00 am The 2x improvement in CHT spread (32 => 17) suggests that the pre-supercharged configuration would have been up to 15F cooler with the baffle improvements FAT implemented during Wayne's installation.

Chris
Hm, is there a post on this? I don't recall. I wouldn't mind checking this out.
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Chris B
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Re: Why We Removed The Supercharger

Post by Chris B »

Rich wrote: Thu Jun 04, 2020 1:25 am
Chris B wrote: Thu Jun 04, 2020 1:00 am The 2x improvement in CHT spread (32 => 17) suggests that the pre-supercharged configuration would have been up to 15F cooler with the baffle improvements FAT implemented during Wayne's installation.

Chris
Hm, is there a post on this? I don't recall. I wouldn't mind checking this out.
Hi Rich -

Check Wayne's PIREP ( bit.ly/wam-sc-pirep ) that he references in his post at the bottom of page 1.

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Re: Why We Removed The Supercharger

Post by Rich »

Chris B wrote: Thu Jun 04, 2020 1:34 am
Rich wrote: Thu Jun 04, 2020 1:25 am
Chris B wrote: Thu Jun 04, 2020 1:00 am The 2x improvement in CHT spread (32 => 17) suggests that the pre-supercharged configuration would have been up to 15F cooler with the baffle improvements FAT implemented during Wayne's installation.

Chris
Hm, is there a post on this? I don't recall. I wouldn't mind checking this out.
Hi Rich -

Check Wayne's PIREP ( bit.ly/wam-sc-pirep ) that he references in his post at the bottom of page 1.

Chris
Link doesn't work. Is it incomplete or something?
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Re: Why We Removed The Supercharger

Post by Chris B »

Rich wrote: Thu Jun 04, 2020 1:39 amLink doesn't work. Is it incomplete or something?
Sorry. Missing "https://"

https://bit.ly/wam-sc-pirep
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Re: Why We Removed The Supercharger

Post by Rich »

Chris B wrote: Thu Jun 04, 2020 2:01 am
Rich wrote: Thu Jun 04, 2020 1:39 amLink doesn't work. Is it incomplete or something?
Sorry. Missing "https://"

https://bit.ly/wam-sc-pirep
Thanks. Unfortunately there aren't any references to the specifics of baffle changes. Something I could use in light of my observed Surefly behavior, if there are some changes that would help. Wayne, could you chime in, here?
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