Why We Removed The Supercharger

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Chris B
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Why We Removed The Supercharger

Post by Chris B »

We recently removed the Forced Aeromotive Technologies (FAT) supercharger from our DA40. Our primary interest was increased climb rate to about 11,500' when operating in the Sierra, and placed a deposit way back in early 2013 (link to 2013 DAN post). About 10% of our flights are above 9000’, but logging >350 hrs/year this represents a meaningful number of hours.

Having successfully replaced the engine in November, we purchased the supercharger kit in January and helped our mechanic install it. After persevering through several installation issues, unfortunately the overall value proposition proved unattractive for us. You might come to a different conclusion if flying predominantly above 9000’, or are unconcerned with elevated CHTs, or have a shop handle routine maintenance.

The supercharger continuously saps power and increases intake temperature 60-80F. Consequently, lower altitude (~3000’) cruise is 5 kts slower with 30F hotter CHTs at comparable fuel flow. Capping CHT at 400F as recommended in the DA40 AFM (4A.3.9), climb to 3500’ degrades by 27% (1 min). Climb to 10,500’ is identical. Climb to 11,500’ improves by 4% (40 sec), which considerably undershoots our expectations. Accepting higher CHTs would improve performance, but would also improve normally aspirated (NA) performance up to ~8000’.

Links to flight profiles below, including comparison with a system installed by FAT having similar performance.

Our climb results to 11,500':
Image
Full-resolution: https://i.imgur.com/TelHOVG.png


The DA40 implementation also adds significant serviceability issues. Unfortunately these were not apparent until installation.
  • Routine maintenance requires detaching the spinner (with limited-life self-locking nut plates) and having a helper assist removing the lower cowling. A complicated “dance” hopefully avoids damage to the cowling, spinner bulkhead, propeller and/or port fuselage paint.

    Here is a video by Brock of the cowling removal:
    https://www.youtube.com/watch?v=3kx7umZZwrI
  • FAT stresses that maintaining supercharger belt tension is critical. Instead of a spring loaded idler pulley, FAT uses a sliding pulley attached with through-bolts. Adjustment requires socket wrenches front and rear (after removing the alternate-air assembly), while a helper braces the propeller and leverages the idler bracket against the starter ring gear. An additional helper to monitor tension with a spring scale is also helpful.
  • Accessing or inspecting the starter mounting bolts requires completely removing the supercharger and its mounting bracket.
For us the modest performance improvement above 9000’ is not worth the combination of poorer low altitude performance, elevated cruise CHTs at all altitudes, serviceability issues and increased fuel consumption.

Chris

*****

Here are links to a few flights with/without the supercharger.

~3000’ LOP cruise 5 kts slower & 30F hotter: Climb to 11,500 (17:00 vs. 16:20): For comparison, a representative climb to 10000 by Wayne’s DA40:
(N211WP, with supercharger installed by FAT) Comparison of Wayne's flight and our supercharged aircraft:
Image
Full-resolution: https://i.imgur.com/6sfqwBg.png

The relatively minor differences may be due to:
  • Propeller (N211WP's composite 3-blade theoretically climbs better)
  • Ambient lift/sink
  • Technique
  • OAT about 7C higher for N211WP
  • N171CB’s gross weight about 100 lbs higher due to extra fuel, fat pilot & aluminum prop.
  • N211WP’s engine is also relatively high time (~2300 hrs), while N171CB’s is newly broken-in (~80 hrs).
  • N211WP has electronic ignition, while N171CB does not.
But overall this suggests that our supercharger installation was “normal.”
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Re: Why We Removed The Supercharger

Post by Antoine »

Wow!
I think Forced Aeromotive need to be given an opportunity to respond before conclusions are drawn...

The IO-360 may be a very robust foundation, but i would certainly not want CHTs to exceed 400 F on a steady state basis.
Some minor changes can considerably affect CHTs, for example ignition advance.

Unfortunately there is no free lunch - compressing air requires horsepower and generates heat.
This is why turbocharged applications frequently come with an air intercooler.
The FAT solution is remarkably compact and lightweight but the lack of an intercooler is a limitation that must be fully understood and accounted for in operation.

FWIW in my turbocharged/intercooled aircraft, I have installed inlet air temperature (CDT/IAT) sensors and set the redline for air inlet temperature at 140 F and the normal limit at 130 F. This is based upon advice from a retired Formula 1 motorist with significant aero engine experience.
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Rich
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Re: Why We Removed The Supercharger

Post by Rich »

Ignition advance should play no role here. Chris doesn't have electronic ignition and in any case neither Electroair nor Surefly advances ignition beyond the standard until MAP < 25". Given the FAT documented behavior and the altitudes involved here I would not expect to see that condition in these tests.

FWIW, removing/reinstalling the alternate air valve needs to be done with care. We removed it when the starter was replaced last year and found that we had to carefully select spacer washers (not shown in the IPC or AMM) installed just so or it will severely bind. This was discovered after I went to operate the alternate air, forced it closed one too many times and snapped the Bowden cable.
2002 DA40: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210.
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Re: Why We Removed The Supercharger

Post by TimS »

I am pretty sure it was discussed previously, the FAT solution helps those who fly in the teens.
I would not expect 11.5 to be high enough to actually take advantage of a super charger.

Tim
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waynemcc999
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Re: Why We Removed The Supercharger

Post by waynemcc999 »

For reference, here is a PIREP on my Supercharged N211WP. bit.ly/wam-sc-pirep
I've recently added a section on Savvy "Report Cards" (pg 4), comparing N211WP pre-supercharged and supercharged versus 133 "cohort" DA40s.

With my priorities for having Forced Aeromotive install the supercharger being (1) improved takeoff climb from high density altitude airports, (2) improved cruise climb rates into the teens, and to a lesser extent (3) increased cruise speed... I'm very happy with my supercharged DA40.
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Re: Why We Removed The Supercharger

Post by Rich »

Chris' post brings up some heretofore not obvious negatives of this option. I do know that numerous turbo/super charged aircraft suffer performance penalties at lower altitudes, so this shouldn't be surprising.

The real message here is it isn't a sensible option for everyone's situation/mission. An additional downside for me would be exacerbating a slight nose-heavy condition, while cutting into useful load. The only cure for the former is to add more weight, further cutting into useful load. :thumbsd: Of course, for other DA40's this is no factor.

While my home airport might be considered borderline high-altitude (summer DA's often 5,500 ft.), my normally aspirated bird handles it fine. Cruise altitudes I use almost always are at or below 11,000 ft (maybe 12,500 ft. DA), are also no problem. And I've been in and out of a number of higher DA airports without drama: KRKS, KFNL, KCYS, KBTM come to mind. (BTW, departing KRKS [Rock Springs] to a cruise altitude of 11K isn't much of a climb :D )
2002 DA40: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210.
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Re: Why We Removed The Supercharger

Post by Chris B »

Rich wrote:
Wed Jun 03, 2020 4:14 pm
...brings up heretofore not obvious negatives of this option.
<snip>
The real message here is it isn't a sensible option for everyone's situation/mission.
Yes. This was the purpose of my post.

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'.

Relevant snips from the 33 page supercharger thread: viewtopic.php?f=8&t=3451
On page 1 (initial post) Brock wrote:The design goal is to achieve sea level power up to between 7 & 9,000'.
On page 20 Brock wrote:...during our take-off tests, which were done at 2800 feet, the full gross take off test seems to be 4 to 500' shorter than the AFM charts indicate. We expect to be closer to the AFM charts at sea level but increasingly better than the AFM charts as the takeoff DA increases.
On page 21 Brock wrote:Max rated power is reached at about 7100' instead of sea level. So where the normally aspirated plane is making less and less power on it's way to 7K we are making more and more.
On page 22 Antoine wrote:(speculation) Sea level climb rates all the way to 7000 ft, thereafter declining gradually. This is in my view the biggest benefit. Not only will the plane operate safely in hot and high conditions, it will be faster from A to B because the climb phase will be shortened. If you fly say at FL 100 for cruise, you will gain 3-4 minutes on the way up.
On page 28 Ian Sage wrote:Best climb is improved by about 500fpm at all altitudes above 6000msl.
On page 30 Ian Sage wrote:Our development plane consistently sees 20kts increased cruise speed above 7000'msl and 500fpm more than you currently get at a given altitude above 7000'msl. Below 7000' the performance increase diminishes.
<snip>
Our systems are designed to provide sea level takeoff power up to 7000'msl and 75% cruise power at 12'000'msl.
<snip>
To potential customers who plan to fly up and down the coast but never above 7000' I warn that you will be disappointed with our product. You will see little benefit because it is not designed for that mission.

Chris
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Re: Why We Removed The Supercharger

Post by Antoine »

There was also a very detailed debate about inlet air temperature on Wayne's Pirep thread...
Rich: is it not so that if mag timing is set incorrectly, CHTs are affected?
As I said above I believe that FAT should be given the opportunity of presenting their analysis. My feeling is that something is wrong and certainly FAT should explain.
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Re: Why We Removed The Supercharger

Post by Rich »

Antoine wrote:
Wed Jun 03, 2020 8:44 pm
There was also a very detailed debate about inlet air temperature on Wayne's Pirep thread...
Rich: is it not so that if mag timing is set incorrectly, CHTs are affected?
I would guess mag timing set too far advanced would do that, since this is what I see with the Surefly when it has advanced, but it's coupled with lower EGTs.
2002 DA40: MT, PF, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210.
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Re: Why We Removed The Supercharger

Post by waynemcc999 »

Antoine wrote:
Wed Jun 03, 2020 8:44 pm
There was also a very detailed debate about inlet air temperature on Wayne's Pirep thread...
Rich: is it not so that if mag timing is set incorrectly, CHTs are affected?
As I said above I believe that FAT should be given the opportunity of presenting their analysis. My feeling is that something is wrong and certainly FAT should explain.
To Antoine's point on inlet air temps, I can't speak to that directly, but only on a macro basis... 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
-- Oil Temp in Cruise up 5 degF (181 to 186)

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