Why We Removed The Supercharger

[Antoine]

Chris I unfortunately do not have the time to dig more in the Savvy files, but in a nutshell:
- look at how Wayne operated his plane - he kept MP very low- he is a very prudent pilot and I know him for being very gentle on his engines.
- your reference for performance should be the plane that supported the STC - Brock's
- of course I agree that 60-80 F of extra inlet air temperature is significant. I think I was among the first here to raise the issue.
- I also agree that a SC costs power, thereby hurting efficiency. But increasing MP from 24 to 30 inches adds a full 25% and I would guess the SC wastes less than 10% based upon heat generation - probably half or more of the power draw is converted into heat - if it ate up 1/4 of the 180 HP it would melt up the engine compartment.
And as Rich pointed out - a power change of 15% will net a much more important change in climb rate.
So I do expect SC planes to climb better (given enough fuel), and I do believe that Brock honestly reported on this, with compelling data. Which brings me back to my original guess: something not OK in the specific install.
Why is FAT not joining this discussion?

PS. i am the proud owner of a 2004 Jaguar XKR. This car is supercharged. Its "sea level" max power is 400 HP versus 300 for the normally aspirated XK8 - same engine otherwise. The XKR has lower efficiency but massively more power...

[waynemcc999]

Link 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?

Rich,
On the CHT spread, I had in late 2015 performed the full GAMI test, sent the results to GAMI, and they said (nicely) "All looks good, you don't need our product". I expect the reduction in Max CHT Spread in Cruise (pg 4 of PIREP; 32 degF before supercharger installed, 17 degF after) came from the baffle tuning that Ian did during the installation of the supercharger. And/or perhaps the pressure-adjusting injectors (or whatever they are called) that are part of the supercharger also helped the spread.
Wayne

[Rich]

Rich,
On the CHT spread, I had in late 2015 performed the full GAMI test, sent the results to GAMI, and they said (nicely) "All looks good, you don't need our product". I expect the reduction in Max CHT Spread in Cruise (pg 4 of PIREP; 32 degF before supercharger installed, 17 degF after) came from the baffle tuning that Ian did during the installation of the supercharger.
Wayne

Well that's my question. In my case I don't have much spread, but the SF does produce aomewhat higher CHTs and lower EGTs. I do have one cylinder (#4) about that much cooler than the other three but it reflects qualitatively EGT variance. GAMI tests show nothing to be gained there.

[Rich]

Chris I unfortunately do not have the time to dig more in the Savvy files, but in a nutshell:
- look at how Wayne operated his plane - he kept MP very low- he is a very prudent pilot and I know him for being very gentle on his engines.
- your reference for performance should be the plane that supported the STC - Brock's
- of course I agree that 60-80 F of extra inlet air temperature is significant. I think I was among the first here to raise the issue.
- I also agree that a SC costs power, thereby hurting efficiency. But increasing MP from 24 to 30 inches adds a full 25% and I would guess the SC wastes less than 10% based upon heat generation - probably half or more of the power draw is converted into heat - if it ate up 1/4 of the 180 HP it would melt up the engine compartment.
And as Rich pointed out - a power change of 15% will net a much more important change in climb rate.
So I do expect SC planes to climb better (given enough fuel), and I do believe that Brock honestly reported on this, with compelling data. Which brings me back to my original guess: something not OK in the specific install.
Why is FAT not joining this discussion?

PS. i am the proud owner of a 2004 Jaguar XKR. This car is supercharged. Its "sea level" max power is 400 HP versus 300 for the normally aspirated XK8 - same engine otherwise. The XKR has lower efficiency but massively more power...

At 120 deg F a given volume of air at a given pressure (30 in. in this case) would have 10% fewer air molecules than at standard. It isn't at all uncommon for SL pressure to be at 30 inches and even higher. That's only barely above standard. Without considering power being lost the FAT itself, your intake manifold starts out at about 3,600 ft. DA. If we guess at a loss of 5 HP due to the FAT, that means you surrender roughly the equivalent of the Powerflow at sea level standard. Likely the 5 HP (or whatever) is constant at all altitudes, so eventually that gets overcome once you climb high enough. My rough calculation is the high-temperature effect is a wash around 3,500 ft.

Your Jag is likely a poor example. Is it limited to 30 in.? If this conversion could somehow allow 36 in. or so (like the diesels) the engine would be putting out oodles of HP at SL.

It's all about loss of efficiencies at lower altitudes. This is a long-known effect for many turbo-normalized piston aircraft. For one thing, the way most of these are built the TC runs at much higher output than the engine can use at low altitudes and wastes the excess output in some way. And the heating effects are real. Even with inter-coolers, the temps are still above normal to some extent.

If you're taking off from Aspen, Jackson or Telluride, etc. the equations is totally different. But from Boeing Field, Sana Monica, you give away some lower-altitude performance at lower flight levels.

[Chris B]

your reference for performance should be the plane that supported the STC - Brock's
<snip>
Which brings me back to my original guess: something not OK in the specific install.

Hi Antoine -

I respectfully disagree that the best comparison is Brock's aircraft. That introduces more variables. His is an earlier model DA40 (SN 649), prototype FAT installation, etc. Wayne's DA40 serial number is close to mine (922 vs. 969) and the supercharger was relatively recently installed by FAT.

But just for you...
...on page 8 in the big supercharger thread Rod references a test flight in July 2011 to 17,000'.
Here is the CirrusReports link: https://cirrusreports.com/flights/N8QQ/317655

Without logs I can't easily do a side-by-side comparison on a single chart, but per this screen shot N8QQ's climb from 300' to 11,500' takes 17:27.



1:07 slower than our supercharged installation, and 0:27 slower than our NA configuration.

There is just no evidence that anything was wrong with our installation. None.

Chris

[Antoine]

Chris I looked up the Cirrus reports files and they indeed support what you say:

Brock too only allowed 29-30 inches at take-off and then throttled back to limit CHTs to around 400 F.
This implies less power than the theoretical max. And yet enough that he was seeing a massive performance boost vs his previous setup?!

For my peace of mind: did you check mag timing and chase the leaks in the baffling after the install?
How was your interaction with FAT, since you did not have them install it? I assume you must have had a lot of exchanges?

[Ian Sage]

Link 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?

Rich,

There are no official baffle changes included in our STC. One of the first things we check when a plane comes into our hangar before the installation starts is the condition of the baffle. As making more power always means making more heat having a good seal in all areas can make all the difference in the CHTs of any plane. Depending on what we see we make an individual recommendation on an aircraft to aircraft basis. Over the years we have identified a number of common problem areas on various aircraft and we use a number of techniques to improve the existing baffle without altering the original design. For instance, the baffle pieces below and between the cylinders in a Cirrus SR-22 often have huge gaps between the baffle and the block and due to their somewhat hidden location often go unnoticed. Cessna 182s usually have a piece of baffle missing that seals a large hole between the oil cooler and the front of the block. In my experience DA-40 baffles have been much tighter but there is still room for improvement around the front of the baffle near the prop, along the back of the baffle near the mags and the baffle between the cylinders as well. Issues with the rubber seal against the cowl aren't really unique to any individual aircraft.

[Chris B]

... did you check mag timing and chase the leaks in the baffling after the install?

Of course. But in any case the timing and baffling are identical in the NA and supercharged N171CB flights referenced in this thread. And the supercharged performance is similar to both Brock & Wayne's aircraft.

I assume you must have had a lot of exchanges?

Extensive. FAT has the entire N171CB data log, from post engine break-in until we removed the supercharger.

I think the data speaks for itself.

Chris

[Ian Sage]

. . .
- of course I agree that 60-80 F of extra inlet air temperature is significant. I think I was among the first here to raise the issue.
. . .

It is worth noting that the 60-80° IAT rise is the peak for a given flight. Any reduction of RPM or throttle position lowers that temperature. I think you also mentioned that it is common for turbocharged aircraft to run 120-140° IAT increase over ambient after their intercoolers. In our experience this is correct. We do not use intercoolers because while they may be able to reduce 250° air down to 140° they are far less efficient at cooling "cool" air. We decided that the minimal gain we would get from adding intercoolers would not justify the additional cost, weight and complexity. Some might disagree. While not directly related, another note on this topic is carburetor icing regulations. During our Cessna 182 STC process we discovered we still had to provide carb heat. Our system does not produce ENOUGH heat to meet the 120° minimum for available carb heat that the engine is required to have available for safe flight. While this does not directly translate to the DA-40 there are a number of aircraft that still provided heated alternate air to fuel injected engines. I am not familiar with the regulation or test results that caused those manufacturers to do so but there are still aircraft being manufactured that are required to provide more heat than our supercharger to ensure safe operation.

. . .
- I also agree that a SC costs power, thereby hurting efficiency . . .
. . .

We bench test every supercharger on the ground to ensure that it draws no more than 8HP to produce 110% of it's certified performance. This is done using a 10HP engine and various anemometers, thermometers and gauges. Now that I think about it, that 10HP engine died on us a few years back and we now use a 15HP engine on our test bench. Regardless, they are all visually inspected then test run to ensure they are within spec before being serialized. This guarantees that a healthy supercharger will never draw more than a peak of 8HP if the worst possible combination of factors and flight conditions conspire against it. Under normal conditions the peak parasitic draw will be 6-7HP and rarely as low as 5HP. This peak draw is always at 7000' +/-. It is always lower at sea level and always lowest in the high teens. At all altitudes, any reduction in throttle position or RPM reduces both the parasitic draw and IAT increase.

. . .
Which brings me back to my original guess: something not OK in the specific install.
. . .

Yes, there were issues with the installation. Unfortunately we at FAT never got to see the aircraft and I am sure those issues contributed to the frustration.

. . .
Why is FAT not joining this discussion?
. . .

As a vendor on the forum all of my posts are reviewed by the moderators prior to being added to the forum. Having watched other forums descend into chaos I fully understand and agree with this policy. It does cause a delay in my ability to communicate here and I need to make sure I don't accidentally slip into a sales pitch but I think that minor inconvenience is well worth the benefit it provides. I think I still have a few posts waiting for approval so hopefully they will be trickling in soon.

[Ian Sage]

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

We are saddened that he feels as though we did not disclose any of what he sees as the drawbacks adequately which is something that we always try to do. We spent a great deal of time on the phone with Chris trying to help him through his installation issues and eventual disappointment in both the performance and CHT rise. Unfortunately we never got to see the plane ourselves and I am confident the issues he encountered during the installation could have been quickly remedied. Additionally, despite the installation being signed off as complete we have been told by another mechanic who has worked on the plane that the supercharger was not installed per the STC. The alterations he described absolutely would have negatively impacted both CHTs and performance. Unfortunately not knowing that until after the fact makes many of our attempts to provide support from afar futile. No doubt this added to Chris' frustration with ongoing support and troubleshooting.

We are sad to loose Chris as a customer, particularly when unresolved technical issues contributed to his decision. It is in our best interest to be as responsive and supportive of our customers as possible. For a company who strives to provide an excellent product and support with an industry leading warranty each unhappy customer is a bitter pill to swallow and loosing Chris is no exception.