Supercharging - What's the catch?

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planecrazy

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planecrazy
I live in Denver where density altitude on a hot summer day sneaks up on 10k. So as I wistfully look towards which airplane I'd like to own, I like the idea of turbos, as it lets me mitigate that altitude penalty pretty easily.

So I ran across these Forced Aeromotive people (you'll have to google, PoA won't let me link). They're selling a supercharger and making pretty fantastic claims about them. I've seen people mention them here on PoA generally favorably, but they're claiming for $30k they can make a stock SR-22 outperform the turbo versions. And it keeps the temps more managable. And it weighs less than 40 pounds. And it only takes 4HP of power to run.

I feel like if all of that is true, they would have been bought out and made standard equipment on Cirrus or Cessna aircraft.

But I can't find any information that reveals any major disadvantages to this. So I thought I'd ask the wisdom of the crowd, what am I missing about this upgrade?
 
http://www.forcedaeromotive.com/

legacy.jpg
 
I'm not turbo expert but length of service is probably a concern for Cirrus and Cessna. I could be wrong, but I would think a TSIO-550 would be cheaper than an IO-550 w/ a 30k supercharger.
 
$30k and 40 pounds are two big negatives.

Dunno if you can still run ethanol-free mogas with that installed (182). I've never looked that closely. If so, that's pretty freaking neat.

I'm sure there are situations where it would be a whole lot better to sell the 182 and add $30k to your piggy bank for a bigger plane.
 
Theoretically by not using exhaust to spin, they run cool...


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I think you would pay a fuel penalty over a turbo charger. In general turbos utilize waste heat to generate intake boost, effectively increasing the available oxygen for combustion. There is basically no power the engine produces consumed to power the turbo. A super charger is powered by the engine via a belt, shaft or gears. Power is consumed by the supercharger to make boost, which translates to increased fuel burn. Depending on the boost it produces it can be a significant amount of power (read fuel) required to make the boost. Other than that they each accomplish the same thing.
 
gsengle said:
Theoretically by not using exhaust to spin, they run cool...


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It helps some, but remember Boyle's law: compressing something increases the heat, so you've still got warmer intake charge. In fact, my Mini Copper S (2006) has a supercharger and an intercooler for just this reason.

John
 
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PaulS said:
I think you would pay a fuel penalty over a turbo charger. In general turbos utilize waste heat to generate intake boost, effectively increasing the available oxygen for combustion. There is basically no power the engine produces consumed to power the turbo. A super charger is powered by the engine via a belt, shaft or gears. Power is consumed by the supercharger to make boost, which translates to increased fuel burn. Depending on the boost it produces it can be a significant amount of power (read fuel) required to make the boost. Other than that they each accomplish the same thing.
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Not exactly. There is no free lunch in physics. The turbo restricts the exhaust and makes back pressure in the exhaust and cylinder higher. The engine has to work harder to overcome that. Some of the energy to run the turbo comes from expanding exhaust gasses and so is "free" as in waste heat, but much of the energy is pumping gasses through the turbo which does impact the load on the engine.

John
 
Since aircraft engines are typically steady-state, there are few concerns about turbo lag, so another advantage for the turbocharger versus supercharger.
 
jsstevens said:
It helps some, but remember Boyle's law: compressing something increases the heat, so you've still got warmer intake charge. In fact, my Mini Copper S (2006) has a supercharger and an intercooler for just this reason.

John
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A supercharger in a car is a bit different application though.

I don't have any such intercoolers on my supercharged R-985s, nor have I seen intercoolers on any of the other supercharged radials I've flown. You don't start seeing intercoolers until you get into the really big stuff like R-2800s in Corsairs.
 
jsstevens said:
Not exactly. There is no free lunch in physics. The turbo restricts the exhaust and makes back pressure in the exhaust and cylinder higher. The engine has to work harder to overcome that. Some of the energy to run the turbo comes from expanding exhaust gasses and so is "free" as in waste heat, but much of the energy is pumping gasses through the turbo which does impact the load on the engine.

John
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That is why I said in general, but on the whole much more power is removed from the engine with a supercharger which is subject to mechanical losses in gearing and gets no free ride which the turbocharger does get. The advantage of the supercharger is that much higher pressures can usually be generated without the intrinsic lag of a turbo. Turbo lag is really not an issue with an aircraft engine though. Careful design of the turbo can minimize the extra back pressure issues. Again, this should be easier for an aircraft engine as the instantaneous turbo response desired in a car application is not needed in an airplane which should allow a less restrictive manifold and pipe design. Anyway it's complicated.
 
gsengle said:
Theoretically by not using exhaust to spin, they run cool...


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Click to expand...

It's not even measurable, that's how small that effect is. Adiabatic heating causes 98% of pre/post-compressor temp delta. If you know your compressor efficiency, pressure ratio and IAT, you can calculate the compressor output temperature within a tenth of a C. The simple reason is, that the air molecule spends so little time(microseconds) inside the turbo that there simply is not much time for heat transfer to happen.
Engine bay temps are lower on supercharged vs. turbocharged cars, but this has no real effect on IATs, especially in airplane engines.
 
PaulS said:
That is why I said in general, but on the whole much more power is removed from the engine with a supercharger which is subject to mechanical losses in gearing and gets no free ride which the turbocharger does get. The advantage of the supercharger is that much higher pressures can usually be generated without the intrinsic lag of a turbo. Turbo lag is really not an issue with an aircraft engine though. Careful design of the turbo can minimize the extra back pressure issues. Again, this should be easier for an aircraft engine as the instantaneous turbo response desired in a car application is not needed in an airplane which should allow a less restrictive manifold and pipe design. Anyway it's complicated.
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Turbochargers used in aircraft engines often have huge turbine housings (pretty sure a 300hp Continental has .95 A/R Garretts), causing huge lag and awful transient response, but good efficient power once spooled up.
Another big benefit is that these engines don't need cats nor ways to keep them hot = easy to design a very low restriction exhaust system.
 
gsengle said:
Theoretically by not using exhaust to spin, they run cool...


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Click to expand...
basic thermo laws....fluids heat when compressed.

From a reliability standpoint....I'd rather turbo normalize than boost. Boosting adds stress above normal design parameters that can reduce engine life.
 
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mtuomi said:
A piston King Air? Which model is that?
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1967 65-A90.

P&W PT6A-20 engines

Still .......had a factory installed "Roots" supercharger. So did the straight 90 and the B90. The C90 was the first KA without a supercharger.
 
bnt83 said:
$30k and 40 pounds are two big negatives.

Dunno if you can still run ethanol-free mogas with that installed (182). I've never looked that closely. If so, that's pretty freaking neat.

I'm sure there are situations where it would be a whole lot better to sell the 182 and add $30k to your piggy bank for a bigger plane.
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Reading the company provided info it is a normalization system, not a boosted system so it shouldn't affect the mogas approval for any technical reasons.

It looks like critical altitude is about 7,000' so it won't give full power on a hot day in Denver.

Supercharger control might be interesting. It appears to be an electronic system rather than mechanical. Maybe there is a pop-off to back it up? Couldn't tell from looking at the kit. I'd sure like to learn more about the controller if I bought a plane with one of these.

One other thing, you can prolly get an engine overhauled for the price of the kit & installation. The cost is definitely no bueno.
 
First, to everyone: Thanks for the responses.

G-Man said:
Since aircraft engines are typically steady-state, there are few concerns about turbo lag, so another advantage for the turbocharger versus supercharger.
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Wouldn't turbo lag be worse with a turbocharger? Seems like the compressible nature of the exhaust gasses would act like a spring versus the more instantaneous belt-driven nature of a supercharger? In my head that was one advantage of getting a 182 and supercharging it versus just getting the T182T (the $50k overhaul cost for the T182T's engine is a bit of sticker shock, too).
 
There is no "turbo lag" in an aircraft engine, normally. They don't have rapid power changes, usually.
 
Fearless Tower said:
A supercharger in a car is a bit different application though.

I don't have any such intercoolers on my supercharged R-985s, nor have I seen intercoolers on any of the other supercharged radials I've flown. You don't start seeing intercoolers until you get into the really big stuff like R-2800s in Corsairs.
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Aren't those carburated? Carbed engines don't need intercoolers thanks to the venturi effect.
 
planecrazy said:
First, to everyone: Thanks for the responses.



Wouldn't turbo lag be worse with a turbocharger? Seems like the compressible nature of the exhaust gasses would act like a spring versus the more instantaneous belt-driven nature of a supercharger? In my head that was one advantage of getting a 182 and supercharging it versus just getting the T182T (the $50k overhaul cost for the T182T's engine is a bit of sticker shock, too).
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It's true but for aircraft applications it really doesn't matter. Remember that an aircraft engine spends the overwhelming majority of it's time in a steady state of power (some where between 65% and 80% probably) in cruise. Turbo lag would only matter on initial acceleration and even in that case, the prop spins up allowing the engine to spin up rapidly which spins up the turbo rapidly then just stays wide open until you back off to cruise climb or cruise power.

John
 
Yes but a non issue in engines that run steady state like airplane engines...


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kgruber said:
1967 65-A90.

P&W PT6A-20 engines

Still .......had a factory installed "Roots" supercharger. So did the straight 90 and the B90. The C90 was the first KA without a supercharger.
Click to expand...

Ahh ok, it wasn't used for the engine though. I thought a supercharged turbine sounded weird!
 
It was gear driven off the left engine and supplied cabin pressurization and a few other things. FAA didn't trust bleed air......yet.
 
Looks like a centrifugal supercharger. Supercharging is great for instant, no lag power as needed, but extracts a penalty all the time in terms of power needed to drive the compressor, and the impact on fuel efficiency. Plus without the intercooler, as mentioned above, you're providing a hotter charge into the engine. At altitude it's likely not going to be too detrimental, but during hot weather / high density altitude, I wonder how much power you'll make given the hot intake temps and parasitic drag of the supercharger unit.
 
It's not like a turbo is free...


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One limitation with that system is you can only produce 30" up to whatever altitude the supercharger's pressure ratio (which is determined by the belt drive) runs out. I thought it was something in the range of 10k, IIRC. Typically turbocharged engines will maintain their maximum MP to a higher altitude than that, somewhere in the 15-25k range, depending on the exact turbo and what the maximum manifold pressure is.

Turbos are normally "set it and forget it" for manifold pressure, provided the controllers are working correctly. As I recall the supercharged planes require you to tweak the throttle position with altitude changes to maintain the desired manifold pressure.

Personally I think they have a neat setup, and I talked with them about adding superchargers to the 310. I'm not a fan of turbos for a lot of reasons. I don't like the inconel exhaust on the Twin Cessnas (big $$$, but necessary for longevity), and the exhausts tend to be less reliable. Turbo controllers and associated oil hoses add parts and reliability issues. Really I would like a supercharger over turbos on paper for a lot of reasons. That said, I have never flown one of their supercharged planes, so I might feel differently once I did.
 
Ted DuPuis said:
One limitation with that system is you can only produce 30" up to whatever altitude the supercharger's pressure ratio (which is determined by the belt drive) runs out. I thought it was something in the range of 10k, IIRC. Typically turbocharged engines will maintain their maximum MP to a higher altitude than that, somewhere in the 15-25k range, depending on the exact turbo and what the maximum manifold pressure is.

Turbos are normally "set it and forget it" for manifold pressure, provided the controllers are working correctly. As I recall the supercharged planes require you to tweak the throttle position with altitude changes to maintain the desired manifold pressure.

Personally I think they have a neat setup, and I talked with them about adding superchargers to the 310. I'm not a fan of turbos for a lot of reasons. I don't like the inconel exhaust on the Twin Cessnas (big $$$, but necessary for longevity), and the exhausts tend to be less reliable. Turbo controllers and associated oil hoses add parts and reliability issues. Really I would like a supercharger over turbos on paper for a lot of reasons. That said, I have never flown one of their supercharged planes, so I might feel differently once I did.
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Supercharger output volume is a function of rpm. In a full blown system with no bypass (which would be borderline insane in a plane), in theory you'd have to increase RPM when you climb to maintain same manifold pressure. In a well suited system, you'd never have to fully close the bypass valve (that is, you never use 100% of the air the compressor is capable of producing).
It's not a simple system, but it doesn't have catastrophic failure modes if designed correctly. Worst case scenario is that your engine turns into a non-charged engine.
 
What about engine cooling? It seems that one can produce full power and heat within the cylinder with the forced induction at higher altitudes but the air higher is less dense, and it seems to me thinner air can't cool the engine as efficiently.

Thoughts about that?
 
Cap'n Jack said:
What about engine cooling? It seems that one can produce full power and heat within the cylinder with the forced induction at higher altitudes but the air higher is less dense, and it seems to me thinner air can't cool the engine as efficiently.

Thoughts about that?
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true....but the OAT is much colder to start with.
 
mtuomi said:
Supercharger output volume is a function of rpm. In a full blown system with no bypass (which would be borderline insane in a plane), in theory you'd have to increase RPM when you climb to maintain same manifold pressure. In a well suited system, you'd never have to fully close the bypass valve (that is, you never use 100% of the air the compressor is capable of producing).
It's not a simple system, but it doesn't have catastrophic failure modes if designed correctly. Worst case scenario is that your engine turns into a non-charged engine.
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So, exactly where is this bypass located on the supercharged aircraft engines of the 30s/40s/50s?
 
Fearless Tower said:
So, exactly where is this bypass located on the supercharged aircraft engines of the 30s/40s/50s?
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Probably nowhere, I said things like "designed correctly" and "well suited system", none of which are likely to apply to supercharged engines from the 30s/40s/50s. I also said borderline insane, which probably is an accurate statement about how those engines are designed. Surely you are not suggesting that those engines, especially their forced induction systems, are designed as well as they could be?
Without any pressure ratio control (such as a bypass), you get most of negatives but only a few positives from mechanical forced induction, especially in an environment where the pressure ratio varies constantly.
 
A Beaver with the Wasp Jr engine has a supercharged engine. It just boosts the manifold pressure by 10" all the way up to max altitude. The engine is made for supercharging. Its pretty much like having a bigger engine.

Turbocharged engines tend to boost the engine more at high altitude and less at low altitude, like keeping 30" of manifold pressure all the way up to Critical Altitude (the highest altitude it can make 30"). So they really go fast at high altitude and go normal at lower altitude. There may be some exceptions, but it gives the plane unique characteristics. Not just like having a bigger engine (its like having a bigger engine at higher altitudes)
 
mtuomi said:
Probably nowhere, I said things like "designed correctly" and "well suited system", none of which are likely to apply to supercharged engines from the 30s/40s/50s. I also said borderline insane, which probably is an accurate statement about how those engines are designed. Surely you are not suggesting that those engines, especially their forced induction systems, are designed as well as they could be?
Without any pressure ratio control (such as a bypass), you get most of negatives but only a few positives from mechanical forced induction, especially in an environment where the pressure ratio varies constantly.
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I never said they were the most efficient.

But as someone who flies behind two supercharged engines, I'm genuinely curious about what is so horrible about them?

Can you weed out the emotion to explain why these engines are so insanely designed? I'm honestly attempting to understand how they were designed so incorrectly. The engines in use today seem to put in plenty of hours before overhaul and don't seem to be blowing up. My only real complaint about them is the fuel burn.

Why those engines are no longer produced has nothing to do with the supercharger va turbo argument. Keep in mind, those large supercharged engines were superseded by turbines. They were never replaced by flat engines with turbos.
 
Fearless Tower said:
I never said they were the most efficient.

But as someone who flies behind two supercharged engines, I'm genuinely curious about what is so horrible about them?

Can you weed out the emotion to explain why these engines are so insanely designed? I'm honestly attempting to understand how they were designed so incorrectly. The engines in use today seem to put in plenty of hours before overhaul and don't seem to be blowing up. My only real complaint about them is the fuel burn.

Why those engines are no longer produced has nothing to do with the supercharger va turbo argument. Keep in mind, those large supercharged engines were superseded by turbines. They were never replaced by flat engines with turbos.
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They obviously do the job they were designed to do, but I'm comparing it to how the system would be designed today (something that I do for living so I'm a bit biased here). I guess it's a bit like driving a '57 Chevy. It's a horrible design if you compare it to today's standards. They don't drive that nice, the AC isn't as efficient, but it sure is 1000x cooler than driving a 2016 Honda :)

My original comments were mainly aimed at the installation that we saw earlier in this thread. Not having any sort of pressure ratio control is just silly. That's like building a new '57 Chevy today.
 
mtuomi said:
They obviously do the job they were designed to do, but I'm comparing it to how the system would be designed today (something that I do for living so I'm a bit biased here). I guess it's a bit like driving a '57 Chevy. It's a horrible design if you compare it to today's standards. They don't drive that nice, the AC isn't as efficient, but it sure is 1000x cooler than driving a 2016 Honda :)

My original comments were mainly aimed at the installation that we saw earlier in this thread. Not having any sort of pressure ratio control is just silly. That's like building a new '57 Chevy today.
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Why do you say they have no pressure ratio control?
 
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