What's an "altitude engine"?

Chief Captain

Chief Captain

Well-Known Member
The regs say that a manifold pressure gauge is needed for each altitude engine, and part 1 defines an altitude engine as:

Altitude engine means a reciprocating aircraft engine having a rated takeoff power that is producible from sea level to an established higher altitude.

What's the difference between an altitude engine and a turocharged engine? My Seminle doesn't produce takeoff power up high, and it still has a manifold pressure gauge.
 
Turbo normalized? I dunno, but looking forward to the answer.

I *think* turbo normalized means an engine that can pull ~29.92 up to a specified altitude well above sea level.
 
A turbo engine is an altitude engine.

Find the data sheet for a seminole and you will see why it has a mp gauge (look at last page)
 
The Pilot's handbook of aeronautical knowledge says that a Sea Level engine is a supercharged engine with only one blower setting, meaning it gives you a power boost but you lose that power with altitude. It further states that as superchargers got more advanced, they started making geared impellers, so that you could have a "low blower" setting for use from low altitudes into the climb, then once you got to a high enough altitude, you'd set the "high blower" setting in, at the higher altitude the faster impeller wouldn't overboost the engine, these were therefore called "Altitude engines."

I guess under the 14 CFR 1 definition, anything with a turbocharger would classify as an altitude engine.
 
turbocharger - an exhaust gas driven air compressor used to increase the power of a reciprocating engine, using a small radial inflow turbine in the exhaust system of the engine to drive a centrifugal type air compressor. Exhaust gases spin the turbine and the compressor compresses air flowing into the cylinders of the engine through the induction system. It uses power from the engine because it increases the exhaust back pressure but, produces a greater power increase than the loss of power caused by the turbine.

altitude engine - a reciprocating engine equipped with a supercharger that allows it to maintain its rated sea level horsepower to a specified higher altitude.

supercharger - an air pump used to increase the pressure of the air taken into the cylinders of a reciprocating engine. the amount of power is determined by the mass or weight of the fuel-air mixture taken into the cylinders. by compressing the air before it enters the cylinders, a greater mass of air can be used and more power can be developed by the engine. Superchargers can be gear driven from the engine, or they can be driven by a turbine spun by exhaust gases (which are called turbochargers)

The difference between an altitude engine and a turbocharged? An altitude engine can have the power boost derived by a gear driven supercharger, a turbo (by definition) must have the power boost derived from a spun turbine.

Good? :)
 
But a Supercharger is less efficient than a turbocharger, because the supercharger is always geared directly to the engine and it's compressor RPM is always directly proportional to the engine RPM - it is always taking energy off the engine. A Turbocharger has a waste gate, so at sea level, all the exhaust gases will be going out the waste gate and not through the turbine impeller, so the engine will be developing power without the turbocharger's assistance.
 
gotWXdagain said:
But a Supercharger is less efficient than a turbocharger, because the supercharger is always geared directly to the engine and it's compressor RPM is always directly proportional to the engine RPM - it is always taking energy off the engine. A Turbocharger has a waste gate, so at sea level, all the exhaust gases will be going out the waste gate and not through the turbine impeller, so the engine will be developing power without the turbocharger's assistance.
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Some super chargered engines have blow off valves, which serve the same function as a waste gate. I.e. the regulate the intake manifold pressure.
 
z987k said:
If we could get some digital ignition and fuel injection and then kept the boost reasonable, it really wouldn't matter at all.
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It's like over clocking a computer. Simply put we raise two components, the voltage into the computer and the speed of it. The faster you make the speed, the more voltage you need to support it. However, with increased voltage comes increased heat; the limiting factor (usually).

You can moderately over clock with little damage from the increased heat. However, like the engine, if you boost the living crap out of it you're going to beat it into the ground much faster.

IMO turbo normalized is the way to go. Higher cruise altitude gives better utility. The ability to get there is greatly limited in today's aircraft. I don't see why turbo normalized can't be a possibility on a large scale in the future. Though with FADEC coming in, boosting it will probably get safer and safer as well.

Who knows, good discussion though.
 
shdw said:
It's like over clocking a computer. Simply put we raise two components, the voltage into the computer and the speed of it. The faster you make the speed, the more voltage you need to support it. However, with increased voltage comes increased heat; the limiting factor (usually).

You can moderately over clock with little damage from the increased heat. However, like the engine, if you boost the living crap out of it you're going to beat it into the ground much faster.

IMO turbo normalized is the way to go. Higher cruise altitude gives better utility. The ability to get there is greatly limited in today's aircraft. I don't see why turbo normalized can't be a possibility on a large scale in the future. Though with FADEC coming in, boosting it will probably get safer and safer as well.

Who knows, good discussion though.
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That's the thing. Digital ignition that can advance and retard timing on the fly is not only crucial but has been commonplace for decades.
EFI is also important to have the correct A/F ratios at all times and between the two will cause a lot less stress on the engine. I don't care how much someone monitors egt's and cht's the computer can do it a lot better and to a finer degree.
With EFI and digital ignition it's a lot easier to run lop with no issues, saving tons of fuel.
We have the technology, we've had it for about 30 years.

There is no reason you can't run 6 or 7 psi(45ish" at sea level) and have no long term problems given the engine is properly designed and managed.

But if you're running 45", there's no way to not fly oversquare, combine that with lop at altitude and the world may actually end.
 
mshunter said:
Some super chargered engines have blow off valves, which serve the same function as a waste gate. I.e. the regulate the intake manifold pressure.
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But as I understand, all that does is allow air to pass out to prevent overboosting, it doesn't change the fact that the engine is spinning a compressor, thereby taking energy away from propulsion.
 
My car is turbocharged. All I know is that I mash the pedal and I go "Weeeeee! Weeeee WEEEEEE!" all the way home like the GEICO commercial.
 
z987k said:
That's the thing. Digital ignition that can advance and retard timing on the fly is not only crucial but has been commonplace for decades.
EFI is also important to have the correct A/F ratios at all times and between the two will cause a lot less stress on the engine. I don't care how much someone monitors egt's and cht's the computer can do it a lot better and to a finer degree.
With EFI and digital ignition it's a lot easier to run lop with no issues, saving tons of fuel.
We have the technology, we've had it for about 30 years.
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Yup, we have all that technology, but the cost of developing it for an airplane, certifying it for an airplane and then covering those costs in engine sales is too high to make it work. The market just isn't big enough to spread the R&D costs thin enough in order to price the engines at a point that will sell, compared to what we have today. Might work in the experimental realm, but that's about it.
 
gotWXdagain said:
But as I understand, all that does is allow air to pass out to prevent overboosting, it doesn't change the fact that the engine is spinning a compressor, thereby taking energy away from propulsion.
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I get what your saying, and your right. A turbo is basically free horsepower. A supercharger is parasitic drag on the engine. They work great in low RPM, "I need it now" applications, like drag racing. But turbo lag is a big deal when you see the green and have to wait another few seconds for boost. It take a specalized engine to handle that stuff. My brothers cars runs two 88mm turbos on a SBC to produuce 2800hp (roughly), and the only way it works is with a ton of tuning. He brings it up on the 1st rev limiter to about 4500rpm and the fuel puddling in front of the turbo then ignites bringing the turbo's up to speed. But he runs a 10.5W tire, so he only leaves the line with about 6-8psi boost. It all comes in as the car makes it way down the track via computers, and goes through the traps with about 34-36 lbs of boost. The supercharged cars just can't compete because it all there at once. Turbo's are a "softer" hit. And the car usually get a season before the engine gets torn down for inspection.
 
KSCessnaDriver said:
Yup, we have all that technology, but the cost of developing it for an airplane, certifying it for an airplane and then covering those costs in engine sales is too high to make it work. The market just isn't big enough to spread the R&D costs thin enough in order to price the engines at a point that will sell, compared to what we have today. Might work in the experimental realm, but that's about it.
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Certification and the cost associated is the only thing holding it back. The rest has been done. That's why it works in the experimental market, because there is no need for certification.
 
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