Explain Turbo Normalized

[AggieMike88]

Being from the automotive industry, I understand the concept of superchargers and turbochargers, including what they do and how they work.

But looking at various aircraft, I encounter the term "Turbo Normalized". What is that and why would I want it on an aircraft?

 

[Anymouse]

I'm no expert, but in a nutshell turbo-normalizing will keep sea level manifold pressure (30 inches or so) on the engine up to a certain altitude. Basically you can get more power higher up without boosting the engine (40 inches or whatever) like a super charger will do.

 

[Capt. Geoffrey Thorpe]

The objective is not to boost the manifold pressure beyond normal sea level values, but to maintain sea level manifold pressures at altitude.

So you don't get more takeoff power (at sea level) but you can maintain power / cruise speeds at altitude and you don't increase the loads on the engine that boosting beyond sea level pressure causes.

 

[docmirror]

Yup, the wastegate(if automatic) is set to provide an aneroid controlled manifold pressure of 29.92" at the intake and will maintain that to critical altitude dependent on when the wastegate is fully closed. At that point, further climb reduces MP just like a non turbo plane.

You want it because it provides extra power at altitude to go faster. Usually critical altitude is somewhere around 8-12k' Imagine having sea level power of 180HP at 10k'. Also good if you operate in high altitudes where take off power is important.

 

[AggieMike88]

If one has the opportunity of putting either on their engine, which is the better selection? TN or TC?

 

[Ted]

If one has the opportunity of putting either on their engine, which is the better selection? TN or TC?

TN is better from an efficiency perspective if it produces the same power. It will require less boost and typically uses high compression to produce the power. That's why you're seeing TN pop up in these newer planes.

 

[Anymouse]

If one has the opportunity of putting either on their engine, which is the better selection? TN or TC?

I vote for TN. Been wanting to put it in my Tango, but haven't been wanting to pay for it. If I did get it install, I'm pretty sure I could get a 200+ KIAS cruise.

 

[Dav8or]

If one has the opportunity of putting either on their engine, which is the better selection? TN or TC?

Well, my understanding is turbo normalized is pretty much automatic, with no pilot input. Traditional turbo charging will require the pilot to adjust the waste gate to keep from potentially imploding the engine. More pilot work load as if there wasn't enough already. My vote would go with the automatic system.

 

[Ted]

Well, my understanding is turbo normalized is pretty much automatic, with no pilot input. Traditional turbo charging will require the pilot to adjust the waste gate to keep from potentially imploding the engine. More pilot work load as if there wasn't enough already. My vote would go with the automatic system.

The majority of turbocharging setups are automatic. Some of the TSIO-360s are not (fixed wastegate) and some of the RayJay aftermarket systems are not (manual wastegate).

 

[Ted]

I vote for TN. Been wanting to put it in my Tango, but haven't been wanting to pay for it. If I did get it install, I'm pretty sure I could get a 200+ KIAS cruise.

Being experimental, you could fab up something fairly cheaply. Have you considered a supercharger?

 

[hindsight2020]

Well, my understanding is turbo normalized is pretty much automatic, with no pilot input. Traditional turbo charging will require the pilot to adjust the waste gate to keep from potentially imploding the engine. More pilot work load as if there wasn't enough already. My vote would go with the automatic system.

It really has nothing to do with wastegate automation. Turbo 182RG for example, the system is turbo-normalized, yet it's not automatic. You have to takeoff/go-around part throttle at low altitudes. Manual wastegates are found both on TC and TN installations.

As to which I would choose, my vote goes for turbonormalized as well.

 

[docmirror]

If one has the opportunity of putting either on their engine, which is the better selection? TN or TC?

TC on an aircraft engine with no detonation protection, and fixed timing is not a good plan. More than that, TC on an NA engine which was not designed for TC pressurization is going to have reliability problems with internal components, and heat dissipation.

 

[Ted]

TC on an aircraft engine with no detonation protection, and fixed timing is not a good plan. More than that, TC on an NA engine which was not designed for TC pressurization is going to have reliability problems with internal components, and heat dissipation.

What do you base this on? How is a factory turbo normalized engine not designed for it? I do agree that in some cases an aftermarket turbo kit on an engine via stc can have the wrong combination, but that doesn't apply to factory turbo normalized engines.

 

[docmirror]

What do you base this on? How is a factory turbo normalized engine not designed for it? I do agree that in some cases an aftermarket turbo kit on an engine via stc can have the wrong combination, but that doesn't apply to factory turbo normalized engines.

The very first letters are "TC" in that post indicating an engine which would be charged beyond sea level MP. "TN" is the generally accepted use for TurboNormalized. I am not, and was not talking about a TN installation, only one where the MP is greater than 29.92" HG for any operation.

I have no problems running any NA(Normally Aspirated) engine using TN methods. It was designed for operation at sea level pressures and can maintain that power just fine up through the altitude to critical. Even though the air becomes thinner, and one would think it would provide less cooling, we can't forget that it also loses about 3F every 1000' so it's like a natural balancing that we gain as we climb. Less air - but it's cooler so the ability to dissipate heat kind of works out in the end.

 

[Anymouse]

Being experimental, you could fab up something fairly cheaply. Have you considered a supercharger?

I'm not the one to go around fiddling with my engine. I'd have to get some one that knows what they're doing. That will take some bucks. I did get a off the top of the head quote from one company of $20k. Too rich for me.

As far as supercharge, I probably won't. Not worth the extra hassle and abuse on the engine.

 

[Sac Arrow]

One of the benefits of a turbo normalized engine, vs. a turbo supercharged engine (i.e. TSIO 360) is that if you have failure of the turbocharger, you still have full sea level power of the engine.

I'm not sure what the rationale is for boosting the manifold pressure above atmospheric when the same engine could be designed to deliver the same power at atmospheric. I guess in theory it could be more efficient. Maybe Ted knows.

 

[Ted]

The very first letters are "TC" in that post indicating an engine which would be charged beyond sea level MP. "TN" is the generally accepted use for TurboNormalized. I am not, and was not talking about a TN installation, only one where the MP is greater than 29.92" HG for any operation.

I have no problems running any NA(Normally Aspirated) engine using TN methods. It was designed for operation at sea level pressures and can maintain that power just fine up through the altitude to critical. Even though the air becomes thinner, and one would think it would provide less cooling, we can't forget that it also loses about 3F every 1000' so it's like a natural balancing that we gain as we climb. Less air - but it's cooler so the ability to dissipate heat kind of works out in the end.

Ok, your post implied that most turbocharged engines out there are somehow bad ideas since they have fixed timing and no detonation protection.

 

[docmirror]

One of the benefits of a turbo normalized engine, vs. a turbo supercharged engine (i.e. TSIO 360) is that if you have failure of the turbocharger, you still have full sea level power of the engine.

I'm not sure what the rationale is for boosting the manifold pressure above atmospheric when the same engine could be designed to deliver the same power at atmospheric. I guess in theory it could be more efficient. Maybe Ted knows.

Not sure if Ted knows but I know one answer. It's interesting that you chose the TSIO 360 as an example. It's one engine where it is derated or uprated depending on altitude. In one case, that engine can maintain certain HP up to a specified altitude, and then a lower HP rating at critical(and above) altitude. In another case of the same basic engine, it is uprated at altitude, where the engine is allowed to produce more power at and above critical. Weird.... OBTW, the MP is the same at all altitudes, so is the RPM. I guess they have decided that there is adiabatic gain from lower temps at altitude and it's intercooled, where the derated engine is not intercooled, Weird....

 

[docmirror]

Ok, your post implied that most turbocharged engines out there are somehow bad ideas since they have fixed timing and no detonation protection.

My post said, nor implied any such thing. It said "TN". You keep going back to "turbocharged". Please learn the difference between the two before correcting me.

Having said that, the fixed timing and no detonation protection which are common in modern auto engines are a serious disadvantage in TURBOCHARGED engines where MP > 29.92" HG. Unless said TURBOCHARGED engine was designed from the beginning for the MP.

Happy?

 

[BiffJ]

The biggest advantage to normalized over boosted is the heat produced by the compressor. The normalized turbo system will produce more heat than a normally aspirated engine because it is compressing air. This will cause more wear and tear on your engine. The next step is boosting the intake pressure with the turbo and this will produce more heat in the form of compressed air as well as more back pressure from the turbo all of which add to the heat in the engine. This means more wear and tear on the engine as a whole. So in addition to adding mechanical complexity with the turbo and its associated hardware (software too in some cases), you are also adding more heat with each step and this means more wear. You don't get something for nothing.

Frank

 

[Ted]

TC on an aircraft engine with no detonation protection, and fixed timing is not a good plan. More than that, TC on an NA engine which was not designed for TC pressurization is going to have reliability problems with internal components, and heat dissipation.

My post said, nor implied any such thing. It said "TN". You keep going back to "turbocharged". Please learn the difference between the two before correcting me.

I do know the difference. So what am I missing in your statements?

I'm not attacking you, as you seem to think.

 

[Henning]

Aside from the MP pressure thing, the big thing about turbo normalized engines and TIO or TSIO factory engines is compression ratio. You carry higher compression NA pistons on a TN engine where as you lose one to two points of compression on a TC engine. TN is a more efficient way to produce the power.

 

[Sac Arrow]

The biggest advantage to normalized over boosted is the heat produced by the compressor. The normalized turbo system will produce more heat than a normally aspirated engine because it is compressing air. This will cause more wear and tear on your engine. The next step is boosting the intake pressure with the turbo and this will produce more heat in the form of compressed air as well as more back pressure from the turbo all of which add to the heat in the engine. This means more wear and tear on the engine as a whole. So in addition to adding mechanical complexity with the turbo and its associated hardware (software too in some cases), you are also adding more heat with each step and this means more wear. You don't get something for nothing.

Frank

I get what you're saying but as a practical matter, the additional heat from the compressed air charge is inconsequential relative to normal CHT's and EGT's. There are other reasons why you can fry your engine with a turbo, like operating the engine at elevated power levels at altitude because you can.

 

[Ted]

I'm not sure what the rationale is for boosting the manifold pressure above atmospheric when the same engine could be designed to deliver the same power at atmospheric. I guess in theory it could be more efficient. Maybe Ted knows.

I wasn't around back then so I wasn't involved in the engineering decisions. My guess is that part of it was that the lower RPM used makes the plane quieter, and that efficiency wasn't as much of a concern in the days of the Cadillac 500 V8. Add to that the fact that many of these planes they figured wouldn't really be operated in the high teens or flight levels (who flies a Navajo at FL250?) and a lot of it was "good enough" engineering.

From talking to the old timers, you'd be surprised how much of that happened. I also think when you're looking at a lot of the turbocharged planes that were often more "luxurious" that noise was a real consideration, for which lower RPM was good.

 

[Dav8or]

Turbo 182RG for example, the system is turbo-normalized, yet it's not automatic. You have to takeoff/go-around part throttle at low altitudes.

This has me puzzled. If the point of TN is for the machine to maintain 29.92", or 30" it implies that it is automatic. If using full throttle is safe for a NA engine at sea level, why can you not use a TN engine full throttle at all altitudes? Is this because the system is not capable of maintaining 30" when the outside barometric pressure is greater than 30"?

 

[Sac Arrow]

This has me puzzled. If the point of TN is for the machine to maintain 29.92", or 30" it implies that it is automatic. If using full throttle is safe for a NA engine at sea level, why can you not use a TN engine full throttle at all altitudes? Is this because the system is not capable of maintaining 30" when the outside barometric pressure is greater than 30"?

Depends on how the turbo is regulated. With a fixed wastegate, you have to use partial throttle to not exceed a specified MP limitation since the turbo is always boosting. With a turbo normalized engine, that's 30 inches. With a turbo supercharged engine, it's higher. Normal sea level takeoffs and go-arounds in my Turbo Arrow were done at partial throttle, 38 inches.

 

[Ted]

Aside from the MP pressure thing, the big thing about turbo normalized engines and TIO or TSIO factory engines is compression ratio. You carry higher compression NA pistons on a TN engine where as you lose one to two points of compression on a TC engine. TN is a more efficient way to produce the power.

Typically true and I agree. Just to point out it isn't always the case, though, certain turbo Aztecs were 7.3:1, others 8.5. Otherwise, power output was the same although the MPs were likely tweaked.

I get what you're saying but as a practical matter, the additional heat from the compressed air charge is inconsequential relative to normal CHT's and EGT's. There are other reasons why you can fry your engine with a turbo, like operating the engine at elevated power levels at altitude because you can.

The heat itself is less the issue, more what it does to the combustion. Less dense air for the same MP so less power, but hotter means more prone to detonation.

 

[Sac Arrow]

Typically true and I agree. Just to point out it isn't always the case, though, certain turbo Aztecs were 7.3:1, others 8.5. Otherwise, power output was the same although the MPs were likely tweaked.



The heat itself is less the issue, more what it does to the combustion. Less dense air for the same MP so less power, but hotter means more prone to detonation.

Good point.

 

[Ted]

This has me puzzled. If the point of TN is for the machine to maintain 29.92", or 30" it implies that it is automatic. If using full throttle is safe for a NA engine at sea level, why can you not use a TN engine full throttle at all altitudes? Is this because the system is not capable of maintaining 30" when the outside barometric pressure is greater than 30"?

It does not imply that it is automatic, it's merely differentiating between two goals of turbos - in this case to hold SL power to higher altitudes.

Some systems at some altitudes can "overboost" at full throttle. By the way, many turbines operate the same way.

 

[Dav8or]

It does not imply that it is automatic, it's merely differentiating between two goals of turbos - in this case to hold SL power to higher altitudes.

Some systems at some altitudes can "overboost" at full throttle. By the way, many turbines operate the same way.

So basically you're saying that some turbo normalized systems are basically just ordinary manually operated turbos were the engine happens to be optimized for 30" manifold pressure operation (compression ratios and timing) with the POH telling the pilot to make adjustments to keep the MP at 30"?

I personally wouldn't buy a turbo that wasn't automatic. The pilot has enough to do already.

 

[Ted]

So basically you're saying that some turbo normalized systems are basically just ordinary manually operated turbos were the engine happens to be optimized for 30" manifold pressure operation (compression ratios and timing) with the POH telling the pilot to make adjustments to keep the MP at 30"?

More or less. Some turbocharged systems also are manual, such as the TSIO-360 that Sac referred to.

I personally wouldn't buy a turbo that wasn't automatic. The pilot has enough to do already.

I definitely agree the manual systems have human factors negatives with them, so I'd say that's sound logic on your part.

 

[Henning]

This has me puzzled. If the point of TN is for the machine to maintain 29.92", or 30" it implies that it is automatic. If using full throttle is safe for a NA engine at sea level, why can you not use a TN engine full throttle at all altitudes? Is this because the system is not capable of maintaining 30" when the outside barometric pressure is greater than 30"?

Where does it imply automation? All it does is gives the operator the ability to match the engine redline on the gauge. Many TN systems are manual, heck even the Piper T-Arrow and Seneca II+ installations are fixed waste gate turbochargers. My Travelair had electric wastegates with toggle switches to control them, many other systems have cables with quadrant or vernier controls.

 

[Sac Arrow]

So basically you're saying that some turbo normalized systems are basically just ordinary manually operated turbos were the engine happens to be optimized for 30" manifold pressure operation (compression ratios and timing) with the POH telling the pilot to make adjustments to keep the MP at 30"?

I personally wouldn't buy a turbo that wasn't automatic. The pilot has enough to do already.

It sounds like bigger deal than it is. Yes, you have to be conscious of your MP redline when you take off, but most fixed gate systems have a relief valve that in theory will protect from overboosting. I've never been tempted to test it to see if it actually works, but I've never inadvertently overthrottled either.

 

[Dav8or]

It sounds like bigger deal than it is. Yes, you have to be conscious of your MP redline when you take off, but most fixed gate systems have a relief valve that in theory will protect from overboosting. I've never been tempted to test it to see if it actually works, but I've never inadvertently overthrottled either.

I'm assuming it's not just take off and that you have to continually adjust it up to your cruise also. Is this not so?

 

[Sac Arrow]

I'm assuming it's not just take off and that you have to continually adjust it up to your cruise also. Is this not so?

You do, but that's no different than in a normally aspirated airplane.

It's actually easier to manage at a high density altitude airport than a normally aspirated plane. For example if I want to take off at KTVL on a 10,000 foot density altitude day in a normally aspirated plane, I'm doing a full throttle static runup and leaning for best power, just before takeoff. In the Turbo Arrow I'm still going full rich on takeoff and climbeout, just like at sea level. Only difference is I'm pushing the throttle more forward than I would at sea level.

 

[Henning]

So basically you're saying that some turbo normalized systems are basically just ordinary manually operated turbos were the engine happens to be optimized for 30" manifold pressure operation (compression ratios and timing) with the POH telling the pilot to make adjustments to keep the MP at 30"?

I personally wouldn't buy a turbo that wasn't automatic. The pilot has enough to do already.

Some of them are fully automated, I think the TAT system is, and that's the system on the Cirrus. I'm pretty sure the original Aerostar engines were TN with full waste gates. There's no reason you cannot have a fully deck compensated wastegate to hold whatever you want automatically. The reason that most aftermarket setups are manual control is that pilots are cheap and full control waste gates cost money.

It really isn't that big of a deal to run a manual wastegate though.

 

[Henning]

I'm assuming it's not just take off and that you have to continually adjust it up to your cruise also. Is this not so?

Unless I was operating out of a high altitude field, I would not even bring the system online until 5000' or so. There I would retard the throttles ones at a time, close the wastegate shut, and throttle back up to whatever, typically 25". From there it's all throttle control to keep bumping up the MP during the climb until I hit the stops.

 

[Ted]

Unless I was operating out of a high altitude field, I would not even bring the system online until 5000' or so. There I would retard the throttles ones at a time, close the wastegate shut, and throttle back up to whatever, typically 25". From there it's all throttle control to keep bumping up the MP during the climb until I hit the stops.

Aside from the overboost potential, that will be less efficient than full throttle and close the wastegates only as needed to maintain MP.

 

[Henning]

Aside from the overboost potential, that will be less efficient than full throttle and close the wastegates only as needed to maintain MP.

Yeah, understood, however tweaking MP with waste gate electric switches wasn't that bloody precise, plus with the carbs on, I could get a good even EGT spread so the efficiency I gave up at the throttle plate I got something back for in mixture. It really was just a matter of the climb for the most part anyway. I cruised that plane 16k, I was WOT LOP by there.

 

[flyingcheesehead]

Well, my understanding is turbo normalized is pretty much automatic, with no pilot input. Traditional turbo charging will require the pilot to adjust the waste gate to keep from potentially imploding the engine. More pilot work load as if there wasn't enough already. My vote would go with the automatic system.

This has me puzzled. If the point of TN is for the machine to maintain 29.92", or 30" it implies that it is automatic. If using full throttle is safe for a NA engine at sea level, why can you not use a TN engine full throttle at all altitudes? Is this because the system is not capable of maintaining 30" when the outside barometric pressure is greater than 30"?

There seems to be some confusion here. Both turbocharged and turbonormalized systems can be "automatic" or otherwise.

Turbonormalized = a system which allows you to main normal sea level MP of ~30" to higher altitudes.

Turbocharged = A system which boosts MP to higher-than-sea-level MP. For example, a Seneca II can be boosted to 40".

That's the difference. I think most aftermarket systems are TN because as far as the engine is concerned nothing has really changed - The intake and exhaust are different, but the engine wouldn't be doing anything different except for running hotter (due to the compression from the turbo) intake air, unless it's intercooled.

Intercooler = A device that cools intake air between the intake side of the turbo and the engine. When outside air is compressed, it becomes hotter (PV = nRT). The intercooler looks somewhat like a radiator but what's passing through it is air instead of coolant.

Critical Altitude = The altitude above which the turbo can no longer provide full power. Upon climbing through the critical altitude, the wastegate (an an automatic or manual wastegate system) is fully closed (or on a fixed-wastegate system, the throttle is fully open) and MP will begin dropping as you climb higher.

Now, there are three types of wastegates, and I think any of them can be installed on either a TC or TN system:

Automatic Wastegate = Just like it sounds. Via mechanical or electronic means, this wastegate is controlled so that you push the throttle all the way in to get full power. At sea level, a TN system with an automatic wastegate will leave the wastegate open because you've already got full MP from the outside air. TN or TC, as you climb MP will be constant until you reach the critical altitude at which point the wastegate is fully closed and the turbo is providing maximum boost.

Manual Wastegate = Also just like it sounds. The pilot is directly in control of the wastegate. In some systems (eg Cessna T182) the wastegate is controlled by a linkage connected to the throttle control and operates from the pilot's perspective somewhat similar to how a Fixed wastegate does (described below). In other systems (eg Piper Comanche), there is a "second throttle" that controls the wastegate independent of the throttle. When there is a second control, you can take off or go around with full throttle, and then as MP drops you can continue to boost MP in the climb by using the wastegate control to increase boost. When the wastegate control is fully forward, you're at the critical altitude.

Fixed Wastegate = There really isn't a "gate" here per se, just a fixed-size orifice that, in terms of operations, resembles a manual wastegate that is partially closed. The amount of boost you get is always constant, and power is controlled by the throttle. Piper Turbo Arrow and Seneca II-V use this type of system. You cannot push the throttle full forward on takeoff or go-around without overboosting the engine - You must set power carefully using the MP gauges, and as you change altitudes you must keep moving the throttle(s) to maintain MP. As you climb, when you reach full throttle at full MP you are at the critical altitude.

I personally don't care for the fixed wastegate systems or the throttle-controlled manual wastegate systems because you can't just push the throttle all the way in for go-around (or takeoff). Automatic is nice, but the fixed manual system isn't bad - You can still use full throttle for TO/GA, and simply make small adjustments for climb and descent. You'll also be able to "turn off" the turbo partway through the descent and have it cooled down nicely by the time you land, whereas the fixed systems tend to require you to idle for several minutes after landing to ensure that you cool the turbo down enough prior to shutdown to avoid the oil left in the bearings at shutdown from getting cooked.

Hope this helps some people's understanding... (Ted et al, feel free to correct me as necessary!)