Wastegates and K models

[Schllc]

I would really like to avoid a debate in this thread over whether turbo or non turbo is better, needed, good or bad, and just focus on  some help describing the modifications and which ones are most favorable to pilot management/mismanagement..

I am helping a friend shop for a mooney, and they are looking at K’s,  I’ve noticed that there are an almost infinite way that the turbo models are described with the various models and modifications.

My basic understanding, which is likely incomplete and or incorrect, is that the K models did not come with automatic wastegates, aka turbo normalized.  
I see there are numerous modifications and stc’s for these models but don’t really understand their impacts, features, advantages or disadvantages, or which ones are even still available  

Is there a particular model, modification or stc that protects from over boosting or operates like a turbo normalizer on the k models, or is that what makes a “K” a 252?

[smwash02]

The 231 does NOT have an intercooler or automatic wastegate from the factory, but one or both can be added through aftermarket modifications.

The 252 has both an intercooler and automatic wastegate. The Encore, basically a 252, similarly has both.

They are all "K" models.

[Schllc]

I gathered that waste gates and intercoolers can be added, but does adding a wastegate means it operates as a turnbo normalizer, does it just open at certain pressure, does the pilot have to activate the waste gate?

I would prefer an automatic waste gate for a turbo personally, one less way to damage the engine accidentally, but don’t know if all waste gates are automatic  

 

[squeaky.stow]

Although the 252 does have an automatic wastegate, that does not make it Turbo normalized.

TN systems control the boost with an automatic wastegate to maintain sea level MPs up at altitude. The 252, like the 231 boosts well above sea level MP at lower altitudes to increase power. It maintains that all the way to its critical altitude, at which point power decreases as you climb higher. But unlike the 231, on the 252/Encore, you just firewall it on takeoff and leave it that way until you level off. 

[Schllc]

Is there a modification to make any of the k models turbo normalized?

[ArtVandelay]

Although the 252 does have an automatic wastegate, that does not make it Turbo normalized.
TN systems control the boost with an automatic wastegate to maintain sea level MPs up at altitude. The 252, like the 231 boosts well above sea level MP at lower altitudes to increase power.

Well above? It only makes 210 HP, only 10 (5%) more than NA Lycoming.

[squeaky.stow]

Not that I am aware of, but I don’t think you would want to. The TSIO360 gets it’s 210hp (or 220 for the Encore) by being boosted to well over sea level MP. For the 252 it is 36” at takeoff.

If you turbonormalized that same engine it would only be boosted to something less than 29 inches with a lot less HP and correspondingly less performance.

[smwash02]

15 hours ago, Schllc said:

Is there a modification to make any of the k models turbo normalized?

I haven't looked, but it would be expensive with no market. The K models are rated for 36" or 39" on take off and reducing that to 29-30" would require redoing all the performance figures and lowering the gross weight. There are turbonormalized kits for pre-K models because they didn't have a turbo and the ones that were made are fixed wastegates you have to control by hand to keep below 30".

With the stock 252 and Encore, you simply push the throttle forward and it will redline at the appropriate 36" or 39" and you are good until you're ready to set up for cruise.

[Schllc]

So once at altitude is it similar to TN engines where you cruise at or very near sea level pressure?

[whiskytango]

Just now, smwash02 said:

I haven't looked, but it would be expensive with no market. The K models are rated for 36" or 39" on take off and reducing that to 29-30" would require redoing all the performance figures and lowering the gross weight. There are turbonormalized kits for pre-K models because they didn't have a turbo and the ones that were made are fixed wastegates you have to control by hand to keep below 30".

With the automatic wastegate modified 231, stock 252, and Encore, you simply push the throttle forward and it will redline at the appropriate 36" or 39" and you are good until you're ready to set up for cruise.

In my experience with a 231 with Merlyn UDC and Intercooler, the engine will exceed the maximum desired 36 inch Hg MAP if you are not careful when pushing the throttle forward.  The pressure relief valve will open at 40 inches MAP, but you do not want to operate your Intercooler engine at that (40 inches Hg) MAP.

[ziggysanchez]

You cannot get an automatic wastegate in a 231. You have to manage your MP with the throttle so you don't over boost the engine.The merlyn wastegate that is installed in many 231's from what I understand helps to keep the engine from bootstrapping but I have found that at some power settings it doesn't always do that very well. However the 252's and Encores do have an automatic wastegate.

[squeaky.stow]

57 minutes ago, Schllc said:

So once at altitude is it similar to TN engines where you cruise at or very near sea level pressure?

For the 252, Max recommended cruise power (78.6%) in the high teens is about 27 to 28 inches MP,  so yes I guess that is similar to TN settings. Most owners I have compared notes with tend to run at lower power settings around 65% LOP however for longer engine life.

[kortopates]

3 hours ago, Schllc said:

Is there a modification to make any of the k models turbo normalized?

No

2 hours ago, Schllc said:

So once at altitude is it similar to TN engines where you cruise at or very near sea level pressure?

No

 

Turbo normalized refers to the combination of adding a Turbo system to a Normally Aspirated engine. Its essentially a hybrid design. Their claim to fame is that they begin with the efficiency of a high compression normally aspirated engine. The compression ratio of a high compression NA engine typically is at 8.5:1 or higher and then add the turbo so that they can continue to put out 100% power up to a much higher critical altitude than sea level. But its the high compression ratios that gives them there higher efficiency from a BSFC engine efficiency standpoint.

Turbo engines are designed to operate at altitude from the beginning by using the turbo to boost far above sea level pressure. Because of the added detonation risk of operating with the added boost above sea level pressure they need a combination of greater octane and/or  lower compression ratio cylinders to ensure adequate detonation margin. With 100LL gas most of the turbo's use a CR or 7.5:1 - which is what is used on the K engines. But when we get up to over 300HP and more like the 350HP variants the CR is down to 7.3:1 - such as the Lyc engine used on the Malibu. But this is the trade-off we make in order to produce a lot more HP in relatively the same size engine and weight all the way up to the flight levels. But the engine efficiency with respect to BSFC is dropping off as CR drops.

Wastegates - Wastegate have nothing to do with whether we're talking about TN or Turbo engines - only what was mentioned above.

The Merlin is an aftermarket pneumatic wastegate designed to maintain the upper deck pressure set by the throttle with a variable wastegate. Its a fantastic improvement over the fixed bolt wastegate it replaced since it raises the critical altitude from ~15K DA to at least 18K by memory. But its still 100% manual. It still over boost and you still have to manually control it as you change altitude. Even changing Fuel flow, will cause you to need to adjust the throttle wastegate setting. But Merlin is the only aftermarket wastegate option for the early entry level turbo's that only came with the blower and fixed bolt wastegate (its kind of an exaggeration to refer to the bolt as a wastegate but that has long been the convention), examples are the M20K 231, Turbo Arrow,  Seneca turbo. 

The aftercooler is another add-on for the 231 and other early turbo's who's turbo installation was limited to only the blower (turbo) and pop-off valve for overboost protection . Suffice to say that without the aftercooler, as you climb higher and higher, the turbo has to compress more and more and as you remember your gas laws from high school chemistry the temperature of the compressed air is going up and up such that your CHTs are going up and up. 

All OEM complete turbo's, both Lycoming and Continental,  use a hydraulically actuated wastegates. The 252 and Encore use the same truly automatic controller and wastegate, that is often referred to as "set and forget" here on Mooneyspace. Its practically makes flying a turbo as easy as flying a NA engine and the complete turbo installation enables it to fly as easily in the flight levels as it does down low.

Lastly we have the marketing department that spreads all the disinformation you can imagine to make their offering sound better than reality. For example when the Acclaim came up, because of perceived poor press on Turbo's with respect to relative efficiencies and maintenance cost, Mooney referred to their fire-breathing Acclaim Turbo as "Like TN" and even called it the Mooney M20TN. The Acclaim isn't anymore TN'd than your any other Turbo - but they suggest it is because it's seemingly low boost of only 33.5" for the 280 HP de-rated installed version and 34" for the full 310HP version. Don't be kidded, its 100% Turbo and comes with the 7.5:1 CR pistons to prove it! In contrast, Cirrus does offer both a TCM TSIO-550 turbo version engine, and a TAT modified TN'd IO-550 engine with the 8.5:1 CR - which is a true TN'd engine unlike our Acclaim. So don't be misled my the hype. However, as much as we all value efficiency,  I think most of value longevity even more and although the TAT engines do great, there is also something to said about an engine that is designed from the onset to produce its power at altitude. But I don't believe we know with certainty which one really have the greatest longevity at least maintenance cost at the present time.

For more about this with some Mooney specific examples see the following:

https://resources.savvyaviation.com/ab-normally-aspirated-savvy-analysis-puzzler-december-2017/

 

 

Edited August 11, 2020 by kortopates

[jlunseth]

Paul has it right as usual. Turbo normalizing refers to adding a turbo that boosts only to normal sea level atmospheric pressure. That’s usually stated to be 30” (a little higher than standard day), but the mechanic adjusts what that is on the ground and it can be a little different. True turbocharged engines can be boosted over normal atmospheric pressure.  That is not “overboosting.” As Paul said, the turbocharged engine has a lower compression ratio to prevent detonation, the boost makes up for it, and the engine is intended to be operated with an induction air pressure greater than sea level pressure. Overboosting refers to allowing the turbo to supply too much air so that the engine operates in excess of its rated horsepower.  The MP limit on a factory TSIO360LB with no add-on wastegate controller or intercooler, is 40”. The engine would be overboosted if the pilot applied, say, 41”. But the engine is not overboosted at 40”.

What protects from overboosting is the wastegate controller.  There are multiple types. The Mooney 231, which is what I fly, had an engine that cam from the factory with no wastegate controller, the wastegate was a fixed opening that could be adjusted only on the ground. A wastegate is what it sounds like, an opening that allows some amount of the exhaust gases sent to the  turbocharger to be wasted overboard to control the pressurization of the induction air. 

The 231 can have a Merlyn wastegate added as an aftermarket item and many do, including mine.  Although the Merlyn was advertised as “automatic,” it is not really an automatic wastegate as that term is normally understood. It is a differential pressure controller. It controls the difference between upper deck pressure (that’s the pressurized air coming out of the turbo) and the pressure in the induction manifold to a set limit.  The purpose of this is to control bootstrapping, where you put in throttle, the engine spools up, that puts out more exhaust so the turbo spools up faster, generating more pressure and causing the engine to power up even further, etc.  It is annoying but not fatal. I is also not common in Mooneys anymore, it would happen only in a 231 that does not have a Merlyn wastegate.  All the other turbo Mooneys have some form of improved wastegate controller.

The best system from the standpoint of setting and forgetting is an absolute pressure controller. With the absolute pressure controller you set a pressure and the wastegate manages the turbo to maintain that pressure all the way to critical altitude (the point at which the engine can no longer make 100% HP, depending on engine and model somewhere around 22k).

There are other controllers that have almost the same effect. The bottom line for purposes of answering your question about overboosting is that all the turbocharged models after the 231 have the ability to manage to a set pressure.

All that said, it is not difficult to manage the MP in a 231.  You just have to know that you don’t shove the throttle in to the firewall, and you the pilot are always the element of the aircraft system that is responsible for setting the MP. It will change with day pressure, or as you ascend or descend, you simply adjust it, its not very hard. The pilot who would have trouble with the 231’s system is the pilot who has the “firewall the throttle” mentality from flying normally aspirated school planes.

 

[gsxrpilot]

M20K 231 - first generation turbo Mooney. http://www.mooneypilots.com/mapalog/M20K231_Evaluation_Report.htm

M20K 252 - second generation turbo Mooney. There were a lot of changes and upgrades to the 252. http://www.mooneypilots.com/mapalog/M20K252_evaluation_report.htm

M20K Encore - third generation K. Upgraded cabin trim, increased useful load. Encores typically have one of the best UL of the Mooney fleet.

[CharlesHuddleston]

FWIW: Our '82 K had the TurboPlus intercooler and Merlyn waste gate already installed. Having said that, It is my impression that I still have to be careful not to overboost, especially on take-off. It is not truly an "automatically adjusting waste gate." Therefore, I can't just push it to the firewall for out take-off roll. You can actually read the details on the Merlyn website. 

[gsxrpilot]

9 minutes ago, CharlesHuddleston said:

FWIW: Our '82 K had the TurboPlus intercooler and Merlyn waste gate already installed. Having said that, It is my impression that I still have to be careful not to overboost, especially on take-off. It is not truly an "automatically adjusting waste gate." Therefore, I can't just push it to the firewall for out take-off roll. You can actually read the details on the Merlyn website. 

That is correct for all 231's. 

The 252's have a fully automatic waste gate. So it's everything full forward for takeoff and climb.

 

[jlunseth]

PS, be a little careful in terminology when you read about these various types of engines, because the words have changed over the years and sometimes the marketing department wants to use something that sounds cool but does not really apply. An example is the set of words used for - I will call them generically, “superchargers.” Originally, “supercharger” was the word for any compressor that fed compressed air into the induction system. There are two basic ways of doing that, (1) by mechanically connecting the supercharger to the engine by gears or chain or belt, and (2) collecting the exhaust gases and having them power a turbine connected to a compressor fan.  In the beginning they were all superchargers. Then the word “turbosupercharger” began to be used to describe those that use method number 2, the exhaust gas and turbine.  The TSIO in the K engine designator stands for “TurboSupercharged-Injected-Opposed” (cylinders are opposed to each other). Then the industry stopped using “Turbosupercharger” and instead, it is generally accepted today that a turbocharger is the turbine driven one and a supercharger is the mechanically driven one. Confusing.  Same with “Turbonormalized.” Mooney designated the aircraft as the M20TN for Turbo Normalized, but it is not, as Paul said, it has a TSIO550 engine with a max pressure of 33.5” and low compression cylinders.. 

[Bolter]

On the topic of K's and upgrading with Merlyns and intercoolers, maybe @kortopatescan summarize the engine types in the K's (LB, MB, etc.)  As I understand it, some still have the old engine which was undesirable for some reason, but many upgraded the engine along with Merlyn's and intercoolers.  

-dan 

[xavierde]

25 minutes ago, Bolter said:

On the topic of K's and upgrading with Merlyns and intercoolers, maybe @kortopatescan summarize the engine types in the K's (LB, MB, etc.)  As I understand it, some still have the old engine which was undesirable for some reason, but many upgraded the engine along with Merlyn's and intercoolers.  

-dan 

From my research before deciding on a 252:

GB -> early 231. Most changed for LB during OH. Temperature issues.

LB -> 231. Still has some temperature issues but not as bad as the GB. 

Some of these have been retrofitted with an intercooler and/or Merlyn wastegate. That helps a lot but requires a bit of engine management.

MB -> 252. Much better with respect to temperatures. Fitted with intercooler and automatic wastegate which make the engine management easier.

SB -> Encore. Essentially the MB with slightly different settings which gives it 10 extra HP. MBs can be converted to SBs.

That’s my very basic understanding of these engines and I’m sure more knowledgeable MSers will elaborate and correct any errors.

[Schllc]

The dearth of information available here never ceases to amaze me. 
Thanks for all the info, it’s like drinking from a firehose!

[carusoam]

Sch...

Pseudo summary....

Write it down, line by line...

Your friend only gets to buy it once and get it right the first time...

It would be easy to Accidentally come home with a sub-optimal combination... Everyone will have their reason to buy what they have... all are good... some are better...

Avoid writing what you don’t want to hear about.... this has a way of sticking in the minds of people responding... focus specifically on what you do want to hear bout....   not everyone is a skilled writer... 

1) Engine block

2) Compression ratio

3) Turbo

4) Manifold pressure controller... the Merlin, or manual, or automatic, or semi-automatic...

5) Intercooler... you get new power charts with this.

6) Turbo chargers and turbo normalizers are similar...

7) Words and names get strewn around... most often by marketing groups...

8) Specific to TNs... these are not K related... Js have them added on... Acclaims have a pair, but... adjusted the CR down a tad anyways...

9) Typically a TN has a max MP of a standard day on the ground... 29.92” or so... TCs can boost up to 36+”...

10) an ordinary NA engine uses about 8.5:1 CR, Some Mooneys us 10:1 CR because they can...

11) an ordinary TC’d engine is more like 6.5:1 CR

12) This is done for thermodynamic efficiency purposes and to make the pilot work harder...

13) When you learn all this stuff... you will be better off at managing the engine and it’s power...

14) It is incredibly easy to use too much power as things go from zero to flying...  It is also Easy to be distracted by engine ops during busy times of flying...

15) It is way too easy to exceed Max TIT limits if not paying attention....  Turning turbo vanes into shorter turbo nubs....

16) Overheating CHTs and TITs just costs some AMUs... for early OH...

17) Updating an engine block, or adding an MP controller, or adding an intercooler can be done... by the time you get the bill... you will think it was better to have everything on the plane already.... cost + effort are quite large...
 

Anything not sound familiar?

MSers did a nice job detailing all the things involved in selecting a TC’d Mooney for your friend...

PP summary, not a mechanic...

Best regards,

-a-