Definitive guide for managing turbo M20K with automatic wastegate?

[Z W]

There are a few 231's that have had the 252 TSIO-360-MB engine hung on them via STC.  They called those "261" or "262" conversions.  They fly happily "full forward on everything" from releasing the brakes to the top of the climb.

Many got dual alternators, electric cowl flaps, extended tanks, and other upgrades to be the same as a 252, except with a 12v electrical system instead of a 24v.  They are usually priced somewhere between the 231's and the 252's, depending on condition.  One is for sale here on the forums.  

Having flown one for quite a while, it can be a little tricky sometimes to figure out which parts you need for repairs, as the STC paperwork is a little light in the way of documentation, but the parts are always from either a 231 or a 252 Mooney, you just have to compare the part on the plane to the drawings in the parts catalog.  Haven't found any other downsides.

[whiskytango]

To the OP: The best source of information on MS concerning 231 operations is @jlunseth.  Read his posts and you will get a wealth of detailed information on 231 engine management.

[hubcap]

23 minutes ago, whiskytango said:

To the OP: The best source of information on MS concerning 231 operations is @jlunseth.  Read his posts and you will get a wealth of detailed information on 231 engine management.

^^^^^^This^^^^^
 

I would also recommend a MAPA PPP training class for any Mooney owner looking for specific instruction.

[jlunseth]

You have some pretty good answers so far. Not sure what I can add, which is gratifying to see. 

The word “automatic” with regard to wastegate controllers is subject to definition. I believe Merlyn markets their aftermarket controller, which is the one found 231’s, as “automatic,” or at least they used to, but the definition has moved over the years and I don’t think - all respect to Merlyn which makes a great product - that their controller is “automatic” in the sense the word is commonly understood today. Paul Kortopates wording is correct if you look at the controller from the pilot’s perspective, that is, who is in charge of managing the MP, and that is manual, the pilot is in charge of managing MP and not the controller.

There a multiple types of controllers. The Merlyn is a differential pressure controller. All it tries to do is maintain a constant pressure difference between the upper deck of the turbo (the induction air side) and the pressure in the manifold. The reason for differential controllers was something called bootstrapping. The turbo depends on pressure from the collected exhaust, so if the engine power increases the turbo power increases and vice versa. So, a pilot would push the MP stick in to increase MP, that would power the engine, which would push the turbo, which would further power the engine, and it could be difficult to get things to an equilibrium if you were the pilot. The Merlyn tamps down bootstrapping. However, things that would normally affect MP must still be controlled for by the pilot. Those would be such things as increases in ram air because of changes in airspeed, and changes in pressure because of altitude. It is up to the pilot to move the MP stick to adjust for these. However, there are other advantages to the Merlyn. The factory wastegate control method was a fixed controller that a mechanic could adjust on the ground, but the pilot could not adjust in the air. It would constantly spill some exhaust overboard regardless of altitude, with the result that the Critical Altitude of the factory model was about 15k. After that, power and climb rates would rapidly diminish. The Merlyn, on the other hand, can fully close and stop wasting exhaust gas. So the CA on my aircraft, based on my testing, is about 22,500, which is plenty for anyone. This yields a much better climb rate into the flight levels.

As previously mentioned, other Mooney models have what a pilot would consider to be a truly automatic wastegate, where the pilot can set an MP and the wastegate control system will keep that pressure all the way to CA where the turbo output is no longer sufficient. I used the term “wastegate control system” here because in at least some of the models with automatic systems, there is more than one type of wastegate controller. As I understand it, the Bravo, for example, has a differential controller and a density controller. The 252 may also.

The posts are correct that all the later model Mooney turbos after the 231 have automatic wastegate control systems. Those are the 252, Bravo, Acclaim, and Ultra, and some even have two turbos, one on each side. However, the price points are substantially higher. I have had a 231 for more than a decade. It turned out that when you understand how the engine operates, it is no big deal to be the manager of the MP. The engine, when properly set up with GAMI injectors and good mags, will operate very well lean of peak. My setting is 34”, 2450 RPMs, 11.1 or so fuel flow, which works for me up to somewhere between 12 and 16k, when the TIT and other temps start to go too high and can’t be adjusted for. This generates 70%HP and nifty speeds on the order of 175 kts. Others are more conservative and run LOP at power settings at or under 65%. The 252 and Encore are capable of the same thing, with probably a little bit better speed, they basically have the same engine. The engine in the 231 is a TSIO360 LB (or factory GB), the 252 is an MB, the Encore is an SB which is 10 more HP than the earlier 360s. After that, the Bravo has 280 HP and a completely different engin which has the reputation of not running LOP very well, although there are some Bravo owners who say their planes can do it, but generally you are looking at higher fuel flows, on the order of 17 GPH+. The Acclaim and Ultra have more horsepower yet, and a reputation for running LOP very well. 

And I said, managing the MP in the 231 is not at all difficult, and if you do it right you can simplify the process quite a bit. 

[Pinecone]

20 hours ago, PeteMc said:

With the Encore you can take off from basically sea level with everything full in?  Not something you can do with the 231 even with the Merlyn.

 

 

20 hours ago, Fly Boomer said:

You can treat the 252 the same.  All in all the way up.

The difference between the -MB (252) and -SM (Encore) engines is basically the max boost and max RPM settings.  There are no other changes to "convert" from one to the other.  You can do the conversion with the engine on the plane.

-MB is 36" and 2700 RPM, the -SB is 39" and 2600 RPM.  210 and 220 HP respectively

I do have to keep and eye on the manifold pressure as it can overshoot by 0.5" or so.  It is allowable up to 41" for up to 2 minutes, but I try to keep it below 39".

Hmm, I wonder how the take off and initial climb would be at 41" and 2700 RPM????? Should be around 235 - 240 HP    And NO, I am not going to try it..

 

[PeteMc]

32 minutes ago, Pinecone said:

I do have to keep and eye on the manifold pressure as it can overshoot by 0.5" or so. 

So it is similar to the 231 in that you need to watch the max MP.  You can't just have "everything full in" and blast off at Sea Level?

 

[Z W]

It depends on the day and pressure altitude.  If it's cold outside, firewalling the throttle can result in 0.5-1 inches over maximum rated MP (36" on my plane).  The cure is just to spin the vernier throttle out about half a turn from all the way in.  The manual says you can run it higher than rated MP for some period of time but I typically just adjust slightly on the takeoff roll.  Then sometimes you have to spin the throttle back in to make 36" in the climb once you have some altitude.

[kortopates]

It depends on the day and pressure altitude.  If it's cold outside, firewalling the throttle can result in 0.5-1 inches over maximum rated MP (36" on my plane).  The cure is just to spin the vernier throttle out about half a turn from all the way in.  The manual says you can run it higher than rated MP for some period of time but I typically just adjust slightly on the takeoff roll.  Then sometimes you have to spin the throttle back in to make 36" in the climb once you have some altitude.

Actually its all due to oil temperature. The turbo charger controller is adjusted to hit redline at normal operating oil temperature of around 175F. On the first takeoff of the day before the oil has fully warmed up, the controller will overboost till the oil fully warms up. And when the OT is above normal, such as 190-200F the controller will underboost and you won't get the full redline boost. This is also why they recommend using a multi-weight oil since it viscosity is less effected by temerature than a single weight oil.  
Of course this only applies to full turbo’s with hydraulically controlled waste gates and even then there is some variation among the different controllers.

[jlunseth]

3 hours ago, PeteMc said:

So it is similar to the 231 in that you need to watch the max MP.  You can't just have "everything full in" and blast off at Sea Level?

 

Loosely similar, yes. In the 231 the pilot never firewalls the throttle on takeoff, not even at Leadville. Most people use 36” as the upper limit, it is actually more like 37. You put in your 36” and as you roll down the runway and the airspeed picks up the MP may climb. You may adjust it down a little. In the MB (252) and SB (Encore) engines the pilot does firewall the throttle and the automatic wastegate controller is supposed to maintain whatever the max pressure is that is set into the wastegate controller, 36” or in Pinecone’s Encore, 40, but the phenomenon Paul is talking about has an effect and the wastegate controller may miss the mark a little.

 

[Pinecone]

21 hours ago, PeteMc said:

So it is similar to the 231 in that you need to watch the max MP.  You can't just have "everything full in" and blast off at Sea Level?

 

I put everything forward and blast off.  If the JPI flashes at me, I may tweak the throttle.  But I am OK (according to POH) of goine 2 inches over for 2 minutes.  So tend not to worry until off the ground, cleaned up, and trimmed for climb.

[tmo]

On 10/16/2023 at 5:06 AM, kortopates said:

Yes, but TIT needs to be below 1400f full rich (preferably lower) else the max FF isn’t high enough.

I thought the TIT limit on a TSIO-360-LB in a vanilla M20K is 1650F, which I round down to 1500F for peace of mind. Should I lower my threshold, or did I miss something in the POH?

[carusoam]

Great discussion gents!

makes me want to add a pair of TNs…

MP controllers…

and inter coolers….

Now where is that STC!

Go Mooney!

Best regards,

-a-

[Crawfish]

3 hours ago, tmo said:

I thought the TIT limit on a TSIO-360-LB in a vanilla M20K is 1650F, which I round down to 1500F for peace of mind. Should I lower my threshold, or did I miss something in the POH?

   I believe 
@kortopates  meant was that if it was hotter than 1400°F at T/O power full rich it might be an indication your T/O fuel flow was set to low. Not that you were busting a limitation.

Not that I want to put words in his mouth. 

[Fix]

Can someone explain to me how to fly ROP an LOP with an Turbo engine, M20K 252/Encore.
I'm familiar how to do it with an NA Engine.
But little unsure about a Turbo.

 

[Pinecone]

It is the same.

But at altitude you can add back in some MP to get back some of the power loss.

As I stated, in my 252/Encore, I take off/climb at full power, full rich.  At level off, after the plane accelerates, I set 29.5 inches, 2300 RPM, 10.1 GPH  Eazy Peazy.

You can check that you are LOP by going richer and seeing the EGTs rise.

[Schllc]

On 10/21/2023 at 4:03 PM, tmo said:

I thought the TIT limit on a TSIO-360-LB in a vanilla M20K is 1650F, which I round down to 1500F for peace of mind. Should I lower my threshold, or did I miss something in the POH?

Pretty sure he was referring to the climb, not cruise.