New K231

**GMBrown** · March 12, 2021

Mooniacs: Giving up the C and pulling the trigger on a M20K 231. Anyone in the Riverside-SoCal- area with a 231 willing to to give me a nickel's worth of the ropes and a heads up on the important dos and donts before I head east to pick it up in Texas? Maybe a short ride? All costs on me of course. Its an LB engine with no intercooler or Merlyn waste gate. Call/text me at 909-615-5881 or email garrybrown7@gmail.com.

Thanks all.

Garry

PeteMc · March 12, 2021

Does the new plane have the Merlyn Black Magic Wastegate? If not, you might seriously consider it.

Without the Merlyn the biggest difference will be to watch for turbo over-boost as you power up for take off and needing to adjusting power as you climb. Otherwise, just get comfortable with the power settings and speeds. Also be sure to let the turbo cool down after your flight. (All in the POH and the time gets greatly reduced with the Merlyn.)

As for tricks, make sure the nose trim is on the nose up end of the takeoff range. The nose will be a lot heavier than you're used to so it will help get the weight off the gear on the TO roll. Actually the elevator is going to be a lot heavier too on your first couple of flights.

**carusoam** · March 12, 2021

4 hours ago, GMBrown said:

Mooniacs: Giving up the C and pulling the trigger on a M20K 231. Anyone in the Riverside-SoCal- area with a 231 willing to to give me a nickel's worth of the ropes and a heads up on the important dos and donts before I head east to pick it up in Texas? Maybe a short ride? All costs on me of course. Its an LB engine with no intercooler or Merlyn waste gate. Call/text me at 909-615-5881 or email garrybrown7@gmail.com.

Thanks all.

Garry

I’m not understanding your question...

But that doesn’t stop me from citing what other people have done in your situation...

You are buying a more powerful, more complex Mooney... than the one you have...

People take the opportunity to learn the ropes of the new 2them plane using something called Transition Training...

Then there is the whole delivery flight...

For that kind of stuff... in the so-cal area... check in with Paul, @kortopates...

There isn’t anyone more qualified for TT, and delivery, of M20Ks in that area...

PP thoughts only, not a know-it-all...

Best regards,

-a-

**Z W** · March 12, 2021

When I moved from a C to a K, I noticed the K model being bigger, heavier on the controls, and as you would expect as a result, harder to slow down. The K is less forgiving of carrying extra speed on final. Easier to get behind the airplane with the K. Overall it was an easy transition though, the planes handle mostly the same. Just be sure you're 80 knots short final, 75 knots over the fence, especially when light, and it will land just fine.

Adding additional engine management may make it worse, although I have no experience in a 231 with the LB engine. From what I've read here, for takeoff, you can't firewall the throttle, but instead add throttle to max MP (40 I think?) before starting your takeoff roll. If you firewall the throttle you can overboost.

Without the intercooler, I have read you may become limited by TIT temps up high, depending on temperature and altitude. 1650 is max TIT and you must reduce power to stay below it by going either rich or lean of peak.

Good luck and have fun!

**GMBrown** · March 12, 2021

Thanks all. That's consistent with what I have read so far.

gsxrpilot · March 12, 2021

10 hours ago, PeteMc said:

Also be sure to let the turbo cool down after your flight. (All in the POH and the time gets greatly reduced with the Merlyn.)

After attending the APS course with Ada, OK at GAMI, I was persuaded that the need to let turbo's "cool down" is actually a myth, old-wives tale, etc. The turbo bearings and surrounding oil is as cool as it will get when touching down. Sitting on the ramp letting it idle, only serves to heat the bearings and oil back up.

Consequently I've never sat at idle to let the turbo "cool down". It certainly didn't have any adverse effect on my turbo. We sent it off for overhaul as part of the engine MOH, with 1830 hours on it. The shop sent it right back saying the turbo is in pristine condition and needed nothing. I guess we'll go another 1800 hours on it.

jlunseth · March 12, 2021

I agree with the advice that you should find a good Mooney instructor and get some transition training in the aircraft. Operation of that engine is not as simple as a C or some other normally aspirated engine. That said, it is not hard either, it is just different. I will give you a few tips so you don't blow the engine on your first takeoff.

First, throw out the window everything you have learned about engine management in an NA aircraft. It does not apply to a turbocharged engine. You do not ever lean on takeoff, for example, regardless of airport altitude, not even Leadville. You will see TIT and CHT's exceeding redline in about 2 1/2 minutes from takeoff if you lean. Turbocharged engines like being operated very rich at full power. The POH says you need 22.5-24.0 GPH at full power, and you really do need that.

The throttle on the 231 must be managed by the pilot. It is set up so that, as the aircraft ascends in the air column, the pilot can put in more throttle and ask more from the turbocharger. This means that it is possible, at a takeoff elevation, to easily overboost the engine. You do not ever firewall the throttle on takeoff. You will also find that, when you add throttle, it takes a little time during your takeoff roll for the turbocharger to spin up and create full power. This is normal and is called turbo lag. You add throttle, the engine spins up and in doing so produces more exhaust, the exhaust powers the turbocharger and that spins up, and when it does you will get a significant boost in horsepower, which in turn causes a stronger exhaust flow yet, which causes more output from the turbocharger, and so on.

On takeoff, when you start your roll, you put in about half throttle, or maybe two-thirds, and let the turbo kick in. Then you gently add or subtract throttle to get to the 40" you need for full power takeoff. You leave the fuel control at all times during takeoff and climb, at full rich. Don't let anyone, including any instructor, tell you otherwise. You pay for the engine.

You will find that the throttle needs a little adjustment during the takeoff roll to keep it at or under 40". Ram air also increases the power output of the engine as the aircraft picks up speed, so you need to watch the MP and if it is higher than what you want, gently pull off a little.

In the non-Merlyn engine there is an issue called bootstrapping, which I mentioned. You put in some throttle, the engine speeds up, a moment later the turbo kicks in which causes the engine to speed up further, which causes the exhaust flow to be stronger, which causes the turbo to put out more air, which causes the engine to create more power, etc., etc. It is not the major issue some make it out to be, but because of bootstrapping you want to make progressive throttle movements, you don't shove the throttle anywhere as you might in an NA engine.

You must keep the TIT inlet temp under redline. It is best when learning, to operate Rich of Peak. Do LOP later, when you understand the engine. If TIT is going too high, put in more throttle and make the mixture richer. If it is still going up and the cowl flaps are not already open (they need to be open on takeoff and long climbs), then crack the cowl flaps to the first position or even full open. If that does not work, reduce power, but it is rare to get into that kind of scenario.

You have a Compressor Discharge Temp limit of 280 dF. Honor it, it is there to protect the engine from detonation caused by too hot induction air. You will find that this limits your ability to climb much above the mid-teens in warm OATs. Doesn't matter what the service ceiling is, your first job is to protect the engine. Don't plan on Flight Level flying regardless of what the POH might say. That's marketing.

As for landing, someone said that speed is harder to control in the K than the C. I have not flown a C so can't make that comparison, but I have flown a J and found that you can throttle the engine back on final in the K and because it is heavier, the aircraft will fall better without adding alot of speed, where the J wants to float forever. You will get the hang of it. You do need to get your airspeeds under control in the downwind and base legs, I use 90 on the descent part of the downwind and add half flaps, and 85 on base, then 75 on final. You probably will find that in heavy gusty crosswinds you need more final speed to get rudder authority, but leave that for later. You will want to trim up on landing, there is alot of engine weight out ahead of you and the trim will help hold the nose up. Not as much trim as, say, a Bravo, but definitely trim up.

The message? Engine full rich, always, on takeoff and climb, no exceptions. Never lean in those flight regimes unless you like big bills for cylinder replacement and cracked turbo rebuild. Throttle movements gentle and progressive, wait for the turbo to kick in to make final adjustments. Keep the TIT and CDT down, if they rise make the engine richer. If that does not do it, open cowl flaps. Don't plan on anything over about 17k until you really know the aircraft. You won't like the climb rate much when you are above critical altitude anyway (about 15.5k).

RJBrown · March 13, 2021

Ancient history for me but. A memory from 1994.

Before my K became a Rocket I flew it about 100 hours.
The oil temperature gauge was an important part of the scan.

Oil temp would start up first if there was any heating issue, kind of the canary in the coal mine.

if you adjusted to reduce temp when oil started to heat nothing else got out of hand.

ALWAYS full rich to climb. Alway open the cowl flaps to climb.

But close cowl flap before you allow the plane to speed up at altitude. The cowl flap is held open by an over center device. Too fast and it gets so hard to move that you could bend the mechanism.

**GMBrown** · March 13, 2021

Great info and mostly consistent with what I have read. After everyone's comments and after going through the generic poh I think I have the info I need to get the plane home in one piece. Regardless, if I can get some time in type before I fly it, I'll sure take advantage. I think I'll print out this string and memorize it. Thanks all.

stevesm20b · March 13, 2021

I sent you a text.

KLRDMD · March 13, 2021

11 hours ago, gsxrpilot said:

After attending the APS course with Ada, OK at GAMI, I was persuaded that the need to let turbo's "cool down" is actually a myth, old-wives tale, etc. The turbo bearings and surrounding oil is as cool as it will get when touching down. Sitting on the ramp letting it idle, only serves to heat the bearings and oil back up.

100% correct, along with another old wive's tale - shock cooling! So many . . .

PeteMc · March 13, 2021

@gsxrpilot Interesting about the turbo cool down being a myth... That was one of the things everyone was drilling in to me as I was buying my plane with the Bolt wastegate. I put the Merlyn in within a few weeks of getting the plane, so I never looked back - but still thought it was true for those turbos that still had a bolt.

ADDED: So now I'm curious... Why is it a wives tale??? I was told that with the bolt wastegate the turbo would sill be spinning at a high RPM and would maintain a high internal temp for quite a while after landing. Then with engine shutdown the oil flow would stop and the oil in the turbo would boil and leave a burt residue on the bearings. Over time, this would cause wear on the bearings. SO.... What is the true story according to George? The oil never really boils/burns? So no gunk to mess up the bearings?

Edited March 13, 2021 by PeteMc

kortopates · March 13, 2021

12 hours ago, PeteMc said:

@gsxrpilot Interesting about the turbo cool down being a myth... That was one of the things everyone was drilling in to me as I was buying my plane with the Bolt wastegate. I put the Merlyn in within a few weeks of getting the plane, so I never looked back - but still thought it was true for those turbos that still had a bolt.

ADDED: So now I'm curious... Why is it a wives tale??? I was told that with the bolt wastegate the turbo would sill be spinning at a high RPM and would maintain a high internal temp for quite a while after landing. Then with engine shutdown the oil flow would stop and the oil in the turbo would boil and leave a burt residue on the bearings. Over time, this would cause wear on the bearings. SO.... What is the true story according to George? The oil never really boils/burns? So no gunk to mess up the bearings?

Really nothing to do with the bolt or Meryln - everything to do with TIT. The turbo still needs a cool down, you don't want to shutdown the engine at cruise TIT temps. But the reality is the cool down began when you pulled the power to near idle and full rich during the final approach. If it was an instrument approach that's near 5 nm out at a low rich power or if a pattern landing that's pretty much entering the pattern and then especially abeam the numbers on the down wind when power is real low. The result is the turbo is cooling down along with oil temp in the final approach phase and you'll notice TIT is actually at its lowest when you touch down - in the 800-900F range. Then as you add some power to taxi it'll may climb back over a 1000F but still cooling down. Add the few 3+ minutes to taxi, and you can see the turbo has been cooling down for plenty of time before you get to parking. Thus further no need to idle before shutdown, you won't be able to get the TIT any lower than what it was before you taxied to parking.

Edited March 13, 2021 by kortopates

PeteMc · March 13, 2021

Okay, so the wives tale apparently is that the turbo with the fixed wastegate/bolt does slow down enough to cool down when coming into the pattern. And I *think* I was told that it was the bearings still being hot because of the turbo speed, not the temp of the exhaust gases passing through.

jlunseth · March 13, 2021

The engine is at idle when you taxi. At idle on start up, two of the cylinders barely fire because they are at the far ends of the induction tubes and don't get much MP. They won't show a CHT on my JPI until I do the run-up or gun the engine for some other reason. That doesn't mean they aren't firing, just that the fire is really low in those cylinders. The engine is not making enough power to push the turbo very fast. I haven't ever done a cool down and my turbo is at about 1200 hours since it was last rebuilt, the engine is more than a hundred hours over tbo. So much for the turbo cool down theory.

The fixed wastegate would not make any difference, you have to have some exhaust going through the turbo to begin with and there just is not very much at idle. Idle for me BTW is 1200, the engine definitely does not like less than 1100 and the electrical charging system likes it even less.

**Mike A** · March 13, 2021

7 hours ago, jlunseth said:

The engine is at idle when you taxi. At idle on start up, two of the cylinders barely fire because they are at the far ends of the induction tubes and don't get much MP. They won't show a CHT on my JPI until I do the run-up or gun the engine for some other reason. That doesn't mean they aren't firing, just that the fire is really low in those cylinders. The engine is not making enough power to push the turbo very fast. I haven't ever done a cool down and my turbo is at about 1200 hours since it was last rebuilt, the engine is more than a hundred hours over tbo. So much for the turbo cool down theory.

The fixed wastegate would not make any difference, you have to have some exhaust going through the turbo to begin with and there just is not very much at idle. Idle for me BTW is 1200, the engine definitely does not like less than 1100 and the electrical charging system likes it even less.

+1 on everything he has said. I have a stock -LB as well.

gsxrpilot · March 13, 2021

10 hours ago, PeteMc said:

What is the true story according to George? The oil never really boils/burns? So no gunk to mess up the bearings?

In the class, George explained, and showed us, how they'd put temp probes into the housing of the turbo where the oil is held to measure the oil temperature, and did the same with bearing its self. Then with the ability to record the temp of the oil around the turbo and the bearings in the turbo, they went and flew the plane. They found that the bearings and the oil is at it's coolest temps on landing. There was no further reduction in temps during the taxi and actually would heat back up if you sat for 5 minutes at idle power. So since a cooler turbo bearing is better. Shut it down as soon as you get to parking. You can't get the temperature any lower with the engine running.

It also makes the line guy happy that he doesn't have to stand there for 5 min holding the chocks, waiting for the prop to stop spinning

**carusoam** · March 13, 2021

APS put a fine video together describing the details....

Where the heat comes from... where it escapes too...

and cuts back on much of the magic and confusion...

The MP controllers are important to understand...

Because if you are thinking they have something to do with the temperature of the oil...

You may be mis-informed about the heat, where it comes from, and where it goes too....

One thing for sure... the turbo will slow very quickly when it isn’t driven by the exhaust... compressing air takes a lot of energy

The difference between the MP controllers is the precision of which they operate...

The turbo works equally hard, no matter who holds the MP constant...

The Really cool info coming from the APS video.... the visual representation of the oil flow through the system...

If you think oil is all about lubrication... another point that has been poorly presented in aviation 101... it is very much a coolant when it comes to the turbo system...

All that hot exhaust is running through the turbo... on the hot side... air being compressed on the other side doesn’t get nearly as hot by comparison...

The oil is at its coolest point coming out of the oil cooler after final approach...

The turbo is at its coolest point under the low MP of approach, with the coolest oil available...

See if you can find the video...

Best regards,

-a-

whiskytango · March 13, 2021

+1 on everything @jlunseth and @gsxrpilot have said. One other comment - you may have to trail the cowl flaps partially open during cruise in hot weather. Otherwise your hottest cylinder will be over the 380 degrees F that the experts (Mike Busch and GAMI) recommend for maximum cylinder life.

231LV · March 13, 2021

On 3/12/2021 at 8:04 AM, gsxrpilot said:

After attending the APS course with Ada, OK at GAMI, I was persuaded that the need to let turbo's "cool down" is actually a myth, old-wives tale, etc. The turbo bearings and surrounding oil is as cool as it will get when touching down. Sitting on the ramp letting it idle, only serves to heat the bearings and oil back up.

Consequently I've never sat at idle to let the turbo "cool down". It certainly didn't have any adverse effect on my turbo. We sent it off for overhaul as part of the engine MOH, with 1830 hours on it. The shop sent it right back saying the turbo is in pristine condition and needed nothing. I guess we'll go another 1800 hours on it.

I agree and do the same...no turbo cool downs on the ramp....I like a nice let down from 16k ft....turbo is as cool as its going to get at touch down

Smiles201 · April 16, 2021

Never knew that old wives sat around and told stories about their days flying turbo Mooney's.

Pritch · April 17, 2021

So here is a question to you 231 pilots. Would you ever take off with the barn door Cowl flaps fully closed in order to have better performance on a shorter runway?

Pritch

**Will.iam** · April 17, 2021

15 minutes ago, Pritch said:

So here is a question to you 231 pilots. Would you ever take off with the barn door Cowl flaps fully closed in order to have better performance on a shorter runway?

Pritch

I wouldn’t your cylinder head temperatures will go way too high and the performance hit is greater at cruise speed than climb speed anyway.

**carusoam** · April 17, 2021

2 hours ago, Pritch said:

So here is a question to you 231 pilots. Would you ever take off with the barn door Cowl flaps fully closed in order to have better performance on a shorter runway?

Pritch

Great question... I’m glad you asked!

Have you seen the video where the M20K pilot experimented on a short field... The engine wasn’t producing full power...

It rough words.... don’t experiment with generating power and lift on a short runway... follow the POH... to get POH performance... prove your plane has the POH performance...

If you want to try this on your own plane... use a device and an app that can measure your exact take off distance in your plane with the current OAT... I use CloudAhoy... and a skyradar... a WAAS gps...

Closing the cowl flaps isn’t going to make a significant difference in drag until going very fast... within seconds, your cylinders are hot, and your plane is flying already...

The video is posted around here, it is really disturbing in the way it didn’t work out...

PP thoughts only, not an experimental pilot.

Best regards,

-a-

jlunseth · April 17, 2021

I agree with @Will.iam, the cowl flaps just do not add enough drag at takeoff speeds to make a difference, and I don’t know why you would need to do that anyway. If you look in the POH, even at full GW (2900 lbs) a 40 degree C day and 8,000’ MSL the takeoff roll is 2600 feet. I have done takeoffs on fields in Minnesota as short as 2,300, the fields here are generally around 1,000’ MSL and I am usually not fully loaded. It would be very unusual circumstances for a 231 to overrun most runways. Remember also that the 231 and other turbos do not suffer an HP penalty at higher altitudes, all takeoffs are at 100% HP even at Leadville (highest airport in the US).

If you were really pressed, and if the ground cover after the departure end of the runway is grass or low brush, a better strategy would be a short field takeoff, pulling the aircraft into ground effect early and then letting it accelerate in ground effect. To accelerate in ground effect you don’t have to be over an actual runway, just over good ground, no trees. The classic short field takeoff takes a little practice in the 231, it is heavy in the nose, I would do some on normal length tarmac first to get the hang of it.

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