M20K 231 Questions

[carusoam]

LW,

The greatest attribute of a factory built airplane is all the data that comes with it...

1) Load the plane in accordance with the WnB data in the POH...

2) Follow the performance data that is in there as well...

3) Be aware of all the things that need to be accounted for...

4) including temp, DA, rain, RH, surface conditions...

 

I have filled my planes to the Max a few times... why not..?

 

The first time you do this... it may not be really wise to load it with people....

There are so many bags of various materials than can be used to simulate weight of people....

Once you have this experience, you get the feeling how performance starts to wane as you approach the limits of WnB...

The plane doesn’t fall out of the sky when you exceed the WnB limits... it just gets mushy and can get worse depending on how things go...

Expand your WnB experience one step at a time... you will notice the difference between fully loaded and fully empty...

Same thing with a Chevy Tahoe....   

There are plenty of videos of T/O failures of too much weight or too little power...

PP thoughts only, not a CFI...

 

Best regards,

-a-

 

[CharlesHuddleston]

13 hours ago, LevelWing said:

 

@CharlesHuddleston loading up with four adults and light bags had to put you near max gross weight, I assume? 

We stepped on the scales with our bags, weighed, and then added the rest in fuel. Yes, we were at max gross. Flew from KSRB (middle Tennessee) to Miami. Spent the night, and flew the next morning to Grand Exuma. Awesome way to travel!!!

[jlunseth]

4 hours ago, LevelWing said:

What is the impact of not having the inter cooler? I've found a few that have the Merlyn waste gate but not the inter cooler.

The intercooler does essentially three things. First, it cools the induction air by around 100 dF in cruise, allowing the engine to run cooler. Second, by bringing the induction air temp. down it eliminates the CDT redline as an issue. Third, it allows the turbo to work a little less hard.

Two and three require a little explanation, one is straight forward, that is the main purpose of the intercooler, to cool the induction air, and somewhere between 75 and 125 dF is what I see on my JPI930. It depends on day temps, altitude, etc.  My 930 has both a CDT probe and an IAT prove, so I am able to see the difference quite well.

On the elimination of the redline as an issue, there will still be a CDT redline for the aircraft because that is required by the aircraft’s certification, it is a limitation in the POH.  However, in the factory engine CDT and IAT were the same thing because no intercooler. CDT is before the intercooler and IAT is after. When the intercooler is added, IAT is much cooler than CDT. The purpose of the CDT redline is not to protect the turbo from an overtemp condition, that function is served by the separate TIT limitation. The purpose of the CDT is to prevent overly hot induction air which will cause detonation in the cylinders, which is devastating to the engine. But with the intercooler, the temp of the induction air is no longer the measured CDT, it is the measured IAT, and as a practical matter IAT is so much lower than CDT that IAT never gets near the redline of 280 no matter how high or hard you climb the aircraft. 

The practical effect of this is simple. I have the intercooler, so my engine runs generally cooler than a GB or nonintercooled LB. But I am able to see CDT in my JPI, and on anything but a really cold day, I will hit the CDT redline before I can get to the flight levels. I will probably hit it somewhere between 17 and 19,000. You can lower the nose and the climb rate, but I get my numbers from a 500 fpm climb, so you are going to have to climb at around 2-300 fpm, which is very anemic, and sooner or later you will run into CDT again.

So to sum it up, the nonintercooled engine is limited as a practical matter to 17-19000 feet unless it is a really cold day.

On the turbo having to work less hard, that is partly true, but not as true as the marketing from the intercooler companies. Generally speaking, the theory is that a parcel of induction air at 100dF has more molecules of O2 than a parcel at the same pressure that is at 200dF. So in theory, by cooling the air you can set the MP lower by very roughly two to three inches and produce the same HP. The flaw in this theory is that the intercooler creates drag from the passage of the air through the radiator fins and the turbo has to work to overcome the drag (nothing is free). So reality is that the effect is very roughly half of what it is said to be. I find that I can drop the MP about an inch at cruise, from what is in the tables, where the adjustment recommended by the mfr. is about 2-3 inches.  

So to succinctly answer your question, without the intercooler your engine will run hotter (never good for longevity), the aircraft will be as a practical matter altitude limited except on really cold days, and you always be running the turbo a little harder.

Another way to answer your question is that in the later turbo models, the factory added a turbo (that’s the MB engine in the 252) and in the most recent models, two turbos, one for each bank of cylinders. So they obviously realized that intercoolers help cooling and longevity quite a bit.

Edited August 28, 2020 by jlunseth

[231LV]

On 8/25/2020 at 6:52 PM, ziggysanchez said:

I have loved owning and flying my 231. I've flown it close to 900 hours in the last 3.5 years. Useful load in mine is somewhere around 930 lbs which is not too bad and has the Merlyn wastegate but no intercooler. I loaded my family in it right after my panel upgrade and flew them to Maine from Oklahoma. It was a little tight width wise but that might be more from me being 6'3" and 280 lbs than the Mooney being too small...lol. Maintenance costs on mine have been extremely low. The 231 is a great airplane. I'm about to trade it to move into an Eagle that has TKS. If you wanna pull the trigger this week and buy mine before I trade it, it would definitely be a nice one to have.

wow! that is a sweet panel!  I have the Aspen 1000 Pro and am looking to pick up the MDF for redundancy. Who did your panel? I also fly a 231 with everything you have PLUS an intercooler and love it! Putting a vernier throttle in at next annual

 

[LevelWing]

On 8/27/2020 at 9:11 PM, jlunseth said:

The intercooler does essentially three things. First, it cools the induction air by around 100 dF in cruise, allowing the engine to run cooler. Second, by bringing the induction air temp. down it eliminates the CDT redline as an issue. Third, it allows the turbo to work a little less hard.

Two and three require a little explanation, one is straight forward, that is the main purpose of the intercooler, to cool the induction air, and somewhere between 75 and 125 dF is what I see on my JPI930. It depends on day temps, altitude, etc.  My 930 has both a CDT probe and an IAT prove, so I am able to see the difference quite well.

On the elimination of the redline as an issue, there will still be a CDT redline for the aircraft because that is required by the aircraft’s certification, it is a limitation in the POH.  However, in the factory engine CDT and IAT were the same thing because no intercooler. CDT is before the intercooler and IAT is after. When the intercooler is added, IAT is much cooler than CDT. The purpose of the CDT redline is not to protect the turbo from an overtemp condition, that function is served by the separate TIT limitation. The purpose of the CDT is to prevent overly hot induction air which will cause detonation in the cylinders, which is devastating to the engine. But with the intercooler, the temp of the induction air is no longer the measured CDT, it is the measured IAT, and as a practical matter IAT is so much lower than CDT that IAT never gets near the redline of 280 no matter how high or hard you climb the aircraft. 

The practical effect of this is simple. I have the intercooler, so my engine runs generally cooler than a GB or nonintercooled LB. But I am able to see CDT in my JPI, and on anything but a really cold day, I will hit the CDT redline before I can get to the flight levels. I will probably hit it somewhere between 17 and 19,000. You can lower the nose and the climb rate, but I get my numbers from a 500 fpm climb, so you are going to have to climb at around 2-300 fpm, which is very anemic, and sooner or later you will run into CDT again.

So to sum it up, the nonintercooled engine is limited as a practical matter to 17-19000 feet unless it is a really cold day.

On the turbo having to work less hard, that is partly true, but not as true as the marketing from the intercooler companies. Generally speaking, the theory is that a parcel of induction air at 100dF has more molecules of O2 than a parcel at the same pressure that is at 200dF. So in theory, by cooling the air you can set the MP lower by very roughly two to three inches and produce the same HP. The flaw in this theory is that the intercooler creates drag from the passage of the air through the radiator fins and the turbo has to work to overcome the drag (nothing is free). So reality is that the effect is very roughly half of what it is said to be. I find that I can drop the MP about an inch at cruise, from what is in the tables, where the adjustment recommended by the mfr. is about 2-3 inches.  

So to succinctly answer your question, without the intercooler your engine will run hotter (never good for longevity), the aircraft will be as a practical matter altitude limited except on really cold days, and you always be running the turbo a little harder.

Another way to answer your question is that in the later turbo models, the factory added a turbo (that’s the MB engine in the 252) and in the most recent models, two turbos, one for each bank of cylinders. So they obviously realized that intercoolers help cooling and longevity quite a bit.

Thanks for the thorough run down on this. I think for the sake of simplicity, it's easier to just find one that has the following:

• Merlyn waste gate upgrade
• Intercooler (Airflow or TurboPlus)
• An upgraded engine (LB or LB1) instead of the GB

If I find one that has those three it sounds like I should be in decent shape for engine longevity and reducing pilot workload. Avionics aside, is there anything else I should be looking for in a 231, such as speed brakes or oxygen (most of the 231's I've seen have oxygen)?

[ziggysanchez]

6 hours ago, 231LV said:

wow! that is a sweet panel!  I have the Aspen 1000 Pro and am looking to pick up the MDF for redundancy. Who did your panel? I also fly a 231 with everything you have PLUS an intercooler and love it! Putting a vernier throttle in at next annual

 

I came up with the layout and Omega Aircraft in Weatherford, Ok did the avionics work. They do great work.

[KLRDMD]

My 231 had 983lb useful load. 1100 would be very unusual from my knowledge of these airplanes.

[carusoam]

1 hour ago, LevelWing said:

Thanks for the thorough run down on this. I think for the sake of simplicity, it's easier to just find one that has the following:

• Merlyn waste gate upgrade
• Intercooler (Airflow or TurboPlus)
• An upgraded engine (LB or LB1) instead of the GB

If I find one that has those three it sounds like I should be in decent shape for engine longevity and reducing pilot workload. Avionics aside, is there anything else I should be looking for in a 231, such as speed brakes or oxygen (most of the 231's I've seen have oxygen)?

once you have loaded the plane with everything available....

Budget and UL becomes your last personal debate... how far, how many people, how much does everybody weigh?

If flying in the FLs often... the quality of your O2 systems becomes paramount...

Flying in the FLs with a single portable O2 system is just silly...

 

It might be wise to get some time in a similar plane prior to purchasing... 

Best regards,

-a-

[jlunseth]

Yes if you are going to fly over 12000 - and you likely will in a 231- you should have a good built in O2 system. i know what the regs say, but i put mine on if i am going to spend prolonged time at 12k or higher. speed brakes are nice when atc gives you a cram down, but don’t get used often.

 

[231LV]

On 8/27/2020 at 4:13 PM, LevelWing said:

Thanks for all of the feedback and thanks to @jlunseth for the detailed write up.

What is the impact of not having the inter cooler? I've found a few that have the Merlyn waste gate but not the inter cooler.

The intercooler makes a significant difference...A previous poster claimed the intercooler lowers temps by around 100 degrees which is what I have seen in my plane. A turbo setup without an intercooler is like a beefed up wrestler with one arm tied behind his back. The Merlyn boosts critical altitude over the fixed bolt that comes from the factory but it really requires a higher workload, IMO....especially during takeoff with a heavy load...extremely easy to overboost the engine which mandates you pull back the throttle all while trying to accelerate...a vernier throttle helps (and I plan to install one at next annual).

[jlunseth]

I was returning from an Angel Flight to SD on Saturday evening and thought to look at the differential temp (CDT minus IAT) at cruise at 15,000 (OAT was 0 C). It was 118 dF with the CDT at around 220 dF. Today on a short flight at 4,500 it was 95 dF. 

I agree there is some throttle management required even with the Merlyn. Its not a “shove it to the firewall” arrangement. Not hard to learn though. 

[LevelWing]

This has all been very helpful information. If I can find the right 231 then it'll be a nice setup. Just a matter of balance, with useful load being a big consideration.

[231LV]

On 9/2/2020 at 8:16 AM, LevelWing said:

This has all been very helpful information. If I can find the right 231 then it'll be a nice setup. Just a matter of balance, with useful load being a big consideration.

As many 231 owners have already said, a 231 is not going to give you a useful load above 1000 lbs. Mine is 960 lbs. Full tanks takes 432 lbs leaving 528 lbs for passengers and baggage. They are not load haulers but they are the most efficient airplane out there.

[Ricky_231]

On 8/25/2020 at 11:12 PM, chrisk said:

Not much to add, but my 231 has a useful load of ~975lbs (from memory).  I'm not sure how folks are getting useful loads in the 1100 lb range.

mine has just under 900lbs! and apart from the large O2 bottle in the back, I'm not sure what else is eating up so much UL. I suspect there's a ton of useless stuff behind the panel (a sirius box, a 14/28V transformer for either the sirius box or the avidyne I can't remember, ADF crap, and who know what else) that I'll have to deal with one of these days. But I can't see how that'd add up to 100lbs.

[Ricky_231]

On 8/29/2020 at 1:30 PM, LevelWing said:

Thanks for the thorough run down on this. I think for the sake of simplicity, it's easier to just find one that has the following:

• Merlyn waste gate upgrade
• Intercooler (Airflow or TurboPlus)
• An upgraded engine (LB or LB1) instead of the GB

If I find one that has those three it sounds like I should be in decent shape for engine longevity and reducing pilot workload. Avionics aside, is there anything else I should be looking for in a 231, such as speed brakes or oxygen (most of the 231's I've seen have oxygen)?

Speed brakes are useful if you live near or under very congested airspace (like NY, DC etc.) where more often than not you'll find yourself awarded the "Stuka arrival" as someone on MS once said to me, and you have 5nm to come down from 9000ft and join the pattern while maintaining "approach speed".

[carusoam]

Fortunately, the NYC top shelf ends at 7k’.  

So... getting down to ground level usually only requires good efficiency.... and not the speed brakes.... for my home drome about 30 nms out....

Some of the heavy things found in a K... that aren’t there in a base level J...
 

Some easy things to add up...

• a pair of extra cylinders and their related case extension...
• the longer nose covering / cowl....
• the turbo and related hardware...
• pressure controller and intercooler, if you are lucky....
• They also got a boat load of heavy instrument panel boxes... everything available.

Hmmm... trading the fourth passenger for a turbo system...... 

One of the kids is not going to be happy....

Of course the kids don’t really like sitting in the back for nine hours straight either....

PP thoughts only, not a plane sales guy...

Best regards,

-a-

 

[Stetson20]

On 9/4/2020 at 10:00 AM, Ricky_231 said:

Speed brakes are useful if you live near or under very congested airspace (like NY, DC etc.) where more often than not you'll find yourself awarded the "Stuka arrival" as someone on MS once said to me, and you have 5nm to come down from 9000ft and join the pattern while maintaining "approach speed".

Either the Stuka or the Swoopenhausen! 

[Mike A]

5 hours ago, Stetson20 said:

Either the Stuka or the Swoopenhausen! 

I read somewhere they were called crowbar approaches - both due to the similar shape as well as you can toss a crowbar out the window and see who gets on the ground first. 

[gsxrpilot]

I once crossed Longs Peak at 17,000 and landed straight in for runway 12L at KBJC.

We had the speed brakes out, gear down, flaps, and thought about opening the door and window  But it all worked out. Landed, taxied to the hangar and put her away. No big deal.

 

[jlunseth]

I did about the same thing at KGPI once. Had some radio problems that got straightened out, then wound up over the airport at 12k. Airport is around 3k as I recall.  Long downwind with the speed brakes and it worked out just fine.