M20B High altitude performance

[bruceyung]

Hello Fellow mooney pilots

I would love to hear from other B or C model owners regarding performance. I have a 355 NM trip on monday and looking forward to fly 9500 or 11500,

anyone who has flown at 11500 could share their performance experience.

Thankyou 

Safe flights.

Bruce

[carusoam]

My 65 C flew 11,500 and 12,500 between NJ and MA all the time.  200nm VFR trip over NYC Class B.

Fully loaded, great flight.  This time of year, it is best to have all the seals working on any cold air entering the cabin...  that high up, the MP limits how much heat is available.

The climb rate is relatively slow getting to the top.  It was worth the climb for a 200nm trip.  Even better for a longer trip...

Best regards,

-a-

[Hank]

I routinely fly my C at 9500 msl, and have flown IFR over the Appalachians at 11,000 msl on a windy day to minimize turbulence. (It was still unpleasant.) I generally fly with the throttle pulled back just enough to make the MP needle move, hoping to create turbulence in the carb and get better fuel atomization. Since I rebuilt my doghouse, I can actually get about 25°LOP, but I've yet to fly very long there as I don't have a full engine monitor, but it's smooth . . .

Anyway, I set the throttle like that and 2500, generally showing 142-145 mph on the ASI, and my G430W calculates 147-149 KTAS. Fuel burn is right in 9 gph block time, and I don't go to many towered fields, so no long taxis at either end of the trip.

Once upon an August afternoon, I grabbed a CFI and an oxygen bottle and went to 15,000 msl. She flew strongly, but ran out of steam in the climb. I had to step climb the last few thousand feet--climb til I couldn't take it, level off and accelerate, then climb some more. The controls were a little mushy, but I think that was as much to do with the low speed than anything. We did emergency descent practice coming back down. Whheeeee!! The next day, with all of the numbers fresh in my head and a googled equation, I calculated the DA to have been 18,800 msl.

So Cs do well at altitude, just don't expect a blistering climb rate. And remember to allow for the descent; my first time up at 9500, I started my descent for home (567 msl) about 54 nm out.

[Wakeup]

I have flown a few times betwen 11,000-12,000 feet in my B to avoid clouds.  I was very tired after each flight.  I purchased an oximeter and checked my O2 saturation on my last flight at 10,000 feet and it was 89% and I am healthy.  Be careful and buy an oximeter.  

[Raptor05121]

6 hours ago, Hank said:

 I generally fly with the throttle pulled back just enough to make the MP needle move, hoping to create turbulence in the carb and get better fuel atomization.

 

I have been told the intake manifold has been designed for maximum performance for wide-open throttle. Does anyone with a digital engine gauge have any data to determine which is best?

[Hank]

3 hours ago, Raptor05121 said:

I have been told the intake manifold has been designed for maximum performance for wide-open throttle. Does anyone with a digital engine gauge have any data to determine which is best?

I made a two hour trip at Thanksgiving last year, out at WOT and back my normal way. Time difference was five minutes, but outbound used several gallons more fuel. I don't do that anymore. Outbound was also east, which should be faster anyway, 41A--> HXD. Maybe the injected engine intakes were optimized for WOT?

[1964-M20E]

10,000 to 12,000 feet should be no problem for the B & C models you will notice climb rated getting slower but that is normal for naturally aspirated engines.

 

As for WOT operations doesn't the carburetors have a fuel jet that is activated at WOT and when you pull back some it closes off?  I have fuel injection so I'm not sure.

 

 

 

[Andy95W]

6 hours ago, Raptor05121 said:

I have been told the intake manifold has been designed for maximum performance for wide-open throttle. Does anyone with a digital engine gauge have any data to determine which is best?

WOT is best for air ingestion with the least obstruction to the air flow.  Hank is talking about "swirling" the fuel as it leaves the carburetor.  This allows for greater fuel atomization and a better distribution to the individual cylinders.  And it works very well.  My JPI EGTs are all over the place at WOT, but with the throttle pulled back just a tiny bit, the EGTs come nicely into line.  When I throw in a VERY small bit of carburetor heat, the EGTs are usually a straight line, like they would be in a fuel injected engine.  The very small bit of carb heat also increases fuel atomization.

 

1 hour ago, 1964-M20E said:

 

As for WOT operations doesn't the carburetors have a fuel jet that is activated at WOT and when you pull back some it closes off?  I have fuel injection so I'm not sure.

Yes, that is the "Economizer".  Mixture still controls the total fuel flow, regardless of which jet the fuel flows through.  With any leaning at all the Economizer basically isn't doing anything extra.

[DanM20C]

I have a stock 69 C and almost always cruise between 9 and 11K.  At those altitudes I see 140kts tas, 2500rpm full throttle(pulled back a tiny bit like Hank and Andy). Above 11K the speed starts to fall off, but so do fuel flows, sometimes it is worth it depending on winds.  Highest I have had it was 17K.

Fuel flows block to block I usually see 8.8 to 9 gph.  Up at 11K the JPI usually shows 8.0-8.4gph.

To sum it up.  Your B should perform great up at 9.5 or 11.5K. 

-Dan

[DXB]

2 hours ago, DanM20C said:

I have a stock 69 C and almost always cruise between 9 and 11K.  At those altitudes I see 140kts tas, 2500rpm full throttle(pulled back a tiny bit like Hank and Andy). Above 11K the speed starts to fall off, but so do fuel flows, sometimes it is worth it depending on winds.  Highest I have had it was 17K.

Fuel flows block to block I usually see 8.8 to 9 gph.  Up at 11K the JPI usually shows 8.0-8.4gph.

To sum it up.  Your B should perform great up at 9.5 or 11.5K. 

-Dan

Ditto.

[carusoam]

Clearing up the one issue at WOT for the O360...

At full throttle all Mooney engines have a way to add extra fuel to the engine.

The O360 got a second fuel jet that is open at wide open throttle.  Coming off the stop just enough closes this extra fuel flow.

The extra FF is intended to aid in cooling during the climb.  Cruising at full throttle does not benefit from the extra cooling.

Hank is good at explaining how to know when the secondary fuel jet is off.

Anyone know how to tell when the fuel pump is on or off in the long body?  This is essentially the same challenge.  It should be visible in the FF gauge.

Best regards,

-a-

[Raptor05121]

15 hours ago, N1395W said:

When I throw in a VERY small bit of carburetor heat, the EGTs are usually a straight line, like they would be in a fuel injected engine.

 

 

Mike Busch seems to disagree with you:

Quote

Right behind the "high EGTs are bad" myth is the "identical EGTs are good" myth. Many pilots believe incorrectly that a flat-topped graphic engine monitor display (with all EGTs equal) is the mark of a well-balanced engine, and that unequal EGTs are a sign that something is wrong. This common misconception tends to be reinforced by digital engine monitors that display a digital "DIFF" showing the difference between the highest and lowest EGT indication."

 

https://www.savvyanalysis.com/articles/egt-myths-debunked

[Andy95W]

Alex- agreed, it's a good article.  Continuing down, Mike Busch then says the following:

The mark of a well-balanced engine is not a small EGT spread ("DIFF"), but rather a small "GAMI spread" - defined as the difference in fuel flows at which the various cylinders reach peak EGT. 

Since our engines are carbureted, they obviously can't have a GAMI spread and we have practically no control over the particular fuel flow to each cylinder as you would have in a fuel injected one. All we can really hope for is a smooth running engine.

Please notice in my post above I never mentioned trying to have a well-balanced engine like Mike Busch was referring to in his article.  I did say that these techniques gave a "better distribution to the individual cylinders."

All I really know is that when my EGTs are more uniform relative to each other I can lean more and still have less vibration then when the EGTs are all over the place.  I can't believe that less vibration is ever a bad thing.

I first read about these techniques more than 20 years ago when I owned my first M20C.  I know the current owner and that engine is within 100 hours of TBO and still doing well.  My current M20C seems happy doing this too.

[carusoam]

Yes and know...

Even a carbed engine has a 'Gami spread' as one cylinder will peak before the others during the Leaning process.

A FF meter would be required to measure the spread.  The roughness occurs as one approaches and peaks before the others. The real roughness occurs as one cylinder starts missing on the lean side.  An engine monitor would be important to see how this is occurring...

There are a few things that affect the spread like MP, altitude, throttle plate position, carb heat, mixture, the secondary fuel jet, OAT.

These are the things that can influence the distribution of fuel.

Unfortunately, there is no four barrel carb for the M20C.  We would be balancing fuel jets with precision.  

Yes you could sort of measure a gami spread on a carbed engine, with FF and JPI.  But improving the spread is quite a challenge.

Happy experimenting...

Best regards,

-a-

[Andy95W]

Thanks, Anthony.  That was a good explanation of GAMI spread, I wasn't using the term correctly.  Learned something new that I thought I'd understood!

[astravierso]

Bruce,

I fly my "B" regularly between 11.5 and 9.5k due the hills in Northern Utah with no issues with a departure alt between 3.5 and 5k. The only advice I would have other than what has already been presented is to pay attention to your density altitude for both you, your passengers  and your plane. As has been mentioned everyone reacts differently to the high altitude environment .

Cheers

[bruceyung]

Thakyou all , sharing a bit of your experience up high was of great help .

safe flights.

Bruce