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New M20B owner


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Hello all,

 
I have just taken possession of an M20B, and was looking for any advice on power settings for climb and cruise. 
 
I've been using 25 squared on the climb just because that's how I was taught years ago. But I recently read a Mapa article suggesting WOT and 2700 all the way to altitude. Thoughts?
 
Been leaning on the climb once the key value falls below 47(approximately 75% power). Cruising at 2400 and WOT, and as lean as I can get it without engine roughness. 
 
One issue I've noticed is that I'm burning a bit high. Did a 56 minute flight yesterday up to ft worth and burned 12.8 gallons @6500, ISA -10 C.  On the way back 1:06 and 13.5 gallons @9500. These are at least 10 to 15% higher than predicted from the charts. The airplane has the exhaust mod installed, so perhaps it's just due to the extra 5hp it supposedly is producing. Also I keep forgetting about automatic enrichment when at WOT; if I back it off full maybe it will help lean it more. 
 
Any general tips on the most efficient way to fly the M20B will be greatly appreciated. 
 
Thanks, 
Brandon
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First of all, congrats!  Consider posting some pix.

Yup - WOT all the way up is the correct thing to do - otherwise you sacrifice some cooling by cutting out the enrichment circuit, lose some climb rate, and gain nothing. I drop rpm to 2650 after about 1000 ft, just a personal preference - it runs a lot quieter for little power sacrifice.

Leaning in climb is great below 75% power, lean  to takeoff EGT or as much as CHTs tolerate - the latter usually limits me in the summer.

Do you have fuel flow?  I typically get 9-10 gph at optimal altitude, 2500 rpm, WOT, leaned to stoichiometric on leanest cylinder, or richer if needed to keep a CHT <380.  Being WOT should make no difference - it still leans the same with enrichment circuit engaged, though I usually pull throttle back just slightly to help mixture distribution.  

Good luck!

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Hello all,
  I have just taken possession of an M20B, and was looking for any advice on power settings for climb and cruise.    I've been using 25 squared on the climb just because that's how I was taught years ago. But I recently read a Mapa article suggesting WOT and 2700 all the way to altitude. Thoughts?   Been leaning on the climb once the key value falls below 47(approximately 75% power). Cruising at 2400 and WOT, and as lean as I can get it without engine roughness.    One issue I've noticed is that I'm burning a bit high. Did a 56 minute flight yesterday up to ft worth and burned 12.8 gallons @6500, ISA -10 C.  On the way back 1:06 and 13.5 gallons @9500. These are at least 10 to 15% higher than predicted from the charts. The airplane has the exhaust mod installed, so perhaps it's just due to the extra 5hp it supposedly is producing. Also I keep forgetting about automatic enrichment when at WOT; if I back it off full maybe it will help lean it more.    Any general tips on the most efficient way to fly the M20B will be greatly appreciated.    Thanks,  Brandon


Brandon -- I can provide guidance from a fuel injected perspective. The 25/2500 is a legacy from way back. I personally leave the levers full forward for the climb and will only begin pulling back the power once I reach my cruise altitude. I may pull back mixture a bit based on what I am seeing on the engine analyzer.

It doesn't sound like you are using an engine analyzer. If this is true, I am not surprised your fuel consumption may be off a bit. If you have the PowerFlow exhaust installed, you may be, as you indicated seeing more HP. Bob Belville has a PF exhaust installed and he can confirm slightly higher burn rates. He has a full engine analyzer.


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Hi Brandon,

I flew a C for about 400 hours or so and just recently sold it. It had the same O360 engine as your B.  I got the best performance and fuel economy when I would climb at WOT and full forward prop all the way to altitude. I'd lean in the climb as you're doing.  Once leveled off in cruise, leave everything where it is to allow the plane to accelerate to full speed. That usually took a couple of minutes. Then I'd pull the throttle back as far as I could without moving the MP needle. Second pull the prob back to 2500 or 2450 just to get things to quiet down. Finally pull the mixture back as far as you can and still run smooth.

Backing the throttle just off the enrichment circuit help smooth out the distribution and allow me to go leaner. Again, just back the throttle back as far as possible but just until the MP needle starts to move.

I was getting 9 gph down low, and as low as 7 gph at 12K or 13K.

You'll enjoy that airplane!

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To my surprise, simply leaning to roughness and enriching just enough to smooth out pretty much puts me just a tad leaner to where I run now, after getting an engine monitor. The engine monitor has been enormously helpful in several ways, but as far as leaning a carb'd plane with very uneven mixture distribution, I was surprised to find it really didn't make me run more efficiently. So you may be doing just fine!

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8 minutes ago, gsxrpilot said:

Hi Brandon,

I flew a C for about 400 hours or so and just recently sold it. It had the same O360 engine as your B.  I got the best performance and fuel economy when I would climb at WOT and full forward prop all the way to altitude. I'd lean in the climb as you're doing.  Once leveled off in cruise, leave everything where it is to allow the plane to accelerate to full speed. That usually took a couple of minutes. Then I'd pull the throttle back as far as I could without moving the MP needle. Second pull the prob back to 2500 or 2450 just to get things to quiet down. Finally pull the mixture back as far as you can and still run smooth.

Backing the throttle just off the enrichment circuit help smooth out the distribution and allow me to go leaner. Again, just back the throttle back as far as possible but just until the MP needle starts to move.

I was getting 9 gph down low, and as low as 7 gph at 12K or 13K.

You'll enjoy that airplane!

exactly what i do, infact even after adding an engine monitor i still use the same method, 

 

Brian

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Thanks gsxrpilot and others. This is exactly the kind of advice I was looking for. I fly commercially but am just now getting back in GA after being out of it for 17 years. Whole different world!

Seems like there is pretty clear consensus on these climb/cruise techniques. Gonna incorporate them into my next trip and report back.

Regarding taxi, I've heard that this engine runs very rich on the ground and is prone to plug fowling. So per some advice I read elsewhere, after start I am aggressively leaning till I see a slight rpm rise. I leave it there till the run up and takeoff. 

Is this the generally accepted technique?

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20 minutes ago, gringoneff said:

Thanks gsxrpilot and others. This is exactly the kind of advice I was looking for. I fly commercially but am just now getting back in GA after being out of it for 17 years. Whole different world!

Seems like there is pretty clear consensus on these climb/cruise techniques. Gonna incorporate them into my next trip and report back.

Regarding taxi, I've heard that this engine runs very rich on the ground and is prone to plug fowling. So per some advice I read elsewhere, after start I am aggressively leaning till I see a slight rpm rise. I leave it there till the run up and takeoff. 

Is this the generally accepted technique?

Yes, in fact you want to lean far enough that if you shove the throttle in without first going rich on the mixture, the engine will stumble and probably die. This ensures you will keep the plugs nice and clean, but also that you won't forget to go rich before takeoff.

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Hey, Gringo!

Lean just like Brian and Paul said, that's exactly what I do in my C--WOT/2700 to altitude, accelerate until it stops, then pull throttle enough to just make the MP needle move. Set 2500 and lean away. I run anywhere from peak to 50ºF Rich using the factory EGT gage. I pretty much have three power settings:

-Low cruise [3000 msl or so], 23/2300

-Mid-Level Cruise [up to 6500/7000 or so], 22/2400

-High Cruise [> 7500/8000] WOT - a tad/2500

On the ground, lean as far as possible; for my O-360, that's generally about 2/3 towards Idle/Cutoff. It's enough to taxi on, but taxiing uphill will require more throttle and a slightly richer mixture; parked in the grass, I can't pull up on the asphalt without adding lots of both [no more throttle = no movement; no more mixture = engine wants to die]. It will keep your plugs clean, with no annoying, power-robber lead buildup, and you'll have nice mag checks, too. You can't take off leaned out like this, the engine will try to die as you advance the throttle.

Welcome to the club, and fly safe!

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Another thing to think about is the descent. The only thing I'd ever adjust is the trim. Leave the throttle/mixture/prop right where they are and trim it for 500 ft/min down. You'll get back all the time you lost in the climb. Just watch the ASI that you don't go over the little red line. Also know that when you level off it's gonna take you several miles to get down to gear speed.

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Brandon, Bs and Cs share the same O360 so I will only add to watch the cylinder temperatures on climb out. They can run very hot specially in the summer. I have an engine monitor and unless I maintain at least 120 mph, cowl flaps fully open, they will climb over 400 very quickly. Sounds like you have only a CHT gage on cylinder 3 which is the factory install. Keep an eye on it.


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Another thing to think about is the descent. The only thing I'd ever adjust is the trim. Leave the throttle/mixture/prop right where they are and trim it for 500 ft/min down. You'll get back all the time you lost in the climb. Just watch the ASI that you don't go over the little red line. Also know that when you level off it's gonna take you several miles to get down to gear speed.


Yes indeed, that descent can be a challenge if you elect to leave the power in. Slowing down can take some time.

If you are flying IFR, especially if you expect to be vectored, I find it easier to begin reducing power to keep the plane closer to gear/flap speed. Especially, if the controller does a slam dunk with you. I normally will reduce to 20" of MP and 2400 RPM and keep it that way through the descent (i.e. keep reducing MP to maintain 20"). I did my IFR training in my plane and it really helped to spend the time up front to understand the power combinations my plane required to achieve different speeds based on the phase of flight.


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Thx everyone for sharing all this great advice and making me feel so welcome. Regarding the descent, I usually have 20"MP and ride a bit in the yellow airspeed arc if its smooth. Slowly enrichen on the way down. Only go full rich if need to do a go around. 

And here are some pics as requested. She's not going to win any beauty contests but she has character and flies great:)

 

C714CC0D-BB87-4257-887C-B67F5E9F09DC.JPG

3753D168-0F92-4F91-8735-202AA90117BA.JPG

68E11958-C7CC-4FF4-82F4-8E9E329025C6.JPG

8F51291E-8E76-4B61-8CC5-3C2AD2CCA9DD.JPG

5F315959-7EE3-4562-8360-74A516B8C7B9.JPG

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Descending is easy--just push for 500 fpm, trim it hands off and every now and then pull the throttle back to your cruise setting and push the mixture forward to cruise EGT. I like to be at pattern altitude a couple miles out so I can work on slowing down, this will usually have me descending around 170 mph, and will settle around 150 at level off.

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