low speed cruise settings ?

[mike28w]

  Hi guys, I'm looking for some wisdom.....    I have an M20C but no longer seem to have any need or urge to go cross country like I used to.  Not flying it as much as it should be flown  :-(.....  I'm strongly considering selling my Mooney and buying a 172 ( or similar).  Something that I can "putt" around in on a nice sunny day.

  It occurs to me that I should try that approach with my Mooney ( before I sell a perfectly good airplane).  Seems that I could accomplish these speeds by either using slow RPMs/ low MP  or higher RPM / with an even lower MP.   (My plane is not supposed to be run continuously between 2100-2300 RPM. )   I'm thinking that I could "putt" around with settings ~ 2500-2600/18-19" .....Can anyone see any harm with this approach ?  Anyone using this approach ?  Any other suggestions or should I just consider selling my plane?

All opinions welcome !   Thanks, mike

 

PS:  Always assuming proper leaning and keeping a close eye out for carb ice.

 

[bonal]

I can only think of 2 reasons to sell a perfectly good 20c for a 172 if you are a volunteer search and rescue pilot (high wing) or for a cheaper annual. I thought I would miss the ground view when I went from C to M but I find that since the wing is so far back you don't lose much looking down and the overall view is much better without the wing blocking so much of the sky. As for the question of flying slower yes a 172 is better for that but as far as fuel burn I can run at 2300 18 to 20MP and get below a 172's GPH and it runs smooth as you like and still faster than a 72 at high power setting.

[MitchS]

I find that mine runs very well at 2400-2500 RPM and with 18-19" of MP I'm at about flap speed.  120MPH.  The fuel burn then is quite low as well.  No problems at all with running that configuration in my experience either.

[carusoam]

Mike,

Nobody would buy a Mooney for slow or inefficient flight, but...

1) Once you have a Mooney, the transaction costs to swap planes are quite a large portion of the equation.

2) A slow flying Mooney is more efficient than a slow flying Brand C or P.

3) Flying at the low end of the power range, leaned properly produces good power and nice CHTs.

4) Flying locally, efficiency is measured in $/hour more than mpg...

5) Selecting an rpm outside the yellow zones makes good sense.

6) Exercising the plane takes all kinds of flights...

- Low power ridge soaring in my C was memorable. Zero ground speed in a Mooney is possible. (Short on cash flights)

- Putting around at approach speeds, LOP, in an R, is better than the alternatives. (Short on health)

7) Being short on cash or being short on health doesn't always mean 'sell'.

8) If you need some instruction on things to avoid while investigating slower flight bring a CFI along.

9) For more background info on the most efficient flight regime, search for Carson's speed on this site.

10) The coolest thing about keeping the Mooney.  When things change (they will) you can always push in the throttle and go somewhere fast and efficiently just like before.

These ideas are my own.  I tried renting after selling my tired C. My tired C was nicer than the tired rentals that are available...

Best regards,

-a-

[DXB]

I may not be the most experienced or knowledgeable pilot, but I'm putting my foot down and forbidding you from buying a C172   When I got my plane not too long ago, I was too much of a coward to go fast on short hops and putted around quite a bit.   20-squared takes you below the rpm restriction and is nice and quiet. Here It csn be leaned down to near 6.5gph at 2500msl.  For me, this gives  120mph-ish indicated- see POH numbers for confirmation. LSA-like performance and economy,  but in a far more capable plane.  

If you really want to use 2100-2300rpm, you can spend 9k on a new Top Prop, which takes away the rpm restriction entirely for the C model.  Not that I would recommend this, but it still might be cheaper than the total cost of swapping to a decent 172.

[BigTex]

Wow DXB, 20 squared gives you 120mph-ish... you must have one pretty special C!  It take mine 2400/20 to see 120mph.

[Jerry 5TJ]

The 1965 M20C manual Figure 3 shows a power setting of 1800 RPM and 17" MP at 2500' MSL allegedly giving 37% power at 5.7 GPH and 109 MPH TAS. 

I've flown the C at that power and recall getting about 100 MPH indicated at low altitude.   There wasn't enough engine heat to keep me warm at 50F outside air temp. 

I suggest 2300 RPM and 20" is a good "going nowhere" power setting and you will get about 120 MPH indicated at about 7-8 GPH.  

[Mooneymite]

When my son was building time, he ran our engine (O-360) at 18-19" MAP and 2300-2350 RPM.  As I recall, he got about 5.5 GPH and still went faster than a C-172.  When he finished time-building, the engine was running well.  At 2600 hours we changed it out for a re-man, so I don't think he damaged it using those settings.

Very inexpensive way for a new pilot to build complex time.

[DXB]

19 minutes ago, BigTex said:

Wow DXB, 20 squared gives you 120mph-ish... you must have one pretty special C!  It take mine 2400/20 to see 120mph.

To be honest, I don't see a big difference in IAS at 2300 vs 2000rpm at low MPs- do you?  I'll look again at the IAS next time, but the POH says the difference should be about 8mph TAS. I enjoy the quiet at the lower rpm.  At 20-squared I actually still can't seem to get the Vlo of 120mph simply by leveling off and have to pull MP back further and pitch up.  

[Hank]

On Plane Ride days at the airport, I run 2300 RPM and whatever throttle is required to not run over the 172 ahead of me. This is generally in the 16-18" range. Finding your sweet spot will be simple, just try a few. My tach is marked 2000-2250 to "Avoid Continuous Operation. But memory says that 16"/2300 is level flight at 105 mph (90 knots) clean, and it takes ~19" with Takeoff flaps. These are all leaned to 50°ROP.

Your basic Instrument Approach settings will be a good place to start (see above for mine). If it's good enough to shoot an approach, it will be good enough to putter around, but you can also dial,it back some, too. The Max. Duration in my Owners Manual is 20"/1900, but I don't like the control feel there.

[MooneyBob]

I am going to take an opportunity and ask the question. 

My POH says to avoid continuos operation below 15" MP, 1800-2200RPM and above 85 knots. How long is the " continuous operation" defined ? It is hard to avoid it on the ILS or RNAV approach. It could last maybe 5 minutes or more.  Is it bad? Any trick how to avoid it? 

I have IO 360 A3B6 with 3 blade prop. 

[carl]

4 hours ago, Hank said:

On Plane Ride days at the airport, I run 2300 RPM and whatever throttle is required to not run over the 172 ahead of me. This is generally in the 16-18" range. Finding your sweet spot will be simple, just try a few. My tach is marked 2000-2250 to "Avoid Continuous Operation. But memory says that 16"/2300 is level flight at 105 mph (90 knots) clean, and it takes ~19" with Takeoff flaps. These are all leaned to 50°ROP.

Your basic Instrument Approach settings will be a good place to start (see above for mine). If it's good enough to shoot an approach, it will be good enough to putter around, but you can also dial,it back some, too. The Max. Duration in my Owners Manual is 20"/1900, but I don't like the control feel there.

I'm just now working on some IFR ground school so this is new to me. 

                             "16"/2300 is level flight at 105 mph (90 knots) clean, "   

Where do you drop your gear, in relation to the approach and this is still too fast for my flaps.(100mph)

 

Carl

[ryoder]

My go to power setting is 2300 and 18.5 MP.  This gives me just over 120 indicated and fuel burn is low.  I use this for instrument training, VFR flights for fun, and just about all of my straight and level flight.  It keeps the engine cool and runs really smooth.  If I run below 2000 the vibration isn't very pleasant.

 

Dont sell the Mooney to go slow.  The Mooney is excellent at going slow and will reward you with fast descents if you keep the power setting intact.  I rarely break 130mph in mine and enjoy the scenery and low fuel burn.  Of course if there is a storm building I can kick it in the ass and get home.

[1964-M20E]

I've gone around with about 16"MP and some where around 2100RPM.  I've even played with how low I could set the power and keep the plane flying.

 

However I agree that when you want to go slow a Mooney does not work well with you since it just wants to goooooo.

[Danb]

Generally drop the gear at the faf, marked by the X on the approach plate this is appro. 5 miles from the DH.

[Hank]

3 hours ago, carl said:

I'm just now working on some IFR ground school so this is new to me. 

                             "16"/2300 is level flight at 105 mph (90 knots) clean, "   

Where do you drop your gear, in relation to the approach and this is still too fast for my flaps.(100mph)

 

Carl

Hey, Carl. One thing you need to do is determine your power settings for 90 knots level, clean and dirty. I like to be 90 knots, Takeoff Flaps somewhere between IAF and FAF (a couple of miles before the FAF). If I have a glideslope,mi drop the gear when it's about 1-1/2 dots above me, coming down; if no glideslope, I drop the gear at the FAF. Your CFII will go over all of this with you.

[mike28w]

My thanks to everyone !  Your input is much appreciated !   mike

[jetdriven]

9 hours ago, MooneyBob said:

I am going to take an opportunity and ask the question. 

My POH says to avoid continuos operation below 15" MP, 1800-2200RPM and above 85 knots. How long is the " continuous operation" defined ? It is hard to avoid it on the ILS or RNAV approach. It could last maybe 5 minutes or more.  Is it bad? Any trick how to avoid it? 

I have IO 360 A3B6 with 3 blade prop. 

Im not sure that that 1800-2200 RPM prop restriction applies to the 3-blade airplanes.

[Raptor05121]

1 hour ago, jetdriven said:

Im not sure that that 1800-2200 RPM prop restriction applies to the 3-blade airplanes.

Per the STC on my Hartzell 3-blade, it still has a restriction. I'd have to pull it out to see what it is, I just remember seeing one on there.

[Hank]

4 hours ago, Raptor05121 said:

Per the STC on my Hartzell 3-blade, it still has a restriction. I'd have to pull it out to see what it is, I just remember seeing one on there.

Mine is 2000-2250 on a '70 C.

[MooneyBob]

1 hour ago, Hank said:

Mine is 2000-2250 on a '70 C.

Thanks but it didn't  t answer my question. What is " continuos operation" and how to avoid it on long ISL approach?

thanks. 

[1964-M20E]

Bob

I asked the same question a while back and while I can't find the email from the prop manufacturer, I have a 2 blade Hartzell, the answer was pretty much stay out of the restricted range except when transitioning to higher or lower RPMs.

 

On an ILS approach you do not want to be loitering in the restricted RPMs.  Yes I find that somewhat challenging at times on base and final.

 

 

[Marauder]

1 hour ago, Hank said: Mine is 2000-2250 on a '70 C.

Thanks but it didn't  t answer my question. What is " continuos operation" and how to avoid it on long ISL approach?

thanks. 

Bob -- I was told it meant for more than a few minutes. In any case, when I learned the power settings for my Mooney, I figured out settings that would keep me out of the range on approaches. I will transition through the red zone for a few seconds but stay out of it as much as possible,

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