Best RPM for Mooney 20 F

[Yetti]

Basics

Mooney 20F   Type data sheet says 2700 RPM

http://www.67m20e.com/Mooney TCDS 2A3 Rev 52 dtd 9DEC10.pdf

 

74" Prop says 2800 is still keeping the tips below supersonic and 2800 is actually getting the prop up to the maximum performance levels

http://www.warpdriveprops.com/propspd2.html

Lycoming says for an HIO360 - Max rpm is 2900

http://www.lycoming.com/Portals/0/techpublications/servicebulletins/SB 369C (04-18-2012)/Engine Inspection after Overspeed.pdf

 

So what is the best RPM?

 

[M20F]

So what is the best RPM?

Best for climb?  Best for cruise?  Best for range?  Best for speed?  Best can mean a lot of differing things.   

[Yetti]

let's try best for Take off

[N201MKTurbo]

If the TCDS says 2700 then it is 2700.

If your hanger fairies choose to turn the screw on the prop governor, I'll never tell. Just remember that the stresses on the prop go up exponentially with RPM. There is no free ride. 

[carusoam]

Best to stay in line with the documentation.  Stresses at T/O are huge.  Temps are not at steady state.  Oil flow is just getting started. Throw in some unusually cold weather or below SL MPs...

Asside from all the warnings...

My experience: The IO550 increases HP by 10% by allowing 200 more rpm. Thus going from 280hp to 310.  The resulting T/O performance goes from 1200’ to 800’.  Initial climb rates are 2000 fpm. Cruise at high altitudes is increased by 50rpm adding a measly 10kts...

Back to the warnings....

If you want to find the details, they are in the POH or in the STC that modified the POH.

Back to how to tell you are using the best settings and procedure...

A Portable WAAS GPS with an app called CloudAhoy allows you to measure actual take-off distance and climb rates pretty accurately and easily.

The costs...The STC, the hardware, the installation, and the Increased FF and external sound for the T/O run and climb period.  (It is worth it)

Not having the documentation is more in line with experimental planes.

Remember...I am a PP, not a mechanic, not making recommendations for anything other than the IO550.

Does that help?

Best regards,

-a-

Edited November 6, 2015 by carusoam

[carusoam]

Additional thoughts using Long Body power to weight ratio data....

How many HP did the...

- PFM have?  217 (Not enough)

- Eagle 1: 244 (2400rpm Max) uses longer runway and carries less gross weight.

- Bravo: 270 TC is nice for keeping plenty of power all the way to the flight levels.  Longer T/O.

- Ovation: 280 (2500rpm Max)

- O3 or Standing O: (2700rpm Max)

-Acclaim 310 TN:  short runway performance, great climb all the way into the FLs...

- Liquid Rocket: 335

Adding a small amount of HP really improves T/O and Climb significantly. Adding a Turbo system really improves speed in thinner air. 

Losing a small amount of HP like having a stuck valve can cause a significant challenge like inability to climb and/or the need to land.

Thoughts of a PP, not a mechanic....

 

Edited November 6, 2015 by carusoam

[Hank]

For my C, it's always Full RPM (2700) for Takeoff and Climb.

Cruise RPM is altitude dependent, base on power setting, but is usually as follows:

• Low level lunch runs, 2300
• mid-altitude level offs (up to ~6500 msl), 2400
• cruise above that (I like 7500-10,000 msl), 2500

Yours may vary if you aren't in a C model.

[Culver LFA]

I take off and climb out at 2700, then around 1000' AGL I will pull it back to 2500/25" (that little bit really reduces the noise level in the cabin and the climb rate is still quite steep for passenger comfort).

Someone commented to me the other day how well the Mooney gets in and out of our little grass strip; It's all the airplane, the performance is really great.  When you are light and leave everything 'in' it will really climb out quite aggressively.  I smile now every time I watch the old club airplanes that I flew (Cessna 172's) come and go as they are just clearing the trees with only one person on board

[Hank]

Reducing power in the climb reduces noise, reduces airspeed, reduces climb rate, increases time to reach altitude (thereby burning more fuel) and increases engine temps by reducing the amount of cooling air pushed through by the slower prop and reduced airspeed.

the best way to climb to altitude is Wide Open Throttle, 2700 RPM. To reduce noise on the ground, climb at Vx for several hundred feet, then climb at Vy. There's an article on MAPA's website written by Bob Kromer, former Mooney test pilot turned Engineering VP, that describes this for several different models. Www.mooneypilots.com and look for Sample Articles.

Also search for Target EGT for details on now to properly and safely lean the mixture during the climb for better speed. It's getting to be the time of year for Standard Day departures to record the Target values.

Enjoy your Mooney and fly safe!

[M20F]

Article in question http://www.mooneypilots.com/mapalog/powersettings.html

I usually dial back to 2600 for noise and really notice no appreciable difference in climb rate and I use 120mph IAS.  I wouldn't personally follow his advice on leaning to 100 ROP in the climb and can only begin to imagine CHT's if you did that at maximum continuous power.

[Culver LFA]

 

Reducing power in the climb reduces noise, reduces airspeed, reduces climb rate, increases time to reach altitude (thereby burning more fuel) and increases engine temps by reducing the amount of cooling air pushed through by the slower prop and reduced airspeed.

the best way to climb to altitude is Wide Open Throttle, 2700 RPM. To reduce noise on the ground, climb at Vx for several hundred feet, then climb at Vy. There's an article on MAPA's website written by Bob Kromer, former Mooney test pilot turned Engineering VP, that describes this for several different models. Www.mooneypilots.com and look for Sample Articles.

Also search for Target EGT for details on now to properly and safely lean the mixture during the climb for better speed. It's getting to be the time of year for Standard Day departures to record the Target values.

Enjoy your Mooney and fly safe!

I read the article and do respect his expertise and agree with his opinion - for most efficient operations.   Running wide open definitely has it's advantages but I would love the opportunity to learn from him discussing his statement of, "There is no reason on a normally aspirated engine to reduce the throttle for climbs. Why sacrifice climb performance for nothing?".  I'm quite certain that we would come to an agreement that there are such times that this could be appropriate.

How about this scenario, I find that people are more comfortable flying if the noise, vibration, harshness levels are reduced and the climb/decent is less aggressive.  Flying is not always about getting to cruise altitude at the highest speed covering the most ground while burning less fuel. Unless the passengers with me are pilots or I know that they are comfortable in 'small' airplanes, I make every attempt to make the flight absolutely as smooth as possible from start to finish.   A smooth transition from rolling down the runway to flight, pitching to the desired climb attitude, and then reducing power settings at a safe altitude is the first opportunity to make a good impression.  Carrying lots of speed at lower altitudes, lots of engine/prop noise, and aircraft pitch changes is not always the best.  Raising the gear and flaps without noticeable pitch changes is challenging enough!  I find that passengers want some distance between themselves and the ground, they get uncomfortable in the early climb and short final stages of flight.  Get the airplane away from stuff on the ground quickly (don't let them count the leaves on the tree branches at the end of the runway), make the airplane cabin environment as comfortable as possible, make the pattern work as smooth as possible with nice gentle inputs, and then grease the landing in the end with proper approach speeds. 

Slightly off topic, but sometimes I wonder if the declining population of pilots is due to the way current pilots handle the airplane on a guest ride, once back on the ground people walk away excited that they are still alive rather than asking how/when/what they need to do to become a pilot themselves!

[ArtVandelay]

Article in question http://www.mooneypilots.com/mapalog/powersettings.html

I usually dial back to 2600 for noise and really notice no appreciable difference in climb rate and I use 120mph IAS.  I wouldn't personally follow his advice on leaning to 100 ROP in the climb and can only begin to imagine CHT's if you did that at maximum continuous power.

My POH says 2600 for normal climb, 2700 for max.

I wait until 1000' before I adjust anything, but I was taught 2500 rpm, WOT and 125-150 ROP, CHTs stay below 380, but will go above if speed drops below 120mph and it's warm.

[Lood]

I always use WOT for climb and then I reduce to where my engine runs nice and smooth. Strange enough, before the engine and prop overhaul, my engine ran best at 2500rpm, but after the overhauls, it seems to be the smoothest at 2450rpm. So, that's where I run it in cruise flight.

[Andy95W]

I always use WOT for climb and then I reduce to where my engine runs nice and smooth. ... after the overhauls, it seems to be the smoothest at 2450rpm. So, that's where I run it in cruise flight.

100% agree, IMHO..  Smooth engine + low CHTs = happy engine

[Bob - S50]

I'm waiting for a clear sky day in the Pacific Northwest (might be awhile now) to do some testing.  After I do I'll post the results, but...

For the climb I use full power with the engine leaned to keep the hottest EGT at about 1300F until about 8000', then I lean to 1350 until about 10,000', then I lean to 1400.

If I don't like the steep climb angle, rather than reduce power, I reduce pitch and climb at a higher speed but lower rate.

For cruise, I'm starting to use WOT for everything above about 4000'.  I'm aiming to set an RPM+MP of 47 (about 65% power on my J), and then lean to about 15 LOP.  My engine does not seem to like cruising over square below about 2200 or 2300 RPM, so if need be I'll increase RPM to 2300 to get less vibration.

The reason I'm doing this is because the lower the RPM, the higher the percentage of power that goes to turning the prop rather than to overcome internal engine friction.  In theory I'll either get a higher speed or better economy for any given altitude.  That is, 2300 RPM and 24" should get better economy for the same performance than 2700 RPM and 20", and be quieter to boot.  You can verify this by comparing fuel flows for equivalent power settings in your POH.

[carl]

this is what i try to do . but sometimes i get all messed up. 

full throttle . two pumps flaps 

 65 mph rotate . 

pitch for 85 vx

gear comes up . johnson bar. 

mp and rpm to 25./25

boost pump off 

85 mph 

pitch downward for 107mph vy

and flaps come up as mph increases above 85 

 im still over.the runway it happens so fast. 

after i clear the runway and have my crash landing spot picked out i pitch for 120 mph climb out and usually start my turnout .

i cruise just about like hank does . 

23 rpm for just flying 

the 24/ 24

25/25 

but my typical trip is to run laundry up to my son at clarion college . 45 minutes by air 2 and a half hours  by car . . sometimes the flights can take all day . cause they are just too fun 

 

carl

 

 

 

[jetdriven]

On November 7, 2015 at 9:15:21 AM, Bob - S50 said:

I'm waiting for a clear sky day in the Pacific Northwest (might be awhile now) to do some testing.  After I do I'll post the results, but...

For the climb I use full power with the engine leaned to keep the hottest EGT at about 1300F until about 8000', then I lean to 1350 until about 10,000', then I lean to 1400.

If I don't like the steep climb angle, rather than reduce power, I reduce pitch and climb at a higher speed but lower rate.

For cruise, I'm starting to use WOT for everything above about 4000'.  I'm aiming to set an RPM+MP of 47 (about 65% power on my J), and then lean to about 15 LOP.  My engine does not seem to like cruising over square below about 2200 or 2300 RPM, so if need be I'll increase RPM to 2300 to get less vibration.

The reason I'm doing this is because the lower the RPM, the higher the percentage of power that goes to turning the prop rather than to overcome internal engine friction.  In theory I'll either get a higher speed or better economy for any given altitude.  That is, 2300 RPM and 24" should get better economy for the same performance than 2700 RPM and 20", and be quieter to boot.  You can verify this by comparing fuel flows for equivalent power settings in your POH.

The POH is one thing but in real life the C214 prop doesn't do well below 2300 RPM. The speed falls off faster than the FF, it's similar to going beyond 50 LOP.  

I did a test at 9500' one day at 2300 RPM peak EGT, 2500 RPM 15 LOP, and 2700 RPM and about 40 LOP.  Same FF for al 3 but 2500 RPM was 2-3 knots faster than 2300, but 2700 was about 7 knots faster.  Same FF.  Free speed.  (Mostly) 

[BDPetersen]

Flew my first Mooneys back in '64, working for a distributor. The factory was encouraging the radical idea of leaving the throttle stuffed in (WOT) for takeoff and climb, backing off the rpms a bit when cleaned up. Funny how half a century later we're still trying to sell that idea. 

Dont forget that at full throttle you have the enrichment valve open adding a bit more fuel to the mix.

If only we could run the carbs like fuel injectors with GAMI's . . .

[Bob - S50]

11 hours ago, jetdriven said:

The POH is one thing but in real life the C214 prop doesn't do well below 2300 RPM. The speed falls off faster than the FF, it's similar to going beyond 50 LOP.  

I did a test at 9500' one day at 2300 RPM peak EGT, 2500 RPM 15 LOP, and 2700 RPM and about 40 LOP.  Same FF for al 3 but 2500 RPM was 2-3 knots faster than 2300, but 2700 was about 7 knots faster.  Same FF.  Free speed.  (Mostly) 

Good to know.  Thanks

[garytex]

12 hours ago, jetdriven said:

The POH is one thing but in real life the C214 prop doesn't do well below 2300 RPM. The speed falls off faster than the FF, it's similar to going beyond 50 LOP.  

I did a test at 9500' one day at 2300 RPM peak EGT, 2500 RPM 15 LOP, and 2700 RPM and about 40 LOP.  Same FF for al 3 but 2500 RPM was 2-3 knots faster than 2300, but 2700 was about 7 knots faster.  Same FF.  Free speed.  (Mostly) 

 That's really interesting, and for me kind of counterintuitive.  I don't think I want to run 2700, just because I don't want the tach clicking over that fast. But it's sure food for thought.  And 7 kn is absolutely not chicken feed 

[M20F]

13 hours ago, jetdriven said:

The POH is one thing but in real life the C214 prop doesn't do well below 2300 RPM. The speed falls off faster than the FF, it's similar to going beyond 50 LOP.  

I did a test at 9500' one day at 2300 RPM peak EGT, 2500 RPM 15 LOP, and 2700 RPM and about 40 LOP.  Same FF for al 3 but 2500 RPM was 2-3 knots faster than 2300, but 2700 was about 7 knots faster.  Same FF.  Free speed.  (Mostly) 

Your test though measured different % of power and the result in speed/FF that doesn't really show what is going to be the most efficient RPM setting at say 65% power.  

[Shadrach]

On November 6, 2015 at 10:29:00 PM, Culver LFA said:

I take off and climb out at 2700, then around 1000' AGL I will pull it back to 2500/25" (that little bit really reduces the noise level in the cabin and the climb rate is still quite steep for passenger comfort).

2500rpm makes sense if you want/need to reduce noise. Pulling the throttle back makes no sense at all, though almost every pilot I know that learned to fly in the 50s, 60s and 70s does it. It is not kind to the engine, it is less efficient and gaurantees you spend more time in a place that is...not kind to the engine and less efficient.

My dad used to do this and it drove me insane.  

[ChrisH]

2 hours ago, M20F said:

Your test though measured different % of power and the result in speed/FF that doesn't really show what is going to be the most efficient RPM setting at say 65% power.  

I've seen similar results, and LOP theory says FF ~ HP, so same FF should be same HP. But, it's hard to jive that much improvement in TAS with just RPM. 

[Shadrach]

On November 7, 2015 at 12:02:46 AM, Culver LFA said:

I read the article and do respect his expertise and agree with his opinion - for most efficient operations.   Running wide open definitely has it's advantages but I would love the opportunity to learn from him discussing his statement of, "There is no reason on a normally aspirated engine to reduce the throttle for climbs. Why sacrifice climb performance for nothing?".  I'm quite certain that we would come to an agreement that there are such times that this could be appropriate.

How about this scenario, I find that people are more comfortable flying if the noise, vibration, harshness levels are reduced and the climb/decent is less aggressive.  Flying is not always about getting to cruise altitude at the highest speed covering the most ground while burning less fuel. Unless the passengers with me are pilots or I know that they are comfortable in 'small' airplanes, I make every attempt to make the flight absolutely as smooth as possible from start to finish.   A smooth transition from rolling down the runway to flight, pitching to the desired climb attitude, and then reducing power settings at a safe altitude is the first opportunity to make a good impression.  Carrying lots of speed at lower altitudes, lots of engine/prop noise, and aircraft pitch changes is not always the best.  Raising the gear and flaps without noticeable pitch changes is challenging enough!  I find that passengers want some distance between themselves and the ground, they get uncomfortable in the early climb and short final stages of flight.  Get the airplane away from stuff on the ground quickly (don't let them count the leaves on the tree branches at the end of the runway), make the airplane cabin environment as comfortable as possible, make the pattern work as smooth as possible with nice gentle inputs, and then grease the landing in the end with proper approach speeds. 

Slightly off topic, but sometimes I wonder if the declining population of pilots is due to the way current pilots handle the airplane on a guest ride, once back on the ground people walk away excited that they are still alive rather than asking how/when/what they need to do to become a pilot themselves!

In an aircraft with a CS prop, there is no discernable difference in noise between WOT and 25". There is a discernable reduction in fuel burn and climb rate, though as a percentage, considerably more in the latter which is why it's less efficient. The angle valve 360 has a tuned induction, when one "throttles" the engine back they negate most of that benefit.  Would you want to hike up a mountain breathing through a partialy obstructed snorkel? Your Mooney does not really care for it either.

THROTTLE - to keep (someone) from breathing by exerting pressure on the windpipe  <I was so angry at what he was saying that I could have throttled him!>

Synonyms garrote (or garotte), strangle, suffocate, throttle

Perhaps there is a reason to throttle back that I've not thought of. Almost everyone I know who does it does so because they were taught to and because they think it's "gentle"...it's not and for engines with any type of enrichment circuit, throttling back borders on abuse.

if you have a reason I've not considered, I'm always curious to learn.

[Shadrach]

23 hours ago, jetdriven said:

The POH is one thing but in real life the C214 prop doesn't do well below 2300 RPM. The speed falls off faster than the FF, it's similar to going beyond 50 LOP.  

I did a test at 9500' one day at 2300 RPM peak EGT, 2500 RPM 15 LOP, and 2700 RPM and about 40 LOP.  Same FF for al 3 but 2500 RPM was 2-3 knots faster than 2300, but 2700 was about 7 knots faster.  Same FF.  Free speed.  (Mostly) 

What I find interesting about your calculations is that at the same FF at 2700rpm the engine has to do almost 7 more revolutions per second than at 2300rpm. That seems like it would add significantly to frictional losses. So the prop must really get inefficient at 2300 if the same amount of fuel can give 10 more knots in addition to the additional output required to turn the engine and prop 17% faster.