M20J Cruise Calculator

[whiskeyone2]

To start off, I am a new Mooney owner and this is my first topic I have created. This calculator is just something I have been using and I thought others might think it was neat. If not, please feel free to not use it. Also, disclaimer, this is not intended to be a replacement for your POH. 

 

With that out of the way, my background is in military aviation and I was always used to having a “whiteboard” to calculate approach and stall speeds, etc. So when I moved over to general aviation, I wasn’t really satisfied with “just set this in climb and this in cruise”. Usually those being the same two numbers for MP and RPM.
 

So I made this calculator based off of MY airplane’s POH. Other airplanes may be similar or exact, but it’s up to you to verify and/or edit a copy for your own use. It is sized to fit a phone screen and easy to use with drop down menus. Once I get to cruise altitude, I use this calculator while my plane is speeding up, and then I verify what settings I want based off my actual OAT and pressure altitude. The Fahrenheit to Celsius converter is just because my plane shows OAT in Fahrenheit, but my 430 TAS calculator takes Celsius. I recently added the “approximate TAS” section and it has been within a few knots when tested on real flights.
 

Anyway, this is more useful to me as an app on my phone than trying to read spaghetti charts in turbulence or just plugging in memorized, generic numbers. But do what works for you. 

Mooney M20J Cruise.xlsx

[elimansour]

Wow! This is great and a fantastic first post!  Can’t wait to try it!

[gsxrpilot]

Everything looks great except for your Best Econ setting of 25° ROP. Just don't use that setting unless you're high enough to be at low power.

[whiskeyone2]

8 hours ago, elimansour said:

Wow! This is great and a fantastic first post!  Can’t wait to try it!

Thanks! Hope it helps or at least is a good starting point for you. 

17 minutes ago, gsxrpilot said:

Everything looks great except for your Best Econ setting of 25° ROP. Just don't use that setting unless you're high enough to be at low power.

I agree, but again that’s just what my POH says. I had heard from a Mooney flying club that under 70% power is okay to lean that far, and a generic POH (mine is in the plane right now) says under 75% power you can use best econ settings. 
 

In practice, I have been setting a 0.5 GPH higher/richer fuel flow than what best econ says, and that has seemed to work well for me. Also, I should mention I am almost always at 65% power or less. 

Edited May 8, 2020 by whiskeyone2

[gsxrpilot]

As long as you're at 65% power or less, you should be fine. At that low power you even run right at peak without any worry. 

You should be able to get just about the same speed by going 25° LOP and use quite a bit less fuel.

I know with the turbo Mooneys, following the POH power tables equals two sets of cylinders per TBO. So we've all learned better now and don't follow the POH.

 

[M20F-1968]

10 hours ago, whiskeyone2 said:

To start off, I am a new Mooney owner and this is my first topic I have created. This calculator is just something I have been using and I thought others might think it was neat. If not, please feel free to not use it. Also, disclaimer, this is not intended to be a replacement for your POH. 

 

With that out of the way, my background is in military aviation and I was always used to having a “whiteboard” to calculate approach and stall speeds, etc. So when I moved over to general aviation, I wasn’t really satisfied with “just set this in climb and this in cruise”. Usually those being the same two numbers for MP and RPM.
 

So I made this calculator based off of MY airplane’s POH. Other airplanes may be similar or exact, but it’s up to you to verify and/or edit a copy for your own use. It is sized to fit a phone screen and easy to use with drop down menus. Once I get to cruise altitude, I use this calculator while my plane is speeding up, and then I verify what settings I want based off my actual OAT and pressure altitude. The Fahrenheit to Celsius converter is just because my plane shows OAT in Fahrenheit, but my 430 TAS calculator takes Celsius. I recently added the “approximate TAS” section and it has been within a few knots when tested on real flights.
 

Anyway, this is more useful to me as an app on my phone than trying to read spaghetti charts in turbulence or just plugging in memorized, generic numbers. But do what works for you. 

Mooney M20J Cruise.xlsx 32.2 kB · 49 downloads

 

What source are you using to reply on your formulas.

John Breda

[whiskeyone2]

gsxrpilot, that is good to know, thank you! Oof, that does sound like a good reason to not follow the turbo POH. I have not had the pleasure yet of flying a turbo though. 
 

6 minutes ago, M20F-1968 said:

 

What source are you using to reply on your formulas.

John Breda

I’m sorry, I’m not quite sure what you are asking for. 

[M20F-1968]

I am addressing the formulas used in the spreadsheet for calculating variables.  The military, I believe, see that pilots understand flight parameters to that level.  I believe there are references that are used.  

I am looking for references highlighting the math invovled in these types of problems.  Is there a reference you can point me to?

John Breda

 

[gsxrpilot]

3 minutes ago, M20F-1968 said:

I am addressing the formulas used in the spreadsheet for calculating variables.  The military, I believe, see that pilots understand flight parameters to that level.  I believe there are references that are used.  

I am looking for references highlighting the math invovled in these types of problems.  Is there a reference you can point me to?

John Breda

 

Did you look at the other two tabs on the spreadsheet?

[M20F-1968]

5 minutes ago, gsxrpilot said:

Did you look at the other two tabs on the spreadsheet?

Yes I did.  I am looking to learn more about the derivation of the math.  Knowing the  physics, and the derivation of the math logic, helps understand and remember.

John Breda

[gsxrpilot]

Ok, got it. I suspect that all he did was use some simple math to convert the tables out of the POH into a easy to read on the iPhone display.

It's really a good spreadsheet. I'd certainly use it myself, maybe with a few minor modifications, if I flew a n/a Mooney. A turbo is just too simple. None of this is required. 

[carusoam]

Welcome aboard W1... and thank you for sharing your spreadsheet.   

Some background about Mooney POH engine data... They were written to inspire great plane performance.... at the cost of using up some  temperature sensitive engine bits... like cylinders...

Since the POHs were corrected over the years... get the most recent copy for the M20J for reference...

Since the last J POH is decades old... engine ops have improved for owners who have to pay the bills...

For references for better engine ops... savvy and APS have done a great job of explaining the red box theory...

https://www.advancedpilot.com

APS is generally the author of the 65% rule to avoid engine detonation... aka avoid the red box...

Quick question for you... what type of military aviation is in your background?  (We have many military and ex-military pilots around here, from a multitude of countries)

Don’t be afraid to be too technical... there are quite a few engineers, pro pilots, scientists and professors around here that support people less technical like me...   

Best regards,

-a-

[whiskeyone2]

59 minutes ago, M20F-1968 said:

Yes I did.  I am looking to learn more about the derivation of the math.  Knowing the  physics, and the derivation of the math logic, helps understand and remember.

John Breda

You can view the equations just by clicking on the Excel cell you are interested in and then looking in the formula bar. Most of it is just lookup formulas from the table itself. 
 

carusoam, 

I will look into those other methods and ideas. I am still learning about the general aviation side of things. I know the POH should be taken with a grain of salt, it seems, but I am used to the aircraft -1 being the end all rule of law. So it’s hard for me to wrap my head around differing theories and concepts without a lot of evidence to support it. Otherwise it’s just an opinion 

[carusoam]

1 minute ago, whiskeyone2 said:

carusoam, 

I will look into those other methods and ideas. I am still learning about the general aviation side of things. I know the POH should be taken with a grain of salt, it seems, but I am used to the aircraft -1 being the end all rule of law. So it’s hard for me to wrap my head around differing theories and concepts without a lot of evidence to support it. Otherwise it’s just an opinion 

I didn’t want to give the opinion that POH should be taken with a grain of salt...

Most of the data in them is quite important.  Especially when it comes to occupant safety...

Some of the data, isn’t wrong... it just means something different than what it sounds like...

 

You are not alone...  Many new 2MSers find out there is a plane load of detail available around here...

Hang out, ask some more questions, update your spread sheet... all is good!

Best regards,

-a-

[Bob - S50]

20 minutes ago, whiskeyone2 said:

You can view the equations just by clicking on the Excel cell you are interested in and then looking in the formula bar. Most of it is just lookup formulas from the table itself. 
 

carusoam, 

I will look into those other methods and ideas. I am still learning about the general aviation side of things. I know the POH should be taken with a grain of salt, it seems, but I am used to the aircraft -1 being the end all rule of law. So it’s hard for me to wrap my head around differing theories and concepts without a lot of evidence to support it. Otherwise it’s just an opinion 

Part of the difference is the difference between jets and piston.  With the jet you just set the N1, EPR, FF or some other reference and you get the desired power.  Other than the throttle you have no control over what the engine does.

With pistons, power produced can be influenced by throttle, prop, and mixture.  And even then, there are differences in prop efficiency depending on the RPM you set for the speed you fly.  To be honest, I never look at the POH for power.  My cruise power setting is almost always 22", 2600 RPM, and just barely LOP which gives me about 9.2 GPH or about 70% power.  If I climb to the point that I can't get 22" then it's WOT, 2600 RPM and barely LOP.  As I climb, the FF and % power decline.

Before we got our yaw damper, I used to count on 10 GPH giving me 145 KIAS, 9 GPH giving me about 135 KIAS, and 8 GPH giving me about 125 KIAS.  I'm now about 5 knots faster than that when the yaw damper is on.  Knowing the IAS and the density altitude I can use my E6B to get my TAS.

[Ibra]

1 hour ago, M20F-1968 said:

Knowing the  physics, and the derivation of the math logic, helps understand and remember.

I guess s/s just interpolate or lookup in POH numbers (which are also interpolated from few flight test )

On "simplified maths" instead of whole POH and real performance, here are few from my M20J, before takeoff BUT you need the IAS from your aircraft on one MP/RPM setting while flying (mine does 135-140ias at 24/24 instead of 147-149kts in POH) 
- Power % = (MP*RPM)/(29*29), say 24*24/(29*29) = 75% power
- Power vs FF: for each +10% power LOP go +1GPH and ROP go +2GPH (more a conservative)
- Power vs IAS: for each 10% power I get +10ias
- TAS vs IAS: go up +10% each +5000ft density altitude but honestly TAS just get scrambled by winds into GS and ATC routings (so let's not talk about temperature corrections, the elephant in the room is precise measurement of wind & turbulences above 1000ft, that needs 7 dimensions ) 

In practice, I don't think much about these now: keep prop at 25RPM and maintain 23MP all times, max is WOT at about +8000ft with LOP10GPH and ROP12GPH, above that the donkey starts to slowdown on power but so fuel burn, the aircraft does 140-145ias at 70% power (the book says 152-155kts)

Edited May 8, 2020 by Ibra

[carusoam]

Another interesting reference for W1...

The MAPA training references power settings in a chart of ‘key numbers’... Similar to Ibra above....

Rough power settings can be simplified by adding MP + RPM/100... 

Depending on airframe and engine... there is a set of key numbers to set your power for 65% or 75%....

Best regards,

-a-

[WaynePierce]

OK, admittedly I'm not the brightest light on the tree when it comes to IT stuff, but ... how would you add this to your iPhone to work out in the air?

 

Thank you and enjoy the fish.

[whiskeyone2]

Just now, WaynePierce said:

OK, admittedly I'm not the brightest light on the tree when it comes to IT stuff, but ... how would you add this to your iPhone to work out in the air?

 

Thank you and enjoy the fish.

I just use the Excel app or Numbers on iPhone would work too. I’m sure there are other apps available. Basically you would just download it to Files on your phone, then open it with your spreadsheet app of choice 

[carusoam]

There is a magic app that turns excel spreadsheets into usable app like presentations...

Somebody (Patrick) showed this skill for their Ovation T/O distance calculations.... around here somewhere...

Best regards,

-a-

[laytonl]

Openasapp.com is what I use.  Lee

[carusoam]

Livened the link that Lee left above...

https://www.openasapp.com
 

-a-

[whiskeyone2]

I took a quick look at OpenAsApp. It does not like the format of the spreadsheet. I think that is because I built the front page as a graphical user interface (GUI) already and not just raw data. It would probably work if I stripped the raw formulas out and uploaded that to be converted to an app. 

[tmo]

8 hours ago, carusoam said:

 

The MAPA training references power settings in a chart of ‘key numbers’... Similar to Ibra above....

Rough power settings can be simplified by adding MP + RPM/100... 

I did try looking at those, but in my stock 1980 M20K the number based on the POH charts can change slightly (+/- 1) with altitude (and I only looked up to FL140, so below critical altitude).

[Fry]

Hi there,

The following is my understanding and approach to leaning, and I would be happy to get your comments on that:

I refer to the M20J and the Lycoming IO-360. (The airflow in turbocharged engines is different, therefore the thoughts below do not apply).

Rich of Peak EGT	Lean of Peak EGT
Combustion process limited by the air/oxygen flow into the engine.	Combustion process is limited by the fuel flow into the engine.
Air flow is proportional to power.	Fuel flow is proportional to power.
Air flow is approx. proportional to the product of MP times RPM, for a given engine displacement.	For the IO-360, fuel flow (in gph) times 7.5 yields power in % of rated power.
(The lines of constant MP x RPM are almost identical to the lines of constant MP + RPM/100. The latter is easy to compute and is called the "key”.)	(To multiply by 7.5, simply multiply by 5 and add 50% of the result).
A given key is a "code" for power. 57=100%, 54=90%, 50=75%, 47=65%, etc.	With a given fuel flow, a higher "key" from the ROP just means more air and thus a cooler engine.
Excess fuel does not participate in the chemical reaction and thus cools the engine. Push the mixture in, you get a cooler engine.	Excess air does not participate in the chemical reaction and thus cools the engine. Push the prop and/or throttle in (and readjust the mixture for the same fuel flow), you get a higher “key” and thus a cooler engine.

With that in mind, I fly LOP like this and get a cool and clean, hopefully long-lasting engine:

•      Below 4000ft with full power (typically in climb), full rich.
•      The following applies only to 4000ft MSL or more, when %BHP is <=75%.
•      Full throttle, RPM as desired, and use the mixture to control power. Tune it to a fuel flow not higher than that indicated by the table.
•      A quick and easy way is to push the throttle wide open, read off the available MP, choose RPM as desired, compute the "key" RPM/100+MP and then look up the corresponding LOP fuel flow from the table at the very bottom (the two rows in the bubble). It's just important to keep below 10.1 gph as that corresponds to 75% BHP. Above that, go full rich.
•      I do not check EGT for leaning in cruise anymore, instead simply use the table. And watch my CHT. I usually end up with 300-340°F in cruise, cowl flaps closed.

Remarks:

•         At Peak EGT, the chemical reaction is complete, no excess air or fuel leads to a maximum thermal efficiency.
•          I do not believe that a faster prop shortens the engine lifetime, at least not for the IO-360, where 2700 continuous RPM is permitted, and because faster means lower forces. Nevertheless, I don't like the noise with 2700 RPMs continuously, so I typically use 2600 in cruise and even lower when flying low.
•          When flying LOP, you should also get less CO (since the combustion tends to be more complete) and thus also lower risk from CO intoxication in the cabin due to a broken heat exchanger or cabin leak.
•           While I do not use EGT for leaning in cruise, it is critical for something else: the mag check at runup. When switching from both mags to a single mag, EGT must rise on all four cylinders. If it doesn't, check the mag and/or the corresponding spark plug.

Feel free to comment on this approach. I hope I'm not preaching to the choir.

Edited May 9, 2020 by Fry