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M20J Performance Spreadsheet


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I wanted to know what the performance of our J was after we installed the GFC500 so I created a spreadsheet.  This should work for most other IO-360 NA powered J models.  It should also work for other 200 HP NA aircraft but may require modification of the IAS to CAS calculations.

Assumptions: 1)  LOP.  2) LOP power is proportional to fuel flow. 3)  At least for the '78 model, CAS is always IAS - 2.  4)  You will use .5 gallons for start, taxi, and takeoff (STTO).  5)  It takes .25 gallons more fuel during a 1000' climb than it does to cover the same distance if you were already cruising at the higher altitude.  In essence, it costs you .25 gallons of fuel to climb 1000'.  6)  Fuel saved during the descent will be consumed in the traffic pattern.  7)  It assumes a given power setting will yield the same IAS regardless of altitude.

How to use it:  Climb to a reasonable altitude that has smooth air.  I took my readings at 4500'.  Set the engine up for LOP operation at the specified fuel flow then wait a minute or two for the speed to stabilize.  Write down the IAS for use in the spreadsheet.  Enter your indicated airspeeds, FOB at engine start, and your desired reserve fuel at landing.  That's it.

With those assumptions, here is what the spreadsheet does:

You enter the IAS, the spreadsheet subtracts 2 knots to get CAS.

I used my E6B to get a CAS to TAS conversion factor for each altitude.  The spreadsheet takes that factor times the CAS to get a TAS for each altitude and power setting.

Since power is proportional to FF, it simply takes TAS and divides by FF to get MPG.

For range it starts with your FOB, subtracts your desired reserve, then subtracts STTO and climb fuel (.5 + 1.5 for 6000' for example).  It divides the result by the FF to get time at cruise and multiplies by TAS to get range.

For headwind ranges, it does the same thing except it subtracts the headwind component from the TAS before it multiplies.

201CB Performance.xls

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Bob, have you seen the method of turning a spreadsheet into an app for your smart phone?

Something to consider if you want app simplicity blended with your awesome Mooney performance spreadsheet...

Best regards,

-a-

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8 hours ago, carusoam said:

Bob, have you seen the method of turning a spreadsheet into an app for your smart phone?

Something to consider if you want app simplicity blended with your awesome Mooney performance spreadsheet...

Best regards,

-a-

No I haven't.  Tell me more.

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Just now, midlifeflyer said:

It's called OpenAsApp https://www.openasapp.com/ 

I've seen some things done with it but haven't tried to create one myself.

I created one on it, once you figure out how to format the data it is pretty easy to use. The biggest drawback was that if I left the app to go to another one it does not save the data that has been input, it refreshes everything to original values.

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On 6/9/2020 at 4:06 AM, Skates97 said:

I created one on it, once you figure out how to format the data it is pretty easy to use. The biggest drawback was that if I left the app to go to another one it does not save the data that has been input, it refreshes everything to original values.

Richard @Skates97,

That was an issue with Openasapp when I first used it.

I requested this mod as well as some others. They've done a good job of implementing it so you now have options to use last, as a one off or every time (can't remember all the options) but it works well. 

The developer has been very responsive to suggestions. 

PS - I have no skin in the game. The guys are out of Germany I believe.

Would be interested in the other one you use

regards

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1 hour ago, patrickf said:

Richard @Skates97,

That was an issue with Openasapp when I first used it.

I requested this mod as well as some others. They've done a good job of implementing it so you now have options to use last, as a one off or every time (can't remember all the options) but it works well. 

The developer has been very responsive to suggestions. 

PS - I have no skin in the game. The guys are out of Germany I believe.

Would be interested in the other one you use

regards

I haven't been following to see what changes have been made. I need to log back in and check it out. I'll upload some stuff tomorrow when I'm on my computer and not phone. 

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