Mike Busch Webinar on Flying Efficiently

[Bob - S50]

Mike Busch's latest free webinar titled "Flying Efficiently in a World of $7 Avgas" is now available on line:

 

https://www.savvymx.com/index.php/webinar

 

The presentation is fairly short but there are a few interesting questions in the long Q & A afterwards.

 

On the other hand I read a quote somewhere that went, "I didn't buy a fast airplane to fly slowly!"

 

Bob

[201er]

Well just flying a Mooney is in itself flying efficiently...

[DrBill]

I moved from a Sundowner to a Mooney and the effeciency improved at least 30%. 

BILL

[PTK]

I watched the webinar. It's awesome as to be expected from Mike Busch. 

 

He only referred to three Cessna models. Would have been interesting to see about the Mooney.

 

Which brings me to my question:

 

From a practical standpoint where is our Carson airspeed? At what altitude, fuel flow and power setting.

 

Byron?

[1964-M20E]

Well my POH has 100MPH as best glide speed so that would be 132IAS.  I tend to see 140IAS between 10k and 12k WOT, 2500RPM, 8.5GPH, CHT 351, EGT 1195, 126HP, 63% power all values +/- so that is close enough for me and it fall into what Mike was saying.

[1964-M20E]

The other thing is to play with is lower RPMs but I'm restricted from operation between 2000 to 2350.  So that does not leve me mcuh to play with 1950 or 2400RPM

[Bob - S50]

Did a little calculating for our '78 J.  Best glide at max gross is 91KIAS.  That makes Carson's speed about 120 KIAS.  At 2200 RPM this happened around 10,000'

 

If you watched the webinar including the Q & A, someone pointed out that the fuel saved at high altitude would be offset by fuel wasted getting that high.  He wondered how far you had to fly to make up for the extra climb fuel.

 

I made a spreadsheet to try and figure this out for our plane.  Bottom line first for the impatient, then the assumptions for those who care to scrutinize.  I think I've attached a PDF file that shows the data, but just in case it doesn't attach, here is what I found:

 

200 nm or less stay as low as terrain and ride permit.

300 - 500 nm, it doesn't really matter, they are all about the same

600 nm or further, go high.

 

If you want a rule of thumb based on my assumptions and calculations, weather, ride, and terrain permitting; use an altitude that is the distance times 20.  That is, if you are going to fly 150 nm, fly at 3000'.  If you are going to fly 450 miles, cruise at 9000'.

 

Here's what I did:

 

* Since my POH did not give settings for 2000 RPM to a high enough altitude I used 2200 RPM.

* I assumed the highest power setting at that RPM for each altitude was WOT (but may not be for lower altitudes).

* Used best rate speed for climb so I could use the time/dist/burn to level off graph.  I never climb this slowly.

* Used the econ cruise leaning data even though it is still richer than I fly (Mooney uses 25 ROP).

* Subtracted distance covered in the climb for each distance to determine cruise distance

* Divided that by cruise speed to get cruise time

* Multiplied that by burn rate to get cruise burn

* Added climb burn to get total burn.

 

In reality, being higher would allow you to save some fuel during a longer descent at reduced power but I had no way to calculate that with my POH.

N201CB Total Burn.pdf

[Bob - S50]

After some thinking I came up with a way to estimate fuel saved during a descent.  Bottom line, I decided if I left the power set, used a descent of about 500 FPM, and assumed the speed increased by 30 - 40 K, it would save about 0.1 gallons for each 1000' of descent.  Based on that I modifed my spreadsheet which is attached.  Now I would have to say that:

 

Up to 300 miles it doesn't really matter.  It should make a difference of less than a gallon.

 

Beyond 300 miles, go high, around 10,000 or 12,000.  Personally I'll probably still fly between 6500 and 9500 just for better breathing air and a nicer view.

N201CB Total Burn.pdf

[Bob - S50]

OK, I'm crazy.  I had some spare time on my hands so I wrote an HTML file that will allow you to enter your own aircraft performance data and compare total fuel used at various cruise altitudes.  It should work for any model of aircraft including brand b, c, and p.  It also allows you to enter different HW or TW values at different altitudes to see if it is worth climbing or not.

 

For example, I saved one version set up for 2200 RPM/WOT on our '78 J and another set up for 2400 RPM (my normal).  Using it I found that at 2200 RPM, it only took an increase of 1.5 knots of HW for each 1000' climbed to competely negate any fuel savings normally gained by climbing.  Using my 2400 RPM data it took about 2 knots/1000'.

 

The default values in the file are for my '78 J using WOT and 2200 RPM.  There are instructions at the bottom of the file that tell you how to modify the default values.  If you want pages for different settings (like I did), simply make the changes then save the file using a new name.  For example I saved one as "Best Altitude Calulator 2400.html" with my 2400 RPM settings.

 

Hope you find it interesting and maybe even useful.

 

Bob

Best Altitude Calculator.html

Altitude Burn Difference Calculator.html

[Awful_Charlie]

Well done Bob

 

Here is an Excel worksheet which does something similar.  It contains macros, hence it is zipped, and has some instructions on the first tab.  It evolved over time, so could be tidied up a bit, for instance with a graphic output like Bob's.

 

Figures are Bravo POH figures (for MTOW where applicable), and with the 50fpm decrement for prop-deice - you may need to adjust.  The wind levels selected are those on the UK Metform 214/414, so you might want to fiddle with those too.

 

The POH tab is a bit convoluted as I tried to minimise the manual conversion of the POH graphs into tabular data, and it also shows some of the anomalies in the Lycoming figures for fuel burn.

 

When you've set the input data, then select an altitude that has your desired speed/fuel economy trade-off, then use the 'D-T-F with wind' tab to look up the time and fuel for your required leg length (in 100's of nm) against the altitude.AltSel.zip

[Super Dave]

Fltplan.com allows you to customize the climb, cruise, and descent fuel flows and airspeeds at various altitudes. Once you've entered the data, it's easy to compare trip times and fuel burns at various altitudes using actual winds aloft forecasts. You can even set up multiple performance profiles if you want to compare LOP, ROP, etc.

[Bob - S50]

Fltplan.com allows you to customize the climb, cruise, and descent fuel flows and airspeeds at various altitudes. Once you've entered the data, it's easy to compare trip times and fuel burns at various altitudes using actual winds aloft forecasts. You can even set up multiple performance profiles if you want to compare LOP, ROP, etc.

DTC DUAT let's you do the same thing.  On DUAT you use an average flow rate for climb, cruise, and descent.  You select your altitude and it retrieves and uses the winds for you.

 

However, I didn't write the file for planning a specific flight, I wrote it more to get a feel for what works best for my plane.  If I start with no wind I can see that at 100 nm, I use the least fuel by staying as low as possible.  At about 170 or 180 miles they all kind of become equal.  Beyond that I start saving fuel by going higer.  However, the difference between best and worst is less than 2 gallons of gas unless I'm going over 400 nm and the difference between 8000 and 12000 is less than a gallon all the way to 600 nm which is about the limit of my posertior endurance.

 

If I put in HW that increases by 3k/2000' from 0k at 2000' to 15k (value of -15) at 12000' it makes no difference what altitude I fly at, they are all the same.  That tells me that an increase of as little as 1.5k of HW for each 1000' of climb will negate any savings.  In other words, since wind (HW in this case) usually increases with altitude, ride and terrain permitting, I might as well stay low.  If the wind increases more than 1.5k/1000 I definitely want to stay low.

 

Just something to play with.

 

Bob

[PTK]

OK, I'm crazy.  I had some spare time on my hands so I wrote an HTML file that will allow you to enter your own aircraft performance data and compare total fuel used at various cruise altitudes.  It should work for any model of aircraft including brand b, c, and p.  It also allows you to enter different HW or TW values at different altitudes to see if it is worth climbing or not.

 

For example, I saved one version set up for 2200 RPM/WOT on our '78 J and another set up for 2400 RPM (my normal).  Using it I found that at 2200 RPM, it only took an increase of 1.5 knots of HW for each 1000' climbed to competely negate any fuel savings normally gained by climbing.  Using my 2400 RPM data it took about 2 knots/1000'.

 

The default values in the file are for my '78 J using WOT and 2200 RPM.  There are instructions at the bottom of the file that tell you how to modify the default values.  If you want pages for different settings (like I did), simply make the changes then save the file using a new name.  For example I saved one as "Best Altitude Calulator 2400.html" with my 2400 RPM settings.

 

Hope you find it interesting and maybe even useful.

 

Bob

Excellent work Bob.

Very interesting and useful indeed.

Thank you.