How fuel planning?

[Bostar 7]

Hi

Maybe someone can clarify this doubt I have when I try to understand how calculate the fuel for this plane.

I'm following the example which appears in the chapter about the performance in the real POH. My doubts appear In the "True Airspeed for Cruise" section, where they calculate the True Cruise Airspeed. For this calculate, they claim "The estimate average cruise weight is approximately 9150 lbs (4150kg)". My problem is I haven't found where come from this figure, how calculate the "average cruise weight".

Something similar happens when they calculate the reseve fuel: "this example assumes the average cruise weight while using Reserve Fuel to be 8600lbs".

So, my question is: how calculate these average weights?

Maybe it's something very basic, but right now I totally lost.

Thank you in advance.

Regards.

[fppilot 4,354]

14 minutes ago, Bostar said:

Maybe someone can clarify this doubt I have when I try to understand how calculate the fuel for this plane.

 

Are you attempting to estimate fuel use for flight planning purposes?  Each time I purchase a new airplane I load it up, fly, and log the fuel burn during climb to typical altitudes, at cruise at those altitudes, and during descent.  I use Fltplan.com for my flight plans.  That site contains a library of tables of performance for quite a number of aircraft.  The C90 was not one of those, so I started with a similar class aircraft, modified that table based on my logged performance, then saved it.  When developing a flight plan I just identify it as the one I will be flying, specify the cruise altitude, and the results are very, very close. 

Here is what my C90 table looks like with the exception that there are four data boxes not seen here where approx climb and descent fuel burn is specified.  Climb FF at 2,000 AGL (1,000); Climb FF at 25,000 (400); Descent FF at 24,000 (360); and Decent FF below 2,000 (400).

[FDEdev 955]

7 hours ago, Bostar said:

So, my question is: how calculate these average weights?

Scratching my head about this one.  In which section did you find this? I didn't find anything in the performance section.

Using average weights for planning doesn't make sense and the performance tables are providing climb data in 500lbs steps and cruise data in 1000lbs steps.

Fuel planning should be done like with all other planes, by using the climb, cruise and descent tables.

 

Edited December 12, 2019 by FDEdev

[Bostar 7]

@fppilot:  Thank you very much for sharing your table. Let me ask you: when you are gathering all this information, do you use the default payload (full load)? My intention is using this plane in FSEconomy so I will have a random payload each flight.

@FDEdev I have found this POH on Scribd.com. As appears in the cover, it was published in 1994 and updated in 2000. You can find the example I mentioned in the first post inside Section V, where there is a complete tutorial about how calculate the fuel and the performance using "a proposed flight from Billing to Denver" detalling all the steps (TO, climb, cruise, etc). It's very informative, except that point about average cruise weight.

Edited December 12, 2019 by Bostar

[FDEdev 955]

Just checked the manual and this is just an example flight, starting at MTOW.

It's says e.g. 'estimated approximate cruise weight' since there are quite a few variables for taxi, take off and climb.

Furthermore weight during cruise is only available in 1000lbs steps, hence it's simply not possible to provide more precise data.

These estimates are based on MTOW for a specific routing and altitude and it shouldn't keep you from precise planning.

Edited December 12, 2019 by FDEdev

[fppilot 4,354]

11 hours ago, Rob_Ainscough said:

Hi Frank,

May I ask what you use to log fuel burn?  Manual or logging to file?

Cheers, Rob.

Rob. Manual.  I just time my climb out to my typical cruise altitude, 20,000 or 21,000 for the C90, and read the elapsed time and remaining fuel at the start and end of the climb. I assume the Fltplan.com calculation is linear. 

For cruise I log burn for a few six-minute intervals and multiply times 10.  Simple.  On a long flight I change cruise altitudes occasionally and observe burn at the new altitude, again 6 minute intervals.  After two or three maiden flights I usually have observed several altitudes 4,000 ft apart.  Ex 8, 12, 16, 20, 24.  I fill in altitudes in between with eyeball/linear method.  

I have used this method all the way back to Flight Assignment: ATP and my role as chief pilot for the very first VA, Sunair, which was founded on Prodigy.  This process and method is amazingly accurate.

[fppilot 4,354]

7 hours ago, Bostar said:

Thank you very much for sharing your table. Let me ask you: when you are gathering all this information, do you use the default payload (full load)? My intention is using this plane in FSEconomy so I will have a random payload each flight.

You do not need to overly complicate it.  You just need to load enough fuel for the trip and a reasonable reserve.  It is entertaining to see how close you can come, but at the end of the flight you should still have a good amount of fuel on board and verify that your planned burn was within an acceptable standard.  If not, you adjust the table until you get acceptable (not perfect) results.  For instance, I do not often place an arrival or approach into my planning as they can change enroute, so I leave a cushion with what I load.

I usually position 4 persons (total) in the cockpit/cabin and reasonable luggage/cargo, and with a more than adequate amount of fuel.  The aircraft I fly most are the Turbine Duke v2, the Milviz B55 Baron and Milviz C310, and recently the Carenado DA62 (still developing table).  My Excel flight log shows an average of 1.99 hours per flight overall, 2.14 hrs for the C90, 2.18 for the Turbine Duke v2, 1.8 for the Baron, and 1.95 for the 310.

I do not over complicate fuel planning.  Fltplan.com will estimate my burn from calculations it performs from the table.  For a planned Baron 55 flight at cruise altitude of 7,000 ft. from Bloomington, Indiana, (KBMG) to Ann Arbor, Michigan, (KARB), with four persons on board, it estimates a 1.12 hour flight.  I rarely fly with only 30 minutes reserve. Fltplan asks how much fuel you have loaded in hours and minutes.  So in this case, providing a cushion, I would likely load for 1.8 hours, which is 01:54.  The resulting flight plan log shows burn estimated at 35.2 gallons.

If instead I entered my loaded fuel as 0400 (4:00 hours) to account for a return flight, due the additional weight of the fuel Fltplan.com estimates the burn at 35.6 gallons (one way).  So the site is clearly taking into account the additional fuel weight. 

If I tell the site 6 persons and 01:54, it estimates burn at 35.7.  So it also clearly increases the weight factor for number of persons aboard.

If I tell it 6 persons and 04:00 fuel , it estimates 36.4 (one way).
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[fppilot 4,354]

Realized later that I posted a table for the C90 (lbs for fuel) but then posted examples for the Milviz B55 Baron (gallons).  For those interested, here is the flight plan with fuel burn in lbs for the C90 for the same flight, but at 17,000 ft.

[Bostar 7]

@fppilot Thank you for detailing all the steps. I sincerely apreciate. Until now I had checked fltplan.com looking for charts (particularly canadian airports) and I didn't know they offer this kind of features too. Very interesting. I'll check it out with attention.

Edited December 13, 2019 by Bostar

[fppilot 4,354]

4 hours ago, Bostar said:

@fppilot Thank you for detailing all the steps. I sincerely apreciate. Until now I had checked fltplan.com looking for charts (particularly canadian airports) and I didn't know they offer this kind of features too. Very interesting. I'll check it out with attention.

Noticed in the above posts that I failed to mention that fuel planning is not so precise as it is based on forecast winds aloft and actual winds will vary.

That said. Bostar.  Fltplan.com is North America and Caribbean only, perhaps Mexico.  it has an app for both IOS and Android named FlltplanGo.  I do not have time to update the information from the link below, and it is from 2015.  Check out the link below to see just what the features were, and they have grown since.

https://www.avsim.com/forums/topic/471387-fltplan-go-app-for-ipad-way-cool/

Edited December 13, 2019 by fppilot