Fuel Calculations

[wilivarob]

Group, I have a question about calculating the fuel needed to make flights.

I found the following information when searching; take how much fuel is consumed in ascent, cruise and descent and from there take the average; the problem is that the manual that comes with the plane (C337 Skymaster) only has cruise tables, nothing about how much it consumes in ascent or descent.

I looked for an original manual from 1971 and found a consumption table for ascent but for takeoff "maximum climb rate...", nothing about normal climbs; even so, nothing about consumption in descents.

In a Facebook group they told me to take the time of a flight and how much I spent on fuel to know the consumption per hour and knowing how much the plane consumes per hour, the calculations could be done.

Still, I would like to know if the airplane manual contains detailed information on the airplane's fuel consumption, only performance charts. Can it be calculated with just that? What would the formula be? What would you do in such a case?

Thanks, I'll keep an eye out.

[CAP1234]

On 1/11/2025 at 2:00 PM, wilivarob said:

Group, I have a question about calculating the fuel needed to make flights.

I found the following information when searching; take how much fuel is consumed in ascent, cruise and descent and from there take the average; the problem is that the manual that comes with the plane (C337 Skymaster) only has cruise tables, nothing about how much it consumes in ascent or descent.

I looked for an original manual from 1971 and found a consumption table for ascent but for takeoff "maximum climb rate...", nothing about normal climbs; even so, nothing about consumption in descents.

In a Facebook group they told me to take the time of a flight and how much I spent on fuel to know the consumption per hour and knowing how much the plane consumes per hour, the calculations could be done.

Still, I would like to know if the airplane manual contains detailed information on the airplane's fuel consumption, only performance charts. Can it be calculated with just that? What would the formula be? What would you do in such a case?

Thanks, I'll keep an eye out.

 

What manual are you looking at ? The actual real POH (pilot's operating handbook) will have all of necessary data in there. From my understanding there are tables in there for fuel consumption during various stages of flight. You can find one on google. 

In order to calculate fuel - I would probably first determine:

• How long it will take to climb to cruising altitude
• How long is the cruise section itself
• Time it takes to descend from cruise to final approach
• You also have think about any diversion fuel (alternate fuel)
• Final reserve (piston engine so I would go with 30 mins day VFR or 45 mins at night), IFR will be 45 mins for piston engine

Once you have figured out the above - you can then go into POH and find out the figures you need. Typically on most POH there is always a example which shows you how to calculate fuel at various stages. 

Edited Monday at 02:55 PM by CAP1234

[wilivarob]

31 minutes ago, CAP1234 said:

 

What manual are you looking at ? The actual real POH (pilot's operating handbook) will have all of necessary data in there. From my understanding there are tables in there for fuel consumption during various stages of flight. You can find one on google..... 

Thanks for your reply, I'm leaving the 2 pdfs, the one of the faired plane and one that I found on the internet from 1971.

On the faired one there are only the cruise tables, nothing about climbs and descents.

In the 1971 one, there is a climb table and the cruise tables, but nothing about descents.

Carenado C337

1971 POH

[CAP1234]

2 hours ago, wilivarob said:

In the 1971 one, there is a climb table and the cruise tables, but nothing about descents.

That's the one - So in this case I would basically assume that fuel included in the cruise portion also includes fuel for descent. Remember for descent you will be using lower power settings so overall fuel consumption will be lower anyway. 

So for example you have a cruise for 2 hours and then descent you have calculated is 20 mins or so (rough estimate). You can potentially use the same figure that you used to work out fuel for cruise to also include that 20 mins for descent. If it is 60lbs/hr in cruise - So you are burning 1 lb for every min, in this case 20 mins for descent will be 20 lbs of fuel which you can add to your cruise fuel. 

2 x 60 = 120 lbs plus 20lbs for descent, 140lbs. (this is just rough estimate but you get the idea of how it works)

Edited Monday at 06:05 PM by CAP1234

[wilivarob]

18 hours ago, CAP1234 said:

You can potentially use the same figure that you used to work out fuel for cruise to also include that 20 mins for descent.

Ok, I'll try to make a flight with this formula to calculate the descent with the cruise values. Right now I'm calculating the descent values, half of what it consumes in ascent.