Finding fuel used in climb and enroute

[skateosiris]

Hi, I im stuck trying to find the fuel to be used during a climb and enroute portion of flight. I know for the start it is 1.1 gallons for start, and taxi. But for climb and enroute do I find that using my E6B or do I use the time fuel and distance chart in the 172 POH?

Any help would be greatly appreciated.

[AuxBatOn]

Hi, I im stuck trying to find the fuel to be used during a climb and enroute portion of flight. I know for the start it is 1.1 gallons for start, and taxi. But for climb and enroute do I find that using my E6B or do I use the time fuel and distance chart in the 172 POH?

Any help would be greatly appreciated.

The E6B isn't aircraft specific isn't it? Pretending it would work for a 172, would it also work for a Cherokee?

The POH is aircraft specific. Use that. The E6B is only to do some calculations. Treat is as an old school calculator.

[Hedley]

In the absence of data in the airframe POH, you
could always look at the engine manufacturer's
manual, but nobody ever does.

I will be sh1t on from great heights for telling you
this, but I fly many many different piston engine
aircraft types, and the following has worked for me
for over 30 years. I know, not very experienced
compared to the "experts" here but ...

Learn about Brake Specific Fuel Consumption (BSFC)
which is easy as falling off a log.

A piston engine will burn slightly less than one half of
a pound of fuel per hour to make one horsepower,
properly leaned. With a rich mixture, it's around
0.5 lbs/hr/hp.

Let's look at your 172. Assuming it's an older 172
with 150hp - I really, really hope you have a clue as
to what engine and horsepower your aircraft has - it's
going to burn 150 x 0.5 = 75 lbs of fuel per hour at
wide open throttle. Avgas is 6 lbs per US gallon, so
in climb you're going to burn 75/6 = 12.5 gph.

That's a very good number to use for your time spent
climbing to altitude. At 70% power, you're going to
burn just under 9 gph.

However. The mixtures are typically quite rich in
aircraft engines at WOT to avoid detonation. Here's
an even easier way to cut it.

With 150hp, on climbout, drop a zero, and you should
see 15 gph climb, 10 gph cruise. Very rough numbers,
but you'd be amazed how well it works.

For example, in the R-985 Stearman I fly, it's 450 hp
so I might expect 45 gph during the climb, and 30 gph
in cruise.

In the 700hp hot-rod Harvard that I fly, I might expect
70 gph on takeoff, and 50 gph in cruise.

Of course, you can always cruise with less power than
70%, and I can't emphasize enough the importance of
leaning the mixture - even in the climb!

[AuxBatOn]

Hedley, I personally think that it's a great way of keeping things simple, however I found that with most people, as soon as there is a bit of "real" Engineering that "is not required" to get the licenses, they don't want to hear a thing about it.

[The Old Fogducker]

Stand-by ... I feel some percolation taking place in my descending colon.

A little sugar to stimulate the peristalsis action, and I'll be ready to drop a five coil steamer....in one continuous piece with a nice curl on the tip if I really concentrate.

What a picture!

Sort of like my own version of an inukshuk to show others I've been here before them.

All in fun Hedley.

Fog

[Hedley]

BSFC is so simple, and works so well, I don't know why
it isn't required training for a PPL.

For example, a while back I had to ferry a PT-22 Ryan.
Never flew one before. First takeoff was solo, checked
myself out in it. No cruise performance data in the dash
one.

But, I did know it had a 24 gallon tank, and a 160hp
engine, so I knew it would burn 16 gph on takeoff and
climb, and 11 gph in cruise, so I knew that I wanted
to make my legs at most 1.5 hours, burning:

11 x 1.5 = 16 gallons, leaving

24-16 = 8 gallons reserve, which is:

8/11 * 60 = 45 min reserve.

Numbers worked out almost perfectly.

But what would I know?

[MichaelP]

The Diamond AFMs publish fuel consumptions for different power percentages.
The Cessna POH has a time distance and fuel consumption chart for the climb.

I usually increase the time to climb while reducing the climb rate as I always look at cruise climbing enroute rather than best climb performance.
If you use 80 - 90 KIAS cruise climb in the Cessna you will gain more power from the engine while reducing the rate of climb by 100 - 200 feet per minute.

By looking at the time and fuel in the Cessna climb chart you can work out how much fuel the Cessna is supposed to use in the climb.
I would add at least 10% to this figure.

I flew a Cessna 172 to Kamloops from Boundary Bay, climbed to 7,500 feet enroute while leaning the mixture for best power in the climb. It used 10.3 USG per hour overall and I did not have enough fuel to fly back with a reserve at that rate.
I landed at Chilliwack on the way back, added some fuel, and increased the gross weight through my own consumption as well!

What is an eye opener is the lean assist system in the G1000.
Leaning the mixture nets a 2 gph reduction in the cruise with the IO-360 engine!
The fuel consumption in a DA40 is a lot less than that of the 150hp C172 I took to Kamloops, but it shouldn't be!
Engine setup and imprecise leaning get us all!

I am a great believer in leaning the mixture, and this is something we all need to practice.
(Unless we fly Rotax 912 engines where the mixture is automatically leaned from the ground up).

So the fuel use in the climb should be based upon the mid altitude full power point of that climb times the time to climb.
Remember you do not get full power with a fixed pitch propeller, and then the amount of power you have is reducing with height gained.

Cruise fuel should be based on TOC (top of climb) to TOD (top of descent).

Descent fuel should be based upon an estimate of the reduced power fuel consumption at the mid descent height.
Then an allowance is made for approach and landing.

[Hedley]

flew a Cessna 172 ... used 10.3 USG per hour overall

With 150hp, on climbout, drop a zero, and you should
see 15 gph climb, 10 gph cruise. Very rough numbers,
but you'd be amazed how well it works.

Q.E.D.

[LousyFisherman]

With 150hp, on climbout, drop a zero, and you should
see 15 gph climb, 10 gph cruise. Very rough numbers,
but you'd be amazed how well it works.

I've got to disagree with this one Hedley, at least for smaller engines (100HP or less). If my C150 (100 HP) ever burns 10gph I better be landing at an airfield with an AME, or a fire truck If it burns 7GPH I better be close to an alternate landing site It burns 5 GPH no matter what. It may burn more if I am doing circuits but the rest of the time.....

However, one thing I always do, which was not taught at my flight school, is to dip my tanks after every (or at least most) flights. This way I am immediately aware of any unusual fuel consumption which usually indicates a problem. This is also how I know it burns 5GPH, no matter what.

LF

[Geko]

Thanks for the tips Hedley.

I will take all of your advice as I want to figure out the rough fuel burn for a newer low airframe/engine time 180hp 172 and then see how well it matches up in the real world.

[Hedley]

180hp 172

BSFC for pilots: drop a zero, and that's your GPH at wide
open throttle, for climb, so 180hp is 18 gph.

Two-thirds of that (for a 66% power cruise) is 12 gph.

Of course, if you run a low cruise power setting, you might
burn 10 or even 8 gph, especially if you bother to lean
the mixture.

my C150 (100 HP) burns 5 GPH no matter what

Fascinating. Ok, I will estimate that a carbureted aircraft
engine (even with smaller, more efficient combustion chambers)
will have BSFC no better (lower) than 0.45, which means that
with 5 us gph you are producing at most:

5 gph * 6 lbs/gal = 30 lbs/hr
30 / .45 = 67 hp

So, with masterful leaning of the mixture, if you are really
only burning 5 gph, you are really only producing at most
67 hp - not 100hp, which is quite possible.

Most people don't lean the mixture that well, especially
with carbureted trainers, who always seem to fly around
with the mixture knob all the way in.

[Geko]

180hp 172

BSFC for pilots: drop a zero, and that's your GPH at wide
open throttle, for climb, so 180hp is 18 gph.

Two-thirds of that (for a 66% power cruise) is 12 gph.

Of course, if you run a low cruise power setting, you might
burn 10 or even 8 gph, especially if you bother to lean
the mixture.

Which is what we burned on my first flight in that plane with an instructor as my annual check ride. I have been trying to do my best at leaning which will be a must for any trips in this plane unless I want to end up in a heap of trouble.

[Hedley]

Every aircraft should have one of these:

http://www.aircraftspruce.com/catalog/i ... essure.php



You will be amazed what difference in the gph you
see as you lean the mixture.

With our Pitts S-2B's, I can burn anywhere between
28 gph and 8 gph, by moving the throttle and mixture,
which is a big difference to my endurance with 23 gallons
usable.

[Geko]

I was thinking the same thing but unfortunately it isn't my aircraft.

[Big Pistons Forever]

It is important to note that the POH figures are the best possible case. That is they represent a new perfectly rigged airplane flown by a test pilot. The chance of actually achieving these numbers in your average PPL piloted 10,000 hr rental machine with its on condition engine climbing with the ball half out of the cage, is virtually nil. Knowing how to use the POH is important but put at least an extra 10 % extra on any fuel burn you calculate...and always plan to land with at least an hour of reserve fuel.

For TLAR calculations I use the same method as Hedley, it works surprisingly well and I have found I always land with a little bit more fuel than planned

[Geko]

It is important to note that the POH figures are the best possible case. That is they represent a new perfectly rigged airplane flown by a test pilot. The chance of actually achieving these numbers in your average PPL piloted 10,000 hr rental machine with its on condition engine climbing with the ball half out of the cage, is virtually nil. Knowing how to use the POH is important but put at least an extra 10 % extra on any fuel burn you calculate...and always plan to land with at least an hour of reserve fuel.

For TLAR calculations I use the same method as Hedley, it works surprisingly well and I have found I always land with a little bit more fuel than planned

I'd agree with that. The only exception is that for the most part all the aircraft at the club I fly with seem to fly within the standards set forth by their respective POHs. Of course that is only true if they are leaned correctly.

[AOW]

The only exception is that for the most part all the aircraft at the club I fly with seem to fly within the standards set forth by their respective POHs. Of course that is only true if they are leaned correctly.

Now, do they actually meet all of the standards set in the poh? does the TAS match what the POH says for a given fuel burn/power setting? If so, that is very impressive, but from most club airplanes I've seen, there is at least a 5% drop in performance compared to the POH. Probably a combination of engines not producing rated horsepower, eroded props, far from clean airframes, etc. In some cases, the POH specifies that performance data is based on an airplane with wheel pants... which are often removed by clubs/schools...

[Hedley]

In most cases, the POH's were written by salesmen

[Geko]

The only exception is that for the most part all the aircraft at the club I fly with seem to fly within the standards set forth by their respective POHs. Of course that is only true if they are leaned correctly.

Now, do they actually meet all of the standards set in the poh? does the TAS match what the POH says for a given fuel burn/power setting? If so, that is very impressive, but from most club airplanes I've seen, there is at least a 5% drop in performance compared to the POH. Probably a combination of engines not producing rated horsepower, eroded props, far from clean airframes, etc. In some cases, the POH specifies that performance data is based on an airplane with wheel pants... which are often removed by clubs/schools...

I'm no expert or experience pilot so there probably is a difference of 5% from the word for word published figures. My old flight planning technique was to use the figures from the POH for taxi, run up, take off, climb, and cruise. No need to jump into any multipronged message board attacks as I realize my lack of critical thinking here.

Ultimately, I guess I meant the other planes are a lot closer to published figures than in comparison to the actual fuel burn in the 180HP 172 versus the amendments in its POH.

[skateosiris]

Hi, thanks for all the replys, but im confused, like say the pressure altitude for the ground is 2300, and for cruise the pressure altitude is 5800, im kinda confused on how to figure it out because the values under the pressure altitude heading increase by 1000's, so would I choose whatever is closest to 2300 and 5800.

Then for distance to climb and time do I have to subtract the values that are associated with 2300, and 5800?

Thanks

[C-GPFG]

Yes, interpolate the value for the ground pressure alt. and cruise pressure alt...find the difference between the two and you'll have your answer. The Cessna POHs give an example of how do to this.

[MichaelP]

The Diamond DA40 with the IO-360 engine and a CSU AFM specifies 65% power as being 8.2 GPH.

At 2,000 feet PA 65% power is 24.2" and 2,200 RPM for the DA40-180, and the G1000 lean system agrees; we see 8.2gph and 1480 to 1510 degrees EGT.

If you fly this power setting full rich the fuel flow is over 10 GPH!

The TAS also agrees with the book figures in our DA40 aeroplane.

Not many people do their ICT calculations in flight to learn what the TAS is, and nor do they do it as part of their preflight planning.

Why do the FD's have the temperature besides the wind for each PA?
So you can work out what the IAS should be for your aircraft that corresponds with the TAS.

[AOW]

Not many people do their ICT calculations in flight to learn what the TAS is, and nor do they do it as part of their preflight planning.

Why do the FD's have the temperature besides the wind for each PA?
So you can work out what the IAS should be for your aircraft that corresponds with the TAS.

This is exactly why I made sure that the nav logs for the school I worked at had a box for IAS for each cruise leg. I saw first hand too many students who ignored some of the basic lessons that they were taught! One student discovered that you could fly a C150 at 68 kts from takeoff to landing! If you set cruise power before setting the cruise attitude, the aeroplane would hold a steady altitude and maintain 68Kts (Vy)!!! I asked him what his flight planned IAS was, and (he had actually filled in the flight planning form correctly; I wouldn't take off until it was complete) we were well below the planned 86 KIAS. [after returning to full power, and following a proper A-P-T procedure, we saw 85 KIAS!]

[AOW]

Hi, thanks for all the replys, but im confused, like say the pressure altitude for the ground is 2300, and for cruise the pressure altitude is 5800, im kinda confused on how to figure it out because the values under the pressure altitude heading increase by 1000's, so would I choose whatever is closest to 2300 and 5800.

Then for distance to climb and time do I have to subtract the values that are associated with 2300, and 5800?

It all comes down to how precise you want to be... you could interpolate for every hundred feet between the published figures and use this (you could even go down to the change for every foot of pressure altitude, but that is a bit of overkill)... or you could round off (2000 feet to 6000 feet)... Ask yourself why you are doing this calculation, and how precise you have to be...
Possibly the MOST important part of the whole table, however, is the NOTES and CONDITIONS section -- READ IT!!!

[AOW]

Here is a scan of the 1977 C172N POH (don't get me started on the H2AD engine!).

TFDtoClimb.JPG (44.44 KiB) Viewed 3509 times

Using the rounded example, you can see that the climb to 6000 feet (from sea level) takes 10 minutes, burns 1.9 Gallons of gas, and covers 12NM (in ZERO wind). But you only want to know the numbers from your takeoff at 2000' PALT, so we look at the time fuel and distance to 2000' (from sea level): 3 min, 0.6 Gal, 3 NM. Now subtract those numbers from the 6000' numbers and you get: 7 minutes, 1.3 Gallons, and 9 NM.

Now, compare the actual temperatures for your day of flight with the ICAO standards (11ºC at 2000 and 3ºC at 6000', etc.) If it is colder than this, don't do anything, but if it is warmer, read Note 3: increase time, fuel and distance by 10% for each 10ºC above standard. This is a nice easy to work with number, so you can go as far as saying that for every 1º above standard, you can add 1% to all of your numbers.

Let's say that the FD's 6000' temperature is +14º. That is 11º above standard, so you need to add 11% to all of the numbers (multiply by 1.11). Now you have 7.77 minutes, 1.443 gallons, and 9.99 nm -- use your head, and round off to usable numbers, as in 8 minutes and 1.4 gal and 10 NM.

Next, factor in the wind. If you want to be really fancy, you can average the wind between ground level and your cruise altitude, and plot that on an E6B along with your average IAS of 71 kts (don't forget to convert to TAS) and figure out how far you will travel in the 8 minutes that you will spend in the climb.

OR, you can figure out the worst case scenario, and use a crosswind chart to determine the effect on your distance: let's say that the wind speed is 15 kts. What's the most that 15 kts of wind can effect you in an 8 minute climb? (8 minutes / 60 minutes/hour) * 15 Nautical Miles/hour = 2 NM. Therefore, if you have a 15 kt headwind, you will cover 2 NM less in the climb, or 8 NM. If you have a 15 kt tailwind, you will cover 12 NM in the climb. If the wind is 60º off your nose, you will cover 9 NM... etc.

All of this distance calculation is also assuming an enroute departure. If you are using an over head departure, you will cover 0 miles in the climb, so you just need to factor in the time and fuel part.