ATPL Performance - Class 8: Range.

Summary

This educational video script by Grant delves into the concept of aircraft range, explaining how it's calculated based on fuel efficiency and various factors like wind, mass, and altitude. It covers specific range formulas for both jet and propeller aircraft, the impact of speed on range, and the strategic 'step climb' technique used in commercial flights to optimize fuel consumption. The script also touches on the trade-offs between speed and fuel efficiency, introducing the 'econ' speed determined by a cost index provided by flight planning departments.

Takeaways

• 🛫 The script discusses the importance of calculating range to ensure an aircraft doesn't run out of fuel mid-journey.
• 📏 'Range' measures the efficiency of an aircraft, dictating how far it can fly with the fuel on board.
• ⚖️ Specific range is the distance an aircraft flies per unit of fuel used, while specific ground range accounts for the effect of wind.
• 🌬 Wind affects specific ground range but not specific air range, as true airspeed (Tas) is unaffected by wind.
• 🔢 The units for specific range are nautical miles per kilogram of fuel used, highlighting the importance of fuel efficiency.
• 🚀 The formula for specific range involves dividing true airspeed by fuel flow, which is influenced by specific fuel consumption and drag.
• 🛩 For propeller aircraft, the formula for specific range includes specific fuel consumption per unit of power instead of just fuel flow.
• 🔝 Factors affecting range include mass, altitude, and wind, with lighter aircraft and optimal altitudes generally offering better range.
• ✈️ The speed for maximum range (VMR or MR) is crucial as it maximizes the thrust-to-drag ratio, affecting both jet and propeller aircraft differently.
• 📉 As an aircraft burns fuel and becomes lighter, its drag reduces, potentially increasing its specific range if flying at the speed for maximum range.
• 🔄 The concept of a 'step climb' in commercial flights is introduced to adjust altitude as fuel is burned, aiming to keep engines in their efficient RPM range.
• 🌪 The impact of wind on specific ground range is explained, with tailwinds increasing ground speed and headwinds decreasing it, affecting range calculations.

Q & A

What is the main topic of this video script?

The main topic of the video script is the concept of range in aviation, explaining how to calculate the distance an aircraft can cover with a given amount of fuel and the factors that affect it.

What is meant by 'specific range' in the context of aviation?

Specific range is the distance an aircraft flies through the air per unit of fuel used, which is a measure of efficiency.

How does wind affect specific range and specific ground range?

Wind affects specific ground range but not specific range. Specific ground range accounts for the distance covered over the ground, which is influenced by wind, whereas specific range is the distance through the air, unaffected by wind.

What is the unit for specific range?

The unit for specific range is nautical miles per kilogram of fuel used.

What is the relationship between true airspeed and fuel flow in the context of specific range?

For specific range, the true airspeed is divided by the fuel flow. Fuel flow is determined by the specific fuel consumption and the drag for a jet, or the power required for a propeller.

What is the significance of specific fuel consumption in calculating range?

Specific fuel consumption is a measure of engine efficiency, indicating the amount of fuel flow needed to produce one unit of thrust or power. It is crucial in calculating range as it directly affects fuel flow and, consequently, the specific range.

What is the speed for maximum range (VMR) in a turbojet aircraft?

In a turbojet aircraft, the speed for maximum range (VMR) is 1.32 times the maximum drag speed (VMD), where the thrust to drag ratio is maximized.

How does the mass of an aircraft affect its range?

The mass of an aircraft affects its range because a heavier aircraft generates more drag, requiring more thrust and thus more fuel consumption, which reduces the specific range.

What is the concept of a 'step climb' in commercial flights?

A 'step climb' is a technique used in commercial flights where the aircraft climbs to higher altitudes as fuel is burned and weight decreases, optimizing the altitude to maintain engine efficiency and maximize range.

What is the role of the cost index in determining the econ speed during a flight?

The cost index is a value between 1 and 50 that represents a trade-off between speed of flight and fuel burn. It is used to calculate the econ speed, which determines how fast the aircraft should fly based on operational requirements.

How does wind influence the specific ground range during a flight?

Wind influences the specific ground range by affecting the ground speed, which is the true airspeed plus or minus the wind component. A tailwind increases ground speed and specific ground range, while a headwind decreases it.

Outlines

00:00

🛫 Understanding Aircraft Range Calculation

This paragraph introduces the concept of calculating the range of an aircraft to ensure fuel efficiency and avoid running out of fuel mid-journey. It explains the importance of range in determining the distance an aircraft can fly and the airports it can reach. The specific range is defined as the distance flown per unit of fuel used, and the specific ground range accounts for the effects of wind. The speaker, Grant, discusses the formulas for calculating specific range and specific ground range, emphasizing the role of true air speed, fuel flow, and wind in these calculations. The paragraph also touches on the importance of engine efficiency, measured by specific fuel consumption, and how it impacts fuel flow and range.

05:04

🔍 Factors Influencing Aircraft Range

The second paragraph delves into the factors that influence an aircraft's range, such as mass, altitude, and wind. It explains how lighter aircraft generally have less drag, leading to a higher specific range due to lower power or thrust requirements. The paragraph also discusses the optimal altitude for range maximization in turbojet and propeller-driven aircraft, highlighting the difference in how each type of aircraft achieves efficiency. The concept of a 'step climb' in commercial flights is introduced, which involves adjusting the flight altitude as fuel is burned to maintain engine efficiency. Lastly, the paragraph touches on how wind affects the specific ground range but not the specific air range, as wind influences ground speed but not true air speed.

10:05

✈️ Commercial Considerations and Range Optimization

This paragraph addresses the commercial aspect of flying, where maximizing range must be balanced with timely arrival for passenger and cargo operations. It introduces the concept of VLRC (Long Range Cruise Speed), which is a speed that offers a trade-off between increased speed and slightly higher fuel consumption. The paragraph also explains the use of an econ speed, determined by a cost index provided by flight planning departments, which dictates the balance between speed and fuel efficiency for a particular flight. The discussion includes the impact of mass, altitude, and wind on specific range, and how these factors are considered in optimizing an aircraft's performance during a flight.

15:07

🌐 Flight Speeds and Their Impact on Range

The final paragraph summarizes the different flight speeds and their impact on an aircraft's range. It mentions MMR (Max Range Speed) for achieving the maximum range and LRC (Long Range Cruise) for a balance between speed and fuel consumption. The paragraph also discusses the use of econ speed, which is adjusted based on a cost index to meet specific flight requirements. The influence of mass and altitude on range is reiterated, with mass increasing drag and reducing range, and optimal altitude improving engine efficiency and increasing range. The paragraph concludes by reiterating the impact of wind on ground speed and specific ground range, emphasizing the importance of considering all these factors in flight planning.

Keywords

💡Cruise

In the context of the video, 'cruise' refers to the phase of flight where an aircraft maintains a steady altitude and speed to cover long distances. It is a critical part of the flight where fuel efficiency is paramount, as the script discusses the importance of calculating the range one can achieve with the available fuel to avoid running out mid-journey.

💡Range

The term 'range' is central to the video's theme, referring to the maximum distance an aircraft can fly without refueling. It is determined by the aircraft's fuel efficiency and is influenced by factors such as wind, engine type, and aircraft mass. The script explains how to calculate range and the impact of various factors on it.

💡Specific Range

Specific range is defined as the distance an aircraft flies per unit of fuel used. It is a measure of efficiency and is differentiated from specific ground range by the inclusion of wind effects. The script uses specific range to explain how to calculate the distance an aircraft can cover in still air versus when wind is a factor.

💡Wind

Wind is a significant factor in航空飞行, especially in calculating specific ground range. The script mentions that wind can affect the ground speed, which in turn influences the specific ground range. A tailwind increases ground speed and range, while a headwind decreases it.

💡Thrust

Thrust is the force that propels an aircraft forward and is generated by the engines. The script discusses how the amount of thrust required to overcome drag is related to fuel consumption, which in turn affects the aircraft's range and efficiency.

💡Drag

Drag is the resistance an aircraft encounters while moving through the air, which opposes its forward motion. The script explains that drag is a key factor in determining fuel consumption and, consequently, the aircraft's range. Reducing drag can improve specific range.

💡Specific Fuel Consumption (SFC)

Specific fuel consumption is a measure of engine efficiency, indicating the amount of fuel required to produce a unit of thrust or power. The script uses SFC in equations to show how it directly impacts the calculation of specific range and overall fuel efficiency.

💡Optimum Altitude

The optimum altitude is the cruising altitude at which an aircraft's engines operate most efficiently, resulting in the lowest specific fuel consumption and, therefore, the best range. The script explains how flying at this altitude can maximize range and how it changes as the aircraft burns fuel and loses weight.

💡Mass

In the context of the video, 'mass' refers to the weight of the aircraft, which affects its drag and, consequently, its fuel efficiency. The script illustrates how lighter aircraft have less drag and thus a higher specific range, while heavier aircraft require more thrust and have a lower specific range.

💡Speed for Maximum Range (VMR)

VMR is the airspeed at which an aircraft can achieve the greatest range. The script explains that for jet aircraft, this speed is typically 1.32 times the speed for minimum drag (VMD), and for propeller aircraft, it is related to the power required curve.

💡Step Climb

A step climb is a flight strategy where an aircraft gradually increases its altitude during the flight as it burns fuel and becomes lighter. The script describes how this practice helps to maintain engine efficiency by keeping the aircraft within the optimal RPM range for fuel consumption.

💡Econ Speed

Econ speed, as discussed in the script, is a flight speed determined by a cost index that balances speed and fuel consumption. It is a trade-off speed used for long-range cruise flights, allowing for a slight increase in speed with a minimal impact on fuel efficiency.

Highlights

The importance of calculating range to avoid running out of fuel during a flight.

Range as a measure of efficiency, dictating how far an aircraft can fly and which airports it can visit.

Specific range is the distance an aircraft flies per unit of fuel used, affected by wind to become specific ground range.

The concept of specific range in still air versus the effect of wind on specific ground range, likened to flying inside a moving train.

Units for specific range are nautical miles per kilogram of fuel used.

Formulas for calculating specific range and specific ground range, involving true air speed, fuel flow, and wind components.

Thrust generation and specific fuel consumption as measures of engine efficiency.

The relationship between specific fuel consumption, drag, and how they affect specific range.

Factors influencing range, such as mass, altitude, and wind, and their impact on drag and specific range.

The speed for maximum range (VMR) and its calculation based on the thrust to drag ratio.

Optimum altitude for maximizing range in turbojet and propeller-driven aircraft.

The step climb technique used in commercial flights to adjust altitude and maintain engine efficiency.

Wind's impact on specific ground range but not on specific air range due to the difference between TAS and GS.

The economic trade-off between speed and fuel burn, represented by the cost index.

The use of econ speed in long-range cruise flights for balancing speed and fuel efficiency.

Influence of aircraft mass on range, where lighter aircraft have lower drag and higher specific range.

How flying at optimum altitude can increase specific range due to lower specific fuel consumption and drag.

Transcripts

when we're flying along the cruise we

need to be able to calculate how much

more distance we can cover with the

amount of fuel that we have in our tanks

otherwise we might run out of fuel

halfway along our journey but how do we

calculate this figure

let's find out

[Music]

hi I'm Grant and welcome to the eighth

class in the performance Series today

we're going to be taking a look at range

which is basically a measure of

efficiency range will dictate how far we

can fly for and which airports we can

visit so it's important to understand

how we calculate the range for the fuel

that we have on board or the maximum

amount of fuel we can put in the tanks

specific range is the distance an

aircraft flies through the air per unit

of fuel used if we add in the effects of

wind we get the specific ground range

the distance we actually cover over the

ground rather than through the air

because wind will cause the parcel of

air that we're flying in to move along

the ground as we're flying through it

think of it like we're flying inside a

big train if the train is stationary we

just fly to the end of the train but if

the train is moving we'll fly to the end

of the train but the whole thing has

moved to our position relative to the

ground will be different if there is no

wind

think of the train being stationary then

our specific range are and our s

uh

our specific ground range sorry will be

the same

the units for specific range will be

nautical miles per kilogram of fuel used

and if we divide by time we can get two

formulas one for a specific range or one

for a specific ground range

the one for a specific range the air

distance would be the true air speed

over fuel flow and for ground range we

just need to factor in wind and we can

do that by using the ground speed which

is the Tas plus or minus any wind

component and then divide that by the

fuel flow as well depending on the

conditions we are flying in we need a

certain amount of thrust that we need to

overcome all of the thrust required or

the drag that is produced when we fly

thrust generation requires us to use up

Fuel and how much fuel depends on the

specific fuel consumption of the engine

this is basically a measure of engine

efficiency and it is the amount of fuel

flow needed to produce one unit of

thrust in a jet aircraft and a propeller

it's the amount of uh

fuel used to produce one unit of power

why is this important though well we

already have a formula for a specific

range in specific ground range but we

can break down the fuel flow into a

little bit more detail if we first have

a look at the jet aircraft then we can

substitute in the value for specific

fuel consumption into the specific range

equation and get specific range

is equal to the true air speed

over the specific fuel consumption times

drag

or the amount of thrust required for

that phase of flight or if we want to

find the specific ground range

we just have to substitute in ground

speed for a propeller it is slightly

different the difference is that bottom

line where we have to have the

consideration of specific fuel

consumption per unit of power so we get

the same equations

but on the bottom line it's power

required

at that phase of flight so why have we

substituted in those values for instead

of fuel flow basically well it basically

allows us to see a bit more clearly the

factors that affect fuel flow and our

specific range so if we look at this one

for example we know that if the specific

fuel consumption is high and the drag is

high that means that we're going to be

dividing by a larger number and that

means our specific range is going to go

down if we take the specific ground

range of the propeller for instance if

we have a low specific fuel consumption

and a low amount of power required we're

dividing by a small number which means

our ground range is going to be high

it's just an easy way to analyze range

is influenced according to a number of

factors most of them you can figure out

by looking at the equations that we've

just worked out but first we're going to

have a look at Mass

if we compare a light aircraft to a

heavy one the total drag curves look

like this mainly because heavier

aircraft need to produce more lift a

more induced drag is generated result

this means that on the lighter aircraft

the drag is lower when we fly at the

speed for max range which now I think

might have not actually talked about the

speed for max range so let's just do a

little sidebar here so max range is

called

VMR or if you're flying at Mach numbers

m m r

speed Mach number

and it occurs where we maximize our

thrust to drag ratio and in a turbo jet

or a jet in general this occurs at 1.32

vmd and this is the tangent on this

curve so if you go somewhere like that

this value here is our VMR which will be

1.32 vmd in a propeller driven aircraft

we take the tangent to the power curve

not this drag curve and it's the same

effect we're maximizing our thrust to

drag or Thruster power required

um ratio

and this actually occurs therefore at

1.32 VMP

speed for minimum power

which coincidentally is actually vmd

because the speed for minimum power is

0.76 vmd and 0.76 times 1.32 equals

close enough one so it's therefore equal

to the speed for a minimum drag so what

was I saying yes lighter aircraft

um have less drag basically

and if you look at the equations for

both turbojet and propeller aircraft

the bottom line has dragging it or power

required which is essentially drag type

speed so if you have a lower amount of

drag that means you're dividing by a

smaller number which means your specific

range goes up simple as that and also

take note that if we are

um lighter or speed for VMR would be a

bit slower as well

so that would be VMR in the heavy

aircraft and then as we get lighter our

speed slows down same for the propellers

if an aircraft is flying at its Optimum

altitude the range will be maximized

this Optimum altitude in a turbojet is

high up basically the engines are

running at their designed RPM because

they're designed to cruise because

that's where they spend most of their

time

and that's where they are most efficient

making the specific fuel consumption low

and also upper altitude the air is less

dense meaning drag is lower so our

specific range goes up on our specific

ground range will go up as well

in a propeller driven aircraft the

optimum altitude isn't as simple as it

depends on throttle position and

propeller RPM combinations and Optimum

combinations and altitudes are often

tested out and put in manufacturer's

manuals so it's hard to see but it's not

going to be quite as high up but it's

going to be the position for basically

maximum throttle open so altitude and

mass are the two biggest influencers on

commercial flights so this is an example

of a step client it's something you see

quite often so say we first reach our

cruising altitude of 30 000 feet we're

heavy and full of fuel and as we Cruise

along we burn fuel and weight as a

result

this means our drag reduces because

we're needing less lift and therefore

the specific range increases which is

good we're lowering our drag specific

range goes up

this reduction in Drag and a lower

um

speed for maximum range requires less

thrust to be used so the engines don't

have to work as hard so the RPM of the

engine of the route can reduce

this means that the engine May no longer

be operating in its ideal range which is

typically

um around 90 to 95 so we counter

intuitively want to make the engines

work a bit harder again to get them back

into this efficient range

we do this by climbing into less dense

air meaning more air has to pass through

the engine in order to generate the

correct amount of thrust and the engine

has to rotate faster as a result pushing

us back up into the ideal RPM range

this means that throughout the flight

our Optimum altitude to keep the engines

working in the efficient 90 to 95 range

steadily climbs as we go throughout the

flight as we burn weight in practice

though we can't slowly climb along as we

fly because if everyone's doing it

there'd be a ridiculous number of

collisions in the air so what we do is

we fly at one altitudes 30 000 feet at

the start maybe slightly above the

optimum altitude then as we burn fuel

the optimum altitude will climb up to

meet us then pass through our level once

it reaches a thousand feet or so above

we would request to climb up to the next

level 32 000 feet then again it would

climb up to reach us and so on and so

forth throughout the flight

um until we reach the structural limit

of the aircraft

this is known as a step climb and it's

something you do almost every flight

when you're flying commercially just to

save fuel by flying as close to the

optimum altitude as possible so wind

influences the specific ground range but

not the specific air range the specific

range is

the specific air range but it's just

called specific range

so basically it's because Taz and ground

speed while Taz isn't affected by wind

and ground speed is equal to Taz

plus or minus whatever wind component

you've got so obviously the wind has an

influence on this specific ground range

but nothing to do with the specific gear

range so if we add a Tailwind our ground

speed goes up

and our specific range wouldn't change

but the specific ground change would go

down as a result

wait did I say Tailwind if it's a

Tailwind it would go up if it's a

headwind to the specific ground range

will go down

so that's how we get our maximum range

out of an aircraft but it does require

us to fly at MMR or VMR which might be a

bit slow to get to our destination on

time to pick up more passengers or pick

up some cargo Etc so there's a

commercial element we need to think

about

for this there's a speed generated for

using

um during the long range cruise and it's

called vlrc

this is a speed that's slightly faster

than the speed for max range so there is

going to be a bit more fuel burn but

it's calculated so that you get

um

about four percent speed increase with

about one percent fuel burn

reduction or reduction range fuel burn

increase and companies use this as a bit

of a trade-off and there's also a speed

which is called

um the econ

to be honest they're very rarely going

to be V speeds they're going to be Max

speeds and the way we figure out the

econ speed is by using the cost index

the cost index which I talked about

briefly in the class before is usually

in a range between 1 and 50 from at

least at least from what I've seen

anyway

you could get higher I don't know

Boeing an Airbus both use it but I'm not

sure about other manufacturers and it's

basically a trade-off between speed of

flight and amount of fuel burn if you

have a really low cost index you'd save

a lot of fuel but fly really slow

and a high cost index would be the

reverse fast flight burning lots of fuel

we're given this cost index by the

flight panning Department

depending on how fast they need us to

fly to arrive on time According to some

timetables or slots or some other

airports we then pop it into a computer

on the aircraft and a Mach number for

econ in the cruise our econ speed is

generated and that's what we fly through

the flight okay so a specific air range

or the specific range is the two air

speed divided by the fuel flow and the

fuel flow is specific fuel consumption

times drag for a jet

and for propeller

it is specific fuel consumption times

power required think of drag as thrust

required maybe that might help

and if you want to convert them into

specific ground range you just need to

factor in the wind and to do that you

just convert the tires into a ground

speed because ground speed equals Taz

plus or minus any wind component that's

helping you this the speeds for max

range speed MMR is going to be 1.32

times vmd that's basically the tangent

to the drag curve where our thrust to

drag ratio is maximized

need a propeller it's slightly different

it's tangent to the power required graph

and and the tangent again means our

ratio of thrust power required is

maximized and that occurs at 1.32 VMP

which just because the maths happens to

be VMT VMT v m d sorry

um yeah because VMP is 0.76

times vmd and 0.76 times 1.32 is

basically one

so things that influence our level of

range our range specific air range for

example is influenced by mass if we have

more mass it means we have more drag and

we have more drag we need more thrust

which means our specific fuel

consumption goes up and that means that

well our specific fuel system option

doesn't go up we just need more thrust

but anyway has the same effect of

reducing our range

altitude for a jet basically means that

we're operating in the ideal zone for

our engines and the drag is lower

meaning the specific range goes up in a

propeller aircraft it's a bit different

you basically fly at what the

manufacturer has tested and found to be

the most efficient

wind has no influence over the specific

air range but it obviously has a huge

impact on the specific ground range

because Tas plus or minus wind equals

ground speed if you have a headwind you

would have a lower ground speed and that

would mean a lower specific ground range

for example

the speeds that we fly if we have MMR

we're going to fire a max range that's

going to be the best for us

and if we fly at long range Crews we're

getting four percent faster for one

percent reduction in range a bit more

fuel burn and normally we fly at M econ

speed which is according to the cost

index that range of 1 to 50 and telling

us how fast to fly

um and how much fuel to burn