ATPL Performance - Class 8: Range.
Summary
TLDRThis 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
🛫 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.
🔍 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.
✈️ 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.
🌐 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.
Mindmap
Keywords
💡Cruise
💡Range
💡Specific Range
💡Wind
💡Thrust
💡Drag
💡Specific Fuel Consumption (SFC)
💡Optimum Altitude
💡Mass
💡Speed for Maximum Range (VMR)
💡Step Climb
💡Econ Speed
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
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