Sustainable Aviation
Cleaner fuels, efficient aircraft and lower emissions: CO₂ accounting, efficiency metrics, wings and engines that burn less fuel, sustainable aviation fuels, contrails, batteries and hydrogen, cleaner operations, and pathways to net zero, with six labs. Free, self-paced, and tied to NASA’s Sustainable Flight National Partnership, NASA-DLR contrail research, DOE’s SAF data and EIA emission factors.
Courses › AERO 470
About this course
This is a free self-study course outline written by Saving Planets. It is not a university course, it carries no academic credit, and no school is involved.
Its scope follows a senior elective on aviation and the environment. It draws on the environmental-factors lecture in MIT 16.885J Aircraft Systems Engineering (free on MIT OpenCourseWare) and on public NASA, DOE, EIA and EPA material, which we link where it helps. None of them endorses this page.
What we add: every unit ties to real work with a cited public source, every number on the page is re-computed by a checking script before it goes live, and every lab runs in a free spreadsheet or simulation.
Work through it in order. Each unit has goals, key ideas, equations, step-by-step examples, practice with full answers, common mistakes, flashcards and a quiz. Your progress is saved only in this browser.
How this course helps save the planet
This whole course is a planet section: DOE’s Alternative Fuels Data Center says aviation produces about 2% of all CO₂ worldwide and 12% of CO₂ from transportation, and contrails add warming beyond CO₂.
NASA’s Sustainable Flight National Partnership works toward the aviation community’s goal of net-zero carbon emissions by 2050. Each unit ends with a short, sourced section. Values that are not from a source are labeled as sample or textbook values.
Before you start
Prerequisites
- Propulsion: thrust, efficiency and TSFC.
- Aircraft Performance: lift, drag and the Breguet range equation.
- Thermodynamics: energy, heating values and cycle efficiency.
- Capstone Design or Avionics & Systems Engineering: requirements and trades.
How to study
- Keep units straight: kg, gallons, liters, MJ and Wh.
- Always ask “per what?”: per flight, per passenger-km, per kg of fuel.
- Separate combustion CO₂ from lifecycle CO₂.
- Check every claimed saving against a baseline.
- Remember non-CO₂ effects such as contrails.
- Do every practice problem on paper before opening the answer, and retake the quizzes a few days later.
Lab equipment (for the wet labs)
- Spreadsheet software (any free one works), or Python.
- A computer or tablet for the free PhET Greenhouse Effect simulation.
- The free MIT 16.885J lecture notes in a web browser.
- A calculator.
Suggested 15-week schedule
About 6 to 9 hours a week: reading, practice problems and, in lab weeks, the lab.
| Week | Unit | Topics | Reading |
|---|---|---|---|
| 1 | Aviation and Climate: Counting CO₂ | Counting CO₂; Lab A | EIA |
| 2 | Efficiency Metrics | Efficiency metrics | NASA SFNP |
| 3 | Aerodynamic Efficiency | L/D and induced drag | MIT 16.885J |
| 4 | Aerodynamic Efficiency | Breguet fuel burn; Lab B | NASA SFNP |
| 5 | Engine Efficiency | Engine efficiency; Lab C | MIT 16.885J |
| 6 | Sustainable Aviation Fuels | SAF basics | DOE AFDC |
| 7 | Sustainable Aviation Fuels | SAF lifecycle; Lab D; midterm practice | DOE AFDC |
| 8 | Contrails and Non-CO₂ Effects | Contrails | NASA-DLR |
| 9 | Electric and Hybrid Propulsion | Batteries and electric range | NASA SFNP |
| 10 | Electric and Hybrid Propulsion | Hybrid systems; Lab E | NASA SFNP |
| 11 | Hydrogen Aircraft | Hydrogen aircraft | MIT 16.885J |
| 12 | Operations, Noise and Air Quality | Operations | NASA SFNP |
| 13 | Operations, Noise and Air Quality | Noise and air quality | EPA |
| 14 | Pathways to Net Zero | Scenarios; Lab F | DOE AFDC |
| 15 | Pathways to Net Zero | Review; final practice | MIT 16.885J |
Your progress
Tick units and labs as you finish them, and take the quizzes. Progress and quiz scores are saved only in this browser, never sent to us.
Turn on JavaScript to track progress.
Unit 1 · Week 1
Aviation and Climate: Counting CO₂
Where aviation emissions come from, emission factors, combustion versus lifecycle CO₂, and aviation’s share of the total.
Learning objectives
By the end of this unit you can:
- Use an emission factor to compute CO₂.
- Convert between gallons, liters and kilograms.
- Explain combustion versus lifecycle CO₂.
- State aviation’s share of global CO₂.
Key concepts
- Burning jet fuel turns its carbon into CO₂; the mass of CO₂ is about three times the fuel mass because each carbon atom gains two oxygen atoms.
- The U.S. EIA gives 21.50 lb (9.75 kg) of CO₂ per gallon of jet fuel burned.
- Lifecycle CO₂ adds production and transport of the fuel; for sustainable fuels, growing the feedstock can absorb CO₂.
- DOE’s Alternative Fuels Data Center says aviation accounts for 2% of all CO₂ and 12% of transportation CO₂ worldwide.
- Aviation also warms the climate through non-CO₂ effects such as contrails and NOx.
Key equations
Worked examples, step by step
Example 1.1 A flight burns 5000 gallons of jet fuel. CO₂?
Show the steps
- 5000 × 9.75.
Answer: 48,750 kg (48.75 t).
Example 1.2 Check EIA’s pound and kilogram values.
Show the steps
- 21.50 × 0.45359237.
Answer: 9.75 kg, consistent.
Example 1.3 How many liters is 5000 gallons?
Show the steps
- 5000 × 3.785.
Answer: 18,927 L.
Practice problems
Work each on paper first, then check.
CO₂ from 1000 gallons?
Show answer
9750 kg.
Mass ratio of CO₂ to carbon?
Show answer
44/12 = 3.67.
Aviation’s share of transport CO₂ (DOE)?
Show answer
12%.
What does lifecycle add?
Show answer
Production, transport and feedstock effects.
Common misconceptions
Myth: CO₂ weighs less than the fuel.
Actually: It weighs about three times more.
Myth: Aviation only emits CO₂.
Actually: Contrails and NOx matter too.
Myth: Lifecycle and combustion CO₂ are equal.
Actually: They differ, especially for SAF.
Flashcards
Emission factor
CO₂ per unit fuel.
Combustion CO₂
From burning.
Lifecycle CO₂
Well-to-wake total.
Non-CO₂ effects
Contrails, NOx, soot.
Jet A
Standard jet fuel.
t CO₂
Tonne of CO₂.
Self-check quiz
How this helps save the planet
The U.S. EIA lists 21.50 lb (9.75 kg) of CO₂ per gallon of jet fuel.
DOE’s Alternative Fuels Data Center says aviation accounts for 2% of all CO₂ worldwide and 12% of all CO₂ from transportation.
On Saving Planets: Solutions · Earth Observation
Sources: U.S. EIA: Carbon dioxide emissions coefficients · U.S. DOE Alternative Fuels Data Center: Sustainable aviation fuel
Free learning resources
Unit 2 · Week 2
Efficiency Metrics
Fuel and CO₂ per passenger-kilometer, energy intensity, and how to compare aircraft fairly.
Learning objectives
By the end of this unit you can:
- Compute fuel per passenger-km.
- Compute CO₂ per passenger-km.
- Apply a percentage efficiency gain.
- Compare fairly across aircraft.
Key concepts
- Total emissions mislead; normalize by passengers and distance.
- Load factor matters: empty seats raise emissions per passenger.
- Energy intensity (MJ per passenger-km) compares different fuels on one scale.
- An efficiency gain lowers fuel per unit of transport, not necessarily total fuel if traffic grows.
- NASA’s Sustainable Flight National Partnership targets 25–30% energy-efficiency improvements in next-generation transports.
Key equations
Worked examples, step by step
Example 2.1 5000 gallons carry 180 passengers 2000 km (sample values). Liters per passenger-km?
Show the steps
- 18,927/(180 × 2000).
Answer: 0.0526 L.
Example 2.2 CO₂ per passenger-km?
Show the steps
- 48,750/360,000.
Answer: 0.135 kg (135 g).
Example 2.3 A 25% efficiency gain on the same trip. New CO₂?
Show the steps
- 48,750 × 0.75.
Answer: 36,563 kg.
Practice problems
Work each on paper first, then check.
Same flight with 150 passengers: g CO₂ per pkm?
Show answer
162.5 g.
Load factor, 180 of 200 seats?
Show answer
0.9.
A 30% gain on 48,750 kg?
Show answer
34,125 kg.
Why normalize?
Show answer
To compare different trips and aircraft fairly.
Common misconceptions
Myth: Bigger planes always emit more per passenger.
Actually: Often less per passenger.
Myth: Efficiency cuts total emissions.
Actually: Only if traffic doesn’t grow faster.
Myth: Seats equal passengers.
Actually: Use load factor.
Flashcards
Passenger-km
One passenger carried one km.
Load factor
Passengers over seats.
Energy intensity
MJ per pkm.
Rebound
Growth offsetting efficiency.
Baseline
Reference case.
Normalization
Per-unit comparison.
Self-check quiz
How this helps save the planet
NASA says the Sustainable Flight National Partnership aims to enable 25–30% energy-efficiency improvements in next-generation transports that can use 100% sustainable aviation fuel and fly optimal trajectories.
This unit’s per-passenger metrics are how such gains are measured.
On Saving Planets: Aircraft Performance · Solutions
Sources: NASA Aeronautics: Sustainable Flight National Partnership
Free learning resources
Unit 3 · Weeks 3–4
Aerodynamic Efficiency
L/D, induced drag and aspect ratio, high-aspect-ratio and truss-braced wings, and fuel burn from the Breguet equation.
Learning objectives
By the end of this unit you can:
- Compute fuel fraction from Breguet.
- Show how L/D cuts fuel.
- Compute induced drag coefficient.
- Explain why long, slender wings save fuel.
Key concepts
- From Breguet, the fuel fraction is 1 − exp(−Rc/(V·L/D)).
- Higher L/D means less fuel for the same range.
- Induced drag C_Di = C_L²/(πeAR) falls as aspect ratio rises.
- Very slender wings need bracing (truss-braced designs) to stay light and stiff.
- NASA’s partnership centerpiece is a full-scale X-plane demonstrator testing an ultra-efficient aerodynamic design.
Key equations
Worked examples, step by step
Example 3.1 3000 km at 230 m/s, c = 0.6 /h, L/D = 17 (textbook values). Fuel fraction?
Show the steps
- Rc/(V L/D) = 3 × 10⁶ × 1.667 × 10⁻⁴/(230 × 17) = 0.1279.
- 1 − e^(−0.1279).
Answer: 0.120.
Example 3.2 Same with L/D = 20.
Show the steps
- 1 − e^(−0.1087).
Answer: 0.103: 14.2% less fuel.
Example 3.3 C_Di at C_L = 0.5, e = 0.85, AR = 9?
Show the steps
- 0.25/(π × 0.85 × 9).
Answer: 0.0104.
Practice problems
Work each on paper first, then check.
C_Di at AR = 12?
Show answer
0.0078.
At AR = 19 (truss-braced class)?
Show answer
0.0049.
Aspect ratio for b = 36 m, S = 120 m²?
Show answer
10.8.
Why brace a slender wing?
Show answer
To keep it light and stiff.
Common misconceptions
Myth: Drag is all friction.
Actually: Induced drag is large at cruise.
Myth: Longer wings are free.
Actually: Weight and gate limits.
Myth: Fuel scales linearly with L/D.
Actually: It follows the exponential.
Flashcards
L/D
Lift-to-drag ratio.
Induced drag
Drag due to lift.
Aspect ratio
b²/S.
Oswald factor
Span efficiency e.
Truss-braced wing
Slender wing with struts.
Fuel fraction
Fuel over takeoff weight.
Self-check quiz
How this helps save the planet
NASA says the centerpiece of its Sustainable Flight National Partnership will be a full-scale X-plane demonstrator built to test an ultra-efficient aerodynamic design, to inform the next generation of single-aisle aircraft.
NASA lists the demonstrator’s first flight as no earlier than late 2026.
On Saving Planets: Aerodynamics I · Aircraft Performance
Sources: NASA Aeronautics: Sustainable Flight National Partnership
Free learning resources
Unit 4 · Week 5
Engine Efficiency
Thermal, propulsive and overall efficiency, bypass ratio, and advanced engine cores.
Learning objectives
By the end of this unit you can:
- Compute propulsive efficiency.
- Combine thermal and propulsive efficiency.
- Explain why high bypass saves fuel.
- Relate efficiency to TSFC.
Key concepts
- Overall efficiency is thermal efficiency times propulsive efficiency.
- Propulsive efficiency 2/(1 + V_e/V₀) rises as exhaust velocity approaches flight speed.
- High-bypass turbofans move more air more slowly, raising propulsive efficiency.
- Hotter, higher-pressure, compact cores raise thermal efficiency.
- NASA’s Hybrid Thermally Efficient Core work develops high-power-density turbine cores for next-generation transports.
Key equations
Worked examples, step by step
Example 4.1 V₀ = 230 m/s, V_e = 400 m/s. η_p?
Show the steps
- 2/(1 + 400/230).
Answer: 0.730.
Example 4.2 Lower V_e to 300 m/s (higher bypass).
Show the steps
- 2/(1 + 300/230).
Answer: 0.868.
Example 4.3 With η_th = 0.5, overall efficiency at V_e = 300?
Show the steps
- 0.5 × 0.868.
Answer: 0.434.
Practice problems
Work each on paper first, then check.
η_p at V_e = 350 m/s?
Show answer
0.793.
Overall at V_e = 400, η_th = 0.5?
Show answer
0.365.
Fuel saving from 0.365 to 0.434 overall?
Show answer
15.9% less fuel for the same work.
What is bypass ratio?
Show answer
Bypass over core mass flow.
Common misconceptions
Myth: Faster exhaust is more efficient.
Actually: It lowers propulsive efficiency.
Myth: Thermal efficiency is everything.
Actually: Propulsive matters as much.
Myth: Bypass is free.
Actually: Bigger fans add weight and drag.
Flashcards
Propulsive efficiency
Useful thrust power fraction.
Thermal efficiency
Cycle efficiency.
Overall efficiency
Product of both.
Bypass ratio
Fan air over core air.
TSFC
Fuel per thrust per time.
Engine core
Compressor, burner, turbine.
Self-check quiz
How this helps save the planet
NASA says its Hybrid Thermally Efficient Core work is accelerating the development and demonstration of advanced turbine engine technologies in a high-power-density core for next-generation commercial transports.
Both efficiencies in this unit feed directly into the fuel burned per passenger.
On Saving Planets: Propulsion · Thermodynamics
Sources: NASA Aeronautics: Sustainable Flight National Partnership
Free learning resources
Unit 5 · Weeks 6–7
Sustainable Aviation Fuels
What SAF is, production pathways, blend limits, lifecycle reductions and national goals.
Learning objectives
By the end of this unit you can:
- Define SAF.
- Compute blended lifecycle savings.
- Size goal-level savings.
- Explain blend limits.
Key concepts
- DOE defines SAF as an alternative fuel made from non-petroleum feedstocks that reduces air pollution from air transportation.
- SAF can be blended at levels between 10% and 50%, depending on feedstock and production pathway (ASTM D7566).
- Blended SAF works in existing aircraft and infrastructure.
- Lifecycle savings scale with blend fraction times the SAF’s own lifecycle reduction.
- The SAF Grand Challenge aims for 3 billion gallons in 2030 and 35 billion in 2050 with at least 50% lifecycle reduction.
Key equations
Worked examples, step by step
Example 5.1 A 50% blend of SAF with a 50% lifecycle reduction. Overall saving?
Show the steps
- 0.5 × 0.5.
Answer: 25%.
Example 5.2 3 billion gallons with a 50% reduction, using the EIA factor as the baseline (simplified).
Show the steps
- 3 × 10⁹ × 9.75 × 0.5.
Answer: About 14.6 million tonnes CO₂ a year.
Example 5.3 Same for 35 billion gallons.
Show the steps
- 35 × 10⁹ × 9.75 × 0.5.
Answer: About 171 million tonnes.
Practice problems
Work each on paper first, then check.
A 10% blend at 80% reduction?
Show answer
8%.
Flights using SAF per ICAO via DOE?
Show answer
Over 360,000 at 46 airports.
Why the blend limit?
Show answer
Fuel properties must meet Jet A specifications.
Does SAF need new engines?
Show answer
Blends work in existing aircraft.
Common misconceptions
Myth: SAF has zero emissions.
Actually: It burns to CO₂; savings are lifecycle.
Myth: Any blend works.
Actually: Limits depend on pathway.
Myth: SAF only affects CO₂.
Actually: NASA-DLR found fewer contrail ice crystals.
Flashcards
SAF
Sustainable aviation fuel.
HEFA
Hydroprocessed esters and fatty acids pathway.
Blend limit
Maximum SAF share.
ASTM D7566
Synthetic jet fuel spec.
Lifecycle reduction
Cut vs fossil fuel.
Drop-in fuel
Works in existing systems.
Self-check quiz
How this helps save the planet
DOE’s Alternative Fuels Data Center says over 360,000 commercial flights have used SAF at 46 airports (per ICAO), and the SAF Grand Challenge aims for 3 billion gallons in 2030 and 35 billion gallons in 2050 with at least 50% lifecycle reduction.
DOE notes that all three existing U.S. plants use the HEFA pathway, with alcohol-to-jet plants expected.
On Saving Planets: Solutions · General Chemistry I
Sources: U.S. DOE Alternative Fuels Data Center: Sustainable aviation fuel
Free learning resources
- U.S. DOE Alternative Fuels Data Center: Sustainable aviation fuel: DOE SAF page.
- U.S. EIA: Carbon dioxide emissions coefficients: EIA factors.
Unit 6 · Week 8
Contrails and Non-CO₂ Effects
How contrails form, why they warm, soot and ice crystals, and how fuels and routing reduce them.
Learning objectives
By the end of this unit you can:
- Explain contrail formation.
- Compute ice-crystal reductions.
- Describe non-CO₂ warming.
- Name mitigation options.
Key concepts
- Contrails form when hot, humid exhaust mixes with cold air and water condenses and freezes on soot particles.
- Persistent contrails can spread into cirrus that trap outgoing heat.
- Fewer soot particles mean fewer, larger ice crystals that disappear sooner.
- NASA and DLR found cleaner-burning sustainable fuels produced 50%–70% fewer ice crystals at cruise.
- Routing around ice-supersaturated air can avoid persistent contrails.
Key equations
Worked examples, step by step
Example 6.1 A sample emission index of 10¹⁵ ice crystals per kg of fuel. With a 50% reduction?
Show the steps
- 10¹⁵ × 0.5.
Answer: 5 × 10¹⁴ per kg.
Example 6.2 With a 70% reduction?
Show the steps
- 10¹⁵ × 0.3.
Answer: 3 × 10¹⁴ per kg.
Example 6.3 A flight burns 15,000 kg of fuel at cruise (sample). Crystals at the 70% reduction?
Show the steps
- 3 × 10¹⁴ × 15,000.
Answer: 4.5 × 10¹⁸.
Practice problems
Work each on paper first, then check.
Why do contrails warm at night?
Show answer
They trap outgoing infrared with no sunlight to reflect.
What seeds contrail ice?
Show answer
Soot and other particles.
Reduction from 5 × 10¹⁴ to 3 × 10¹⁴?
Show answer
40%.
One operational fix?
Show answer
Route around ice-supersaturated air.
Common misconceptions
Myth: Contrails are just water, so harmless.
Actually: They can add warming.
Myth: All contrails persist.
Actually: Only in ice-supersaturated air.
Myth: Only CO₂ matters.
Actually: Non-CO₂ effects are significant.
Flashcards
Contrail
Condensation trail.
Contrail cirrus
Spread persistent contrails.
Ice supersaturation
Air able to grow ice.
Soot
Carbon particles.
Emission index
Amount per kg of fuel.
Non-CO₂ forcing
Warming besides CO₂.
Self-check quiz
How this helps save the planet
NASA reports that cleaner-burning jet fuels made from sustainable sources can produce 50%–70% fewer ice crystal contrails at cruising altitude, from joint NASA and DLR (German Aerospace Center) research.
NASA notes ice-crystal contrails can linger in the upper atmosphere for hours and affect the way Earth is heated and cooled.
On Saving Planets: Earth Observation · Heat Transfer
Sources: NASA: NASA-DLR study finds sustainable aviation fuel can reduce contrails (2021)
Free learning resources
Unit 7 · Weeks 9–10
Electric and Hybrid Propulsion
Battery energy density, drivetrain efficiency, electric range, and where hybrid systems help.
Learning objectives
By the end of this unit you can:
- Compare battery and fuel energy density.
- Account for drivetrain efficiency.
- Compute electric aircraft range.
- Identify suitable missions.
Key concepts
- Jet fuel stores about 43 MJ/kg (11,944 Wh/kg); today’s batteries store a few hundred Wh/kg (textbook values).
- Electric drivetrains convert energy far more efficiently (about 90%) than turbines (about 35%), shrinking the gap (textbook values).
- Battery-electric range is R = (e η/g)(L/D)(m_b/m).
- Batteries don’t get lighter as they discharge, unlike fuel.
- NASA says electrified aircraft propulsion offers new possibilities for reducing fuel and energy use, from small passenger aircraft to single-aisle transports.
Key equations
Worked examples, step by step
Example 7.1 Jet fuel at 43 MJ/kg in Wh/kg, and ratio to a 250 Wh/kg battery?
Show the steps
- 43 × 10⁶/3600 = 11,944 Wh/kg.
- 11,944/250.
Answer: 47.8 times.
Example 7.2 Adjust for efficiency: turbine 0.35, electric 0.9.
Show the steps
- 47.8 × 0.35/0.9.
Answer: About 18.6 times.
Example 7.3 Range with e = 250 Wh/kg, η = 0.8, L/D = 15, battery fraction 0.3.
Show the steps
- 9 × 10⁵ × 0.8/9.80665 × 15 × 0.3.
Answer: About 330 km.
Practice problems
Work each on paper first, then check.
Range if battery energy doubles to 500 Wh/kg?
Show answer
About 661 km.
250 Wh/kg in J/kg?
Show answer
9 × 10⁵.
Why do hybrids help?
Show answer
Electric power boosts takeoff and climb while fuel provides range.
Best first missions?
Show answer
Short regional and training flights.
Common misconceptions
Myth: Batteries will soon equal jet fuel.
Actually: The gap is large even after efficiency.
Myth: Electric means zero emissions.
Actually: It depends on the grid.
Myth: Battery weight falls in flight.
Actually: It stays constant.
Flashcards
Specific energy
Energy per mass.
Drivetrain efficiency
Battery-to-shaft efficiency.
Hybrid-electric
Fuel plus electric power.
Battery fraction
Battery over aircraft mass.
Wh/kg
Battery specific energy unit.
Grid intensity
CO₂ per kWh.
Self-check quiz
How this helps save the planet
NASA says electrified aircraft propulsion offers new possibilities for reducing fuel and energy usage in aviation from small passenger aircraft to single-aisle transports, using new technologies, concepts, test aircraft and ground facilities.
This unit’s range equation shows why the first electric aircraft fly short routes. Energy densities here are textbook values.
On Saving Planets: Circuits · Solutions
Sources: NASA Aeronautics: Sustainable Flight National Partnership
Free learning resources
Unit 8 · Week 11
Hydrogen Aircraft
Hydrogen’s energy per mass and volume, tank sizing, water emissions, and design trade-offs.
Learning objectives
By the end of this unit you can:
- Compare hydrogen and jet fuel by mass and volume.
- Size a hydrogen tank volume.
- Compute water produced.
- Explain design trade-offs.
Key concepts
- Hydrogen holds about 120 MJ/kg, 2.8 times jet fuel, but liquid hydrogen is only about 70.8 kg/m³ (textbook values).
- Per liter, liquid hydrogen holds about 8.5 MJ versus about 34.4 MJ for jet fuel, so tanks are about four times larger.
- Burning or using hydrogen in a fuel cell makes water, about 8.9 kg per kg of hydrogen, and no CO₂ at the aircraft.
- Cryogenic tanks are bulky and heavy, shaping the whole aircraft.
- Green hydrogen depends on clean electricity for electrolysis.
Key equations
Worked examples, step by step
Example 8.1 Hydrogen vs jet fuel by mass?
Show the steps
- 120/43.
Answer: 2.79 times more per kg.
Example 8.2 Volumetric energy of liquid hydrogen?
Show the steps
- 70.8 × 120/1000.
Answer: 8.50 MJ/L.
Example 8.3 Tank-volume ratio vs jet fuel (0.8 kg/L, textbook)?
Show the steps
- 34.4/8.50.
Answer: About 4.05 times larger.
Practice problems
Work each on paper first, then check.
Water from 100 kg of hydrogen?
Show answer
About 894 kg.
Jet fuel volumetric energy?
Show answer
0.8 × 43 = 34.4 MJ/L.
Why are hydrogen tanks heavy?
Show answer
Insulated cryogenic walls.
When is hydrogen low-carbon?
Show answer
When made with clean energy.
Common misconceptions
Myth: Hydrogen is light, so tanks are small.
Actually: Low density means big tanks.
Myth: Hydrogen aircraft emit nothing.
Actually: They emit water vapor, which can form contrails.
Myth: All hydrogen is green.
Actually: Most today is made from fossil gas.
Flashcards
LH₂
Liquid hydrogen.
Cryogenic
Very cold storage.
Fuel cell
Electrochemical power source.
Electrolysis
Splitting water with electricity.
Volumetric energy
Energy per volume.
Green hydrogen
Made with clean power.
Self-check quiz
How this helps save the planet
NASA’s Sustainable Flight National Partnership works across advanced vehicle technologies, efficient operations and sustainable aviation fuels; this unit adds hydrogen as a further option, where tank volume is the main design challenge.
Hydrogen values in this unit are textbook values, not NASA figures.
On Saving Planets: General Chemistry I · Thermodynamics
Sources: NASA Aeronautics: Sustainable Flight National Partnership
Free learning resources
Unit 9 · Weeks 12–13
Operations, Noise and Air Quality
Efficient taxi and trajectories, decibel arithmetic, airport noise, local air quality and leaded aviation gasoline.
Learning objectives
By the end of this unit you can:
- Estimate taxi fuel savings.
- Add sound levels in decibels.
- Apply the inverse-square law.
- Explain the leaded-fuel issue.
Key concepts
- Operations matter: single-engine taxi, continuous descents and optimal trajectories cut fuel with today’s aircraft.
- Decibels add logarithmically: two equal sources are 3 dB louder, not twice the number.
- In open air, sound level drops about 6 dB per doubling of distance.
- Engine NOx, particles and CO affect air quality near airports.
- EPA says most aircraft using leaded fuel are piston-engine aircraft carrying 2–10 passengers; commercial jets don’t use leaded fuel.
Key equations
Worked examples, step by step
Example 9.1 Two 80 dB sources together?
Show the steps
- 10 log₁₀(2 × 10⁸).
Answer: 83.0 dB.
Example 9.2 Level drop from doubling distance?
Show the steps
- 20 log₁₀ 2.
Answer: 6.02 dB.
Example 9.3 Taxi 10 minutes on one engine instead of two at 0.1 kg/s each (sample). Fuel and CO₂ saved?
Show the steps
- 0.1 × 600 = 60 kg.
- 60 × 3.16.
Answer: 60 kg of fuel, about 190 kg of CO₂.
Practice problems
Work each on paper first, then check.
Ten equal 70 dB sources?
Show answer
80 dB.
Drop when distance quadruples?
Show answer
12.0 dB.
Fuel for two engines over 10 minutes?
Show answer
120 kg.
Which aircraft use leaded fuel (EPA)?
Show answer
Mostly piston-engine aircraft.
Common misconceptions
Myth: Decibels add linearly.
Actually: They add logarithmically.
Myth: Operations can’t cut emissions.
Actually: They cut fuel today.
Myth: Airliners burn leaded fuel.
Actually: EPA says commercial jets don’t.
Flashcards
Decibel
Log measure of sound.
Inverse-square law
Intensity falls with r².
Single-engine taxi
Taxi on one engine.
Continuous descent
Idle descent without level-offs.
NOx
Nitrogen oxides.
Avgas
Aviation gasoline.
Self-check quiz
How this helps save the planet
EPA says the majority of aircraft operating on leaded fuel are piston-engine aircraft, typically carrying 2–10 passengers, and that jets used for commercial transport do not use leaded fuel.
EPA has issued a final determination that lead emissions from certain aircraft engines endanger public health and welfare, triggering duties for EPA and the FAA to set standards.
On Saving Planets: Solutions · Aircraft Performance
Sources: U.S. EPA: Regulations for lead emissions from aircraft
Free learning resources
Unit 10 · Weeks 14–15
Pathways to Net Zero
Traffic growth, efficiency, SAF, new aircraft and offsets combined into scenarios toward 2050.
Learning objectives
By the end of this unit you can:
- Project traffic growth.
- Combine reductions multiplicatively.
- Build a simple wedge scenario.
- Discuss policy tools.
Key concepts
- Emissions = traffic × energy per traffic unit × carbon per energy.
- Growth compounds: 3% a year doubles traffic in about 24 years (sample rate).
- Reductions multiply: (1 − efficiency gain) × (1 − SAF lifecycle saving).
- Remaining emissions need new aircraft, more SAF, or removals.
- DOE notes ICAO’s CORSIA caps net CO₂ from international aviation at 2020 levels through 2035.
Key equations
Worked examples, step by step
Example 10.1 Traffic grows 3% a year from 2026 to 2050 (sample). Growth factor?
Show the steps
- 1.03²⁴.
Answer: 2.03.
Example 10.2 With a 25% efficiency gain, emissions relative to today?
Show the steps
- 2.033 × 0.75.
Answer: 1.52.
Example 10.3 Add SAF with a 50% fleet-wide lifecycle saving.
Show the steps
- 1.525 × 0.5.
Answer: 0.762, still 76% of today’s level.
Practice problems
Work each on paper first, then check.
Doubling time at 3%?
Show answer
23.4 years.
Saving needed to reach 0 from 0.762?
Show answer
The full remainder: new aircraft, more SAF and removals.
Years from 2026 to 2050?
Show answer
24.
What does CORSIA cap?
Show answer
Net international aviation CO₂ at 2020 levels through 2035.
Common misconceptions
Myth: Reductions add.
Actually: They multiply.
Myth: Efficiency alone reaches net zero.
Actually: Growth outpaces it.
Myth: Offsets cut emissions at the engine.
Actually: They compensate elsewhere.
Flashcards
Net zero
Emissions balanced by removals.
Wedge
Slice of a reduction plan.
CORSIA
ICAO offsetting scheme.
Traffic growth
Rise in passenger-km.
Removal
Taking CO₂ from the air.
Scenario
Consistent set of assumptions.
Self-check quiz
How this helps save the planet
NASA says its Sustainable Flight National Partnership works with industry, academia and other agencies toward the aviation community’s goal of net-zero carbon emissions by 2050.
DOE notes that ICAO’s CORSIA caps net CO₂ from international aviation at 2020 levels through 2035.
On Saving Planets: Solutions · Capstone Design
Sources: NASA Aeronautics: Sustainable Flight National Partnership · U.S. DOE Alternative Fuels Data Center: Sustainable aviation fuel
Free learning resources
The lab (Sustainable aviation lab)
The lab is the hands-on part of the course. Here it is free and for practice only, with no credit.
Every lab runs in a spreadsheet or a free simulation, so there are no fuel, battery or hydrogen hazards. Do not handle fuels, batteries or pressurized gases for this course. Take screen breaks, sit with good posture, and keep cables out of walkways.
Safety reference: OSHA: Walking-working surfaces (slip, trip and fall hazards)
Lab A: Flight CO₂ calculator
Week 1
Goal: Build a spreadsheet that turns fuel burned into CO₂ and CO₂ per passenger-km.
Procedure
- Enter fuel in gallons for three sample flights.
- Compute CO₂ with EIA’s 9.75 kg/gal.
- Divide by passengers × km.
- Compare short and long flights.
Data table
| Fuel (gal) | CO₂ (kg) |
|---|---|
| 1000 | 9750 |
| 5000 | 48,750 |
| 20,000 | 195,000 |
Computed sample values.
Sample calculation
- 5000 × 9.75 = 48,750 kg.
- 20,000 × 9.75 = 195,000 kg.
Safety
- Computer only.
Home or virtual alternative
- Any spreadsheet works.
U.S. EIA: Carbon dioxide emissions coefficients
Planet link: EIA: 9.75 kg CO₂ per gallon of jet fuel. U.S. EIA: Carbon dioxide emissions coefficients
Lab B: L/D and fuel burn
Week 4
Goal: See how lift-to-drag ratio changes fuel for a 3000 km trip.
Procedure
- Enter R = 3000 km, V = 230 m/s, c = 0.6 /h.
- Compute the fuel fraction for L/D = 15, 17 and 20.
- Compute the saving relative to L/D = 17.
- Add aspect-ratio effects on induced drag.
Data table
| L/D | Fuel fraction |
|---|---|
| 15 | 0.135 |
| 17 | 0.120 |
| 20 | 0.103 |
Computed sample values.
Sample calculation
- 1 − e^(−0.1449) = 0.135.
- 1 − e^(−0.1087) = 0.103.
Safety
- Computer only.
Home or virtual alternative
- Any spreadsheet works.
Planet link: NASA’s X-plane demonstrator tests an ultra-efficient aerodynamic design. NASA Aeronautics: Sustainable Flight National Partnership
Lab C: Propulsive efficiency explorer
Week 5
Goal: Compute propulsive and overall efficiency across exhaust velocities.
Procedure
- Enter V₀ = 230 m/s and η_th = 0.5.
- Compute η_p for V_e = 400, 350 and 300 m/s.
- Compute overall efficiency.
- Relate to bypass ratio.
Data table
| V_e (m/s) | η_p | η_o |
|---|---|---|
| 400 | 0.730 | 0.365 |
| 350 | 0.793 | 0.397 |
| 300 | 0.868 | 0.434 |
Computed sample values.
Sample calculation
- 2/(1 + 350/230) = 0.793.
- 0.5 × 0.793 = 0.397.
Safety
- Computer only.
Home or virtual alternative
- Any spreadsheet works.
Planet link: NASA: Hybrid Thermally Efficient Core develops high-power-density turbine cores. NASA Aeronautics: Sustainable Flight National Partnership
Lab D: SAF blend calculator
Week 7
Goal: Compute lifecycle savings for blends and SAF reductions.
Procedure
- Enter blends of 10%, 30% and 50%.
- Enter a SAF lifecycle reduction of 50%, then 80%.
- Compute the saving and CO₂ saved per 1000 gallons.
- Compare with the Grand Challenge goals.
Data table
| Blend | Saving at r = 50% | kg CO₂ saved per 1000 gal |
|---|---|---|
| 10% | 5% | 487.5 |
| 30% | 15% | 1462.5 |
| 50% | 25% | 2437.5 |
Computed sample values.
Sample calculation
- 0.3 × 0.5 = 15%.
- 9750 × 0.25 = 2437.5 kg.
Safety
- Computer only.
Home or virtual alternative
- Any spreadsheet works.
U.S. DOE Alternative Fuels Data Center: Sustainable aviation fuel
Planet link: DOE: SAF can be blended at 10% to 50% depending on pathway. U.S. DOE Alternative Fuels Data Center: Sustainable aviation fuel
Lab E: Electric aircraft range
Week 10
Goal: Compute battery-electric range for several battery energy densities.
Procedure
- Enter η = 0.8, L/D = 15, battery fraction 0.3.
- Compute range for 250, 400 and 500 Wh/kg.
- Compare with a 300 km regional route.
- Change the battery fraction.
Data table
| e (Wh/kg) | Range (km) |
|---|---|
| 250 | 330 |
| 400 | 529 |
| 500 | 661 |
Computed sample values.
Sample calculation
- 400 × 3600 × 0.8/9.80665 × 15 × 0.3 = 529 km.
- 500 Wh/kg doubles the 250 Wh/kg range.
Safety
- Computer only.
Home or virtual alternative
- Any spreadsheet works.
Planet link: NASA: electrified aircraft propulsion can cut fuel and energy use. NASA Aeronautics: Sustainable Flight National Partnership
Lab F: Net-zero wedge model
Week 14
Goal: Explore warming in PhET Greenhouse Effect, then build a 2026–2050 aviation scenario.
Procedure
- In PhET Greenhouse Effect, add greenhouse gases and watch the temperature respond.
- Enter 3% traffic growth for 24 years.
- Apply a 25% efficiency gain and 50% SAF saving.
- Find the growth rate at which the two measures hold emissions flat.
Data table
| Case | Emissions vs today |
|---|---|
| Growth only | 2.03 |
| + efficiency | 1.52 |
| + SAF | 0.762 |
Computed sample values.
Sample calculation
- 1.03²⁴ = 2.033.
- 2.033 × 0.75 × 0.5 = 0.762.
Safety
- Computer only.
Home or virtual alternative
- Any spreadsheet works.
Planet link: NASA: the aviation community’s goal is net-zero carbon emissions by 2050. NASA Aeronautics: Sustainable Flight National Partnership
Exam prep practice sets
Time yourself: about 10 minutes per problem. Then compare with the full solutions.
Midterm practice set (Units 1–5)
CO₂ from 2000 gallons of jet fuel?
Show full solution
- 2000 × 9.75.
Answer: 19,500 kg.
g CO₂ per passenger-km for 19,500 kg, 150 passengers, 1000 km?
Show full solution
- 19,500,000/150,000.
Answer: 130 g.
Fuel fraction for 3000 km at L/D = 15 (Unit 3 values)?
Show full solution
- 1 − e^(−0.1449).
Answer: 0.135.
η_p for V₀ = 250, V_e = 350 m/s?
Show full solution
- 2/(1 + 1.4).
Answer: 0.833.
Saving from a 40% blend at 70% lifecycle reduction?
Show full solution
- 0.4 × 0.7.
Answer: 28%.
Final practice set (Units 1–10)
Ice crystals after a 60% cut from 10¹⁵ per kg?
Show full solution
- 10¹⁵ × 0.4.
Answer: 4 × 10¹⁴ per kg.
Electric range with 300 Wh/kg (Unit 7 values)?
Show full solution
- 330.4 × 1.2.
Answer: About 396 km.
Liquid-hydrogen volume for 1000 MJ?
Show full solution
- 1000/8.50.
Answer: 118 L.
Three equal 75 dB sources?
Show full solution
- 75 + 10 log₁₀ 3.
Answer: 79.8 dB.
Growth factor at 2% for 24 years?
Show full solution
- 1.02²⁴.
Answer: 1.61.
Emissions vs today at 2% growth, 25% efficiency, 50% SAF?
Show full solution
- 1.608 × 0.75 × 0.5.
Answer: 0.603.
Formula sheet
Constants
| Constant | Value |
|---|---|
| Standard gravity | g = 9.80665 m/s² |
| Jet fuel CO₂ (EIA) | 9.75 kg CO₂ per gallon (21.50 lb) |
| Jet fuel heating value (textbook value) | 43 MJ/kg |
| Hydrogen heating value (textbook value) | 120 MJ/kg |
| Liquid hydrogen density (textbook value) | 70.8 kg/m³ |
| Gallon | 3.785411784 L |
Source: NIST: CODATA value, standard acceleration of gravity
Free texts and sources
Use these free lectures, data pages and simulations alongside the course.
- MIT OpenCourseWare 16.885J Aircraft Systems Engineering (Fall 2004), Lecture 8: Environmental Factors: Free MIT lecture notes.
- NASA Aeronautics: Sustainable Flight National Partnership: NASA program.
- U.S. DOE Alternative Fuels Data Center: Sustainable aviation fuel: DOE SAF data.
- U.S. EIA: Carbon dioxide emissions coefficients: EIA emission factors.
- NASA: NASA-DLR study finds sustainable aviation fuel can reduce contrails (2021): NASA contrail study.
- PhET: Greenhouse Effect: Radiation balance.
Glossary
- Aspect ratio
- Span squared over wing area.
- Avgas
- Aviation gasoline for piston engines.
- Blend limit
- Maximum SAF share in jet fuel.
- CORSIA
- ICAO carbon offsetting scheme.
- Contrail
- Condensation trail of ice crystals.
- Decibel
- Logarithmic sound measure.
- Electrified propulsion
- Electric or hybrid aircraft power.
- Emission factor
- CO₂ per unit of fuel.
- Energy intensity
- Energy per passenger-km.
- Induced drag
- Drag caused by lift.
- Lifecycle emissions
- Well-to-wake CO₂.
- Liquid hydrogen
- Cryogenic hydrogen fuel.
- Load factor
- Passengers over seats.
- Net zero
- Emissions balanced by removals.
- Non-CO₂ effects
- Warming from contrails, NOx and particles.
- Passenger-km
- One passenger carried one km.
- Propulsive efficiency
- Share of jet power producing thrust.
- SAF
- Sustainable aviation fuel.
- Soot
- Carbon particles in exhaust.
- Specific energy
- Energy per unit mass.
Self-assessment rubric
No grade or credit is given. Use this to judge honestly where you are in each unit.
| Level | What it looks like |
|---|---|
| 4 · Mastery | Accounts for CO₂ and non-CO₂ effects with correct units and baselines, combines reductions correctly, and explains trade-offs between options in plain words. |
| 3 · Proficient | Solves the practice and exam sets with minor slips and checks units. |
| 2 · Developing | Follows worked examples but mixes up combustion and lifecycle CO₂ or adds reductions instead of multiplying. |
| 1 · Beginning | Quotes savings without baselines or units; needs to revisit the units. |
Suggested weighting if you want a score
| Part | Weight |
|---|---|
| Practice problems | 20% |
| Labs | 25% |
| Midterm practice set | 25% |
| Final practice set | 30% |
Aim for level 3 or better in every unit before moving to the next course.