---
title: 'Induced drag vs parasite drag'
description: 'Compare induced drag vs parasite drag, understand why their speed trends differ, and read a total-drag curve with clear assumptions and a worked example.'
lastModified: 2026-10-31
---

**Induced drag comes from producing lift on a wing of finite span. Parasite drag includes skin-friction, form and interference drag.** Both contribute to the force opposing motion through the air. Slowing down can reduce one component while increasing the other. [1](https://www.easa.europa.eu/sites/default/files/dfu/Annex%20II%20to%20ED%20Decision%202016-008-R.pdf#page=465), [2](https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/induced-drag-coefficient/).

A drag curve makes sense only when you know what stays fixed. Here, it compares steady level flight at different speeds, with the same weight, air density and configuration.

## What causes induced and parasite drag?

A lifting wing of finite span creates a trailing vortex system and downwash, a downward component of airflow. This changes the local airflow direction. The resulting aerodynamic force has a rearward component relative to the undisturbed airflow: **induced drag**, also called vortex drag or drag due to lift. [2](https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/induced-drag-coefficient/).

Parasite drag is not just drag from the fuselage. A wing produces parasite drag too. In the usual introductory breakdown, it includes:

| Component             | What causes it?                                                               | Example                        |
| --------------------- | ----------------------------------------------------------------------------- | ------------------------------ |
| Skin-friction drag    | Air viscosity and shear at the surface                                        | Air flowing over the wing skin |
| Form or pressure drag | The pressure distribution around a shape, including effects of separated flow | An exposed undercarriage wheel |
| Interference drag     | Interacting airflows around adjoining parts                                   | A wing–fuselage junction       |

EASA’s aeroplane learning material groups these three components under parasite drag. A wing can therefore contribute to both parasite and induced drag. [1](https://www.easa.europa.eu/sites/default/files/dfu/Annex%20II%20to%20ED%20Decision%202016-008-R.pdf#page=465).

Terminology varies between manuals. Some distinguish **zero-lift drag** from **lift-dependent drag**, which can include more than vortex drag alone. For the simple model below, the parasite term is treated as a constant-coefficient zero-lift term, and the lift-dependent term is represented by induced drag. [4](https://assets.publishing.service.gov.uk/media/5e1883e1e5274a06bfa721cc/Volume_01_Principles_of_Flight.pdf#page=49).

## Why induced drag rises as you slow down in level flight

Assume straight-and-level, constant-speed flight, with lift balancing weight and no significant vertical thrust component. Keep weight, air density and configuration fixed. Compare speeds in attached, low-speed subsonic flow, away from the stall and significant compressibility effects, and outside ground effect.

At a lower **true airspeed (TAS)**, the wing must still produce the same lift. It therefore needs a higher **lift coefficient**, the measure of lift relative to dynamic pressure and wing area. This normally requires a higher angle of attack. The induced drag coefficient rises with the square of the lift coefficient. [2](https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/induced-drag-coefficient/).

Combining the lift and drag relationships gives two useful trends in the simplified model:

- **Parasite drag force is proportional to TAS²**, if its drag coefficient stays constant.
- **Induced drag force is proportional to 1/TAS²**, if the required lift and the wing’s efficiency stay constant.

The UK CAA-hosted ANCON technical report uses the underlying model: a constant drag-coefficient term plus a term proportional to lift coefficient squared. Its assumptions are what make those speed trends possible. [3](https://www.caa.co.uk/publication/download/12420#page=18).

The force and its coefficient are different quantities. A drag coefficient can increase while speed decreases; calculate the force using both the coefficient and dynamic pressure.

## Read the total-drag curve under its stated conditions

Adding the rising parasite-drag curve and falling induced-drag curve gives a U-shaped total-drag curve. On its slower side, reducing speed increases total drag. On its faster side, increasing speed increases total drag.

The lowest point is the **minimum-drag speed**, often written **VMD**. At fixed lift, minimum drag also gives the maximum lift-to-drag ratio, **L/D**. The ICAO and aircraft-manufacturer training aid identifies this minimum-drag point in its performance discussion. [5](https://www.icao.int/sites/default/files/safety/LOCI/AUPRTA/full.html).

![Simplified induced, parasite and total drag curves against relative true airspeed. Induced drag falls, parasite drag rises, and their sum reaches a minimum at relative speed one. The component curves cross below the minimum point on the total-drag curve.](/blume-assets/content/content/knowledge/principles-of-flight/induced-vs-parasite-drag.png)

_Original dimensionless teaching model, not aircraft performance data. Weight, density and configuration are fixed, with constant parasite coefficient and wing efficiency; each plotted point represents a separate steady level-flight condition. The plotted range does not define a flight envelope._

In this model, parasite and induced drag are equal at minimum total drag. Their crossing is not itself the total-drag value: add the two components to reach the point on the upper curve.

Minimum drag is a **force** minimum. Aerodynamic power required is **drag × TAS**, so its curve is different. Minimum power occurs at a lower speed in this simplified model. A drag curve alone does not establish an aircraft’s endurance, range or operating speeds. [4](https://assets.publishing.service.gov.uk/media/5e1883e1e5274a06bfa721cc/Volume_01_Principles_of_Flight.pdf#page=60).

## A speed change affects the two components differently

Use an original example with arbitrary drag units. At the reference speed, let parasite drag and induced drag each equal **1 unit**, giving **2 units total**. The reference is the minimum-drag speed of this invented model.

| Relative TAS    | Parasite drag | Induced drag | Total drag |
| --------------- | ------------: | -----------: | ---------: |
| 0.8 × reference |          0.64 |         1.56 |       2.20 |
| 1.0 × reference |          1.00 |         1.00 |       2.00 |
| 1.2 × reference |          1.44 |         0.69 |       2.13 |

For the slower case, parasite drag becomes **0.8² = 0.64** of its reference value. Induced drag becomes **1/0.8² = 1.5625**, rounded to 1.56. Total drag is approximately **2.20 units**.

The parasite component has fallen, but the induced component has risen by more. Weight is unchanged. The aircraft still needs the same lift, and the induced-drag cost of producing it has increased.

## Change the conditions and you change the curve

If weight increases while steady level flight, TAS, density and wing efficiency remain comparable, the aircraft needs more lift. In the simplified model, induced drag varies with **lift squared**, so it rises with **weight squared** in this particular flight condition. [3](https://www.caa.co.uk/publication/download/12420#page=18), [4](https://assets.publishing.service.gov.uk/media/5e1883e1e5274a06bfa721cc/Volume_01_Principles_of_Flight.pdf#page=57).

Configuration changes can alter both terms. Extending flaps, for example, changes lift characteristics as well as drag. A turn changes required lift; changing air density changes the relationship between TAS and dynamic pressure. Recheck the assumptions before carrying the original curve into any of those cases. [1](https://www.easa.europa.eu/sites/default/files/dfu/Annex%20II%20to%20ED%20Decision%202016-008-R.pdf#page=466), [5](https://www.icao.int/sites/default/files/safety/LOCI/AUPRTA/full.html).

Near the stall or where compressibility matters, the constant-coefficient model becomes inadequate. Do not extend the drawn lines to zero speed or use the minimum as a flight instruction.

## Check your understanding

Suppose weight increases by **20%**. Compare steady level flight at the same TAS and air density, with configuration and the induced-drag model coefficient unchanged.

1. Can you keep using the original induced-drag curve unchanged?
2. By what factor does the model predict induced drag will change?
3. Does the original minimum-drag speed remain valid for the heavier case?

**Answers:** No. Required lift increases with weight, so induced drag becomes **1.2² = 1.44 times** its previous value: a **44% increase**. The total-drag curve changes, and its minimum moves to a higher speed in this model. Keeping speed unchanged does not keep induced drag unchanged when required lift changes.

## References

1. [EASA, Annex II to ED Decision 2016/008/R](https://www.easa.europa.eu/sites/default/files/dfu/Annex%20II%20to%20ED%20Decision%202016-008-R.pdf): subject 081, induced drag and parabolic polar, pp. 464–465; parasite components and total drag–speed graph, pp. 465–466. Historical learning material used for theoretical relationships, not a claim about current licensing requirements.

2. [NASA Glenn Research Center, _Induced Drag Coefficient_](https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/induced-drag-coefficient/): finite-wing flow, induced force and lift-coefficient relationship.

3. [UK CAA-hosted R&D Report 9842, _ANCON: Improvements in Version 2_, June 1999](https://www.caa.co.uk/publication/download/12420): sections 4.6–4.8, pp. 7–8, drag and lift equations and parabolic drag polar. Historical NATS research prepared for the UK Department of the Environment, Transport and the Regions; not an aircraft operating manual.

4. [UK Ministry of Defence, _AP3456_, Volume 1, chapter 1-5, May 2011](https://assets.publishing.service.gov.uk/media/5e1883e1e5274a06bfa721cc/Volume_01_Principles_of_Flight.pdf): paragraphs 2–4 and 26, terminology; paragraphs 34–35, lift and speed effects; paragraph 46 and Figure 10, minimum drag and minimum power.

5. [ICAO and aircraft manufacturers, _Airplane Upset Prevention and Recovery Training Aid_, revision 3, February 2017](https://www.icao.int/sites/default/files/safety/LOCI/AUPRTA/full.html): sections 6.4.5 and 6.5.1, load factor and minimum-drag speed. Used for general theory, not handling or recovery procedures.