# Does deploying flap change the aspect ratio of the wing?

Specifically when a Plain flap is defleted the geometry of the wing will be altered (Camber is increased). Does this have any effect on aspect ratio? What's the connection between Camber and aspect ratio?

• There is no connection. Aspect ratio is based on a projection of the wing in the x-y-plane. Camber is in z direction. – Peter Kämpf Oct 17 '19 at 5:42
• Short answer: it depends. Some flaps extend backward (increasing chord and thus reducing aspect ratio), other don't. See The section about type of flaps on the Wikipedia page so that you can evaluate if you want to restrict your question to specific type of flap. – Manu H Oct 17 '19 at 5:44

The aspect ratio of a wing is defined as:

$$\text{AR} \equiv \frac{s^2}{A} ,$$

where $$s$$ is the wingspan and $$A$$ is the total wing area.

Some types of flaps are not only increasing wing camber, but also the wing area:

The Fowler, Fairey-Youngman and Gouge types of flap increase the wing area in addition to changing the camber.

Since the wingspan is unchanged, this will decrease the aspect ratio. Other types of flaps, like a plain flap, are not changing the aspect ratio.

You can see the flap types that change the aspect ratio in the following image (modified from Wikimedia):