# Is Fluid Structure Interaction considered in aircraft design?

Fluid Structure Interaction (FSI) causes an aeroplane’s geometry to change and hence the forces on the different surfaces of an aeroplane become different than the forces expected according to initial calculation.

1. Is this Fluid Structure Interaction considered while calculating forces (and hence the final design) of aircraft while finalizing the designs for aircraft?
2. If it is considered, what are the available software packages which could be used to analyse this?
• Another common term is aero-elasticity. Jun 1 '15 at 10:49
• Aero-elasticity is a very vague term, and you can consider FSI to be a subset of aero-elasticity. but the particular problem where you find iteratively the effects of aerodynamic forces on structure, and then find the forces on the deformed structure is FSI Jun 1 '15 at 11:02
• Terms are as vague your definitions of them. I don't think as FSI as a subset of aero elasticity, quite the opposite. FSI deals with all kinds of fluids and structures, e.g. hydraulic lines, pumps, cardiovascular mechanics. Aero-elasticity is a subset of FSI, it only deals with the interaction between flow of air and non-rigid structures. Jun 1 '15 at 11:24
• ^^Edited the question, and thanks for the further insight, turns out I was wrong :D Jun 1 '15 at 12:41

Just one example: Good designers put the aileron pushrods away from the elastic axis of the wing to enable the deformation of the wing to create a damping deflection of the ailerons. This is especially helpful for high aspect ratio wings:

When the wing flexes, the pushrod will not be compressed, so will become relatively longer than the surrounding wing structure. This will create a negative aileron deflection which works against the lift force which flexes the wing in the first place. Doing this is particularly helpful in damping wing flutter.

Generally, the engineers make sure that every aircraft component works as intended even when the structure is deformed. Another example: To compensate for differences in the thermal expansion of different components, pushrods in glass fiber fuselages have two halves, connected by a pivoting lever, so that changes in their length will compensate.

1. deflections must be considered, if relevant in the force (pressure) distributions and if relevant for the aerodynamic and structural design of the aircraft. In addition to that, flutter, buffeting and other fluid-structure (aeroelasticity) effects must be considered as well. In addition to that, when relevant, aero-servo-elasticity (the dynamic behavior of the aero-structure AND the response of the control system to that behavior) is also considered. This becomes a critical analysis for some designs (like, high aspect ratio or highly flexible aircraft), and has historical stories (good, funny or bad consequences).

2. For static aeroelasticity, you can go iteratively by hand or by using simple calculations. But especially for dynamic cases, if you do not go into simplified approaches, it generally requires Nastran or other off-the-shelf of home-developed FSI capable solvers.

This page has a picture showing the relationship between flight related phenomena: http://www3.imperial.ac.uk/aeroelastics/projects/flexibleaircraft (aeroelasticity , flight mechanics, flexible body dynamics)

Aero-elasticity is indeed considered in design and certification of aircraft.

One software package that I know is capable of aero-elasticity computations is NASTRAN / PATRAN. No doubt there will be others.

After consulting with some seniors, I've come to know that Ansys workbench (Which effectively uses NASTRAN on the backend) has the proper tools for achieving this using combination of FEM and CFD