...I've been waiting for some of the front-runners of our sport to experiment with the application of aeroelastic tailoring to our wings...

From : Don Stackhouse

Actually Derek, Joe and I have been experimenting with and doing this for years, and it works well for certain applications IF it's done right. However, it takes some pretty good structural analysis cababilities to make it work.

The first level of aeroelastic tailoring is simply making sure that the aircraft remains STRUCTURALLY stable. The classic problem of forward-swept wings wanting to tear themselves off because of bending-induced twist changes (such as on the X-29) is one example.

The second level of aeroelastic tailoring is predicting how the structure will deflect in flight, then correcting things like the manufactured washout so that the in-flight shape while deflected matches the shape you designed for initially. This is a good job for PROPERLY CALIBRATED finite element stress analysis ("FEA"). This is pretty much standard practice in the full-scale propeller business, at least at the place where I used to work. Propellers see extremely high loads and the associated high deflections, and they are also extremely sensitive to twist (even a quarter of a degree can be very significant). If you don't allow for this in the design and manufacturing of the blades, you can waste a lot of efficiency.

The next level is to use the changes in load at different operating conditions to cause a beneficial change in the shape to make the airframe's configuration more optimum over a wider variety of flight conditions. For example, the optimum twist for high speed low-Cl flight is usually not the same as for high-Cl flight. In some models you can use bending-induced twist changes at different 'G' loadings to make the twist of the wing close to optimum at BOTH flight conditions. This particular type of aeroelastic design is much more complicated than the other two, and requires some fairly close cooperation between your FEA and aerodynamic analyses.

We've tried all three of these on a variety of models. In the right cases it can make a difference, but which level (if any) is appropriate depends on the individual case. In any case, it's usually a lot of work, and you have to have the right tools and the experience to use them effectively. If you don't know what you're doing you can easily spend a huge amount of effort and end up making things worse instead of better. It's not something you can learn overnight from a book, and it's not usually something for the faint of heart!

Don Stackhouse
DJ Aerotech