# Tip Fences for Reduction of Lift-Generated Airframe Noise 

### These simple, easily retrofitted devices reduce drag as well as noise. 

#### *Ames Research Center, Moffett Field, California*

Tip fences have been invented to reduce the noise generated in the
airflows about the high-lift systems (the flaps and slats) of airplane
wings. Tip fences also afford an important secondary benefit by
increasing lift-to-drag ratios.

Typical modes of operation of the flaps and slats of an airplane wing
are the following: In preparation for takeoff, the flaps are partly
extended, and the slats are fully extended to provide a clean airflow
over the main element of the wing. Shortly after takeoff, the slats are
retracted to increase the lift-to-drag ratio during climbout. During
landing, the slats and flaps are fully extended, and significant
aerodynamic noise is generated at their tips. Tip fences can reduce the
noise generated during takeoff and climbout, but more importantly during
approach and landing.

Tip fences are so named because they are fencelike barriers and are
mounted at or near some or all of the inboard and outboard tips of the
flaps and slats (see Figure 1). These mounting locations are chosen
because they are as close as possible to the aerodynamic-surface
discontinuities where

  Figure 1. **Tip Fences** can readily be added to flaps and slats to
reduce noise and drag.

vortices associated with noise form when flaps and slats are extended.
Tip fences can be made of any suitable rigid material (e.g., metal or
composites) and can be attached to the tips of flaps and slats by
riveting, welding, bolting, or other conventional means. They can be
easily and inexpensively retrofitted to most pre-existing airplanes,
with minimal design changes.

A tip fence can be formed from a flat plate, or, if desired, it can be
fabricated as a more complex, aerodynamically contoured body. In a
typical application, the tip fences would extend below the lower surface
of a slat or flap, as depicted on the right side of Figure 1. However,
other combinations of tip and fence configurations are also possible.

In a demonstration of the benefits of tip fences, two different versions
of a wing with flap extended were tested in a wind tunnel and in flight
on a Lanceair IV airplane. In one version, the flap was equipped with
tip fences; in the other version, it was not. The flight data is shown
in Figure 2, demonstrating that the tip fences caused less noise to be
generated over a broad range of frequencies. The wind-tunnel data showed
that tip fences can also reduce the profile or viscous drag
significantly.

![](media/image1.png){width="3.4375in" height="2.123611111111111in"}\
Figure 1. **Tip Fences** can readily be added to plaps and slats to
reduce noise and drag.

 

![](media/image2.png){width="2.615972222222222in"
height="1.8659722222222221in"}\
Figure 2. **Less Noise Was Generated** by the airflow over a wing
equipped with flap tip fences than by the airflow over same wing without
flap tip fences under otherwise identical test conditions.

*This work was done by James C. Ross and Bruce L. Storms of* **Ames
Research Center.** *For further information, access the Technical
Support Package (TSP)* **free on-line at www.nasatech.com/tsp** *under
the Mechanics category.*

*This invention has been patented by NASA (U.S. Patent No. 5,738,298).
Inquiries concerning nonexclusive or exclusive license for its
commercial development should be addressed to the Patent Counsel, Ames
Research Center, (650) 604-5104. Refer to ARC-14009.*

*Tech Briefs article published February 2002.*