Large Model Wings Level Yaw capability to be available soon at AEDC

  • Published
  • By Deidre Ortiz
  • AEDC/PA
ARNOLD AIR FORCE BASE, TENN. --  Arnold Engineering Development Complex (AEDC) engineers are presently working on a multimillion dollar fast-track design and build effort for the 16-foot transonic wind tunnel called Large Model Wings Level Yaw (WLY).

It's likely that the new WLY capability will be available to AEDC's test customers by the end of 2014.

Marvin Sellers, flight systems senior engineer, explained the reason behind this accelerated effort.

"The current WLY capability, built in the mid-1980s, does not have sufficient capacity to handle the loads [generated by] some of the new aircraft being tested," he said. "We have used the existing WLY for all of the Global Hawk tests performed at AEDC with great success. The WLY system uses a second roll mechanism offset by a prebend from the primary roll mechanism, which is installed on the pitch sector. By rolling the two roll mechanisms approximately the same amount in opposite directions and adjusting the pitch sector, the model yaws while keeping the wings level to the floor."

Sellers noted that test articles with larger load requirements needed to use the primary support system which includes the pitch sector and primary roll mechanism.

"Yaw angles are achieved by pitching and rolling the model to obtain the correct orientation relative to the wind," he said. "This requires more roll movement than when using the WLY mechanism and takes a small amount of additional time to set model attitudes. But our advanced control capabilities have allowed data to be acquired in a continuous sweep fashion for many years using this pitch/roll technique."

A discovery was made during a study on the first Global Hawk test that high-aspect ratio wings (large wing span) experience flow variations as a model is rolled in the wind tunnel.

"Data acquired with WLY were compared with pitch/roll combination and indicated the wings were experiencing non-uniform flow in the corners of the tunnel as the model was rolled," Sellers said. "Although corrections could be applied to the pitch/roll data to minimize the effect, the complete effect could not be removed."

All of the Global Hawk test data was acquired with the WLY technique. New aircraft with large wing spans and high aerodynamic loads needed to use the WLY technique but haven't been able to because of limits with the current mechanism.

"The new large model WLY capability will provide improvements in data quality and productivity for AEDC's customers," Sellers said.

In addition, the yaw range for WLY will be increased from 15 to 16 degrees, and the capacity of the new WLY will be doubled with the possibility to increase roll-moment capacity by almost three times.