by Dale Satran
There were several research goals for this test. The B777 aircraft was already certified and in public use but there were some discrepancies between previous wind tunnel test data and the flight test results. The research goals were to establish a high Reynolds Number database for a full-span model in the 12-Foot Pressure Wind Tunnel, to evaluate stability and control characteristics, and to evaluate a new high lift design.
The model mounting system is different in the 12-Foot from the mounting system used in other wind tunnels where the B777 had previously been tested. The 12-Foot mounting system created some wind blockage and upwash, which could not be directly corrected for in this tunnel entry. In other words, the data could not be compared directly with data from previous wind tunnel tests. The data from the test was useful to the B777 program but only incrementally. A future test was planned to account for the model mounting interference by testing the model upright and inverted. Unfortunately at this time, that test has been canceled due to budget cuts.
The incremental data from the test provided Boeing with some new insights into the performance of the B777. A large matrix of different control deflections were documented for different tunnel conditions. Several minor configuration changes were evaluated for future incorporation into the B777 configuration. The Advanced high lift design work was unfortunately eliminated due to budget cuts.
As a part of this test, we built a semi-span model to be tested in the National Transonic Facility, NTF, which is a cryogenic wind tunnel. The NTF has the capability of testing the B777 model at flight Reynolds Numbers. When the data from that test is available, it will be compared to the full-span data from the 12-Foot and other wind tunnel tests. One of the results will be to determine what Reynolds Number is required to accurately predict the performance of an aircraft.