Document Review
“Future Test Needs of U.S. National Wind Tunnels for NASA’s Aeronautics Test Program: An Approach
for Mapping Ground Test Facility Usage Projections into Capability Projections”, Kalliman, et. al, AIAA
2011-1069
Review by Dunn
Current State
Future/Vision State
Gaps/Challenges
Recommendations
Future work includes collecting data across the nation by capability categories (e.g., from the GTTC,
DoD). Facility-level forecasts remain valuable, however, as additional data points and perspectives to
near-term capability level analysis.
Interfaces
GT Context
Figure 1. NASA Wind tunnel Tests Hours and Changes over Time
Figure 2. NASA Wind tunnel Test Hours and Percentage of Test Hours for FY2003 to FY2011
Broadly speaking, there are two approaches to forecasting future wind tunnel testing needs: top-down
and bottom-up. Top-down forecasting involves assessing major aeronautic research, development, test,
and evaluation
(RDT&E) programs and identifying and estimating their wind tunnel testing needs. This is very
challenging
The bottom-up approach is based on individual facility or test-center forecasts. Those forecasts usually
come from the organization or center which owns the facility. Facility projections are based on what
customers (NASA, DoD, or industry) indicate. Customers have incentives to schedule tests to ensure the
facility is available regardless of need. Historically, there has been no penalty for cancelling or delaying
tests. This is especially true now given surplus capacity. Facilities may also have an incentive to
overestimate their demand in order to receive extra annual funding or maintain staffing levels. As a
result, aggregating individual facility forecasts have been consistently higher than actual use.
The bottom-up approach involving facility projections lends itself to national projections of future
needs. Wind tunnel testing facilities may sometimes be interchangeable. Test characteristics limiting
interchangeability of test facilities are speed regimes (i.e. subsonic, transonic, supersonic, hypersonic),
test section size, special capabilities (e.g. icing, acoustic sensors, propulsion integration) needed, and
existence of baseline data at a particular facility.
Each of these issues can be addressed at some cost. Smaller models can be tested in larger tunnels, but
runtime costs will increase. Special capabilities can be moved or replicated in other tunnels at a cost.
Programs rarely consider such investments, generally leaving it to operators to find the resources to
upgrade a facility. Tunnels may be consolidated if the costs of upgrading one tunnel are less than the
costs of operating two or more tunnels with the same capabilities. Costs of moving to a new tunnel are
typically born by a program, but operators can decrease these costs with additional calibration testing.
Determining potential benefits depends on good future needs assessments, which in turn depends on
combining the disparate facility projections into national aeronautics testing capability projections.
Building a national future need assessment from facility projections tends to suggest that every current
facility is needed to some degree.
Forecasts are made at different points in time during the annual planning and execution cycle. The
differences can be traced to many reasons, including
- program schedule changes
- continual development of test plans
- unplanned facility downtime
- funding issues, including program cancellation and the desire to spend funds in next fiscal year.
The total capacity available for testing helps identifying gaps in needed capabilities. Each estimate for
demand is different, but the total capacity of subsonic wind tunnels within NASA can generally be made
as a point estimate. We estimate total capacity of a wind tunnel by analyzing need for maintenance and
upgrades, available workforce, number of work-shifts the tunnel can operate, and other characteristics.
EFD/CFD Integration
EFD/CFD Context
CFD
Context
Current
Future
Gap
Recommendation