The Honorable Philip E. Coyle
Operational Test and Evaluation
Office of the Secretary of Defense
Washington, DC 20301
Senate Armed Services Committee
Russell Senate Office, Room 232A
March 25, 1998
The Department defines operational effectiveness as the degree to which a weapon system accomplishes its mission. Operational testing must involve the conduct of realistic operational mission scenarios for the weapon system under test. We often compare a new system to an existing baseline system, in addition to a comparison to the expected threat. In the case of the F-18E/F, we will be evaluating its operational effectiveness in both air-to-air and air-to-ground mission areas as compared to the F-18C/D. Similarly for the F-22 we will compare, as part of our assessment of operational effectiveness, the accomplishment of its missions compared to the F-15C.
In early assessments of weapon systems there is limited opportunity or capability to conduct completely realistic mission operations. Therefore, we have to look at the various weapon systems’ characteristics demonstrated during early testing and use modeling, simulation and operational judgment to assess how these characteristics may impact operational effectiveness. That is what we have done with the results of the ongoing tests of the F-18E/F. Our assessment of the wing drop fix at this stage of developmental testing will focus not only on the technical degree to which flight parameters are affected and controlled, but attempt to assess the degree that the resultant flying qualities will have on mission effectiveness.
The Navy is conducting an aggressive F/A-18E/F test program. The Integrated Test Team (ITT) concept, which combines contractor and Navy personnel into one cohesive team conducting the developmental testing program, has proven effective at identifying and solving problems. Early involvement of the operational testing community, including the conduct of three early operational testing periods to date and the participation of Navy operational test force pilots, has contributed a great deal to the early understanding of the operational effectiveness of the F/A-18E/F. My staff works with the ITT and has access to management meetings, test events and pertinent test data. I want to compliment the Navy on their management of the combined test team, and on the forthright and open way in which they have worked with my office and the operational test force.
The Secretaries of Defense and the Navy are both on record that the decision for full funding for 20 more aircraft in Lot II, and advanced funding for 30 aircraft in Lot III, will not be made until the wing drop issue is suitably resolved. The Navy has also stated that they will not consider wing drop to be resolved until the Commander, Operational Test and Evaluation Force (COMOPTEVFOR) concurs that the solution effectively eliminates wing drop while not imposing undo penalties from an operational perspective. In particular, there will be a special test period, consisting of pilots from the operational test force flying representative mission profiles, which will be conducted after the ITT has determined that the wing drop solution is stable and there are no predicted large adverse affects to performance as the result of the modifications. Although no date has been set at this writing, this testing should occur soon, perhaps in the next few days, weather permitting. I have been closely monitoring the developmental test flights and will closely monitor this operational testing when it occurs and provide an independent assessment of wing drop resolution to the Secretary at that time.
Wing drop on the F/A-18E/F is an uncommanded, abrupt rolling motion of the aircraft that occurs in the heart of the maneuvering envelope and results from asymmetric air flow separation from the upper wing surface. The Blue Ribbon Panel experts, who examined the problem recently, concede that this problem is not atypical for a high performance fighter/attack aircraft development program and that it could not have been predicted prior to flight test. Wind tunnel techniques and computational procedures are necessary, but are not sufficient tools, and real open air flight testing is needed as well to adequately study this problem.
My staff has been tracking the progress of the wing drop issue very closely, including observing wind tunnel testing, receiving briefings from members of the Blue Ribbon Panel on the results of their in-depth investigation, and regular updates on flight test status. The process has been extremely thorough, including nearly1300 hours of wind tunnel testing, and over 290 flight test sorties and 400 hours of flight time with a sound technical approach applied. Clearly, the Navy has been trying to do the right thing. Many potential solutions have been considered, including some that might have had large negative impacts on other performance parameters. The chosen solution is expected to be a combination of modified flap scheduling programs and some configuration of a porous fairing over the upper surface of the wing fold. The final configuration may also include small stall strips or tripper strips on the upper and lower wing surfaces.
The first attempts with a porous fairing controlled the lateral wing movement that occurred in a large part of the flight envelope; however, it seems to cause unacceptable airframe buffeting at about 500 knots true airspeed with unloaded weapons pylons in place. There is a link between the porous wing fairing solution and airframe buffeting, but the root cause and subsequent modifications to the design are still being investigated. Because testing has dramatically narrowed the problem, I am confident that an acceptable solution can be found with some relatively minor modification of this design. The impact this solution will have on other performance parameters such as range, acceleration and radar signature are still being assessed, but are not expected to result in any significant failures to meet key performance parameters or other performance thresholds. For example, the porous wing fold fairing might reduce range by about 10 or 20 nautical miles, a relatively small amount.
We will not have a complete understanding of the impact of the wing drop design fix until the completion of operational testing at the end of 1999. There are many weapons configurations and mission profiles that must be flown to adequately assess the F/A-18E/F’s operational effectiveness and determine if wing drop will be a factor. Although predictions can be made to assess the impact of the porous fairing design modification on other performance parameters and life cycle costs, a great deal of testing, scheduled over the next 22 months, must be done to confirm those predictions. However, a limited test period designed to focus on the root problem of uncommanded lateral wing movement in maneuvering flight, in a basic aircraft configuration including weapons pylons, can provide an early assessment of the operational impact of the wing drop fix. It should be understood that this testing will be conducted on developmental hardware that will not exactly replicate the production configuration. Also, icing and other operational considerations will not be tested until later. If successful, this operational testing should give us confidence that both the wing drop and buffeting phenomena are controlled and that the design is stable.
The F/A-18E/F program remains on track towards dedicated operational test and evaluation scheduled to begin in May, 1999. The seven developmental test aircraft have completed over 1580 sorties and 2380 flight hours. Flutter testing throughout the flight envelope is complete for the clean configuration and about 68% complete with external stores. Weapons separation testing has demonstrated very good results and is about 69% complete. The engine development program has accumulated over 19,565 hours on 33 different engines and is 98% complete. Overall, the developmental flight test program is about 64% complete.
Despite the schedule slips caused by past engine problems and more recent wing drop testing, the program has a schedule recovery plan to complete developmental testing on time. Historical test program performance indicates they will be able to meet the sortie generation rates required to meet the recovery plan. While there is not much schedule margin, barring additional large, unforeseen complications in development, the operational test and evaluation should start on time.
The results of three early operational testing periods have been very positive. Highlights include:
There is a great deal of development ahead of the F/A-18E/F before the completion of operational test and evaluation and a recommendation to proceed Beyond Low Rate Production. The next operational testing period is scheduled for mid 1998 with a greater emphasis of weapons systems performance and will include a larger operational flight envelope. The results of this testing will be key to the Navy decision at the end of 1998 to proceed with Lot III full funding and begin advanced funding for Full Rate Production. The following are issues that I feel should be focused on during the upcoming testing.
There is no doubt that some of the problems identified in the F-18E/F can have significant impact if not corrected. Already these problems have been substantially mitigated, once operational testers have had an opportunity to fly the modified aircraft, we will know more about mission impact, if any.