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:
- Range requirements are being met with some margin. Even when the negative impact expected as a result of wing drop modifications is factored in, the F/A-18E/F meets its tightest range margin in the Fighter Escort configuration.
- The requirement to land with a 9000 pound recovery payload of fuel and weapons, known as "bringback", is being met. In addition, this prediction is based upon the design specification aircraft weight and the aircraft is currently underweight. This weight margin can provide even greater bringback capability. The ability of the F/A-18E/F to land with a greater payload of weapons and fuel than the F/A-18C/D will provide much greater tactical flexibility and a greater margin of safety.
- Weapons separation and delivery accuracy testing are progressing well and have revealed no major problems. Undesirable bomb-to-bomb collisions have occurred in some delivery profiles and a software fix to modify release parameters will be tested. Testing to date has indicated that the E/F will be as good as, or better, than the C/D in freefall weapons delivery accuracy.
- Operational flight test and data analysis using the validated performance data base indicate that the F/A-18E/F will meet its performance metrics. Despite its increased size, fuel load and weapons loadout capability, maneuvering performance is essentially the same as the F/A-18C/D. Takeoff and climb performance of the E/F are greater than the C/D. Subsonic acceleration of the E/F is also comparable to the C/D. One area of concern is level acceleration to supersonic speeds: though the E/F is predicted to meet its stated acceleration metric, the E/F is slower to accelerate to supersonic speeds in this scenario than the C/D. COMOPTEVFOR has highlighted supersonic acceleration in level flight as a major deficiency. COMOPTEVFOR has also highlighted maximum velocity and level transonic acceleration as major deficiencies. The operational impact of these deficiencies will be assessed in future operational tests.
- Initial carrier suitability trials were conducted in January 1997 with favorable results. The F/A-18E/F is expected to meet its key performance parameters for launch and recovery Wind Over the Deck (WOD) requirements and provide improvements over the C/D. The initial threshold requirement was for less than 30 knots of wind required to launch at a typical, tactical operating gross weight. The initial 17 knot prediction yielded a 13 knot margin. Though the wind speed threshold has not changed, the characteristic of this requirement has been increased to maximum gross takeoff weight. Due to this tougher requirement, the predicted WOD requirement of 29 knots has cut the margin to only 1 knot. By comparison, an F/A-18C/D requires 43 knots of WOD to launch at maximum gross takeoff weight. The predicted WOD required for carrier recovery at maximum gross landing weight is only eight knots, yielding a margin of seven knots.
- Improved survivability of the E/F compared to the C/D is a stated requirement. The increased fuel and weapons capacity of the E/F are themselves considered to be enhancing survivability features though the quantitative nature of these improvements must be borne out in modeling and testing. Increased fuel capacity should allow a greater "combat package" of fuel available for air combat maneuvering, as well as the ability to avoid more threats by deviating around them. In the air-to-air role, greater weapons carriage should improve survivability by allowing the E/F to carry more missiles. In the strike role, increased weapons carriage capability should allow the E/F to attack similar targets with fewer sorties than the C/D. This reduced exposure to the threat should increase overall survivability. Test data indicates that design modifications intended to enhance survivability by reducing radar signature are meeting specifications and should be effective at reducing the aircraft's radar cross section in some configurations.
- Concerns with electronic warfare systems are the greatest issues related to operational mission performance. The performance of the Radar Warning Receiver as installed in the F/A-18E/F with its required antenna configuration, particularly in relation to its performance in the F/A-18C/D, has not yet been demonstrated. Accurate threat radar identification and direction of arrival are key factors in providing the pilot with the situational awareness needed to effectively employ both offensive and defensive tactics. Therefore, concerns about the potential performance of the radar warning system in the E/F make it a high risk item.
- The ALE-50 towed decoy, or the radar transmitter in the case of the Integrated Defensive Electronic Countermeasures System (IDECM), is deployed behind the aircraft on a tow cable which also carries electronic signals. Testing to date indicates a problem with the tow cable being burned off by engine exhaust under certain conditions. The allowable flight envelope has not been fully determined; however, it is expected that the limits of the towed system will be less than the limits of the basic airframe. The tactical implications of such a limit due to cable burn off will be determined during future operational testing. The unique survivability enhancing features of the towed decoy will provide endgame protection against certain threat missiles not available to the F/A-18C/D, but concerns about its performance in some regimes make it a high risk item.
- Other items that have been highlighted as deficiencies during early operational testing are related to avionics subsystems in the F/A-18E/F that are common to the C/D. In particular, deficiencies related to radar performance in a jamming environment and the Targeting Forward Looking Infrared (TFLIR) have been identified in previous testing and operational use of the F/A-18C/D and are expected to have similar performance in the E/F. Long-term solutions to these deficiencies are being addressed with separate hardware upgrade programs.
- The F/A-18E/F Live Fire Test and Evaluation (LFT&E) program is based on extensive live fire testing of earlier versions of the F/A-18. Vulnerabilities identified during this prior testing were used during design activities to improve the survivability of the F/A-18E/F. Testing to date has included ballistic tests at the component level on the wings, fuel system, engines, selected portions of the fuselage, and new fire extinguisher technologies to replace halon-based systems which are banned by international agreement. Testing will culminate with a series of ballistic tests using a test article representative of the complete aircraft. Based on the component tests conducted to date, I expect the F/A-18E/F airframe and engine to be less vulnerable when compared to the F/A-18C/D.
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.
- The configuration of the porous wing fairing flown during developmental testing, and to be flown by the operational test pilots, does not incorporate the production wing fold mechanism. The air flow characteristics of a production representative, folding, porous wing fold fairing may be different than the developmental hardware. I recommend further wing drop flight testing with a production representative design, when it becomes available, to confirm the flight characteristics remain the same.
- A relationship has been established between the porous wing fold fairing added to the upper wing surface to address wing drop and the airframe buffeting that occurs when flying with an empty pylon configuration. Although not completely understood, there may be air flow turbulence around the weapons pylons introduced by the wing fold fix that was not present during early weapons separation testing. Because the force imparted to a dropped bomb is considerably greater than the air flow associated air frame buffeting, the porous wing fairing may not have changed weapons separation characteristics. However, I feel it is prudent to do some regression testing of weapons separation, particularly from the inboard pylon, to verify that these characteristics have not been altered by the wing redesigned wing fold fairing.
- Though the ALE-50 towed decoy has been integrated into the F/A-18E/F and will be the defensive system tested during the operational test and evaluation, IDECM is the defensive system intended for the airplane in operational use. System performance of these two systems, including tow line characteristics, are different. Every effort must be made during upcoming testing to ensure IDECM performance and integration issues are addressed by the F/A-18E/F program.
- Operational testing with surrogate threat systems is a limitation in many major test programs when the actual threat systems are not available. This compromise is not necessary if threat resources are supported and made available for test and evaluation. I support every effort to make real threat systems, actual MiG-29 aircraft in particular, available for F/A-18E/F and other future operational testing of tactical aircraft and weapons systems.
- The report of the independent Blue Ribbon Panel of aeronautical experts assembled to assist in solving the wing drop problem highlighted the deficiencies of the national aerospace community to thoroughly understand the wing drop phenomena. They stated that wing drop is not atypical for a high performance aircraft program and the root cause is not well understood. I support the Blue Ribbon Panel's recommendation to initiate a longer term research effort to systematically study this phenomena. The goal should be to develop appropriate wind tunnel techniques, computational codes and analysis and simulation techniques to support future design efforts.
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.
|Join the GlobalSecurity.org mailing list|