After months of debate over the controversial CSAR-X program with losing companies Lockheed Martin and Sikorsky batting around accusations of contract and source selection malfeasance Boeing has finally emerged from the shadows to confront its competitors.
In a telephone news conference this morning that spanned nearly an hour, top officials with the companys winning CSAR-X program briefed reporters on the key questions that have emerged over the Air Forces choice of the HH-47 Chinook as the winner.
Recent stories have focused on the Chinooks size, downwash and brownout problems, culminating in a letter written to Air Force Secretary Michael Wynne from Louisiana Sen. Mary Landrieu saying the Chinook was unsuitable for rescue operations during Katrina because excessive downwash from its huge, twin rotors made it impossible to pluck survivors from atop flood-bound buildings.
Boeing program officials Rick Lemaster and Van Horn fired back with both barrels, claiming their twin-rotor helicopters downwash was actually less than that of its competitors the Lockheed Martin EH-101 and Sikorsky S-92, both single rotor in the key areas where rescue personnel would be operating and that theyd solved the brownout problems with new flight control systems already field tested and proven to mitigate a problem that plagues every helicopter in dusty or snow-covered environments.
The CSAR-X System Requirements Document was the document that told us what we had to be capable of doing.
This document said that downwash horizontal velocities shall not exceed 65 knots when measured from 0-6 feet above ground level while performing rescue operations, including providing emergency life saving measures to isolated personnel, placement of a non-ambulatory personnel in a hoist recovery device, overland movement, self protection, communication, and swimming.
Boeing committed to deliver the Air Force an HH-47 that will meet these downwash requirements. To support this commitment, in our proposal we told the Air Force about real-world testing that Boeing has done showing that the maximum horizontal downwash velocity will in fact be significantly less than its 65 knot requirement.
Furthermore, this testing also showed that the highest downwash velocity occurs only in fairly small regions on either side of the hovering aircraft. Outside of those spaces, the downwash is even lower.
Additionally, during the CSAR-X Source Selection, the Air Force held a Basic Aircraft Flight Evaluation (BAFE) demonstration with each competitor to evaluate the ability of the pararescue team to approach the aircraft at mid-mission gross weight at different hovering altitudes -- from 200-feet to 50-feet in 50-foot increments, then down to 20 feet.
The HH-47 successfully met all of the requirements during these tests, and personal routinely operate underneath hovering HH-47 aircraft around the world today. In fact, US Special Operations forces are currently procuring additional HH-47G aircraft because of these and other, unmatched capabilities
One important factor that continues to be overlooked regarding downwash is disc loading. This means the amount of energy contained in the rotor wake of a hovering helicopter is proportional to the aircrafts disc loading (i.e., thrust divided by disc area).
The greater the disc loading, the higher the vertical velocity, or downwash, generated underneath the vehicle. Mathematically, downwash is proportional to the square root of disc loading. I can explain this further in the Q/A session if you need additional clarification.
And even though the HH-47 is heavier at the mission midpoint than either of the competitors aircraft, its disc loading is considerably less because it has a greater rotor disc area. In fact, the HH-47 has about 75% more disc area (the rotorcraft equivalent of wing area in a fixed wing aircraft) than the EH-101 and 127% more disc area than the S-92.
This additional disc area means the weight of the vehicle is supported by more lifting surface, resulting in a lower downwash velocity under the aircraft where rescue operations take place.
Using the relationship between disc loading and downwash, we determined that the downwash velocity of the HH-47 is less than that of either competitor at the midpoint rescue. The predicted horizontal component downwash for our CSAR competitors is between 3-10 percent greater than the HH-47 based on the Navys PAXMAN analytical tool
Finally, we want to address some incorrect information on brownouts. A recent media article made an assumption that the Air Force reached the wrong choice for the CSAR-X mission acting either through incompetence or through ignorance, when in fact the Air Force conducted a complete and through evaluation and had access to more complete and factual information than the author of this inaccurate article.
As I have already mentioned, the Air Force put all three of the CSAR-X competitors baseline aircraft through extensive real-world testing at Nellis AFB that was designed to specifically measure and evaluate performance in relevant environments.
Brownout conditions are a challenge for all rotorcraft operations. The U.S. Army CH-47D missions in both OIF and OEF have mainly been to transport cargo payloads, operating at or near max gross weights. These missions are not similar to CSAR missions.
The HH-47 incorporates the latest technology capabilities available from MH-47G, CH-47F and other aviation technology developments. In terms of its key features and basic platform, the HH-47 has limited commonality with the current CH-47D other than its proven rotors and drive systems and its well established survivability characteristics.
Of the many major improvements being delivered in the CH-47F and being incorporated into the HH-47, two are especially relevant to brownout environments: the Common Avionics Architecture System cockpit (CAAS) and the Digital Automatic Flight Control System (DAFCS).
CAAS greatly improves air crew situational awareness; and DAFCS provides dramatically improved flight control capabilities through features such as "hover hold," "altitude hold" and "beep down" that improve performance and safety in brownout and throughout the flight envelope.
These state of the art capabilities will - in terms of performance, safety, and supportability - be equal to or better than any rotorcraft flying today.
To give just one example, using the beep down feature, an HH-47 pilot will be able to take the aircraft from a hover down to the ground by using a button on his control stick to beep the aircraft down a little bit at a time, in any low visibility condition, whether due to sand or snow, or fog or smoke, or simply darkness.
The CH-47F, newly developed for the U.S. Army, has recently passed Operational Testing with flying colors; demonstrating the capabilities in extensive operational testing.
Horn said that the Landrieu letter addressed an older version of the aircraft and that she cited experts who were misquoted.
These claims amount to a strong defense of the Boeing helo. But one of the strongest arguments and one thats hard to counter is that all the protests, and all the arguing, amount to a protracted delay in fielding a capability thats badly needed in the war zone now. The HH-60 Pave Hawk suffers from the same overload problems as other legacy helicopters: keep adding on new flight control systems, computers and hardware and your performance goes down.
Lemaster and Horn were confident that even though more than $100 million has been slashed from the program by lawmakers based largely on the delay, if the protests by Sikorsky and Lockheed are overturned, the Air Force will have a convincing case to restore the funds quickly and get the new bird in the air.
Defense Tech participated in the teleconference and has been in touch with Boeings competitors to get their impressions of the defense. A spokesman for Lockheed Martin strongly questioned Boeings claim that the rotor wash was the same or less than the EH-101. He was unable to address the Landrieu letter and added the EH-101 platform has been combat proven with the British military in Iraq.
-- Christian
