The Industry Cooperation in the Lockheed Electra Investigation.

The outboard nacelle- the Achilles heel of the Lockheed Electra

In my previous blog entry, I had discussed how subcontracting was a way of building goodwill between aerospace competitors, the example from I talked about was in reference to the Space Shuttle program. However, even aside from financial incentives, there have been times in aviation history that corporate rivals have cooperated beyond that of a joint venture and one unheralded example of such cooperation was the extensive investigation into the loss of two Lockheed L-188 Electras shortly after the type went into service. The first loss was on 29 September 1959 when Braniff International Airways Flight 542 went down near Buffalo, Texas, on a flight from Houston Hobby Airport to Dallas Love Field. The second loss was on 17 March 1960 when Northwest Airlines Flight 710 went down near Tell City, Indiana, on a flight from Chicago Midway to Miami. 

The cooperation of Lockheed's competitors began after the Braniff crash. A Dallas warehouse was used to reassemble the wreckage as part of the investigation. Using a chicken wire frame, pieces were added in a gigantic jigsaw puzzle from October into November. In January 1960, the investigators with the Civil Aeronautics Board (CAB) were no closer to determining the cause of the loss of Braniff 542 and invited representatives from Eastern Airlines and American Airlines, both operators of large Electra fleets, along with NASA to join the investigation. The following month Lockheed invited engineers from Boeing, Convair, and Douglas to review what had been done so far in the investigation. But the loss of the second Electra when Northwest 710 went down shook the airline and aviation industry as aircraft like the Electra were the leading edge of the jet turbine age that would revolutionize air travel. There was near unanimous sentiment in American aviation that the cause of the loss of two Electras in passenger service had to be found and rectified for the good of the entire industry. 

NASA immediately put its resources at Lockheed's disposal (the decision to ground versus speed restrict the Electra will be subject of a future post for this blog). Allison, the maker of the Electra's engines, initiated its own flight test program with its own company Electra. Boeing and Douglas made their resources also available to Lockheed- with both companies fielding their own advanced jetliner designs for the day, helping Lockheed determine the cause of the Electra crashes was vital to confidence in both the Boeing 707 and the Douglas DC-8. With Lockheed engineering staff getting pulled from various projects to the Electra investigation, Boeing's chief Bill Allen dispatched his own engineers and his best aerodynamicists from Seattle to assist Lockheed in Burbank. The investigation and any fix needed had a name- Lockheed Electra Achievement Program, or LEAP. To everyone involved, it became Operation LEAP. 

Part of Operation LEAP was the use of a specially instrumented Electra that was flown by Lockheed and government test pilots over the Sierra Nevada range looking for mountain wave turbulence that would shake the test aircraft as no airliner had ever before been punished in-flight. Lockheed had actually pioneering the methods for testing inflight loads on structures back in 1949 that became the industry standard in flight testing. Sixty nine flights into the rough air offered a clue- the load instruments noted that the outboard nacelles were taking a rougher beating than expected. Flutter of some sort became the suspect cause- every aircraft has some degree of flutter, the air moving over various parts and imposing loads can cause them to vibrate and if unchecked, those vibrations increase in amplitude until structures fail. Aircraft structures are designed in part to dampen these oscillations. 

With flutter as the suspect, Douglas had sent over to Lockheed a vane exciter that was basically an actuated vane mounted on the wingtip that could move quickly to induce flutter in the wings. Even in smooth air, the vane exciters could really dole out some punishment to the wing structure. Douglas had used the device in the DC-8 flight test program and put them at Lockheed's disposal. The devices in combination with the rough air flight testing showed the outboard engine nacelles were the source of the flutter and a review of the wreckage from the Braniff and Northwest crashes showed that the outboard nacelle structure in combination with the wing structure allowed an obscure type of flutter called "whirl mode"- in short, gyroscopic movements of the propeller caused oscillations in the nacelle which were then transferred to the wing which caused the wing to fail. 

Though commercial rivals, Boeing and Douglas were only keenly aware that Lockheed was well respected in the business and its engineering and design methods were top notch. Much of how Lockheed went about the design and testing of the Electra wasn't all that dissimilar to how Boeing and Douglas went about the design and testing of their jetliners. If there was something Lockheed had missed, then it was something that left their designs  and the processes used open to question as well. 

On 12 May 1960, Lockheed chairman Robert Gross announced the cause of the loss of Braniff 542 and Northwest 710 as unstable whirl mode. Think about the technology of that day as this was well before computer modeling was available. Now think about the time frame- Braniff 542 went down at the end of September 1959. Northwest 710 went down in the middle of March 1960. And by the middle of May 1960 the cause had been identified. It's one of the great herculean efforts of American aviation that an obscure flutter mode was found to be the cause in just seven months. That amazing time frame wouldn't have been possible if Lockheed didn't have the cooperation of its commercial rivals as well as NASA, Allison, and the airline operators of the Electra. 

Source: The Electra Story: Aviation's Greatest Mystery (Bantam Air & Space Series No. 9) by Robert Serling. Bantam Publishing, 1962, 1991. Illustration: Flight Simulator X screenshot.

The First Steps to a Turboprop Transport, Part One

The YC-131C in flight. Note the 3-bladed propellers.

By the time of the Korean Armistice in 1953, the US Air Force was busy absorbing the lessons of airlift accrued over a less-than-ten-year span from the logistics flights to support World War II to the Berlin Airlift to the strategic airlift partnership forged with the commercial airlines in the Korean War. In pace with advances in aerodynamics and propulsion, the USAF began a four-step process in exploring the possibilities of turboprop propulsion given that pure jet engines of the day were still incredibly fuel-thirsty. The first steps were taken in 1945 with the test program of the Convair XP-81 turboprop fighter that also had an Allison J33 jet engine for additional power. The next steps were the testing of turboprop engines on existing high-speed jet designs that would result in the XF-84H "Thunderscreech and test versions of the Boeing B-47 Stratojet and the McDonnell XF-88 that flew with turboprop engines. The third step was the installation of turboprops on existing transport designs to evaluate their performance on large transports. And the final step was the introduction of production-standard turboprop transports which would result in the Lockheed C-130 Hercules and the Douglas C-133 Cargomaster. 

On 15 June 1954, the headquarters of the Military Air Transport Service (MATS) activated the 1700th Test Squadron (Turboprop) at Kelly AFB, Texas, with the task of developing maintenance procedures and techniques for the employment of turboprop transport aircraft pending the arrival of the C-130 and C-133 into the USAF service. The squadron had three flights with each flight dedicated to a single type for the testing of standard transport aircraft that had been converted to turboprop power. The first of the three flights to be activated would operate the Convair YC-131C. Two aircraft were converted from standard C-131 Samaritan transports (the USAF version of the CV-340 airliner) to use early test versions of the venerable Allison T56 turboprop. The YT56 turboprops replaced the piston engines of the C-131 and drove three-bladed Aeroproducts propellers. As this was the combination planned for the Lockheed C-130A, Allison was, needless to say, keen on being involved in getting flight time for the new engine. Tail numbers 53-7886 and 53-7887 were pulled from USAF service and modified by Convair at their Fort Worth facility at Carswell AFB. After initial flight testing at Edwards AFB, the first YC-131C was flown to Kelly AFB on 20 January 1955 with the second aircraft arriving three days later. 

Ground run of the YT56 engines at Convair Fort Worth.

As the goal of the test program set up by the 1700th TS was to fly the turboprop aircraft assigned to it as much as possible, the YC-131Cs were assigned to a scheduled military passenger service that operated between Kelly AFB in San Antonio and Andrews AFB outside of Washington, DC. The first services began on 14 March 1955 as the first scheduled turboprop passenger services in the United States. Covering a distance of just over 1,200 miles, the YC-131Cs took 4 hours 20 minutes on the first flight, approximately 20 minutes faster than a piston C-131 on the same route. By May of that year a regular flying schedule was established that would have the 1700th TS flying the two YC-131Cs 3,000 flight hours in nine months. As maintenance at destination stations was not expected to be adequate, each scheduled route flown by the YC-131C always returned back to Kelly AFB where the squadron had proper maintenance facilities. By July the Civil Aeronautics Administration (the CAA, the predecessor agency to the FAA) assigned four pilots to the 1700th TS to gain knowledge and experience in scheduled turboprop transport operations. That particular month, the second YC-131C became the first American-built turboprop aircraft to exceed 1,000 flight hours. 

The second YC-131C being handed over the USAF.

In the first six months the YC-131Cs were flown intensively, sometimes over 30 hours per day between the two aircraft. The initial time between overhaul (TBO) on the Allison YT56 engines was set at 100 flight hours at the start of the program but the engine proved to be highly reliable and as the program progressed, the TBO was increased progressively up to 200 flight hours. Though the engines could have safely flown with a longer TBO than 200 hours, Allison engineers were anxious to teardown and study the engines to improve the planned production T56 that would be used on not just the Lockheed C-130 but also on the same company's L-188 Electra airliner. During the nine month test program, 55 engines were changed out and sent back to Allison for analysis. The three-bladed Aeroproducts propellers also had TBO limits, starting at 300 hours and then extended out to 1,000 hours by the end of the test program. With a reliability well in excess of what was possible with piston engines, the two YC-131Cs also became the first USAF turboprops to exceed 1,000 flight hours with one day a record being set with an astounding 46 hours and 20 minutes flown in a 24-hour period, evenly split between the two aircraft. 

On 15 December 1955 the test program with the YC-131C ended, 45 days early thanks to the reliability of the YT56 engine. The USAF gained important data on fuel planning for turboprops, ATC procedures, holding patterns and ground operations that was also shared with the airline industry. In addition, the first squadrons that would be receiving the first C-130A Hercules aircraft at Sewart AFB, Tennessee, Ardmore AFB in Oklahoma, and Eglin AFB in Florida, sent their initial cadre of maintenance personnel to the 1700th TS in San Antonio for familiarization with the T56 engine. Both aircraft were eventually declared surplus and passed on to civilian owners before being scrapped. 

The next blog post will look at the second of the three turboprop conversions operated by the 1700th TS. Stay tuned!

Source: Remembering an Unsung Giant: The Douglas C-133 Cargomaster and Its People by Cal Taylor. Firstfleet Publishers, 2005, p29-43. Photos: Smithsonian Institution, SDASM.

The Achilles Heel of the Douglas B-66 Destroyer

The B-66 Destroyer ended up only resembling the A-3 Skywarrior

In January 1952 when the US Air Force issued its official General Operational Requirement (GOR) for a tactical bomber and reconnaissance jet aircraft to replace the Douglas B-26 Invader and the "interim" Martin B-57 Canberra, the selection of a minimum change version of the Douglas A3D Skywarrior as the B-66 Destroyer made sense. Douglas's proposed changes weren't all that major- deletion of the folding wings, catapult gear and arresting gear, addition of ejection seats and anti-icing, strengthening the airframe for the stresses of low altitude flight and an enlarged search radar antenna. Since the aircraft was "off the shelf", no prototypes were ordered. Eventually the USAF's GOR evolved to cover four distinct versions- the B-66B, a nuclear capable bomber version to replace the North American B-45 Tornado, the RB-66B, an all-weather day/night reconnaissance version, the RB-66C, a tactical electronic reconnaissance aircraft, and the WB-66D weather reconnaissance aircraft. Douglas agreed to an ambitious timetable to get the B-66 in production and operational, but the USAF kept requesting changes that ended up making the B-66 Destroyer a totally different aircraft that literally shared nothing in common with the Skywarrior. It's a testament to Douglas's abilities that the schedule slipped only two years as a result of constant changes being requested by the USAF! The B-66 ended up weighing just over 10,000 lbs more than the A3D Skywarrior as a result of all the changes. 

Had it gotten the J57 engine, the B-66 might have had a longer career

But being overweight wasn't the biggest flaw in the B-66 design. Ed Heinemann and his Douglas team recommended the Pratt & Whitney J57 turbojet for the B-66 after the A3D was switched from the anemic Westinghouse J40 turbojet to the more powerful J57 (the first production turbojet in the world to exceed 10,000 lbs of thrust). However, the Air Force held a competition for the engine to power the B-66- in addition to the recommended J57 engine, the Allison J71, General Electric J73 and surprisingly the Westinghouse J40 were submitted. Not surprisingly the J40 was dropped early on and the J73 soon followed for technical reasons. To the surprise of Douglas, the USAF then selected the J71 for the Destroyer, not only an engine that had yet to fly but it was also less powerful than the J57 by nearly 2,000 lbs of thrust! The official reasoning was that the Allison J71 was readily available (a bit of a stretch here on the part of the USAF) and the B-66 had lower priority than other USAF programs that used J57 engines- namely, the Boeing B-52 Stratofortress, the Boeing KC-135 Stratotanker, the North American F-100 Super Sabre, the McDonnell F-101 Voodoo, and the Convair F-102 Delta Dagger. At the time the Voodoo was under development as a long range penetration fighter for SAC, so it became obvious to many that SAC dominated the USAF budget and would receive any and all J57 engines possible. The main reason the F-100 got any J57s at all was that the F-100 was central to the Tactical Air Command's desire to have its own tactical nuclear attack force built around the F-100. 

Ordinarily those assigned to the B-66 Program Office at Wright Patterson AFB would have pushed for the J57, but politically the B-66 was seen as primarily a reconnaissance aircraft and only in interim bomber. Those with fighter experience in TAC wanted the F-100, those with tactical bomber experience in TAC wanted the Martin XB-51. And SAC was determined to preserve its budgetary allocation at all costs. In the end, no one really fought for the B-66 Destroyer when it was given the clearly less-powerful Allison J71 engine. Allison had trouble getting the J71 prototypes bench tested to at least 50 hours without any problems and only barely made the cut which exacerbated the schedule slippage of the first operational Destroyers. And even at that, the test pilots at Edwards AFB flying the first B-66s hated the J71- it was slow to spool up for more power, it surged often, and even would flame out and stall while taxiing. On 8 October 1955 the pilots of the AFTC (Air Force Flight Test Center) filed an extremely unsatisfactory report on the J71. The test force concluded that the J71 engine was accepted by the USAF only partially developed and a replacement engine was needed, the preference being for the J57 used by the Skywarrior. It was alleged that on a hot summer day in Denver with a typical combat load, the B-66 Destroyer couldn't even get airborne!

The tail guns were soon removed and replaced with ECM tailcone

Unfortunately for the B-66 program, the Secretary of Defense at the time, Charles Wilson, came to the Defense Department as the CEO of General Motors, of which Allison was one of its divisions. Wilson's 1953 confirmation hearings before the Senate were highly controversial because of his reluctance to sell his GM holdings and comments that alluded to him possibly favoring GM as Secretary of Defense. The loss of the J71 contract would have been a severe blow to Allison at the time. As a result, the Destroyer kept the J71 engines and Allison tweaked the engine further to bring the engine up to 9,700 lbs of thrust. While this satisfied the USAF given the mission profiles of the Destroyer in the 1950s, the addition of heavy electronic warfare equipment to the Destroyer to created the EB-66, the only tactical electronic warfare aircraft available in Vietnam, strained the limits of the J71 in the hot tropical environment of Vietnam. Destroyer crews nicknamed the aircraft "The Airplane with One-Way Engines" in reference to the fact that outside of the lackluster McDonnell F3H Demon, the other design to use the J71 was the Northrop Snark cruise missile. However, in 1956, Northrop switched the Snark's engine from the J71 to the- you guessed it- J57. 

Source: Glory Days: The Untold Story of the Men Who Flew the B-66 Destroyer into the Face of Fear by Wolfgang W.E. Samuel. Schiffer Military History, 2008, p24-38.