Here is one more story of superb airmanship that I hope will interest Pprune readers.
In the early Fifties, it was common to see copies of military flight safety magazines in RAAF crew rooms. These included RAAF Spotlight and the latest Crash Critiques, Air Clues and Tee Emm from the Royal Air Force, as well as USAF and US Navy magazines and the occasional Royal Canadian Air Force flight safety journal. In those days, Townsville, was the home base of No 10 (Maritime Reconnaissance) Squadron, equipped with four engine Lincoln Mk 31 bombers. As an aircrew member of the Squadron, I was particularly interested in reading the USAF Military Air Command (MAC) Flyer flight safety magazine especially as the MAC operated long range four engine transports over the vast reaches of the Pacific.
As a way of introduction to the main story, in May 1956, a Pan American Airways Boeing 337 Stratocruiser was en-route from Honolulu to San Francisco when the No 1 propeller ran away creating tremendous drag. The crew were unable to feather the propeller. High power was being used on the remaining three engines to enable the aircraft to hold height, when the No 4 engine lost power and its propeller had to be feathered. The aircraft gradually lost altitude until it was flying only a few hundred feet above the ocean. When it became clear that fuel would be exhausted before reaching the destination and after flying over a ship weather station, the captain decided to ditch the aircraft near the ship. All on board the Boeing 337 were rescued.
From reading the MAC Flyer I discovered runaway propellers were not uncommon in big radial engines and I wondered if the in-line liquid cooled Rolls Royce engines of our Lincolns could face the same trouble if the pilot was unable to feather the propeller; especially during long range SAR and maritime reconnaissance flights missions over the sea. Although I had experienced several engine failures in Lincolns, we had been able to feather the propellers.
Then I read about another incident involving this time a USAF MAC Boeing C 97 Stratofreighter en-route Honolulu to Travis Air Force Base near San Francisco. If I recall correctly, the C97 had four Pratt and Whitney R4360 air cooled radial engines; the largest radials ever produced. Now I am falling back on my memory for this story so please bear with me. The following are the facts as I recall them from the magazine.
After leaving Hickham AFB on Hawaii and shortly after passing the point of no return between Hawaii and the west coast of USA, the Stratofreighter suddenly had a runway propeller on the No 1 engine which the crew were unable to feather. The drag from the huge propeller caused the aircraft to lose speed and the pilot was forced to descend even with using maximum continuous power on the remaining three engines. High power could soon lead to overheating engines.
The immediate danger was fire that could erupt in the engine caused by friction building on the propeller shaft. One of the first actions to minimise the drag from a windmilling propeller is to reduce airspeed. The crew did that but were still unable to feather the propeller. The danger was the propeller might eventually come loose and fly off causing fatal damage to the No 2 engine next to it and possibly to the aircraft.
The captain directed the flight engineer to feather the propeller of the No 2 engine so that if the No 1 propeller flew off then with a bit of luck it would not go through the arc of the No 2 propeller and cause untold damage.
All the time the C97 was steadily losing height and the crew prepared for ditching. The captain then further directed the flight engineer to pull the firewall shut-off valve to the No 1 engine which cuts off the fuel, engine oil and hydraulic oil supply. The intention was to starve the engine of oil leading to engine seizure and hopefully have the windmilling propeller fall into the ocean. The flight engineer then proceeded to pull the No 1 engine firewall shut-off valve intermittently until the friction caused by lack of oil to the propeller shaft would slow down the propeller.
Soon the reduction gear casing of No 1 engine was seen to go red hot and the propeller started to wobble. It was vital that the propeller not hit the aircraft if and when it departed.
With the No 2 propeller feathered to minimize damage if the spinning propeller of No 1 engine hit it, the time had come to force the runaway propeller to leave the aircraft. Judging when the time was right by observing the wobbling propeller and the red hot casing of the reduction gear, the captain placed the aircraft into a steep right bank and at the same time bunted by pushing hard on the control column. Gyroscopic forces caused by the combination of the direction of rotation of the runaway propeller and the direction of control column movement caused the propeller to break clear and go under the aircraft. On the way it clipped one of the feathered blades of No 2 propeller severely damaging it. The wise precaution to feather No 2 paid off.
With the No 1 propeller gone and serious damage to a blade of the No 2 propeller, it was clear to the crew that starting No 2 engine was not an option since the probability of catastrophic vibration caused by its unbalanced propeller could be fatal. As the aircraft neared sea level it was noticed that with maximum continuous power on both starboard engines the C97 could just maintain height with no further loss in airspeed. A ditching was avoided for the time being. As time passed, with the C97 holding height on two engines at 50 feet above the sea, it was noticed that airspeed was gradually increasing and it became possible to even reduce power to maintain a safe two engine airspeed. Although the crew probably were unaware of it, it was the phenomena later known as `ground effect` that had caused a reduction in induced drag and thus slight airspeed gain.
Ground effect takes place when an aircraft flies over the ground or water at a height equal to roughly half the total wing span. The wing span of the Stratofreighter was 141 feet. It meant if the aircraft could hold its current altitude of below 100 feet there was a good chance the aircraft could still reach Travis AFB. With several hours to go, the crew were able to maintain a safe cruising speed as fuel was used and even climb to a more comfortable height.
The aircraft reached Travis safely but fate played its hand just one more time. On final approach on two engines the pilot was forced to go-around again when another aircraft entered the runway in front of it. The go-around was successful and so was the final landing. The crew were praised for displaying fine airmanship under harrowing conditions.
Reading that story in the MAC Flyer magazine at Townsville got me thinking and I wondered if ground effect applied to the Lincoln. After all, it would be useful thing for our crews to know. Trials with the Lincoln revealed that an extra eight to ten knots of indicated airspeed could be attained when flying at 50 feet over water in ground effect.