PPRuNe Forums - Wing Drop in some wartime aircraft

Wing Drop anyone? Try the Lockheed Hudson

A recent proposed amendment to Part 61 Manual of Standards would remove the requirement for the induction of, and recovery from, spins at the incipient stage in favour of spin avoidance training with greater emphasis on slow flight, stall recognition and recovery from wing drop at the stall, making Australian training practice consistent with spin avoidance and stall recovery training principles specified by ICAO for UPRT.

The majority of light training aircraft are designed to have benign stalling characteristics. That wasn’t the case with aircraft of WW2 design where wing drops at the point of stall could be severe and require a lot of height to recover to level flight. These were true wing drops and not the artificial wing drops at the point of stall we see nowadays where instructors deliberately and often quite violently throw the aircraft around with exaggerated movements of the controls to show the student a wing drop in order to tick the box. That method used is not the result of a stall but more a deliberately flown manoeuvre that apes a wing drop.

The following examples of stall characteristics are extracted from WW2 RAF/RAAF Pilots Notes for the aircraft type. If readers have never heard of these aircraft then Google is your friend. The term “Snatching” means the control column whips sharply left and right caused by airflow changes to the ailerons. A painful crack on the knee can result.

Beaufighter. Stall with undercarriage and flaps down

The nose and one wing usually drops sharply at the stall especially if the throttles are slightly open.

Sea Fury. Warning of the approach to stall is given by buffetting and at the stall the nose will drop gently. If the control column is pulled back at all sharply, however, the aileron will snatch and the nose and port wing will drop. Warning of a stall under typical approach conditions is given by aileron snatching. In addition, the nose attitude will be markedly nose up and a large amount of left rudder will be necessary to maintain directional trim.

When the stall occurs the starboard wing drops sharply and since this action is assisted by torque, the throttle should be closed when initiating recovery action: if this action is not done, difficulty in regaining control at once may be experienced resulting in unnecessary loss of height. Ample warning of the approach to stall in a steep turn is given by aileron snatching and a tendency for the aircraft to flick out of the turn.

Mustang. If the stick is held back at the stall a wing will drop very rapidly and the aircraft will become inverted.

If the aircraft is stalled in a steep turn either wing will drop very rapidly. The stall is preceded by pronounced juddering. Power on spins should never be intentionally performed. As many as five or six turns may be made after recovery action and 9000 - 10,000 ft lost.

Lockheed Hudson

An August 2020 article by Robert Wilson of Flight Safety Australia magazine has this to say.

“Eighty years ago today—August 13, 1940—an air crash in Canberra around 11 am decapitated Australia’s wartime government.

On board the Royal Australian Air Force (RAAF) Lockheed Hudson were 10 people—three cabinet ministers, the Chief of the General Staff and his liaison officer, the private secretary to the Minister for Air and four RAAF crew.

The aircraft took off from Essendon, Melbourne, at 9.30 that morning. In Canberra it was a cool clear day with a 15-knot wind from the north-west. Shortly before 11 am the Hudson arrived and flew a left-hand circuit, passing over Queanbeyan on base leg and over a low rugged ridge on final as it approached the airfield from the east. For no clear reason, it went around for another circuit.

The Hudson crashed into the top of the ridge between Canberra Airport and Queanbeyan. The Air Court of Inquiry into the accident found that it was most likely the Hudson had stalled on landing approach, resulting in loss of control at a height too low to recover.”

From reading the Air Court of Inquiry there was evidence from several witnesses that the Hudson was turning on to final at 500 feet when one the left wing was seen to drop sharply. The nose dropped and the Hudson went into an incipient spin and crashed. Although there was no report of the steepness of the turn on to final, it seemed obvious that the Hudson had stalled during the turn. Further evidence was given by RAAF instructors on Hudsons that at least 800 feet could be lost during recovery from a stall.
For a more detailed description of the circumstances surrounding that accident read: https://press.anu.edu.au/publication...-camerons-farm

On 17 January 1942 a formation of four RAAF Hudsons took off from Ceduna in fine weather for a loose formation flight to Perth. Each takeoff was at a close interval. The last Hudson to takeoff was seen to initially climb steeply to 800 feet compared to the others then momentarily level out to retract the flaps which were used for takeoff on that occasion. The other Hudsons did not use flaps for their takeoff. It was thought the pilot climbed steeply to avoid slipstream from the other three aircraft

As the flaps were retracting the port wing dropped sharply and the aircraft entered an incipient spin from which the pilot was unable to recover. All crew and passengers were killed.

30 October 1947. Hudson VH-SMJ. Muswellbrook NSW. The Sydney Morning Herald operated Hudsons on newspaper dropping operations to Northern NSW from its base at Camden. The aircraft was set up as freighter aircraft operated as single pilot and one loader. The rear entrance door was open during the flight with the door itself stowed at the back of the fuselage. At the same time a moveable chute was placed in the open doorway on which bundles of newspapers could be stowed.
On arrival over the drop zone the pilot would reduce speed and signal the loader down the back to tip the bundles overboard. After the drop was completed the loader would move to the cockpit and act as co-pilot where needed. The loaders were usually qualified pilots although not necessarily on type. The height of each drop was around 300 feet and an agent in the field below would collect the bundles and take them to the newsagents in town. A similar configuration was used during Hudson supply dropping during the war.

On this occasion the Hudson was observed by witnesses to turn steeply while lining up to run over the drop zone at Muswellbrook. Suddenly the left wing dropped sharply and the aircraft dived into the ground killing both crew members. The subsequent investigation by the Department of Civil Aviation revealed that with newspaper bundles stowed at the entrance door situated at aft end of the aircraft, coupled with the loader also at the aft end, placed the Centre of Gravity a long way outside the aft limit making the aircraft unstable to fly.

As the aircraft turned in for its run the stability of the aircraft was seriously compromised and the aircraft stalled in the turn too low for effective recovery. Here is a link to the accident report.

https://reports.aviation-safety.net/...4_(VH-SMJ).pdf

During the course of the official investigation the following letter was received from a former RAAF pilot who had flown Lockheed Hudsons on wartime supply dropping operations for Australian Army units fighting against the Japanese in New Guinea. He wrote:

"Whilst a member of the RAAF I carried out a considerable amount of flying on Lockheed Hudson type aircraft and one time was attached to No 1 Operational Training Unit which was to proceed to New Guinea for the purpose of dropping supples to the army during the Buna campaign. I recall on one occasion when dropping supplies from a Lockheed Hudson aircraft over the Seputa strip when for no apparent reason at all my aircraft became uncontrollable.

At the time we were flying about 150 feet above the strip and were in the process of actually dropping the supplies when the nose of the aircraft rose sharply then nosed down to a steep angle towards the strip. I applied full power and pulled the stick back which had no immediate effect in fact it felt that I had no elevator at all as the control column came back loosely in my hands. On nearing the ground the aircraft suddenly flattened out and went into a steep climb to a height of about 200 feet, At this height whilst still maintain full power and with full forward stick the aircraft commenced to level off. As this happened the left wing commenced to drop and the nose continued to go down until the aircraft assumed a dive of 45 degrees to the ground and had turned about 45 degrees to the course I was on. I finally regained control at tree-top height. I made a further run over the target at a speed considerably faster than the first.

After this I returned to base without further event. On landing I reported the occurrence and to the best of my knowledge the aircraft was checked before being flown again but the cause of the unusual behaviour was never found. However, the following day the same aircraft was flown by Flt Lt Pedrina on a similar mission over the same strip. On completion of his run and when commencing a left hand turn the aircraft was seen to nose down suddenly and dive into the trees. There was one surviving member of the crew who was badly injured and was not found until some considerable time after the accident.

I first flew this aircraft on the day mentioned and it gave me the impression it was not particularly stable fore and aft. This I attributed to the fact it was the first time I had flown a Hudson with both the door and escape hatch open. I have never had another experience of this nature on other Hudson aircraft I have flown under similar conditions. I formed the opinion it was due to a blanketing effect on the elevators caused by the airflow passed the open doorway.

On more than one occasion a heavily laden Hudson has been known to climb very steeply after take-off, consequently stalling and crashing. On one occasion I was taking off with a heavy load using 30 degrees of flap. The aircraft first climbed normally to a height of about 100 feet. The nose then commenced to rise and normal application of control failed to bring it down. I was able to regain full control by applying full power and retracting the flaps."

1 January 1950. Hudson VH-SMK. Night takeoff at Camden NSW. The aircraft was observed to climb normally after liftoff. At about 150 feet the aircraft stalled and crashed about 400 yards beyond the departure end of the runway and 200 yards to the right of the extended centreline. The weather was slight drizzle with high humidity. Conditions were conduicive to carburettor icing. .
See: https://recordsearch.naa.gov.au/Sear...aspx?B=8937639

Investigation revealed the left engine was at high power at impact and the right engine at low power. Both crew members were killed on impact. As the reason for the stall accident could not be determined, the chief pilot (a former RAAF Chief Instructor on Lockheed Hudson aircraft in WW2) was asked by the investigating team about the possibility of carburettor icing on the Hudson.

In reply, he stated "From my own experience the Ceco carburettor as fitted to Lockheed engines will ice badly under humid conditions when taxying to the take-off point or running slowly. All Lockheed aircraft operated by the Sydney Morning Herald carry a warning notice on the dash stating CAUTION: Check carb for ice before takeoff. This notice was originated within the SMH organisation but so far as I am aware, this is standard procedure for all Lockheed aircraft - although no instructions are contained in the Lockheed manuals to this effect. I have never experienced icing on Lockheed Hudson engines during the actual take-off."

In each of these accidents the aircraft had stalled at low altitude. While todays advice includes avoidance of aileron to pick up a dropped wing as this may further aggravate the severity of the wing drop, it is probable the first thing the pilot would do at such a low altitude is to instinctively apply full aileron to try and stop the wing drop. Most light aircraft such as the Cessna series are designed so the ailerons are effective below the stall. With these aircraft, if a pilot tries to use aileron to stop a wing drop at the point of stall at very low altitude, then given the design of modern aircraft there is a good chance it might be effective. But don’t count on it.

From reading these accident reports, it is easy to gain the impression the Lockheed Hudson was a potentially dangerous aircraft to fly in that a wing drop at stall led to the accident. However, in each instance, the stall occurred at a very low altitude giving the pilot no hope of recovery. Other wartime types may have had similar characteristics.

The Australian produced Wirraway was useless as a fighter aircraft but later became a fine wartime trainer. Its stall characteristics were notorious in that either wing would drop sharply at the point of stall. In the old days the scrape marks from wing drops could be seen on Point Cook runways caused by students and instructors holding off too high during landing. A sharp full pull back on the stick would produce a flick roll – deadly at low altitude but a good confidence builder at a safe height. Today, civilian aircraft are subject to stringent certification requirements designed to eliminate potential faults at the design stage.

One final lesson here is to avoid turning steeply on final approach to land. It is there that the airspeed will be close to landing speed and we all know that the stall speed increases during a turn. During flying training both at civil and RAAF flying schools we were told to increase speed if forced to bank steeply on to final. That was sound advice especially if gliding to a dead stick landing.