N110PX was an experimental amateur-built, twin-engine, single-seat, tailwheel monoplane built as a replica of the Bugatti-DeMonge 100P, a 1930's era air racer that was never flown. There was only one original airplane produced, and the accident airplane was the first and only replica produced to the date of this report. According to airworthiness documents, the airplane was constructed to duplicate the original airplane's structure, systems, and dimensions. The accident airplane was powered by two Suzuki Hyabusa reciprocating, clutched motorcycle engines mounted in tandem aft of the cockpit. The engines drove two coaxial two-blade contra-rotating Hercules fixed-pitch wooden propellers. The forward engine was installed with the output drive shaft forward and was directly connected to the propeller reduction gearbox through universal joints and drive shafts on the left side of the fuselage. The rear engine was installed with the output drive shaft aft and was indirectly connected to the propeller reduction gearbox through a chain drive and sprockets that drove the drive shafts and universal joints on the right side of the fuselage. Both engine gearboxes were set in 6th gear and could not be changed. The propeller reduction gearbox was contained in a single housing with two separate drive trains to drive the forward and aft contra rotating propellers. The forward engine engaged the left gearbox drivetrain and drove the forward propeller. The aft engine engaged the right drivetrain and drove the aft propeller.
Engine throttle control was accomplished through two levers installed side-by-side on the left side of the cockpit with the left throttle lever controlling the forward engine and the right throttle lever controlling the aft engine. Engagement of the hydraulic clutches on the engines was accomplished independently by two levers mounted side-by-side on the right side of the cockpit. Each engine could be run without propeller movement until the respective clutch was engaged.
The airplane's maximum gross weight was listed as 2,939 pounds and its empty weight was 2,470 pounds. The airplane received its FAA Special Airworthiness Certificate in the experimental category on August 4, 2015.
The airplane was equipped with several onboard cameras that captured video footage of the accident flight. The video revealed that the left/forward engine began surging after liftoff and reached its maximum operating speed (red line) twice during the short flight. Although the pilot attempted to control the forward engine rpm with the throttle lever, the throttle inputs had no apparent effect. Based on the design of the propeller drive train, it is a possibility that the forward engine clutch was slipping. The airplane's airspeed decreased below its design stall speed and the angle of attack increased; the airplane then rolled left and subsequently impacted the ground. A postaccident examination of the airplane did not reveal any preimpact flight control anomalies. Examination of the engines did not identify a reason for the surging of the forward engine or slipping of the clutch. The sequence of events as described by witness statements and the onboard video was consistent with a loss of airspeed following an engine anomaly and a subsequent aerodynamic stall.
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Re: Contra-rotating props...
Posted: Sun Oct 11, 2020 9:39 am
by Pontius Navigator
TGG, like the Wyvern, but the Gannet was probably the only twin engined one to see service.
On patrol it could shut one engine down to improve endurance. This led to one ignorant senior RAF officer to ask why the Shackleton could not do likewise.
The Mk3 Shack had an endurance of over 24 hours so getting even more was questionable.
TGG, like the Wyvern, but the Gannet was probably the only twin engined one to see service.
On patrol it could shut one engine down to improve endurance. This led to one ignorant senior RAF officer to ask why the Shackleton could not do likewise.
The Mk3 Shack had an endurance of over 24 hours so getting even more was questionable.
I asked the same question of a kind SAAF pilot who allowed me to come on board his Shackleton based at Ysterplaat in Cape Town, albeit I was aged only 12 , assuming in my youthful ignorance that each propeller would need its own engine.
Re: Contra-rotating props...
Posted: Sun Oct 11, 2020 2:22 pm
by Boac
The 'Bugatti' crash is puzzling. No conclusion from NTSB in that link. I would have thought that 9500rpm on 'No 1' would have prevented that loss of airspeed. No mention of prop control? Was it VP? If so had it gone into fine? Do you have more?
The 'Bugatti' crash is puzzling. No conclusion from NTSB in that link. I would have thought that 9500rpm on 'No 1' would have prevented that loss of airspeed. No mention of prop control? Was it VP? If so had it gone into fine? Do you have more?
No, only the aviation safety.net link posted above. It was put down to a stall spin accident due to pilot distraction as a result of the engine overspeed. Like you that doesn't satisfy me, not least because the pilot was a very experienced airline transport pilot and no mechanical reason for the over speed was discovered.
Re: Contra-rotating props...
Posted: Sun Oct 11, 2020 4:16 pm
by Boac
and "no reason for the loss of airspeed mentioned".
It is not clear why Wilson did not add more power to the rear engine, which might have resulted in a positive rate of climb, but van Dalen noted that clutch slippage problems that the team had encountered during the development and test program might have undermined Wilson’s confidence that the power train, particularly the chain drive, would have held up under the increased load. It was also a decision made during just a few seconds that elapsed between liftoff and the crash.
“In case Scotty had decided to accept the risk of a chain drive failure and had applied full throttle on the rear engine, my performance estimation shows that a climb rate of 390 ft/min would have resulted,” van Dalen wrote.
Well found. It appears the NTSB report we have seen was woefully inadequate - it talks of "9.500 rpm' on the forward engine but fails to mention that the associated power was not getting to the prop! I had 'assumed' direct transmission, and the 'surging' is now explicable. It all makes sad sense now.
The Brabazon had a similar arrangement four times over, it was powered by an arrangement of eight Bristol Centaurus radial engines which drove a total of eight paired contra-rotating propellers set on four forward-facing nacelles.
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Re: Contra-rotating props...
Posted: Sun Oct 25, 2020 12:27 pm
by k3k3
It looks like an aircraft that could have been built by Brunel.