Mosquito Asymmetric Handling
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GQ2 - I agree completely, the Mosquito was by all accounts a superb combat aircraft; I am just a bit of a spotter and having relatively recently completed my ME training, I am interested in the technical aspects of actually flying such a high performance aircraft. Discussion of the Vmc and EFATO issues were not a criticism more a "well, I can just about do it in a light twin, I wonder what one of the thoroughbreds would be like" thought.
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There was another interesting article in Aeroplane magazine a couple of years back by a post-war Mosquito pilot. Allegedly the RAF stopped practising single engine landings because they were having more (fatal) training accidents than accidents caused by real engine failures.
Unfortunately a house move has meant that I've binned all the relevant magazines, but they're out there. The scenario was undershoot on aproach, open up the good engine a bit, uncontrollable yaw, roll ..............
But as others say, it wasn't only the Mosquito. The Beaufort allegedly went inverted very quickly if an engine failed on takeoff. The Beaufighter was also said to be similarly dangerous. In "Night Fighter" Jimmy Rawnsley describes John Cunningham reassuring nervous groups of traineee Beau pilots by regularly chopping an engine on takeoff - but then a) He knew it was coming, b) He was John Cunningham.
They were all much braver blokes than me, that's for sure.
Unfortunately a house move has meant that I've binned all the relevant magazines, but they're out there. The scenario was undershoot on aproach, open up the good engine a bit, uncontrollable yaw, roll ..............
But as others say, it wasn't only the Mosquito. The Beaufort allegedly went inverted very quickly if an engine failed on takeoff. The Beaufighter was also said to be similarly dangerous. In "Night Fighter" Jimmy Rawnsley describes John Cunningham reassuring nervous groups of traineee Beau pilots by regularly chopping an engine on takeoff - but then a) He knew it was coming, b) He was John Cunningham.
They were all much braver blokes than me, that's for sure.
Last edited by astir 8; 9th Jan 2012 at 14:18.
Gentleman Aviator
Allegedly the RAF stopped practising single engine landings because they were having more (fatal) training accidents than accidents caused by real engine failures.
GQ2,
As far as I am aware he had an airspeed indicator failure and even though he was offered another aircraft to fly alongside to verify his airspeed, he declined. He came into too fast and I believe ran out of runway, or lost control, but I could be wrong , I heard the story long ago.
Tony Ben's brother was killed in an EFATO (Engine Failure After Take-Off) in a Mossie for example.)
The RAAF lost a Mosquito after the war doing an assymetric touch and go, either very brave or bloody stupid!
Interstingly enough after the war when Piper, Cessna and Beechcraft started to build light twins to sell to the masses, pilots being pilots decided to reinvent the wheel with assymetric training. Piper PA-30's gained a very bad reputation as being killers of pilots, for the simple reason being that ace instructors decided to do things like VMCa demonstrations at low level and wondered why they rolled onto their backs and speared into the terrain, engine failures at lift-off, assymetric go around with full flap etc.
Interstingly enough after the war when Piper, Cessna and Beechcraft started to build light twins to sell to the masses, pilots being pilots decided to reinvent the wheel with assymetric training. Piper PA-30's gained a very bad reputation as being killers of pilots, for the simple reason being that ace instructors decided to do things like VMCa demonstrations at low level and wondered why they rolled onto their backs and speared into the terrain, engine failures at lift-off, assymetric go around with full flap etc.
A variation in safety speeds occured on most aircraft of the 2nd World War because the propellors on a particular aircraft went the same way. On Mosquito they were clockwise looking from the tail. This meant that the torque reaction from each engine would tend to roll the aircraft to the left.
1. Should the starboard engine fail the assymetric thrust would yaw and input roll to the right. The port engine is still inputing torque roll to the left which will reduce the total roll moment therefore reducing the amount of rudder required to oppose the assymetric thrust. Not a lot; but maybe enough to avoid a disaster..
2. Should the port engine fail then the assymetric thrust would turn and roll the aircraft to the left assisted by the starboard engine which is still torque rolling to the left. You now need stacks more rudder than before.
It would have been far too difficult with multi engined aircraft to publish different safety speeds for different engine configurations so the worst case would have been used as the datum.
Royal Air Force airfield circuits are predominately to the left so there is an overwhelming desire for the pilot to turn left into the circuit if he has a problem. On a multi engined piston aircraft with a failure on the port side this is the first step into oblivion because you are turning into the dead engine.
A step forwards from the Mosquito was the de Havilland Hornet. A similar configuration except that the propellors went in opposite directions; a technique know as 'handed'. On the Hornet the starboard propellor rotated anti-clockwise from behind. A bonus from this was that on take off the torques would cancel each other so minimal rudder was needed to keep the aircraft straight on the runway. Very useful when launching off a carrier with a Sea Hornet.
Should a starboard engine fail then the effect is still the same as in example 1 above. However, if the port engine fails the torque from the starboard engine is acting the opposite way than in example 2 so the the result is the same as in example 1.
Unfortunately you still had the problem of turning into the dead engine.
1. Should the starboard engine fail the assymetric thrust would yaw and input roll to the right. The port engine is still inputing torque roll to the left which will reduce the total roll moment therefore reducing the amount of rudder required to oppose the assymetric thrust. Not a lot; but maybe enough to avoid a disaster..
2. Should the port engine fail then the assymetric thrust would turn and roll the aircraft to the left assisted by the starboard engine which is still torque rolling to the left. You now need stacks more rudder than before.
It would have been far too difficult with multi engined aircraft to publish different safety speeds for different engine configurations so the worst case would have been used as the datum.
Royal Air Force airfield circuits are predominately to the left so there is an overwhelming desire for the pilot to turn left into the circuit if he has a problem. On a multi engined piston aircraft with a failure on the port side this is the first step into oblivion because you are turning into the dead engine.
A step forwards from the Mosquito was the de Havilland Hornet. A similar configuration except that the propellors went in opposite directions; a technique know as 'handed'. On the Hornet the starboard propellor rotated anti-clockwise from behind. A bonus from this was that on take off the torques would cancel each other so minimal rudder was needed to keep the aircraft straight on the runway. Very useful when launching off a carrier with a Sea Hornet.
Should a starboard engine fail then the effect is still the same as in example 1 above. However, if the port engine fails the torque from the starboard engine is acting the opposite way than in example 2 so the the result is the same as in example 1.
Unfortunately you still had the problem of turning into the dead engine.
Thread Starter
As I recall though, the P38 had outward rotating propellors, so although by definition it didn't have a critical engine as such, the asymmetric blade effect meant that a failure on either was pretty brutal to deal with.
Yes Jwscud - I was about to post the same point.
Presumably there were other reasons for making the P-38's handed prop rotations appear to be the "wrong way round" in assisting engine-out behaviour?
Presumably there were other reasons for making the P-38's handed prop rotations appear to be the "wrong way round" in assisting engine-out behaviour?
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Re P-38 prop rotation. The chart explains all. Minimum trim change between power on and off, simplifying the pilots task in having a more stable gun platform.
Thanks for that Brian.
I can't see the rotation arrows very clearly, but doesn't that seem to suggest that the rotation "a la Hornet" (the props' upper blades moving towards each other) gives near zero pitching moment throughout, rather than the P-38's upper blades moving outwards scenario?
I can't see the rotation arrows very clearly, but doesn't that seem to suggest that the rotation "a la Hornet" (the props' upper blades moving towards each other) gives near zero pitching moment throughout, rather than the P-38's upper blades moving outwards scenario?
Today, of course, we have the A400M 'Grizzly' with handed propellors, two props on each side both rotating in opposite directions and each with eight blades!
The reason, I suspect, is to retain symmetrical airflow over the wing to avoid the sort of thrust/drag assymetries which seemed to dog the C-130J through its handling and stall development/certification programme.
The reason, I suspect, is to retain symmetrical airflow over the wing to avoid the sort of thrust/drag assymetries which seemed to dog the C-130J through its handling and stall development/certification programme.
Reducing power on the good engine can be a good idea
IIRC the CAA would not give an airworthiness certificate to the Boeing 707 until it was fitted with a power assisted rudder to cure this problem as subsequently fitted all 135/707s.
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Mossie - small airframe, two socking big engines both turning the same way, relatively small rudder and fin. Superb performance with that low drag, but you'd expect EFATO to require careful handling.
The surprise is, reading this thread, it doesn't seem to have been that much worse in that respect than other twins that looked a lot less 'minimal' than dH's lovely design. And our aeroplane (dHC1) has inherited those lovely tail feathers.
A (now deceased) friend of mine I used to fly the Chippy with who was on Lancs during WW2 remembers watching a Wellington take off on its maiden flight from Hawarden. One engine failed at a few hundred feet, and it rolled over and 'went in'.
The surprise is, reading this thread, it doesn't seem to have been that much worse in that respect than other twins that looked a lot less 'minimal' than dH's lovely design. And our aeroplane (dHC1) has inherited those lovely tail feathers.
A (now deceased) friend of mine I used to fly the Chippy with who was on Lancs during WW2 remembers watching a Wellington take off on its maiden flight from Hawarden. One engine failed at a few hundred feet, and it rolled over and 'went in'.
Looking at the graphs of the P38 the left hand line (propellors turning inward at the top) seem to suggest that there is the maximum pitching effect between thottles closed/open. The opposite, right hand line (propellors turning outward) shows little difference between thottles open and closed. To explain this one has to imagine an aircraft looking at it from the tail.
On the de Havilland Hornet with the props turning inwards the corkscrew effect causes a vortex with the downwards component running along the fuselage and impinging on the tail. This, together with the pitch up induced by the engine thrust line being below the drag line, would cause the aircraft to pitch up. The friction of the fuselage would however,reduce the effect from the propellor wash.
Looking at the P38 from the tail with the early inwards rotating propellors than the vortex effect is the same but this time there is NOT a fuselage to absorb the effect so we have a strong pitch up with the combination of this plus the thrust effect. This is becauuse the P38 has a pod, two booms and a single horizontal tailplane. This sort of behaviour is not conducive to having a good gun platform.
With engines rotating the same way one engine cancels out the other so there is just the thrust effect.
When the propellors are turning outwards at the top the vortices push the tailplane up so that this cancels the pitch effect of the thrust. The result is that the aircraft is stable in the pitching mode irrespective of the throttle handling. Far better when using it so disassemble other aircraft.
Whether it would work on a conventional fuselage aircraft would depend on the position of the engines and tailplane.
On the de Havilland Hornet with the props turning inwards the corkscrew effect causes a vortex with the downwards component running along the fuselage and impinging on the tail. This, together with the pitch up induced by the engine thrust line being below the drag line, would cause the aircraft to pitch up. The friction of the fuselage would however,reduce the effect from the propellor wash.
Looking at the P38 from the tail with the early inwards rotating propellors than the vortex effect is the same but this time there is NOT a fuselage to absorb the effect so we have a strong pitch up with the combination of this plus the thrust effect. This is becauuse the P38 has a pod, two booms and a single horizontal tailplane. This sort of behaviour is not conducive to having a good gun platform.
With engines rotating the same way one engine cancels out the other so there is just the thrust effect.
When the propellors are turning outwards at the top the vortices push the tailplane up so that this cancels the pitch effect of the thrust. The result is that the aircraft is stable in the pitching mode irrespective of the throttle handling. Far better when using it so disassemble other aircraft.
Whether it would work on a conventional fuselage aircraft would depend on the position of the engines and tailplane.
Last edited by Fareastdriver; 14th Jan 2012 at 12:16. Reason: spelling
Thinking about the assymetric problem a little bit more, and depending on the aircraft take-off weight, fuel load, flap setting, payload or bomb load being carried, external stores, centre of gravity position, undercarriage up or down, power setting for take-off would all effect Vmca, stall speed and finally the take-off safety speed.
