Mosquito Asymmetric Handling

[Jwscud]

Bit of a geeky question this one, but I have heard on the grapevine that the Mosquito had a very high Vmca compared to liftoff speed and that asymmetric handling was very difficult indeed.

Suggestion was that an EFATO below a certain speed was exceptionally difficult to handle and likely to end up in a Vmc departure and crash unless very well handled. Googling and searching on here hasn't uncovered any helpful information - can anyone point me in the right direction?

[dixi188]

IIRC About 20 years ago the only flying example crashed at an airshow (Barton I think) with an engine failure during a climb below VMCA.

[Chris Royle]

See Neil Williams' book "Airborne" for his description of flying what became Kermit Weeks' Mosquito and experiencing such an event at Booker (Wycombe Air Park). The valley adjacent to the aerodrome helped to save the day.

[Atcham Tower]

The Handling Notes say that Vmca (although they didn't call it that in those days of course) on a fully loaded Mossie was 200 mph (174kts). Lightly loaded and fitted with the narrow blade props it was a lot less but still pretty horrendous.

[treadigraph]

Neil Williams' problem at Booker isn't included in "Airborne", but it was published in Pilot - might be able to put my hands on a copy this evening.

[Jwscud]

Thanks for the replies - in the region of 160/170kts is a pretty scary number :eek: Is there a copy of the pilots notes available anywhere or do you know what typical unstick speeds were? Having had enough trouble learning to control an SE Taildragger on T/O and Landing I'd hate to try a beast like that OEI!

I have read the AAIB report into the loss of the Mosquito at Barton and though very illuminating regarding engine issues it has very little detail on the operational side of things.

[DeepestSouth]

You could try The Mosquito Page at:The de Havilland Mosquito Page (http://www.mossie.org/Mosquito.html)

The Forum users (which includes some Mosquito aircrew and some absolute experts on the aircraft) either know or can find out most things about the Mosquito. They are also a cracking source of stories and a search on the site, or a query, might throw up all sorts of interesting tales about Mosquito assymetry.

Alternatively, in the 70s and 80s, Crecy published copies of the Pilot's Notes for several variants of the Mosquito and you might be able to find a copy somewhere.

Regards,

DS

[Atcham Tower]

I can't find my repro copy of the Pilot's Notes at the moment but I remember that safety speed, having once discussed it with an HS 748 pilot. I think the 748's is about 95 Kts!

[twochai]

do you know what typical unstick speeds were?

If I remember correctly from three brief flights on the BMk35 fifty years ago, at max T/O weight lift off speed was around 120-125 knots, Vmca was 175 Knots IAS, but it took almost 50 seconds to get the gear up and accelerate through Vmc on a summer day. The only alternative was to reduce power on the live engine!

The very slow retraction time of the pneumatic gear retraction system was the big culprit; IIRC it had no pneumatic accumulator, or if it had one it was very small!

[spekesoftly]

About five years ago there was an excellent article in Aeroplane magazine describing what is was like to fly and display RR299 - the last airworthy Mosquito. It was written by former BAe test pilot Peter Henley, and there is considerable detail about the slow undercarriage retraction etc. Although the brakes were pneumatic, the undercarriage was hydraulically operated, and even with both engines and hyd pumps working, the U/C took about 25 secs to retract. On one engine (and only one pump) this increased to about 45 seconds. The RAF Pilot's Notes state: "Although safety speed may be a little less in some cases, particularly at light loads and with narrow-blade propellers, it is recommended that a speed of 175kt be attained before starting to climb, especially if paddle blades are fitted". Mosquito RR299 did have paddle-blade propellers, and 100kt was a typical unstick speed. A long time to be at risk from the consequences of an engine failure after take-off.

[ChrisVJ]

The question the uninitiated would ask is "Why?"

Was it the sheer power of the good engine overcoming the rudder? High wing loading? Not enough fin or rudder area? Just not enough rudder authority? Cross section area of the dead side? Drag from the dead prop? Was the prop on a dead engine featherable?

One would have thought that a Merlin on full throttle would have little problem overcoming even the drag of undercarriage in such a low drag aircraft

Interesting comparison with the pictures I have seen of a shackleton flying two dead engines on the same side (for display) apparently quite manageably.

[spekesoftly]

Was the prop on a dead engine featherable?
Yes it was. Peter Henley described it thus:-

"The tasks facing the pilot were daunting. Drag reduction was paramount, so the undercarriage and flaps had to be retracted as soon as possible, while flying the aeroplane with the left hand, because undercarriage and flap levers were in the centre of the instrument panel. Drag from the windmilling propeller of the failed engine would have been very high, so manual feathering would have to be carried out dextrously while flying, first with the right hand and retracting the relevant throttle and pitch levers (to the left of the pilot's left thigh), then changing hands to free the right hand to reach the feathering buttons, which were in front of the right-hand seat".

[twochai]

a shackleton flying two dead engines on the same side (for display) apparently quite manageably

That's a case of good energy management - feathering two engines of a four engined aircraft at relatively high speed (i.e. well above Vmca) is a very different thing than feathering an engine from below Vmca, while trying to accelerate to it.

While operating below Vmca the control issue is of primary importance, drag being a secondary challenge if control can be maintained. By definition it cannot, of course, without reducing power or increasing speed.

[treadigraph]

I found the Neil Williams article about his Mosquito Moment at Booker - also includes a fraught few minutes in Philip Mann's Yak 11!

If anyone would like to see a PDF copy, PM me your email address.

[Brian Abraham]

The following comes from the Pilot Notes for the Mosquito FB6.

40. Take-off
(i) Carry out items (95) to (105) in the Pilot's Check List.
(ii) Taxy forward a few yards to straighten the tailwheel.
(iii) Open the throttles slowly, checking any tendency to swing by coarse use of the rudder and by differential throttle movement. There is little tendency to swing if the engines are kept synchronised.
The travel of the throttle levers is very short for the power obtained.
Coarse use of the throttles will aggravate any tendency to swing.
(iv) When comfortably airborne, brake the wheels and raise the undercarriage, check that the undercarriage locks up; if it does not hold the selector lever up for five seconds.
(v) Safety speed at a weight of approximately 17,000 lb. flaps up or 15° down at +9 lb./sq. in. boost is 155 knots. At + 18 lb./sq. in. boost it is 170 knots. These speeds however, may vary considerably with individual aircraft.
(vi) Before raising the flaps, if used, trim the aircraft slightly tail heavy.

55. Engine failure during take-off
(i) The handling characteristics of individual aircraft differ considerably according to age and load. Except in cases where it is known to be less ; at approximately 17,000 lb., safety speed should be assumed to be 155 knots at + 9 lb./sq. in. boost and, if the engines have not been de-rated 170 knots at + 18 lb./sq. in. boost.
(ii) If safety speed has been attained, the aircraft will climb away on one engine at climbing power at about 135-140 knots provided that:—
(a) The propeller of the failed engine is feathered and the radiator shutter closed.
(b) The flaps are fully up.
(iii) The drag of a windmilling propeller is very high and unless feathering action is taken immediately, control can only be maintained at the expense of a rapid loss in height.
(iv) The aircraft accelerates slowly to the safety speed at + 18 lb./sq. in. boost. If high power is used for take-off, it is recommended that climbing power is used as soon after take-off as is possible.

57. Single-engine landing
(i) While manoeuvring with the flaps and undercarriage up, a speed of 140-150 knots should be maintained ;
(ii) A normal circuit can safely be made irrespective of which engine has failed. The checks before landing should be carried out as for a normal landing, but it should be remembered that the undercarriage will take longer to lower on one engine—approximately 30 seconds at 2,850 r.p.m. —and, owing to its high drag, height will be lost once it has started to lower.
(iii) When across wind, flaps may be lowered 15° and the live engine used carefully to regulate the rate of descent. Speed should not be allowed to fall below 135 knots until it is clear that the airfield is within easy reach ; flaps may then be lowered further as required and power and speed reduced as height is lost, aiming to cross the airfield boundary at the speeds quoted for an engine assisted landing.

58. Going round again on one engine
Going round again is only possible if the decision is made while ample height remains and before more than 15° of flap is lowered. The height is required in order to maintain the speed above the critical speed, for the high power necessary, while the undercarriage and flaps are retracting. When the decision to go round again has been made:—
(i) Ensure that the speed is not less than 135 knots, and then increase power on the live engine to +9 lb./sq. in. boost and 2,850 r.p.m.
(ii) Raise the undercarriage.
(iii) Increase speed to 140-150 knots.
(iv) Raise the flaps and re-trim.
(v) If the engines are not de-rated, power higher than +9 lb./sq. in. should only be applied carefully and within the limits of rudder control.

Handling
The controls are light and effective and manoeuvrability is good. The rudder should not be used violently at high speeds. When two-tier R.P. or rails are carried, aileron control is poor at low speeds, i.e., during take-off and approach to land.

By way of comparison, the take off safety speed for the Beaufighter (Merlin engines) was 139 knots, and for the P-38 113 knots. A little disparity arises when comparing figures as the Beaufighter is at take off power whereas the P-38 advises to reduce power on the good engine to contain the yaw. Excessive yaw will result in stalling of the vertical tail surfaces and the rudder forces reverse. The power on the good engine will then have to be materially reduced, and considerable rudder force will be necessary to regain control.

[papajuliet]

Read Colin Cummings excellent books on RAF aircraft accidents to gain some idea of the Mossie's horrendous record.Not something we realised in those postwar years.

[GQ2]

Experienced Mosquito pilots are getting very thin on the ground now. I knew a few, and they always spoke of the a/c in very, very glowing terms. Sure, if you look at the figures - especially the blue-line speed, and compare it with more modern, more benign machines, it might look a bit scary. In truth, many, if not most wartime a/c would feel a bit scary to modern pilots, especially when bombed-up and full of fuel....and in the dark... The records show that the Mosquito had a vastly lower rate of loss than the Lanc' for example. It was not unusual for damaged a/c to fly home all the way from Germany on one engine, - and never drop below 200mph to boot. They also flew home with heavy damage.
I have an excellent wartime book, 'Low Attack' by W.Cdr Wooldridge. I think they were 105Sq. and based at Marham from memory. They'd been using the Blemheim previously and were glowing in their praise of the Mossie. It was light years ahead.
Unlike many modern 'warbird' pilots, wartime crews flew these a/c all the time and often at night. They knew the limitations of the a/c very well and acted accordingly. Sure there were accidents (Tony Ben's brother was killed in an EFATO in a Mossie for example.). At least the Mossie would fly on one engine and even accelerate and climb if correctly handled. Many other types of that period were very vulnerable to an EFATO and were only going one way after an engine failure ..... DOWN. Many heavily-laden bombers crashed on t/o, especially at night.
For around three years there wasn't anything in enemy hands that could catch it. The PR versions roamed the length and breadth of Axis-held Europe with virtual impunity at up to twice the altitude of most a/c. The Mossie could carry the same load as a B17, faster, higher and further, for vastly less casualties, less fuel, less materials, less manpower to produce etc....oh, and they were churning them out from furniture factories. It was also the original 'MRCA', and filled every role and flew in every theatre - a truly amazing record.
The Mossie was a military a/c, mostly flown under combat conditions. Any narrow discussion of one very narrow aspect can give a very false and distorted impression to what was, arguably, the finest a/c of the war. As an a/c to go to WAR in, it was absolutely in a league of it's own....

[ChrisVJ]

GQ2
I have never doubted that and, as you say, a discussion of a narrow quality of an aircraft without context is somewhat unhelpful, however I was just curious as to the compromises made to get such a fine war instrument.

There were other planes that were good for purpose but otherwise "difficult" for instance the Typhoon. The compromises, flying qualities and constuctipon/engines are an endless fascination.

[twochai]

they always spoke of the a/c in very, very glowing terms

Well said, GQ2, you're absolutely right.

The thing I remember most clearly from my very brief exposure to the Mossie 50 years ago was the utterly exquisite harmonisation of the flight controls. Until experienced it is very difficult to define control harmonisation, yet it is probably the single most important contribution, after meeting the regulatory requirements, that a test pilot can make to the satisfactory developoment of an aircraft's handling characteristics.

Mosquito control force gradients in all three axes could not be more perfect and was the standard against which all aircraft I subsequently flew were judged. Geoffrey deHavilland and John Cunningham certainly got it right that time!

[TBM-Legend]

Interesting:


Mosquito Manufacturing 1944 - YouTube (http://youtu.be/D3mGOLmWWbg)

[Jwscud]

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.

[TBM-Legend]

Many twin of that era had "high" single engine safety speeds as it was called. The B-25 Mitchell SESS is 145mph as is the A-26 Invader. The B-26 Marauder similar....

[astir 8]

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.

[teeteringhead]

Allegedly the RAF stopped practising single engine landings because they were having more (fatal) training accidents than accidents caused by real engine failures. ... but presumably failed to take the lesson on board for the Canberra!

[rolling20]

GQ2, Tony Ben's brother was killed in an EFATO (Engine Failure After Take-Off) in a Mossie for example.)
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.

[Rory57]

The matter of controlling a twin on one engine is dealt with in some depth in Up in Harms Way by Mike Crossley. An excellent read.

[Stationair8]

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.

[Fareastdriver]

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.

[TBM-Legend]

P-38's had "handed" engines [except for a few early ones]...

Reducing power on the good engine can be a good idea as well but this does not sit naturally with a pilot....

[Jwscud]

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.

[DH106]

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?

[Brian Abraham]

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.

http://i101.photobucket.com/albums/m56/babraham227/s0009.jpg

[DH106]

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?

[twochai]

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.

[Fareastdriver]

Reducing power on the good engine can be a good idea

I was told many years ago; though do not quote me and I do not know whether it is true; that the early Boeing C135 had a severe assymetry problem. Basically the rudder was not man enough to correct the yaw if an outer engine failed. To address this thrust switches were incorporated so that if an outer went the opposite outer would be throttled back to maintain yaw control. In extremis; certain conditions meant there would be insufficient thrust to keep airborne, but at least you crashed with the ball in the centre.

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.

[Shaggy Sheep Driver]

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. :ok:

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'.

[Fareastdriver]

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.

[DH106]

Ahhh - okay I see now, it's the difference in pitching moment between power off & on that's critical here, not the absolute value of the pitching moment.

[Stationair8]

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.