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Thread: Halifax rate of climb

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    Default Halifax rate of climb

    I'd like to determine the height of what I'm assuming is a fully laden Halifax, about 3 minutes after take-off. I believe the aircraft in question was still flying along the centre line of the runway - ie no devviation. Any takers for this one?

    Brian

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    At an initial rate of climb, 750 ft/min (3,81 m/sec), about 1250 feet, give or take, depending on model and load

    A

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    I assume your 750fpm comes from some legitimate source, but I must point out that any such number will have been quoted at the optimum climb speed, flaps up, and the aircraft will have needed some time accelerating to reach this speed. Between lift-off and achieving the climb speed there has to be some trade-off between speed and height gains. This is likely to be dependent upon the speed at which the flaps can be retracted, and the local terrain. The acceleration would be much lower with flaps down.

    I believe that good airmanship calls for speed to be gained before establishing a steady climb, and suspect that the aircraft will not have been above 500 ft.

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    Many thanks gentlemen. I hope you will forgive me when I confess that I didn't provide all the information, but I was seeking an unbiased estimate.

    The aircraft concerned was Halifax DT642 of 1674 HCU, which crashed on the western outskirts of Antrim om 29 July 1944, some 3-4 minutes after take-off. In the absence of any other information I'd assumed (always, always, fatal) that it was heading north. However Mervyn (aka Fletch) has kindly sent an account, based on eyewitnesses, that shows the pilot was attempting to turn onto a reciprocal course. The aircraft appears to have lost flying speed and height from a low level, with fatal consequences.

    Graham's suspicion of the aircraft not being above 500 ft appears to me to be consistent with the eyewitnesses description of of the accident, indeed as the aircraft was clearly in trouble it was probably lower.

    My thanks again, and also to Fletch.

    Brian

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    There is an old rule in flying: it you have engine trouble shortly after take-off do not attempt to turn. It sounds as though this crew broke the rule - circumstances may have forced their hand, of course. Have you looked at the nearby terrain - nothing like a hill directly ahead to encourage a change of direction?

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    To add to Graham's excellant post: The rate of climb of a heavly loaded aircraft will be very dependant on airspeed, and that is very dependant on the pilot paying attention to pitch attitude and power settings. Loss of climb rate due to pilot's attention wandering is frequently reported in modern accident reports, for aircraft equipped with data recorders. Note that the r.o.c. may decrease if the airspeed is above or below the optimum speed.

    Joining Lyffe in the dangerous business of assumption, any distraction to the pilot resulting from the unspecified trouble could be assumed to decrease the height reached below the numbers quoted previously. Of course, if the problems resulted in a loss of engine power than r.o.c. will immediately go down. There is a formula for climb rate based on aircraft weight and excess power (that I can't remember right now). Even in an aircraft as heavy as a Halifax, 750 feet/minute doesn't take a whole lot of excess horsepower, compared to the power available from 4 engines. Even a partial power drop on one engine would show up right away as a loss of climb rate.

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    The equation is Thrust-Drag, multiplied by velocity, divided by weight.

    Thrust can be obtained from the power output, the propellor efficiency, and the airspeed.

    I would only add that there is no "may" about it - if you stray from the optimum climb speed, faster or slower, then you will reduce your climb rate.

    Modern aircraft quote 500fpm as the service ceiling - above which height gain is so slow it it not normally worth bothering with. 750fpm is awfully close to that - any problem with engines or added drag (undercarriage failed down?) would give a very slow rate of climb indeed, if you were lucky.

    What must be avoided is getting too slow: this will put you up the wrong end of the lift curve. You need a large angle of attack to get the lift to keep you up, but this gives so much drag you can only slow, which means more angle of attack..... the only ways out are to dramatically reduce weight (jettison bombs and/or fuel) or to dive - clearly not always possible. Attempting a turn (to get back to a runway) will require increased angle of attack, triggering this kind of situation ending in a stall (perhaps with wingdrop and spin) or just sinking and ploughing in.

    Of course, it would be wrong to speculate too much on this specific crash without more information. They may have been other factors.

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    Other limitations in the rate of climb and attained speeds of Halifaxes with HCU's are the age and maintenance of the war-weary aircraft involved. My father indicated that in September 1944, when he was with 1659 HCU, he flew Halifax II and V's, which were "terrible, clapped-out old aircraft with engines that constantly gave trouble." These were powered with Merlin XXI (H-bag II's) and Merlin XXII (H-bag V's).

    Why was this aircraft fully loaded? Was it tasked to drop mines?

    Jim
    Last edited by JDCAVE; 26th September 2008 at 20:39.

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    Jim,

    The task of 1674 HCU was to train crews for Coastal Command activities; this particular crew was training for a meteorological reconnaissance role. The flight was a night navigation and meteorological exercise over the sea, so it is possible, but unlikely, there were some munitions on board in the event of it coming across a sub.

    My post which started this thread was simply for me to gain some idea of the height the aircraft would have attained 3-4 minutes after take-off; in the absence of any definitive load I suggested it was fully laden - not unreasonable for a maritime flight.

    In the absence of any Court of Inquiry report, and only eyewitness statements to go by, everything in this thread has, of necessity, been assumed which - as I've admitted - is far from satisfactory.

    One can imagine a number of scenarios, probably the most likely being a loss of power on one or two engines (or even the loss of an engine) immediately after take-off, resulting in an inability to maintain speed and height - which perhaps morrors your father's experience. There must have been contact between the crew and Aldergrove, but such evidence appears to be lost/destroyed.

    In view of Jim's comment re the 'clapped out' aircraft of 1659 HCU, can anyone provide a unit history for DT642?

    Brian

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    Its only previous service was with 58 Sq. It was in a batch delivered between 21st and 29th November 1942, so it was a fairly elderly aircraft at the time of the crash.

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