Convair 340 (C-131D) ZS-BRV crash Pretoria, South Africa
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It appears to me that the loss of left aileron control occurred quite early in the video as viewed from the cabin. Compare the aileron in the first few seconds vs around 20 seconds. At the 20 second point it appears to me that the aileron is full deflection up.
Measuring distance against time, a rough estimate of speed downwind is in the region of 180 knots. I am thinking it was the intention of the crew to make a quick low level circuit for landing, but the fire in the nacelle progressed quicker and more fiercely than the pilots or the onboard engineers thought would occur.
On base the loss of aileron and the loss of power from the left engine combined to make the aircraft no longer flyable.
Indeed in the last 30 seconds, there was a report from the author of the video that the left engine should be shutdown.
Measuring distance against time, a rough estimate of speed downwind is in the region of 180 knots. I am thinking it was the intention of the crew to make a quick low level circuit for landing, but the fire in the nacelle progressed quicker and more fiercely than the pilots or the onboard engineers thought would occur.
On base the loss of aileron and the loss of power from the left engine combined to make the aircraft no longer flyable.
Indeed in the last 30 seconds, there was a report from the author of the video that the left engine should be shutdown.
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Hey guys we can kick this around until the cows come home but suggest waiting for a preliminary report or the like. In the meantime let us focus our energy on hoping for a speedy recovery of Doug, Ross and the other injured. Seems like a marvellous bit of flying here to achieve almost complete survival in what is a very confusing scenario. I will certainly buy them a beer if I get a chance.
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I also think that the cable (or one of the cables) for the left aileron burned through due to the engine fire. The airstream / lift will then push the aileron all the way up.
That would make any further right turn more or less impossible. Full right aileron would just have given them a balanced situation. Of course both ailerons all the way up will add quite some drag.
Great airmanship to keep it flying and not crashing doing a snap roll to the left.
That would make any further right turn more or less impossible. Full right aileron would just have given them a balanced situation. Of course both ailerons all the way up will add quite some drag.
Great airmanship to keep it flying and not crashing doing a snap roll to the left.
Are we not seeing an unusual aileron configuration in the still photo at post 11? It would appear there is a significant upward deflection of the starboard aileron, along with a slight UPWARD deflection of the port aileron too. I'm not sure when that shot was taken, but certainly after the fire had started.
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Are we not seeing an unusual aileron configuration in the still photo at post 11? It would appear there is a significant upward deflection of the starboard aileron, along with a slight UPWARD deflection of the port aileron too. I'm not sure when that shot was taken, but certainly after the fire had started.
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Well EDML, I'm not going to take the bait! But I'm not sure that a change of only 20 (prop) RPM would look totally different. That would be only one blade per second on a 3-blader, and my pocket camera records at 25 frames per second.
BTW, I gather the RPM on a R2800 at take-off is 2800 RPM at sea-level, but may be 2700 RPM at about 5000 ft. According to Janes, reduction gearing is 0.375 : 1 (3 : 8) - giving prop speeds of 1050 RPM or 1012 RPM respectively (roughly 52 or 50 blades per second).
BTW, I gather the RPM on a R2800 at take-off is 2800 RPM at sea-level, but may be 2700 RPM at about 5000 ft. According to Janes, reduction gearing is 0.375 : 1 (3 : 8) - giving prop speeds of 1050 RPM or 1012 RPM respectively (roughly 52 or 50 blades per second).
from what I could find out the reduction gear for the R-2800 is 16:9. With a framerate of the camera of 25fps that would be 2666 engine RPM for the prop to look stopped: (25 RPs * 60 * 16) / 9.
That is pretty much in line with the 2700 RPM for the R-2800 at T/O power.
Hard to tell what that means for the perceived rotation of the prop.
Marcus
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Maybe the left aileron upfloat is due to damage the left aileron primary control cable. (The upfloat changes from the first few seconds, of the latest video, to the 20 second mark, where upfloat is at its maximum, and stays there until impact. An NTSB report regarding a possibly similar occurrence refers. See NTSB ERA11LA117. The left aileron, with what appears to be close to maximum deflection, would make turning to the right on base challenging. With a left engine most likely producing less power in the final minute or so, manoeuvring the aircraft would be difficult. To me the engine note changes, in the video from inside the aircraft, in an attempt to keep wings close to level close to the ground.
https://www.ntsb.gov/about/employmen...11LA117&akey=1
You may know more than I do about aileron upfloat, its degree and possible effects, but I find it hard to accept that it would be full deflection. Why would a control that is effectively feathered in the airflow be at full deflection and producing a full rolling moment?
Hi Chris,
from what I could find out the reduction gear for the R-2800 is 16:9. With a framerate of the camera of 25fps that would be 2666 engine RPM for the prop to look stopped: (25 RPs * 60 * 16) / 9.
That is pretty much in line with the 2700 RPM for the R-2800 at T/O power.
Hard to tell what that means for the perceived rotation of the prop.
Marcus
from what I could find out the reduction gear for the R-2800 is 16:9. With a framerate of the camera of 25fps that would be 2666 engine RPM for the prop to look stopped: (25 RPs * 60 * 16) / 9.
That is pretty much in line with the 2700 RPM for the R-2800 at T/O power.
Hard to tell what that means for the perceived rotation of the prop.
Marcus
You haven't stated your source for a 16:9 engine-to-prop reduction-ratio. Mine, from Janes for 1957/8, giving an engine : prop ratio of 8:3 (i.e., 16:6), would give a prop RPM only two-thirds of yours. Also, we don't know the frame-rate of the video camera used.
You'll agree that each of the three blades is not individually distinguishable. So, with a frame rate of 25 per second, a prop would appear stationary at 25 blades per second (500 prop-RPM), 50 blades per second (1000 prop-RPM), 75 blades per second (1500 prop-RPM) or even 100 blades per second (2000 prop-RPM).
So there's plenty of room for ambiguity, but we would certainly need the camera's frame-rate before postulating from the video. My assumption is that the engine RPMs would have been more or less equal (at about 2700 RPM) as the a/c was getting airborne at the beginning of the video. My GUESS is that the failing port engine was not much slower than the starb'd until the a/c passed over the perimeter fence. After that, it may have started to lose RPM (and therefore propellor thrust) by a significant amount. But I stand to be corrected.
Chris
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Pratt and Whitney manufactured a whole bunch of different radial engines with 2800 cubic inches of displacement. Some models are pretty dissimilar with no interchangeable parts The engines installed on the Convair were almost certainly either CA series or CB series engines, both of which had a drive ratio of 9:20 or .45:1 Reference is the Type Certificate Data Shees for the respective engine series.
Pratt and Whitney manufactured a whole bunch of different radial engines with 2800 cubic inches of displacement. Some models are pretty dissimilar with no interchangeable parts The engines installed on the Convair were almost certainly either CA series or CB series engines, both of which had a drive ratio of 9:20 or .45:1 Reference is the Type Certificate Data Shees for the respective engine series.
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You may know more than I do about aileron upfloat, its degree and possible effects, but I find it hard to accept that it would be full deflection. Why would a control that is effectively feathered in the airflow be at full deflection and producing a full rolling moment?
In any case the aileron may not have been disconnected - could have jammed either as an unfortunate coincidence, or as result of excessive heating of pulleys, rods etc. Unlike more modern aircraft, that generation did not have control disconnect circuits or back up systems.
It certainly appears that they were faced with a compound failure and probably not one that anyone could have anticipated or would ever train for.
It certainly appears that they were faced with a compound failure and probably not one that anyone could have anticipated or would ever train for.
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I don‘t think it was jammed. No way to counteract a full or almost full left aileron. If it was jammed the other side would have been full down generating the max. possible roll rate to the left. No way to counteract that. They would have crashed performing a roll to the left.
I tend to agree a disconnect is more probable than a jam, but with fire in that area who knows? Possibly the section outboard of the fire had seized and the section inboard had sheared in such a way that remaining controls were still free. Or vice versa. To really confuse matters, the Convair was built at a time when the FAA, or designers, were going through a phase of favouring rudder/aileron interconnects. The CV- 580 had this, and what awful, heavy controls they were, too. If ever there was a contraption it was the 580.
The centred rudder in the video taken from outside the aircraft still suggests close to symmetric power - whether a lot or a little at the time is not so easy to deduce simply from estimating prop RPM. You'd need to know the manifold pressure and TAS to get a better idea.
The centred rudder in the video taken from outside the aircraft still suggests close to symmetric power - whether a lot or a little at the time is not so easy to deduce simply from estimating prop RPM. You'd need to know the manifold pressure and TAS to get a better idea.
Pratt and Whitney manufactured a whole bunch of different radial engines with 2800 cubic inches of displacement. Some models are pretty dissimilar with no interchangeable parts The engines installed on the Convair were almost certainly either CA series or CB series engines, both of which had a drive ratio of 9:20 or .45:1 Reference is the Type Certificate Data Shees for the respective engine series.