They got the gear up very early while still being over the runway. That shows that they where aware of the situation pretty soon.

Anyone know if #1 prop was feathered at any point,and, if the aircraft used water/water-meth. injection...?

Hmm, could be, but my recollection of flying in the piston era was that the gear coming up early was fairly standard.

You'd select gear up as soon as you had a positive indication of climb. That's usually over the runway.

On a South African forum it was reported that they had planned to use water/meth for this take off. Apparently this was infamous for causing backfiring leading to the auto feather engaging so many crew didn't arm the auto feather. The use of water/meth could well explain the popping we hear on take off. They also had a habit of exhaust system fires aft of the engine.

Looking at the vid from the Cessna I would guess that they had both engines running until they turned onto base considering the speed they were doing. Something happened on the base leg for them not to turn onto final. May be they shut down the engine and it wouldn't feather.

Most likely Cylinder head cracked then blew off thus constant smoke out one exhaust on that cylinder side. If it dropped a valve it will maintain power at 30 inches or barometric but will PUFF Smoke not stream smoke. If smoke trailing from both exhausts it is a blown supercharger drive seal or broken supercharger drive the later will have the engine stop and windmill, if it breaks the front reduction gearbox gear may end up with a run away prop.
With blown off cylinder head you can in emergency keep running the engine at higher power (or barometric if its banging to much with the blown cylinder ) which is what you maybe seeing going on from the Cessna video and the takeoff. It shakes like hell for few minutes but will put out until the piston comes apart, breaks the rod at which time you feather it . Sometimes will run 1 minute sometimes 2-3mins dependent where the cylinder head comes off. Had 8 failures myself with R1830-92 and R2800-CB16s. 1 Master rod, 1 rod, 2 dropped valves the others were cylinder head blew off some through the cowl. When these big radials stop suddenly from seizure other things break and shear it is a lot of mass and moving parts
All my failures on takeoff or first stage power reduction. All at sea level and that was bad enough. Just some technical thoughts but the investigators will advise later.

They did a good job with what they were given on the day, speedy recovery to all..

amazing, 8 failures would give you grey hair, thank goodness for the jet age

Sorry to be pedantic but at, or soon after rotate the VSI, depending on the type of aircraft may well give erroneous readings. As correctly pointed out above, a positive climb is reliably indicated by the altimeter.

Sounds like an Old Wives Tale. Flying the Convair 440 I have used ADI on hundreds of occasions. Not once did I experience back-firing on take off. Certainly we experienced occasional rough running due to spark plug fouling with 115/145 Octane fuel but it usually cleared itself during initial climb. As far as I recall autofeather was armed for every take off. .

Positive Climb
 

I do not dispute the point regarding erroneous VSI indications, however the call often is "Positive Rate, Gear Up"

Only airplane with a radial engine I have ever flown was a T-6/Harvard (also in South Africa). Of course that is no airliner and it has plenty of power.

Anyways, from your experience would you rate the climb while over the runway (and of course still accelerating) as normal for these kind of aircraft? Of course the density altitude of at least 5,000ft (not sure about the OAT that day) plays a big role, too.

I am just interested if they still had power from the left engine at that point. There is no visible yaw and no bank towards the "good" engine but unfortunately you can't see the rudder on the video or any of the pictures after lift-off.

Does anybody know the blue line speed of a CV-340?

I had never heard of ADI causing backfiring either, at least not a properly functioning system. I did have one incident where I rejected a takeoff due to backfiring and it turned out to be a ruptured diaphragm in the ADI regulator. However that problem made itself evident as soon as the throttles were pushed up far enough for the ADI flow to start. WE didn't arm auto feather, but it was only required for takeoffs over 100,000 lb, and our operations were relatively short legs so were were always landing weight limited, so never needed to depart over 100,000lb.

Meaningless semantics. A Positive Climb is inherently also a positive rate of climb. The SOP call at my current airline is "Positive Climb"

Post WWII most piston airliners were certified on 115/145.

On 100LL derates have to be applied. Engine out performance on 100LL will be less than on 115/145.

Same as in my company: I believe it's an Airbus standard call out. Also in our SOP, the '' Positive Climb'' call out is based on RA, not on VSI or altimeter as both will increase while the main gear are still on the ground.

My time radial engined airplanes was all in far northern climates at close to sea level. Given that this was, as you say, a much higher elevation and possibly warmer OAT I wouldn't consider the low initial climb extraordinary.

As someone else noted earlier, it is quite possible for an engine to have a cylinder failure and still be producing a substantial amount of power.

I haven't flown the Convairs, but I'd expect that it didn't have a blue line, but rather V speeds which were calculated based on takeoff weight, altitude and OAT. Blue-line is more light twin figure. It's possible though, that era was kind of a transitional period for aircraft performance theory.