Propeller Blades Bent Back Into Shape!!!

According to the DH Hydromatic manual, and this one is dated 1969, there is no upper limit for the angle of bend which can be straightened, only how bent it can be against sectional area, before it has to be annealed prior to straightening.
It also states that any blade can be straightened twice but must be annealed prior to straightening a third time. (probably easier to find a better pilot at this stage!!)
If there is a bend in the first 8.2″ from the shank end on a Merlin blade it cannot be reworked.

In reality I know that they are often scrapped when bent nowadays.

Pete

The difference to remember between now and then is that was wartime, and it was expected that the aircraft would not last more than 30 or so missions… maybe 150 hours… before being shot down, damaged beyond repair, or sent back for complete refurbishment.

The most that was expected of a repaired prop (before being repaired again) was maybe 50 of those hours, as they were replaced fairly frequently.

Nowadays, CAA/FAA/military standards require a lifetime of hundreds, if not thousands of hours, even of repaired props, and thus the “repair/trash” ratio is far different.

One of the old de Havilland Gazettes shows some seriously bent props being straightened out. They also dressed out bullet holes and nicks – its amazing what they could do!

Bruce

In the book ‘Airsrews for Models’ 1942. There is a photo of de Havilland props that are bent. The caption says, Two badly damaged metal airsrews return to the factory for repair. About 80 per cent of such “casualties”are capable of being made fit for service again.

Dave

Bent props

I’ve seen that photo too. I think most of those propellers in the photo would be sent for scrap judging by their condition. It was only those blades which were within certain conservative limits which could be recovered.
Of course, in many cases even though the blades would be knackered the hubs and internal parts would be re-usable.
Regarding modern propellers I remember an engineer telling me that if an aircraft (in this case a Seneca) had struck one or two blades, the hub was reusable. If it had struck all three it was a scrapper, even if it checked out OK. WW2 props (de-H licensed built Ham-Stan types) were much larger and stronger built and those hubs without deep nicks or scratches were probably fine for re-use – subject to the necessary inspections.
I’ve stripped down old WW2 hubs which were serious crashers with snapped-off blades – and they weren’t even distorted.

In todays world, propellers have to be within certain limits to be straightened out. I´m not sure what the exact limits are. I´ve seen props that are bent outside the limits and were cast away, and I was thinking to myself “well…..all I need to get this right is a hammer and an anvil”:diablo: True, they were bent, but not to a great extend.

What they did in wartime is anybodies guess, but metal behaves much the same now as it did 60 years ago. Severly bent blades would most probably have been sent to the scrapyard!

I just love that statement…….

In todays world, propellers have to be within certain limits to be straightened out. I´m not sure what the exact limits are. I´ve seen props that are bent outside the limits and were cast away, and I was thinking to myself “well…..all I need to get this right is a hammer and an anvil”:diablo: True, they were bent, but not to a great extend.

What they did in wartime is anybodies guess, but metal behaves much the same now as it did 60 years ago. Severly bent blades would most probably have been sent to the scrapyard!

True. It’s still done. Depends, I presume, on the state of the metal.