F4U-1D Corsair R/H Inboard Flap Step Present.... Yep, after 4425.

[Juggernut]

I did an examination of the Vought blueprints for a post on another modeling website and thought the folks here may like to know what I distilled from looking at them.  The upcoming Tamiya kit will have the option of a step in the R/H inboard flap, one closed with a plate and one completely open through the flap.  The wing erection drawing (VS-10000) for the F4U-1, F3A-1, FG-1 indicates that at revision O, Vought Engineering authorized the use of the flap p/n VS-37769 (with a step in it) somewhere between April and what looks like May of 1944 (but does not preclude the use of the old flap p/n VS-10069).  The microfilm scan is not clear enough to read the exact date when this was authorized.  Nor does the blueprint state which aircraft it was installed with.  Note 13 on the blueprint says that Engineering will be informed when this change is made but the field of the note is blank with respect to any serial/construction number information. It is my belief (call it a hunch as I have no basis of fact for it) that the war ended before this flap made it to the production line and that it was primarily installed on post war F4U-4's and later. But for the sake of the argument....

Having said that and absent of any photographic evidence (or more definitive information), there is no way of knowing which aircraft (in construction at that date or thereafter) were fitted with this particular R/H inboard flap and which were not.  Aircraft manufacturing experience leads me to the opinion that there was a stock of flaps prebuilt for installation on the production line and that would have to be used up prior to this specific flap being installed on the production line (unless the flap stock was pulled and modified but that takes a lot of time and most likely was not done given the exigant circumstances of war).  However, if the aircraft was manufactured prior to said authorization (April-May 1944) it is doubtful it would have had such a flap installed from the factory.  This also does not indicate that aircraft produced after this date will definitely have the step flap.  Like I said, any stock of existing flaps (VS-10069) would have most likely been exhausted prior to this flap (VS-37769) being installed on the production line.

This does not preclude field replacements on older aircraft as it appears as though they were interchangeable.  I should think any replacement flap with a step would have stuck out like a sore thumb on a combat aircraft given the fading and wear of the paint job on the airframe vs. the newer flap.

 

Again, this is my opinion based on examining the actual Vought Corsair blueprints for the subject parts.  If there's any errors, they're mine alone and I'm perfectly happy if more/better information is brought to the discussion as it makes us all the better for it.

Edited May 21, 2017 by Juggernut

[Juggernut]

Well, rather sheepishly, I must admit that I didn't do as thorough a job as I thought I did as the construction number for the step flap is listed on the flap drawings (10069 and 37769) and not on the higher level drawing which I examined.  Add to that the fact that Dana Bell had already done this quite thoroughly and is included in his Aircraft Pictoral No. 8.  complete with bureau number cross refererences.  I should have known he'd be on top of something like this.  Anyway, it turns out that the step flap was indeed introduced into the production line in the FG/F4U-1D production line at aircraft number 4425.  Refer to Dana's aforementioned book to see what Bureau No. this corresponds to.  I have his book but don't have access to it at the moment. 

 

Now the remaining question is how do we determine which aircraft of F4U/FG-1D were post 4425 (insert Bureau No. here) from the extant photographs where that information is not readily discernable?

Edited May 21, 2017 by Juggernut