P-51D "Creamer's Dream"

[drgondog]

IMO - you outlined all the external changes from D-10 that I was aware of except the fuel drain access door on rear cowling. For grins I'll hunt the drawing number to see the effectivities but it certainly would not have been limited to only Inglewood 51's.

Just looked - take a look at the Effectivity Block Notes - upper LH corner, zone 8, 109-25001 (S51 ref for image 000000130 in Folder "S")

USED ON P-51D-10-NT SUBS
USED ON P-51D-15-NA SUBS
ALSO ON LAST 600 OF BLOCK P-51D-10-NA
" " " 200 OF BLOCK P-51D-5-NT

Taking it to the Next Assembly Dwg 106-31001 (Ref R159 Effectivity Notes 2. 3 - Zone 1) for 25001-3 Fin

NAA 109 44-14253 Sub, NA 111 44-11153 Sub.----> same blocks as above - just specifying serial number instead of Contract ship #

That would place the 'Straight' DFF into production starting on #201 through #800 of P-51D-10= 44-14253
and would start the Dallas production with the P-51D-5-NT #1 starting at 44-11152.

The 200 D-5-NT preceded the K series, then 1500 K's were built plus 160 F-6K's (44-11353-44-12852) and then the rest of the Dallas line finished up the P-51D-20NT through 45-11742 plus one P-51M 45-11743.

Personally, I believe the Drawing Effectivities which means that the straight DFF seen on any P-51D/K during WWII started with P-51D-10-NA 44-14253 and P-51D-5-NT 44-11153. Stated another way Only the P-51D-5-NA through the 200th P-51D-10-NA had the curved DFF.

Having said this I have seen mid range P-51D-10-NA's that do not appear to have perfectly straight DFF making me pause and speculate that some got out of the barn after the Effectivity Block break.

Back to Creamer's ship. It Could very well be a -15-NA, but there is nothing definitive to state with certainty that it was a -15 absent the serial number as the P-51K-5 and Subsequent also had square aperture w/plastic cover..

I am also curious regarding when the 332nd first received D's. I have a hard time believing that they did not get early -10's or damaged/repaired -5's, but there was discrimination and not out of the question that somebody at 15th AF level Logistics delayed P-51Ds..

I'll take a look at Baugher's site as well as Aviationarcheology.com

 

[drgondog]

Searching Accidents and MACRs the losses started on Dec 15, 1944 with a D-15 and then the distribution was

D-5 - 2
D-15- 8
D-20- 2
K-1 - 2

Not sure how to grab the Mustang allocations for 332nd but doesn't seem to be much activity on P-51D/K until December 1944.

 

[Tourist]

Personally, I believe the Drawing Effectivities which means that the straight DFF seen on any P-51D/K during WWII started with P-51D-10-NA 44-14253 and P-51D-5-NT 44-11153. Stated another way Only the P-51D-5-NA through the 200th P-51D-10-NA had the curved DFF.

Drgondog, you cannot see the forest for the trees.
Your methodology is flawed.
Belief has nothing to do with it, all the photos of P-51D-10's and D-15's clearly show the swayback DFF, that's a fact.
If what you see in the drawings does not match the photographic evidence it just means that you're missing a piece of information, not that the photographs are wrong.

Back to Creamer's ship. It Could very well be a -15-NA, but there is nothing definitive to state with certainty that it was a -15 absent the serial number as the P-51K-5 and Subsequent also had square aperture w/plastic cover..

I am also curious regarding when the 332nd first received D's. I have a hard time believing that they did not get early -10's or damaged/repaired -5's...

Creamer's Dream was a P-51D-15 and I never said that the 332nd FG received only P-51D-15's.

I cannot continue this back and forth, it takes too much time.
Everything I said can easily be verified by anyone willing to look at period pictures.

Regards,
Christian.

 

[drgondog]

Drgondog, you cannot see the forest for the trees.
Your methodology is flawed.

Prove that anecdotal evidence trumps NAA design drawings - ESPECIALLY since you were the first to bring them up?

Belief has nothing to do with it, all the photos of P-51D-10's and D-15's clearly show the swayback DFF, that's a fact.

But you are SO convinced that it is ONLY a P-51D-15, I have further comments on this below.

If what you see in the drawings does not match the photographic evidence it just means that you're missing a piece of information, not that the photographs are wrong.

Yo, I hope you discerned that I understand that the photos of P-51D-10s, P-51K-1s and P-51K-5s exhibit 'curve' in the DFF.


Creamer's Dream was a P-51D-15 and I never said that the 332nd FG received only P-51D-15's.

Yes, you suggested that they mostly had -15-NA's - with no proof. Zero proof. Still no proof.

I cannot continue this back and forth, it takes too much time.
Everything I said can easily be verified by anyone willing to look at period pictures.

So, you wish to provide some, say 200+, photos of all 332nd P-51D/Ks.

Regards,
Christian.

I am now officially amused Christian. You were the first one to reference NAA 104 and 109 DFF Drawings

I went to the trouble of actually reviewing the DFF drawings, the Effectivities and quoted the data, the drawing numbers and the Smithsonian Index scheme for YOU to verify what I posted. You didn't like that. I hurt your feelers, I guess.

"I am fatigued in your response. Is that J'suis Fatigue?"

I pointed out to you that NAA drawings SPECIFICALLY Place the new straight line 109-25001-3 DFF having an effectivity starting in the early phase of the P-51D-10-NA and P-51K-1-NT - NOT the P-51D-15NA that you were trying to BS everybody to substantiate your "Opinion'. So what do you say to NAA?

NOW, having said this I Can give you a POTENTIAL explanation for reasons to continue the 109-25001-1 DFF on later models than P-51D-10-NA 44-14253. IF NAA had an inventory of -1's, they easily could have written a Change E.O. to PERMIT NAA Manufacturing/Production group with the authority to use them up - the cut over to the straight DFF when the curved ones were all gone. The AAF and NAA Engineering would have bought off on it. I have zero proof that this occurred. I have 100% proof regarding the ENGINEERING Effectivity. You have zero proof for your own theories - so far. It's OK to be wrong - I was wrong about the B/C and early D curve as you pointed out.

But, Since you threw out the P-51 Drawings card to support your arguments -

The ball is NOW in your court to a.) Provide proof that NAA did NOT use 25001-3 per the Effectivity blocks I cited, b.) and, that the serial number of Creamer's Dream is NOT a P-5D-10/P-51K-10 through end of P-51D series.

 

[Tourist]

I am now officially amused Christian. You were the first one to reference NAA 104 and 109 DFF Drawings

I went to the trouble of actually reviewing the DFF drawings, the Effectivities and quoted the data, the drawing numbers and the Smithsonian Index scheme for YOU to verify what I posted. You didn't like that. I hurt your feelers, I guess.

"I am fatigued in your response. Is that J'suis Fatigue?"

I pointed out to you that NAA drawings SPECIFICALLY Place the new straight line 109-25001-3 DFF having an effectivity starting in the early phase of the P-51D-10-NA and P-51K-1-NT - NOT the P-51D-15NA that you were trying to BS everybody to substantiate your "Opinion'. So what do you say to NAA?

NOW, having said this I Can give you a POTENTIAL explanation for reasons to continue the 109-25001-1 DFF on later models than P-51D-10-NA 44-14253. IF NAA had an inventory of -1's, they easily could have written a Change E.O. to PERMIT NAA Manufacturing/Production group with the authority to use them up - the cut over to the straight DFF when the curved ones were all gone. The AAF and NAA Engineering would have bought off on it. I have zero proof that this occurred. I have 100% proof regarding the ENGINEERING Effectivity. You have zero proof for your own theories - so far. It's OK to be wrong - I was wrong about the B/C and early D curve as you pointed out.

But, Since you threw out the P-51 Drawings card to support your arguments -

The ball is NOW in your court to a.) Provide proof that NAA did NOT use 25001-3 per the Effectivity blocks I cited, b.) and, that the serial number of Creamer's Dream is NOT a P-5D-10/P-51K-10 through end of P-51D series.

Now you are being offensive and you reason like a child.
The DFF proof is in all the P-51D-15 period pictures, they are NOT anecdotal.
You do realize that all one needs to do is look at P-51D-15 photos (as well as P-51K-1 through K-10's included) to see that they all have a swayback DFF, don't you?
Denying the consistent photographic evidence makes you wrong, period.
I am not throwing out the P-51 Drawings "card", I'm saying that when your findings are contradicted by the facts it means that you're missing a piece of the puzzle or that your interpretation of the data is lacking.
If it is the first time you notice a discrepancy between NAA documents and photo evidence you're in for a surprise.
That's where true research comes in.
It took you three years to realize that I was right about the existence of the swayback DFF (a rather well know fact amongst people who research Mustangs), maybe by 2018 you'll get this too.

I have already explained why Creamer's Dream was a D-15, you even pretended to understand what I was talking about.
The other possibility I mentioned would be a K-10 but there is zero evidence for the 332nd FG flying K-10's in early 1945 and the canopy would be wrong.
Once you factor in the fact that early 1945 332nd pictures show MOSTLY D-15's, you have the necessary context to draw conclusions.

I'm not sure what your poor attempt at French was all about but yes, tu me fatigues.
Done here.

 

[drgondog]

Now you are being offensive and you reason like a child.
The DFF proof is in all the P-51D-15 period pictures, they are NOT anecdotal.

See below

You do realize that all one needs to do is look at P-51D-15 photos (as well as P-51K-1 through K-10's included) to see that they all have a swayback DFF, don't you?

See below

Denying the consistent photographic evidence makes you wrong, period.

I think you and I are hung up on the phrase 'swayback, so I have included a sample of P-5D-10-NA and -15-NA to be given a tutorial by you

I am not throwing out the P-51 Drawings "card", I'm saying that when your findings are contradicted by the facts it means that you're missing a piece of the puzzle or that your interpretation of the data is lacking.

Er, actually you Did throw out the drawing card regarding the DFF's for B/C/D mods and C production - did you not?

If it is the first time you notice a discrepancy between NAA documents and photo evidence you're in for a surprise.

I have seen discrepancies but I also know that the drawing package that I have from the Smithsonian do not also include the Temporary Engineering and Manufacturing Change Orders. If YOU don't have them - You don't have all the important facts about decisions made regarding effectivities on delivered aircraft. If you do have them, please trop out any Temp ECO that relates to delivery of 'swayback 109-25001-1 in lieu of the -3?

That's where true research comes in.

But this is where the pompous surface, to pontificate on their vast research but you are a little light on the documentation and heavy handed with respect to your belief systems

It took you three years to realize that I was right about the existence of the swayback DFF (a rather well know fact amongst people who research Mustangs), maybe by 2018 you'll get this too.

No,it took me just enough time to run down the DFF drawings - but it took me that long to cross that particular thread again. You once again make judgments absent facts

I have already explained why Creamer's Dream was a D-15, you even pretended to understand what I was talking about.

I have the Supplements for all the Updates to Changes including the December 2, 1944 Weekly Service News - Supplement Vol 3 - 14 describing the changes to the P-51D-15NA and the P-51D-15-NT - which also details some previous Block Dallas updates including to the K-5-NT as well as D-10-NT in the same Supplement.

I also have the Dec 9 Supplement describing the Updates to the _20NA, and -10NT.

The first mention of the MCR-C479-3 "Cowling, Fuel Door Access Change is for -20-NA beginning at 63160 and -10-NT 11953 (which also is #801 of the NA 111 contract. By Inference neither the P-51D-5-NT, nor the P-51K-1 and -5-NT had the mod in production. You will note that the K-10NT is the primary reference for 44-11193. The NAA Drawing number is 109-310228 "Door Assembly - Engine Cowl, Fuel Strainer Access" - but you knew that.

So, the 15-NA did not have that Fuel Door Access change but the D-10-NT did.

The other possibility I mentioned would be a K-10 but there is zero evidence for the 332nd FG flying K-10's in early 1945 and the canopy would be wrong.

Canopies change all the time, there were many prop replacements for the Aeroproducts prop so there wasn't always a 'tell' for the P-51K's by inspection - The K-10 is alternately referenced as D-10-NT by NAA

So far there is zero evidence that they did Not have K-10s unless you can definitively eliminate all possibilities via IARCs or 15th AF records or 332nd Engineering records. So far it is your desire to be brilliant and wave off facts to justify your claim. But you could be right - just haven't proved it.

And there is evidence that they flew the K-1-NT based on the Accident Report

Once you factor in the fact that early 1945 332nd pictures show MOSTLY D-15's, you have the necessary context to draw conclusions. LoL. When does 'Mostly' become all inclusive to a true scholar. If you had said "IMO, it is a P-51D-15-NA for the following reasons I would not have quibbled the point.

Now you are inferring from Lack of evidence You have in hand - and extrapolated to facts Not in hand. Correct? And you made unkind comments about my reasoning ability...

I'm not sure what your poor attempt at French was all about but yes, tu me fatigues.
Done here.

OK. I don't have the pic you are alluding to so can't comment regarding what you see or think you see to draw your conclusions.

Curved DFF, Slightly bowed DFF, Straight DFF all exist in Blocks 5, Mods to Block 5, Block 10 and Block 15 for NA series as well as equivalent Dallas Blocks.

Square Gun Camera Aperatures exist in not only -15 NA but also -1K-NT. I would not be surprised to see same on late model D-10's but I have not. Image posted below of OSB 44-11194 P-51D-5-NT.

 

[drgondog]

I also have a DFF that I can agree is a swayback and appears to have a closer approximation for the 109-25001-1 shown on the drawing.

The effectivity for the 'non' swayback 109-25001-3 are as shown below. Note the comment of
"Also the last 600 of P-51D-10NA"
" " " " 200 of P-51D-5NT"

This should mean to 'Christian' what it means to me-
The new dash number P-51D Dorsal Fin Fillet applies to every P-51D from D-10NA 44-14253 through every Inglewood Block of P-51D's following 44-14252 and all the Dallas built P-51D (and K's) after serial number 44-11752.

That includes all the P-51D-15-NA's which follow the -10

 

[BiffF15]

Dragondog,
Is that last shot a D or H model tail? 413253?
Cheers,
Biff

 

[drgondog]

Dragondog,
Is that last shot a D or H model tail? 413253?
Cheers,
Biff

Biff - that is P-51D-5-NA, #1 in the Block. NAA retained it for most of WWII, modified as noted with the first, or one of the first DFF's as well as the rudder cap to explore yaw stability improvements. It was restored and returned to AAF and was lost with 35th FBW in Korea - 1952

One of the real mysteries to me is that the Brits modified one of the early merlin Mods, AL 963, with both a DFF as well as a mod to increase the chord of the vert stab to increase area in Jan/February 1943. Improvements were cited in a major meeting between NAA, Rolls and RAF in February, 1943 but I have found no trace of any P-51B so modified prior to the detail DFF drawings completed in late March, 1944.

The photo above seems pegged to the XP-51F flight tests (including the XP-51G and XP-51J variations) leading to the installation on the P-51H.

NACA took delivery of 44-13257 in December, 1944 - which was similarly modified but I have not found any flight test data on it. It was designated NACA 102

 

[BiffF15]

It is a curious thing that the fillet and vertical tail extension were both tested but not both adopted until the H. I have seen the mod on D's as well as the Cavalier 2 seaters. Does it make a noticeable difference in flight characteristics (vert tail ext)? Seems like an easy mod both in the field as well as on the line.

Cheers,
Biff

 

[drgondog]

The DFF was adopted as a Mod for all existing B's in the ETO, all D's preceding the 44-13903 and did make a difference along with metal elevators and Reverse Boost Rudder tab in both Yaw and dive stability at high speed.

The H had the DFF in production and the rudder cap at ~ #50, but the major difference for yaw stability was extending the fuselage 13" and lowering the fuselage tank capacity to 50 gallons. My father said that the takeoff at full power were much more 'benign' with respect to rudder control

 

[Tourist]

OK. I don't have the pic you are alluding to so can't comment regarding what you see or think you see to draw your conclusions.

Curved DFF, Slightly bowed DFF, Straight DFF all exist in Blocks 5, Mods to Block 5, Block 10 and Block 15 for NA series as well as equivalent Dallas Blocks.

Square Gun Camera Aperatures exist in not only -15 NA but also -1K-NT. I would not be surprised to see same on late model D-10's but I have not. Image posted below of OSB 44-11194 P-51D-5-NT.

Oh boy, here we go again.
We've been talking about two issues here.
1- the block number of Creamer's Dream.
2- when the change from swayback to straight DFF actually occured.
_
1-Let's start with Creamer's Dream.
By confirming that the Fuel Strainer door was already on K-10's you've just proven that Creamer's Dream was indeed a P-51D-15-NA, that was the only other possibility left, thank you.
You now claim that the gun camera opening was already square on the D-5 NT block by showing a supposed D-5NT picture.
It is false and your photo does NOT show a P-51D-5NT, nice try.
If you insist it is a D-5NT, prove it.

Here is a real P-51D-5NT see the nice round gun camera window?

PROOF; serial number:

Now, let's prove "Creamer's Dream's" identity once and for all:

-Square gun camera port and no fuel strainer door:

-Early canopy handle, N-9 gunsight, no APS-13 (circumstantial).

-Early fuel and pressure lines for the drop tanks.

-Early oil tank tank access door.

It is a P-51D-15-NA, period.
And just in case you claim it could be a K-5, here another nice round gun camera port on a K-5:

_
2-Now the DFF.
I call it swayback because that's how Charles Neely who was the first to notice and discuss the different dorsal fin fillets years ago called it.
Charlie is in many ways the father of modern P-51research so the term stuck.
If you want to call it curved, 109-25001, -1 or whatever else, that's fine by me it's all the same thing.
All your pictures show the swayback DFF, confirming it was still there on D-10's D-15's and only became straight with the D-20-NA, regardless of what you think the drawings say.
If you cannot tell the difference between a curved and a straight DFF in your own photos, print them and put a ruler on the DFF, you'll see immediately that none of them is straight, I invite anyone reading this to do the same thing if they have any doubt.

Here are photos directly contradicting your claim about the straight DFF being on as early as P-51D-10's in Inglewood and P-51D-5NT's in Dallas (or K-1's, or K-5's your claims keep changing).
We have a P-51D-10, a P-51D-15, a P-51K-1, a P-51K-5 and a P-51K-10, swayback DFF on all:

I think that some Pacific based K-5's might have been retrofitted with a straight DFF but that's the closest as I've seen to any of your claims regarding Dallas build P-51's being true.



_
It's not a contest but for the record, I also have the NAA drawings and a fairly large collection of NAA Weekly Service News (including the ones you mentioned with the summaries of changes).
On top of that I have the so called "Dallas" NAA drawings set that includes drawings for the D-25, D-30 and P-51M.
Then there are dozens of T.O's Reports, over 60 Mustang related manuals, thousands of photographs (quite a few from private collections), books, magazines etc...
More importantly, for years I have exchanged information and compared notes with extremely knowledgeable Mustang enthusiasts in places such as the P-51SIG or privately.
Does this mean I have everything about the P-51?
Of course not, far from it, that's why I always compare the data to period pictures when possible.
Sometimes it's the only way to find out there's a missing piece in the puzzle.
You ignore photo evidence concentrating solely on the data, I try to corroborate everything.

There is no point in continuing this exchange, we're turning in circles and I don't want to waste any more time.
We both said what we had to say.
The pictures you provided actually prove my point, thank you.
By now, Alberto and the other forum members have enough elements to form their own opinion about "Creamer's Dream" and the DFF's.

 

[drgondog]

Yo, tourist - the P-51D-5-NT of McComas is serial number 44-11280? is a HIGHER number D-5-NT that I showed you above by nearly 90 ships.

The photo below of OSB 44-11194 Super Sal II is an earlier production serial number than McComas' ship above. The serial number is visible in the data block

The P-51D-10-NA 44-14095 is LOWER -10-NA than 44-14253, confirmed by the Effectivity Block of 109-25001-3 as the STARTING number for the new DFF... which I posted for you to help you clear up any misunderstandings.

If you are in the mood to go hunting, quit picking your toes as aiming points? Walking efficiently will be more difficult.

I know Neely and respect him and if you can subjugate yourself to torture you may find some discussions between us in which we Both learned. I know Gruenhagen and have been engaged for some time over a range of subjects including the 85 gallon tank history, mods in US Depots and mods in BAD2 Warton and 8th/9th AF operational history. I have learned from him as he has learned from me as our sources and backgrounds are quite different.

Your vision of curved/swayback and straight are confusing to say the least but your repeated insistence to ignore NAA documents in order to make sense out of your viewing perspectives are just plain silly.

At any rate - pick better rebuttal examples.

 

[drgondog]

Here is the original DFF for the P-51D completed 25 March 1944. The Fin appears 'curved' but there is no radius specified for tooling or manufacturing and QA. The -1 effectivity was for NA 109 #1 (n=by future retrofit) through NA 109 #1000 = 44-14252.

There is no 'straight' DFF represented, but there is a 109-25001-3 DFF with effectivity NA109 #1001 44-14253 and above.

The discussion about differences between 'swayback', 'curved' and 'straight' is a fantasy of optics but not the Engineering.

From a manufacturing POV, 'breaking or forming with press or stamping machine' a symmetrical shape like the fin is not easy to maintain tolerances. To actually define a radius - or straight line to the top surface- would be risky from a QA/QC standpoint when a.) either would suit aerodynamically or structurally, and b.) would suit from ant installation/manufacturing process POV.

 

[Tourist]

Yo, tourist - the P-51D-5-NT of McComas is serial number 44-11280? is a HIGHER number D-5-NT that I showed you above by nearly 90 ships.

The photo below of OSB 44-11194 Super Sal II is an earlier production serial number than McComas' ship above. The serial number is visible in the data block

The P-51D-10-NA 44-14095 is LOWER -10-NA than 44-14253, confirmed by the Effectivity Block of 109-25001-3 as the STARTING number for the new DFF... which I posted for you to help you clear up any misunderstandings.

If you are in the mood to go hunting, quit picking your toes as aiming points? Walking efficiently will be more difficult.

Your vision of curved/swayback and straight are confusing to say the least but your repeated insistence to ignore NAA documents in order to make sense out of your viewing perspectives are just plain silly.

At any rate - pick better rebuttal examples.

Look, a late P-51D-10 with a swayback DFF!

Did I mention that both DFF's were manufactured differently with different parts?

You are one sore looser and a sorry character.
You keep deflecting left and right to cloud the rather simple issues.
I have established Creamer's Dream ID beyond any doubt and I have shown both DFF's and the appropriate blocks for them.
The photos prove it, the rest is just you dancing around the facts.
Goodbye.

 

[GregP]

According to Planes of Fame pilots who have flown both the standard tail and the extended fin, they can't tell the difference between the two unless they look at it before flying it. I have specifically asked as I was curious. They DID allow that it might make a slight difference at low speed, just at stall. So it might be the better tail for carrier ops. if you were so inclined ( nobody really has done so with any regularity), but in the normal flight regime, you can't tell any difference in flight.

One of our pilots frequently flies a 2-seat TF-51 with a low tail and reports no difference between the high tail and the low tail in his opinion.

 

[GrauGeist]

Tourist, why don't you quit being such a douchebag and back it down a notch

 

[GregP]

It appears to me as if the "curve" comes from forming the rear part upwards. Maybe they simply did another straight hit from a press brake on the later one after making the part. I have done a few parts where I didn't like the slight curve and simply made one more press, and it would also be self-centering since there IS an existing "trough" for the press to fit into. I don't really know, but a second press operation is somewhat common in restoration after making the original part. All you do is let the upward-curved back end stick out of the press brake (hanging in the air) and it isn't affected by the second press operation.

Don't know for sure, but it's one explanation, and we DO make the occasional P-51 dorsal fin at the shop.

Another plausible explanation is to go from forming the fins with hardened Aluminum (as in 2024-T3) to O-Aluminum and then doing the heat treating. The soft Aluminum might not make much of a bend due to the upward curve at the back. Depends on the mold or the technique used. A VERY plausible explanation is that some employee simply found a better way to do it and it got "standardized." That happens all the time in restoration, so it can happen in production as well.

I have even discovered a technique or two on my own from just trying something different after a few repetitive failures made me try another technique. It isn't uncommon.

And ... one point ... just because it works with Aluminum doesn't mean the same method works with steel. Steel is generally more ductile than hardened Aluminum ( not that nay DFFs were steel ...).

 

[al49]

Hi,
I'm happy that I started such interesting technical discussion.
From my modelling view point I can be satisfied as well because:
- Kit's wings shows a suquare camera port
- I'm trying to obtain 110 gallons tanks from Lone Star Models
But I have a question, could someone point on picture the position of that "Fuel Strainer Door"?
Many thanks
Alberto

 

[drgondog]

It appears to me as if the "curve" comes from forming the rear part upwards. Maybe they simply did another straight hit from a press brake on the later one after making the part. I have done a few parts where I didn't like the slight curve and simply made one more press, and it would also be self-centering since there IS an existing "trough" for the press to fit into. I don't really know, but a second press operation is somewhat common in restoration after making the original part. All you do is let the upward-curved back end stick out of the press brake (hanging in the air) and it isn't affected by the second press operation.

Don't know for sure, but it's one explanation, and we DO make the occasional P-51 dorsal fin at the shop.

Greg - there many plausible 'explanations' - specifically the scenario you posted - for variations of the straight vs slight vs more discernible. I ran into more than a few situations at both Bell and Lockheed where a part that was formed was not 100% to the Lines Drawings as specified or flawed in a small way but 100% functional that were covered with a Temporary Change E.O.

Another plausible explanation is to go from forming the fins with hardened Aluminum (as in 2024-T3) to O-Aluminum and then doing the heat treating. The soft Aluminum might not make much of a bend due to the upward curve at the back. Depends on the mold or the technique used. A VERY plausible explanation is that some employee simply found a better way to do it and it got "standardized." That happens all the time in restoration, so it can happen in production as well.

This is what I believe to be true on the 109-25001-3 as I have not found either a replacement for 109-25001 Dorsal Fin Assembly until the P-51H 117 series.

I have even discovered a technique or two on my own from just trying something different after a few repetitive failures made me try another technique. It isn't uncommon.

And ... one point ... just because it works with Aluminum doesn't mean the same method works with steel. Steel is generally more ductile than hardened Aluminum ( not that nay DFFs were steel ...).

Having said that I am always curious why the actual drawing for the 109 And 104-25001 DFF were slightly bent on the drawing without a reference to a Radius, or a Note to explain that the part was to be manufactured as a straight edge, but a slight bend was 'acceptable'.