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Does anybody know? Mustangs and the puttied panel joints


RidgeRunner

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Hi all, 

 

I'm appealling, I hope, to the many Mustang experts that frequent BM. My question is about the putties panel joints and did maintenance depots continue to maintain the putty after WW2, through the Cold War period (hence this forum)? My real interest is those aircraft that made their way to Latin countries. I made a statement in one post recently that post-WW2 this putty wasn't replaced after majot overhauls but the truth is that I have no evidence to support this. 

 

I hope that somebody knows :). Thanks in hope!

 

Martin

  

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The answer to this (and most other questions) is, “it depends”.  It depends on which specific aircraft, user, and time period you’re talking about.  There is not one all-encompassing answer to that question.  Was the airplane supplied under MDAP directly from stocks held in storage in the US?  If so, then it probably looked exactly how it looked when it rolled out of the NAA factory in 1945 (hundreds of Mustangs went from the factory directly into storage at the end of the war).  Was it a used airplane that had seen ANG service in the US, or with another non-US user?  Are we talking 1950 or 1970 here?  Lots of variables.

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Oh this a can that smells strongly of worms!

If you want to join the bun fight see https://forum.largescaleplanes.com/index.php?/topic/82849-mustang-wing-panel-linesfrom-the-preeminent-mustang-restorers-point-of-view/

 

My view, and experience in aviation is , if the maintenance manual says it should be there, 99% of the time it is.

 

Dave

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I've seen a claim on the internet that during WW2 ground chiefs doubted the value of this filler, removed it completely on one aircraft and found that it made no difference.  Thereafter it was not replaced.  Frankly, I think this a bar story.  Having had some practical experience in aircraft performance, there is no way such a casual approach could give convincing results - apart from what it might imply about the education and indiscipline within the USAAF (or at least that unit) at the time!

 

Having said that, it has to be admitted that the effects of the so-called laminar flow wing was much over-rated, the true superiority of the design coming from the superb integration of the fuelling system and the high standard of the surface finish.  Of which the filler played some part.

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4 hours ago, Graham Boak said:

I've seen a claim on the internet that during WW2 ground chiefs doubted the value of this filler, removed it completely on one aircraft and found that it made no difference.  Thereafter it was not replaced.  Frankly, I think this a bar story.  Having had some practical experience in aircraft performance, there is no way such a casual approach could give convincing results - apart from what it might imply about the education and indiscipline within the USAAF (or at least that unit) at the time!

 

Having said that, it has to be admitted that the effects of the so-called laminar flow wing was much over-rated, the true superiority of the design coming from the superb integration of the fuelling system and the high standard of the surface finish.  Of which the filler played some part.

 

There is zero evidence to support that.  Over the years I have spoken with several WWII and one Korean War P-51 crew chiefs in the USAAF/USAF, and one then-current P-51D owner, and none of them remembers anyone messing with the wing finish.  It would have been a huge project to remove the putty, and the gain from doing it would have been negligible to nonexistent.  And there is no photographic evidence indicating that it happened.  

 

At the time, no one, including NAA or the NACA, really knew the benefits or lack thereof of having a smoothed wing finish vs. leaving it alone on a laminar flow wing.  In the end, it turned out not to matter enough to be bothered with it, but all Mustangs left the factory with the putty and paint on them.

 

 

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11 minutes ago, NorthBayKid said:

 

There is zero evidence to support that.  Over the years I have spoken with several WWII and one Korean War P-51 crew chiefs in the USAAF/USAF, and one then-current P-51D owner, and none of them remembers anyone messing with the wing finish.  It would have been a huge project to remove the putty, and the gain from doing it would have been negligible to nonexistent.  And there is no photographic evidence indicating that it happened.  

 

At the time, no one, including NAA or the NACA, really knew the benefits or lack thereof of having a smoothed wing finish vs. leaving it alone on a laminar flow wing.  In the end, it turned out not to matter enough to be bothered with it, but all Mustangs left the factory with the putty and paint on them.

 

 

I have to agree in principle with the first paragraph, but certainly not the second.  Everyone knew that the key point about a laminar flow wing was keeping it spotlessly clean - hence the comment that having a fly deposit on the leading edge would ruin the laminarity.  Smoothness is everything.  But then what is loosely termed a laminar flow wing, on the P-51, P-63 etc, was a PR term not aerodynamically real.  The idea of these wings was that moving the point of maximum thickness aft would reduce the drag, and perhaps it did, though it also provided increased volume within the section for (eg) fuel.   And making the surface finish as smooth as possible, with as few steps and gaps as possible, also reduced the drag.  But it didn't make the flow laminar after the first 10% or so, much like any other wing.

 

Genuine attempts at a laminar flow wing, late in WW2 and postwar into the 50s, makes for interesting reading, but the message that comes back each time gets boringly repetitive.  Not in the real world.

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7 hours ago, Graham Boak said:

I've seen a claim on the internet that during WW2 ground chiefs doubted the value of this filler, removed it completely on one aircraft and found that it made no difference.  Thereafter it was not replaced.  Frankly, I think this a bar story.  Having had some practical experience in aircraft performance, there is no way such a casual approach could give convincing results - apart from what it might imply about the education and indiscipline within the USAAF (or at least that unit) at the time!

 

Having said that, it has to be admitted that the effects of the so-called laminar flow wing was much over-rated, the true superiority of the design coming from the superb integration of the fuelling system and the high standard of the surface finish.  Of which the filler played some part.

With all due respect, what does that have to do with the OP's question?

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See post 4, immediately above mine.  Which is about filling panel lines, whether it was or wasn't done. 

 

Or are you simply referring to my last comment?  If so, restricting the quote to that would have made it clearer.  Well, it is (I feel) useful in explaining the circumstances around why it was done.  You may consider it a digression if you like, but widening the thread to include other matters brought up is hardly unique to me.

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12 hours ago, Graham Boak said:

I've seen a claim on the internet that during WW2 ground chiefs doubted the value of this filler, removed it completely on one aircraft and found that it made no difference.  Thereafter it was not replaced.  Frankly, I think this a bar story. 

Shades of grey perhaps, and I agree that the story is all a little too convenient.

 

I would have been quite unhappy if a crew chief had taken that decision on an aeroplane of mine without some pretty convincing trials. I think it is very likely that the filler made at least some difference on a new aeroplane. But on one which had had people working on the wings for fuelling and arming it for several months, I can quite believe that the wing skins could have lost the degree of precision tolerance required for the filler to make the same difference. The stripped one might have been an old dog.

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Chaps, I never expected to raise hackles ;). My focus is on aircraft delivered to the Latin operators between the late 1940s and the mid-1960s. The later ones had often been through companies like Cavalier. Many of the air raft went through maintenance in Panama. I think, and one of you said, do it as you like and who is going to prove you wrong 100% :). My problem is that I like to get it right! ;)

 

Thanks to all and Merry Christmas!

 

Martin

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I've browsed many pictures of Mustangs in Latin America service and I've noticed all variations.. wings painted in silver with no trace of panel lines, aircraft with no sign of panel lines on wings and fuselage, wings in natural metal with visible panel lines and camouflaged aircraft with panel lines visible on wings and fuselage..

I'll elaborate further in the next days, I have my idea based on when pictures were taken. In any case at some point somewhere paint was stripped from the wings of a number of Mustangs and the filler was also removed

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For what it is worth, CAC Mustangs built for the RAAF had filled wings up until A68-120; thereafter the wing filling was deleted and A68-121 to A68-200 were  delivered unfilled ex-factory.

It should be remembered that the CAC airframes were built at a slow production rate post-war primarily to keep the skilled workforce intact.

Hence they had a better fit and finish than those off the NAA wartime lines and thus less need for the filling and this may have contributed to the decision.

There was a cost saving benefit - probably the main reason behind the decision - but it anticipated no material performance advantage.

Either way, it is hard to pick out panel lines on these late production CAC Mustangs unless the images are both close and sharp.

 

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9 hours ago, Graham Boak said:

But then what is loosely termed a laminar flow wing, on the P-51, P-63 etc, was a PR term not aerodynamically real.  The idea of these wings was that moving the point of maximum thickness aft would reduce the drag, and perhaps it did, though it also provided increased volume within the section for (eg) fuel.   And making the surface finish as smooth as possible, with as few steps and gaps as possible, also reduced the drag.  But it didn't make the flow laminar after the first 10% or so, much like any other wing.

 

Genuine attempts at a laminar flow wing, late in WW2 and postwar into the 50s, makes for interesting reading, but the message that comes back each time gets boringly repetitive.  Not in the real world.

Interesting fact.

Yakovlev fighter WW2 have Clark wing profile, Lavochkin  fighter WW2 have NACA wing profile, after WW2 Lavochkin fighter since from La-9 have laminar profile wing. Original La-9 with original profile wing without repainted unknown now, but save original laminar profile wing

from jet fighter La-152 in Kharkov aviation institute. Wing La-152 puttied panel joints, no see panel line only access hatch for control rods are visible. In fact, large aerodynamic studies laminar flow wing were carried out in TsAGI during the 2WW in the Soviet Union and if puttied panel joints would not affect on laminar flow wing characteristics, then we can see panel line on jet fighter La-152, but this is not so!

 

B.w. some experts  believe what

La-9/11 it's 

creatively rethought development of the Mustang concept with radial engine.

 

B.R.

Serge

Edited by Aardvark
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2 hours ago, David M said:

For what it is worth, CAC Mustangs built for the RAAF had filled wings up until A68-120; thereafter the wing filling was deleted and A68-121 to A68-200 were  delivered unfilled ex-factory.

It should be remembered that the CAC airframes were built at a slow production rate post-war primarily to keep the skilled workforce intact.

Hence they had a better fit and finish than those off the NAA wartime lines and thus less need for the filling and this may have contributed to the decision.

There was a cost saving benefit - probably the main reason behind the decision - but it anticipated no material performance advantage.

Either way, it is hard to pick out panel lines on these late production CAC Mustangs unless the images are both close and sharp.

 

There was also some post war flow visualisation work done by the Aeronautical Research Laboratories, (flight tests), that showed there was little difference between the smoothed wing surface, (not just puttied joints), and a wing without that treatment. CAC would have been aware of this.

 

This was just a minor part of the research into laminar flow that ARL, (and many other organisations), were carrying out at this time. Looking for the Holy Grail of aerodynamics - turned to out to be a bust. There was a lot of interesting work done. Most involved the need for suction to keep the flow laminar, and this in turn required using engine bleed air, or a separate power unit, meaning more weight in the airframe. ARL went as far as modifying a D.H.A. Glider, (commonly known as 'The Suction Wing Glider'), with a GLASS II section wing, (of extreme thickness), for flight tests. It was though that the use of such a section would make 'flying wing' aircraft more practical as, for a reasonably sized wing span and chord, the extra depth would make payload disposition more practical. This turned out to be yet another dead end. As Graham said in an earlier post the advantages of laminar flow wings have proven to be largely illusionary.

 

My apologies to Ridge Runner for sidetracking his original query, but I couldn't resist adding a few comments. However, I think the facts speak for themselves. As operators slowly realised that 'laminar flow wings' were not laminar flow in practice, the need to maintain the high quality of finish vanished, and operators could save a considerable amount of time and money. I'll be interested to read Giogio's comments on his research re the latin American A/C.

 

Peter M

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Given that judgement on the P-51's build standard has always considered it outstandingly good, I doubt whether that achieved by CAC was significantly superior.  Not to criticise CAC workers at all.

 

One additional point to bear in mind is that in post-war service there is less requirement for that final edge in performance, particularly bearing on mind that prop fighters were seen as outdated and there was a shortage of skilled maintainers in the services.  Jobs requiring much work for what could be seen as little reward would be discarded.

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One point that may be overlooked in the old "laminar flow doesn't work in the real world" debate:

(For the point of illustrating my thought, I'm using some figures.  These are not "facts", so please don't get hung up on that!)

 

Suppose that some NACA mathematician calculated that, theoretically, maintaining laminar flow back to 40% wing chord, instead of the more typical 20%, could yield a drag reduction of 25%.  (This would be the drag of the airfoil and lift effects, not overall aircraft drag.)  It is obviously understood that surface finish is critical, which is why North American took such pains with the Mustang.  Now, in the real world, it becomes clear that it is simply impossible to maintain that smoothness- insects, mud, dings, dents, scuffing from the shoes of the mechanics and armourers (Yeah, that's great- don't you know there's a war on?)  The net result is that, because of all these local imperfections, the flow is tripped in a bunch of different spots.  Turns out the wing only yields a 5% reduction compared to a normal airfoil.

 

Interpretation 1: "Laminar flow" is one of those lab-coat ideas that doesn't work in the real world.

Interpretation 2: "And how do you plan to achieve a 5% reduction in drag on a major component of your aircraft?"

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45 minutes ago, Graham Boak said:

One additional point to bear in mind is that in post-war service there is less requirement for that final edge in performance, particularly bearing on mind that prop fighters were seen as outdated and there was a shortage of skilled maintainers in the services.  Jobs requiring much work for what could be seen as little reward would be discarded.

Good point Graham, but jobs can't just be discarded in aviation, there's usually some official instruction to that effect, or am I applying modern standards to a problem?

 

Is there anything in post war edition F-51 maintenance manuals about this?

 

Dave

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Bob: There's no fair criticism for trying it, at the time.  However if you want a short list of possible alternatives, try improving the cooling system ( North American, Supermarine, Messerschmitt, Arado...), thinning the wing (Supermarine, Hawker, Republic), lighten the airframe (Mitsubishi, Yakovlev, Arsenal...). Or better still, all of them.  Not that they don't end up contradictory, or overruled by other requirements, but that's the trials and tribulations of designers.

 

There's nothing wrong with the laminar flow wing except that it wasn't, yet still is being credited with benefits that strictly belong elsewhere.  Not that any of it matters in The Big Picture, but in our little corner let's try?

 

Dave: yes people were sacked overnight at the end of the war, as companies had to reduce dramatically.  This was perhaps more extreme in the US than elsewhere, but even more socially aware societies had to adapt pretty rapidly as the contacts were cancelled or at best savagely reduced.  However I was thinking perhaps more of the Services, with majorities of conscripts expecting to go home Soon, if not Now.  Numbers fell dramatically and all suffered shortages of skilled personnel.

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22 hours ago, Graham Boak said:

See post 4, immediately above mine.  Which is about filling panel lines, whether it was or wasn't done. 

 

Or are you simply referring to my last comment?  If so, restricting the quote to that would have made it clearer.  Well, it is (I feel) useful in explaining the circumstances around why it was done.  You may consider it a digression if you like, but widening the thread to include other matters brought up is hardly unique to me.

Hi Graham. Sorry -- didn't intend to be combative. I was (whether rightly or not) concerned that the thread seemed to be heading in the direction of debating the efficacy of laminar flow wings, while the OP was looking for solid information about what was done to postwar airframes.

Cheers, Pip

Edited by Seawinder
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7 hours ago, Graham Boak said:

Dave: yes people were sacked overnight at the end of the war, as companies had to reduce dramatically.  This was perhaps more extreme in the US than elsewhere, but even more socially aware societies had to adapt pretty rapidly as the contacts were cancelled or at best savagely reduced.  However I was thinking perhaps more of the Services, with majorities of conscripts expecting to go home Soon, if not Now.  Numbers fell dramatically and all suffered shortages of skilled personnel

Sorry Graham, my fault for the confusion, I intended to refer to the task of puttying the panel lines as a job, not the downsizing of the workforce.

If it's on the maintenance task card and in the MM that the putty has to be maintained it can't be discarded at will, the job has to be signed off and if you're not doing it there has to be an official document or instruction to say so and refer to on the task card.

I realise that there is a belief that crew chiefs can do as they like and third world operators of old aircraft don't maintain their charges as well as they ought but that is a massive assumption.

So my question is, did North American issue an official directive/service bulletin post war that the puttying of wings could be discontinued?

 

Dave

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On 20/12/2019 at 12:40, RidgeRunner said:

Hi all, 

 

I'm appealling, I hope, to the many Mustang experts that frequent BM. My question is about the putties panel joints and did maintenance depots continue to maintain the putty after WW2, through the Cold War period (hence this forum)? My real interest is those aircraft that made their way to Latin countries. I made a statement in one post recently that post-WW2 this putty wasn't replaced after majot overhauls but the truth is that I have no evidence to support this. 

 

I hope that somebody knows :). Thanks in hope!

 

Martin

  

Hi 

Found this at an old and deleted forum on ARC about puttied panels

P51_Av_4509_ad_p050_W

Pics here posted are under the fair use images for illustration purposes only;

 

original post at http://www.arcforums.com/forums/air/index.php?/topic/21362-mustang-wings-and-panel-seams/page/6/

Edited by SouthViper
more clear answer
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