B-17 Bomber Paint Vs No Paint, Unexpected Results

[RAF4EVER]

Just found this on You Tube,hope it helps

 

 

[Graham Boak]

Interesting. I do have to point out that a thorough study would include several aircraft over a series of flights, but this was not made clear.  The smooth shape of the resulting curves does look more like predictions made from the results of such a programme that actually being raw data.  Nothing wrong with that, of course.   It highlights that for aircraft of this period considerable improvement can be made by filling all joints and gaps.  Further, a high standard of manufacturing to avoid steps and gaps pays dividends.  This is of course exactly what was claimed for the P-51 and its wing, and makes nonsense of claims that removing such filler in service made no different to the aircraft's performance.

 

 

[Giorgio N]

The results are not unexpected as the matter of the effect of surface finish on performance is well known. A painted finish can sure improve the surface finish and this was one reason why British aircraft retained painted surfaces even if the usefulness of passing to unpainted finishes was discussed. Of course at the same time a badly applied painted finish can impact the same performances and here comes one problem of the whole video....

Performance is important but the availability of the aircraft is even more important. The elimination of paint from the finish not only meant more aircraft built in the same time but also meant a reduction in the maintenance requirements as paint was something that needed maintenance. Reduced maintenance means more aircraft ready to take to the air at any given time. In bigger scheme of things the USAAF was mostly concerned with having as many aircraft as possible leaving the production line as fast as possible. Any reduction in performance was not a big deal, afterall the american logistic chain was capable of delivering fuel in quantity with little problem,

There is one other aspect that the author of the video forgets: a 3% difference may sound like a lot but falls within for example the engine output power tolerances. Yes that particular painted B-17 may have needed 3% less fuel but at the same time an identically painted B-17 may have needed a bit more fuel simply because one of the engines had slightly worse consumption. And another painted B-17 of course could have needed a bit more fuel because of a worn finish on the wing leading edge. Even the original painted B-17 may have needed less fuel at some point in her life and then started to need more and more as the finish wore off with every flight hour. Extrapolating something from a comparison between 2 single aircraft is not really so easy....

[alt-92]

All this talk about smooth finishes... Baah, humbug 🤡  
 

How about the weight savings NOT carrying all that paint over 1000's of aircraft saves on fuel - and that's a cascade effect as transporting said paint is also no longer needed.

[Ed Russell]

1 hour ago, Giorgio N said:

Extrapolating something from a comparison between 2 single aircraft is not really so easy....

Exactly correct!

[Graham Boak]

Not really.  The video points out that fuel use is less for a painted aircraft, outweighing the weight of the paint.  Further, these aircraft were painted after assembly, so the logistic cost of the paint would be restricted to carriage between paint factory and aircraft factory, which would generally be in the same state, or at least local (by US standards).  Extra paint required in theatre for touch-ups would be comparatively small.  Compare that to the logistic cost of transporting the extra fuel over half the world.

 

The cost of military logistics is terrifyingly large.  War is a huge waste.

[Jochen Barett]

Knowing the Wehrmacht used illegal drugs to achieve the first successes ( https://en.wikipedia.org/wiki/Methamphetamine#History,_society,_and_culture ) and now having this open dispute should be well worth to refight WW II (as soon as all the other messes on this planet are cleared up and we can afford the CO2 emissions of the reenactment).

 

Anyway, interesting video!

[alt-92]

3 hours ago, Jochen Barett said:

illegal drugs

*ahem* Pervitin (and its equivalents) was pretty widespread in those days, and far from illegal.

Heck, even Queen Wilhelmina had it prescribed as painkiller and stimulant (which does explain several behaviours previously discarded as stress-related).

[Jochen Barett]

[Ed Russell]

On 7/12/2022 at 8:06 PM, Graham Boak said:

The video points out that fuel use is less for a painted aircraft

Not really. It points out that one particular painted aircraft used less fuel etc than one particular unpainted aircraft without determining that these aircraft were representative of all B-17 aircraft. There are tables, readily available in medical statistics textbooks, showing how many subjects are needed to acheive a particular level of confidence in a trial. It's always more than one or two.

[Peter Roberts]

2 hours ago, Ed Russell said:

Not really. It points out that one particular painted aircraft used less fuel etc than one particular unpainted aircraft without determining that these aircraft were representative of all B-17 aircraft. There are tables, readily available in medical statistics textbooks, showing how many subjects are needed to acheive a particular level of confidence in a trial. It's always more than one or two.

 

Quite so Ed. In medical circles a 5% confidence level is usually standard, and statistical analysis is undertaken to determine the participant sample size needed to provide for that confidence level. It is then up to the efficacy of a medication/treatment to see if that level of confidence can be achieved. Further, there is usually careful monitoring of participants to ensure that all arms of a study have similar characteristics and appropriate processes are in place throughout the study. This includes blinding - that is, those undertaking the study do not know from which participants the data is coming. To compare one or two random subjects of a large population and then attempt to draw any meaningful conclusion from that comparison for the rest of the population would be a nonsense. 

 

I am not sure that medical study standards and criteria can be applied here though; I don't see how you could get enough aircraft of similar standard in each arm, imagining there are going to be a wide range of variables across each subject - length of service, engine(s) condition, battle damage, general wear and tear, etc. Maybe using a brand new aircraft, and the same setup, painted and unpainted, then repeat across a given number of new aircraft? Hang on, what? You need these for bombing duties? Sorry, you'll have to wait....

 

And - seriously? One coat of paint is going to smooth panel joins??

 

Thanks for posting RAF4EVER, some interesting footage. Not so sure about the commentary. I'm sure it will spark some good debate though!  

Edited July 14, 2022 by Peter Roberts

[Graham Boak]

If you look back, the need for a number of aircraft to be involved was in my first sentence.  It is not clear whether the trials used did involve a number of aircraft, rather than just two.  The raw data was lacking.  Given the number of aircraft sitting around at the manufacturers and elsewhere in the delivery system, and at test centres or other secondary roles in the US, it would not be difficult to obtain a number of such aircraft.  It would be better if the same aircraft were used for painted and unpainted comparisons, and if it was all done under the full conditions for strict trials.  Which we don't know.  If you want to make assumptions, then the painted aircraft will be older and probably more used than the unpainted one, which would result in quite the opposite result.

 

Of course a coat or paint will not smooth out steps between panels, but a smooth coat will still be of benefit.  It would help more if the surface was filled and rubbed down, but every little helps. 

[Work In Progress]

 

19 hours ago, Ed Russell said:

Not really. It points out that one particular painted aircraft used less fuel etc than one particular unpainted aircraft without determining that these aircraft were representative of all B-17 aircraft. There are tables, readily available in medical statistics textbooks, showing how many subjects are needed to acheive a particular level of confidence in a trial. It's always more than one or two.

 

Just popping in to sign the visitor book and to correct a mis-conception which seems important.  It is quite correct in general to point out that individual engines and airframes have production tolerance variations even when new, and that their variations widen as an aircraft is used and abused over its operational life. But that general case is inapplicable to this test.

 

This was not a test of three different examples of the B-17G. It was a test of THE SAME AEROPLANE in three different conditions. It was first tested as delivered in natural metal, and then refinished for the other tests as described.

 

This is clear from the front page of the report, as seen in the video, which names the aircraft as 42-97656, and the remainder of the report which describes the refinishing work done on the aircraft at each stage before re-testing. 

 

Those who wish to read the rest of the report may find it here http://www.wwiiaircraftperformance.org/B-17/B-17G_42-97656_Eng-47-1722-A.pdf

[Ed Russell]

4 hours ago, Work In Progress said:

It was a test of THE SAME AEROPLANE in three different conditions.

That is much more significant and more statistically valid. The statisticians amongst us would like to see them repeat it three times in total before they were convinced, to allow for different conditions on each test. 😄

[Phoenix44]

On 14/07/2022 at 10:23, Graham Boak said:

If you look back, the need for a number of aircraft to be involved was in my first sentence.  It is not clear whether the trials used did involve a number of aircraft, rather than just two.  The raw data was lacking.  Given the number of aircraft sitting around at the manufacturers and elsewhere in the delivery system, and at test centres or other secondary roles in the US, it would not be difficult to obtain a number of such aircraft.  It would be better if the same aircraft were used for painted and unpainted comparisons, and if it was all done under the full conditions for strict trials.  Which we don't know.  If you want to make assumptions, then the painted aircraft will be older and probably more used than the unpainted one, which would result in quite the opposite result.

 

Of course a coat or paint will not smooth out steps between panels, but a smooth coat will still be of benefit.  It would help more if the surface was filled and rubbed down, but every little helps. 

Which the report says they tried but the crown head rivets made it difficult.

[vppelt68]

I found the video (on several B-17 related groups I'm a member of) both fascinating and convincing. But. Operationally they were quite insignificant. A bomb group calculated the fuel needed for a B-17G to fly a specific mission and the maximum bomb load for that trip. Did they specify different amount of fuel for the painted or unpainted planes? No. Each plane got a same dose of aviation fuel, regardless of its surface finish. So no savings in weight. Did they specify different payload for the painted or unpainted planes? No. No additional bombs carried due to less fuel compared to other planes in the same formation.

Thus the results are interesting, academically but not practically, I believe.

V-P

 

[Graham Boak]

As you describe it, this is only true for a mixed formation.  Also you forget that fuel unused will be brought back and saved for another day.  The prediction for the fuel used can be corrected to a better average for the fleet.  Yes there will be simplifications and complications but the fuel saved won't just disappear.

[gingerbob]

You're all missing an important point- by eliminating the paint, it saves us agonizing about the best match, whether and how much to pre and post shade, etc etc.  Of course it ends up being academic, because then we're faced with figuring out how to accomplish a "real" looking natural-metal finish...

[noelh]

It  is interesting academically but in the context of the time it was written not something that was a priority for the USAAF. 

On the other hand if you happen to own a B17 or indeed any warbird. It is useful information. Any fuel saving is to be welcomed. B17 Sally B is painted largely as an anti corrosion measure but no doubt they'll be gratified to realise it saves fuel as well.