Bf 109E blue air intake cover?

[Jamie @ Sovereign Hobbies]

Avoiding the salty stuff, I would like to chip in from my day-job professional life in the engineering world (and I hold an Honours degree in Mechanical Engineering, if anyone needs to know my credentials on the subject) that Graham is absolutely correct in stating that exhaust recycling down the air intake is absolutely to be avoided and the thermodynamics stated is likewise correct and fairly concisely explained.

 

I agree that the intakes on some of these photos appear to have a blue similar to RLM24, but I can offer no rationale why. What I can say with absolute confidence by virtue of my education with certificates to prove it, is that there is no scenario whereby heat from exhausts could be tolerated if it affected air intakes to the extent that a heat resistant paint were needed. The intense heating of the intake charge could not be avoided if that were the case and Graham's explaination of Delta-T is bang on. Your maximum temperature is constrained by the fuel and the materials used, therefore the initial temperature must be as low as possible. There isn't a massive difference in fuel used, but there is a huge difference in power output with the initial temperature at +5degC and that if it were +45degC - let alone hot enough to burn paint.

 

The expansion of gas in the cylinder after ignition is what pushes the piston down and thus where the torque comes from. If you want a big enthusiastic expansion of gas you must have a large difference in temperature (Delta T).  This is a product of the Ideal Gas Law which intrinsically links Pressure, Volume and Temperature (actually the Ideal Gas Law says P*V*T=constant which is never fully achievable in real life because you can always soak away your temperature through the walls of whatever is containing your gas, amongst many other things). This is something actually very tangible. We know that PVT are linked from every day life. If you raise temperature, but volume is fixed, then pressure goes up too. l

 

That's why intercoolers are used on planes and almost all modern turbocharged cars to get rid of unwanted temperature from compressing the intake air before sending it to the cylinders.

 

If you need heat resistant paint on your intake lip, you've crucified your potential to make power and either your intake is in the wrong place or your exhausts are wrong.

 

As Graham also points out - nobody elses' normal paints burned off the fuselage behind the exhaust stacks.

 

Whatever the reason for the blue on those intake lips, we're barking up the wrong tree considering temperature resistence.

[JackG]

Stew, yes I noticed the discoloration, so it could very well be painted the same as the fuselage. 

Which if is the case back then, it might explain the light and dark examples of the filter's rim.  Particularly when the Luftwaffe's fighter scheme went from a light colour on the fuselage sides to dark, and then back to light again during the BoB time frame.  The off coloured filter is just the remnants of the previous scheme?

 

Jamie, you make good sense there.   Maybe the argument for heat resistant paint was looked at the wrong way,  and it was not for protecting the metal underneath, but  more as a durable paint that would not easily blister and disintegrate?

 

regards,

Jack

[Crimea River]

Can anyone comment on the assumption that painting of the intake grille might have been discouraged to prevent paint chips from being ingested into the supercharger? As I mentioned in my initial response, I had been led to believe that the intake piece attached to the engine was typically left as bare metal and the reasoning makes some sense to me, especially if the metal was anodized as suggested. There's no question that the original post topic shows a blue painted part but should we not be careful in concluding that "non-blue" intakes were then either 02 or 65?

[Stew Dapple]

Yes definitely there is no conclusive evidence* that I have yet seen that the intake covers were always/ever painted either 02 or 65 or 04, and the idea that at least some were left in natural/anodised metal is as valid as any of the colours suggested above. However the same thought applies as with the supposition that it was heat-resistant paint: if the intake cover were left unpainted for engine protection (in this case to avoid the possible 'inhalation' of paint fragments) then in all likelihood you would expect to see it apply on all 109 intake covers and they would not have been repainted if the rest of the aircraft was?

 

Jack, regarding your point about the covers retaining the colours of the previous colour scheme after a repaint; the same thought had occurred to me, I don't know how the ground crew went about a repaint, but if they removed the cowlings and painted them separately - which would be more convenient I imagine - that would be a viable suggestion. As for the heat-resistant paint being used outside the direct exhaust area for durability, again a possilbility, but the paints used on German aircraft were very durable anyway, at least as good as any of the other combatants and significantly less prone to chipping etc. than the paints used by some other nations, and I don't remember ever seeing anything noticeable in the way of heat-blistering or flaking on Luftwaffe aircraft that haven't had the area around the exhausts painted in anything other than the usual camouflage paints.

 

Cheers,

 

Stew

 

* In my previous post/s I hope I did not give the impression that I was stating conclusively that one of those two colours were used, I was just stating what colour I would go with in the absence of any other evidence.

[Jamie @ Sovereign Hobbies]

8 hours ago, Crimea River said:

Can anyone comment on the assumption that painting of the intake grille might have been discouraged to prevent paint chips from being ingested into the supercharger? As I mentioned in my initial response, I had been led to believe that the intake piece attached to the engine was typically left as bare metal and the reasoning makes some sense to me, especially if the metal was anodized as suggested. There's no question that the original post topic shows a blue painted part but should we not be careful in concluding that "non-blue" intakes were then either 02 or 65?

 

I think as per the general subject of heat soak, if your Daimler Benz has no filter of mesh screen before the throttle body in the intake, then it's going to injest dust and grit from general airfield operations - e.g. taxying around with other Bf109s etc.

 

If the possibility of your own paint going down your air intake is worrying, then I'd suggest that the solution isn't to use special non-chip paint but to prevent foreign bodies of more likely and plentiful sources going down the intake first.

 

Both the ideas of heat resistant paint to avoid any adverse effects of being located "close" to the exhausts and that of trying to mitigate paint chips going down the intake are proverbially papering over cracks in the walls. They address a symptom, not a cause. In the former case, heat soak will have killed any potential to make useful engine power long before it would be enough to affect paint. In the latter, we've taken action to avoid paint flakes entering the supercharger whilst failing to address the infinitely more likely and serious problem of debris from the ground being kicked up (by wind and/or other aircraft) and injested whilst taxying, taking off or landing.

 

These "solutions" fail to address the vastly more serious implied root causes of the perceived problem, thus either the perceived problem is a red herring or the Germans were dreadfully incompetent engineers.

[Fin]

Then may I ask another question? Why would they leave the front cover of the supercharger unpainted (since everything around was obviously painted)? As I`ve said, the bare metal intake is one of the rules you find in books and decal instructions dealing with the Yugoslav Emils. Not that any of them cite anything in support of this axiom.

[Ed Russell]

I imagine it is possible that engineering officers at the unit level thought that heat resistant paint on these exposed surfaces in proximity to the exhaust was a good idea at the time, even if it was later shown not to be worthwhile. It may have been a cosmetic solution to a problem little more than cosmetic.

[Jamie @ Sovereign Hobbies]

Did the intake have electrical deicing or similar possibly?

[JackG]

Here's something fun, and I don't know if my method of calculating colour shift  holds any water ...

 

Using the following screen grab,

 

 

Entering the image into a software paint program (Corel), an eye dropper tool is used to pick out digital samples of the 'blue' on the air filter, same thing with the green right next to it and still on the filter body:

 

 

Note how it looks more purplish than blue.  I went further and found what is purported to be the RGB value for RLM 71 Dark Green from here:

http://www.clubhyper.com/reference/colourcharts/Digital Luftwaffe WW2 colours.pdf

 

I then calculated the amount values had to be adjusted to go from the film image RGB 94/93/91 to attain (RLM 71)  RGB 82/88/66.  The differences were subtractions of -12/-05/-25, and this was also applied to the blue sample, arriving at 92/102/107.    This new value has no exact match to any of the swatches from the digital colour chart linked above, the closest being RGB 88/101/107 (RLM 74v.2 grey-green), which has less red.

 

regards,

Jack

 

edit, I made a spelling error on the colour swatches, it should be RGB on all of them, but all values are presented in the correct order R=Red, G=Green, B=Blue

 

Edited April 30, 2018 by JackG

[Crimea River]

Thank-you Jamie for the thoughtful reply. Your points are all well taken and I see the logic of your argument.

 

14 hours ago, Fin said:

Then may I ask another question? Why would they leave the front cover of the supercharger unpainted (since everything around was obviously painted)? As I`ve said, the bare metal intake is one of the rules you find in books and decal instructions dealing with the Yugoslav Emils. Not that any of them cite anything in support of this axiom.

 

Thank-you Fin. This is the question that I am trying to determine the answer to as well. Notwithstanding the blue examples, are the typical intakes actually painted or are they bare or anodized metal?

[Stew Dapple]

18 hours ago, Fin said:

Then may I ask another question? Why would they leave the front cover of the supercharger unpainted (since everything around was obviously painted)? As I`ve said, the bare metal intake is one of the rules you find in books and decal instructions dealing with the Yugoslav Emils. Not that any of them cite anything in support of this axiom.

 

Well as noted above it definitely wasn't always unpainted and I can't recall seeing a single picture where I could say for certain that it was definitely unpainted - and that of course proves nothing either way as to whether some of them were or not. With regards to the bare metal intake cover cited in the books and decal instructions, by my guesstimate there are three possible options:

• they all have definite information or evidence that the bare metal intake cover was a feature on the Yugoslav Emils (for whatever reason);
• one of them has definite information or evidence that this was a feature on the Yugoslav Emils (for whatever reason) and the other references used this source as a reference;
• one of them studied pictures of Yugolslav Emils and concluded rather than being painted grey, or blue or yellow or white, bare metal intake covers were a feature on the Yugoslav Emils (for whatever reason) and the other references used this source as a reference.

I've no idea which of these might actually be the case, nor indeed if there should be four, five or six possible options that I haven't even considered  

 

Jack, I can barely grasp what you did there, but would the colour shift necessarily be the same for greens and blues?

 

Cheers,

 

Stew

[fewr9fkr9595]

On 28/04/2018 at 20:09, Jamie @ Sovereign Hobbies said:

If you need heat resistant paint on your intake lip, you've crucified your potential to make power and either your intake is in the wrong place or your exhausts are wrong

 

Thats the most sense I’ve read in this thread and a mistake I doubt they would have made. 

 

I’m not disputing that black paint of a heat resistant variety was used, its clearly visible. However for all his ranting and raving and providing pictures of other black painted exhaust areas to back up his claim, there is one thing lacking - another intake of sorts that needs heat paint that would perhaps shown this to be a more common thing? 

 

Unless the bf109e had the worst intake location out of the whole Luftwaffe and was the only plane that needed it? 

[Jamie @ Sovereign Hobbies]

37 minutes ago, Tony Oliver said:

 

Thats the most sense I’ve read in this thread and a mistake I doubt they would have made. 

 

I’m not disputing that black paint of a heat resistant variety was used, its clearly visible. However for all his ranting and raving and providing pictures of other black painted exhaust areas to back up his claim, there is one thing lacking - another intake of sorts that needs heat paint that would perhaps shown this to be a more common thing? 

 

Unless the bf109e had the worst intake location out of the whole Luftwaffe and was the only plane that needed it? 

 

The way to test that would be to ask if the DB601 made noticeably different power outputs in the Bf109 as compared to other aircraft using that engine with different intake arrangements such as the Dornier Do215 or Bf110. If the answer is "no", then the Bf109's intake wasn't exposed to abnormal heat exposure. For further confirmation, we can ask if the DB601 produced noticeably lower specific power (BHP or KW per litre capacity) at sea level than other V12s of contemporary vintage.

[JackG]

Stew, thank you for the interest, as you can see I'm approaching the question of the blue edging on the intake from a different angel (albeit this may be the case of a different rabbit hole).

 

Basically what I did, since we know the aircraft in question is sporting the 70/71 scheme, and combined that with the digital color studies done by W.S. Marshall.

The lighter of the two camou colours must be RLM 71, and using it's RGB value compared it against that found on the digital screen grab from the film.  The difference of the values was then also applied to the blue we see on the filter, the result being a different colour.  Essentially my approach is stating that painting a model kit with a blue edged filter may be only emulating what is seen on the photograph and not necessarily what was actually there.

 

Now to the question about colour shift, I think you are asking if this shift would be constant throughout the whole image - unfortunately the answer is yes and no.  I think colour shift of the film after it was developed would be the same throughout.  This would be things like exposure to light, how it was stored, aging, etc. and obviously conversion to digital).  I think what I've illustrated in my samples is probably colours that are more closer to what the film looked like when it first was developed? 

 

Now to why I also answer no to the shift question, that is based on second hand knowledge found in discussion of the Agfa film product -  back then it had low sensitivity to red.   This means any areas of the image that would have faint red , the film would not pick this up, resulting for example, blues that are more blue than actual.  Thing is we do see red in the skies of the linked film at the start of this thread, so to me that says the blue has deteriorated from the finished product.

 

regards,

Jack

 

 

[Garry c]

 On some of the F3F/F4F Wildcats, black landing gear doors can be seen. The spare doors are black and were sometimes installed without repainting.

Perhaps the replacement supercharger grill was shipped in blue/grey colour?

 

 Garry c