Wartime engines & fuel question.

[Tiger_mate]

I am completing a painting of a WWII USAAF bomber and in research note that it has sooty, black stained engines whereas british bombers tended to have a white dust stain their engines and wings. I appreciate that the dynamics of a Merlin are different to that of a Wasp radial but both share a combination of pistons and combustion.

Can anybody deliver a laymans answer to why the by-product symptoms of WWII aviation were so different when surely the source of aviation fuel was the same. I say this because I have always been led to believe that the white stains on UK bombers was explained by the quality (or otherwise) of the fuel.

.....and does anybody know if frost .formed beneath the wings of wartime bombers fuel tanks and if so was the descent sufficiently slow to ensure all had melted before landing

[cyflyer]

I was given to understand that the white stain on the underside, and on the side of fighters for that matter, was due to the high lead content of the fuel at that time.

[Tiger_mate]

Brian; the aeroplane in question is a UK based USAAF B24:


From what I can gather, there are many factors that influence the visual appearance of the engines. Technically speaking the engine temp itself depends on how much by-products are burned in combustion. The tuning or mixture controls as over rich equals black soot. I have seen enough 'Ice pilots' on TV to note the oil retention properties of the cyclone engines and accept fully the explanation above. I have read on the net that UK bombers effectively created a polution cloud all the way to Berlin and back of toxic poisons in unburned fumes. How often the aircraft were cleaned or the weather of the day (rain=wash) effected appearance.

In summary, I reckon that I could just as easy have a gleaming pristine engine cowling as a dented filthy one and both would to some extent be realistic. I appreciate you taking the time to write your inputs here which certainly provided food for thought.

[Agaricus bisporus]

I have read on the net that UK bombers effectively created a polution cloud all the way to Berlin and back of toxic poisons in unburned fumes.

A perfect example of why you shouldn't believe all you read on the net.
"Toxic poisons" indeed! Are they different from the nutritious type then? There are so many nonsenses in that short statement it is pointless even trying to list them.

Some witless - and technically ignorant - tree-hugger trying to put an imaginary ecological downer on WWII I think.

Good picture!

[ShyTorque]

I agree that white exhaust deposits come from the tetraethyl lead additive in aviation fuel (I think they are lead halide salt deposits but it's many years since I studied chemistry).

I have a car that's occasionally used for off road competitions and when using it off road I mix a gallon or two of AVGAS in the tank of unleaded MOGAS to increase the octane rating. The engine loves it but the exhaust outlet always has a whitish grey coating afterwards; normally it's solid black carbon.

There's still a lot of lead in 100LL, btw. The "LL / Low Lead" suffix really means "less lead" than they used to put in the stuff.

[Blacksheep]

UK bombers effectively created a polution cloud

Yeah. In technical language its called "Aluminium Overcast".

[sycamore]

T-M, in respect of `hoar frost` on the underside of the wings,it would depend on whether the aircraft had `integral` tanks,or self-sealing tanks,the latter providing a measure of insulation from the wing undersurface.Also ,on the time of year,as in winter ,a descent from altitude to a sub-zero airfield,would probably not allow the `frost` to sublimate away,especially after a 5-8 hour sortie; that would also depend on how much residual fuel was left in the tanks.

[Agaricus bisporus]

I don't think hoar frost ever forms on wing surfaces in flight, its fine crystalline nature wouldn't be strong enough to form or remain there. Icing on leading edges and anything with/near a stagnation point is another matter but that is nothing like hoar frost.
Hoar frost on wings usually forms on the ground after a cold-soak but I doubt WWII bombers would have returned with much fuel left and in modern aircraft with integral tanks the amount of fuel present seems to affect the severity of frost accumulation (more fuel stays cold longer). This would surely be a much less likely event with bag-tanks as the cold fuel is not in contact with the wing skin.

Airframe icing melts faster at higher speeds, not lower ones (due to higher TAT) so WWII a/c being slower would be far more prone to airframe icing than modern ones. Even so, this isn't hoar frost.

Re battered cowlings - why not give it a shiny new one (or in primer) as though it had just been replaced due to damage?

[Jhieminga]

I think most US bombers had rubber fuel cells fitted (aka self-sealing tanks, certainly the B-25 had them) and these would provide a layer of insulation against the cold air outside, they are several centimetres thick.

[Hipper]

Have a look at this thread which shows post war Lancasters painted black and white.

I see only black stains (see posts 7, 8, and 33) but perhaps 'white' in squadron photo of post 33.

http://www.pprune.org/aviation-histo...-merged-2.html

[Noyade]

In summary, I reckon that I could just as easy have a gleaming pristine engine cowling as a dented filthy one and both would to some extent be realistic.

Either way, it'll be a very nice painting.

For what it's worth, this Italian artist went for black...



However I've noticed in some photos and paintings exhaust is seen/depicted as a 'rusty' colour?

[Tiger_mate]

You have all been very helpfull for which you have my sincere thanks. I now have two high quality photos taken from 7 oclock low of aircraft in flight during the war. Although B&W photos, the quality is good enough and one is USAAF bare metal; the other Coastal Command white, both of which clearly show the staining.

Ironically in a thread about engine staining, the best bit for me is the knock on effect on the tail assembly. The vertical fins get really quite dirty which for me is music to my ears.

I am wondering what caused the staining on the outer portion of the wing on the Coastal Command aircraft photo above, especially as I doubt that CCmd aircraft engaged in formation bombing ie staining from a lead aircraft.

Can anybody confirm the normal status of the engine cowling flaps (Apologies if terminology is wrong; I am a turbine man). ie Are they only open at a particular stage of flight or indeed starting, or are they individually adjustable as part of a tuning process.

[Noyade]

Morning mate.

I am wondering what caused the staining on the outer portion of the wing on the Coastal Command aircraft

Interesting observation. Higher resolution below. Starboard tip appears clean?



No so the port...



I'm still finding some artists who prefer not to 'dirty' their Liberators...




Lots of smoke when you're being shot down though...




Cheers.

[twochai]

Cowl flaps would usually be open during ground operations, closed for min drag on take-off and set to trail (i.e. find their own position between the two slipstreams between hot engine cooling air exit and ambient air flow) for climb and cruise. If the cylinder head temps were running high in cruise they might be cracked opened.

[Tiger_mate]

The expertise here never fails to impress: Cheers guys.

[longer ron]

Ref post 15...Always a little tricky with photos but the stbd outer wing looks a little too clean (as do the bomb doors) - partial/local respray perhaps ??

[Tiger_mate]

I think I got a good balance of muck - soot and second hand oil, although clearly not finished yet and subject to ammendment. (especially the fin/rudder)

[Tiger_mate]

To finish off this thread; thank you to all who contributed to the engine questions with both observations and opinions all of which were invaluable. the painting still needs a few 'i's dotting etc such as aerials missing but is largely complete, and I am very happy with it.