Hellcat exhaust streaking colour

[LooseSeal]

Hi guys, this may be a pretty stupid/obvious question, but...

 

I'm just doing initial research and planning before starting Airfix's 1/24 Hellcat, and one thing I've noticed in some reference photos (but not all of them) as well as a few builds is that the streaking from the exhausts is sometimes a whiteish/grey colour, as opposed to the black/brown I'd have imagined or seen on most other warbirds. I was wondering if anyone could shed light on what might have caused that colouration? Was it heavy use perhaps? The sea air? Different fuel types/producers? I genuinely have no idea, but don't want to get it entirely wrong.

 

Thanks if anyone has any ideas!

[Black Knight]

The white residue is caused by the lead added to the petrol to increase both the octane level and add extra bearing material to the piston and tappets. Being non-burnable it comes out in the exhaust.

A different type of lead additive was used within the UK giving the red coloured streaking which can be seen on Hurricane nightfighters

[Work In Progress]

It depends entirely on how the aeroplane has been flown recently. If you've yelled off the deck defensively and burned round the sky for 25 mins in full rich and max power downing attacking dive bombers, then mucky black, because most of what you're depositing is soot.  If you've just done an uneventful two hour CAP at economy cruise, with the mixture leaned right out, then light grey, because most of what you're depositing is lead compounds.

 

If you've done the second after doing the first, without wiping the aeroplane off in between, then grey deposits over the wider black mess. 

Edited February 24, 2020 by Work In Progress

[LooseSeal]

That's really interesting to know! Thanks guys. It's part of the reason I love this hobby that I get to learn stuff about the subjects I'm working on.

You've given me something to think about, Work in Progress, as I'll be doing the 'Paper Doll' aircraft. So if he'd just got onto the USS Essex from his '5 kill' sortie then I'd imagine the engine has been under a pretty extreme workload. So I'm thinking a touch of brown/grey to show a previous easier mission, then black/brown over that again for the Leyte Gulf mission.

Thanks Black Knight, too! Good to see someone else from NI! 😄

[FinnAndersen]

Word of caution: If you have a photo of your bird showing that look, then you're on.

 

If not, well... Carrier planes were generally very well maintained, being struck down in a hangar soon after each flight and was given a general clean over.

 

Shore based aircraft was an entirely different matter.

 

/Finn

 

 

[LooseSeal]

There is one photo of Paper Doll, and oddly enough not only does it seem to have the white/grey exhaust stains but actually some substantial chipping on the leading edges of the wings, which you'd think would be unusual for Hellcats with the Gloss Sea Blue paint.

I'm also toying with the idea of bullet hole damage, as both the plane and pilot didn't come back in great shape during the Battle of Leyte Gulf. So much so that it was immediately pushed overboard to make room for other aircraft.

In general, though, I prefer a slightly worn/dirty look. But also... a kit this big and well-detailed is like a canvas crying out to be painted and shown off 🙂

[TheRealMrEd]

I agree about the carrier-based planes;  land based often were not as sharply maintained or cleaned at times.  Usually the light grey exhaust would be the largest stain, with possibly light brown from combustion, the atop that a smaller (usually) area of soot, and in the worst cases some oil streaks!

 

Sort of like depicted on my P2V-3 Neptune flying out of Korea:

 

 

Ed

 

 

Edited February 25, 2020 by TheRealMrEd

[Jamie @ Sovereign Hobbies]

On 2/24/2020 at 11:01 AM, LooseSeal said:

There is one photo of Paper Doll, and oddly enough not only does it seem to have the white/grey exhaust stains but actually some substantial chipping on the leading edges of the wings, which you'd think would be unusual for Hellcats with the Gloss Sea Blue paint.

I'm also toying with the idea of bullet hole damage, as both the plane and pilot didn't come back in great shape during the Battle of Leyte Gulf. So much so that it was immediately pushed overboard to make room for other aircraft.

In general, though, I prefer a slightly worn/dirty look. But also... a kit this big and well-detailed is like a canvas crying out to be painted and shown off 🙂

 

Most "chipping" on leading edges is erosional wear most commonly inflicted by flying through rain.

[pat d]

 Not in color but perhaps these will help?

[11bravo]

This picture may help a bit, I know it's not a Hellcat but it's got the same engine, same GSB paint and presumably, burns the same grade avgas.  

 

 

Picture is from the truly awesome Dana Bell book on the F4U series.  Mandatory reading for anyone building a later -1 / 1D Corsair.   Exhaust staining is not as concentrated as the Hellcat's due to a different exhaust system but it shows the characteristic brownish grey staining pretty well.  The pic also shows that late war US Navy GSB aircraft could get pretty beaten up.   The pic above was taken during a period of heavy operational tempo. Note the various staining and scuffing.   Still nothing close to the land-based aircraft but it goes to show you that you can replicate a somewhat beaten up Hellcat if that's what floats your boat.   I'm sure once the CV moved off the line, these aircraft were cleaned up pretty quickly.  

[JWM]

On 2/23/2020 at 11:12 PM, Black Knight said:

The white residue is caused by the lead added to the petrol to increase both the octane level and add extra bearing material to the piston and tappets. Being non-burnable it comes out in the exhaust.

the white stuff is lead oxide. In fuel there was lead tetra ethylene, so it was actually burned and became lead oxide...

[dogsbody]

In the old days of leaded car gasoline, you could tell if your engine was running well by the colour on the inside of the tailpipe. If it was grey, then it was okay. If it was a sooty black, then it need to go to a mechanic soon, to check out why. Now days with unleaded fuel, I don't know.

 

 

 

 

Chris

[LooseSeal]

Thanks for the extra photos and advice guys! It's been nice to learn about this, hopefully should make a nice point of interest if I somehow manage to pull it off with some success.

[72modeler]

On 2/25/2020 at 9:55 AM, Jamie @ Sovereign Hobbies said:

Most "chipping" on leading edges is erosional wear most commonly inflicted by flying through rain.

Jamie,

 

Well, I'll be- I always heard it was caused by flying through hairspray or salt! Hee hee! 😜

Mike

 

Seriously, as has been stated by others, cruising at lean mixture settings and high boost would cause the grey deposits; A-26 Invaders were notorious for leaving  heavy leaded deposits 

Edited February 26, 2020 by 72modeler
corrected spelling

[melvyn hiscock]

A good friend of mine, who flew warbirds, told me that when taxiing a Corsair you keep one eye looking where you are going, and the other watching the exhaust colour and leaning to keep it from sooting. 

 

Good advice when I had the Rearwin, with it’s unmassive 145hp radial, I still had to lean the mixture when on the ground. Light grey exhaust staining was good 

[303sqn]

3 hours ago, JWM said:

the white stuff is lead oxide. In fuel there was lead tetra ethylene, so it was actually burned and became lead oxide...

No it's not. There are three oxides of Lead, Lead(II) Oxide - colour red or yellow, Lead (IV) Oxide or Lead dioxide - colour black, Lead (II,IV) Oxide contains Pb(II) and Pb(IV) in the ratio 2:1, colour red.

 

It's Tetra Ethyl Lead, commonly called tel. -ene means there is a C=C bond, there are no C=C bonds in tel.

 

Tel burns to form lead.

 

(CH3CH2)4Pb + 13 O2 → 8 CO2 + 10 H2O + Pb

 

The lead can then be oxided to fom lead(II) oxide but any oxide formed will be quickly reduced by the hydrocarbons in the fuel to matallic lead. Reduction of metal oxides by the reducing agents hydrogen, carbon, and carbon monoxide is 'O' Level chemistry.

 

The substance is Lead(II) Bromide. Too busy at  the momrnt to explain. I'll be in the next few days to do so.

 

 

Edited February 26, 2020 by 303sqn

[303sqn]

2 hours ago, dogsbody said:

In the old days of leaded car gasoline, you could tell if your engine was running well by the colour on the inside of the tailpipe. If it was grey, then it was okay. If it was a sooty black, then it need to go to a mechanic soon, to check out why. Now days with unleaded fuel, I don't know.

That is correct. In most case it would be the mixture being too rich. These days with fuel injection and engine management systems you will get an amber light on your dash board.

[72modeler]

17 hours ago, 303sqn said:

Too busy at  the momrnt to explain. I

Pay close attention and take notes, gents- I fear a pop test is coming in Organic Chemistry 301 on Friday! Way to go, @303sqn!

Mike

[Troy Smith]

18 hours ago, 303sqn said:

The substance is Lead(II) Bromide

where does the Bromine come from?   Ah, yes, 

https://en.wikipedia.org/wiki/Tetraethyllead

Quote

Pb and PbO would quickly over-accumulate and destroy an engine.[citation needed] For this reason, the lead scavengers 1,2-dibromoethane and 1,2-dichloroethane are used in conjunction with TEL—these agents form volatile lead(II) bromide and lead(II) chloride, respectively, which are flushed from the engine and into the air.

 

 

On 23/02/2020 at 23:21, Work In Progress said:

If you've just done an uneventful two hour CAP at economy cruise, with the mixture leaned right out, then light grey, because most of what you're depositing is lead compounds.

 

 

 

 

 

@LooseSeal

  

On 23/02/2020 at 22:01, LooseSeal said:

and one thing I've noticed in some reference photos (but not all of them) as well as a few builds is that the streaking from the exhausts is sometimes a whiteish/grey colour, as opposed to the black/brown I'd have imagined or seen on most other warbirds.

 

there is no substitute to studying period photos.   Not just the colours of the deposit, but also the shapes of the deposits.   The above show different forms.

DO NOT look at models, unless they look like the above!  There is a negative feedback where model fashion influences other modellers to make make a model that looks like the latest model fashion..  Of course, It's your model, do what you like, but as you asked about exhaust deposits and why the difference.

 

The other thing is when in it's life is your plane, as has been stated, on carriers they are taken below deck and serviced, and cleaned.  All the above are new planes,  after coming back from a mission, they could be pretty dirty

 

all these from here which has a load of pics

https://www.asisbiz.com/il2/Hellcat/F6F-3.html

 

A google image search will turn up more.   I'll repeat myself.  Study photos, the old cliched a picture is worth a thousand words could have been written with the modeller in mind.   And now there is no excuse not to do so.  (except laziness... like not have a computer next to the model bench or happily working away and not wanting to spoil you flow)

Ground pastel chalk is good for this kind of staining, and applied at the end, can be cleaned off if you are not happy.  If you don't touch the chalks, it doenbs't need to be sealed either, and is then a realistic surface deposit...

 

Note if you are planning on doing a USN plane I suggest reading this

HTH

[Dave Fleming]

here is a negative feedback where model fashion influences other modellers to make make a model that looks like the latest model fashion.{/quote]

 

And avoid light grey p[anel line son dark aircraft, except around the area where the Pb compund staining might be!

[Jamie @ Sovereign Hobbies]

One leady and one sooty

 

[Michael Taylor]

Tamiya Skyraider

 

 

 

 

 

 

[72modeler]

There was another recent Skyraider build I saw (maybe here on BM?) that also illustrated the vertical staining seen on Skyraiders that @Michael Taylor has posted. The R-3350 was notorious for the amount of oil it leaked and blew out of the exhausts, so the exhaust flow aft from the stacks also contained copious amounts of oil that streamed downward. I remember one of my friends, who was a flight engineer on B-29's, telling me that the two jobs B-29 ground crews hated the most was pulling those huge HS props through before startup, and wiping all of the  oil off of the nacelles after a mission.

Mike

[303sqn]

British gasoline used the same lead containing additive as the US, and everybody else for the matter, tetraleadethyl, commonly called TEL. It was the only lead additive allowed. By law the maximum allowable concentration of lead in any fuel, for commercial purposes, was 3.6 cc per imperial gallon. For governmental and/or military purposes the concentration was allowed to be increased to 7.cc per imperial gallon.

 

When first introduced it was in an extremely cavalier fashion. The original intention was that it would be added at the point of sale when filling up with petrol. Salesmen would dip rag in it and wave it in front of the air intake of a knocking engine and the knocking would cease instantaneously. (TEL provides full knock resistance with only one part in 1,360). Not a good idea as lead is extremely poisonous especially in organic form when it is easily absorbed through the skin, inhalation or mouth. It soon resulted in a scandal that some have called the ‘Three mile Island’ of its day.

 

Most authorities believed that when TEL was dispersed in the atmosphere, it would pose no health hazard. Workers, however, including drivers, manufacturing employees, and garage attendant faced a more concentrated dose, which raised some concern among public health experts. Workers at the production plants reported stomach complaints This followed by the usual denials that TEL was harmful and Thomas Midgley toured the plants washing his hands in bowls of the stuff and advising the workers to line the stomachs with plenty of milk. In February 1923 Mr Midgley would spend the month in Florida receiving treatment for lead poisoning. Delco’s laboratory researchers had developed health problems. Hochwalt recollected, “We all had lead poisoning.… You could see the lines of lead in the bones (in X-rays), but it disappeared. I used to get nauseated over food.…” Hochwalt used his six-week honeymoon to recover.

 

During 1923 and 1924 Kettering and GM hired medical consultants to evaluate TEL. They reported no insurmountable problems, and the company went ahead with its expansion. Then the brown stuff hit the fan. On October 22, 1924, workers at Standard Oil’s TEL plant at Bayway, New Jersey, started falling ill. By October 31, five had died, and at least 35 others were hospitalized. A report summarized the symptoms: “The patient becomes violently maniacal, shouting, leaping from the bed, smashing furniture and acting as if in delirium tremens; morphine only accentuates the symptoms. In two fatal cases, the body temperature rose to 110 degrees just before death occurred.” It made made the front page of The New York Times .

 

Not long afterwards six men died at a DuPont run TEL plant in Deepwater, New Jersey, that used a supposedly safer process. Workers called the Deepwater plant the House of Butterflies, for the hallucinations induced by TEL. About the same time,one researcher died and four were hospitalized after breathing concentrated TEL vapours at a Standard Oil laboratory in Elizabeth, New Jersey.

 

In April 1925, in reaction to the workers’ deaths Kettering was removed as president of Ethyl Co. Early the next month the company suspended sales of TEL until its safety could be established. A few weeks later U.S. Surgeon General H. S. Cumming convened a conference on its hazards. Kettering testified that the additive was essential to stretching fuel supplies. Midgley called his creation “not so much a dangerous poison as it is a treacherous one.” It was unsafe, he said, only when improperly handled, a circumstance that was already being remedied. Frank Howard of Standard Oil called TEL a “gift of God,” which prompted the labour leader Grace Burnham to reply that it had been no gift of God for the workers.

 

Cumming appointed a committee of prominent physicists, chemists, health experts, andothers to investigate. In January 1926 the    committee reported mild health effects from the useof lead, but nothing drastic enough to justify a ban. TEL was dangerous only in concentrated form, the report said, not when diluted in gasoline. If mixing was performed at distribution centres instead of at the point of purchase, and if extra precautions were taken to protect the health of workers, there would be no cause for concern. Filling-station owners scrapped their Ethylizers and installed separate pumps, and in May 1926 Ethyl gas went back on sale. A few critics remained, most prominently Alice Hamilton of Harvard, a founder of the field of public health. She called TEL “a probable risk to garage workers and a possible risk to the public.” Most people, however, accepted the committee’s findings. Increased ventilation and other plant improvements reduced the workplace hazard to a level considered acceptable by 1920s standards.

 

There are many organometallic compounds which exhibit antiknock value, however, lack of one or more of the essential qualities of solubility, volatility, stability, and low cost has so far ruled out all but two, the lead alkyls and iron carbonyl. The latter was used in Germany in the 1930s but the deposits of iron oxide resulted in a great increase in engine wear.

 

Methylcyclopentadienyl manganese tricarbonyl (MMT), was used, post war, in the USA as supplement to leaded gasoline until banned by the EPA from 27 Oct 1978, but was approved for use in Canada and Australia. In the 1990s EPA ban was overturned, and MMT can be used up to 0.031gMn/US Gal in all states except California (where it remains banned ).

 

This leaves only the lead alkyls, of which there are many, varying in intrinsic antiknock effectiveness, volatility, stability, and cost. The original selection of tetraethyllead from this group was due to it having about the maximum antiknock effectiveness of the group; it possesses good stability; its volatility is a happy compromise between the high value desirable for use in the fuel and the low value desirable for safety in manufacturing and handling; its cost is also about the minimum.

 

Tetraethyllead is entirely stable at ordinary temperatures in the absence of light or oxygen. At one time there were some problems involving instability in gasoline, but small amounts of the usual antioxidants, plus the practically complete removal of bismuth in the manufacture of the tetraethyllead itself, practically eliminated the formation of solid deposits in gasoline in storage.

 

The low volatility of tetraethyllead (2 mm. of mercury at 50° C ) , while a great advantage in reducing manufacturing and handling hazards, may result in some maldistribution relative to fuel in individual cylinders of multicylinder engines. Research indicated that this was a most complicated problem, but in general the practical effects were not serious. The use of mixed lead alkyls of higher volatility than tetraethyllead would fail to provide a practical solution, as their intrinsic antiknock value is lower than that of tetraethyllead and their manufacturing higher.

 

The effectiveness of tetraethyllead as an antiknock is markedly reduced by one of the normal constituents of gasoline - sulphur. The different types of sulphur compounds show varying degrees of tetraethyllead destruction, but all have a deleterious effect, and as much as two thirds of the effectiveness of tetraethyllead maybe lost in a gasoline high in sulphur.

 

Tetraethyllead when burned alone with gasoline in the engine leaves lead deposits in the engine. Lead has a very high boiling point, much higher than the combustion temperatures in an engine. As a result the deposits cannot vaporise and be expelled in the exhaust gases.  This was early recognized, and numerous agents were designed to eliminate the deposits or otherwise minimize. Organic bromides and chlorides were found to be the most effective scavenging agents, and nothing better has been discovered. Later research has shown that the proper kinds and proportions of these halides vary with the nature of the engines and the conditions of operation. The actual mixtures now used are designed to give over-all optimum results for the use to which they are to be put; thus, aircraft and automotive engines require different mixtures.

 

The first scavenger used was dibromoethane. Post war dichloroethane was added, partly for reasons of cost but it was also found the there was synergic effect, i.e., when used together they are more effective than when used on their own. They react with the lead to form Lead dibromide (or chloride) which has a much lower boiling point close to the temperatures in the engine and so vaporise and is expelled with the exhaust gases.

 

TEL and dibromoethane are added to gasoline as ethyl fluid, a mixture of the two. Ethyl fluid is rated/described in Theories, 1 Theory containing, theoretically, the exact amount of bromine to neutralise all the lead. The fluid is dyed blue.

 

Composition of Ethyl Fluid 1-T

 

TEL 61.42%

Dibromoethane 35.68%

Kerosene and impurities  2.65%

Dye 0.25%

 

Nothing is perfect, and dibromoethane form corrosive combustion products when it combusts, chiefly hydrobromic acid. Originally the insulating material in spark plugs was the mineral mica. The acid attacked the mica and so new insulating materials had to be found that were impervious to the combustion products. The Germans had a special lead free running out fuel that they ran through an engine before it was put into storage.

 

Nor is it 100% effective. There were lead fouling problems with high-leaded 100 Octane aviation gasolines used during WWII. Spark plug lifetime with US 100/130 grade was about 25 hours, about five missions. When British 100/150 grade was introduced, within a month there were reports of it causing plug fouling. They tried to cure this by using 1.5 T ethyl fluid. The resulting fuel became known as PEP. It worked, but before long surplus bromine was causing damage to the engine valves. So they went back to using 1T ethyl fluid.

 

During WWII the US experimented with TCP. That’s tricresyl phosphate, not the TCP you buy from Boots, that’s a different TCP. 

 

Whereas spark knock appears as a gas-phase spontaneous ignition near the end

of the combustion process, and thus at a high pressure level, pre-ignition is a

forced ignition at low pressure, and is also dependent on the combustion temperature

of the previous charges that caused the deposits to glow. Consequently, fuels do not necessarily exhibit comparable resistance to these two phenomena. (If you think that knocking is pre-ignition, it is not. What engineers and petrochemists call spark induced knock or detonation happens after ignition by the spark - hence spark-induced. You can learn all about knock and pre-ignition from this article, found here: http://www.contactmagazine.com/Issue54/EngineBasics.html

 

The author designs engines for GM so knows what he is talking about.)

 

Although isoparaffins resist pre-ignition as well as spark knock, the hot burning aromatics do not. The problem can be solved largely by restricting the

extent of deposition, and also by raising the glow temperature of those deposits that do eventually accumulate. This can achieved by the use of a phosphorus additive. As a useful side effect, the phosphorus compounds increase the electrical resistivity of the deposits , which restricts misfire due to electrical leakage from the sparking plug electrodes, and consequent fouling of the cold plug. Boron has also been investigated as a scavenger.

 

By 1930, the U.S. issued an aviation gasoline specification, including octane rating and requiring the use of TEL, and the first British specification for avgas was issued as DTD 134. This limited cracked spirits to a trace only, and stipulated that the anti-knock value be equal to a 50/50 mixture of benzene and hexane in a standard single-cylinder engine at 900 rev/min (equivalent to an octane number of 74). Benzole was limited to 20 per cent by volume because higher percentages caused freezing in carburettor jets. In 1933 this specification was replaced by DTD 224, which raised the octane level to 77. In the same year DTD 230 was issued , requiring 87 octane and permitting the use of TEL up to 4 ml/Imperial gallon for the first time.

 

In 1937 , the U.K. Air Ministry issued its first provisional specification for 100 octane fuel. In 1938 a new test method, the rich-mixture rating, was introduced and this, as well as a lean-mixture rating, was incorporated in U.K. specifications for 100 octane fuel. It had been noted that fuels of the same lean-mixture rating behaved differently when tested under supercharged or rich-mixture conditions, and the sensitive fuels giving higher maximum power under rich conditions were preferred . The 100 octane fuel had to meet the performance of isooctane plus 1 ml TEL/U.S. gal when tested in a supercharged CFR engine under rich-mixture conditions. This isooctane plus TEL comparison became the basis of the Performance Number scale, the rating scale used above 100 octane. In 1942, the rich-mixture rating was also specified by the U.S. Army, and the grade became known as 100/125. The rich-mixture rating was then upgraded to isooctane plus 1.25 ml TEL/U.S. gal, and the grade became 100/130. The figure of 130 was based on the Performance Number (PN) scale, where a PN of 100 matches pure isooctane in a supercharged engine, and a PN of 130 would permit 130 per cent of the power available from isooctane alone at the mixture strength for maximum power with isooctane.

 

The Rolls-Royce engines of the Schneider Trophy competitors ran on exotic fuels formulated by Rod Banks of the Ethyl Export Corp. To begin with he added benzole and TEL to aviation fuel. It was this mixture that the S6 used to win in 1929. To raise the power for the 1931 attempt 10% methanol was added allowing RR to increase the rev and supercharger boost. For the absolute speed record a mixture of 60% methanol, 30% benzole, and 10% acetone with 4.2 cc of TEL per gallon. More paint stripper than fuel, it dissolved paint and tank sealing compounds and caused leading of the spark plugs. Fine for use for short periods in a racer but totally unsuitable for everyday civil or military use.

 

The 100 Octane fuels use during WWII were required to consist entirely of hydrocarbons with a a few permitted additives. That means no oxygenates, e.g., methanol, ethanol,  no ketones, e.g., acetone, no ethers. Aromatics were limited to a maximum of 20%. The principal hydrocarbons included in 100-octane gasoline were isopentane, isohexanes, isooctanes and the aromatics, toluene, xylene and cumene. US 100/130 grade contained 2.5% aniline as an anti-knock additive as did British 100/150 grade.

 

Edited March 12, 2020 by 303sqn

[bhouse]

Anti-knock, chlorofluorocarbons, medical devices...

Midgley's inventions killed millions. Including himself.