pushing the throttle how much?

[whistlingdeath77]

in all the ww2 birds flying today. How far can the plane and engine be pushed before it's considered unsafe? In a corsair, can that still top 400mph in level flight or having the lack of high octain fuel not make the engines do what they used to in ww2? This question goes for all the fighters and bombers.

[John Dupre]

Definitely the engines cannot pull the same manifold pressure that they did with war time fuel of 115/145 octane. Just what the limits are with 100LL I am not sure and they would vary between engines and perhaps even between aircraft installations with the same engine. I know I have seen references occasionally to what the limit are with 100LL. Good question.

[Lynn Allen]

If my pea brain remembers right, we took off in the Rose at 40"MP as 44" was max and 45" was an engine overhaul....

[BTromblay]

Hi,

100LL limits how much throttle can be put into an engine. However 100LL is only limiting if that is what you use. Higher octane fuel is still available. The Reno air races use 135 octane, I think. So with that fuel, you can still operate the plane as designed.

Cheers

[warbirddriver]

If you check it out you'll see that 100 octane is what they had during WW2. And according to ASTM D910, the SAE fuel specifications, the 100/130 Green gas and the current 100LL are the same except for color and lead content. Also, when the engine is operated at it's rated power you also get the benefit of the power enrichment valve that puts more fuel into the engine during takeoff; when it's needed most for cooling. I flew a B25 many years ago and when we took off at 44" the CHT's were in the green. When we took off at 40" the CHT's were in the yellow. The TBM I currently fly, we use 48" for take off as per the book and with 450 hours on the engine have yet to have any cylinder issues and the CHT's remain fairly low.

My 2-cents, FWIW.

Glenn

[muddyboots]

does lead in the fule make any difference in performance?

[warbirddriver]

Lead increases the octane rating of the fuel. For 100LL, they still use some lead, but also more "chemistry" to get the 100/130 ratings.

[muddyboots]

Thanks Warbirddriver, I knew that part. But it also seems like there was a lubrication issue or something with leaded back in the day. Am I wrong? It seems like the lead also helped as a lube or something.

[b29flteng]

When we flew FIFI with the old engines, the manifold pressure book value was 49 inches with wartime 100/130 octane. We flew it using 47 inches to be on the safe side. One other consideration with the engines is the cylinder head aluminum deteriorating over the years more susceptible to cracking?

[tom d. friedman]

lead additive is quite expensive in it's own right. i know what it is for old boat engines, i can imagine the price for warbirds!!

[JDK]

in all the ww2 birds flying today. How far can the plane and engine be pushed before it's considered unsafe? In a corsair, can that still top 400mph in level flight or having the lack of high octain fuel not make the engines do what they used to in ww2? This question goes for all the fighters and bombers.

It's not about fuel. Remember these are aircraft for 'play' or commemoration, not fighting wars.

Few warbirds fly with the loadings or equipment that the would have done in their primary service. (There's an inverse ratio of 'activity' between the heavilly restored fully complete with original widgets warbirds, which are flown careful, and limited, by and large, against the stripped back, gunless hot-rod fun 'planes.)

Apart from at Reno, there's no good reason for pushing the airframe, engine (and pilot) as hard as they were in wartime, where there was a supply-chain to back up wastage, including, we remember here, of aircraft and crew.

No warbirds fly at wartime operational heights, with oxygen, for instance.

Sure, you can make more noise and speed with the aircraft by pushing the throttle; but your costs go rapidly up straightaway, and for Americans, Uncle Sam's not funding that this time. So there are a few who fly hard at times, but the majority don't.

Thanks to Reno, there are options for going as fast (low down) as W.W.II but the engine (and airframe) consumption rate reflects that. And don't forget that pushing the envelope cost lives back then; doing it now would increase the number of warbird accidents.

Muddy; Lead (euphemisms Ethyl, TEL, tetraethyllead) helped reduce 'knocking' and allowed greater power out of engines, and 'lubricated' things like valves to avoid the valve head leaving parts on the valve seat - all at the great cost of literally putting cumulative heavy metal poison into every man, woman and child on the planet.

I'm sure there are those here who can explain the lead fuel additives benefits better than I can, meanwhile if you'd like to see how amazingly we can screw something up on a global-effect level by believing a business when they tell us something's harmless, may I introduce Thomas Midgley Jr and the Ethyl Corp?

http://en.wikipedia.org/wiki/Thomas_Midgley,_Jr.

Just a few thoughts...

[warbirddriver]

Lead is some bad-ass nasty stuff. But I have never seen any reliable data that suggests that lead is/was a lubricant in anyway.

Glenn

[JDK]

Lead is some bad-ass nasty stuff. But I have never seen any reliable data that suggests that lead is/was a lubricant in anyway.

Fair cop! I'm no chemist / engineer Glenn, so I put the lube in quotes. However this is a reference to my understanding of the point, the bit related to my previous point being highlighted, but a rider specific about lubrication coming after as well - the latter not my original thought, I should add. Lubrication may not be the best/correct term, but it does get used in this context. Better explanations welcome!

But leaded petrol had even more benefits. As it burns, tetraethyl lead turns into a tan-coloured layer of lead oxide, which covers the valves and the combustion chamber. The valves hit hard against the valve seats several thousand times each minute. The lead oxide acts as a cushioning agent, and protects the valve and the valve seats. The lead oxide is also a lubricating agent. This reduces wear in the valve guides, as the valves slide inside them.

If you start running your old leaded engine on unleaded petrol, the lead oxide quickly wears away. Damage begins, but only if your engine was made with "soft" metallurgy, and only in high-temperature areas - exhaust valves, exhaust valve guides and exhaust valve seats.

http://abc.com.au/science/k2/trek/4wd/lead2.htm

Last edited by JDK on Mon Jan 31, 2011 12:58 am, edited 1 time in total.

[bdk]

Lead oxide is the white residue you see down the side of a P-51. Lead oxide was also used to make white paint for about 100 years, so I'm not sure that gasoline is really to blame for everything. Also Freon was conveniently banned about the time the Dow patent ran out I'm told.

[JDK]

Lead oxide was also used to make white paint for about 100 years, so I'm not sure that gasoline is really to blame for everything.

Yeah, leaded petrol isn't responsible for boy bands, I agree, or commercial TV advertising. I'd like to add them to the indictment, if I can, though?

Lead was used for more than just white paint, but a huge range of colours.

The issue with TEL was the guaranteed conversion rate into the atmosphere, by the burning of fuel as against the stable use of leaded paints in mostly inert form, the issue being sucking lead-soldiers or disposal (post use) issues. Specifically in the US, the effects on humans can be traced back specifically to leaded petrol - other lead uses may well be contributory factors, but it's unarguable which is the main one.

One of the things 'the Romans done for us' was lead piping for their water. Just think how much more they'd have conquered if they hadn't been drinking 'make-you-stupid' juice?

Regards,