Warbird Information Exchange

Hello Glenn,

You might want to question your "engineer" friend!

http://www.walshcarlines.com/pdf/mechanicalimplications.d4e.pdf

Pratt & Whitney published a book entitled "The Aircraft Engine and It's Operation". I'm not going to bother taking the time to dig it out, but I'm pretty sure it covers the lubricating properties of lead in aviation fuel.

You might want to find a copy of it!

In the "olden days" of cast iron heads that had valve seats machined into the head material itself, the lead left deposits that aided in valve seat life. This was due to the molecular deposits left behind in the combustion process. Much like the residual lead that will coat the matrix in a catlytic converter. When the lead was legislated out of the fuel due to toxic issues, the auto industry was forced to develop hardened valve seat inserts in order to maintain valve seat durability. This is not a secret and is well documented if you do the research.

The aircraft industry may have followed a different path but I would lay dollars to donuts that the material used in steel valve seat inserts in the heads also followed this path to a more hardened seat. It is understood that the lead was a predominate octane booster but the "lubrication" effect is legit, none the less.

_________________
"There are old pilots and bold pilots but few old, bold pilots."

We use Phillips 66 25X60 (for radial engines) on the AC-47.

There are alot of threads on the internet that propagate all the old wives tails.
Gosh I read something about an RR publication written in the sleeve valve days, that mentioned how detrimental lead was to poppet valves. That seems counter to all this lead lube theory.
It is not the lubricative properties it is the cooling affect, and most likely is why it is such a good ant detonate additive. How come a softer material like stainless is the cure for the valve burning problems associated with unleaded fuel? If anything it should wear worse than the nonstainless counter part. The reason is because it will not deteriorate from chemical attack at high temperatures. The major culprit is the higher heat from unleaded fuel. And a nonstainless steel is subject to rapid corrosion, just look at how a acetylene cutting torch works, high temp oxidation.
I read about some problems with the Mooney TLS eating exhaust valves, and the cure was to increase oil flow to the guides and stems for added cooling.
The only information that is needed, "the data" is honest research data, and chemical analysis of deposition of TEL on a valve or seat face. Not someone just spreading the same old story we have all heard for years.

I use Phillips 25w-60 in all of the radial engines that I operate. R3350-26WD, R1340, R975-E3.

Full power 48 and 2800, for takeoff in the Skyraider. Purely, for cooling properties, at only 16,000lbs., I could take off at a much lower power setting. If I had access to 130/145 fuel I would have no qualms about using 60" and 2800 rpm for take off. I bet it would be a real hoot at the feather light weight of 16K.

36" and 2250rpm in the T6.

Full throttle in the Yale. It needs everything it has to get airborne.

_________________
Eric

"I spent most of my money on alcohol, women and skyraiders....and the rest of it I just wasted."

Excessive amounts of lead accumulation are bad for everything, including spark plugs. I think we would need to know more about the content of the RR report and how that conclusion was arrived at. At the time that conclusion was reached they may have been adding excessive amounts of lead as they were experimenting with higher octane fuels and high levels of boost.

Cast iron auto cylinder head exhaust valve seats lasted a long time in the old leaded gas days. Valve seats started eroding after the switch to unleaded fuels, so the process of induction hardening was introduced on exhaust valve seats to solve the problem. Valve seat inserts are not made of "stainless steel," they are typically made of high temperature steels like stellite or inconel. Stellite is a VERY hard material.

What is your source for the conclusion that lead has cooling properties? Lead increases octane (up to a point of diminishing returns). By preventing detonation temperatures are reduced, but that isn't the same as cooling. Detonation is to be avoided at any cost with or without lead.

"Stainless steels" at high temperatures do oxidize and change colors (i.e. stain). Aircraft exhaust systems are typically made from these materials. Exhaust systems live in a very corrosive environment and the high temperatures make things worse. "Stainless steels" are named such because they don't typically corrode when used for architectural purposes (ambient environmental conditions).

The only cooling for an exhaust valve comes from the guide and the dwell on the seat. Increasing oil to the guide helps cool the valve. Sodium filled exhaust valves were used in some applications to help carry heat from the valve head to the stem as an aid to cooling.

Another issue with aircraft engines is their relatively low RPM. This keeps the heat in the cylinder longer and the large displacements result in a huge surface area for the heat to transfer to the cylinder, head, valves and piston. High torque/low RPM (high BMEP) engines have higher octane requirements than do typical high RPM/low torque automotive applications. This is how an 11,000 RPM motorcycle engine can live on the street using pump gas with a 13:1 compression ratio, while aircraft engines typically have compression ratios on the order of 6:1 to 8:1.

Note: Not all wive's tales are false!

Hey warbirddriver,

Look what's in the newspaper todayabout lead in fuel !!

Would that be defined as research?

If you think this topic is fun, wait 'til we start with ethanol! I know about a million guys who have been stranded towing their race cars in the days when we had carbs and "jets" that could be changed. Twice the fuel to make the same power just meant, double your jet size, dump the methanol in the tank and get to the next town.

If ethanol cost half of what gasoline does today, simple trade off. However, that does not seem to be the case now does it?

Believe it or don't, lead does help valve train life. Drop a valve and you're toast. Valve train durability has always been the primary factor in auto racing. Seems to still be an issue.

Thanks Glenn!

_________________
"There are old pilots and bold pilots but few old, bold pilots."

Hi Scott,

Yea, but what do the Nextel Cup guys know about fuel anyway. They are only making close to 900HP form a little over 5L displacement with a single 4BBL carburetor (with jets) on gas with two valve heads and a distributor!!!

Oh yea....and they do that for 500 miles!

I like how a magazine article is taken as the full gospel on a subject.
And how the guys engineer friend that also works for a large OIL COMPANY, and who is a specialist in that sort of thing, is considered the idiot here, because he will not support a massive wives tail.

I want to see the data on how lead can adhere to a valve or seat that is exposed heat many times more the melting point ?
Its every thing to do with high temperature errosion not a lubrication issue.


Sorry for getting so exicited here.

Hello engguy,

This is not a "magazine article".

[url]http://www.sae.org/technical/papers/860090[url]

I would certainly welcome some evidence backing up your argument that lead does nothing other than alter the Octane rating. So far all that we have from you is a statement agreeing with another poster quoting what an "engineer" friend told him!!!! I seem to recall something about engineers claiming a certain ship to be unsinkable!

As for your test with the VW engine, you sure you are not comparing apples with oranges? Did you notice the difference in composition and specific gravity between aviation fuel and auto fuel? Your test is like saying "I ran an engine on gasoline and then switched to Methanol using the same fuel flow and it wouldn't even run, so gasoline is better"! Are you sure that the only difference between auto fuel and avgas is the lead content? Check the fuel spec sheets as to be conclusive, the fuels would have to be of identical composition with the exceptiuon of lead content.

You might actually want to READ the information. It's the lead salts created by the lead in the fuel being burned that adhere to the valve surfaces to create the lubricating effect.

Glenn

So, a couple questions. Ask your engineer buddy why leaded fuel cannot be used with a catalytic converter. It has to do with the lead DEPOSITS coating the matrix and rendering the converter useless. The lead deposits are MOLECULAR not a lead paste that will melt at combution temperatures. It is at this mollecular level that the "coating" action aids in prolonging valve seat life whether you wish to call it "lubrication" is up to you but the effect is the same.

By the way, how old is your engineer friend? Sometimes the younger lads don't necessarily go back in history to see what was going on at the time.

_________________
"There are old pilots and bold pilots but few old, bold pilots."

It looks like this is one of those subjects,like religion and politics,that most people have strong and set opinions.No amount of documentation or arguments from personal experience is likely to win anyone over to the "Other Side".All that I can claim is reasonable reliability in operating radial engines from R-985's through R-3350's for over 13,000 hours in the last 35 years.

It does get more difficult as time goes on to maintain and operate these engines to the same standards of reliability as was possible 20-30 years ago.Part of the problem is due to lack of spares.Part is due to the lack of availability of the fuel grade for which the higher power radials were designed.It is also difficult to find pilots, mechanics and flight engineers with operational experience in this field.

Being able to successfully operate and maintain large radial engines is an impressive skill,but its soon going to fall into the same category as being proficient in operating a steam locomotive.There isn't much call for either profession these days and the situation isn't likely to improve.

You can actually see these lead deposits by the way when you disassemble one of these engines.

Glenn, it says on that article "contributed by associated press".
And most likely it is also copyrighted, so pasting on here may not be appropriate.
There is nothing I have yet found in any professional information that supports what you and others claim.
What TEL does and what most anti detonates do, is resist prereaction during compression with in the normal ranges of compression ratios. Just as if you where to use ADI fluid, it "cools" the process, since most would agree that the H2O is not going to burn, especially at a much lower temperature than what disassociation would occure at.
It was very obvious that the cylinder head temperatures were lower with the highly leaded fuel vs the zero leaded fuel.