Hacker News Reader

Comment by phkahler | Hacker News Reader

It's interesting that aircraft still use leaded fuel. From what I can tell this is ultimately due to cost concerns.

Only in priston engines, and it’s mostly due to the fact that changing the engines, which are currently reliable and in many cases have been for decades, could introduce new issues. It’s a snails pace industry due to safety and reliability concerns for the most part. It’s super annoying because i always want the best new thing to go with a plane, but when you’re in the cockpit, it’s comforting knowing the plane is 8000 hours in and nothing significant has changed since it was initially made (other than what was mandated by the maker) so it’s probay going to be fine for your 1.5 hour flight.

Also, most small airports only carry one fuel, i imagine those making new planes don’t get customers excited about planes you cannot take everywhere due to limited availability of fuels.

I love/hate flying for all these reasons.

Some engines (such as Rotax) can be run on mogas, available at gas stations. Obviously you then need to transport it to the airport yourself, which isn't always convenient.

Rotax can run on either MoGas or 100LL, so if you're at an airport that doesn't offer MoGas you can just fill up with AvGas and go.

Doesn't most mogas STC's cover only alcohol-free gas, which AFAIK is increasingly hard to acquire in many places?

It seems that longer term, in many places of the world, particularly outside the US, the answer is diesel aero engines, which can run on jet fuel.

You can actually still buy leaded fuel for automotive use in the UK, although it is very expensive and limited to few garages around the country - basically it serves extremely limited group of antique vehicles which are kept in original state - unmodified engines which have to run on leaded petrol.

http://www.fbhvc.co.uk/legislation-and-fuels/fuel-informatio...

Is there a reason to use actual leaded gas rather than a lead substitute? I don't know that much about classic cars but my dad uses a lead substitute for his as opposed to actual lead.

“Simply put, unleaded fuel burns less smoothly than leaded and the toluene and benzene, which is added to the fuel to act as a lead substitute, burns to form what are called peroxides. Unfortunately peroxides are inherently unstable and explode, forming shock waves that cause detonation. This explains why engines designed to run on unleaded from the outset feature sophisticated knock sensors, which retard the ignition setting at the onset of harmful detonation.”

https://www.classiccars4sale.net/classic-car-how-to-guides/r...

Right, but that article goes on to talk about various non-lead substitutes you should add... I know why unleaded vs leaded, but there are substitutes for lead that are designed for use in classic cars but don't actually contain lead, that's what I was asking the difference of.

Basically, why use actual lead in gas when lead substitute exists and is recommended for classic cars as an additive to unleaded fuel?

I believe that lead in petrol / gasoline still exists as there are not one but two effects from lead.

One is that lead helps promoting burning of the gasoline versus explosion or knocking.

Two is that lead is a great lubricant for the valve surfaces, preventing them eroding, leaking or sticking as they open / close. Eroding causes the engine to lose compression and efficiency, and sticking (as I have experienced first-hand) can cause a major engine failure by breaking the mechanism that opens/closes the valve.

This is correct, but it's also been overstated how important the lubricating properties of leaded gasoline were in these engines - while the harmful health effects were understated. [1]

[1] www.walshcarlines.com/pdf/mechanicalimplications.d4e.pdf

I've found it varies by engine type. International Harvester light line SV engines for example definitely benefit from lead additives to fuel. Zinc additives in oil is another 'be kind to your engine' additive https://zddplus.com

Engines of previous eras were designed to leverage the 'lead' in gasoline as a lubricant and act as a 'cushion' to the valve seats and valves as the fuel flowed through the engine. Not adding a 'lead' substitute can damage your valves, and ethanol is to be avoided at all costs to protect the engine.

Engine 'knock' (multiple explosions on a single piston ignite cycle as different pockets of fuel mixture ignite) is also minimized by having 'lead' in the fuel.

Have '48 Chevy - can confirm that lead-substitute exists and classic cars will run with it. I never use the car without it so its possible the stuff doesn't actually do anything.

I suspect(and this is just my guess) that if you have a true classic that is worth millions of pounds, you don't want to risk running it on additives - so for those extremely rare occasions when you want to start the engine(car shows usually) you might as well run it on the £5/litre genuine leaded petrol.

The engines used in most small aircraft are basically unchanged since the 1950s or 60s. Aircraft are required to have regular maintenance, including major overhauls, so while these engines are archaic in terms of technology they keep running fine and have a track record of reliability. Newer designs would have to be certified by the FAA, which is apparently an extremely expensive process. General aviation is already so expensive that it's inaccessible to most people, so no one really wants to push the price tag up even more.

Reply on news.ycombinator.com