Thread: Katoomba Monthly Temp average set to be SMASHED!!! AGAIN!!!

More weight requires a higher approach speed and consequently more runway to pull up. Undercarriages, especially tyres, are designed to withstand heavy landings but not necessarily involving a maximum all up weight. It all comes down to design criteria.

You can buy an electric self-launching glider or one which has an altitude sustaining motor today. I wouldn't fly in one without a parachute because there's been a number of in-flight fires caused by gel batteries over the past few years.

mick

Originally Posted by FenceFurniture

Yebbut I thought they jettisoned fuel to mitigate the chances of explosion during emergency landing?

Brett

Not absolutely sure on this one, but to my mind a partially empty tank of fuel is more explosive than a full tank. Once the tank ruptures of course there is now more fuel to continue a fire/explosion if the tank was full in the first place.

I think the maximum take-off weights are higher than the maximum landing weights, but there is a qualification here: The aircraft can land at the maximum take-off weight, but I should insert the word "safely." The aircraft can land but then has to be taken out of service for checks to the landing gear to ensure it has not been overstressed. Most times the plane will fly around for a while to burn off fuel or if needed and possible fuel will be dumped. We could be talking fifty tons plus. I don't think it would be practical to take the plane out of service every time it flew so a reduced payload would be order of the day.

So in practical terms the landing weight is less than take-off weight. All that assumes that the plane was fully loaded with cargo or passengers (ie. at it's maximum take off weight).

Regards
Paul

Originally Posted by Bushmiller

Not absolutely sure on this one, but to my mind a partially empty tank of fuel is more explosive than a full tank.

Yes, as the air increases the explosive mixture point approaches (which I think is where there is enough oxygen to burn all of the remaining fuel). That was an experiment we saw at High School (with natural gas in a can).


Well I suppose all that just means that the undercarriage would have to be completely redesigned for an electric plane and the whole plane would no doubt be redesigned anyway. Hard to see them being viable for large aircraft though because of the sheer weight of batteries required to move such a heavy object for the distances required at the speeds required - not to mention incredible recharging times at the various stopovers. Sounds like more of a job for Hydrogen.

This Wiki article has an interesting explanation of Hydrogen vs Kerosene (that link will go straight to the relevant paragraph).

It's not about explosion, it's about fire and its fuel. There have been a few instances when aircraft have run out of fuel and landed safely. No fire = no explosion.

In the case of takeoff, you're dealing a with a steady weight on the undercart which reduces gradually as the wings develop lift, the aircraft rotates and liftoff occurs. All very gentle. The process of landing involves a vertical deceleration over the few seconds when the wheels touch the runway and the various elements designed to spoil lift and/or increase drag kick in.

The maximum all up weight of an A380 is about 570 tonnes.

mick

Originally Posted by FenceFurniture

Well I suppose all that just means that the undercarriage would have to be completely redesigned for an electric plane

Also the wings in a current plane store significant fuel, and they flex considerably. The additional force in a heavy landing exerted on wingtips is not insignificant, and that'd be a significant new stressor for an E-Plane if there was any battery weight in wings.

In that Wiki link they mention that Hydrogen can't be stored in the wings either, which changes the dynamics of things.

A large (fast) aircraft would surely have to be using jet engines, and I can't think how electricity can be utilised for that (anyone?). Supersonic jets can't be propeller driven either can they?

Originally Posted by bushmiller

millmerran to the blue mountains: 40 days: Easy. Some methane production so not entirely pollutant free.

........... : ~)

Originally Posted by FenceFurniture

Yes, as the air increases the explosive mixture point approaches (which I think is where there is enough oxygen to burn all of the remaining fuel). That was an experiment we saw at High School (with natural gas in a can).

Probably as simple as the LEL and UEL (lower and upper explosive limits) Oxygen comes into that. H2 lower limit is 4%, upper limit is 75%. Petrol hardly has a lower limit! A 44gal drum that once contained petrol although empty will still keep vapours in the seams. Petrol is a bastard when it comes to explosions. If cutting or welding a 44gal drum it is recommended to rinse it three times with water before cutting or welding.

I noted in your Wiki link to Hydrogen fueled planes that the Hydrogen can't be stored in the wings, but is considerably lighter than the equivalent conventional fuel of the same energy so maybe it balances out or close.

Perhaps a point we should remember is that an alternative may not exactly replicate the conditions of fossil fuels. There may well be small downsides; Even sacrifices. This has happened before. We went from leaded petrol to unleaded petrol.

Regards
Paul

I have been referring to commercial aircraft using petrol. that is untrue as they use a kerosene blend which has a much lower volatility. Something I did not mention about Hydrogen is that it does not necessarily need an ignition source to inite at least no in the conventional sense. It can ignite from friction as in the gas escaping through a slit.

It is not as forgiving as the current fuels so considerable attention would be required to make it safe. We also have to make it more cheaply than at present. This may come with technology and increased demand.

Regards
Paul

Originally Posted by NeilS

Commercial aviation makes a similar contribution to greenhouse emissions to shipping, so still a lower order problem to solve, IMO.

As fascinating as it is to solve the greenhouse gas emissions from aviation, it is not, IMO, a first order problem to solve.

The global aviation industry produces around 2% of all human-induced carbon dioxide (CO2) emissions. Aviation is responsible for 12% of CO2 emissions from all transports sources, compared to 74% from road transport. Facts & figures

Road transport is now the US' largest contributor to emissions. I expect it will be similar here.

In 2017, greenhouse gas emissions from transportation accounted for about 28.9 percent of total U.S. greenhouse gas emissions, making it the largest contributor of U.S. greenhouse gas emissions. Sep 13, 201 www.epa.gov

Electricity generation and road transport are the Mr and Mrs elephants in the room for us here in Australia.

The second order problem to solve is manufacturing, but not here in Australia as we have outsourced almost all of that to China. As the world's factory, China is emitting greenhouse gases on our behalf.

CO2 Emissions | Global Carbon Atlas

But, per capita, Australia emits more than twice the amount of CO2 compared to China.

CO₂ emissions per capita - Our World in Data

For an analysis of CO2 transfers.

https://www.carbonbrief.org/mapped-w...ters-exporters

We need to find a way of making countries that import manufactured goods to be responsible for the CO2 emissions associated with those goods. But, if we haven't found a way of locally taxing the Googles and Facebooks of this world, I'm not sure if and how we might do that.

Originally Posted by FenceFurniture

Yebbut I thought they jettisoned fuel to mitigate the chances of explosion during emergency landing?

fuel is jettisoned to reduce weight

sourced from Boeing and Airbus

B747
Maximum Take Off Weight -- 447.5 Tonnes
Maximum Landing weight -- 344.28 tonnes
Fuel capacity -- around 190 tonnes

A380
Maximum Take Off Weight -- 575 Tonnes
Maximum Landing weight -- 386 tonnes
Fuel capacity -- around 254 tonnes

Originally Posted by poundy

no. Well maybe that as well, but the big thing they are doing is reducing weight because that reduces forces on the plane when it is at it's most vulnerable, moving downward into the immovable land.

Originally Posted by Glider

Originally Posted by Bushmiller

So in practical terms the landing weight is less than take-off weight.

Originally Posted by ian

fuel is jettisoned to reduce weight

Ok, reasonably clear on that now.

On Jets, not just for landing weight and safety, I would have thought it would be for efficiency too.

Of what point is hauling an extra 200 tons of fuel to the destination? Surely it would be best to land literally on vapours, as the overall "cost" of fuel used for the trip would be less - plus lighter is faster (think F1 cars).

Multiply this by 1 million flights and that's a very big number.


I suspect this is driven more by accountants than lawyers/safety Nazis.

Designing a plane to land with a full fuel load doesn't strike me as a big deal. It all reeks of cost/benefit analysis with total weight (of the Needed Extra Beefiness) vs fuel.