Producing that thrust will require more fuel, as jet engines are meaningfully less efficient at lower altitudes. An important reason is air temperature: best efficiency comes when the air entering the engine is really cold - as is the case at 35,000’.
You also forgot to mention that the engines are fans. They are fans that keep the pilot cool. Turn them off and the pilot starts to sweat.
Please think about what you wrote for a moment. Is it really your contention that it takes over a million dollars in fuel to get a 747 from London to Orlando in 8 hours? That is about $2500 a passenger, which makes the $400 fare quite a bargain.
In any case I found a program to do fuel calculation for a 747 in MS flight simulator. Apparently simulator pilots don’t want to run out of simulated fuel in the middle of the simulated ocean.
The altitude it let me select was only between 41,000 and 31,000. I did the numbers for 400nm using the defaults and then tripled it to get 10,000 ft and divided by 7 to translate pounds to gallons and came out with around 2,200 gallons as opposed to my guess of 3,000 gallons. I doubt that a linear rate is correct, but even if the number is triple my guess, my logic is still pretty good.
I actually ran the numbers for London to Orlando through the calculator and came up with 55 gallons per passenger. I’m sure the actual number is higher, since I didn’t know what to add for passengers and luggage for 400 people.
So… if this goes on for several months or so, what are the likely adjustments that will be made? Sure, this will depend on exactly where the ash cloud drifts, and for how long, but still.
Overseas travelers will have to keep adjusting to get to the nearby airports that are open, right? What other forms of transportation are there that can be used? Zeppelins shouldn’t have any trouble with the dust cloud, right?
Zeppelins still need engines to move otherwise they just drift with the wind.
Well the Queen Mary is still parked in Long Beach…
As it appears the prevailing weather patterns impede penetration into the Mediterranean (although Barcelona closed this AM, as I franticly looked at other routes for some business trips), alternatives for a ‘long closure’ (as that bastard volcano is pumping ash like crazy with no sign of let up) might involve significant use of the Iberian and southern Italian airports and rail to bus networks.
I already spent this weekend putting together just such a trip, although bloody hell there’s hardly any seats availability.
Except much ride-sharing going on as well.
I assume turbo-prop engines would be affected the same way as jets but what about piston engine planes? Is it time to dust off the Spruce Goose?
So maybe we oughta start looking at plugging up the volcano. But then some other part of Iceland might explode.
^ And that is why I avoid number crunching in regards to big airliners - I get it wrong, because that’s not my area of aviation.
Although I must point out that that is consumption at normal cruising altitude, not the hypothetical 10,000 cruising.
Piston engines are not affected in quite the same way, but it’s still very bad for them. Clogging up air filters, for example, can cause the engine to fail since it blocks oxygen from the combustion chambers. Also, very bad if it gets into oil or mechanical parts.
My understanding is that the problem is a temperature limit. Good efficiency comes with a high compression ratio, but a high compression ratio raises the temperature inside the combustion chambers. If you start with a low intake temperature, you can use a high compression ratio and not exceed the temperature limits of engine materials, but if the intake temp is already warm, then that limits the allowable compression ratio before you start damaging the engine with high internal temps.
Going back to my standard atmosphere model, there’s a 90-degree (Fahrenheit) difference between 10K feet and 35K feet. Not having much direct experience with practical numbers for gas turbine engines, I’m at a loss to estimate how this will affect efficiency. But with aerodynamic drag we’ve already nearly cut the range in half. If we take a SWAG and suppose the engine’s efficiency drops by 1/3, then our range goes from 64% of design to just 42% of design. Not only are you not going to make it all the way in one hop, but your passengers will not be happy about having to buy more than twice as much fuel to get there.
Also, would still have the same problem of sandblasting the airframe and windshield.
Absolutely - a fogged window is a fogged window at any altitude or with any engine. Although the window fogging may not be quite so bad as piston planes typically fly slower, reducing the force with which the ash impacts the airplane, but I’m not up to the math to figure that out for sure.
Remember, too - ash erodes props, too. Granted, it would take awhile to grind a prop entirely away, the erosion of the prop material could change aerodynamics, making the prop less efficient. I don’t know if it would cause or aggravate existing prop damage/wear to the point of failure, I’m not sure if anyone knows that.
Basically, no aircraft is designed through fly through sand and ground glass no matter how fine the particles are.
Right - it appeared that your fuel cost estimate (post #17) was also for normal cruise.
True, but I like your posts on the subject better. Let’s pretend mine didn’t happen and use yours, m’kay?
I’m thinking a ballo0n, an oxygen mask and a “no hurry” attitude.
Perhaps a application for a ramjet engine, so the air just passes through and doesn’t have to go through a compressor/turbine. Though I think you would need a conventional engine to get up to speed, or even rocket assisted.
The whole issue may be moot. The airlines have conducted test flights and haven’t had any unusual problems. There is a lot of pressure from Airlines and Air Freight companies to resume normal flight operations.
I suspect some sort of compromise solution will be adopted with changes to flight profiles to minimize ash exposure and inspections after every flight for air freight and then resuming passenger service if no unusual problems happen.
Given the enormous financial incentives the airlines have to resume flights, and the pressure the management is under, I’m not sure I trust them to make an objective decision here. When there is the prospect of a company going under financially (which is a really possibility if this continues much longer) then management might get stupid about risky decisions.
There is no denying that Finland has several F-18’s damaged by volcanic ash, which fact some people seem to cheerfully ignore. The ash cloud and the potential to damage engines is not entirely a made-up tale, there is real proof there was an actual hazard up there and some very expensive repairs required for some military jets to show for it.
Such a widespread phenomena will not be uniform over its entire extent, and those test flights were only an hour or so long - how long would some of the resumed fights be? Several hours? Can we rely on the ash cloud to remain thin throughout the flight path of those routes? How are we going to determine safe altitudes if those planes can’t fly at normal cruse? Who will be responsible for monitoring conditions, and how often?
You see, it might be safe to fly over Germany at 2 pm on Tuesday, but not safe an hour later when a thicker part of the ash cloud moves in, but at the same time flight over Paris is OK, but not the next morning. Ash sampling is important, and it was very generous of these airlines to make these test flights since, after all, if the airplanes had discovered thick ash the aircraft and crew might have been lost. But again, it was the financial incentive that urged these executives to send human beings into a potentially hazardous situation. I’m not saying it was unjustified - someone had to do it, and the airlines have the biggest stake in the results - but just a few flights may not be enough data to make a sound decision.
Also, I note the results of those test flights use such phrases as “without apparent damage” (a BBC quote of Lufthansa, in this article) No apparent damage? What does that mean? Someone stuck his head in the engine cowling, eyeballed the engine for 10 seconds, and said “it looks OK to me”? Some more in-depth analysis?
Perhaps we should make it a rule that any airline that wishes to resume travel under present conditions must have its executives sit on these flights while they occur. I’m sure that putting their own physical safety on the lie will make them much more objective than they might otherwise be. Even so, the history of aviation is littered with executives and generals who went to their graves CERTAIN they were right in that they perceived no hazard.
As long as the wind blows from Iceland to Europe and the volcano continues to erupt a hazard remains. I’d rather the planes stay on the ground another week while people who actually known the data first hand work on solution with minimal risk than have people rush back into the air too quickly and we have a multi-plane tragedy on our hands. Yes, it will be expensive. So would an airliner crashing into a major European city. Or worse yet, more than one plane in the same day.
Really, it would be best if the wind simply changed course to the dust goes someone where it won’t affect air travel. Unfortunately, there may not be any such direction. The present situation can not continue, but that does not mean we can go back to normal, either.
For everybody wondering if prop planes work, I took my plane to the southern edge of Frankfurt airspace today, no problems.