Hot answers tagged

105

The F-111 has, like many aircraft, a fuel dump port so it can get rid of a lot of heavy fuel rather quickly. Most aircraft have the dump ports on the wings, the F-111 designers put it in the tail between the engines. End result is if you dump fuel and briefly light the afterburner you will ignite the liquid fuel in your wake creating a rather spectacular ...


100

You can persuade a turbine engine to run on just about anything that can burn. So the decision of which fuel to actually use depends on the side factors including, but not limited to: availability cost emissions hot section temperature chemical reactions with engine parts Specific examples: Coal dust is rather difficult to pump around, and the rampies don'...


81

Jet-A (and all turbine fuels) are far cheaper than 100LL (at least in bulk; retail prices vary due to local supply and demand as well as different regional tax regimes on aviation fuel) for several reasons. Scale Southwest Airlines alone burned through 1.9 billion gallons of Jet-A in 2015, dwarfing the mere 175 million gallons of 100LL that the entire US ...


76

Broadly speaking, there are three families of motor fuel that you're probably interested in: Diesels, Kerosenes, and Gasolines. The difference between the families mainly has to do with the molecular weight (and thus boiling point / vapor pressure) of the fuel components - in order above from heaviest to lightest. The differences within each family are ...


76

If the aircraft is cruising at FL350 it is operating in Reduced Vertical Separation Minima (RVSM) airspace (between FL290 and FL410). With an altimetry discrepancy between the two altimeters of more than 245ft, the aircraft is no longer RVSM approved. It shall therefore descent or climb out of the RVSM altitude block. For the Airbus A321 the operating ...


65

There was at least one occasion when the dump-and-burn was used in combat. During the 1986 attack on Libya the U.S. pilots, desperate for fuel, jostling with one another in the air to get access to aerial refueling tankers. Unable to break radio silence, they could not locate the giant KC-10A Extenders and KC-135R Stratotankers that would keep them from ...


54

Because of the quantity of water in the fuel, as opposed to a careful introduction of water into the combustion process. Typical water contamination is bad in fuel tanks as water is denser than aviation fuels and settles at the bottom of the tanks. Aviation fuels are also hydrophobic (non-polar) and so do not readily mix with water. Therefore water will ...


49

That scenario only makes sense if your airplane stays at cruising altitude: although taxi and takeoff does use up fuel it's really the ascent to cruise that takes the most. You aren't really going to be able to drop cargo accurately from cruising altitude, so you'll have to descend pretty low, then you'll need to climb up again, and that would suck up lots ...


47

Maybe This is dependent on the air frame and varies from plane to plane and not all planes have capability of moving fuel although most large planes do. The Concorde moved fuel all over the place from its 13 tanks to cool the nose cone as well as trim the aircraft. It was perhaps one of the most complex implementations of such a system and kept the flight ...


45

One of the main reasons wing tip tanks were used was to counteract some of the forces of wing bending by adding mass to the end of the wings. As time has progressed and our understanding of materials has grown as well as our ability to design structures better the need for tricks like this has gone away. As our general understanding of aerodynamics has ...


43

Unlike with driving, in aviation the major variable when planning fuel consumption isn't how far you're traveling but how long you're traveling: Distance traveled in aircraft is a derived value (calculated from groundspeed and time - groundspeed also being a derived value affected by many factors including wind). A pilot may not readily know their ...


37

The short answer to both your questions are Yes. The long answer is, it's not so simple. The ATR 72 you have pictured has a top speed of 276 knots and a range of 1,300 miles. It can carry around 70 passengers. This document provides detailed comparisons of burn rates. So we can see the ATR 72 burns about 810 Liters per hour (about 214 gallons/hr). A Boeing ...


37

Although turbines could be designed to run on ethanol it's actually a lousy aviation fuel (actually it's a lousy fuel in general). Petroleum-based jet fuel is high grade kerosene which has lubricant properties, which ethanol lacks, and ethanol has different characteristics which mean you can't pour it in and use it as a replacement. Some problems with ...


34

There is nothing "special" about an aircraft engine that requires lead in the fuel -- Engines don't much care about the lead in tetraethyl lead, nor do they much care for it (it gets everywhere, fouling sparkplugs and contaminating the oil). What they care about is the octane (anti-knock) rating of the fuel. Many "low performance" aircraft engines run just ...


34

Looking purely at operational cost of the aircraft, yes. You save time, burn less fuel, don't have to pay for the landing etc. But dropping the cargo makes the cargo more expensive. You have to provide parachutes (and return them after use, inspect them etc). You have to combine cargo into parachute loads. You have to package the cargo for a hard landing, ...


34

Wake Island has had aircraft divert there before, as it serves as an ETOPS diversion airport. Per the remarks on AirNav and the NOTAMs: RSTD: VERY LIMITED OPERATIONS STATUS, AVBL FOR EMERG LDG AND MIN PRIORITY TFC. TRAN ALERT: SVCG FEES RQD. TRAN SVC HRS 2000-0400Z (0800L-1600L) TUE-SAT. CLSD SUN, MON, HOL. FUEL: FLIGHT CREW REQUIRED TO ASSIST ...


32

The LL of 100LL stands for Low Lead as it has tetra-ethyl lead added as a detonation inhibitor for high-performance engines. Despite the "low" moniker there actually is a lot of it in there, and it's toxic. This fuel is expensive for a number of reasons: The lead itself is expensive The lead additive means that a refinery must shut down and clean the lead ...


32

Is it true that they must dump excess fuel before they land? Nope. You don't siphon your car just before your destination. Fuel is money. Except in emergency in big planes, fuel then is a potentially lethal burden (weight). ... in case there's a problem with the landing and they need to abort? Contingency fuel just for aborted landings, weather ...


32

According to the Washington Post, Air Force One never refueled in mid-air with the president on board. If it needs to refuel, it usually does so at one of the U.S. military bases across the world. The retrofitted Boeing 747 that usually serves as the presidential jet can indeed refuel in flight — but it has never done so with the president on board, ...


31

Much like water, exposing fuel to below freezing temperatures does not instantly make it freeze. It takes some amount of time, and as long as the fuel is not exposed to below freezing temperatures long enough to make it freeze, it won't be a problem. How much time? That depends on a number of factors like: Type of fuel Jet A (common in the US) has a ...


31

Short answer In flight, unless you use external energy sources like the Sun, each change in the use of electricity leads to a proportional change in the quantity of fuel burnt in the engines (or in the APU). On an aircraft, generators only convert fuel potential chemical energy into something else, usually electricity, hydraulic energy or pneumatic energy. ...


31

There are a number of factors that go into it: Economies of Scale Jet-A is used in a much higher volume than 100LL. All the jet engine commercial aircraft each day burn through orders of magnitude more Jet-A than piston aircraft burn through 100LL. That means that there is a much higher production volume, and therefore a cost savings as a result. Buying ...


30

If a "terrorist takeover" like this were to happen in the real world... ...and the tower still had communication capability: The tower controllers would advise pilots of the situation, and likely instruct them to return to the Approach frequency to coordinate their next steps (probably a landing at an alternate airport). Presumably the tower would still ...


28

For short distances, turboprops are more fuel efficient than jets. On the longer flights, the jet (turbofan) engines win the race. Turbofan engines perform best at high altitudes. At medium and low altitudes, the turboprops are more efficient engines. Since all flights start and end at low altitudes, the high altitude cruise segment needs to be long enough ...


28

The following includes the changes you allude to (which were proposed in ICAO State Letter SP 59/4.1-11/8 on June 30, 2011). Commercial Flights Per ICAO Annex 6, Part I, section 4.3.6 "Fuel Requirements," airplanes should calculate their required fuel quantity as follows (summary; see below for actual ICAO text): Taxi fuel Trip fuel (to reach intended ...


28

In regions and weather conditions where this is likely to be a problem, other fuels are used instead of Jet-A. For example, Jet-B has a freezing point of -60C and is used during the winter in some parts of Russia and other very cold places. For information about fuel freezing in flight, see this previous question/answer.


28

Water-injection in jet engines and piston engines is mixed with fuel before it enters the combustion This is actually somewhat wrong (or at least imprecise) and I think it is adding to the misunderstanding. The water and fuel are never "mixed" in the traditional sense as liquids. An aerosol of fuel is injected... Also, an aerosol of water is injected. The ...


27

Being a ground attack aircraft, the Su-25 has an operational ceiling of 23,000 ft and will not encounter the low temperatures to which a Boeing 777 is regularly exposed. Therefore, the risk of diesel fuel gelling and clogging the fuel lines is much lower. On the other side of the temperature scale, gasoline could vaporize in hot environments and equally ...


26

Generally, smoke comes from incomplete burned fuel. Normally, a jet engine burns a very lean mixture (due to turbine temperature constraints). Nevertheless, getting all the fuel to burn is a considerable challenge, primarily because the air/mixture flows faster in the engine than the flame front. So in order to provide stable burn, many tricks come into ...


26

As others have noted, airplane engines and car engines have very different duty cycles. An airplane engine will typically run at full power for a few minutes during takeoff & climb, then at a large fraction of max during level flight, which may last for hours, and be throttled back only during descent and landing. An auto engine, by contrast, only ...


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