Questions tagged [efficiency]

Efficiency is the (often measurable) ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and without waste.

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Why are longer wings with foldable wingtips used on the B777X instead of lighter ones with original size?

The new Boeing 777X has longer wings to improve efficiency, but has to adopt foldable wingtips to "fit" into all original airports that host its predecessor. Tendentially, longer wings would ...
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1answer
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Can ramjets reach higher thermal efficiencies than gas turbines?

Since a ramjet isn't constrained by turbine inlet temperature like a gas turbine is, it seems to me that it should be able to achieve a higher thermal efficiency, given that it's operating at a speed ...
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Can thermals or high density altitude improve fuel efficiency?

Suppose a pilot is just cruising around building flight time. In order to get the most flight time for fuel, would flying on a dry cold day or on a hot thermal filled day save fuel?
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188 views

Can turboprops use a recuperator?

A recuperator is a device which extracts heat from the exhaust of a turbine and transfers it to the front air. This heats the air, which means the turbine uses less fuel to heat the combustion chamber ...
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Can the plane Celera 500L be eight times more fuel efficient than a jet of similar size and capacity?

Celera 500L (see Otto Aviation site for more details) is a plane with a single propeller powered by a piston diesel engine. The constructor claims it is 8 times more fuel efficient than a jet of about ...
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1answer
227 views

Can I take position behind a plane for V formation legally?

First, I must find a plane with the same capabilities to fly in its wake. As a pilot, what would I need to locate other planes near me? Or find and weight on a plane going in the direction with equal ...
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1answer
101 views

Do aircraft obtain better milage by flying high or by using “ground effect?” [duplicate]

It has been said the most fuel efficient way to fly is by flying in thinner air. On the other hand the largest plane in the world was the Russian "Caspian Sea Monster" Ekranoplan, which is ...
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Can you ride a storm to save fuel?

Cargo sailboats, of the old, depended on wind direction. Like these ships, planes also save time by flying with the wind. On the extreme end, could a plane use storm fronts or hurricanes by flying in ...
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Flying in V formation with multiple planes

Logistically choreographed using air-traffic controllers to pair like planes headed in the same direction or by scheduling flights together, how much fuel could be saved pairing planes to fly in a ...
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1answer
108 views

How does 'standalone' propeller efficiency change with altitude?

I've seen questions regarding propeller aircraft and altitude and their interaction. But I'm wondering what the relationship between just the propeller and altitude (changing air density) is. How does ...
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Based on this fuel flow chart, why isn't it more optimum to remain at an intermediate altitude rather than climbing?

I am having a bit of confusing as to why people say planes gets more efficient as they fly higher. Because on a typical long haul flight the Fuel Flow of the aircraft will obviously be much more that ...
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Do the blades of the rear disk have different geometry to the blades of the front disk on a contra-rotating assembly?

If my understanding is correct, the air flow is accelerated by the front propeller toward the rear propeller in a contra-rotating prop assembly. Therefore, the rear disk would be receiving air at ...
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Would a piston or turbine engine be best suited for a small UAV flying 8000miles?

I am trying to devise a concept that would airdrop medical supplies around remote regions of Africa: vaccines, medicine, blood... etc. I image the payload would be anywhere between 1-2 ton. I think a ...
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Does jet engine exhaust velocity relative to itself remain constant despite speed changes?

Maybe this is a stupid question. I seem to have been told, the velocity of the exhaust leaving an airbreathing jet engine relative to the engine, is constant despite changes in airspeed. However, to ...
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1answer
117 views

Why is the thrust-specific fuel consumption much worse for high bypass turbofans at cruise?

General Electric GE90 Takeoff: 0.278 lb/lbf/h (28.3 kg/kN/h) Cruise: 0.545 lb/lbf/h (55.6 kg/kN/h) Source: https://en.wikipedia.org/wiki/General_Electric_GE90#Specifications I assume this is typical ...
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How does fuel economy quantitatively depend on altitude for a jet?

We already have a few questions and answers about the qualitative effects of altitude on fuel economy: How do I determine the best altitude to fly for fuel economy? Why does fuel consumption decrease ...
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226 views

Which is more efficient: a jet engine or a rocket-powered engine?

Knowing that rocket powered engines have higher speeds than jet engines, it raises the question: are jet engines more efficient than rocket powered engines? This is of course in terms of fuel ...
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2answers
687 views

Why do autogyros exist? [duplicate]

This question has been intriguing me for some time. In Autogyro the rotary blades merely acts as what fixed wings act in normal aircrafts to generate lift. So why not simply have a fixed wing instead ...
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Why would a B-29 consume more fuel at 17 kft than at 9 kft?

According to Wikipedia, one of the factors which almost caused B-29 44-27297 (Bockscar) to run out of fuel and crash at the end of its 9 August 1945 strike mission was the selection of an excessively ...
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Could an airliner be as efficient lower and slower?

Could an airliner ever be as efficient at 15 or so meters using ground effect as it is at 50,000 km even if it has to go slower and be shaped differently?
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5answers
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How efficient would an airliner be if it did not have to carry its own fuel?

Hypothetically, if all the fuel was supplied externally or pulled from the atmosphere to where the plane had never to carry any fuel on board, how much more efficient would an airliner be? The plane ...
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3answers
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Could we make a Hybrid Plane, But not use batteries?

What if we had wind turbines on planes. These would not power a battery but would instead power a smaller engine. Perhaps once a pilot goes to the cruising level he could activate the wind turbines to ...
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What are the average per-passenger-kilogram carbon emissions of common commercial passenger aircraft per kilometer? [duplicate]

Or said in another way, does packing lighter on a trip actually make a dent in one's co2 emissions? According to The carbon independent site, CO2 emissions from aviation fuel are 3.15 grams per ...
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1answer
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Do planes depreciate like cars? [duplicate]

Let's say I was in the market for buying a Cessna. What benefits would buying a new Cessna have over an older one? With cars, the resale value does hit a floor as long as it is safe to drive. Are ...
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1answer
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The principle in 'Trompe' is applied to airplanes?

'Trompe' (see Wikipedia) is a water-powered air compressor, commonly used before the advent of the electric-powered compressor. A trompe is somewhat like an airlift pump working in reverse, used to ...
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Fuel consumption database using ICAO codes?

I will preface this by saying I do not have any level of knowledge in Aerodynamics - I'm a freelance journalist and so apologies for the poor level of general understanding. I'm attempting to create ...
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How does increasing the size of a jet engine make it more fuel efficient?

The design trend is there: 8, 4, 3, 2 jet engines on powering the large cargo or passenger aircraft. Is it mostly to accommodate the larger, more efficient fans, or are there also benefits in the ...
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1answer
255 views

What is the difference in performance between variable pitch prop and two fixed propellers for take-off and cruise speeds?

Push-pull configuration aircrafts usually feature identical engines and propellers working only in tandem for multiple reasons like higher speed, better climb rate, reliability, cost, ease of ...
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Can ekranoplans (GEV) be more efficient than traditional airliners?

Ekranoplans or Ground Effect Vehicles (GEV) fly low enough to the ground that their wings stay in the ground effect. This increases lift and efficiency. But GEV fly in the lower atmosphere (...
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1answer
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How can I calculate turbofan efficiency as a function of turbine inlet temperature?

I know that increasing the turbine inlet temperature (TIT) increases the overall efficiency of the jet engine. So I wanted to find the overall efficiency as a function of TIT. I used the equations ...
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1answer
166 views

Why are there no large turboprop passenger airliners? [duplicate]

If turboprop engines are more efficient than turbofan/jet engines at lower speeds, and have a lower specific fuel consumption, why are there no large passenger airliners that utilize the turboprop ...
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1answer
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Is there an equation for jet engine efficiency as a function of turbine inlet temperature?

I know that there is a relation between the turbine inlet temperature and the engine's efficiency. But, can anyone provide an equation or efficiency as a function of just the turbine inlet temperature?...
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How do I obtain the max endurance altitude?

There are excellent explanations of the physics that determine maximum endurance speed here, here, and here. I was thinking of aircraft that have to be "on station" without an indicated altitude and ...
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182 views

How does fuel efficiency depend on wing configuration?

Which of the following wing configurations is the most fuel-efficient?
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1answer
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When Airplane is reducing altitude from flight level (cruise), which one is more efficient

When an airplane is reducing altitude, say due to preparation for landing, the nose is tilted down. That I got from a video on Youtube which explains the way an airplane is going down until it reaches ...
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1answer
169 views

How much can a plane benefit from another planes wake?

Could a smaller plane fly in a V formation behind a much larger plane to reduce fuel consumption significantly more than a plane its own size? At what point does flying in a larger planes wake become ...
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1answer
206 views

Could a rotor head wing be plausible?

Could a helicopter support a detachable wing with no controls on top of the rotor head in place of a radar dome? Could the rotor head be made to support more weight? Would it be more fuel efficient at ...
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1answer
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How is a Flying-V more efficient than current fuselage-over-wing designs?

It's claimed the plane will use 20% less fuel than the Airbus A350-900 while carrying a similar number of passengers -- the Flying-V will seat 314, while the Airbus A350 seats between 300 and 350. The ...
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Did airlines fly their aircraft slower in response to oil prices in the 1970s?

Modern airliners generally have lower cruise speeds than those of comparable aircraft from 40 years ago (the venerable Boeing 737 seems to be something of an exception; it has always had a more ...
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1answer
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What is “Carson cruise” and can I determine it myself?

Mike Y. just posted an answer containing the following: With today’s fuel costs, the Carson cruise angle of attack, which represents the most efficient way to fly fast with the least increase in ...
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Is it cheaper to drop cargo than to land it?

Is it more fuel efficient to drop cargo onto a runway from the air en route to a final destination than to land and unload it using a more fuel efficient plane?
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1answer
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What values can/should be used for the isentropic efficiency of a compressor and turbine?

I was trying to model an turbofan aircraft engine using Matlab and Simulink. In the process I have fixed certain parameters to some specific values which are nominal operating values of the parameters....
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Why is the A330neo more efficient than the A350 on shorter routes?

For A330neo Wikipedia page, is written: A330neo enables profitability on shorter ranges where the longer-range A350 and Boeing 787 aren't optimized. For what reasons it is true? A330 and A350 ...
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1answer
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Why does the rotor thrust decrease at smaller tip clearance for shrouded rotor?

Consider this system, rotor with shroud: From this research, we see that: at the same rpm, the rotor thrust decreases,the shroud thrust increases as tip clearance decreases. But why does the rotor ...
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6answers
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What are the advantages of using a ramjet in an air-to-surface missile?

Which are the advantages of using a ramjet compared to a rocket engine in an air-to-surface missile? I suppose the cost rises a lot, so why do some countries use ramjets as a way of propelling ASM ...
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Is it possible to calculate possible fuel savings of known turbofan engines if operational heat could be increased [closed]

Starlite is liquid paint like substance invented in 70s and perfected in the 80s by the late British inventor Maurice Ward (1933-2011). It is said to be able to withstand heat from 78 nuclear ...
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How do I optimize a turbofan engine to fly lower and slower instead of higher and faster?

I was reading something about someone who was doing this and I'm intrigued, but I have no idea what you actually do to optimize the engine to be better at lower altitudes and lower speeds?
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What passenger airplane has the lowest fuel efficiency?

What is the airplane with the lowest fuel efficiency? To set some parameters, let's limit it to the following: Must be manufactured between 1960 and modern day. Must be a non-military passenger ...
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6answers
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Why then don't aircraft fly even higher, for even greater efficiency? [duplicate]

After reading various superb QA on here I now see that (basically) aircraft are more efficient per passenger-mile, at higher altitudes. Why don't we go even higher, than current typical airliner ...
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3answers
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Does shrouding a propeller minimize induced drag by equalizing the downwash velocity along its blades?

EDIT: It's not a duplicate of Are ducted fans more efficient? That question and the answers doesn't address the reason for the higher theoretical efficiency, it is more about efficiency in practice (...