# 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 does adding more blades to a propeller/fan not show a decrease in efficiency?

According to this answer increasing blade solidity increases the blade area by either enlarging chord or increasing blade count both of which reduce efficiency via reducing the lift coefficient and ...
1 vote
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### When using momentum theory for estimating power needed to hover, is propulsive efficiency accounted for?

I am using momentum theory to estimate power needed for an eVTOL. I have read past papers where the results got from momentum theory was direcly use to estimate the power needed from the battery. How ...
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### Extrapolating Oswald Efficiency Factor from CL^2 vs CD Graph

I have plotted this CL^2 vs CD graph for a glide test performed in a flight simulator. I want to find the Oswald Efficiency Factor, e from it and I assume I can do that from its gradient. With a wing ...
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### Power calculation of propeller

This is probably a very simple question, but I have been really struggling and need your help. I have simulated a propeller with these parameters on Ansys: Thrust: 2000 N Angular Velocity: 314 rad/s ...
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### What is the meaning of "Contra-Rotating Propeller Increases Efficiency"? How is it calculated?

This picture is taken from here. In that video is mentioned that contra-rotating propeller increases efficiency up to 6-16%. Regardless of the number that could be vary from one airplane to another, ...
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### Would blade-less (Dyson style) jet engines work? [duplicate]

Is it possible to design an aircraft with blade-less (same concept as Dyson) design to generate thrust? What are some of the key benefits, drawbacks and examples of attempts (if any) at this kind of ...
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### How efficient is a Scramjet?

I searched about the subject, but I couldn't find any place where the overall efficiency of the scramjet is compared to the other types of engines. All they say is how the "Scramjet is more ...
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### Can a Magnus/Coanda effect be used on wings with hot gases for more efficiency? What are current aircrafts that uses such system?

Well, I don't know much about this type of mechanism, and the only post I could find that has something similar to what I'm asking is this one, but isn't quite what I'm asking. So, the idea would be ...
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### For maximum glide range, should I minimize glide angle or AoA?

I'm currently taking an aeronautical engineering course in school. For an upcoming project, we're going to build balsa toss gliders and we have to design our own wings. The program we're using (Aery32)...
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### Are there any aircraft where wing, horizontal empennage and optionally canards produce positive lift?

Planes are more stable if the center of mass is ahead of the center of lift. But this means that the tail must provide downforce to keep the nose up, which is inefficient. Are there any designs where ...
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### Why does the optimum cruise altitude depend on the weight of the airplane?

In this answer, Bianfable notes: [O]ptimum cruise altitude for a 777-200LR at a weight of 340 t is only FL285, but after burning 100 t of fuel it has increased to FL360 Why is that? Is it simply ...
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### Comparison: e-aircraft vs. ground EV modes (car, coach, rail)

I'm looking for (and struggling to find) a comparison for any e-aircraft vs. ground EV modes (car, coach, rail) carrying an equivalent payload, an equivalent distance. So basically, if you fly from ...
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### Why is my calculated seat-miles per gallon of small aircraft higher than of big aircraft?

I've calculated the seat-miles per gallon for three planes. This factors in the speed; it basically means how much does it cost to transport 1 person 1 mile. Plane Seats Cruise (MPH) gph seat-mpg ...
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### How does bypass air work?

As far as I’m aware, high-bypass engines have far higher fuel efficiency than low-bypass engines, and as a result the effective specific impulse of the engine is increased. What I’m trying to figure ...
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### Why is thrust inverse to speed in piston engines?

It is said that piston engines have constant power output, and thus their thrust is inverse to speed (e.g. here), while turbines have relatively constant thrust. I'm looking for an intuitive ...
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### How to calculate the efficiency of a rubber powered propeller

I made a simple test rig together with a stopwatch to measure the thrust (in grams) with respect to time of a rubber powered propeller. This enabled me to compare the performance of different ...
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### When, and how to calculate this, you can expect too much Wing Dihedral generates Dutch Roll, increases in Drag? [closed]

The question comes from the Arup designs, and the engineer who turned it into blueprints, Hoffmann, ('A Novel All Wing Airplane', Raoul J Hoffman, Popular Aviation, March 1935, pp 163 and 196), they ...
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### What is the function of the aft stator in CFM's open rotor engine design?

CFM revealed their design for a open rotor propfan engine with two stages of blades - one active set of blades rotating in the forward and an static sets of blades on the aft. According to The ...
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### What's the optimal cruise lift to drag ratio of the Piaggio Avanti?

I'm interested in the maximum L/D this plane can achieve. I can't find the necessary data to do the calculation myself. If I knew the "long range cruise" engine power and assumed 85% ...
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### Formula for comparing drag on planes flying at different speeds at different altitudes. Ex: Mach .80 at 40,000 ft, vs Mach 5 at 100,000 ft

I am interested in getting a sense of how much extra energy is needed to overcome drag at different speeds and altitudes. For example, for me a baseline would the drag on an airplane flying something ...
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### What factors cause a turbine aircraft to have decreasing fuel burn over time?

Consider a fictional aircraft with a fuel schedule similar to the following: ...
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### Why hasn't the US military performed aftermarket modifications on certain aircraft?

The US military emits more CO2 annually than several countries. Winglets have been proven to work well in the commercial sector to reduce fuel burn, therefore reducing both CO2 emissions and fuel cost....
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### Why does propeller slip (efficiency) change during the flight (fixed-pitch)?

I was wondering how the efficiency of a fixed-pitch propeller changes during different stages of flight and why it does so. I suppose when we are talking about propeller efficiency we are actually ...
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### What is the approximate thrust at sea level for a C-130J Hercules?

I am looking for the approximate thrust of a C-130J Hercules under ISA sea level conditions. Also the efficiency of its propeller would be of help. An answer to this question would really help my ...
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### How come the hover efficiency for tiltrotors is better than tiltwings?

How do you compare the hover efficiency of tilt-rotor and tilt-wing aircraft? The Wikipedia page Tiltrotor mentions: Tiltrotors generally have better hover efficiency than tiltwings (...) But I was ...
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### What surface materials do airplanes use to reduce friction?

Full swimming body suits were banned from Olympic Games a few years ago because some materials have less friction than skin and contestants that could not afford gear to increase their performance ...
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### Efficiency of the Kuznetsov NK-88 or NK-89 engine burning hydrogen

It's tough to find data about turbofan efficiency running on hydrogen. The Tupolev Tu-155 has been used as a test bed for exotic fuels right before the fall of the soviet union, without much follow-up....
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### Would it be beneficial to have rotors AND propellers instead of a tiltrotor?

Would it be beneficial for tiltrotor aircraft if they had BOTH rotors and propellers, instead of the hybrid proprotors that are neither good propellers nor good rotors? Like imagine the V-22 Osprey ...
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### How much is a swashplate system more energy efficient than a fixed blade system for the same load

When reading about the lifting capacity of swashplates (as found in helicopters) vs fixed blade systems (as found in e.g. DJI drones), I read a lot of comments about the fact that the bigger rotors of ...
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### Does a constant speed prop maintain the optimal angle of attack at all time?

From an answer on this site: The governor just knows: Speed too fast, flyweights move out, routes pressure to move the blades more coarse; speed too slow, flyweights move in, routes pressure to move ...
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### Can any conclusions about aerodynamic efficiency be drawn on the basis of fly-by noise?

Edit: I'm beginning to think this is more suited to the physics stack exchange, but I'll keep this here for a while... Being bored mindless, surfing the interwebz, I came across this video, where a ...
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### increasing lift in a plane by placing engine in such a way that the air coming out of it washes over the wings to create more lift [duplicate]

I was wondering if the engines of a plane can be placed in such a way so that the air coming out of the engines goes from over the wings so that the velocity of air over the wing is higher and more ...
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### Is high propeller pitch inherently inefficient?

For an airfoil, in general, the aerodynamic force is more or less perpendicular to the chord line. A low-pitched propeller blade has it's chord line more perpendicular to the direction of flight, ...
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### Would large, low aspect ratio fan/propeller blades be more efficient? Why not?

With reference to this answer We read in the above that accelerating a larger mass of air by a smaller amount is (theoretically) more efficient. This is an advantage of a larger propeller than is ...
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### How to find capture area of an engine inlet?

I tried to relate intake pressure recovery in terms which do not involve efficiency of an inlet and capture area, i was able to formulate pressure recovery without intake efficiency but now i need to ...
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### How is the Dash 8 Q400 so fast?

The Q400 has a cruise speed of 360kts, and on flightradar24 most Q400s that I looked at reached similar speeds during cruise. The ATR 72 has similar specifications yet only flies at 280kts. I'm ...
1 vote
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### Is it incorrect to say that "passenger jets like to cruise at higher altitudes because there's less drag"?

I hear it stated quite often that aircraft like to fly high because there's less drag at higher altitudes.  \text{Range} = \frac{V}{g} \frac{1}{\text{SFC}} \frac{L}{D} \ln \left( \frac{W_\text{...
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### Why are wings not tapered all the way to reduce vortex drag?

Wingtip vortices are created by, well, wingtips. These vortices create drag. One of the approaches to reducing this drag is taper the wing, source source Will eliminating the wingtip, as on the ...
1 vote
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### Are there any situations where having high lift but low lift to drag ratio would be beneficial?

From my understanding, high lift to drag ratio could make an aircraft efficient during cruising conditions. This is when the aircraft is in equilibrium, lift is equal to weight, and thrust is equal to ...
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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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### How do anhedral and dihedral affect the efficiency of a wing?

Higher pressure air on the underside of a wing generally rolls outboard around the wingtip and over the top of the wing reducing lift and therefore increasing induced drag. My intuition would tell me ...
1 vote
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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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### 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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### 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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### 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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