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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 is it inefficient to expel high speed gas?

I'm reading the wikipedia page on turbofans, where it says turbojets are inefficient at low speeds because: energy is wasted as the propelling jet is going much faster rearwards than the aircraft is ...
CaptainCodeman's user avatar
1 vote
1 answer
237 views

Most Efficient Commercial Aircraft Design? [closed]

What was the most efficient aircraft design (based on factors such as lift, drag, and fuel consumption) but not developed or scrapped due to issues with long term viability and maintenance, operations ...
Gokul Nath KP's user avatar
1 vote
1 answer
114 views

Determining Required Fuel from Payload/Range Diagram

I would like to determine the amount of fuel required for a flight at a given range/payload combination - ideally from the payload/range-diagram [1] of the corresponding aircraft alone. I know that ...
Wasserwaage's user avatar
  • 1,704
3 votes
1 answer
224 views

Max Range Relationship to Altitude for Propeller-Driven Aircraft

Chapter 11 of the PHAK states, "If a change in altitude causes identical changes in speed and power required, the proportion of speed to power required would be unchanged. The fact implies that ...
Terry's user avatar
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1 vote
0 answers
47 views

Are Runway Profile Descent charts available to non-121 carriers? If so, where can I find them?

AIM 5-4-2(c) says: When crossing altitudes and speed restrictions are issued verbally or are depicted on a chart, ATC will expect the pilot to descend first to the crossing altitude and then reduce ...
Steve V.'s user avatar
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17 votes
2 answers
6k views

Why did Airbus mix "colored light means ON" and "colored light means OFF" in the overhead panel?

Disclaimer: I don't have a real Airbus A330 at hand, nor am I a pilot. After having crashed twice due to icing in rainy weather (not to talk about that here) with an Airbus A330 in X-Plane 12 ...
U. Windl's user avatar
  • 468
0 votes
0 answers
34 views

What are the parameters typically used by airlines to assess the fuel economy and efficiency for their flights?

Are there parameters that are typically being used by airlines to assess the fuel economy and efficiency done in their flights? And how exactly those parameters are being used to do the assessments ...
Luthfi Ahmad's user avatar
10 votes
6 answers
3k views

Function of the compressor in a gas turbine engine

I am trying to understand the importance of having compressed air in the combustion chamber of a gas turbine engine. As far as I understand it, the reasons are twofold. Firstly, the compressor is ...
bchen's user avatar
  • 103
12 votes
4 answers
8k views

Which engine is more financially economical to operate, a turboprop or gasoline engine?

I've seen a discussion about this somewhere before. I'm aware that there's no real way to calculate this. So rather then comparing weight and volume for efficiency, let's compare prices. Which engine ...
Mateo's user avatar
  • 746
22 votes
3 answers
4k views

Why is a dedicated compressor more efficient than using bleed air to pressurize the cabin?

Bleed air is air "stolen" from the compressor of the jet engine and has traditionally been used to pressurize the cabin. The alternative is to use a separate compressor just to provide cabin ...
Kevin Kostlan's user avatar
4 votes
1 answer
543 views

Does Oswald Efficiency make a significant difference on RC-aircraft?

As we know, Oswald Efficiency ($\epsilon$) is caused by change in downwash over the span of the wing, thus causing a change in effective angle of attack over the wing and therefore induced drag ...
Ankit's user avatar
  • 140
0 votes
1 answer
197 views

How to calculate boundary layer thickness?

So I have a flat plate with a surface of 7sqm and an aspect ratio of 12 with air blowing straight at it (like a wing) at a speed of 50km/h. I would like to manually calculate the thickness of the ...
Vincent Cerowski's user avatar
0 votes
2 answers
96 views

Trailing edge flaps use [duplicate]

Why is it that trailing edge flaps are only used at lower speeds? Can they be used at higher speeds too?
JohnM's user avatar
  • 3
3 votes
3 answers
435 views

Carbon footprint & fuel efficiency vs flight distance

I was looking into my carbon footprint related to flying and seem to have came across somewhat of a contradiction. WIKIPEDIA says "mid-range is better" https://en.wikipedia.org/wiki/...
Hilmar's user avatar
  • 131
4 votes
4 answers
1k views

Why does an aircraft require less power when it is flying slower than the most efficient speed?

While I understand the derivation of Power required, I fail to understand why minimum power required corresponds to a velocity that is lower than velocity corresponding to minimum thrust required. My ...
Akshay Kashyap Panda's user avatar
1 vote
1 answer
89 views

Examples of jet turbine values for combustions, fuel flow, Q of fuel, temp of exhaust, etc. for classroom use

I am trying to build jet turbine examples for a class and I want to use actual values for the mass flow of fuel and air, combustion temps, exhaust temps, exhaust composition (CO, CO2,H20,o2, NOx) ext… ...
Michael's user avatar
  • 21
-3 votes
2 answers
200 views

What is the optimal jet engine size for maximum range? [closed]

I under stand the flying wing has been calculated to have an optimal length. Is their an optimal blade length within a turbine engine for planes as well?
Justintimeforfun's user avatar
1 vote
0 answers
122 views

Are Foward Swept Wings for a Rear Propeller Airplane Feasible?

Would going with a forward swept wing design, with the same cord and length of the "A Wing", bring more air the the propeller and tail to increase range, power, or stability? Consider the ...
Justintimeforfun's user avatar
4 votes
4 answers
3k views

What difference does altitude make on fuel efficiency? [duplicate]

Most commercial flights are between 29,000 and 42,000 feet in altitude apparently. But I realise I don't know why. My guesses are: If you fly too high the air pressure gets very low and you have to ...
Simd's user avatar
  • 193
0 votes
0 answers
383 views

What exactly does "efficiency" mean in XFLR5 wing analysis?

Can somebody please tell me what it is / how is it calculated? I initially thought it might be something with the Cl/Cd but I have another design with close to the same Cl/Cd, but with more than ...
Vincent Cerowski's user avatar
0 votes
1 answer
62 views

Has the use of a radiator surface on the inside of duct ever been tried?

I wonder if using radiating surface on the inside of a ducted fan to dispel the waste heat of an engine would provide an economic advantage by increasing thrust? Since a typical engine “wastes” some ...
Numpty One's user avatar
7 votes
2 answers
2k views

Why are the wheels of aircraft relatively small?

I was wondering why the wheels of aircraft are relatively small compared to for example cars? I could imagine that it is more efficient when traveling to have smaller wheels. The majority of ...
Quinten's user avatar
  • 1,158
2 votes
3 answers
323 views

Will a heavier aircraft be more efficient at high speeds(cruise)? [closed]

Since heavier aircraft have more mass and inertia, they will have less drag because it will be easier for them to push through the air so does that mean that we can achieve the same cruise speed with ...
Fan's user avatar
  • 31
2 votes
0 answers
196 views

Would a Tip Jet be more efficient or practical the bigger/longer it gets?

In summary, a tip jet is a jet nozzle at the tip of some helicopter rotor blades, used to spin the rotor without much torque. Source of the picture (it is an article) One of the types of Tip Jet is ...
mandiokai's user avatar
  • 620
0 votes
0 answers
154 views

Sea-Going Ground-Effect Vehicle

Is a Ground-effect vehicle (a.k.a. ekranoplan) practical in seas near the coast (e.g. the US East Coast, West Coast, and Gulf of Mexico)? I'm looking for a practicality answer, like, nope, cannot be ...
ekranoplan's user avatar
0 votes
0 answers
184 views

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 ...
usernamechecksout's user avatar
1 vote
1 answer
140 views

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 ...
P Ek's user avatar
  • 41
1 vote
1 answer
766 views

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 ...
SpeedBird789's user avatar
3 votes
3 answers
6k views

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 ...
P Ek's user avatar
  • 41
0 votes
0 answers
188 views

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, ...
AirCraft Lover's user avatar
-3 votes
1 answer
16k views

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 ...
TayE's user avatar
  • 6,595
19 votes
3 answers
6k views

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 ...
mandiokai's user avatar
  • 620
-2 votes
1 answer
127 views

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 ...
Fulano's user avatar
  • 121
7 votes
2 answers
2k views

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)...
MD88Fan's user avatar
  • 2,494
2 votes
3 answers
342 views

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 ...
Kevin Kostlan's user avatar
8 votes
2 answers
2k views

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 ...
Joe's user avatar
  • 182
2 votes
2 answers
260 views

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 ...
Green Sky Thinking's user avatar
7 votes
1 answer
664 views

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 ...
Isaiah Taylor's user avatar
0 votes
3 answers
556 views

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 ...
TheEnvironmentalist's user avatar
16 votes
5 answers
4k views

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 ...
ciamej's user avatar
  • 293
4 votes
2 answers
793 views

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 ...
Adriel Mattheuz Estolano's user avatar
1 vote
1 answer
101 views

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 ...
Urquiola's user avatar
  • 1,631
10 votes
1 answer
1k views

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 ...
karthikeyan's user avatar
1 vote
1 answer
459 views

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% ...
Peterr de Vries's user avatar
0 votes
1 answer
76 views

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 ...
Charles847's user avatar
1 vote
1 answer
156 views

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: ...
Steve V.'s user avatar
  • 23.3k
4 votes
4 answers
583 views

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....
MD88Fan's user avatar
  • 2,494
2 votes
2 answers
996 views

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 ...
Ted Staggs's user avatar
3 votes
1 answer
979 views

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 ...
Bill Shao's user avatar
  • 157
6 votes
2 answers
678 views

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 ...
red kit's user avatar
  • 61

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