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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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9 votes
2 answers
3k views

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 ...
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 ...
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 ...
3 votes
1 answer
226 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 ...
18 votes
5 answers
8k views

Why does the Piper Cherokee (PA-28-140) engine have such low horsepower despite the very large displacement?

I'm sure this question could apply to many other plane engines, but specifically I'm looking at the Piper Cherokee PA-28-140. Surprisingly, it appears that the engine used, the Lycoming O-320, has ~...
1 vote
1 answer
3k views

Why is the ratio of TSFC at altitude vs. sea level different for hi-bypass vs. lo-bypass turbofan engines?

I've read up on how the thrust-specific fuel consumption of turbofan/turbine engines increases with altitude, and the Georgia Institute of Technology plot in particular seems to indicate that, for ...
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 ...
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 ...
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 ...
1 vote
3 answers
2k views

Propeller Characteristics at Different Altitudes

Assuming I have a propeller with a given diameter (D), pitch, blade twist, and number of blades, I can theoretically analyze discrete airfoil sections in XFOIL and come up with lift and drag polars ...
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 ...
7 votes
2 answers
672 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 ...
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 ...
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 ...
4 votes
1 answer
544 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 ...
32 votes
2 answers
44k views

What are the advantages of more than 4 propeller blades?

I have heard that propellers with more than four blades are not as efficient as 4 or less blades because of lower thrust which may result from interfering prop-streams. But I see the ATR-42/72 and ...
0 votes
1 answer
198 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 ...
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?
16 votes
3 answers
42k views

Are ducted fans more efficient?

As far as static thrust, does a shrouded/ducted propeller outperform an un-shrouded propeller? It seems that the guide blades on the bottom of the duct would allow little more thrust to be extracted ...
18 votes
4 answers
9k views

Why is max endurance different for jet and props?

Max endurance speed is not the same for gliders, propeller planes (also for turbo prop, right?) and jet planes. While for for jet planes max endurance is at the minimum drag speed ($V_{md}$), for ...
3 votes
3 answers
438 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/...
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 ...
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… ...
77 votes
7 answers
23k views

Do helicopters use more fuel when hovering?

This answer says A helicopter uses a LOT more fuel hovering than it does in forward flight. Is this correct? Why?
21 votes
4 answers
7k views

Why the lack of faster piston-powered planes?

There aren't very many fast piston airplanes in production. By "fast" I mean, if you look back in the early to mid 20th century, before turbines won out, there were lots of piston airplanes in ...
-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?
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 ...
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 ...
13 votes
4 answers
10k views

Why do some airports have more than 2 runways, when LHR can get by with 2?

I was looking at aerial imagery of various airports and noticed how some have a large number of runways (4-6), while others have a small number. Specifically, I noticed that Heathrow (LHR) only has 2 ...
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 ...
0 votes
0 answers
387 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 ...
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 ...
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 ...
2 votes
3 answers
324 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 ...
12 votes
5 answers
7k views

Do gyroscopic forces (from rotating engines) significantly affect yaw or pitch?

It occurs to me that jet engines are very heavy objects operating at high RPMs. This must have a very high angular moment and thus a high gyroscopic force. This would restrict rotation when trying to ...
2 votes
0 answers
197 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 ...
10 votes
4 answers
2k views

Would a coaxial propeller with the second prop slower and larger improve speed?

Looking at various propeller designs, I started wondering about these limitations: Large propellers at high speeds have tips going supersonic Scimitar props attempt to keep prop tip from going ...
6 votes
4 answers
463 views

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 ...
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 ...
12 votes
3 answers
7k views

Why aren't larger airliners such as the A380 more efficient than smaller ones?

A recent Washington Post article, titled "Five myths about air travel" noted: The difficulty is that economies of scale don’t always work for airlines, because planes generally don’t increase in ...
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 ...
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 ...
1 vote
1 answer
768 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 ...
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 ...
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 ...
24 votes
9 answers
8k views

Why are winches not used for towing commercial planes up?

In this video a glider is pulled up by a winch on the ground, like this: (Source) I would say you could apply the same principles with bigger planes, possibly even using sustainable energy sources. ...
0 votes
0 answers
189 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, ...
-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 ...
0 votes
2 answers
912 views

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 ...
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 ...

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