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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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What is the propeller efficiency, $μ_p$, of modern propellers for light sport aircraft?

Roskam's book on preliminary design gives a value of 0.7 for "homebuilt" aircraft and 0.8 for general aviation. What explains this difference in propeller efficiency? The content of Roskam's book is ...
user26358's user avatar
  • 469
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 ...
SMS von der Tann's user avatar
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?
Delta Oscar Uniform's user avatar
24 votes
2 answers
4k views

Is a golf ball surface a good idea for wings or fuselage?

I searched for an infamous golf ball question on this site but did not find any, so I guess it's time for one. Would a dimpled surface like a golf ball somehow improve the aerodynamics of an airplane?...
DrZ214's user avatar
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29 votes
2 answers
14k views

How much of an improvement would a 1% weight decrease on an airplane be to the industry?

Say I thought of a very easy and inexpensive way to reduce the takeoff weight of a commercial airplane (body, fuel and passengers) by 1%. How much would this mean to the industry? Would it make much ...
TheEnvironmentalist's user avatar
49 votes
3 answers
27k views

Why is the Tu-95 so efficient despite having propellers that spin faster than the speed of sound?

I've ready many, many times that propellers are not efficient near the speed of sound because it's so hard to get a tip-speed above Mach 1. Then I came across this: It's the Tu-95 "Bear", a ...
DrZ214's user avatar
  • 17.8k
25 votes
6 answers
28k views

Are turboprops more efficient than piston engines (thrust per fuel consumption)?

I want to compare two types of engines: Turboprops and piston engines. I want to know which one is more efficient. There are many types of efficiencies, so I will specify: thrust (in newtons) per fuel ...
DrZ214's user avatar
  • 17.8k
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 ...
yankee's user avatar
  • 1,073
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 ...
Daniel Caoili's user avatar
18 votes
2 answers
2k views

What is the cost savings of using electronic motors to taxi?

Aircraft manufacturers are now planning to use High Torque electric motors on the nose wheel of the aircraft, which is powered from the APU, to taxi the aircraft from the gate to the runway without ...
Victor Juliet's user avatar
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 ...
DrZ214's user avatar
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40 votes
9 answers
34k views

Why increase the number of cylinders in an engine instead of increasing their volume?

I've been reading about WW2 planes lately. Some of them have 12 or even more pistons in their engines. But if your goal is to increase power, why would you add more pistons instead of simply ...
DrZ214's user avatar
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11 votes
4 answers
5k views

How is the D8 Double Bubble aircraft by NASA so efficient?

How does the 'double bubble' fuselage cross-section of the "Double Bubble D8" aircraft (developed by MIT for NASA) help improve overall efficiency by around 70%? Image credit: NASA/MIT/Aurora Flight ...
Victor Juliet's user avatar
4 votes
2 answers
403 views

Can lift be equated to how much air is moved?

The explanation for lift that I find easiest to visualize is that air is deflected downward by the wing. This downward action causes an equal and opposite reaction of an upward force against the plane,...
YAHsaves's user avatar
  • 1,211
13 votes
2 answers
3k views

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 (...
RoboKaren's user avatar
  • 8,071
23 votes
6 answers
20k views

Could airline tires be deflated in mid-flight to reduce weight?

As a means of weight reduction to reduce fuel consumption, could the tires on an aircraft’s landing gear be deflated once airborne then re-inflated just prior to landing? Is that feasible and safe?
securitydude5's user avatar
9 votes
1 answer
2k views

How does the efficiency of a turbofan compare between take off speeds and optimal conditions?

I know turbofans are less efficient than propellers due to accelerating a smaller mass of air faster. So my question here is not comparing turbofans vs other engines, but compare how inefficient is a ...
Southbob's user avatar
  • 1,089
6 votes
1 answer
4k views

What is the fan tip speed at maximum thrust?

What is the fan tip speed at maximum thrust? Is it any different for a Rolls-Royce Trent 900 (powers the Airbus A380) and Pratt & Whitney PW6000 (powers the Airbus A318)? Are they efficient at ...
securitydude5's user avatar
3 votes
2 answers
590 views

Is solar power used (as auxiliary power) on commercial aircraft?

Are there any commercial aircraft that use solar energy in terms of auxiliary (not as main power source, as of now) power source ? If Yes, In what forms is the solar power used? If No, Why isn't ...
steam7137's user avatar
  • 353
2 votes
4 answers
2k views

How can larger wingspan decrease the strength of wingtip vortices?

In the last paragraph from the link below, it states that Vortex Strength is inversely proportional to Wingspan. Why is this? http://avstop.com/ac/flighttrainghandbook/wingtipvortices.html EDIT: ...
Lorenzo Capasso's user avatar
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 ...
Charles847's user avatar
20 votes
14 answers
19k views

Why is mid-air refueling worth it? (or is it at all?)

Surely, mid-air refueling is a cool thing, but is it worth it? It's obvious that the military, for one, has some requirements to keep aircraft airborne so that they can keep patrolling, for example. ...
user2962533's user avatar
19 votes
1 answer
20k views

Which jet engines have the highest thermal efficiency?

Some automakers (Mercedes-Benz, Toyota) have recently been making news about the improved thermal efficiency of their engines, stating that they reached the 50% mark. I was wondering if it was the ...
clueless007's user avatar
19 votes
4 answers
10k views

Did any Boeing 787 operator achieve the 20% fuel efficiency improvement over the 767?

Is there any airline which are able to get the complete 20% fuel efficiency on their 787 with respect to 767 it is going to replace, as told by Boeing. I have read that one of the early customer like ...
NitinG's user avatar
  • 6,889
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
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 ...
RoboKaren's user avatar
  • 8,071
11 votes
5 answers
2k views

Do aircraft use the majority of their fuel to overcome friction?

It was asserted (tangentially) in this question that airliners use most of their fuel to overcome frictional losses. Is that a true statement? If so, ...
FreeMan's user avatar
  • 16.3k
10 votes
2 answers
3k views

How much thrust is gained from placing a propeller in a duct?

Assuming that the power and diameter are the same, how much extra thrust can be gained by placing a propeller in a duct? How does it influence the RPM? To clarify: take any prop, place it in a well-...
White Knight's user avatar
9 votes
1 answer
4k views

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 ...
Luca Detomi's user avatar
  • 1,992
7 votes
1 answer
877 views

Are two twin-jet flights more efficient than one quad-jet flight?

Ignoring for this question the issue of flexibility for the airline, would it be more (fuel, cost) efficient to have a single flight with a 4 engine plane than to have two flights with 2 engine planes....
Dohn Joe's user avatar
  • 1,318
7 votes
1 answer
2k views

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 ...
Joe Wie's user avatar
  • 71
4 votes
1 answer
1k views

Propeller Efficiency calculation different by two methods

Please refer to this MIT page which I used for my calculations: https://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node86.html I calculated my aircraft propeller's prop, thrust, and torque ...
dumbpropnerd's user avatar
3 votes
1 answer
6k views

What is the efficiency of the turbine of a modern jet engine?

What is the turbine efficiency of a modern jet engine? Just the turbine efficiency only. What percentage of fuel energy the turbine converts into mechanical energy.
Neville p's user avatar
2 votes
1 answer
2k views

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 ...
Abdullah is not an Amalekite's user avatar
1 vote
4 answers
2k views

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 ...
SharkyPanda's user avatar
24 votes
6 answers
12k views

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 ...
Fattie's user avatar
  • 1,932
18 votes
1 answer
5k views

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 ...
Vikki's user avatar
  • 28.4k
13 votes
2 answers
3k views

Is it more efficient to have many or a few rotors?

Wouldn't it be smarter to design VTOL rotorcraft with many smaller rotors than one big rotor? With more rotors you have more redundancy and smaller blade velocity (and perhaps better stabilisation) ...
Daniel Caoili's user avatar
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 ...
Appletank's user avatar
  • 101
10 votes
1 answer
1k views

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 ...
CrossRoads's user avatar
  • 8,795
10 votes
4 answers
2k views

When are multiple hops more efficient than single leg?

Considering a very long route (equal to the max ferry range of an aircraft[1]). Would it be more fuel efficient to fly multiple legs or a single one ? Multiple legs would allow you to use less fuel,...
Antzi's user avatar
  • 4,222
9 votes
3 answers
1k views

How is a 436 seater A330 fuel efficient?

Cebu Pacific is a Philippine low-cost airline , which has 6 A330 in its fleet. The capacity of each of them is 436 . As far as I know, one of the reasons why airlines introduce First Class cabins is ...
anshabhi's user avatar
  • 11.5k
8 votes
1 answer
2k views

How does cost per seat-mile differ between commercial and private jets?

I was reading an article the other day that mentioned many smaller private jets are more efficient, faster, can climb quicker and land with less space than larger commercial aircraft. Some of the ...
Shaun's user avatar
  • 81
8 votes
2 answers
6k views

How can I calculate the optimum loiter airspeed for an aircraft?

I am in the conceptual phase of designing a 10 seater amphibian aircraft. I have done the initial sizing using Raymer and Roskam's methods. I have got my design point. To do a constraint analysis as ...
Anirudh Prabhu's user avatar
7 votes
2 answers
4k views

Is 1 propeller always more efficient than 2?

Based on other answers I've read here (1) (2) (3), a single large blade propeller is the most efficient type of thrust you can get. There are 2 reasons for this (as I understand it). Firstly, ...
YAHsaves's user avatar
  • 1,211
7 votes
1 answer
663 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
6 votes
1 answer
3k views

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 ...
Steve V.'s user avatar
  • 23.3k
6 votes
1 answer
4k views

Why are podded engines preferred over engines fitted inside the fuselage or wing?

Given the fact that podded engines on the wings of airplanes cause much drag (and thereby contribute to a lot of loss of efficiency), why do airliners still prefer podded turbojet engines over ...
Victor Juliet's user avatar
5 votes
1 answer
7k views

What are some differences that make the new 737 MAX winglets more efficient than a conventional winglet? [duplicate]

I was reading this article about the Boeing 737 MAX final assembly and it was saying something about the new winglet generating lift and increasing efficiency. Can you explain to me how this works, ...
Ethan's user avatar
  • 9,349
5 votes
1 answer
814 views

Does the direction of counter-rotating props affect efficiency?

From my brief Wikipedying, if counter-rotating props' tops go towards each other, each has a reduced P-factor so the loss of either engine won't yaw the aircraft as hard as if the bottoms come ...
Nick T's user avatar
  • 181