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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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44 views

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....
4
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1answer
346 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 ...
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1answer
120 views

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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3answers
168 views

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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3answers
115 views

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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2answers
312 views

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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2answers
523 views

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
8k 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 ...
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3answers
246 views

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 (...
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0answers
45 views

Does Froude Efficiency represent an upper bound for propellers in certain flight / aircraft conditions?

I used the Simple Propeller Theory to calculate the Froude Efficiency for my theoretical propeller-driven craft (at 65k feet). Here are the results: https://ibb.co/kPPqzU. My results were that, for ...
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2answers
146 views

How is a propeller diameter for given application determined?

let's say I need 1000 N of thrust for a given aircraft and flight velocity. I have available a fixed pitch propeller with a given shape, and thus given performance to advance ratio curves. Let's say ...
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1answer
408 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.
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2answers
206 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 ...
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1answer
161 views

Would increasing rotor disc diameter increase efficiency in a helicopter by reducing disc loading?

Despite the obvious drawbacks of a larger rotor diameter would the reduced disc loading increase efficiency during hover and forward flight?
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1answer
240 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 ...
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2answers
202 views

Does wing paint colour improve airplane fuel efficiency?

If birds that fly very long distances like seabirds have darker colours on top of the wings and lighter colours underneath the wing, is it possible that painting airplane wings similarly may improve ...
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3answers
350 views

Why are helicopters less efficient than planes?

At higher speeds, advancing helicopter blades will operate at velocities approaching mach 1, reducing efficiency. But what about lower speeds? A helicopter is basically a wingless plane with a giant ...
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1answer
220 views

Why divide the blades of a 9 blade propeller into 3 groups?

In a youtube video an airboat is featured with two contra-rotating propellers, each holding nine blades. Interestingly those nine blades are not spaced evenly, but grouped into three groups. I've ...
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2answers
153 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,...
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2answers
876 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, ...
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0answers
34 views

How turbofan engine efficiency increases over altitude or speed? [duplicate]

I am confused a lot about the efficiency and thrust relation with altitude and velocity of an aircraft. If thrust is related to air mass flow and velocity diffrence of bypassed air - exhaust gases ...
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2answers
190 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: ...
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1answer
109 views

Propeller Curve Modification on Test Rig

this is my first stack exchange question so please bear with me if I have missed a rule: I tried searching for this question to no avail. I have an off-the-shelf propeller for the purpose of eventual ...
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1answer
134 views

How can you explicate the efficiency of a turbofan engine with Carnot's theorem?

From Carnot's theorem, we know that efficiency is $$ \eta = 1-\dfrac{T_c}{T_h}$$ where $T_c$ is the temperature of the cold reservoir and $T_h$ the temperature of the hot reservoir. But what do we ...
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1answer
394 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....
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2answers
526 views

Why is there still a preference for turboprop airliners over the new regional jets? [duplicate]

In the 1950s and in the early 1960s, jets were mostly available as fighter/military or big, long haul aircraft. Regional aviation was based primarily on piston aircraft that could operate in smaller ...
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1answer
2k views

How to select the most efficient airfoil for low speed flight?

What airfoil (or family) has the highest $C_L/C_D$ ratio at speeds in the $50\:km/h$ range. The use case would be an ultralight with a max speed of $50\:km/h$
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2answers
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Are two little engines or one big engine more efficient for an ultralight?

For an ultralight, should two engines weighing 10kg each and making 7hp each OR one engine weighing 20kg and making 14hp be used?
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4answers
246 views

How bad is the efficiency of jet engines under low loads?

VTOL operations need 4-5 times more thrust than a conventional take-off of an aircraft. If you don't want to install additional lift-engines into a hypothetical aircraft and use thrust vectoring to ...
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1answer
310 views

How much fuel is used for preheating the outer engines of a four-engine airliner that were not used for taxiing?

Many questions and observations here have highlighted the idea of using some kind of electric towing system for towing airplane to and from the runway, instead of using fuel to taxi. One of the ...
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1answer
5k 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 ...
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2answers
265 views

Is a propeller with two long blades more efficient than one with three shorter blades? [duplicate]

Is a longer, two-bladed propeller more efficient than a three-bladed propeller with a smaller diameter?
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1answer
182 views

Would an extra fan make turbofans more efficient in cruise?

A turbo fan engine cannot use all of its available thrust in cruise any longer that it normally does at today's technologies, otherwise it would risk a meltdown of the internal hot engine parts and ...
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2answers
433 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 ...
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0answers
76 views

Would this be an accurate method of fuel consumption comparison?

I'm looking to compare the fuel consumption of regional jets in the US and the stated efficiency of the Bombardier CS100. At the moment, I'm considering using data from the Bureau of Transportation ...
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1answer
202 views

At what Mach Number do variable cycle engines (VCEs) start showing benefits over turbofans?

Currently, most supersonic engines engines are low bypass turbofans. However turbofans start becoming infeasible as the mach number increases. Variable Cycle Engines, still have noise and weight ...
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1answer
62 views

At what temperatures would the gearing for geared turbofans be rendered unnecessary? [closed]

If geared turbofans were fitted with material science technologies or other engineering innovations that would allow them to operate at higher temperatures exceeding their current most optimum ...
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0answers
64 views

At what operating temperatures would the Trent 900 need to operate, to equate to the efficiency of current geared turbofans?

What is the minimum optimum operating temperature (in degrees Celsius) that would be required for the Trent 900 to operate at, for it to attain the level of fuel efficiency of current geared turbo ...
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3answers
383 views

Would removing heat from the compressor and adding heat to the turbine increase a gas turbine's efficiency?

Since a compressor compresses air, the air temperature increases due to P1/T1=P2/T2. When the temperature is increased it would be harder to compress - so would removing the heat from the air inside ...
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8answers
6k 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. ...
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1answer
1k 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 ...
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2answers
344 views

Could the wing struts on the SUGARVolt cause problems?

On Boeing's concept aircraft, the SUGARVolt, there are wing struts connecting the fuselage and the wings, which is for making sure that the wings do not bend too much during flight. Could the wing ...
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1answer
707 views

Is there a mathematical formula to find the most efficient propeller? [duplicate]

Is there a mathematical formula to find the most efficient propeller? Is a five-blade better than a four-blade? Does software exist to aid in the calculations there?
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2answers
372 views

Why is a contra-rotating High Pressure section more efficient? [duplicate]

In the Rolls Royce Trent 900 marketing material, the use of contra-rotating HP system is described as increasing the efficiency of the engine. Can anyone explain why/how that increases the efficiency?
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2answers
160 views

On SEP airplanes, why does the fuel consumption decreases with temperature, pressure and airspeed being equal?

Looking at the cruise performance tables in the POH of the C150, C172 or C182, one can see that for the same pressure altitude, the same RPM and the same true airspeed, the fuel consumption is reduced ...
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1answer
148 views

Could adding a gearbox to the Trent 900 improve the efficiency of the A380?

Could adding a gearbox to the Trent 900 improve the efficiency of the A380 so that it performs better than a smaller jet, i.e with economies of scale? Is the absence of a gearbox in the Trent 900 the ...
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7answers
15k 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?
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1answer
200 views

Is it possible for an airliner to cruise at engine full thrust?

What would happen if the pilot of a modern airliner like the boeing 747-800 or Airbus A380 left the throttle at full thrust at cruise altitude for an extended period of time e.g 4 hours if the ...
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2answers
9k 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 ...
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6answers
19k 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?