Questions tagged [thrust]

Questions about the propulsive force of a powered aircraft.

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26
votes
1answer
20k views

What provides the greatest thrust in a high-bypass turbofan engine?

I'll try to make as much sense as I can with this question. I've been flying quite often in 2015, and I have recently wondered this question regarding high-bypass turbofan engines. I know that there ...
25
votes
2answers
4k views

Do multi-engine jets need all engines with equal age to reduce asymmetry in thrust and fuel consumption arising out of deterioration?

Let's assume, one of the engines on a twin-jet needs replacement and the jet is is fitted with an old engine and a newer engine after the due replacement, the older engine would tend to produce less ...
16
votes
10answers
7k views

Can hydrogen gas be an alternative fuel source for a gas turbine engine?

I want to do research for an alternative fuel source for a commercial aircraft that will reduce the cost for flights. Will the hydrogen gas be ignited in the combustion chamber and produce enough ...
16
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7answers
9k views

How do rocket engines produce more thrust than aircraft jet engines?

I can't find the reason why rockets are able to produce so much thrust when compared to turbojets. I do know that the rockets carry their own own supply of oxygen since there is no oxygen in space or ...
16
votes
2answers
6k views

What does it mean to “firewall” an aircraft engine?

I (think) I understand what a firewall is (at least, in a single engine aircraft where the engine is at the front of the fuselage), but what does it mean "to firewall" an aircraft's engines, as ...
11
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2answers
4k views

How (and why) does engine thrust change with airspeed?

I'm interested in how the thrust of a turbofan engine is affected at higher airspeeds (TAS). I know (I believed) that engine thrust(at constant N1) was relatively constant like in the following graph (...
9
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2answers
668 views

Are thrust levers synchronized by default when pushed/pulled? [duplicate]

When I watched this video about the last flight of Juergen "J.R." Raps from SFO to FRA in an A380 (before his retirement) I noticed he lines up or synchronizes the four thrust levers as shown between ...
9
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4answers
1k views

How does an operator change the engine thrust rating?

If, for example, an operator has a Boeing 737-800 with CFM56-7B engines set at a 22K thrust rating, but the next operator wanted to operate the engines at 24K thrust rating, what would they need to ...
9
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3answers
903 views

Why is thrust available constant with speed for turbojet engines, when it varies with speed for turboprop engines?

Similarly, why is power available (nearly) constant with speed for a propeller engine, while it varies for a jet engine?
9
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2answers
228 views

Why isn't there some optional setting that can precisely move thrust levers jointly?

In the screenshots beneath (top, bottom), Capt Juergen Raps is fidgeting the A380's 4 thrust levers with his fingers to align them to the same thrust position. Isn't it unproductive for pilots to ...
8
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3answers
3k views

How does the bypass air provide thrust?

To my knowledge, bypass air produces 80% of total thrust. But I don't understand to how it does that. By accelerating the air, by increasing the speed or increasing the pressure of the air? Is it ...
8
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3answers
948 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 ...
7
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4answers
3k views

How can lift be less than thrust that is less than weight? [duplicate]

Physics in schools teaches two contradictory and mutually exclusive things: That the upward lift force on an airplane in flight equal its weight (Lift = Weight = Mass x Gravity). This is based on ...
6
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2answers
219 views

How do engine manufacturers derive varying amounts of thrust from a single engine model?

What changes do manufacturers make to an engine to vary the amount of thrust it produces for different applications? Take the GE CF34 for example where there is a 10780lb difference between the thrust ...
6
votes
3answers
5k views

How does the line of thrust affect longitudinal stability?

I’ve been studying Pilots Handbook of Aeronautical Knowledge FAA-H-8083-25B and on p 5-17 they talk about thrust line and stability. Can someone explain why the moment changes when thrust is applied? ...
5
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2answers
929 views

Flex temperature isn't actually “fooling” the FADEC, right?

I'll be using Airbus terminology here because that's what I know, but I guess the concepts are universally applicable. The way I understand flex temperature is: It's a user interface for pilots to ...
5
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1answer
607 views

Does a turboshaft's exhaust provide any thrust?

See the below figure. Does the exhaust gas coming out through the nozzle have any force? If the exhaust gas has force then how is it controlled by the helicopter?
5
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2answers
2k 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, ...
5
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3answers
237 views

Can Flex thrust be lower than climb thrust?

Let's restrict this question to airliners with 2 jet engines. For the remaining of the question, I'll use the term flex to designate reduced take off thrust as I'm more familiar with airbus's systems....
5
votes
2answers
201 views

Do surfaces ahead of propellers decrease thrust?

I have had this question for ages, nearly impossible to find anything on the web. My experiments confused me even further! Its concerning the blockage effects of surfaces ahead of a propeller. For ...
5
votes
1answer
6k views

How to calculate required thrust for take-off knowing gross weight and L/D?

I know that many variables play into the required thrust for a take-off and for climb. Most of those specs boil down to a targeted gross weight, wing loading and L/D ratio. Intended flying speed range ...
5
votes
1answer
333 views

Why does a subsonic nacelle inlet have a throat before the diverging section?

Aircraft propulsion 2nd edition by SAEED FAROKHI" p.340 Aircraft propulsion 2nd edition by SAEED FAROKHI" p.123 As we can see from the image, the nacelle slightly converges towards a throat, before ...
4
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5answers
846 views

How do thrust reversers in high-bypass turbofan engines counteract initial thrust?

I've been searching the internet for awhile and haven't really come across a good answer for this question. So: I have a basic understanding of the principles of flight (thrust, lift, drag, etc). But ...
4
votes
1answer
4k views

Is it best to use a thick airfoil or an undercambered airfoil for slow speed flight?

The more the thickness,the more the frontal resistance,hence the more the drag a thick airfoil will produce. Under cambered can help increase lift without increasing the airfoil thickness , therefore ...
4
votes
2answers
216 views

Jet engine throttle-down time

Apparently airline jet engines lose ~80% of their thrust within 1 second after fuel is cut. However this seems to conflict with long throttle-down times noted in another question. This lead to a ...
4
votes
1answer
787 views

Does the P&W F100 turbofan engine of the F-16 really produce this much power?

I've been trying to calculate the power a P&W F100 engine on a F-16 is producing using some of the available data on thrust and velocity and I ended up with a number that I want to confirm. Here's ...
3
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2answers
237 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,...
3
votes
3answers
94 views

Can briefly explain the principle behind the inversion on this power required curve?

I’ve noticed on several graphs in the “Advanced Pilot’s Flight Manual”, that power available is lower for any given speed at 10,000 feet as compared to sea level flight. The power required curves ...
3
votes
1answer
173 views

Why does the thrust limit page display the thrust in percentage (« % ») and not in pound-force?

When the pilot sets the takeoff engines thrust on the Flight Management thrust limit page that displays on the CDU (or MCDU) interface, the selection will finally show as a percentage. The direct ...
3
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2answers
2k views

How to realistically model propeller static thrust?

I am graphing static thrust vs prop diameter for a 600 kW motor and a prop diameter up to 5 m. I have seen the post 'What is the equation for calculating static thrust?' and using its formula and ...
3
votes
3answers
261 views

How does the power distribution change for a turbofan engine from being stationary to going at full speed?

I have found out that a turbofan engine of say an F-16 is producing zero power when stationary since $Power = Thrust × Velocity$. But assuming that the engine is producing the same thrust, it appears ...
3
votes
1answer
302 views

Can a Bombardier CRJ derate the takeoff thrust?

I have recently been flying a Bombardier CRJ 700 in a simulator and wondered how to derate the engines for takeoff. I know how the takeoff thrust derating is selected in Airbus and modern Boeing ...
3
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1answer
343 views

On a ducted propeller, how does duct length affect thrust?

So if we are looking at an aircraft with a ducted propeller (or a high bypass turbofan engine), does it matter how long the duct is? As an extreme example, would having a duct that extends 100 feet ...
3
votes
2answers
146 views

How do turbofan internals handle the load from the thrust?

To my understanding, turbofan engines get the majority of their thrust from the fan in front of the engine, up to around 70-80% while the core flow generates around 20-30%. Forward movement is ...
2
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2answers
2k views

Pros and cons of a pull-push propeller configuration [closed]

What are the pros and cons of a pull push propeller in comparison to a counter rotating propeller?
2
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2answers
231 views

Is it true that high-bypass engines are inherently inefficient at higher speeds?

Power consumption=Kinetic energy=$1/2mv^2$. Thrust=momentum change=$mv$. I keep being told that aircraft engines are most efficient when their exhaust velocity closely matches the freestream. The ...
2
votes
2answers
117 views

Is this plasma-thruster experiment actually measuring thrust? [closed]

This experiment, which is being presented as an initial exploration of the feasibility of using microwave-generated plasmas in a sort of electic jet engine, has been attracting some attention in the ...
2
votes
1answer
121 views

How much the Concorde secondary nozzle contribute to thrust?

Does anybody knows how much did secondary nozzles bucket type on the Concorde's engines contributed to the increase of thrust during take of and sub-sonic flight? This is picture of the nozzles and ...
2
votes
1answer
217 views

How can I calculate the relationship between propeller pitch and thrust?

I am trying to design a WWI propeller so I started calculating. The propeller comes with a specified pitch of 1.75m. The engine is supposed to run at around 1900 rpm and 147kW. These are most likely ...
2
votes
1answer
173 views

why some airplanes have their exhaust gases vectored above the wing?

I was looking at images of the SkyCourier shown below and i have noticed the asymmetrical exhaust pipes in both engines (one pointing up and one is straight), doing my research on the internet, i ...
2
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2answers
3k views

Why does the diffuser section generate thrust in a jet engine?

I am studying the thrust distribution of jet engines. But I'm now a bit confused. In Rolls-Royce's "The Jet Engine" book, http://aeromodelbasic.blogspot.com/2012/05/thrust-distribution-distribution-...
2
votes
2answers
318 views

What's the thrust coefficient for a convergent nozzle?

As you know, the Ideal Thrust Coefficient of convergent-divergent nozzle is calculated using this equation: But what about a convegent nozzle? Is there any equation to calculate the Ideal Thrust ...
2
votes
1answer
135 views

Which is better: a rotor / prop followed by a stator, or contra rotating rotors / props?

It is all in the title. I'm interested in power absorbed/used for a given thrust, or thrust generated for a given power (same diameters of course). Just thrust and power. Ignore materials, electric ...
2
votes
0answers
192 views

Can the assumed temperature be lower than the flat rated temperature?

I was playing with reduced takeoff thrust in a Boeing 737-800 simulator yesterday and was surprised that I could enter assumed temperatures below the flat rated temperature of the engines. The ...
2
votes
1answer
152 views

How to design a near vertical take off airplane?

How to design a near vertical take off airplane, conceptually? Say I have an airplane, similar to a Zenith 701. Say that it has a stall speed of 50 mph and a wing area of 60 sq ft, and it weighs ...
1
vote
1answer
212 views

Can the maximum thrust of a turbofan engine be estimated by its intake diameter?

I have no clue in aeronautics. How to estimate maximum thrust (at any rated condition, such as altitude, speed, rotation velocity- any given condition) by intake diameter?
1
vote
1answer
1k views

How do I determine the engine thrust required to give a specific climb rate?

New pilot here and I am playing around with a flight simulator game for the B737-800. I need some help understanding where/how one can find out if one has enough engine thrust (%N1) to meet a required ...
1
vote
1answer
143 views

Why don't we see diverging nozzles or diffusers?

When it comes to fully subsonic propulsion, all outlets are converging nozzles (I did say fully subsonic so no converging diverging). From what I understand, they are flow regulating devices (changing ...
1
vote
2answers
356 views

Mach Factor - Factor increase of thrust due to the ram effect

In the book of Corke, Chapter 7 about engine selection, he speaks about the Mach factor which is a factor larger than 1 in supersonic to take into account the ram effect. In his case study he takes 2,...
1
vote
1answer
146 views

What is the thrust balance between compressor and exhaust nozzle for a turbojet engine?

I had this question asked in university and the teacher was unable to provide more than a theoretical estimate. The ratio I was given was 15/85. Obviously in the case of a turbofan this ratio ...