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# Questions tagged [thrust]

Questions about the propulsive force of a powered aircraft.

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### 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 ...
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### Why limit the bank angle to 10° when passing through FL300 on a B737-800?

When passing thought FL300, we are instructed to set the bank angle limiter on the MCP to 10°. I know one of the reasons for this is that we are thrust limited so maneuver capability decreases. Are ...
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1 vote
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### Is there any equation on propeller thrust that takes into account the number of blades [duplicate]

I had a look at both What is the equation for calculating static thrust? and Is there any equation to bind velocity, thrust and power? However, it does not mention how much would the thrust be ...
4k 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 ...
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### How does landing gear affect thrust on a light twin-engine airplane?

I'm working on my commercial multiengine rating. And I got this question from my examiner, and I answered: landing gear produces penalty drag, so it decreases thrust. But the examiner says this isn'...
318 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 ...
241 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 ...
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### 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 ...
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1 vote
494 views

### How to measure thrust produced from combustion chamber of Gas Turbine Engine?

I'm conduction a scale model experiment of thrust production in combustion chamber by using different types of fuel source. Comparing the thrust produced by using hydrogen gas, kerosene and petrol. ...
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1 vote
669 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?
420 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 ...
868 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 ...
520 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 ...
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### 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 ...
1 vote
142 views

### Compute Thrust from RPM and Induced Velocity

I'm attempting to calculate the difference in thrust in a secondary propeller operating in the wake behind a primary propeller, in the context of a trailing quad-copter following a leading quad-copter ...
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### 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 ...
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### Which propeller configuration is the one that generates the least turbulent flow in a wind tunnel?

I looked at the post here but still have some questions Why are push-propellers so rare, yet they are still around? This is along the same idea but the answers are not too helpful either. Pros and ...
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### 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 ...
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### How to calculate power required to drive an isolated fan of a TurboFan engine?

If I isolate the fan from a TurboFan jet engine (specifically GE90) and power it electrically with a motor, how much power is required for the electrical source to drive the fan to give the same ...
705 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 ...
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1 vote
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### 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 ...
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### 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? ...
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### What are the Boeing 777 thrust calculations? [closed]

Can someone show typical calculations for a Boeing 777 jet engine for the following criteria: Take off thrust of the engine at 170 mph take off speed and 45 degrees F Cruising thrust required at 500 ...
335 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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### How does radius of a propeller affect its performance?

Let's say we have a conventional two-bladed fixed-pitch propeller. All things being equal, would the same propeller but with half the size -- 50% radius, have 50% of the performance of the first ...
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### 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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### 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 ...
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### 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 ...
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### 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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### 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 ...
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### 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-...
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### 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 ...
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### What creates most drag during flight: fuselage or wings?

From pic 1, I know the drag line is below the thrust line, but I am puzzled about where the drag line is in pic 2? Secondly, what creates most of the drag in flight, is it the fuselage or the wings?
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### How much air does a GE90 ingest at sea level and at cruise level per meter?

I just wanted to know how much air PER METER a GE90 turbofan engine sucks in considering the same thrust output at different altitudes to better understand how the engine can travel further while ...
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### Is it possible to fly 'in neutral'?

Sometimes, when I am driving, I knock the car 'out of gear' or set the stick to the neutral position, to save fuel. This is most easily done when cruising down a hill or when you have some good speed ...
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1 vote
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### 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,...
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### 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?
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### 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 ...
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### 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 ...
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### 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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### 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 (...
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