Questions tagged [thrust]
Questions about the propulsive force of a powered aircraft.
66
questions
2
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1answer
124 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 ...
0
votes
1answer
73 views
What is the takeoff thrust of a CFM56 engine?
So, to be more clear I currently have an assignment about the Boeing 737-800.
I have to find out the total takeoff distance of the aircraft. I'm using Anderson's book " Aircraft Performance and ...
0
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2answers
118 views
How to increase payload capacity of plane?
Keeping thrust, wing span, weight (of plane) constant, can we increase the payload capacity (nearly 50% more)? Adding payload to plane, it decreases thrust/weight ratio, how does it affect the control ...
2
votes
1answer
155 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 ...
3
votes
2answers
127 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 ...
5
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3answers
210 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....
0
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0answers
73 views
GE90-115b turbine horsepower
The GE90-115b is rated at 513 kN maximum thrust and is often said to have 110,000 shaft horsepower, but I have yet to find any document or specification that backs the claim on horsepower figure.
A ...
1
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1answer
375 views
Are there any airliners capable of vertical climb with engine thrust only by pointing the nose up?
So, sort of inspired by this question, I was wondering if there were any passenger airliners with enough thrust to fly straight up, supported purely through the thrust of their engines rather than the ...
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3answers
319 views
How can Lift = Weight; if airliners fly with Thrust-to-Weight ratios = 0.3? [duplicate]
Question:
I'd appreciate it a lot if anyone could explain how the wings can generate lift that is 3.3x more than engine thrust? Is there any experimental proof that this? Or is the assumption that ...
1
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1answer
135 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 ...
0
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2answers
113 views
What are the criteria for conceptual design of thrust reverser in the use of braking?
I'm doing a project: Study of aircraft braking and pre-sizing of associated subsystems. We tried to find criteria for the reverser in the braking phase. I read FAR 25, but I did not find it.
Is there ...
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 ...
1
vote
1answer
161 views
Turboprop vs Turbofan: How to compare Specific Fuel Consumption
I understand that Turboprop engines have a lower Specific Fuel Consumption (SFC) than Turbofan engines, on average. I want to see this for myself by analysis, ideally by comparing values of SFC for ...
1
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1answer
84 views
Can someone please tell me all the units for the propeller thrust equations?
This answer is excellent:-
Is there any equation to bind velocity, thrust and power?
except that it is (in practice) unusable, since all the units are missing.
I'm guessing we use meters for length ...
2
votes
1answer
118 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 ...
8
votes
3answers
564 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?
2
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0answers
149 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 ...
1
vote
1answer
121 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 ...
25
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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 ...
5
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2answers
194 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 ...
9
votes
2answers
634 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 ...
5
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1answer
536 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?
3
votes
1answer
236 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 ...
2
votes
1answer
146 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 ...
0
votes
1answer
264 views
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 ...
1
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1answer
96 views
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 ...
7
votes
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 ...
0
votes
1answer
124 views
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'...
9
votes
2answers
218 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 ...
3
votes
1answer
169 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 ...
9
votes
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 ...
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2answers
259 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.
...
1
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1answer
185 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?
4
votes
2answers
199 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 ...
5
votes
1answer
259 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 ...
3
votes
3answers
218 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 ...
4
votes
1answer
669 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 ...
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0answers
81 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 ...
16
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10answers
6k 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 ...
-1
votes
1answer
302 views
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 ...
16
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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 ...
0
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2answers
235 views
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 ...
2
votes
2answers
279 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 ...
1
vote
1answer
937 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 ...
5
votes
2answers
4k 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?
...
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1answer
740 views
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 ...
3
votes
2answers
226 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,...
0
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2answers
318 views
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 ...
5
votes
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, ...
3
votes
1answer
323 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 ...
