Skip to main content

Questions tagged [thrust]

Questions about the propulsive force of a powered aircraft.

Filter by
Sorted by
Tagged with
27 votes
2 answers
5k 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 ...
jayS's user avatar
  • 918
26 votes
1 answer
25k 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 ...
magicmq's user avatar
  • 363
19 votes
7 answers
9k views

Why do pilots slowly give the plane more thrust during takeoff?

I have mostly seen pilots slowly pushing the throttle to toga during takeoff. But why? Why don't they just directly put the throttle to toga? Wouldn't that save runway length?
Ishaan Manish's user avatar
17 votes
7 answers
12k 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 ...
user avatar
17 votes
2 answers
10k 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 ...
user7645895's user avatar
16 votes
9 answers
8k 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 ...
cat's user avatar
  • 402
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
13 votes
2 answers
11k 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 (...
Darjan's user avatar
  • 1,157
11 votes
4 answers
2k views

If the pitch of a bypass fan blade in a turbofan is fixed how does it manage to provide thrust over such a large speed range?

A fixed pitch propeller is only good for aircraft that do around 100kts because the angle of attack on the propeller decreases as the forward airspeed of the aircraft increases, limiting the thrust ...
Ian's user avatar
  • 111
10 votes
3 answers
2k views

What exactly is the pressure thrust component and why does it exist?

I'm teaching PowerPlants on a ATPL theory course and honestly have some trouble wrapping my head around this one: Most literature describes the term "pressure thrust" – as opposed to "...
A.Pilot's user avatar
  • 169
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
9 votes
3 answers
6k 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 ...
Yakup şeker's user avatar
9 votes
5 answers
3k views

Why is the Cirrus Vision SF50's turbine angle so acute?

I saw a Cirrus Jet on the ramp and was struck by how much its engine points upwards. I can't recall having seen this kind of positive thrust angle, and so wondered what the explanation was. A picture ...
Kenn Sebesta's user avatar
  • 5,142
9 votes
1 answer
1k views

How can a turbofan's fan generate thrust in cruising flight if air is being slowed down?

High bypass turbofans in airliners generate most of their thrust from their fans, not their "cores". However, at cruise they are actually spilling some air past the intake rather than ...
Kevin Kostlan's user avatar
9 votes
2 answers
1k 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 ...
PerlDuck's user avatar
  • 3,186
9 votes
4 answers
6k 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 ...
Jono 's user avatar
  • 608
9 votes
3 answers
6k 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?
Nirmal's user avatar
  • 319
9 votes
4 answers
14k 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? ...
JScarry's user avatar
  • 7,464
9 votes
2 answers
335 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 ...
user avatar
8 votes
3 answers
2k views

How do airplanes with thrust lines above CG still fly without a down pitch moment?

Mainly the Icon A5. I remember trying to make an RC aircraft similar to it, but the moment i'd spin up the motors the aircraft would understandably pitch down. i couldnt fly it at all. So how do these ...
Tarik Agcayazi's user avatar
8 votes
3 answers
2k views

What is the general mathematical relationship between increasing an airplane's weight and the needed thrust to fly?

I understand that increasing an aircraft's weight without changing any other properties means that its takeoff, stall and cruising speeds all increase since you need to generate additional lift. So ...
J-bob's user avatar
  • 183
7 votes
2 answers
3k views

Why do turboprops not have a thrust value in the specifications? [duplicate]

When looking through aircraft engine specifications, turbofans always provide a thrust value, e.g. in JT8D engine: https://prattwhitney.com/products-and-services/products/commercial-engines/jt8d In ...
Msegade's user avatar
  • 173
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
2 answers
281 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 ...
J.FLLT's user avatar
  • 1,231
6 votes
4 answers
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 ...
Nick's user avatar
  • 77
6 votes
5 answers
3k views

What determines maximum speed of a propeller aircraft - Thrust or Power?

I'm reviewing training materials1 for straight and level flight. The content focuses on drag types and explains that the required thrust curve is equivalent to the total drag curve. It then introduces ...
Crabsticks's user avatar
6 votes
2 answers
3k 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 ...
trehn's user avatar
  • 163
6 votes
1 answer
2k views

Why is thrust said to be constant over speed for a jet engine?

I'm just interested in some basic facts regarding flight. On reading the rather "low level" book "Understanding Flight, David F. Anderson, Scott Eberhardt), I recently came up to the ...
MichaelW's user avatar
  • 251
6 votes
4 answers
1k 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....
Manu H's user avatar
  • 16.5k
6 votes
2 answers
5k 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-...
Jono's user avatar
  • 161
6 votes
3 answers
603 views

Why is thrust (in a high bypass turbofan for e.g.) non-linear with respect to N1?

I've been studying jet engines for a short while now and I think I have a pretty decent understanding of how thrust is generated, but one thing I'm struggling a bit with is how thrust varies across ...
jpsharif's user avatar
  • 119
6 votes
1 answer
12k 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 ...
VladBlanshey's user avatar
6 votes
1 answer
1k 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 ...
user avatar
5 votes
4 answers
1k views

How can the wing generate more lift than the thrust? [duplicate]

I recently checked about the max takeoff weight of an A380 and the thrust it can provide at TO/GA power and I was quite shocked by the results. The total thrust by the engines was only about 127000 ...
Sambhav Khandelwal's user avatar
5 votes
2 answers
689 views

If a jetliner is giving TOGA thrust but never releases the (parking) brake, will the brakes heat up?

From my - admittedly - limited knowledge of physics, the energy generated from the engines needs to go somewhere; will it go into the brakes or does it just dissipate into the air?
Nico's user avatar
  • 53
5 votes
1 answer
2k 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?
Santhosh Kumar's user avatar
5 votes
1 answer
999 views

Is Flight Idle a constant?

Is "Flight Idle" for a jet engine a constant N1% value or does it vary with Altitude, and OAT?
Stamatis Vellis's user avatar
5 votes
2 answers
428 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 ...
Eric's user avatar
  • 61
4 votes
7 answers
3k views

How does a fan in a turbofan engine suck air in?

I watched lots of video related to sucking process of a fan in a turbofan engine, but I'm confused at a point. In this link and many videos like this, I found the fan'...
Jawel7's user avatar
  • 244
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
4 votes
5 answers
2k 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 ...
Hot_Doug's user avatar
4 votes
2 answers
790 views

How to calculate the efficiency of a rubber powered propeller

I made a simple test rig together with a stopwatch to measure the thrust (in grams) with respect to time of a rubber powered propeller. This enabled me to compare the performance of different ...
Adriel Mattheuz Estolano's user avatar
4 votes
2 answers
256 views

Using a spring balance to find static EDF Thrust

I have been attempting to measure the static thrust of my EDF with a spring balance. It is part of a group university project. The EDF specs are as follows: 90mm freewing 9 blade 1900 Kv thats rated ...
Johan M's user avatar
  • 69
4 votes
1 answer
2k 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 ...
Abanob Ebrahim's user avatar
4 votes
1 answer
9k 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 ...
David Teahay's user avatar
  • 2,885
4 votes
1 answer
558 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 ...
Ibrahim Jaafar's user avatar
4 votes
2 answers
531 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 ...
Christian Aichinger's user avatar
3 votes
6 answers
1k views

Why can't you have sail-powered airplanes?

So, sailing boats take the kinetic energy of a crosswind and turn it into thrust by using their sails as lifting surfaces, and the discussion I had in the comment section of this question made me ...
nick012000's user avatar
3 votes
1 answer
581 views

Is thrust larger than weight in a vertical climb?

Image source Very much related to the many questions and great answers to lift and weight in a climb - if an F-16 climbs vertically at a constant speed, is thrust greater than weight?
Koyovis's user avatar
  • 61.8k
3 votes
5 answers
6k views

What is the GE90-115b turbine power output in 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 ...
Erik's user avatar
  • 433