What is Thrust: Definition and 344 Discussions

Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that system.
The force applied on a surface in a direction perpendicular or normal to the surface is also called thrust. Force, and thus thrust, is measured using the International System of Units (SI) in newtons (symbol: N), and represents the amount needed to accelerate 1 kilogram of mass at the rate of 1 meter per second per second. In mechanical engineering, force orthogonal to the main load (such as in parallel helical gears) is referred to as static thrust.

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  1. A

    Help calculating static thrust for a given engine and propeller

    Hi guys, I need to be able to estimate the thrust that a turboprop propeller produces at sea level static. Say I have an 1100 hp pt6a engine and a 80 percent efficient propeller. I have seen formulas that calculate the thrust but you need to be moving. I want to know the static (your airplane...
  2. G

    Creating a 40-Pound Thrust Pulsejet: Design, Testing, and Fueling

    Hello everyone this is the biggest engine i have ever made. You could see at the end i ran away leaving the cylinder and the camera woman ran away. Really i didnt expect so much sound. Used one pair of injectors and fueled only two intakes. Actually i closed one of the intakes because my tank...
  3. narrator

    Bottle Rocket Thrust for Elementary Numeracy?

    Hi, I'm wanting to do a fun numeracy exercise for my students. I'm planning to have them construct bottle rockets, take measurements and then calculate/graph how high their rockets get using simple triangulation. From that, I was hoping to get them to calculate what the thrust was of their...
  4. R

    Upside down motor mount and Thrust bearing

    I wanted to use a disco ball motor to rotate an object weighing approximately 125lbs. The motor was rated for 25 lbs. Motors rated for higher weights had much higher costs, beyond what would be practical. It was suggested that using an arrangment like the one described in the attached pdf would...
  5. S

    Thrust to Power Ratios for Modern Propulsion Systems

    Does anybody know some ballpark figures for thrust to power, Newtons per watt, ratios for modern propulsion systems, mechanical drive train ie cars trucks, propeller driven craft, boats planes, and rockets. I've found one reference that states the F/P ratio for a DC-9 jet engine is 0.016 N /...
  6. S

    Calculating Thrust and Resistance

    Homework Statement i built a boat for physics class with an electric motor. we are asked to calculate the thrust of the motor and the resistance of the hull using Newton's second law of motion. i conducted an experiment (to collect data in order to find resistance) that required a string...
  7. O

    Maximum thrust - theory of rocket propulsion

    Hello all, Just wondering if anyone can give me some guidance on this: the problem is an apparent contradiction I've stumbled upon. Some sources (e.g. www.braeunig.us) suggest that maximum thrust is achieved when Pe=Pamb (i.e. exhaust pressure = ambient pressure)l whereas others say that...
  8. A

    How exactly does a gas turbine engine produce thrust?

    Hi I have been trying to figure out the force experienced by individual components of a gas turbine engine. Generally, the thrust of the engine is defined / calculated as the change in the momentum of the fluid. Usual formula is mass flow X (C_jet - C_intake) + the pressure difference in...
  9. A

    Connecting motor shaft to thrust bearing

    Hi there - I built a small electronic turntable with the following components: 1- Arduino 2- Sparkfun easy stepper driver 3- Stepper motor 4- Servocity set screw hub. 5- Thrust bearing from mcmaster-carr (square turntable, found here http://www.mcmaster.com/#swivel-plates/=eltxix) 6-...
  10. P

    Calculation of lift and thrust

    I need some information and guidance on how to calculate net lift and thrust produced by wings of an MAV(micro air vehicle) which are flapping and active pitching. I know only about one method which is the Blade Element Analysis, but it is just an approximation and doesn't accounts for...
  11. S

    Thrust and weight verse g force upon object

    Thrust and Mass verses g force upon object Have designed a solid fuel and liqiud fueled rocket engine. Not great in mathmatics! Have total weight of fuel engine and power supply at 2.3 pounds Have an engine that burns for 3.3 seconds and produces 47 pounds thrust for 2.1 seconds. If I...
  12. T

    Calculating motor/calculator thrust

    Hi I am building a quadro-copter, and I'm curious to know how i can calculate the thrust generated by a motor/propeller combo. The motors are brushless electric motors for which i know the max RPM. The propellers are two bladed for which the diameter and pitch are known. Is there a simple...
  13. D

    Thrust of a Rocket: Calculating Force

    Homework Statement [PLAIN]http://img714.imageshack.us/img714/8184/rocketj.png I am not sure if the problem has enough information to find. However, i tried some of the works. g=10m/s2( i use gravity as 10 .) Homework Equations No idea... The Attempt at a Solution I am...
  14. R

    Discover the Formula for Calculating Static Thrust and RPM Ratio

    i want to know the relation between thrust/rpm. what is the formula to calculate it?
  15. R

    How Is Static Thrust Calculated for Quad Rotor UAVs?

    I want to make a quad rotor UAV. i studied a lot but i did not find how static thrust is being calculated. In physics forum i have found an equation which is given below but i can not understand what is 'frac' and 'rho'. Equation is: T=\frac{c_T}{c_p}\frac{P}{nD} Where: P = power (ft-lb/s...
  16. D

    Calculating Constant Thrust for Jet-Powered Drag Car in Vehicle Dynamics Class

    I'm a math guy taking engineering classes more or less for fun, so some of the stuff I should know I probably missed in a basic dynamics class. I feel really dumb that I can't figure this out. I'm in a vehicle dynamics class and I have to calculate the constant thrust T for the following...
  17. A

    How to interper thrust of the rocket

    For example then talking about the rocket the trust is: F_thrust = u*dm/dt where u is speed of the gases relative to the rocket, and dm/dt rate of change of ejected mass of gases. Now if the rocket is being launched vertically so force of gravity acts upon it and: F_net = F_thrust -...
  18. N

    Quad Thrust Fuel Transit Drive

    First of all this is not a perpetual motion machine and is not the previous U Reusable Fuel Transit Drive I designed earlier. This type of transit drive, which doesn't reuse fuel, works in theory by having two combustion chambers and their respective exhaust nozzles positioned parallel to the...
  19. C

    A different approach towards Thrust Engines

    Is there any Advanced concepts , theories out there; Instead of the combustion. We're not limited ; direct conversion of electricity to thrust is here, so if you have any ideas leave it here, *Electricity-conversion- microwave- to thrust (radiation pressure difference) *Electricity-conversion-...
  20. M

    Horizontal water rocket thrust calculations - HELP

    Horizontal water rocket thrust calculations - HELP! Hi All, I want to accelerate a 90kg body at a rate of 2 m/s2 for a period of 1 second using thrust developed from a number of water bottle rocket jets. Based on the drag coeff calculated I believe I need to develop 190N of force. A...
  21. W

    Regarding angular momentum axial thrust force etc. space stations

    Disclaimer: I'm not a physicist nor do I know calculus, but I'd appreciate a little guidance with a concept I've been thinking about. I know one would usually pay for this kind of advice, but since it's just for entertainment, I'm not asking for any equations to be solved, unless you're in the...
  22. N

    Looking for specific data about thrust, hydrogen, and celestial bodies

    first off, thanks to any that respond w useful info :) the end answer i need to find on the first topic is how many atoms of hydrogen are required to propel a mass of "x" at an acceleration of 1g in space (assuming no gravitic influence) but i would settle for how to figure out what the fuel...
  23. K

    How do you calculate the enrgy required to maintain a given thrust?

    Homework Statement I would like to be able to calculate the energy use per second, to maintain a rocket of given mass, at zero velocity, i.e. hovering, at, say, sea level. Homework Equations I have Thrust = Force times velocity, but can't work out the energy due to the velocity of the...
  24. A

    Railcar Operating Loads: Cargo Side Thrust Forces

    Dear native English-speaking professionals! I am making up an info table concerning railcar operating loads, and I’m a bit stuck with one term - I’m not sure if it sounds comprehensible enough to an Enflish speaking reader. Here is the part I’m struggling over: "Load description: cargo...
  25. S

    Can sound from any source create thrust?

    Can sound from any source create thrust?? hi there, since I'm new to this forum, i don't know whether this the place to put up a question like this...! if I'm wrong my sincere apologies let me head to the topic now... i wanted to whether the sound waves created form any source can...
  26. A

    CFM conversion to thrust Help

    Hey guys! I'm new to the forums here and was after some help for something that I am currently working on. I need help converting cfm to thrust, i have found the formula though i can't get my head around it. Here it is: CFM = Cubic Feet per Minute = Volumetric Flow Rate Mass Flow Rate =...
  27. T

    Uncovering the Mechanics of Thrust in a Turbojet Engine

    Hi! I have a question about how thrust is made from a turbojet engine. The most common explanation goes something like "As the fluid gets accelerated there is a net force". I don't think this explanation is either good nor rigorous. The force that accelerates the fluid is, of course, the...
  28. B

    Kinetic Friction and skis thrust

    Homework Statement Sam, whose mass is 71.0 kg , takes off down a 51.0 m high, 11.0 degree slope on his jet-powered skis. The skis have a thrust of 210 N . Sam's speed at the bottom is 41.0 m/s . Homework Equations I'm not sure which equation(s) to use. Net Force= ma and some kinematic...
  29. R

    My logic vs. Calculated Results: Plots of Thrust, RPM, Spillage

    I finally figured out what my previous problem was in my last question posted. I have obtained the plots required but I am a little confused about the trends. (1) At low Mach, should my thrust be lower compared to the value at a higher Mach? (2) Should the RPM decrease with an increase in...
  30. A

    Thrust to weight ratio and lift

    hello a plane would need a thrust to weight ratio of 1 of fly straight up without losing speed but how can a plane in level flight maintain its altitude with <1 TWR since to maintain a level flight you need to have lift = weight so your engine needs to supply enough power to generate...
  31. C

    Does Higher Specific Impulse Mean Greater Distance Traveled in Space Probes?

    Imagine there are 2 space-probes in space. Both of them start their engines in the same time. The first space-probe has a very low level of thrust but a very high specific impulse. The second space probe has a very high thrust but a very low specific impulse. Both of them have an equal amount...
  32. S

    Can someone confirm this power to thrust relation?

    This is not my homework this is just a random thought. Say you have a 1 kg helicopter hovering in midair. The question is, given perfect efficiency, how much power is it using to hover? My approach is to think of the given information first. We know that g= 9.8. So you have a 1 kg mass that...
  33. G

    Interested in Building a Thermojet Engine for Your Next Project?

    hello guys iam ganesh..iam a mechanical engg student and iam new to this forum and this is my first post here.. these plans are uploaded by eric and technical help given by metiz..take a look at it..
  34. R

    Calculation of Thrust and Wing Area

    I posted I question in regards to shock angles on this very same problem earlier but now I have a new problem. I need to calculate the heat rate required in the combuster in order to ensure that the vehicle will cruise (delta z=0). I also need to find the mass flow rate of the fuel. h for the...
  35. J

    Car with mass of 1500kg and thrust of 4000N

    Sorry; this is like soooooooo hard Homework Statement A car with a mass of 1500 kg has en engine which can produce 4000N of thrust. Assume that the air resistance on the car is a constant 500N. If the car starts from rest, how fast will it be moving after 10 seconds. Homework Equations...
  36. A

    Helicopter Thrust Calculation | Fuel Mass Included

    can anyone help me out to calculate the thrust when helicopter takes off with mass of fuel?
  37. E

    Calculating Thrust in Propeller Engines: Can Anyone Help?

    Can anyone help me? I'm doing a question on aircraft propulsion technology and I'm stuck. The question is: 'If the mass of air through a propeller is 1000 Kg/s, the aircraft's velocity is 100 m/s and the slipstream velocity is 120 m/s, calculate the thrust? Attempt at answer...
  38. C

    Acceleration, thrust, and propellant velocity?

    Homework Statement What is the average acceleration until burnout of a spacecraft engine creating 53.2MN of thrust with a propellant velocity of 4.78km/s? The initial mass is 2.12x10^6 kg and final ,*** is 7.04x10^4. Homework Equations 0 = m(subscript_f)v(_f) + m(_r)v(_r) The...
  39. S

    Conceptual Problem with Thrust

    Hi everyone, as you can tell from the title, I'm having some trouble understanding thrust. Here's what my textbook says: "m(dv/dt) = -u(dm/dt) [where u is the speed of the exhaust relative to the rocket and dm/dt is negative] Now dv/dt is the acceleration of the rocket, so the left side of...
  40. N

    Finding required thrust power for jet engine aircraft.

    Homework Statement I need to find required thrust power for lockeed s3a. I know Thrust=Drag in horizontal flight. For take off, need to use the take off angle, split the Weight (G) into 2 components using the takeoff angle... Same for landing. Given: G=19278kg ---> 19278*9.81=189,1kN...
  41. A

    Altitude of rocket with 2E5 N thrust

    Homework Statement A polaris missile has a mass of 1.4 x 10^4 kg and its engine has a thrust of 2 x 10^5 N. If its engines fire in the vertical direction for 1 min starting from rest, to what vertical height would it rise in the absence of air resistance? Homework Equations F=ma W=mg...
  42. X

    Maximizing Rocket Thrust: Doubling Velocity and Tripling Fuel Burn Rate

    If a rocket doubles it's relative exhaust velocity while do tripling the "burn rate" of fuel, the thrust... A) doubles B) Triples C) increases 5 times D) increases 6 times E) none of the above! Thrust=dv/dt=lVe(dM/dt)l I just plugged in 2 for V and 3 for dM and 1 for dt giving me 6
  43. F

    Calculating Turbojet Thrust with Exhaust Deflection

    Homework Statement The idling engines of a landing turbojet produce forward thrust when operating in a normal manner, but they can produce reverse thrust if the jet is properly deflected. Suppose that while the aircraft rolls down the runway at 150 km/h, the idling engine consumes air at 50...
  44. E

    Rotation and Angular Momentum: Solving for thrust of a rocket

    1. A solid bar of length L = 0.5m and with W = 0.1m weighs 2kg. It also has two constant-thrust rockets attached on either end. Each rocket is small enough to be considered a point mass of 0.25kg. If the bar is initially at rest and in two seconds after the rockets are fired it achieves a...
  45. C

    How to calculate laser thrust?

    Greetings, I want build an interstellar probe. Given the power of the laser beam and the mass of a mirrored object a laser is shining on, how does one calculate the thrust or acceleration? Thanks
  46. A

    Calculating Thrust & Initial Acceleration of Saturn V

    Homework Statement The first stage of a Saturn V space vehicle consumes fuel at the rate of 47400 kg/s, with an exhaust speed of 2820 m/s. The acceleration of gravity is 9.8 m/s2 . Calculate the thrust produced by these en- gines. Answer in units of N. (part 2 of 2) 10.0 points Note...
  47. T

    How much lift thrust would a 252 CFM 120mm fan provide?

    Hey guys, I'm a college student looking to build a miniature RC plane based off this picture here: [PLAIN]http://www.kruxor.com/wp-content/uploads/2010/07/SC2_Banshee_Art.jpg As you can see, the thrust needed to lift and mobilize the plane is provided by the two fans on the sides (does this...
  48. D

    Why thrust decreases then increases with velocity?

    Hello, I was trying to find out why net thrust decreases then increases with velocity. I recall there is pressure and momentum thrust, however I can not recall why one of them falls away and the other increases. Is momentum thrust the one that picks up as the mass flow increases with...
  49. V

    How to find rocket thrust, force impulse of energy method?

    Homework Statement The 3rd and 4th stages of a rocket, mass 40kg and 60kg respectively, coast in space with a velocity of 15,000kmh when the 4th stage ignites, with thrust T and causes separation. If the velocity of the 4th stage is 10m/s greater than the 3rd stage at the end of the 0.5...
  50. M

    Calculating Propeller Thrust Using Given Data

    i need to calculate thrust produced by a propeller whilst flying, using the data show below. all equations i have come across require the propeller induced velocity which is not given. things i know; -propeller efficiency -indicated and true airspeed of aircraft -temp. and pressure at...
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