The power-to-weight ratio is a common expression used when discussing the relative power of an engine. Since most engines are attached to vehicles that move, the weight of the vehicle on which the engine is mounted must be included in the calculation of the power-to-weight ratio. The power-to-weight ratio is significant because it allows different vehicles to be compared, based on the relative power of each. The units can be converted easily once you find the conversion algorithms.

Conversion algorithms are available online. The power-to-weight ratio will reflect only the power-to-weight ratio of the engine alone if you do not find the net weight of the vehicle before calculating.

This article was written by the It Still Works team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information. To submit your questions or ideas, or to simply learn more about It Still Works, contact us. Items you will need Pencil Paper Calculator. Tips The units can be converted easily once you find the conversion algorithms. The completed power-to-weight ratio is expressed in the units you chose to calculate.

References AjDesigner. About the Author This article was written by the It Still Works team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information.Thrust-to-weight ratio is a dimensionless ratio of thrust to weight of a rocketjet enginepropeller engine, or a vehicle propelled by such an engine that indicates the performance of the engine or vehicle.

The instantaneous thrust-to-weight ratio of a vehicle varies continually during operation due to progressive consumption of fuel or propellant and in some cases a gravity gradient. The thrust-to-weight ratio based on initial thrust and weight is often published and used as a figure of merit for quantitative comparison of a vehicles initial performance.

The thrust-to-weight ratio can be calculated by dividing the thrust in SI units — in newtons by the weight in newtons of the engine or vehicle and is a dimensionless quantity. Note that the thrust can also be measured in pound-force lbf provided the weight is measured in pounds lb ; the division of these two values still gives the numerically correct thrust-to-weight ratio.

For valid comparison of the initial thrust-to-weight ratio of two or more engines or vehicles, thrust must be measured under controlled conditions. The thrust-to-weight ratio and wing loading are the two most important parameters in determining the performance of an aircraft. The thrust-to-weight ratio varies continually during a flight.

Thrust varies with throttle setting, airspeedaltitude and air temperature. Weight varies with fuel burn and payload changes.

The Aerodynamics of Flight

For aircraft, the quoted thrust-to-weight ratio is often the maximum static thrust at sea-level divided by the maximum takeoff weight. In cruising flight, the thrust-to-weight ratio of an aircraft is the inverse of the lift-to-drag ratio because thrust is the opposite of dragand weight is the opposite of lift.

For propeller-driven aircraft, the thrust-to-weight ratio can be calculated as follows: [6]. The thrust-to-weight ratio of a rocket, or rocket-propelled vehicle, is an indicator of its acceleration expressed in multiples of gravitational acceleration g. Rockets and rocket-propelled vehicles operate in a wide range of gravitational environments, including the weightless environment.

The thrust-to-weight ratio is usually calculated from initial gross weight at sea-level on earth [8] and is sometimes called Thrust-to-Earth-weight ratio. The thrust-to-weight ratio for a rocket varies as the propellant is burned. If the thrust is constant, then the maximum ratio maximum acceleration of the vehicle is achieved just before the propellant is fully consumed. Each rocket has a characteristic thrust-to-weight curve or acceleration curve, not just a scalar quantity.

The thrust-to-weight ratio of an engine exceeds that of the whole launch vehicle but is nonetheless useful because it determines the maximum acceleration that any vehicle using that engine could theoretically achieve with minimum propellant and structure attached. For a takeoff from the surface of the earth using thrust and no aerodynamic liftthe thrust-to-weight ratio for the whole vehicle must be more than one.

In general, the thrust-to-weight ratio is numerically equal to the g-force that the vehicle can generate. The thrust to weight ratio of rockets typically greatly exceeds that of airbreathing jet engines because the comparatively far greater density of rocket fuel eliminates the need for much engineering materials to pressurize it. Many factors affect a thrust-to-weight ratio.

How to Calculate Power-to-Weight Ratio

The instantaneous value typically varies over the flight with the variations of thrust due to speed and altitude along with the weight due to the remaining propellant and payload mass. The main factors include freestream air temperaturepressuredensityand composition.

Depending on the engine or vehicle under consideration, the actual performance will often be affected by buoyancy and local gravitational field strength. From Wikipedia, the free encyclopedia. Fielding, Introduction to Aircraft DesignSection 4. Fielding, Introduction to Aircraft DesignSection 3. The Drive. Retrieved The Internet Encyclopedia of Science.

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Aviation Stack Exchange is a question and answer site for aircraft pilots, mechanics, and enthusiasts. It only takes a minute to sign up. I know that many variables play into the required thrust for a take-off and for climb. Intended flying speed range is also known but probably not even needed for this estimate. Using these specs then I can roughly assume that many specs have been taken into account for a thrust calculations.

For ex. Based on above numbers how to make rough estimate of the minimal thrust required for a reasonably short take-off say within to 1,ft roll of runway?

Note: please keep in mind I am familiar with many other conditions and aircraft specs affecting the required thrust. Yet for years practical aircraft designers used very simple math approach to estimate needed thrust. I personally knew one of old generation designers who did this well in many of his successful designs using simple math dealing with few numbers he passed away years ago. Please share if you know the answer. This source has been really helpful for me in calculating takeoff time and takeoff distance.

In this method, the author uses thrust as an input to calculate takeoff distance, but obviously you could re-arrange the equations to calculate for thrust if you knew the other variables. You will likely need to know the static thrust zero speed thrust of your engine and then can calculate for thrust required at takeoff.

I would recommend putting the equations into an excel spreadsheet where you can then play with all the inputs until you reach a desired result. Hope this helps!

how to calculate thrust to weight ratio

Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Ask Question. Asked 1 year, 11 months ago.

What Is Thrust-To-Weight Ratio?

Active 3 months ago.This power-to-weight ratio calculator provides a quick and easy way to determine the power-to-weight ratio PWR of any vehicle. Car Weight: kg. Engine Power: W. Car Weight: lb.

Engine Power: hp. The power-to-weight ratio represents the ratio between a vehicle's power and its total weight. The higher the PWR, the faster the vehicle will accelerate.

It is for this reason that motorbikes accelerate quicker than most cars. They may not be as powerful but they are lightweight; as such, they are likely to be faster because they have a higher PWR. Let's say we have a vehicle that weighs pounds and has a horsepower hp of Its PWR will be as 0. It's very easy to calculate a power-to-weight ratio. Simply divide the power output of a vehicle by its weight. For example, if you have a car that weights pounds and has hp, the PWR will be as follows:.

The power-to-weight ratio calculator uses the following formulas to calculate the power-to-weight ratios:. You may also be interested in our Quarter Mile Calculator. You can calculate a PWR in four simple steps: 1.

Select the unit system you would like to use from the drop-down menu 2. Input the curb weight of the vehicle 3. Enter the engine's power 4. Car Weight: lb Engine Power: hp. What is the power-to-weight ratio? PWR calculations are commonly used to predict vehicle speed. Calculating PWR It's very easy to calculate a power-to-weight ratio. Currently 4. Join with us.Home Discussions Workshop Market Broadcasts.

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Last edited by Endevours ; 11 May, pm. Showing 1 - 8 of 8 comments. I have to say that this is kinda disappointing. Not much i thought one would need a website or app for. What it also does is exceptionally use of wrong terminology, which gets obvious with the above equation they use.

However the mass gets wrongly named "weight" as usual for so many people. Likewise it is kN and not kn which in the best case is knots and thus velocity. But going down that path, Kg is wrong too as there is no K prefix but only k and thus kg. I even wonder why the worst case scenarios got the wrong Kg when the wrongly named "weight" got the proper kg.

Anyhow, besides that, in case the author reads this, i would suggest to extend the form in such a way that the inputed values are somewhat preserved. After pressing "calculate", all that is known, if someone got a short term memory issue, is the number of thrusters but not the initial configuration of mass, gravity and thruster force. However the fundamental issue right there is the limitation of a single thruster.

how to calculate thrust to weight ratio

What a really great tool would be is selecting the ships mass and a type of planet with presets for gravity and atmosphere as well as a custom one where these values can be manually entered that then returns the weight and thus the minimum thrust needed to hover. With that and the planets environment it could give suggestions like prefering atmospheric thrusters, electric thrusters or hydrogen. Optionally a desired upward acceleration could be defined that will be used for the thrust calculation as simply hovering doesnt get you off a planet.

Ancient View Profile View Posts. Originally posted by Ancient :. Fury6 View Profile View Posts.Learn something new every day More Info Thrust-to-weight ratio reflects the amount of forward momentum an engine can generate in comparison to its weight.

Aircraft and rockets use thrust to overcome drag and move through the air. The higher the thrust-to-weight ratio, the quicker the craft will be able to accelerate, and the faster it can go. Engineers and other members of development teams use a variety of methods to control the weight of engines and the craft they power to compensate for weight and drag. There are several ways to calculate this ratio. Some calculations just look at the weight of the engine, while others may consider the whole craft.

In addition, the thrust-to-weight ratio can change depending on throttle speed and some other factors, like the role of gravity in craft that fly extremely high. For the purpose of technical specifications, developers may discuss the starting thrust and weight, noting that these can change in flight. This provides a general overview, and more specific data may be made available upon request. Heavier engines tend to produce more power, but come with a thrust-to-weight tradeoff.

Developers can use tactics like employing lightweight metals in engine construction and utilizing very light cowling to protect the engine. The same construction techniques can also be considered in the design of craft to reduce weight as much as possible.

Designers also need to think about laden weight in fully fueled craft with a maximum payload of passengers and cargo. Craft with a very high thrust-to-weight ratio can take off with a steeper angle, on shorter runways. Examples of this can be seen with military jets, many of which can safely take off and land on aircraft carriers, where there is little margin for error.

These craft are surprisingly light, considering their design and payloads, and their engines are extremely powerful. This allows them to generate a high thrust-to-weight ratio. Commercial aircraft, cargo jets, and other craft may have lower ratios, for a variety of reasons.

Designing high ratios tends to be expensive, and can involve tradeoffs in safety and comfort, depending on the craft. Creators of aircraft do not want to design deliberately unsafe aircraft, but may be more comfortable with low margins of error in some settings, and not others. Military pilots, for example, receive hours of training and constantly practice, which prepares them for a variety of incidents.

Commercial pilots carry precious cargo and may be less experienced, which makes safety considerations very important. Cost-benefit analysis helps engineers determine which design features to implement, given the potential applications of an aircraft. What will happen to the thrust to weight ratio, keeping everything constant at a higher altitude?Thrust-to-weight ratio is a ratio of thrust to weight of a rocketjet enginepropeller engineor a vehicle propelled by such an engine.

It is a dimensionless quantity and is an indicator of the performance of the engine or vehicle. The instantaneous thrust-to-weight ratio of a vehicle varies continually during operation due to progressive consumption of fuel or propellant. The thrust-to-weight ratio based on initial thrust and weight is often published and used as a figure of merit for quantitative comparison of the initial performance of vehicles. The thrust-to-weight ratio can be calculated by dividing the thrust in SI units — in newtons by the weight in newtons of the engine or vehicle.

It is a true ratio.

how to calculate thrust to weight ratio

For valid comparison of the initial thrust-to-weight ratio of two or more engines or vehicles, thrust must be measured under controlled conditions. The thrust-to-weight ratio and wing loading are the two most important parameters in determining the performance of an aircraft.

The thrust-to-weight ratio varies continually during a flight. Thrust varies with throttle setting, airspeedaltitude and air temperature. Weight varies with fuel burn and changes of payload. For aircraft, the quoted thrust-to-weight ratio is often the maximum static thrust at sea-level divided by the maximum takeoff weight. In cruising flight, the thrust-to-weight ratio of an aircraft is the inverse of the lift-to-drag ratio because thrust is equal to dragand weight is equal to lift.

For propeller-driven aircraft, the thrust-to-weight ratio can be calculated as follows: [5]. The thrust-to-weight ratio of a rocket, or rocket-propelled vehicle, is an indicator of its acceleration expressed in multiples of gravitational acceleration g. Rockets and rocket-propelled vehicles operate in a wide range of gravitational environments, including the weightless environment. It is customary to calculate the thrust-to-weight ratio using initial gross weight at sea-level on earth.

The thrust-to-weight ratio of an engine is larger for the bare engine than for the whole launch vehicle. The thrust-to-weight ratio of a bare engine is of use since it determines the maximum acceleration that any vehicle using that engine could theoretically achieve with minimum propellant and structure attached. For a takeoff from the surface of the earth using thrust and no aerodynamic liftthe thrust-to-weight ratio for the whole vehicle has to be more than one.

In general, the thrust-to-weight ratio is numerically equal to the g-force that the vehicle can generate. Many factors affect a thrust-to-weight ratio, and it typically varies over the flight with the variations of thrust due to speed and altitude, and the weight due to the remaining propellant and payload mass.