Thrust to weight ratio and lift

In summary, a plane needs a thrust to weight ratio of 1 to fly straight up without losing speed. However, in level flight, the plane must maintain its altitude by balancing lift and weight. This can be achieved with a <1 TWR by utilizing the lift to drag ratio of the wing, which minimizes the power needed to generate lift force. By increasing the amount of mass flow, the required power is reduced.
  • #1
ayoyoayoyo
2
0
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 enough lift, how can it do this with <1 TWR

thanks
 
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  • #2
It's because the lift to drag ratio of a wing is much less than 1. In the case of a high end glider, lift to drag ratio of the glider is 60:1. If glider and pilot weigh about 1500 lbs, then while in a steady decent with a forward speed of 60 mph the decent rate is 1 mph, which translates into the fact that it only takes 4 hp (the power from gravity on a 1500 lb object decending at 1 mph) to go forwards at 60 mph.

The idea of a wing is to minimize the amount of power it takes to generate lift force, with some compromises due to cost to build and size. The force is related to momentum change of the air, mass flow times velocity, while the power is related 1/2 mass flow times velocity2. By increasing the amount of mass flow (moving more air, usually with a longer wing span), the required power is reduced.
 
  • #3
:) thanks for your answer
 

1. What is thrust to weight ratio?

Thrust to weight ratio is a measure of the amount of thrust produced by an aircraft's engine compared to its weight. It is important because it determines the aircraft's ability to accelerate and climb.

2. How is thrust to weight ratio calculated?

Thrust to weight ratio is calculated by dividing the maximum thrust of an aircraft's engine by its weight. This can be expressed as a decimal or as a percentage.

3. Why is thrust to weight ratio important for flight?

Thrust to weight ratio is important for flight because it determines the aircraft's ability to generate enough lift to stay airborne. A higher thrust to weight ratio means the aircraft can accelerate faster and climb more efficiently.

4. What is the relationship between thrust to weight ratio and lift?

Thrust to weight ratio and lift have a direct relationship. A higher thrust to weight ratio allows an aircraft to generate more lift, which is necessary for flight. Without enough lift, an aircraft will not be able to overcome the force of gravity and stay airborne.

5. How does thrust to weight ratio affect an aircraft's performance?

Thrust to weight ratio greatly affects an aircraft's performance. A higher thrust to weight ratio allows an aircraft to have a better rate of climb, faster acceleration, and increased maneuverability. It also allows an aircraft to carry more weight and perform more efficiently at higher altitudes.

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