Aerodynamics of gliding - simplified?

In summary, to maintain flight at a constant speed, a glider must be placed in a dive to maintain forward motion, with the force of gravity equaling the drag on the aircraft. The most efficient angle of attack for the wing is the angle of the dive, and the weight of the glider must be adjusted to maintain the best L/D ratio and lowest sink rate. For radio controlled model gliders, weight can be added for increased air speed, and the entire trailing edge can be slightly raised to reduce drag at higher speeds. It is important to find the right balance of weight and drag for optimal flight performance.
  • #1
aeroseek
49
0
For a glider to sustain flight at a constant speed, the aircraft must be placed in a dive so that the forward motion is maintained by the component of gravity acting along the glide slope ( as a ball rolling downhill ). This force must equal to the drag on the aircraft. The less drag, the lower the dive angle needed.

For an aircraft wing there is an angle of attack at which the drag is the lowest value for the lift that is produced: ( The L/D) ratio. This is the most efficient angle of attack for the wing and corresponds to the angle of the dive (relative to the fuselage centre line) .

My question is: how does one arrive at the correct weight necessary to maintain the forward force needed to maintain the required forward speed to obtain the best L/D ratio?

How do you arrive at the correct weight for an Radio Controlled model glider for the lowest sink rate and the greatest distance?

I am a little confused at the moment. This seems to address the issue:

http://aviation.stackexchange.com/q...last-if-it-is-trying-to-stay-aloft-without-an
 
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  • #2
aeroseek said:
My question is: how does one arrive at the correct weight necessary to maintain the forward force needed to maintain the required forward speed to obtain the best L/D ratio?
That is more a question of trimming than of how much weight you add. Distributing the weight and moving the COM allows to trim with minimal additional drag from the stabilizer.
 
  • #3
aeroseek said:
My question is: how does one arrive at the correct weight necessary to maintain the forward force needed to maintain the required forward speed to obtain the best L/D ratio?
Lowest sink rate will occur with least weight (within reason), at a bit below the speed of best L/D ratio. On windy days, radio control gliders use weight (ballast) to increase air speed at speeds higher than best L/D ratio, needed to return upwind after chasing a thermal downwind. In addition, most contest type gliders can raise the entire trailing edge (both flaps and ailerons) slightly to reduce camber for lower drag at higher speeds (again well above the speed of best L/D ratio).

The best L/D ratio remains about the same within a range of weight for a typical radio control or full scale glider, given the limitation of how much ballast the glider is designed to utilize. The speed of best L/D ratio is relative to the square root of the weight (note that lift and drag are related to speed squared), so adding ballast doesn't result in a big increase in speed.
 
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  • #4
Suppose the glider is a model of a jet plane such as P-80 shooting star, is there such a thing as too light? To fly realistically it will have to fly rather fast, and be able to do loops and rolls and high speed passes. I know there are gliders capable of doing this, however with the fatter fuselages typical of jet fighters what can be done to reduce drag to the minimum and maintain long duration flights? On my model sim a light glider that is also high drag needs to have its nose pointed down quite a bit to obtain enough force to move forwards. Increasing the weight may help but then then wings may not sustain lift.
 
  • #5
aeroseek said:
Suppose the glider is a model of a jet plane such as P-80 shooting star, is there such a thing as too light?
Even if it doesn't fly, a very light feather will have a lower sink rate than most model aircraft, so for minimum sink rate, it's difficult to be too light. As an example of actual radio control gliders, the time duration contest ones used for discus / hand launch have a 1.5 meter wingspan (about 59 inches), thin wings, and weigh only 9 to 10 ounces.

http://en.wikipedia.org/wiki/Discus_Launch_Glider
 
  • #6
aeroseek said:
Suppose the glider is a model of a jet plane such as P-80 shooting star, is there such a thing as too light?

yes.

To fly realistically it will have to fly rather fast, and be able to do loops and rolls and high speed passes. I know there are gliders capable of doing this, however with the fatter fuselages typical of jet fighters what can be done to reduce drag to the minimum and maintain long duration flights? On my model sim a light glider that is also high drag needs to have its nose pointed down quite a bit to obtain enough force to move forwards. Increasing the weight may help but then then wings may not sustain lift.

Everything you say is correct. It's why modern competition gliders are very clean/low drag and have the ability to carry water ballast. You can't throw a light weight model biplane off a cliff into a gale and expect it to go forwards. You need enough weight to counter the drag at the required airspeed. If you want it to go forwards that airspeed must be faster than the wind. However you can't increase weight indefinitely. Not everything is capable of gliding.
 
  • #7
PS Consider what happens if the terminal velocity of a plane in a dive is lower than the wind speed. There is no possibility of it gliding upwind of it's launch point.
 

1. What is the concept of aerodynamics in gliding?

The concept of aerodynamics in gliding refers to the study of the forces and movements that affect an object as it moves through the air, specifically in the context of gliding. This includes the lift, drag, and weight forces that act on a glider, as well as the angle of attack and airfoil design that affect its performance.

2. How does gliding differ from other forms of flight?

Unlike powered flight, gliding relies on the natural forces of lift and gravity to keep a glider in the air. It also differs from other forms of unpowered flight, such as parachuting or hang gliding, in that it involves using the shape and design of the glider to generate lift and maintain a controlled descent.

3. What factors influence the aerodynamics of gliding?

The aerodynamics of gliding are influenced by a number of factors, including the shape and design of the glider, the angle of attack, the air density and temperature, and the wind conditions. The pilot's skill and technique also play a significant role in controlling the glider's aerodynamics.

4. How do pilots use aerodynamics to control a glider?

Pilots use their understanding of aerodynamics to control a glider by adjusting the angle of attack and the position of the control surfaces, such as the ailerons, elevator, and rudder. By manipulating these controls, they can generate lift, reduce drag, and change the direction and speed of the glider's flight.

5. Can aerodynamics be simplified for beginner glider pilots?

Yes, aerodynamics can be simplified for beginner glider pilots by focusing on the basic principles of lift, drag, and weight, as well as the effects of airfoil design and angle of attack. By understanding these concepts, pilots can learn to control the glider and make safe and efficient flights.

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