ATPL theory question
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ATPL theory question
I know itīs a silly question but I would really like to get this straighten. Can anyone tell me how does wind and weight make both range and endurance vary ? I thought weight made them both vary but Iīve been told this is wrong 
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Wind does not effect Endurance but decreases Range, and weight decreases Endurance but has no effect on Range, I believe thatīs so, someone correct me if Iīm wrong
Last edited by GuilhasXXI; 16th Jan 2013 at 12:23. Reason: misspelled
As LM has said, wind does not affect endurance......it just makes you crash in a different place.
Before answering your question it would be best confirm what exactly you are asking.
For example, if you are asking about powered flight and a weight increase has been caused by extra fuel, then both the range and endurance will increase. But if the weight increase was caused by extra payload then both the range and endurance will decrease.
If however we are talking about gliding flight, then changes in weight will not affect best glide range, but will affect best glide speed and best glide endurance.
So are you asking about powered flight or gliding flight and are you asking about the speeds for best range and best endurance or are you asking about the best range and best endurance?
Before answering your question it would be best confirm what exactly you are asking.
For example, if you are asking about powered flight and a weight increase has been caused by extra fuel, then both the range and endurance will increase. But if the weight increase was caused by extra payload then both the range and endurance will decrease.
If however we are talking about gliding flight, then changes in weight will not affect best glide range, but will affect best glide speed and best glide endurance.
So are you asking about powered flight or gliding flight and are you asking about the speeds for best range and best endurance or are you asking about the best range and best endurance?
Last edited by keith williams; 16th Jan 2013 at 12:29.
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Yes, sorry about that, I was talking about glide. I think it has been said, wind does not affect endurance, only range, and weight affects endurance but not range. I guess if it was powered flight the best endurance would be achieved on Vmp (minimum power speed) right ?
POWERED FLIGHT RANGE
The term range refers to the distance flown over the ground using the fuel load available. To maximize range it is necessary to maximize the ratio of ground speed to fuel flow. When an aircraft is flying into a headwind the ground speed is reduced by an amount equal to the wind speed, but the fuel flow is unaffected. This means that range decreases with increasing headwind speed. In order to minimize the loss of range in a headwind it is necessary to reduce the time during which the aircraft is flying into the wind. This is done by increasing the airspeed slightly It should however be noted that the required increase in speed is considerably less than the wind speed.
POWERED FLIGHT ENDURANCE
The term endurance refers to the time that an aircraft can fly using the fuel available. In order to achieve maximum endurance it is necessary to consume the fuel as slowly as possible. Fuel consumption in a piston engine aircraft is proportional to the amount of power being generated by the engines. So to achieve maximum endurance it is necessary to fly at the speed at which power required is minimum. This speed is VMP.
Fuel flow in a jet aircraft is proportional to thrust, so to achieve maximum endurance a jet must be flown at the speed at which thrust required is minimum. This speed is Vmd.
EFFECT OF WEIGHT CHANGES
If weight is increased by adding fuel this will increase both range and endurance. If weight is increased by increasing payload (without increasing fuel) this will increase the drag and the power required. These changes will decrease both range and endurance.
GLIDE ENDURANCE
The purpose of aircraft engines is to provided energy to the aircraft. In flight this energy is continuously being used to push the aircraft forward through the air. If the engines fail then this energy can no longer be replenished. Throughout the subsequent glide the kinetic energy and potential energy stored in the aircraft will gradually be dissipated. When the energy is completely exhausted the aircraft will be stationary on the ground.
This means that the glide endurance will be greatest and the sink rate will be lowest when gliding at the speed at which energy dissipation rate is minimum. But energy dissipation rate is power required, so glide endurance is greatest and sink rate lowest when flying at the minimum power required speed Vmp.
Changes in weight will change the drag and the power required, and these changes will change the maximum glide endurance. So weight increases will decrease glide endurance and decreases in weight will increase glide endurance.
GLIDE RANGE
Glide range in still air is equal to the lift to drag ratio multiplied by the height at which the glide is commenced. So glide range from any given height is a maximum when gliding at the speed at which lift to drag ratio is maximum. This is the minimum drag speed Vmd. Although changes in weight will change the value of Vmd, they will not change the lift to drag ratio at Vmd. So provided the glide speed is adjusted to take account of any changes in weight, weight changes will not affect the best glide range.
Although headwinds or tailwinds will not change the glide endurance, they will change the ground speed. This means that headwinds will reduce the maximum glide range and tailwinds will increase maximum glide range.
The term range refers to the distance flown over the ground using the fuel load available. To maximize range it is necessary to maximize the ratio of ground speed to fuel flow. When an aircraft is flying into a headwind the ground speed is reduced by an amount equal to the wind speed, but the fuel flow is unaffected. This means that range decreases with increasing headwind speed. In order to minimize the loss of range in a headwind it is necessary to reduce the time during which the aircraft is flying into the wind. This is done by increasing the airspeed slightly It should however be noted that the required increase in speed is considerably less than the wind speed.
POWERED FLIGHT ENDURANCE
The term endurance refers to the time that an aircraft can fly using the fuel available. In order to achieve maximum endurance it is necessary to consume the fuel as slowly as possible. Fuel consumption in a piston engine aircraft is proportional to the amount of power being generated by the engines. So to achieve maximum endurance it is necessary to fly at the speed at which power required is minimum. This speed is VMP.
Fuel flow in a jet aircraft is proportional to thrust, so to achieve maximum endurance a jet must be flown at the speed at which thrust required is minimum. This speed is Vmd.
EFFECT OF WEIGHT CHANGES
If weight is increased by adding fuel this will increase both range and endurance. If weight is increased by increasing payload (without increasing fuel) this will increase the drag and the power required. These changes will decrease both range and endurance.
GLIDE ENDURANCE
The purpose of aircraft engines is to provided energy to the aircraft. In flight this energy is continuously being used to push the aircraft forward through the air. If the engines fail then this energy can no longer be replenished. Throughout the subsequent glide the kinetic energy and potential energy stored in the aircraft will gradually be dissipated. When the energy is completely exhausted the aircraft will be stationary on the ground.
This means that the glide endurance will be greatest and the sink rate will be lowest when gliding at the speed at which energy dissipation rate is minimum. But energy dissipation rate is power required, so glide endurance is greatest and sink rate lowest when flying at the minimum power required speed Vmp.
Changes in weight will change the drag and the power required, and these changes will change the maximum glide endurance. So weight increases will decrease glide endurance and decreases in weight will increase glide endurance.
GLIDE RANGE
Glide range in still air is equal to the lift to drag ratio multiplied by the height at which the glide is commenced. So glide range from any given height is a maximum when gliding at the speed at which lift to drag ratio is maximum. This is the minimum drag speed Vmd. Although changes in weight will change the value of Vmd, they will not change the lift to drag ratio at Vmd. So provided the glide speed is adjusted to take account of any changes in weight, weight changes will not affect the best glide range.
Although headwinds or tailwinds will not change the glide endurance, they will change the ground speed. This means that headwinds will reduce the maximum glide range and tailwinds will increase maximum glide range.
