Question about a plane taking off
Discussion
No conveyor belts.
The load on the main wheels on aircraft with nose landing gear.
As the aircraft accelerates, rotates and takes off, how does the load change? With the nose wheel it is simple to imagine the load remaining constant until rotation, then quickly reducing to zero, but what about on the main gear?
The load on the main wheels on aircraft with nose landing gear.
As the aircraft accelerates, rotates and takes off, how does the load change? With the nose wheel it is simple to imagine the load remaining constant until rotation, then quickly reducing to zero, but what about on the main gear?
Not entirely sure what you're asking, Sir.
I take it you're referring to the weight being exerted downwards through the gear on to the runway?
If so, it's pretty dynamic during rotation:
As the aircraft accelerates down the runway, the wings develop lift, and consequently less weight is exerted throughout the gear.
When the nose wheel lifts off, and the aircraft starts to point up, there is naturally an increase in the vertical component of weight felt though the main gear/fulcrum, relative to total weight. This is offset by further acceleration/increased angle of attack and therefore increased lift, resulting in the main great lifting off.
So, if you weren't going fast enough to achieve this, but could zoom down the runway with the nose gear raised, all the downward weight would be felt/supported by th mains. This weight figure would, however, be less than the total mass of the aircraft, as the wings would be carrying much of that. How muck however, would be determined by the actual load distribution on th aircraft.
This is all assuming loading is within the envelope.
I take it you're referring to the weight being exerted downwards through the gear on to the runway?
If so, it's pretty dynamic during rotation:
As the aircraft accelerates down the runway, the wings develop lift, and consequently less weight is exerted throughout the gear.
When the nose wheel lifts off, and the aircraft starts to point up, there is naturally an increase in the vertical component of weight felt though the main gear/fulcrum, relative to total weight. This is offset by further acceleration/increased angle of attack and therefore increased lift, resulting in the main great lifting off.
So, if you weren't going fast enough to achieve this, but could zoom down the runway with the nose gear raised, all the downward weight would be felt/supported by th mains. This weight figure would, however, be less than the total mass of the aircraft, as the wings would be carrying much of that. How muck however, would be determined by the actual load distribution on th aircraft.
This is all assuming loading is within the envelope.
Ayahuasca said:
No conveyor belts.
The load on the main wheels on aircraft with nose landing gear.
As the aircraft accelerates, rotates and takes off, how does the load change? With the nose wheel it is simple to imagine the load remaining constant until rotation, then quickly reducing to zero, but what about on the main gear?
On most Airbus and Boeings, the load on the nose gear reduces during the take off roll so the pilots usually apply slight forward pressure on the control column to keep the nose gear sufficiently in contact with the ground. The load on the main wheels on aircraft with nose landing gear.
As the aircraft accelerates, rotates and takes off, how does the load change? With the nose wheel it is simple to imagine the load remaining constant until rotation, then quickly reducing to zero, but what about on the main gear?
The nose gear is used for directional control on take off at lower speeds before the rudder becomes effective with increased airflow.
Edited by el stovey on Wednesday 3rd December 22:41
On the triple we have this:
Semi levered main gear
The semi-levered gear consists of an additional hydraulic actuator that connects the forward end of each main gear truck to the shock strut. During takeoff, the actuator locks to restrict rotation of the main gear truck and allow takeoff rotation about the aft wheel axle, thereby improving airplane performance capability. During landing, the actuator is unlocked to permit rotation of the main gear truck and provide additional damping.
Straight from the fcom. Engineers think of everything.
Semi levered main gear
The semi-levered gear consists of an additional hydraulic actuator that connects the forward end of each main gear truck to the shock strut. During takeoff, the actuator locks to restrict rotation of the main gear truck and allow takeoff rotation about the aft wheel axle, thereby improving airplane performance capability. During landing, the actuator is unlocked to permit rotation of the main gear truck and provide additional damping.
Straight from the fcom. Engineers think of everything.
Not sure about the wear to be totally honest but the bulk mainly comes from a stationary tyre contacting the runway and spinning up.
Whilst on the ground, the aircraft rotates around its main gear before moving to its centre of gravity when airborne, the semi levered gear actually provides greater take off performance for the 1st climb segment.
Whilst on the ground, the aircraft rotates around its main gear before moving to its centre of gravity when airborne, the semi levered gear actually provides greater take off performance for the 1st climb segment.
Kempus said:
Whilst on the ground, the aircraft rotates around its main gear before moving to its centre of gravity when airborne,
Doesn't that imply that there must be a momentary increase in load on the main gear at the point of rotation (when the nose gear breaks contact with the ground)?The aircraft wants to rotate about the cg, but is momentarily prevented from doing so by the main gear, which by definition must be behind the cg (otherwise the aircraft would be a tail-sitter). So a load proportional to the distance between the cg and gear fulcrum will be seen by the main gear legs?
dr_gn said:
Doesn't that imply that there must be a momentary increase in load on the main gear at the point of rotation (when the nose gear breaks contact with the ground)?
The aircraft wants to rotate about the cg, but is momentarily prevented from doing so by the main gear, which by definition must be behind the cg (otherwise the aircraft would be a tail-sitter). So a load proportional to the distance between the cg and gear fulcrum will be seen by the main gear legs?
The aircraft wing generates lift at a relatively low speed. As the airflow across it increases as it accelerates the lift thus increases. The aircraft wants to rotate about the cg, but is momentarily prevented from doing so by the main gear, which by definition must be behind the cg (otherwise the aircraft would be a tail-sitter). So a load proportional to the distance between the cg and gear fulcrum will be seen by the main gear legs?
If the aircraft was to rotate before Vmu, the weight is all firmly on the gear, however to do so at Vr, the angle of dangle is increases by the nose rising and generating more lift and taking load off the main gear. As you said the aircraft is forced to rotate around the main gear, pivot point if you wish, as it is still in contact with the ground but, the aircraft weight is now acting against the centre of pressure caused by the lift. As soon as the engines are lit the aircraft also starts getting lighter as it burns fuel at a rate of around 250kg a minute on take off so the weight on the main gear is actually always decreasing.
edited for grammar
Edited by Kempus on Friday 5th December 09:11
If you are flying a light single with a big prop on the front, and tailwheel undercarriage, it gets much more complicated.
Swinging on take off and the resultant ground loop, has caused many a problem for a novice (and not so novice!) aviator since someone thought that putting great whirling around things on the front of a flying machine.
A pokey tailwheel single, with a narrow undercarriage, and a relatively small rudder/fin area which is positioned relatively close to the centre of gravity (and hence with a small moment arm) will provide all the ingredients for entertaining handling.
Most folk are quite surprised when you tell them that when you have completed all your checks, and are lined up, and ready to go on the end of the runway, that the aircraft doesn't just track straight and true into the distance when you open the throttle all the way, and all you have to do is keep the rudder pointing straight, after all, the wheels are pointing straight down the runway, so surely it should be simple, right?
Typically, most (but by no means all) aircraft have a prop which rotates clockwise when viewed from the pilot's seat, and if you are in a tailwheel aircraft the prop blade on the right side of the aircraft will have a higher angle of incidence (alpha) than the one on the left, causing an asymetric thrust to the left
The slipstream off the prop will wash over the fuselage, and end up acting more on one side of the fin/rudder than the other. Depending on the length of the fuselage, the airspeed, and the power setting, if you are unlucky, then this might kick the tail out to the right, and of course causes the aircraft to veer left.
When you do get rolling, and have enough air speed, the tail will rise, and that big whirly thing on the front will make its presence felt by acting like a big gyroscope, and try to twist the nose left.
The prop will normally be very inefficient at low air speeds, when you are just starting to roll, and only starts to bite once you get some speed on, when the prop bites, it tries to rotate the whole fuselage around the engine, and since you are still on the ground, and this can't happen, because the ground pushes back, the resultant force once again tries to make the aircraft go left.
Happily, the resultant of all these seperate forces acting on the aeroplane can be delt with by application of right rudder, although the effects of all the above are felt differently at different speeds, and the effectiveness of the rudder will work differently at different air speeds.
Basically, you have to be ready for the swings, and prompt in dealing with them. Some aircraft are so evil in their ground handling that they need a drag of brake at certain phases of takeoff to keep pointing straight.
Thats why when watching most WWII era fighters, you can see the pilot waving the rudder back and forth enthusiastically on take off and landing.
Swinging on take off and the resultant ground loop, has caused many a problem for a novice (and not so novice!) aviator since someone thought that putting great whirling around things on the front of a flying machine.
A pokey tailwheel single, with a narrow undercarriage, and a relatively small rudder/fin area which is positioned relatively close to the centre of gravity (and hence with a small moment arm) will provide all the ingredients for entertaining handling.
Most folk are quite surprised when you tell them that when you have completed all your checks, and are lined up, and ready to go on the end of the runway, that the aircraft doesn't just track straight and true into the distance when you open the throttle all the way, and all you have to do is keep the rudder pointing straight, after all, the wheels are pointing straight down the runway, so surely it should be simple, right?
Typically, most (but by no means all) aircraft have a prop which rotates clockwise when viewed from the pilot's seat, and if you are in a tailwheel aircraft the prop blade on the right side of the aircraft will have a higher angle of incidence (alpha) than the one on the left, causing an asymetric thrust to the left
The slipstream off the prop will wash over the fuselage, and end up acting more on one side of the fin/rudder than the other. Depending on the length of the fuselage, the airspeed, and the power setting, if you are unlucky, then this might kick the tail out to the right, and of course causes the aircraft to veer left.
When you do get rolling, and have enough air speed, the tail will rise, and that big whirly thing on the front will make its presence felt by acting like a big gyroscope, and try to twist the nose left.
The prop will normally be very inefficient at low air speeds, when you are just starting to roll, and only starts to bite once you get some speed on, when the prop bites, it tries to rotate the whole fuselage around the engine, and since you are still on the ground, and this can't happen, because the ground pushes back, the resultant force once again tries to make the aircraft go left.
Happily, the resultant of all these seperate forces acting on the aeroplane can be delt with by application of right rudder, although the effects of all the above are felt differently at different speeds, and the effectiveness of the rudder will work differently at different air speeds.
Basically, you have to be ready for the swings, and prompt in dealing with them. Some aircraft are so evil in their ground handling that they need a drag of brake at certain phases of takeoff to keep pointing straight.
Thats why when watching most WWII era fighters, you can see the pilot waving the rudder back and forth enthusiastically on take off and landing.
Kempus said:
dr_gn said:
Doesn't that imply that there must be a momentary increase in load on the main gear at the point of rotation (when the nose gear breaks contact with the ground)?
The aircraft wants to rotate about the cg, but is momentarily prevented from doing so by the main gear, which by definition must be behind the cg (otherwise the aircraft would be a tail-sitter). So a load proportional to the distance between the cg and gear fulcrum will be seen by the main gear legs?
The aircraft wing generates lift at a relatively low speed. As the airflow across it increases as it accelerates the lift thus increases. The aircraft wants to rotate about the cg, but is momentarily prevented from doing so by the main gear, which by definition must be behind the cg (otherwise the aircraft would be a tail-sitter). So a load proportional to the distance between the cg and gear fulcrum will be seen by the main gear legs?
If the aircraft was to rotate before Vmu, the weight is all firmly on the gear, however to do so at Vr, the angle of dangle is increases by the nose rising and generating more lift and taking load off the main gear. As you said the aircraft is forced to rotate around the main gear, lever arm if you wish, as it is still in contact with the ground. The actual aircraft weight is now on the centre of pressure caused by the lift. As soon as the engines are lit the aircraft also starts getting lighter as it burns fuel at a rate of around 250kg a minute on take off so the weight on the main gear is actually always decreasing.
Wouldn't there be a fractional decrease in acceleration on rotation as the drag increases from increasing angle of attack? Plus the load transfer from the rotation about cg vs rotation about leg fulcrum would be instantaneous, whereas the increasing lift effect would be subject to a bit of inertia? I suppose we are talking tiny load variations over very short periods of time. not sure what the O/P had in mind.
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