- Mon Feb 03, 2014 4:17 am
#344912
A hang glider will pitch up when the wing loading is increased suddenly.
The increase in load can be a from sudden increase in lift, a gust, or the glider rapidly changing direction.
An increase in lift is more immediately noticed than a drop in lift. In sink it can be several moments before the pilot realizes he is going down (flying without a vario)
Moving into increasing lift the harness is immediately squeezed in and the control bar tries to pull forward. Circling off-center in the thermal with periodically changing lift gives a regular, repeated pull upwards on the harness. It could be used as an aid to judge position in the thermal.
Continuing on from the last post, let's say the circuit flown is pear shaped, viewed from above. The narrow radius is nearer the hill, the climb is flatter than the return, and the wider "base" part of the pear is where the glider flies across the "wind" before returning.
The radius represents the angle of bank of the glider, not the actual path flown, which to an observer viewing from above may be more circular or elliptical.
Imagine a line drawn out from the hill side. With the pilot always turning right, trying to center in what he thinks is the thermal, the area to the left of the center line where the glider flies away from the hill, is the upwind leg.
To the right is the downwind leg, where the pilot flies back towards the hill. (This can be compared directly to the Renner/Reichmann demonstration of dynamic soaring).
The pilot has done one circuit, has turned and rolled the glider flat and is starting to head away from the hill again with a good excess of speed.
On entering the thermal (if it is still there), the glider will pitch up as it impacts the gust, the gradient of increasing airflow. The pilot keeps the bar firmly pulled in until the pressure from the control bar pulling against him eases.
The glider may still be pitched up even while the pilot is still grimly holding the control bar in during the climb.
If the climb is very steep both glider and pilot are pitched up, with the bar firmly held in. At the top of the climb if the pilot has scrubbed off of all the excess speed, the nose of the glider drops by itself, and the bar returns to its normal position (just held in, if it is trimmed tail down).
In a "stick thermal"with no gradient, the pilot pulls speed then eases the bar out and pushes it forward slightly to get the glider to climb. Flying in the described gradient, there is no need to push the bar out to climb. So it is not a stick thermal, or a stick thermal imposed on a gradient. The bar is only eased out as the climb slackens.
Just before the climb, the drop from the sharp bank has been suddenly arrested by the pilot banging the glider flat, causing an increase in load, so the glider pitches up. The bar is held in.
Just before that, when the pilot threw the glider up into a steep bank the load increased, causing the glider to pitch up in the turn. Only "up" is more towards the center of the turn. He may have the impression of bouncing of the wall of the thermal if he is flying with speed in hand. The pull on the bar may momentarily ease before the glider goes "flat".
The three load increases follow on from each other and effectively run almost continuously, but the impact from the thermal (if it is still there) is usually the most marked.
So fly back in a tail wind, start to bank, rapidly roll up, bounce, bang flat, hit the thermal, and climb steeply up into the prevailing wind.
The final roll up and roll flat must be one movement.
The maximum bank will be before the apex of the turn (assuming an elliptical pattern), the roll flat will be completed just after the apex, before the glider has turned completely outwards to face the wind.
This is for a small well defined thermal that might be found when a pilot is trying to go from slope soaring to circling in a thermal. The first circuit maps out the thermal roughly, the pattern then closes up, and becomes smaller as the moves become regular and repeated with less hesitation, (possibly becoming more circular). If successful, as the glider climbs, the pattern opens right up again till the pilot can climb no higher. He can maintain height by swooping round in circles, but if he faces into wind like everyone else the glider fairly quickly drops down again.
The pilot is not trying to dynamic soar, he is trying to roughly center in a thermal (real or imagined) without a vario, using the regular repeated change of feel from flying off center. When successful he anticipate what is (should be) coming next (in the sequence)and make adjustments (and adjust) , helped by flying with speed in hand, to keep up the steady rhythm.
The increase in load can be a from sudden increase in lift, a gust, or the glider rapidly changing direction.
An increase in lift is more immediately noticed than a drop in lift. In sink it can be several moments before the pilot realizes he is going down (flying without a vario)
Moving into increasing lift the harness is immediately squeezed in and the control bar tries to pull forward. Circling off-center in the thermal with periodically changing lift gives a regular, repeated pull upwards on the harness. It could be used as an aid to judge position in the thermal.
Continuing on from the last post, let's say the circuit flown is pear shaped, viewed from above. The narrow radius is nearer the hill, the climb is flatter than the return, and the wider "base" part of the pear is where the glider flies across the "wind" before returning.
The radius represents the angle of bank of the glider, not the actual path flown, which to an observer viewing from above may be more circular or elliptical.
Imagine a line drawn out from the hill side. With the pilot always turning right, trying to center in what he thinks is the thermal, the area to the left of the center line where the glider flies away from the hill, is the upwind leg.
To the right is the downwind leg, where the pilot flies back towards the hill. (This can be compared directly to the Renner/Reichmann demonstration of dynamic soaring).
The pilot has done one circuit, has turned and rolled the glider flat and is starting to head away from the hill again with a good excess of speed.
On entering the thermal (if it is still there), the glider will pitch up as it impacts the gust, the gradient of increasing airflow. The pilot keeps the bar firmly pulled in until the pressure from the control bar pulling against him eases.
The glider may still be pitched up even while the pilot is still grimly holding the control bar in during the climb.
If the climb is very steep both glider and pilot are pitched up, with the bar firmly held in. At the top of the climb if the pilot has scrubbed off of all the excess speed, the nose of the glider drops by itself, and the bar returns to its normal position (just held in, if it is trimmed tail down).
In a "stick thermal"with no gradient, the pilot pulls speed then eases the bar out and pushes it forward slightly to get the glider to climb. Flying in the described gradient, there is no need to push the bar out to climb. So it is not a stick thermal, or a stick thermal imposed on a gradient. The bar is only eased out as the climb slackens.
Just before the climb, the drop from the sharp bank has been suddenly arrested by the pilot banging the glider flat, causing an increase in load, so the glider pitches up. The bar is held in.
Just before that, when the pilot threw the glider up into a steep bank the load increased, causing the glider to pitch up in the turn. Only "up" is more towards the center of the turn. He may have the impression of bouncing of the wall of the thermal if he is flying with speed in hand. The pull on the bar may momentarily ease before the glider goes "flat".
The three load increases follow on from each other and effectively run almost continuously, but the impact from the thermal (if it is still there) is usually the most marked.
So fly back in a tail wind, start to bank, rapidly roll up, bounce, bang flat, hit the thermal, and climb steeply up into the prevailing wind.
The final roll up and roll flat must be one movement.
The maximum bank will be before the apex of the turn (assuming an elliptical pattern), the roll flat will be completed just after the apex, before the glider has turned completely outwards to face the wind.
This is for a small well defined thermal that might be found when a pilot is trying to go from slope soaring to circling in a thermal. The first circuit maps out the thermal roughly, the pattern then closes up, and becomes smaller as the moves become regular and repeated with less hesitation, (possibly becoming more circular). If successful, as the glider climbs, the pattern opens right up again till the pilot can climb no higher. He can maintain height by swooping round in circles, but if he faces into wind like everyone else the glider fairly quickly drops down again.
The pilot is not trying to dynamic soar, he is trying to roughly center in a thermal (real or imagined) without a vario, using the regular repeated change of feel from flying off center. When successful he anticipate what is (should be) coming next (in the sequence)and make adjustments (and adjust) , helped by flying with speed in hand, to keep up the steady rhythm.