I would like to ask some questions to help me progress further.
In still air, a 2-liner glider is making steady 18 seconds 360 turns with weight shift only.
1. What happens to the speed of the glider compared to the trim speed in a straight glide?
2. Assuming the speed of the glider is increasing due to an increased sink rate, what happens to the sink rate when the AOA is increased by equally pulling both rear risers such that the speed in the turns is now equal to that of trim speed in a straight glide?
3. Assuming the sink rate was slightly decreased with the said AOA adjustment, what happens to the bank angle and turn radius?
4. Can one maintain such turns by pulling on both risers equally while maintaining the weight shift?
I have my own responses and look forward to the discussion.
Thank you for your responses in advance.
Happy and safe flying!
PG Pilot progression questions
Re: PG Pilot progression questions
oh oh... was this a two liner question on Watts-App?
The question now looks like your discussing a steady state in various conditions. From what I have gathered on the two liners is the cascades determine the shape of the wing, doubtful that all wings are made the same (cascade wise) so attempting to change the AOA might not have the same effect in every case.
On my ATOS, totally rigid, fixed twist but variable camber (via flaps) and my AOA is trimmed with an elevator. If my camber is set, and my AOA trimmed optimally for bank/turn, your questions get answered like this (retaining optimal sink rate):
1- Airspeed will have increased
2- In my case this means slowing down (Alter the AOA via the elevator), moving below optimum airspeed and sink rate would increase.
3-this depends on a byproduct of span and roll stability, my rigid wing would maintain a steady state that is directly related to radius of the turn (of course up to a point)
4-The essence of your question(s) seems to be in the direction seeking out the utopia of of so called "flat turns"? (the elusive search of a turn that cost you nothing in performance)... and since your saying "pulling both risers equally" I suggest "no" Especially if your insisting on equal airfoil inputs. Your likely to find if you want a steady state turn with weight shift being the primary input then your going to find your input needs to be symmetrical to create a "steady state".
Your also likely to find you may be more efficient to establish a "unstable state", the glider has a tendency to roll out or roll in, and combine this condition with cross control input to create a artificial stable condition. "cross control" on the ATOS is achieved with more camber (more flap) and higher bank angle, to maintain this bank I require spoiler inputs on the high wing to stop the glider from rolling into the turn. In some air, this is a very efficient way to get the most out of the lift....other times is a small flap setting and a low bank angle produces a very stable turn requiring only AOA inputs to control the turn (via pitch/ trim).
A modern two liner can't be much different than a rigid wing airfoil...
Way too much thinking and not enough drinking.
Comrade Martin
The question now looks like your discussing a steady state in various conditions. From what I have gathered on the two liners is the cascades determine the shape of the wing, doubtful that all wings are made the same (cascade wise) so attempting to change the AOA might not have the same effect in every case.
On my ATOS, totally rigid, fixed twist but variable camber (via flaps) and my AOA is trimmed with an elevator. If my camber is set, and my AOA trimmed optimally for bank/turn, your questions get answered like this (retaining optimal sink rate):
1- Airspeed will have increased
2- In my case this means slowing down (Alter the AOA via the elevator), moving below optimum airspeed and sink rate would increase.
3-this depends on a byproduct of span and roll stability, my rigid wing would maintain a steady state that is directly related to radius of the turn (of course up to a point)
4-The essence of your question(s) seems to be in the direction seeking out the utopia of of so called "flat turns"? (the elusive search of a turn that cost you nothing in performance)... and since your saying "pulling both risers equally" I suggest "no" Especially if your insisting on equal airfoil inputs. Your likely to find if you want a steady state turn with weight shift being the primary input then your going to find your input needs to be symmetrical to create a "steady state".
Your also likely to find you may be more efficient to establish a "unstable state", the glider has a tendency to roll out or roll in, and combine this condition with cross control input to create a artificial stable condition. "cross control" on the ATOS is achieved with more camber (more flap) and higher bank angle, to maintain this bank I require spoiler inputs on the high wing to stop the glider from rolling into the turn. In some air, this is a very efficient way to get the most out of the lift....other times is a small flap setting and a low bank angle produces a very stable turn requiring only AOA inputs to control the turn (via pitch/ trim).
A modern two liner can't be much different than a rigid wing airfoil...
Way too much thinking and not enough drinking.
Comrade Martin
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Martin Zak
- Posts: 17
- Joined: Sun Oct 20, 2019 11:33 am
Re: PG Pilot progression questions
Disclaimer: This is my understanding, but by no means do I truly know what I am saying.
As you weight-shift you load one half of the wing more. As the glider is an arc, the loaded side will pull more and bank the glider (even if just a little). The entire lift vector tilts to the loaded side. Now, part of the wing is generating force, pulling you sideways and still making all the drag. You are technically flying a smaller and also less optimal glider. You are also heavier because of the centrifugal force (credit: Danny). The entire polar glider curve shifts down and sideways (but more down). No matter what your AOA is (based on your input), you are still just moving on the polar curve and, ultimately, have a worse glide ratio.
Summary:
1) you'll fly faster
2) the sink rate will be worse
3) Not sure. I'd say the bank angle remains the same (it's only affected by asymmetric loading). Turn radius increases. You are moving at the same speed, but the lift vector is smaller, and therefore also the part of the vector pulling you sideways.
4) I probably don't understand the question.
What is your motivation behind this question?
As you weight-shift you load one half of the wing more. As the glider is an arc, the loaded side will pull more and bank the glider (even if just a little). The entire lift vector tilts to the loaded side. Now, part of the wing is generating force, pulling you sideways and still making all the drag. You are technically flying a smaller and also less optimal glider. You are also heavier because of the centrifugal force (credit: Danny). The entire polar glider curve shifts down and sideways (but more down). No matter what your AOA is (based on your input), you are still just moving on the polar curve and, ultimately, have a worse glide ratio.
Summary:
1) you'll fly faster
2) the sink rate will be worse
3) Not sure. I'd say the bank angle remains the same (it's only affected by asymmetric loading). Turn radius increases. You are moving at the same speed, but the lift vector is smaller, and therefore also the part of the vector pulling you sideways.
4) I probably don't understand the question.
What is your motivation behind this question?
-
admin
- Webmaster
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- Location: Vancouver, BC, Canada
- Contact:
Re: PG Pilot progression questions
I moved this post to the General Forum, that way other members (not just Club members) can respond to this question.
Pedro Pedersen (as webmaster)Re: PG Pilot progression questions
Thank you for the expert responses!
During this winter, I've been messing around with a 2-liner glider in sunnier places.
And I had some unusual encounters/observations when I was trying new things which made me curious about the "why" part.
So the motivation is to become more knowledgeable for safer and more fun flying.
Here are my observation and thoughts:
1. What happens to the speed of the glider compared to the trim speed in a straight glide?
- The GPS vario is not reliable in turns, so I have not measured speed, but the speed seems to increase.
2. Assuming the speed of the glider is increasing due to an increased sink rate, what happens to the sink rate when the AOA is increased by equally pulling both rear risers such that the speed in the turns is now equal to that of trim speed in a straight glide?
- I forgot to include that the turns were in a thermal. Not sure if that would make any difference in the answer, however,
- I am not sure if I was actually reducing the speed to the straight glide trim speed, but when I increased the AOA to the point of maximum tension on both risers (maximum pressure; glider feels engorged with air / stiff canopy), I saw an increased lift on the Vario. In a marginally lifty thermal, this seems to let me have a better chance of not losing the thermal by providing clearer feedback - i.e. The pressure on the outside riser would go from tight to soft, and I can correct the turn to re-pressurize the riser feel.
- One time, I had an issue with the left brake so I tried to spiral (wing perpendicular to ground, not nose down) with a left rear riser instead. The glider was flying very fast (so high G), but the sink rate was very poor. So it was a bad way of descending, but conversely, it could mean the turns were more efficient.
- Another time, I was practicing for brake failure landing. Instead of slowing down, the glider shot up when I flared. I used to land with D-riser (4-liner back in the '90s) routinely, so I was caught off guard.
All these observations made me curious to know if:
a. My perception/observation is accurate
b. physics behind
3. any practical utility
3. Assuming the sink rate was slightly decreased with the said AOA adjustment, what happens to the bank angle and turn radius?
4. Can one maintain such turns by pulling on both risers equally while maintaining the weight shift?
- As mentioned, at some rear riser tension levels, my perception was that the Volt 4 lift in thermal improved with equal pressure on the risers during the maintenance phase of turns.
- I did not want to make the question complex so I simplified, but I think I might have inadvertently introduce a variable that may alter the outcome, so I will explain how I typically fly.
- I usually fly with 25~35% bar pushed all the time while pulling the rear riser mailons to the level of the A riser mailons to fly in trim. One of the purposes is to allow me a longer rear riser travel length before stall/spin.
- If I encounter a thermal, I will make a big wt shift, release the outer riser and pull the inner (the bar is still engaged. I do not let the bar go). With this, I find that I can make 12~14 second turns in Volt 4 (a bit more tricky with Scala).
- Once the turns are going well with satisfactory centering, sometimes I pul equally on rear risers (back to trim AOA or sometimes a slightly higher AOA than trim) especially if the lift is weak.
- If I am in a broad thermal or more often drop out of thermal, the bank angle increases. If I am in a tight thermal, the bank angle remains.
- I was thinking that based on Newton's 3rd law (AOA increase) and Bernolli's principle of wing lift (faster air flow at the outer wing), the outer wing section experience higher lift than the inner, but if the core is small such that the inner wing lift is higher than the outer, then the bank angle does not steepen. Sometimes, if I do not re-center, I find that the wing gets positioned in an equilibrium location where the inner wing is in greater enough lift (The wing transmits upward pulsing motion as it turns like going over speed bumps) to keep the bank angle the same.
I was just curious about this stuff.
Thank you and have safe flights! See you in the air soon
During this winter, I've been messing around with a 2-liner glider in sunnier places.
And I had some unusual encounters/observations when I was trying new things which made me curious about the "why" part.
So the motivation is to become more knowledgeable for safer and more fun flying.
Here are my observation and thoughts:
1. What happens to the speed of the glider compared to the trim speed in a straight glide?
- The GPS vario is not reliable in turns, so I have not measured speed, but the speed seems to increase.
2. Assuming the speed of the glider is increasing due to an increased sink rate, what happens to the sink rate when the AOA is increased by equally pulling both rear risers such that the speed in the turns is now equal to that of trim speed in a straight glide?
- I forgot to include that the turns were in a thermal. Not sure if that would make any difference in the answer, however,
- I am not sure if I was actually reducing the speed to the straight glide trim speed, but when I increased the AOA to the point of maximum tension on both risers (maximum pressure; glider feels engorged with air / stiff canopy), I saw an increased lift on the Vario. In a marginally lifty thermal, this seems to let me have a better chance of not losing the thermal by providing clearer feedback - i.e. The pressure on the outside riser would go from tight to soft, and I can correct the turn to re-pressurize the riser feel.
- One time, I had an issue with the left brake so I tried to spiral (wing perpendicular to ground, not nose down) with a left rear riser instead. The glider was flying very fast (so high G), but the sink rate was very poor. So it was a bad way of descending, but conversely, it could mean the turns were more efficient.
- Another time, I was practicing for brake failure landing. Instead of slowing down, the glider shot up when I flared. I used to land with D-riser (4-liner back in the '90s) routinely, so I was caught off guard.
All these observations made me curious to know if:
a. My perception/observation is accurate
b. physics behind
3. any practical utility
3. Assuming the sink rate was slightly decreased with the said AOA adjustment, what happens to the bank angle and turn radius?
4. Can one maintain such turns by pulling on both risers equally while maintaining the weight shift?
- As mentioned, at some rear riser tension levels, my perception was that the Volt 4 lift in thermal improved with equal pressure on the risers during the maintenance phase of turns.
- I did not want to make the question complex so I simplified, but I think I might have inadvertently introduce a variable that may alter the outcome, so I will explain how I typically fly.
- I usually fly with 25~35% bar pushed all the time while pulling the rear riser mailons to the level of the A riser mailons to fly in trim. One of the purposes is to allow me a longer rear riser travel length before stall/spin.
- If I encounter a thermal, I will make a big wt shift, release the outer riser and pull the inner (the bar is still engaged. I do not let the bar go). With this, I find that I can make 12~14 second turns in Volt 4 (a bit more tricky with Scala).
- Once the turns are going well with satisfactory centering, sometimes I pul equally on rear risers (back to trim AOA or sometimes a slightly higher AOA than trim) especially if the lift is weak.
- If I am in a broad thermal or more often drop out of thermal, the bank angle increases. If I am in a tight thermal, the bank angle remains.
- I was thinking that based on Newton's 3rd law (AOA increase) and Bernolli's principle of wing lift (faster air flow at the outer wing), the outer wing section experience higher lift than the inner, but if the core is small such that the inner wing lift is higher than the outer, then the bank angle does not steepen. Sometimes, if I do not re-center, I find that the wing gets positioned in an equilibrium location where the inner wing is in greater enough lift (The wing transmits upward pulsing motion as it turns like going over speed bumps) to keep the bank angle the same.
I was just curious about this stuff.
Thank you and have safe flights! See you in the air soon
-
Jeremy Séguin
- Posts: 4
- Joined: Wed Oct 26, 2022 8:23 am
Re: PG Pilot progression questions
On point number 1, considering that the mass under the wing is the "engine" of the system, the fact that when a turn is initiated, the G-force goes up (and therefore the weight pulling on the wing) could explain why the speed increases above trim speed, could it not?