"the more lifting force behind the fulcrum (CG)"XCanytime wrote:Danny,
...Didn't say that the rotation was around the CG.
Bacil
marc
Something else to argue about (AGAIN)-- Wuffos and HR
Moderator: CHGPA BOD
-
Flying Lobster
- Posts: 1042
- Joined: Fri Feb 25, 2005 4:17 pm
Re: CG/CP
marc
Great Googly-moo!
okay, i'll take a gamble on sounding stoopid. has any of this stuff changed since Pagan wrote his books? although Danny's stuff is actually a specific analysis addressing standing on the ramp as well as how the particular 'stance' affects what's going to happen as/after you jump off. not trying to be cute, 'cause i found that an understanding of this stuff helped visualize (for me) what was going on with the glider and how 'screwing around' with the 'tuning' was going to affect things.
CG would be a fixed fulcrum (of the control frame) when earthbound and not the changing CG as in flight? (CP is always aft of CG?).
CG would be a fixed fulcrum (of the control frame) when earthbound and not the changing CG as in flight? (CP is always aft of CG?).
garyDevan
-
Danny Brotto
- Posts: 708
- Joined: Mon Feb 14, 2005 9:29 pm
AOA etc.
I hope this thread is interesting to enough people. I appreciate that it may be minutia to some. I’m not a good gauge of this because I find this subject read interesting and helpful. Pipe up if you feel this is dragging on. I won’t be offended and I, at least, will suspend tying up the bandwidth.
Bacil, your example of helicopter blades translates to the complete glider taking the full brunt of the wind. Sites that I have flown with these characteristics include Makapuu in Hawaii, South Point in Utah, Smithburg, and any number of costal site such as Ft. Funston, Marina Beach, Kitty Hawk, etc. The sensation is similar to standing on flat ground with a strong wind. In these unrestricted situations, the entire glider is being exposed to the prevailing wind so in effect the entire wing can be flying. Lowering the angle of attack does help stabilize the forces in these situations… when most of the glider generates lift. In lighter conditions as the nose is raised, the glider dances as the root exceeds critical AOA (stalls) and is simply floating on the wingtips.
My example of what happens on the HR cube conforms more or less to what’s described in the last sentence of the above paragraph. The root is pretty damn stalled in the initial stages in just about all instances of launching off the cube. In the many hundreds of flights I’ve had from HR, I recall only a dozen or so where I believe that the root was unstalled. I could tell from the terror in the eyes of my crew as they started being lifted off the ramp J. These flights were with earlier versions of the ramp that were higher and further out in the airstream than the present cube.
I suspect that
1) if one is comfortably “kiting” a glider at an aforementioned unobstructed site
2) and a 10 ft wide barrier were to suddenly pop up
3) the root will stall while the tips would continue to fly
4) and the glider would rotate with a “sucking forward” sensation.
Another point is that AOA is not an angle to the horizon or keel position. AOA is the airfoil relative to the airstream; you need airflow to have an airstream.
Danny Brotto
Bacil, your example of helicopter blades translates to the complete glider taking the full brunt of the wind. Sites that I have flown with these characteristics include Makapuu in Hawaii, South Point in Utah, Smithburg, and any number of costal site such as Ft. Funston, Marina Beach, Kitty Hawk, etc. The sensation is similar to standing on flat ground with a strong wind. In these unrestricted situations, the entire glider is being exposed to the prevailing wind so in effect the entire wing can be flying. Lowering the angle of attack does help stabilize the forces in these situations… when most of the glider generates lift. In lighter conditions as the nose is raised, the glider dances as the root exceeds critical AOA (stalls) and is simply floating on the wingtips.
My example of what happens on the HR cube conforms more or less to what’s described in the last sentence of the above paragraph. The root is pretty damn stalled in the initial stages in just about all instances of launching off the cube. In the many hundreds of flights I’ve had from HR, I recall only a dozen or so where I believe that the root was unstalled. I could tell from the terror in the eyes of my crew as they started being lifted off the ramp J. These flights were with earlier versions of the ramp that were higher and further out in the airstream than the present cube.
I suspect that
1) if one is comfortably “kiting” a glider at an aforementioned unobstructed site
2) and a 10 ft wide barrier were to suddenly pop up
3) the root will stall while the tips would continue to fly
4) and the glider would rotate with a “sucking forward” sensation.
Another point is that AOA is not an angle to the horizon or keel position. AOA is the airfoil relative to the airstream; you need airflow to have an airstream.
Danny Brotto
The see-saw
"the more lifting force behind the fulcrum (CG)"
That's the see-saw dude, not the hang glider.
Bacil
That's the see-saw dude, not the hang glider.
Bacil
Right
Brian,
The article from the 1995 newsletter is summarized in the second paragraph from the previous post. No need to see the original.I could tell from the terror in the eyes of my crew as they started being lifted off the ramp J. These flights were with earlier versions of the ramp that were higher and further out in the airstream than the present cube.
"I suspect that
1) if one is comfortably “kiting” a glider at an aforementioned unobstructed site
2) and a 10 ft wide barrier were to suddenly pop up
3) the root will stall while the tips would continue to fly
4) and the glider would rotate with a “sucking forward” sensation.
Another point is that AOA is not an angle to the horizon or keel position. AOA is the airfoil relative to the airstream; you need airflow to have an airstream."
Danny Brotto
Danny,
I highly doubt that ramp suck is experienced in light winds. I believe that it mainly occurs in the higher winds where the root is exposed to wind, coupled with the fact that the pilot probably holds the nose at a lower AOA than normal. This can create the "ramp suck" phenomenon that we have been describing.
Bacil
The article from the 1995 newsletter is summarized in the second paragraph from the previous post. No need to see the original.I could tell from the terror in the eyes of my crew as they started being lifted off the ramp J. These flights were with earlier versions of the ramp that were higher and further out in the airstream than the present cube.
"I suspect that
1) if one is comfortably “kiting” a glider at an aforementioned unobstructed site
2) and a 10 ft wide barrier were to suddenly pop up
3) the root will stall while the tips would continue to fly
4) and the glider would rotate with a “sucking forward” sensation.
Another point is that AOA is not an angle to the horizon or keel position. AOA is the airfoil relative to the airstream; you need airflow to have an airstream."
Danny Brotto
Danny,
I highly doubt that ramp suck is experienced in light winds. I believe that it mainly occurs in the higher winds where the root is exposed to wind, coupled with the fact that the pilot probably holds the nose at a lower AOA than normal. This can create the "ramp suck" phenomenon that we have been describing.
Bacil
-
Flying Lobster
- Posts: 1042
- Joined: Fri Feb 25, 2005 4:17 pm
Re: Right
Happens with my Litespeed RS in light winds sometimes. Like Danny says--I believe this is mostly a phenomenon related to airspeed (windspeed) and AOA relative to those portions of the wing generating lift and those not. I suspect that in those light wind instances that my Litespeed does experience ramp suck my Falcon probably would not.XCanytime wrote:Brian,
The article from the 1995 newsletter is summarized in the second paragraph from the previous post. No need to see the original.I could tell from the terror in the eyes of my crew as they started being lifted off the ramp J. These flights were with earlier versions of the ramp that were higher and further out in the airstream than the present cube.
"I suspect that
1) if one is comfortably “kiting” a glider at an aforementioned unobstructed site
2) and a 10 ft wide barrier were to suddenly pop up
3) the root will stall while the tips would continue to fly
4) and the glider would rotate with a “sucking forward” sensation.
Another point is that AOA is not an angle to the horizon or keel position. AOA is the airfoil relative to the airstream; you need airflow to have an airstream."
Danny Brotto
Danny,
I highly doubt that ramp suck is experienced in light winds. I believe that it mainly occurs in the higher winds where the root is exposed to wind, coupled with the fact that the pilot probably holds the nose at a lower AOA than normal. This can create the "ramp suck" phenomenon that we have been describing.
Bacil
marc
Great Googly-moo!
'attempt to be clearer: "has any of this stuff changed ?" - 'cause i heard Bernoulli getting his butt kicked the other week by the dude on NPR who does the weekly science show, "Science Friday". 'love the guy - he's got a new book out that i'd like to get.
" 'cause i found that an understanding of this stuff helped . . . (for me) ".
" 'cause i found that an understanding of this stuff helped . . . (for me) ".
garyDevan
Gary -
You'll find that Dennis Pagen never mentions the Bernoulli effect. He dislikes it as much as I do for trying to visualize the forces involved with flight. In the discussion above note that all we need to know is that force increases with the AOA (up until stall), and the direction of the total aerodynamic force (excluding parasitic drag) leans forward from the perpendicular to the wing at an angle roughly half the AOA.
So if you are on the block with wind coming from more below than it does on the training hill, with your nose down, the total aerodynamic force will have a forward component. That's my simple theory for ramp suck.
Then you look at the locations of the forces, and you can get a rotation that feels like it's pulling you forward (stall recovery). That part isn't so simple because if you raise the nose on HR the 'ramp suck' goes away, which is why varying amounts of blockage is required to make that explanation work.
You'll find that Dennis Pagen never mentions the Bernoulli effect. He dislikes it as much as I do for trying to visualize the forces involved with flight. In the discussion above note that all we need to know is that force increases with the AOA (up until stall), and the direction of the total aerodynamic force (excluding parasitic drag) leans forward from the perpendicular to the wing at an angle roughly half the AOA.
So if you are on the block with wind coming from more below than it does on the training hill, with your nose down, the total aerodynamic force will have a forward component. That's my simple theory for ramp suck.
Then you look at the locations of the forces, and you can get a rotation that feels like it's pulling you forward (stall recovery). That part isn't so simple because if you raise the nose on HR the 'ramp suck' goes away, which is why varying amounts of blockage is required to make that explanation work.
Brian Vant-Hull
I think one thing people are forgetting is that in this case - as opposed to free flight - the landing gear is more or less connected to an immovable object. The landing gear is also located a significant distance below the CP. Hmmm.brianvh wrote:Gary -
You'll find that Dennis Pagen never mentions the Bernoulli effect. He dislikes it as much as I do for trying to visualize the forces involved with flight. In the discussion above note that all we need to know is that force increases with the AOA (up until stall), and the direction of the total aerodynamic force (excluding parasitic drag) leans forward from the perpendicular to the wing at an angle roughly half the AOA.
So if you are on the block with wind coming from more below than it does on the training hill, with your nose down, the total aerodynamic force will have a forward component. That's my simple theory for ramp suck.
Then you look at the locations of the forces, and you can get a rotation that feels like it's pulling you forward (stall recovery). That part isn't so simple because if you raise the nose on HR the 'ramp suck' goes away, which is why varying amounts of blockage is required to make that explanation work.
eliminating ramp suck
Brian,
I don't see why eliminating ramp suck by lifting the nose of the glider seems to be such a mystery. Permit me to draw a y axis perpendicular to the surface of the ramp, and a z axis along the net lift line of the glider. I think we all agree that in all realistic launch conditions including glider nose angle, the z axis will tilt toward the front of the ramp relative to the y axis. (Some extreme angles of attack might violate this premise but I don't think we would deliberately launch that way.) Now in any nose down position there is going to be a portion of the lift vector along the x axis toward the valley. This portion is the ramp suck. The other portion is perpendicular to the surface and is the lift. I thing this is essentially the same description that you provided two posts ago
Now to the second part, as we raise the nose of the glider the forward vector diminishes. Also the majority of the wind is hitting the front of the glider which will cause it to rotate backwards if we were holding onto it. If the glider wants to rotate backwards, it clearly isn't being sucked forwards. Where's the mystery?
Oh and the hand of god might rescue us from the trees one day but it isn't pulling us up to the clouds, there is no cloud "suck". It's more molecules hitting the bottom of the wing than the top that's pushing us up.
It's winter and it's getting cold, while flying is more fun than talking about it, talking about it is more fun than watching TV. Keep the conversation going, hearing other views is fun.
Dan T
I don't see why eliminating ramp suck by lifting the nose of the glider seems to be such a mystery. Permit me to draw a y axis perpendicular to the surface of the ramp, and a z axis along the net lift line of the glider. I think we all agree that in all realistic launch conditions including glider nose angle, the z axis will tilt toward the front of the ramp relative to the y axis. (Some extreme angles of attack might violate this premise but I don't think we would deliberately launch that way.) Now in any nose down position there is going to be a portion of the lift vector along the x axis toward the valley. This portion is the ramp suck. The other portion is perpendicular to the surface and is the lift. I thing this is essentially the same description that you provided two posts ago
Now to the second part, as we raise the nose of the glider the forward vector diminishes. Also the majority of the wind is hitting the front of the glider which will cause it to rotate backwards if we were holding onto it. If the glider wants to rotate backwards, it clearly isn't being sucked forwards. Where's the mystery?
Oh and the hand of god might rescue us from the trees one day but it isn't pulling us up to the clouds, there is no cloud "suck". It's more molecules hitting the bottom of the wing than the top that's pushing us up.
It's winter and it's getting cold, while flying is more fun than talking about it, talking about it is more fun than watching TV. Keep the conversation going, hearing other views is fun.
Dan T