Koos de Keijzer, Raymond Caux, Oyvind Ellefsen, Klaus Taenzler, Gerolf Heinrichs, Dennis Pagen and the FAI lawyer.
In response to my question: How do we know that sprog settings are a major factor in accidents involving tumbling?
Dennis Pagen wrote:
We know that dynamic stability comes from static stability and dampening. Dampening in a tailless glider comes from inertia and surfaces moving obliquely to the airflow. By far sprogs are the greatest contributor to pitch dampening in negative angles of attack in a similar manner as the tail of a conventional aircraft. There are many aerodynamic texts that illuminate the matters of pitch stability.
Ignoring Dennis' condescending tone (he always uses it with me), I wrote back:
So no statistics (or just even plain old numbers) are available on sprog settings and tucking and tumbling accidents then? He wrote back:
No, and one of the things the working group is going to address is how to get these numbers. Essentially we can only require (request with a carrot and stick) that meet directors measure sprogs and VG settings when a tumble occurs. The other side of that is we will probably know a pilot's sprog settings already if we are measuring. Without funding we cannot conduct tests. The DHV did dynamic stability tests in 1986 (I believe) which, of course, were with completely different gliders.
When I showed Dennis' answer to a very knowledgeable source, he sent back this quote from the indicated source:
"The basic complaint is that the Bush White House puts political ideology over science when writing policy or when determining who sits on advisory panels set up to provide expert input into decision making."
Dennis wrote in the USHPA Hang Gliding and Paragliding Magazine in February, 2009:
"...but they [sprogs] only come into play when we fly at very low angles of attack (usually with half or more VG pulled and the bar at least to our waist)."
I asked a knowledgeable top competition pilot about this statement. He said that in fact as you pull in to your waist the sail rises up and pulls (undersurface pushes) the sprogs up with it. The cable that keeps the sprogs from going down goes slack and the sprogs are doing nothing at all in this situation. That is they are not "in play" at very low angles of attack. So Dennis' statement is completely false.
I suggest that the committee contact Andreas Olson re this issue. Also check here:
Listen to the sounds and watch the sail rise at about 1:20 into the video.
So the question naturally arises if the chairman of CIVL's sprog committee doesn't know how sprogs work in reality how can we expect a technically correct decision from the committee?
