Constant speed or constant attitude?

On Sun, 17 Aug 2003 11:04:23 +0100, Robin Birch
wrote:


I
On 15 Aug 2003 22:58:24 GMT, John Galloway
wrote:

What you guys are discussing is the 'Yates effect'
as described by Derek Piggot in 'Understanding Gliding'
Appendix A and also published in Gliding magazine in
1951 by Dr A.H. Yates.


One day I'll get round to reading that.

As you enter lift the glider accelerates forward due to the lift
vector tilting forward in the flight direction. Entering sink the
reverse effect occurs. This is a short lived effect for sharp edged
gusts with time constants of the order of 0 .15 to 0.5 seconds for
typical glider airspeeds and wing loadings.
It also has interesting effects on TE varios and is one of the reasons
that TE varios seem much quicker or more "nervous"in response than
uncompensated varios connected to static sources. The other is the
sensitivity of the TE vario to horizontal airmass changes"horizontal
gusts".
There is an article on our website about this.

Mike,
That is the clearest reason for it happening that I have ever seen.
When you sketch out the lift and drag vectors and then see what happens
when extra lift is added and removed it's obvious.

Agreed. I must try to consciously use constant attitude cruise. I'm
slowly approaching that way of flying in any case, but still have the
habit of clicking on 10 knots if the vario groans.... and am probably
going too fast as a result.


--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :