Landing over obstacles--interesting article

[jaylw314]

I finally found a research article I read a long time ago, then couldn't find even with the Google lady's help until now.  It goes by the rather boring title of "Investigation of Aircraft Landing in Variable Wind Fields."  In brief, they wanted to simulate what controls adjustments are required to land when there is headwind over a plateau or a drop-off on final.  The take home points seem to be:

• With flat terrain, the headwind decreases as you descend due to boundary effect, so if you don't adjust the controls, you will always land SHORT of your aiming point.
• With a plateau (or a long building, or a stand of trees) on final, the wind blows up but slows down.  Even though the wind blows up, the slower windspeed causes a loss of lift that causes aircraft to DROP.
• With a valley on final, the wind blows down but speeds up.  Even though the wind blows down, the net effect is an increase in lift that causes an aircraft to CLIMB.

Those conclusions are sort of intuitively obvious, but I found it interesting to see the explanation why.

Now I've got to try to find that lost article about engine cooling...

[Seymour]

1 hour ago, jaylw314 said:

With flat terrain, the headwind decreases as you descend due to boundary effect, so if you don't adjust the controls, you will always land SHORT of your aiming point.

OK, that may be intuitively obvious to the casual observer.   ...but not me.   If headwind decreases, why would you land short?

I had to open the article to read about boundary effect to get the gist.   Now I'm curious enough to read the entire paper.   Thanks!

[jaylw314]

It's like windshear from headwind to tailwind--your GS might increase a little bit, but your descent rate increases by a larger amount.

I looked this article up during my PPL training because I had the impression that if you can't simply hold your power and pitch steady before your roundout.  In other words, even a "stabilized approach" requires you to make adjustments as you near the ground, and if you don't the tendency will be to land short.