From: rdd@cactus.org (Robert Dorsett)
Newsgroups: sci.aeronautics,rec.aviation
Subject: How to land a 727 (summary)
Date: 30 Aug 92 03:44:51 GMT
Organization: Capital Area Central Texas UNIX Society, Austin, Tx

A few weeks ago, there was a short-lived burst in the oft-discussed
how-to-land-a-727 thread.  There were three major replies, only one
of which was in public.  Here's a summary of the traffic.  Names have
been removed to protect the guilty:

From ... let's call him Abe:

> I got to spend some time in one of (GenericAirline's) 727-200 simulators
> about two years ago.  When they were teaching me to land they tought me
> the following procedure:  When the pilot-not-flying calls 50 feet, start
> flaring, with the intent to have roughly a 0 fpm down speed at 20 feet.  When
> (s)hecalls 20 feet, start pushing the stick forward to roll the aircraft
> onto the runway.
>
> They told me that the reason this odd procedure is needed, is because the
> CG, and therefore the center of rotation, is in a position, so as to
> pull the gear higher as the nose rotates higher, and the only way to get the
> gear to move towards the ground is to push forward, in effect lowering
> the gear. 


This one's from Scott Dunham (M21208@mwvm.mitre.org).  Note that it's
almost the complete opposite of uh, Abe's reply.

> One of my neighbors flies for American, and had to learn to land 727s right
> after being a Cheyenne driver for a few years.  His account of the problem
> is that the main gear is fairly far behind the pitch axis.  As a result, if
> you realize the sink rate is a bit high right before touchdown and pull the
> nose up to compensate (perfectly normal response!), you can actually drive the
> mains onto the runway rather smartly.  Ideal performance is to arrest the
> sink while you're still high enough to avoid planting the gear, but if you get
> it wrong (i.e., late) there's no real smooth way to recover...
 

And finally, this one's from...  let's call him... "Tweetie Bird."  

> IMHO (well, not so humble; I've been there!) the 727 landing problem comes
> about because of ground-effect.  Did you ever take a look at a 727 on the
> ground with flaps fully extended?  If so, visualize the airplane in landing
> attitude.  There is a tremendous amount of air "caught" in the pocket formed
> by the wing on top, the flaps behind, and the ground beneath.
> 
> Assuming a no-wind condition, and a perfectly stable approach, there is a
> noticeable decrease in the rate of descent as you encounter that cushion
> of air.  At that point, a slight forward pressure on the stick will decrease
> the AOA and allow the descent to continue.  At the same time, the nose-
> down rotation will cause the gear to rise, decreasing the rate of descent
> of the wheels.  When this is done correctly you get a grease-job every
> time.
> 
> However, one rarely has a no-wind condition, and the approach is rarely
> *perfectly* stable.  Headwinds, crosswinds, gusts, and variations in the
> approach all introduce a destabilizing element into the neat scenario I've
> outlined above.  Thus the cunning 727 pilot will "feel" his way down,
> trying to keep the approach well-stabilized while feeling for the
> ground effect.  If it seems to be there he can drop the nose and push
> through it.  If not, he may have to raise the nose to decrease the rate
> of descent for touchdown.  If he has to raise the nose, he had better do
> it early; if he does it at the last minute he will literally rotate the
> gear into the ground.
> 
> Such are the vagaries of landing a 727.  Actually, landing any airplane
> is a lot like parallel parking; no matter how good you are, you'll only
> get it right eight times out of ten.




---
Robert Dorsett
rdd@cactus.org
...cs.utexas.edu!cactus.org!rdd
Xref: sparky sci.aeronautics:1906 sci.environment:10948