ATO #108 - May 12, 2000

PART 1: Upcoming Chats
PART 2: Project News
PART 3: ALL Airplanes Are Low-Speed Airplanes Part 1!

You are all invited to participate in an informal survey from our management here at NASA Ames Research Center. To express your views on NASA Quest and Aerospace Team Online go to http://quest.nasa.gov/common/feedback.html

We will reward your help by sending you an assortment of NASA pictures and posters.

UPCOMING CHATS

QuestChats require pre-registration. Unless otherwise

noted, registration
is at:  http://quest.nasa.gov/aero/chats/

Aerospace Team Online QuestChat with Craig Hange
Wednesday May 24, 2000 10 - 11 AM Pacific

Craig is an aerospace engineer at NASA Ames Research Center. His research
has included the Joint Strike Fighter Program and the Wright Flyer.
Currently he is working on STOVL powered lift and low speed research.

Read his bio at 
http://quest.nasa.gov/aero/team/hange.html

PROJECT NEWS

Regimes of Flight Art Contest, Contest ends May 26, 2000

The entries are coming in!
For more information go to


http://quest.nasa.gov/aero/events/regimes/contest.html#art

ALL AIRPLANES ARE LOW-SPEED AIRPLANES, PART 1

By Craig Hange

I'm very fortunate that I can sit at my desk and look out the window   
(instead of actually doing work) and watch airliners setting up to land at
San Francisco International Airport. They are easy to watch at this point
in their flight because they are closer to the ground, and are flying a
lot slower than they did earlier in the flight. Some of the big airliners
like the 747 or 777 seem like they are just hanging there, and it sure
looks like they are going too slow to remain airborne.

Of the different flight regimes airplanes fly in, the one they all have in
common is take-off and landing. Not all airplanes go fast, and not all go
high, but they all at some point have to go slow and come down to the  
ground. No matter how long an airplane can stay in the air, they all have 
to start and end their day on the Tarmac at zero speed. So, no matter what
the mission or objective an airplane has, low-speed characteristics will
always need to be addressed.

Of course, low-speed is a relative term. A small general aviation airplane
whose maximum speed is less than 100 mph doesn't come close to the
"low-speed" of 160 mph that a jet airliner has during take-off. At NASA,  
we generally consider low-speed to be between zero and 300 mph, so
relative to other types of vehicles such as race cars, our low-speed can
still be very fast. However for aircraft, low-speed flight is
characterized by the need to generate a lot more lift than is needed
during the faster portions of the flight. And, aerodynamically speaking,
that can be a big challenge.

The amount of lift an airplane generates needs to be equal to the weight  
of the airplane. There are two ways to get a given size wing to generate
more lift. One is to use more air by flying faster, and the other is to   
deflect the air going over the wings through a greater angle. At  
high-speed the first choice is easy to do, because the airplane is moving
fast enough, the wings can push a lot of air through a small deflection
and generate a lot of lift. This amount of lift is more than enough to
balance the weight of the airplane.

At low-speed though, there is less air flowing over the wings.
Now, to generate enough lift, the airflow will need to be deflected much  
more. This is accomplished by increasing angle of attack or deploying   
flaps and slats on the wings. Usually a pilot does a little of both. If   
you have ever sat behind the wing next to the window in an airliner you
have seen these flaps and slats deploy just before the take-off and
landing. On some airplanes these are so cleverly concealed that the wing
looks like it's coming apart when these pieces start to move. By deploying
these flaps and slats, the wing now has more camber, or curvature. By
increasing angle of attack and using flaps and slats the wing can generate
more lift through the greater deflection of the airflow. This makes up for
the loss in lift caused by the aircraft going slower. On a typical jet    
airliner, the landing and take-off speed is one quarter to one third of 
the cruising speed. On supersonic airplanes, the ratio is even bigger.    

This seems easy enough, so where's the challenge?

Continued Next week in ATO# 109