njoizflyin
Posts: 37
Joined: Thu Jul 01, 2004 8:05 am

Questions

Tue Aug 24, 2004 1:32 am

Hi,
I was wondering if anyone could tell me what those canoe-like pieces along the wings of jetcraft are and their function? They bend with the flaps and have rods sticking out of them sometimes I imagine those are for measurement of speed perhaps but i don't know for sure. Also, I don't fully understand the function of APUs and how they are powered. Thanks in advance
njoyzflyin
 
SafetyDude
Posts: 3654
Joined: Fri Sep 07, 2001 10:02 am

RE: Questions

Tue Aug 24, 2004 1:36 am

APUs are Auxiliary Power Units, which are basically (I will let someone else give you more in-depth information) used to power the plane while the engines are off (such as when the plane is at the gate but the lights are on). In emergency situations, the APU can be used.

Generally, it helps when your topic is a bit more specific.  Big grin

-Will
"She Flew For What We Stand For"
 
User avatar
Starlionblue
Posts: 17097
Joined: Fri Feb 27, 2004 9:54 pm

RE: Questions

Tue Aug 24, 2004 3:34 am

The canoes are flap-track fairings. Simply an aerodynamic fairing that decreasses the wind resistance around the flap tracks and also protects them somewhat from damage while on the ground. The flap tracks are attached to the wing and to the flaps and are used to make the flaps move. Many aircraft can dispatch without a fairing if one is damaged but fuel consumption will be slightly higher.


APUs are turbines (although before the 60s many aircraft had little piston engines) and run on jet fuel. Simply jet engines like the ones hanging under the wings, but without the fan.

Most APUs provide electrical power for the systems and bleed air for engine starts.

Some more fun APU facts:
- The engine cores on the BAe-146/Avro-100 started life as APUs, for example on the 767.
- The APU for the Classic 747 has 1100 Shaft Horsepower. That's about the same as both engines on the Twin Otter combined.
- The 727 originally only had the APU as an option.
- The 727 APU could obviously not go in the tail so it is located in one of the main gear wells. It can only be used on the ground and is prone to set things on fire. Also, it often creates a tongue of flame snaking over the wing on startup. Pretty good if you want to scare the pax  Big grin
- I'm not entirely sure, but I think the 737NG APU intake is right under the exhaust:
View Large View Medium

Photo © Islam Chen







[Edited 2004-08-23 20:35:47]
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
geoffm
Posts: 2082
Joined: Fri Feb 27, 2004 5:58 am

RE: Questions

Tue Aug 24, 2004 4:41 pm

Those canoe-like things, he doesn't mean the mini fuel tanks strapped under the wings does he? I know on some aircraft they bend with the leading edge flaps/slats, and they kind of look like canoes due to their aerodynamic profile.

Geoff M.
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Questions

Tue Aug 24, 2004 4:49 pm

Just a little bit more information on APUs.

On the 744 there are 2 generators one of which will provide all the power requirements for the airplane. In addition, the APU provides bleed air which in turn provides air to the airconditioning packs (Air Cycle Machines) which are used to heat and cool the cabin and cockpit on the ground.

The 744 APU can be used in flight, however, it can not be started in flight. There is no APU for emergency use as a previous poster mentioned.

The canoe like structures are often referred to as canoes (I assume you mean on the trailing edge underside of the wing). On the 744/747, they provide an aerodynamic structure, to reduce drag, for the jackscrew and transmission which is used to extend and retract the trailing edge flaps. It is permissible to fly without one of those canoes. However, there is a performance penalty and increased fuel burn.
Fly fast, live slow
 
Anair
Posts: 47
Joined: Thu Dec 14, 2000 9:03 pm

Questions

Tue Aug 24, 2004 6:04 pm

The canoes you are talking about are called Kuchemann carrots or Whitcombe
bumps, and are used to create a vortex movement of the air passing around them. It improves the performance of the wings.
Besides, are usually used to reduce drag of the flaps mechanism.



View Large View Medium
Click here for bigger photo!

Photo © Oliver Brunke




Go ahead Airbus!!!

En un lugar de La Mancha....
 
User avatar
Starlionblue
Posts: 17097
Joined: Fri Feb 27, 2004 9:54 pm

RE: Questions

Tue Aug 24, 2004 8:43 pm

Those canoe-like things, he doesn't mean the mini fuel tanks strapped under the wings does he? I know on some aircraft they bend with the leading edge flaps/slats, and they kind of look like canoes due to their aerodynamic profile.

The canoes are not fuel tanks. Fuel tanks hanging from the wings are exceedingly rare nowadays on civil aircraft, and the canoes on modern jets and props are just flap track fairings, full of mechanics but mostly empty. On older planes such as the Lockheed Jetstar there are tanks hanging in or under the wings.

The canoes you are talking about are called Kuchemann carrots or Whitcombe
bumps, and are used to create a vortex movement of the air passing around them. It improves the performance of the wings.


If the flaps are built in such a way as not to require a protruding flap track, there is no need for a canoe. A clean wing, like that of the 727, is more efficient (in simple terms). Adding canoes just to create vortices would create too much drag. If you want to create vortices, you use much smaller vortilons (also known as other things) which have small drag components. Pic of 727 and pic of ERJ vortilons.


View Large View Medium
Click here for bigger photo!

Photo © Fabio Laranjeira
View Large View Medium
Click here for bigger photo!

Photo © Stefan Ehrbar

"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
geoffm
Posts: 2082
Joined: Fri Feb 27, 2004 5:58 am

RE: Questions

Tue Aug 24, 2004 8:57 pm

Okay, fair enough. You learn something new (or get something corrected) every day! They just looked too big to be housing pistons or screw rods.

Geoff M.
 
User avatar
Starlionblue
Posts: 17097
Joined: Fri Feb 27, 2004 9:54 pm

RE: Questions

Wed Aug 25, 2004 3:53 am

They are pretty large, but the mechanism moves up and down, requiring the fairings to be larger. But that's not the main reason. They are full of air.

Making them a bit fat in the middle gives a better aerodynamic shape. Think of the shape of a shark. It's not an even thickness along it's length. So while you could make it just large enough for the flap tracks that shape would be less beneficial if you're going to add the fairing anyway.

The fairings do shape the airflow just like vortilons do, which is sometimes needed at the edges of the flaps.

Having said that, the best shape is of course no fairing or flap track at all  Big grin



"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
Starlionblue
Posts: 17097
Joined: Fri Feb 27, 2004 9:54 pm

RE: Questions

Wed Aug 25, 2004 12:30 pm

As I took my two flights today I figured out that I needed to amend my post  Big grin

If your wing profile is marred by engines you will may need vortilons to ensure that airflow is good around those areas where the flaps are "opened up" to allow engine exhaust to pass. If you have canoes due to flap tracks they will be beneficial. This is why you will find the canoes typically on aircraft with wing mounted engines.

Ok four more flights in the next 2 days. Can you believe I have to change at ATL 3 times in 3 days  Nuts
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo