747 kruger and VC flaps

[roughrider]

I understand that the 744 has krugers inboard and VC mid and outboard, but why? Is it just to induce the stall at the root or is there something else. Also do they extend electrically, hydraulically or pneumatically. I did a search but I didn't find an answer to either question.thanks

[spannersatcx]

Primary control is pneumatics secondary control is electric.

[rigpiggy]

electrically selected hydraulically actuated. the 27 and 37 are similiar.

[SeldomFixit]

"out of " Rig Pig - you may wish to RTFQ, then utilise the edit function.

[rigpiggy]

wtf over. I realize us colonials don't have a grasp of the queens own. why they went to the 2 different le devices is beyond me. but on the 27 it used to be commonplace to pull the le cb's and select flap 1 to get extra height for cruise. until one time the f/e came back from the lav, and reset the cb's which caused an upset.

[Intruder]

Regardless of what you may have done "on the 27," the LE flaps on the 747 (all models) are powered by the air system, with electrical backup. No hydraulics are used for the LE devices.

I have no idea why they were designed with 2 different types of flaps. My best guess is that the slotted VC flaps provide better airflow to the ailerons at high angle of attack.

[CV880]

All 747 models have electrically signalled, pneumatically powered LE devices with electrical motor back up. Is not a similar combination of inboard krugers and outboard slats used on the 727 and 737? The Convair 880M also used the same kruger/slat combination. The 747 differed only in that it used variable camber LE devices in the mid and outboard positions instead of slats and used pneumatics for normal operation. Presumably stall characteristics drove the decision to use krugers inboard on all these models.

[rigpiggy]

I stand corrected

[Frank Poncherello]

Hi guys, if i can offer my tu'pence worth on the subject (having worked 4years as an aerodynamicist on the A380),.........

Kruger flaps are a cheap option (more or less a flat plate with hinges, but aerodynamically not the best solution). They are relatively predictable (as in they will stall at a given alpha, that will change very little with conditions),.......

With regards the big-bus, we were unable to install Krugers on the inboard section due to the high camber (curves), and the complexity this added to the design (unable to locate the hinges basically)

Further outboard, a Kruger becomes less beneficial. The loss of lift between a Kruger and a Slat is high on the outboard sections, and is manageable on the inboard. Added to this, there are complications with regards to locating the actuation devices within a relatively thin section of wing, which may add weight, rather than save weight (which would be the reason of trying to bring Krugers into the design anyway!!)

Hope this adds confusion!!!

FP

[Maurice Chavez]

Rigpiggy:

on the 27 it used to be commonplace to pull the le cb's and select flap 1 to get extra height for cruise. until one time the f/e came back from the lav, and reset the cb's which caused an upset.

Flown the 27, think I missed something on the flap gate, I can't seem to find the flap 1 gate....Perhaps you can point it out? Also unable to find the cb for L/E's.....Maybe different cockpit config in Canada ,like they tried with the Diesel 8??

[LGB]

Variable camber does stall at a higher AoA than Kruger flaps. In a stall, ailerons are still effective when placing krugers inboard and VC outboard (other factors also contribute to this), so it is not just the 747 which has this setup. For this reason the rudder is not used in a stall the same way on large transport aircraft as it is on a light aircraft. I believe this is a FAR25 requirement.

(This is how it is tought JAR ATPL students anyway)

As mentioned, Kruger flaps are flat:

http://www.b737.org.uk/led_200adv.jpg

as

variable camber flaps are ... variable camber:

http://photos.airliners.net/middle/5/5/8/352855.jpg

(for some reason the above picture will not insert. See http://www.airliners.net/open.file/352855/M)

[H721]

to add more confusion,

once come across that B747 wings are not of linear sweptback, inner part (inboard of inboard engine) designed for low speed performance whereas outer wing cater for higher speed optimisation. hence different forms leading edge devices used.

confused enough......



not much of an engineer

[LGB]

H721,

You might be right regarding the wings inner and outer section vs speed, but I cannot see where leading edge devices are involved here - as they are not used on cruise, but only at speeds typically 250 knots or less.

Unless you apply the CB trick mentioned above, as desribed here http://fromtheflightdeck.com/Reviews/727/TWA727/ and someone pushes the breaker in again!