747 Stall Characteristics

[OZBorn]

I have some info that states that the 747 pitches nose down at the stall which I am trying to confirm or deny. Being a swept wing, I would expect that with the air pooling at the tips (from spanwise flow) and the boundary layer losing energy as a result, that the tips will stall first and the CoP will move inward (thus forward on a swept wing) causing a pitch up to occur. So which is right?

Secondly, does the 747 have a stick pusher as well as a stick shaker?

[slam_dunk]

I think that by design aircraft should be designed so as that the nose drops if the A/C is stalled.

I'm trying to recall the last time i did a stall with the 747 :} must be in the sim years ago. i'm pretty shure it didn't pull up when it stalled.

No the 74 doesn't have a stick pusher.

[411A]

Swept-wing jet transports stall just like any other transport aeroplane, that is properly loaded...the nose falls through, down.
How do I know?

During an airtest after a D check, and with a Lockheed production test pilot in the RHS. the aeroplane (L1011 standard body) was stalled in both the clean and approach flap configurations, at 8000MSL, west of JED.

Perfectly normal behavior, provided of course that you don't pounce on the rudder, American Airlines style...:rolleyes:

[Captain Airclues]

The 747 will pitch nose-down at the stall with any flap set. However there is no pitch either up or down when clean. Clean stalls are no longer carried out on air tests due to the excessive buffeting.

Airclues

[wileydog3]

I have some info that states that the 747 pitches nose down at the stall which I am trying to confirm or deny. Being a swept wing, I would expect that with the air pooling at the tips (from spanwise flow) and the boundary layer losing energy as a result, that the tips will stall first and the CoP will move inward (thus forward on a swept wing) causing a pitch up to occur. So which is right?
Secondly, does the 747 have a stick pusher as well as a stick shaker?

I would not imagine the 747 would stall that much differently from the 737 which we did full stalls straight ahead in a number of years ago. There was a noticeable buzz in the airframe as we slowed. The buzz turned into a vibration and that into a hard shaking as though "Do you really want to do this?" Plenty of natural stall warning although we were well into the shaker. Full aft stick and when it stalled, the nose fell through like a big C-150. Release back pressure, add a bit of power and away we went.

Clean, partial flaps and full dirty.. all the same. No real vices shown.

(737-300 in the late 80s at Boeing)

[Capn Bloggs]

Theoretically and IMO, on a swept-wing aircraft, washout ensures that the tips stall last (or the roots stall first), meaning the centre of pressure moves aft just during the stall and therefore the nose drops. I very much doubt any aeroplane would be certified if the nose pitched up during a stall. The thing would shortly after flick and spin, and all would die.

[DC-Mainliner]

I was fortunate enough to work briefly with the Flight Test Department at a previous company I worked for. We had B-737, B-757/767, B747, DC-10 at the time. I was able to make it in the jumpseat on several test flights, several on the B-737, one on the B-747 and several on the DC-10.

The B-737 stalls like a really nice flying airplane should. We didn't bring the 747 into a stall for the test run I was on. However we did stall a DC-10 when we had to re-certify the AOA/Stall vane. It was a very - VERY interesting experience and I can tell you that a DC-10 acts far different (think nasty) than a 737 when you start talking about departing controlled flight.

In a discussion after the test flight, the lead test pilot told me about stall characteristics of the various aircraft he'd tested, and was very favorable about the 737 and the 747 as being fairly conventional. He did not have the same comfort level with the DC-10 or the DC-8 from years previous. He mentioned the term "slicing off to one side", meaning a pronounced yaw or almost "flick stall" toward the edge of the envelope when discussing the DC-10, where he wasn't too concerned about the 747.

[OZBorn]

Thanks to everyone who contributed. Most appreciated.

[Captain Airclues]

In his book 'Handling the Big Jets', D.P.Davies states that the lack of pitch during a clean stall is unique to the 747. He also states that this was accepted as an "equivalent level of safety" exercise. I havn't had time to re-read the book to find out what he means by this.

Airclues

[TruBlu351]

The nose pitch up tendency of a "raw" swept wing aircraft has to be engineered out so that it recovers from the stall.

The 747 will pitch nose down due to the points mentioned already:
Washout
Stick Shaker
Stick Pusher

Additional features are also the:
Camber shape of the wing
Leading Edge flap devices

This pic shows really well the washout on a 747 (angle off attack much lower at the wing tips than root).

http://eu.airliners.net/graphics/nonFrontpageLogo.jpg

The 747 is fitted with Kruger leading edge flaps on the INBOARD section as opposed to slotted flaps on the leading outboard section. Kruger flaps are basically a section of wing that folds forward from underneath the leading edge. Slotted flaps are far more efficient WRT keeping the boundary layer attached on the outboard sections.

The big Kruger "scoops" also create more upwash and induced AoA which brings on the stall earlier.

This pic shows the inboard Krugers and slotted outboards.

http://eu.airliners.net/photos/middle/0/1/3/1044310.jpg

[Dan Winterland]

As an aside, Boeing considered any form of stall protection unecessary in the 747 as the stall was so benign. It was UK certification (by Mr Davies) which required that it should be fitted - so the stick shaker was adde. Thats why the installation looks like it's the product of an afterthought.

[skiesfull]

TruBlu351
I've flown 149 different 747's from -100's to the latest 400's and none of them have stick-pushers!! Are you sure??

[TruBlu351]

TruBlu351
I've flown 149 different 747's from -100's to the latest 400's and none of them have stick-pushers!! Are you sure??

Sorry mate, I just associated what I'd read in HTBJ with 747's.....my bad assumption! Can't argue with that :ok: cheers.

[gaunty]

ALL aircraft are designed to meet the certification requirements of their country of manufacture and generally they all agree on the same basics.
http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=8d577497e35be1d23952a077a77bd654&rgn=div5&view=text&node=14:1.0.1.3.11&idno=14
FAR Part 25 Section 25.201-7 inc. describes what the certification authorities (FAA in this case) want you to demonstrate in stalls.

Manufacturers over the years have over the years, gone to all manner of fandangling to "fix" their aircraft characteristics in order to comply.

It is an interesting forensic study to look at the various types over the last 40-50 years and see what/how the various manufacturers solved their problems.

Nowadays with the very sophisticated and powerfulcomputational fluid dynamics programmes available they can get it more than right first time.

Having said that they still get surprises when the ship actually flys which is what makes it still fun to do.

DP Davies may be quick to tell you that all countries will "have a go" around the edges of the envelope if it suits their own countries manufacturers purposes. Sometimes another country will say "OK but if it is going to fly here we want you to 'do this' or it wont.:E " := vis a vis Boing and Scarebus. ;)

And in the old days in OZ the DCA used to make you take the whole aircraft down to its component parts and reassemble it just to be sure the manufacturer hadn't dudded you on a few rivets and bits and pieces of tin here 'n there notwithstanding that you had already paid for a standing army of their staff to follow the aircraft down the production line. :rolleyes:

[Re-entry]

The 747-200 has a stick nudger. It is active only in flaps up config. It pushes the control column forward with the equivalent of 15 lbs force. The increase in stick force improves the longitudinal stability when approaching a stall.

[411A]

Well, quite frankly, I think Capt DP Davies ability to keep manufacturers in line with regard to aircraft handling characteristics, deserves appreciation.
For example.
The old original B707 long-body (-300 series).
This aeroplane had what many would consider doggy handling under strong gusty wind conditions (takeoff or approach), as the yaw damper had to be switched off during these phases of flight, but it was Davies who absolutely insisted the rudder power/feel system needed to be improved, before being allowed on the British register.
Boeing of course, modified the design for all aircraft.

I, for one, having flown these old designs, say hats off to him.
He will be sadly missed, in my opinion.

New pilots who read his book today, would probably be completely astonished if they were strapped into the pointy end of some of these old aeroplanes today.
Is what he wrote...true?
Yer darn right, in spades.

[gaunty]

411A :ok:

Amen to that, he is IMHO an unsung hero.

And it wasn't just for Transport types either, there were a number of aircraft he either refused point blank or demanded things like an active or no go Stability Augmentation System.

One famous example ultimately revealed outright dudding of flight test data, which captured a fairly high profile person.

I have been saying for years that his book should be a primer and examinable part of the ATP syllabus at least and probably the CPL as well if only as an insight into the basics of the certification process. I dont believe you can really understand what the performance regs applied on a daily basis are requiring without it.

[Re-entry]

411A. He's also the reason the 747-200 has that little mirror next to the mag compass. Cos he was such a shorta@@, he couldn't see the position of the flap lever, as it was obscured, to him, by the thrust levers.