Mystery of Yaw Damper

[grounded27]

aterpster

BTW, our last 10 727-200s were the "advanced" model with, I believe, the Sperry 250. It would do a poor man's CAT three quasi-auto-land. It would flare but not de-crab nor provide roll-out guidance. We were trained on it in the sim but no one in his right mind would actually use it.

I worked a very large fleet of dual mode SP-150 722's that were just about all maintained to CATIII A minima. They were reliable, the most common problem with the 727 A/P was a result of elevator position sensors, caused alot of disconnects during autoland logic, porpusing, disconnects et cetera. I believe the a/b mode SP-150 would likely be the advanced mode you are thinking of.

[Chris Scott]

Quote from JammedStab:
"Upgoing right wing means the right side of your artificial horizon line is going down. It is easy to mix up and make the wrong input."

True. Further to my earlier post about recovery on the VC10, my previous (older) types had had A/Hs on which the bank indicator pointer was at the bottom of the instrument, whereas the VC10's followed the later practice of incorporating a skid/slip bubble-indicator at the bottom, displacing the bank indicator to the top. That is less intuitive, IMO, and can create confusion. It could easily have led me to apply aileron/roll-spoiler in the wrong direction. Not a good idea... Has anyone else ever had that problem?

[FE Hoppy]

It could easily have led me to apply aileron/roll-spoiler in the wrong direction. Not a good idea... Has anyone else ever had that problem?

See it all the time in the sim on initial type ratings. It's a major learning point for many. We see it with both EDS/EFIS and HUD. It's easily corrected by learning to look at the centre of the ADI first and only use the sky pointer for fine tuning.

[Pugilistic Animus]

Simply read Handling the Big Jets....

[Chris Scott]

Quite. No doubt Dai Davies would be turning in his grave (assuming he is dead?) on reading most of our stuff.

I now find that he is yet to get a Wiki entry, despite that book - and being responsible for the redesign of the early B707's empennage (ventral fin added) to improve directional stability.

[Chris Scott]

D P Davies and the B707

This may be old-hat to the afficionados, but I've found a well-researched article on the 'net, originally published in a magazine called "Airways" (?) in 2010, here courtesy of the Renton (Washington, US) website:

http://rentonwa.gov/uploadedFiles/Li...20combined.pdf

Compare the fins (VSs) on the photos on pages 32 & 33. The account of the British certification process that led to the modifications starts on the right column of page 35.

I hadn't realised that the ventral fin retrofitted to those early models was dual-purpose - it also stopped the a/c over-rotating on take-off, in the absence of a suitable stick-shaker for that purpose. ** The other part of the B707 "fix", the top extension, is clearly visible when you compare the two photos.

The B707-320B/C "Advanced" types, such as I flew in Caledonian/BCAL, had dispensed with the ventral fin, apparently for the reasons stated on page 36 (yaw-damper and a stick-shaker).

OFF-TOPIC
Although the stick-shaker was supposed to prevent over-rotation on T/O, I once over-rotated (and probably rotated at too-high a rate) on a MTOW departure at LAX, and had to check forward slightly before the a/c would unstick.

** The British certification authority, the ARB, had pioneered the test of taking-off with the tail scraping along the runway, and the concept of Vmu (minimum unstick speed), as a result of accidents on the Comet 1.

[yanrair]

Maxarets? Think that is the name.

[FE Hoppy]

Maxarets are mechanical anti skid devices.

[Chu Chu]

I ran across an incident report about a 737 yaw damper behaving badly:

Air Accidents Investigation: 1/1998 G-BGJI

[DozyWannabe]

Originally Posted by Chris Scott

Quite. No doubt Dai Davies would be turning in his grave (assuming he is dead?) on reading most of our stuff.

I'm not so sure. His MO always seemed to be to make sure that the engineers got things as right as possible so that pilots would only have to use their superior skills in seriously abnormal situations. That said, the fact that he wrote HTBJ implies that he felt pilots should have a deeper understanding of what advanced aircraft were doing!

I now find that he is yet to get a Wiki entry, despite that book - and being responsible for the redesign of the early B707's empennage (ventral fin added) to improve directional stability.

Same for his colleague (and later successor) Gordon Corps - who was instrumental in the Concorde minimanche testing and development programme, and later, the A320 flight control system design and development. I've long said that if more people knew about him then there would be far less misunderstanding of the impetus behind that system. I've also long held that one of the biggest tragedies in aviation was his premature death from altitude sickness before he had the chance to write *his* book (which could have had the potential to do for line pilot understanding of modern digital FBW systems what HTBJ did for swept-wing jets).

Early yaw dampers, stick-shakers and stick-pushers were essentially the electro/hydro-mechanical forebears to the modern flight control systems with envelope protections.

[Grunff]

Here is rather self-explaining video of what happens when you disconnect yaw damper(s). It's made by Dutch students...doing, errr... Dutch roll...

PH-LAB (4/7): Dutch Roll - YouTube