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B747-400 no stick pusher

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B747-400 no stick pusher

Old 3rd Apr 2007, 05:22
  #1 (permalink)  
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B747-400 no stick pusher

I was asked about this during my interview and I wasn't sure about the answer so I said "I'm not sure". Anybody?
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Old 3rd Apr 2007, 05:34
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No Stick Pusher - only Stick Shaker. Stick Pushers were primarily installed in high tail airplanes like the VC10, BAC 1-11 (not sure about 727).... because they suffered deep stalls (super stalls) which rendered the stabilisers ineffective at the stall & could be unrecoverable. This is because at high angles of attack the high tail would sit in the turbulent flow of the wing and be aerodynamically useless. The purpose of the stick pusher was to prevent this from occurring by producing a forward pressure on the elevators during the approach to stall, before this condition was reached.

The 747-400 - not being a high tail - does not suffer the deep stall, and so has no need for a stick pusher.
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Old 3rd Apr 2007, 05:44
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That makes sense, thanks gengis.
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Old 3rd Apr 2007, 06:32
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No stick pusher on the B 727-200...i currently fly the type
anyway..i always wondered what's a stick pusher
any thoughts?
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Old 3rd Apr 2007, 06:34
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Oooooops i just re-read Gengiz's explanation..
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Old 3rd Apr 2007, 08:20
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Nice explanation from gengis.

However, why therefore does the 747 classic have a stick nudger/pusher?
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Old 3rd Apr 2007, 11:46
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While Ghengis' explanation gives one reason for installation of a stick pusher, it doesn't give the whole reason.

Stick pushers (and indeed also shakers) may be installed where the 'natural aerodynamic stall characteristics' of the aircraft are unacceptable and do not meet the regulatory requirements of sections 201, 203 and 207 of the relevant regs. They are an alternative to actually fixing whatever the underlying aerodynamic problem is.

Therefore, if there is no or insufficient natural airframe buffet or other 'stall warning' such that the requirements of section 207 cannot be met, one option available is to install an artificial stall warning system, or 'stick shaker'. This allows the onset of warning to be tailored to the configuration, and does not impose an aerodynamic penalty (which, for example, a stall strip on the leading edge might).

If the stall characteristics AT the natural stall are unacceptable with regard to the requirements of sections 201 and 203, then a stick pusher may be installed, set to fire at a lower angle of attack than where the natural stall occurs, in order that a relatively benign stall characteristic is obtained. Since the unacceptable characteristics may be a sudden wing drop or a pitch up, but not necessarily related to the tail vertical position, this may be required on any aircraft, depending on the detail wing design. In this case we would typically refer to this as a "pre [natural] stall pusher".

Finally, the T-tail/deep stall case may require a post-stall pusher i.e. set to fire AFTER the natural aerodynamic stall is acghieved, but intended to prevent overshoots of angle-of-attack in, for example, the dynam,ic stall case, which might cause a concern for a deep stall.

Without knowing the details, I'd suspect the 747 classics fall into the "pre stall pusher" case, likely as a result of a less-than-pleasant natural stall characteristic.
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Old 3rd Apr 2007, 11:57
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I'm getting old but I recall British reg 72s had stick pushers mandated?

Dan Air's being the 1st?
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Old 3rd Apr 2007, 15:07
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For such a large aircraft, the 747 had a very benign stall, even demonstrating a gentle nose down moment at the stall which is unusual in a swept wing design, most of which have a nose up pitch moment. Boeing considered a pusher or shaker unecessary. The early 100 series airfrmes delivered to US carriers had neither. However, while being certified for the UK register, the CAA's test pilot on the aircraft decided that some sort of artificial warning was needed. So the shaker was added, and Boeing considered that it was a good measure to include it as standard equipment thereafter as it wasn't a complex or expensive modification. This is why it is a simple elecetric motor with an eccentric weight attached to the control column by jubilee clips - and looks like it's been designed by Heath Robinson.

Incidently, the test pilot was DP Davies, author of 'Handling the Big Jets'.
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Old 3rd Apr 2007, 15:54
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Dan Air's original 727-100s were the first on the U.K. register and as such were required by the CAA to have a Stick Pusher fitted i.e. a pneumatic actuator that snatched the column out of your hands (nearly). The system fitted was similar to that used on the 1-11 and, presumably, the Trident.
If I remember correctly, but I may not - it's been a long time !, the -200 series aircraft were allowed onto the register without the pusher fitted and relied on the standard stick nudger, a spring device which was much more gentle.
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Old 4th Apr 2007, 16:44
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Stick pushers aren't only found on T-Tail A/C,
True - Not that it's really relevent, but the Swearingen Metro's also have stick pushers.
It's usually disabled by most pilots though, as no Metro pilot dares get remotely close to the stalling angle, and the only time the SAS (Stall Avoidance System) works on them is when you're flaring - It pulls the stick out of the pilots hands and makes the plane land hard on the nosewheel, then bounce, bounce, bounce ....
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Old 4th Apr 2007, 17:15
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I have flown to the push many times on a BAC 1-11. As one pulled, the igniters would come on first, then the shake, and really quite a heave later the aircraft would start to wallow just prior to the push.

Claxons let you know that nitrogen had fired onto a piston-pushing the stick forward-should you miss the significance of seeing green fields and little houses in your windscreen.

I'm kidding, it really was quite benign, and of course much more predictable than a stall in an unfriendly type.

I recall the description given by one of our contemporaries, of the Mike Lithgow tape. As they were going down their dialog was very measured at first, becoming........well, less so, shortly before impact.

The crash footprint was not much different to the shape of the aircraft.

The Pappa India crash is of course the most significant in terms of handling and CRM. A police officer at our shooting club was one of those attending. He said that if so many people had not stopped to look at the crash, they may have saved some lives. I don't know about that, but he was there, I wasn't.

As the afore mentioned Davis says (well, a rough interpretation ) in a later edition of his book -- a true appreciation of the characteristics of your aircraft is of paramount importance. He went on to give an almost impassioned plea for more real handling training...on real aircraft.
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Old 5th Apr 2007, 08:13
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As I recall, of all the N/VH/P2/VP/G registered B707 I flew, only the G- had a stick nudger, they all had a stick shaker.
For anybody who actually did a full Flap 50 stall in air, the violence of the pre-stall buffet, well before the stall break, leads me to wonder how anybody but the comatose could not recognise what was happening.
The B707, 120, 300 and 320, did have a very slight nose up pitch at Flap 50 only, before the nose went down. In training, most pilots didn't notice, such was the pre-stall buffeting. Simulators of the day did not nearly simulate the buffeting of the "real thing".
Hence, in early days, BOAC -436 limited to Flap 40 landings, great for tyre and brake salesmen.
In retrospect (Danair at Lusaka) I wonder how much cumulative damage we all did to the horizontal stab, or the whole tail section, with all the post maintenance and training stalls. And we have not forgotten what turbulent airflow from speed-brake did to the said posterior of a B707.
The 100/200 B747 was even worse buffeting in the stall at Flap 25 and 30.
Some may recall that the FAA FAR 25, (ex-SFAR 422B) had a different approach to low speed handling compared to our former ARB Chief Test Pilot and well known author.
As was proved the hard way, demonstrating "Tiger Moth" 1G stalls in a Trident was not a life enhancing exercise.
The B727 was never certified on 1G stall, but on "demonstrated minimum controllable airspeed", and as I recall, this held until the B767-200.
B767-300 and the B747-400 were certificated on low speed figures based on V Cl/Max, and the V Ref (25/30) for approach is 1.2 V Cl/Max, not 1.3 Vs, as about 99% of pilots assume.
It was with the Concorde that ARB/CAA had to re-think finally, ain't no such animal as a 1G stall in a delta.
In that well known tomb, Mishandling the Big Jets, D.P was finally forced to admit that early B747 were really quite nice handling aeroplanes, and Boeing did actually know something about building big aeroplanes, but he was, in my opinion, rather naughty is virtually recommending departure from Boeing recommended non-normal procedures for double engine failures.
In some (many?) quarters it is heresy and blasphemy to question DP, but on the basis of rather a lot of "close up and personal" experience in the area and era, (including some ARB approvals) I will, so there you go.
Tootle pip!!
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Old 5th Apr 2007, 08:41
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However, why therefore does the 747 classic have a stick nudger/pusher?
That's news to me. The classic does not have a stick nudger/pusher. It has a stick shaker motor mounted on the capt's control column which is activated by a signal from the stall warning computer. A torque tube interconnecting the two control columns transfers vibration from the captain's control column to the first officers control column.
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Old 5th Apr 2007, 10:04
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That's news to me. The classic does not have a stick nudger/pusher. It has a stick shaker motor mounted on the capt's control column which is activated by a signal from the stall warning computer. A torque tube interconnecting the two control columns transfers vibration from the captain's control column to the first officers control column.
If you read AMM chapter 27-32-00 it states:
C. With trailing edge flaps full up, activation of the control column shaker automatically energizes a stick nudger which moves the control column forward to alleviate the approaching stall condition. The stick nudger installation consists of a control column actuator, a relay, and
connections to inboard and outboard flap switches. When both flap
switches indicate flaps up, the stick nudger relay is energized by the
same warning computer output which shakes the control columns.
When ever you do the stall warning test you get the control column shaking and it also pushes forward. Sounds like a stick pusher to me.

It also has a shaker on each comtrol column:

The control column shakers vibrate the control columns when energized by
a signal from either stall warning computer. A shaker is clamped to the
front of each pilot's control column.
Each shaker consists of a motor
and a coaxially mounted weighted ring. Energizing the motor rotates the
out-of-balance ring, and the resulting vibration shakes the control
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Old 5th Apr 2007, 12:27
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Just because they weren't fitted to your B747s Hotdog doesn't mean that they weren't fitted to any B747s. From what Spanners quotes and describes it certainly sounds like he has them fitted to his....

Don't quote me, but I vaguelly remember reading something about that in "Flying the big jets" ..... that right?
The UK CAA made Mr Boeing add a few extra things to keep them happy.
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Old 6th Apr 2007, 02:57
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You have to differentiate between stick pushers and stick nudgers. Pushers were fitted to aircraft with serious stall problems such as the BAC1-11 to avoid a deep stall etc. Nudgers were fitted to a number of Boeing's and possibly other types, often for UK CAA certification, because they had a slight pitch up tendency before exhibiting a classic nose down pitch at stall. DP Davies did not like this slight pitch up as he states somewhere in Handling The Big Jets whereas the FAA accepted it given there was a natural nose down pitch at the stall. The nudger fitted on the 747 simply operated at the same time as the stick shaker and applied about a 5 pound push to the column to prevent the pre- stall pitch up.
DP Davies required about 20 Special Conditions for UK certificaton of the 747 but later CAA test pilots have vitrually eliminated them all.
Incidentally Boeing was horrified to find that airlines operating to UK CAA rules were stalling 747's on their air tests as they reckoned the wing wake buffet could take the horizontal stab close to its ultimate load and insisted a severe turbulence inspection be carried out after any stall. Eventually the full stall on the CAA air test was abandoned and the aircraft in my company were only taken to stick shaker onset.
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Old 6th Apr 2007, 03:49
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Well, it sounds like the nudger was an option - as the classics I flew didn't have them.

The British passion for stick pushers was obviously as a result of the fact that a lot of their designs had T -tails. I used to fly the VC10. The pusher was tested on every pre-flight. The push was considerable and would have probably stuck you to the ceiling if you weren't strapped in.

Last edited by Dan Winterland; 6th Apr 2007 at 06:53. Reason: grandma
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Old 6th Apr 2007, 05:51
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I'm quite certain that our B727-200ADV have no stick pushers installed..IMHO, this was something mandated by the British civil aviation law
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Old 7th Apr 2007, 15:30
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The classic DC-9 series, 10, 20, 30, 40, 50, had no stick pusher. The first MD-80, of which you recently no doubt saw the tail fall off, via YouTube, didn't have a pusher either. While doing deep stalls, it got into an unrecoverable stall, falling leaf, upon which they deployed the chute.

That's why all MD-80 have stick pushers.

Remember 1979, the year of the AA DC-10 crash at ORD, and the ANZ DC-10 on Mount Erebus in Antartica? Between those two events was an AeroMexico drama that barely made the US news.

They took off from Frankfurt, fully loaded headed for MIA. The Capt. put it in V/S climb, 1500'/min. At 27K ft, the engines could no longer keep up that climb/speed rate, and the A/P began hauling back the speed. The plane stalled at 31K feet, even shaking the cabin panels down, etc. They called a Mayday. The Capt., not recognizing the stall, pulled the power to the #3 engine, which put them into a spiral. He recognized that, and recovered at 10K ft, and canceled the Mayday.

Upon arrival at MIA, the Capt said the flight was normal. The guy doing the walkaround noticed both elevator horns missing, aileron damage, etc., so they quickly wrote up a report. The Capt was demoted to F/O for six months. He blamed the plane for not having a big red STALL light on the panel, like the DC-9, and maybe DC-8 he used to fly.

If they had gone in the drink, that may have been the end of the DC-10 in pax service.

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