View Full Version : can you answer any of the following questions?

power lever
20th Jul 2002, 11:30
Hi there,

Could any of you be kind enough to answer any of the following questions.

1) what is a JET UPSET?

2) what happens to a stall at very high altitudes?

3) what are active controls?

4) what is the purpose of a mach trimmer?

5) what is a direct lift control?

6) why is EPR set by 60/80 kts?

7)where is the best place for C of G in flight?

8)what is dithering?

9) difference between diff/non diff spoilers?

10) what are the requirements for ETOPS?

Thanks for any replies to the above.

PL:confused: :confused:

20th Jul 2002, 11:43
OMG, talk about ... "In the beginning..."! :eek:

power lever
20th Jul 2002, 12:03
come on then OZ, put your money where your mouth is and answer some pal.

20th Jul 2002, 13:14

Well...errrm :eek:

Dithering is something to do with the GPS atomic clocks


power lever
20th Jul 2002, 14:01

Great, thanks alot.


20th Jul 2002, 14:50
Jinkster your right about dithering, i believe it was a method used by the US military to alternate the times in the atomic clocks in the gps satellites so that your position would be less precise when you are using a "civil" gps-system. The military did have the special code to reveal what the real timing was so they could be more precize, and maintain the advantage on users of the civil-system.

And ETOPS requirements have to do with reliability and maintenance of the engines of the aircraft, they have to be proven to be within certain limits (i'm sure you can find them at google)

gas path
20th Jul 2002, 15:43
No 3 Active controls.
Ailerons respond to gust load imposed on the wing. The L1011-500 had them. The outboard ailerons (normally locked out with the flaps up) respond simultaneously and symetrically to absorb the increased wing root bending moment, limit the load on the wing and negate the need to beef up the wing structure.

No 5 Direct lift control.
Another L1011 thing. Used on the approach the spoilers are deployed to a null position and modulate around that point, improves pitch axis control and handling.

Not only engine reliability but systems reliability and redundancy also, including, for instance, the ability of the APU to be started in flight after a cold soak.
Engine health monitoring is also a requirement.

20th Jul 2002, 16:35
The same questions are appearing quite frequently, what exam are they from? Aren't the answers covered in the training syllabus?


20th Jul 2002, 18:56
Question 6 (http://www.pprune.org/forums/showthread.php?threadid=59626)

Bally Heck
20th Jul 2002, 19:11
Q 1 From Boeing FCT Manual.

An upset can generally be defined as unintentionally exceeding the following
pitch attitude greater than 25 degrees nose up, or
pitch attitude greater than 10 degrees nose down, or
bank angle greater than 45 degrees, or
within above parameters but flying at airspeeds inappropriate for the

20th Jul 2002, 21:29
Since no one else has replied to this one...

What happens to a stall at very high altitudes?

As an aircraft climbs, TAS becomes much greater than CAS. This occurs because CAS is an airspeed based on dynamic pressure, but assuming sea level air density. It is not an accurate measure of airspeed at high altitude (low air density).

As an aircraft climbs the stall speed (CAS value does not change much with altitude) gets closer and closer to the maximum allowable speed - based on TAS or Mach Number.

At an aircraft's absolute ceiling the airspeed indicator will show a value just above the aerodynamic stall buffet, but TAS will be high enough to be just below max TAS or Mach buffet.

If the aircraft were to be allowed to stall, how will the pilot recover? You must lower the nose to reduce angle of attack, but this will inevitably result in an increase in airspeed so you exceed max TAS or even get Mach buffet. Both of these (of course) are very bad for the aircraft structure, and may result in structural limits being exceeded and/or bits falling off.

To fix this, aircraft capable of flying at very high altitudes have a certificated maximum altitude to avoid getting near this flight regime (sometimes called "coffin corner".)

Note 1: there are many other reasons why an aircraft may have a specified max altitude - this is just one aerodynamic one.
Note 2: as far as I know supersonic aircraft do not have the same problem - it's a civil air transport issue.

O8 :)

power lever
20th Jul 2002, 22:55
BIK, as requested the edit has been done. I just feel that sometimes on pprune you ask a simple question and you get some very stupid replies!

And to all the guys that have hepled in answering my questions, I thank you.

Take care


Weight and Balance
21st Jul 2002, 03:18
One more use of "dithering", although this may show my age.

Back in the 60s and 70s, dithering was used in the earliest electrohydraulic servo controls to minimize the breakout friction present when the control was first commanded to move.

A high frequency, very low amplitude electrical signal was continually sent to the EHSV (electrohydraulic servo-valve). This was called a dithering signal. This kept the moving parts (EHSV coils, control spools and hydraulic actuator pistons) in constant motion, but of such small amplitude that there was no effect on the airplane (or whatever) the system was installed in.

When a real control input came along, there was no static friction to overcome before things started to move.

21st Jul 2002, 05:58
Power Lever,

Arent you going to tell us what exam paper we are trying to answer?


21st Jul 2002, 07:56
Mutt: Does it matter? If you have the issues explained as thoroughly as they have been here then you can answer any question on them in any paper, can't you? I've always believed understanding the subject is better than trying to question-spot!

21st Jul 2002, 09:27

I have no reason to question spot. I'm just interested in knowing why the same questions keep coming up.


21st Jul 2002, 09:42
Mutt, the questions are from the Cx tech quiz for new pilot applicants.

power lever
21st Jul 2002, 10:42

very true, I feel the answers to my questions have been answered very well indeed.

Thanks guys.:D

21st Jul 2002, 11:05
I guess that I can now see why people were reluctant to answer my question in the first place. :)