View Full Version : Turning a jet

2nd Feb 2005, 18:52

Prob a silly ques, but what is normal AoB for a commercial jet when flying manually? 30?

Plus, what about holds? I know obviously rate one, but with no rate of turn indicator, what then??


High Wing Drifter
2nd Feb 2005, 19:41
TAS/10+7 = Approx angle of bank for Rate 1.

I think the bank limits are generally no more than 25 deg and never under normal circumstances more than 30 deg so you will spend most of the time turning at less than Rate 1.

2nd Feb 2005, 20:03
A standard hold should be flown at 25 deg AoB or Rate 1, whichever requires the lesser AoB.

2nd Feb 2005, 20:56
BEagle has it spot on although most autopilots will turn at 28 AOB.

In addition, many autopilots will have the facility to selecte a lower bank angle - the B737-200 has the option to set 15 or 20 and the HS125-800 has a "half bank" facility giving 14. These lower bank angles may be useful at higher altitudes when the IAS is close to the low speed buffet boundary.

Plus, as long as you have a yaw damper you don't need to apply "top" rudder - the pedals become footrests!

High Wing Drifter
2nd Feb 2005, 22:17
Plus, as long as you have a yaw damper you don't need to apply "top" rudder - the pedals become footrests!
Always a little confused with this statement. We were told at Ground School that Yaw Dampers wern't for autocoordination but to help prevent dutch roll. I assume this statement came about because modern Class A kit doesn't suffer from adverse yaw.

2nd Feb 2005, 22:51
Well, a couple of reasons really.

1 ) At jet speeds, the fin is more effective and as such naturally tends to resist slipping into the turn.

2 ) the yaw damper system detects the slip and applies top rudder.

and yes, it is primarily designed to counter Dutch roll, the autoco-ordination bit is a bonus.

Other than on a Jet Provost (no yaw damper) I have only ever had to use the rudders on jets to control the aeroplane on the take-off/landing roll or when asymmetric.

Trust me, it works!

3rd Feb 2005, 07:35
Not so much 'yaw damping' (which indeed exists to prevent Dutch Roll), but aileron/spoiler-rudder cross feed......

Earlier swept wing a/c suffered from excessive 'dihedral effect' due to their sweep angle and positive dihedral; at high level any sideslip would cause a powerful restoring rolling moment in the opposite sense to the sideslip; thus the yawing moment resulting from the fin would become out of phase with the rolling moment caused by dihedral stability and at higher levels with adverse IAS/TAS ratios this could become divergent if left uncorrected. Rate gyros were thus fitted to detect the onset of sideslip and apply corrective signals to the rudder PCUs before the Dutch Roll could start.

The Russian solution was cleverer - pronounced anhedral (Il 62, Tu 154) to prevent the rolling moment ever becoming excessive!

Incidentally, anyone flying at such heights/weights that 15 deg of bank is the maximum to avoid low speed buffet boundary problems would be flying way, way outside the certification limit of a modern airliner! Even in the dark ages when we used to operate with a 20 knot spread between the 1.2 g HSB and LSB, we always had 25 deg of bank available! Really the 15 deg AoB detent is only there to enhance 'passenger comfort' - and to avoid unnecessary performance-sapping large angles of bank in the cruise (less drag, obviously).

Piltdown Man
3rd Feb 2005, 12:28
Approx. 30 degrees (it's easy because, one there's a mark on the PFD, Horizon or whatever you want to call it) and that is generally what the autopilot will give you unless, as has been mentioned before, you select it for 15 degrees. If you remember Perf A. expects that AoB follwing an engine failure when you have to turn during your V2 climb. Most company SOP's also expect turns no greater that 30 degrees. And as for Holds, yes they are designed for 25 degrees of bank - but in real life: you type them into the FMS and drink tea while doing sums on endurance etc...

3rd Feb 2005, 13:12
Thanks for all the useful advise guys, much appreciated!

However piltdown, if you don't have an FMS onboard, the tea would have to wait!!

High Wing Drifter
3rd Feb 2005, 19:40
Thanks too to BEags, moggie and Piltdown for the explanation :ok:

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