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Martinlest
Topic Author
Posts: 91
Joined: Sun Nov 06, 2016 9:54 pm

Max speed while banking?

Thu Sep 06, 2018 4:23 pm

I often find that I arrive at a sharp turn in my flight plan (or more usually SID with a long first 'leg') when the aircraft (I mean a320/b777 or the like, not c172) has climbed beyond 10000' and, being in CLB/VNAV mode, has already accelerated to 340kts or whatever. (Talking X-Plane here BTW, not passenger-bearing real-world aircraft!).

Would a real-world a/c happily do a 120 deg bank (slow one of course) at that speed, or should there be some speed restrictions in the flight plan? I would need to write those in myself I suppose.. they are not part of the SID?? If there is a speed restriction for banking, what are the 'rules'?

Thanks!

Martin
 
GalaxyFlyer
Posts: 8584
Joined: Fri Jan 01, 2016 4:44 am

Re: Max speed while banking?

Thu Sep 06, 2018 4:28 pm

Its NOT a bank; it’s a turn (change in direction) of 120⁰ and a plane, given the airspace can do 360s all day long at Vmo/Mmo. If the SID/STAR has a speed restriction, then it should appear in the FMS flight plan or be manually entered. Speed limits are for airspace containment usually. Faster speed equals larger turn radius equals spill-outs.

The FD commonly limits bank (roll) to 25⁰ and often reduces the bank limit at higher altitudes.

GF
Last edited by GalaxyFlyer on Thu Sep 06, 2018 4:30 pm, edited 1 time in total.
 
BravoOne
Posts: 4094
Joined: Fri Apr 12, 2013 2:27 pm

Re: Max speed while banking?

Thu Sep 06, 2018 4:28 pm

120 degree bank????? Stand back, this is going to be good.
 
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Horstroad
Posts: 608
Joined: Thu Apr 08, 2010 8:19 pm

Re: Max speed while banking?

Thu Sep 06, 2018 4:35 pm

Bank angle limit is a function of true air speed. For the B777 it looks something like this:

Image

Additionally bank angle is limited to 8° below 200ft.

That's an automatic function.
 
Martinlest
Topic Author
Posts: 91
Joined: Sun Nov 06, 2016 9:54 pm

Re: Max speed while banking?

Thu Sep 06, 2018 4:40 pm

Haha! Turn, yes, not bank of course. Brain on autopilot again...

I was supposedly asking about doing turns at high speed. I suppose if the bank angle is always small, there's no issue. But in the real world, when pilots know that there is a big turn in a SID, especially if the aircraft would be normally be at high speed at that stage, do they enter a speed restriction so that the turn is taken more slowly (or there is already one in the SID??). Or is that not a factor?
 
GalaxyFlyer
Posts: 8584
Joined: Fri Jan 01, 2016 4:44 am

Re: Max speed while banking?

Thu Sep 06, 2018 4:47 pm

No, just fly it at the appropriate climb schedule. The speed is for best performance and the procedures are designed for the expected aircraft flying them. If terrain clearance or airspace is st issue the procedure will contain a limit.



Gf
 
Redbellyguppy
Posts: 257
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Re: Max speed while banking?

Thu Sep 06, 2018 6:14 pm

Unless it is a fly over fix, the fmc will round off the corner as it goes by the fix in the turn. A single turn of 120 degree bearing change would mean that the aircraft would start turning quite a bit before the fix. I don’t think I’ve ever seen that sharp of a turn though, ever. That said I can build a hold with a leg length of 0.1... in essence a circle, and the plane will do it all day long at vmo/mmo
 
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Starlionblue
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Re: Max speed while banking?

Thu Sep 06, 2018 11:43 pm

Martinlest wrote:
Haha! Turn, yes, not bank of course. Brain on autopilot again...

I was supposedly asking about doing turns at high speed. I suppose if the bank angle is always small, there's no issue. But in the real world, when pilots know that there is a big turn in a SID, especially if the aircraft would be normally be at high speed at that stage, do they enter a speed restriction so that the turn is taken more slowly (or there is already one in the SID??). Or is that not a factor?


If there is a speed restriction, it will be followed. If there isn't one, there is no need for one. The procedure was designed with normal speed in mind.

As GalaxyFlyer says speed limits in SIDs are typically for terrain or airspace management. Lower speed means a tighter turn.

Example 1: ILS 34 into Macau. Chart 11-2 here http://www.fly-sea.com/charts/VMMC.pdf. There's a note about "Max Approach turning speed 190kts". The missed approach has an immediate right turn. It is speed limited so you avoid entering the Mainland China airspace to the north.

Example 2: Gimpo departures to the Northwest are speed limited so you don't stray into North Korean airspace. http://aim.koca.go.kr/eaipPub/Package/2 ... RKSS/(2-13)%20SID.pdf
 
Martinlest
Topic Author
Posts: 91
Joined: Sun Nov 06, 2016 9:54 pm

Re: Max speed while banking?

Fri Sep 07, 2018 7:42 pm

One example - the SID SSN2C out of LEBB - the a/c I am flying (an a319 here) has no chance of making the tight 180-degree turn at D313H (it's at 300kts by then). Basically, you folks are saying that, if there are no speed restrictions indicated, then the much wider turn is fine? (In this case it's over the ocean).

Thanks for the links etc.

Martin
 
GalaxyFlyer
Posts: 8584
Joined: Fri Jan 01, 2016 4:44 am

Re: Max speed while banking?

Fri Sep 07, 2018 8:23 pm

Well, a couple thoughts, chart I have 10-3C Jepp 10/2/2017. First, it’s 250 knots until leaving FL080, so you might still be operating at 250 knots or less at 8 miles. Likely, in fact. Second, as a pilot on that SID, flying out the SID without radar control turning me direct to FEBRI, I’d probably go manual speed 210 knots (or a comfortable speed for the type I’m flying) until completing the reversal back to BLV just to make the turn easier. There’s no rush to fly it at 300 knots. There’s also no restriction to doing so, as there is for the SSN 2A.

All that said, in real life, ATC would give you a vector toward FEBRI once on radar and above the terrain.

GF
 
Woodreau
Posts: 2173
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Re: Max speed while banking?

Fri Sep 07, 2018 9:40 pm

Looking at the chart

https://ais.enaire.es/AIP/AIPS/AMDT_305 ... D_4_en.pdf

The departure is asking you to do is fly over the BLV R-313 D8.0 DME fix at or above 3000ft and then turn right direct back to BLV VOR. Since the initial altitude is FL080 you’re not going to be doing the turn any faster than 250kts. You start the turn after flying over the 8dme fix and your turn is done when you’re direct back to the BLV VOR.
 
Martinlest
Topic Author
Posts: 91
Joined: Sun Nov 06, 2016 9:54 pm

Re: Max speed while banking?

Sat Sep 08, 2018 10:10 am

OK, that's clear. The SID I enter into the FMS doesn't have this elevation restriction, so the a/c accelerates after FL100 of course (the a319 climbs quite powerfully when I engage CLB and has reached that altitude before D313H).. I need to enter this manually I think (and yes, probably a speed restriction too - 210kts sounds about right). Thanks.
 
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Starlionblue
Posts: 20864
Joined: Fri Feb 27, 2004 9:54 pm

Re: Max speed while banking?

Sat Sep 08, 2018 1:23 pm

There should be an automatic speed restriction at 10000 feet that changes the managed speed from 250 to LRC or ECON.
 
BoeingGuy
Posts: 6671
Joined: Fri Dec 10, 2010 6:01 pm

Re: Max speed while banking?

Sun Sep 09, 2018 12:11 am

Horstroad wrote:
Bank angle limit is a function of true air speed. For the B777 it looks something like this:

Image

Additionally bank angle is limited to 8° below 200ft.

That's an automatic function.


That’s only for the HDG SEL mode and only if your bank angle selector is in the AUTO position. LNAV can command a 30 degree bank angle.

Also the 787 and 777X will command up to 30 degree bank angle in HDG SEL.
 
GalaxyFlyer
Posts: 8584
Joined: Fri Jan 01, 2016 4:44 am

Re: Max speed while banking?

Sun Sep 09, 2018 2:27 am

To put some comparative turns for speeds

At 300 KIAS, the TAS is 350 knots at 8,000 and the approximate turn diameter (180*) is 8.0 nm.

At 210 KIAS, the TAS is 240 knots at 8,000 and the turn diameter is only 3.1 nm.

The high speed turn would cover 75* or result in an inbound course of about 205*; while the slower turn would only cover about 25* and result in returning to the BLV VOR on a course of about 160*.

GF

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