Page 1 of 1

Extension of flaps and landing gear during turns on large aircraft

Posted: Wed Apr 07, 2021 8:50 pm
by phugoid1982
Obviously this question will depend on the aircraft but for larger widebody aircraft what are the limitations for gear extension and flaps extension during turns (if this can even be done at all). I can't believe in all my time being a passenger I never paid attention to this. This includes flaps in transit and initiating an extension. I was particularly thinking of lateral stresses on large control surfaces as well as on the gear due to centripetal acceleration as well changing pitching moments as well as increased induced drag due to increasing CL due to flaps at a particular thrust setting that could instantaneously slow you down.

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Wed Apr 07, 2021 9:17 pm
by GalaxyFlyer
Zero limits within the aircraft limits. The plane, even in a turn, is symmetrically loaded, why wouldn’t they go out? We’d put the crazy gear and flaps on a C-5 at 45 degrees of bank turning tactical arrivals. Even with aero elasticities, flight controls including high lift devices are designed as advertised.

I’m not sure what you mean in that last sentence. Thrust and Cl are unrelated and the plane doesn’t instantaneously slow down like it a wall.

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Wed Apr 07, 2021 9:37 pm
by phugoid1982
GalaxyFlyer wrote:
Zero limits within the aircraft limits. The plane, even in a turn, is symmetrically loaded, why wouldn’t they go out? We’d put the crazy gear and flaps on a C-5 at 45 degrees of bank turning tactical arrivals. Even with aero elasticities, flight controls including high lift devices are designed as advertised.

I’m not sure what you mean in that last sentence. Thrust and Cl are unrelated and the plane doesn’t instantaneously slow down like it a wall.


Yeah that was confusing. I meant increased Induced Drag, which is proportional to Cl^2 from extending flaps at a constant thrust setting (wasn't thinking about autothrottle) would result in deceleration. I know it's not dramatic. Trouble is I've been spending too much time being lazy playing flight sim and just dumping the flaps non-incrementally which is obviously not a good idea. Coincidentally, given your moniker, I was actually flying a C-5 into Ponce (TJPS) because someone said they used to land there on 12 back when the runway was only 6900 feet long and runway 12 has an 800 ft displaced threshold so only 6100 ft landing distance. At a a small landing weight I wasn't too concerned about getting it stopped rather maneuvering around those narrow taxiways. Not easy. Just

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Wed Apr 07, 2021 9:39 pm
by Flow2706
There is no limitation regarding extending flaps during turns. The load on the flap mechanism is not increased due to the turn, there is no safety risk involved.
The speed at flap extension is more critical though. On my type (A320) many pilots try to avoid flap extension close to the limit speed (unless operationally required). Obviously the flaps are certified to extend at the limit speed, but routinely extending the flaps close to the limit will wear out the mechanism faster and increase maintenance cost. It is also considered good airmanship not to move the flaps and the gear at the same time to avoid peak loads on the green hydraulic system (this is also not a limitation/procedure, but is considered good airmanship).

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Wed Apr 07, 2021 9:43 pm
by GalaxyFlyer
Yeah, we rarely would go in there and MCAS Barking Sands, HI, 6006’ available. Be on your A game at both places. I’ve never seen a limit on bank angle, thrust or anything else on configuration changes other than indicated airspeed or Mach. Obviously, these aren’t aerobatic types, so you can’t fly it upside and put the gear out because it’s outside the flight envelope. BTW, the two fighters I flew didn’t have limits, either except speed. The Blue Angels put the gear out inverted, I believe.

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Thu Apr 08, 2021 1:48 am
by Starlionblue
If you're using manual thrust, smoothly increase as needed as the slats/flaps and gear come out. The biggest drag change is the gear, but you more or less know how much you need to increase the thrust to compensate. Set an approximate value as the gear comes out, and adjust once a speed trend becomes apparent.

There's a lot of inertia in airliners, and neither flaps nor gear drop instantaneously. Plenty of time to adjust.

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Thu Apr 08, 2021 2:01 am
by Max Q
Flow2706 wrote:
There is no limitation regarding extending flaps during turns. The load on the flap mechanism is not increased due to the turn, there is no safety risk involved.
The speed at flap extension is more critical though. On my type (A320) many pilots try to avoid flap extension close to the limit speed (unless operationally required). Obviously the flaps are certified to extend at the limit speed, but routinely extending the flaps close to the limit will wear out the mechanism faster and increase maintenance cost. It is also considered good airmanship not to move the flaps and the gear at the same time to avoid peak loads on the green hydraulic system (this is also not a limitation/procedure, but is considered good airmanship).



Yes

Flaps are for flying slower, not for slowing down

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Thu Apr 08, 2021 11:11 am
by SAAFNAV
GalaxyFlyer wrote:
Zero limits within the aircraft limits. The plane, even in a turn, is symmetrically loaded, why wouldn’t they go out? We’d put the crazy gear and flaps on a C-5 at 45 degrees of bank turning tactical arrivals. Even with aero elasticities, flight controls including high lift devices are designed as advertised.


The C-130 has a limitation of using flaps in the turn. It can be done non-standard, but should be limited to once the bank is established and not during the roll-in. Also commander's call only, and when operations require it.
The asymmetric flap brake is reportedly a bit temperamental with the differing torsional loads.

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Thu Apr 08, 2021 1:31 pm
by GalaxyFlyer
Some planes were temperamental on flap/slat extension, but wasn’t a -1 limitation.

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Thu Apr 08, 2021 1:51 pm
by extender
SAAFNAV wrote:
The C-130 has a limitation of using flaps in the turn.


From the -1:
"It is recommended not to change flap settings while executing turns to facilitate crew identification of flap malfunctions."

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Thu Apr 08, 2021 2:15 pm
by GalaxyFlyer
Well, that explains the -130 guys questioning it.

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Thu Apr 08, 2021 6:05 pm
by VSMUT
Flow2706 wrote:
It is also considered good airmanship not to move the flaps and the gear at the same time to avoid peak loads on the green hydraulic system (this is also not a limitation/procedure, but is considered good airmanship).


I asked about this on a training course in Toulouse once. The manufacturer says its complete bogus, the hydraulic system is in no way negatively affected by doing 2 actions at once. It may have applied to WWII piston bombers, but not for modern airliners.

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Fri Apr 09, 2021 2:20 am
by Starlionblue
VSMUT wrote:
Flow2706 wrote:
It is also considered good airmanship not to move the flaps and the gear at the same time to avoid peak loads on the green hydraulic system (this is also not a limitation/procedure, but is considered good airmanship).


I asked about this on a training course in Toulouse once. The manufacturer says its complete bogus, the hydraulic system is in no way negatively affected by doing 2 actions at once. It may have applied to WWII piston bombers, but not for modern airliners.


Love it.

Regardless, I'd get a thrashing if I asked for flaps three as the gear was still moving. Convention is a powerful thing. :D

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Fri Apr 09, 2021 8:56 am
by VSMUT
Starlionblue wrote:
VSMUT wrote:
Flow2706 wrote:
It is also considered good airmanship not to move the flaps and the gear at the same time to avoid peak loads on the green hydraulic system (this is also not a limitation/procedure, but is considered good airmanship).


I asked about this on a training course in Toulouse once. The manufacturer says its complete bogus, the hydraulic system is in no way negatively affected by doing 2 actions at once. It may have applied to WWII piston bombers, but not for modern airliners.


Love it.

Regardless, I'd get a thrashing if I asked for flaps three as the gear was still moving. Convention is a powerful thing. :D


A more important lesson is probably that you shouldn't get yourself into a position where the gear and flaps extension needs to be rushed.

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Fri Apr 09, 2021 10:13 am
by Flow2706
Starlionblue wrote:
Regardless, I'd get a thrashing if I asked for flaps three as the gear was still moving. Convention is a powerful thing. :D

In my previous company flaps 3 with gear still in transit apparently resulted in an FDM event. I was quite surprised when the safety department asked me to submit a report regarding this issue..

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Fri Apr 09, 2021 3:48 pm
by VSMUT
Flow2706 wrote:
Starlionblue wrote:
Regardless, I'd get a thrashing if I asked for flaps three as the gear was still moving. Convention is a powerful thing. :D

In my previous company flaps 3 with gear still in transit apparently resulted in an FDM event. I was quite surprised when the safety department asked me to submit a report regarding this issue..


I've had FDM events on completely normal stuff well within limits as well. FDM madness.

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Fri Apr 09, 2021 7:41 pm
by chimborazo
VSMUT wrote:
Flow2706 wrote:
It is also considered good airmanship not to move the flaps and the gear at the same time to avoid peak loads on the green hydraulic system (this is also not a limitation/procedure, but is considered good airmanship).


I asked about this on a training course in Toulouse once. The manufacturer says its complete bogus, the hydraulic system is in no way negatively affected by doing 2 actions at once. It may have applied to WWII piston bombers, but not for modern airliners.


Have been in the 737 sim a few times with someone who trains pilots and the procedure they use when intercepting the glide slope on an ILS is: PF calls “Gear down, flaps 15”. It’s done together so the gear warning horn doesn’t come on but shows that there’s no issue with doing two actions that use the hydraulics at the same time.

Not related to hydraulic loads but in GA I was taught specifically not to move the flaps in a turn: if you’re in say a left bank and you extend the flaps and the left one doesn’t move that can cause an upset banking you over more with additional lift on the starboard wing - not good when you’re likely to be relatively low and slow when positioning base to final for example. Less “important” in a PA-28 where you manually pull the flaps and it’s very quick and easy to revert, but more so in a 172 when the flaps are motorised.

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Fri Apr 09, 2021 8:23 pm
by GalaxyFlyer
Asymmetric flap protection, required on larger planes, prevents that problem.

Re: Extension of flaps and landing gear during turns on large aircraft

Posted: Sat Apr 10, 2021 4:38 am
by Starlionblue
VSMUT wrote:
Starlionblue wrote:
VSMUT wrote:

I asked about this on a training course in Toulouse once. The manufacturer says its complete bogus, the hydraulic system is in no way negatively affected by doing 2 actions at once. It may have applied to WWII piston bombers, but not for modern airliners.


Love it.

Regardless, I'd get a thrashing if I asked for flaps three as the gear was still moving. Convention is a powerful thing. :D


A more important lesson is probably that you shouldn't get yourself into a position where the gear and flaps extension needs to be rushed.


An excellent point. :D