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-   -   is Vmca mean stall speed? (https://www.pprune.org/tech-log/530245-vmca-mean-stall-speed.html)

dolpinsky 19th Dec 2013 11:38

is Vmca mean stall speed?
 
quick search from internet..
MINIMUM CONTROLLABLE AIRSPEED—An airspeed at which any further increase in angle of attack, increase in load factor, or reduction in power, would result in an immediate stall.

so are they the same?

flyboyike 19th Dec 2013 12:01

No, they're not the same. You searched on the wrong internet.

justasmallfire 19th Dec 2013 12:05

Vmca
 
I wouldn't rely on that information,try here
V speeds - Wikipedia, the free encyclopedia

Lowest speed that you still have directional control(control surfaces still have an effect)
Any lower speed and you will lose control when asymmetric,then yes you could possibly spin /stall

latetonite 19th Dec 2013 12:10

He did not only search on the wrong page, he is still on the wrong URL now.

dolpinsky 19th Dec 2013 12:33

thx guys for the help ;)

pattern_is_full 19th Dec 2013 16:14

"Vmca" as a published limitation speed applies only to multi-engine aircraft - the lowest speed at which the rudder (or other flight controls) can maintain straight and level flight with one engine failed (asymmetric thrust). Slower than that speed, and the rudder will be at full deflection, and yet still not providing enough yaw force to maintain straight and level flight - whether the wing is stalled or not.

Since there is no such thing as "Vmca" for a single-engine aircraft, even though a SE aircraft will have a stall speed - obviously the two mean different things.

I can see where some confusion sets in, however, since a basic maneuver in (single-engine) flight training is called "flight at minimum controllable airspeed" - maintaining altitude and making gentle turns while on the edge of the stall. But without a failed engine in the equation.

Maneuvering at Minimum Controllable Airspeed

But "Vmca" - for a multi-engine aircraft* - means something different than paddling a single-engine Cessna or Piper around the practice area with the stall buzzer screeching. Despite the identical wording.

*always excepting the "push-me-pull-yous" like the 337. ;)

misd-agin 19th Dec 2013 16:24

Pattern is correct.

You won't stall/spin as soon as you slow below VMCA in a MEL. The plane will start to turn in the direction of the failed engine.

dolpinsky 20th Dec 2013 03:59

ty pattern and misd :)
it really helps a lot ;)

barit1 20th Dec 2013 14:48

Now check out Vmcg, and its effect on flight planning.

dolpinsky 21st Dec 2013 04:04

em..min controllable speed on ground

if an multi-engine aircraft is accelerating on the runway and one engine fails, even pilots apply full rudder they would still cant keep the aircraft on the centerline.
so i guess the importance of vmcg is that it gives pilots time to decide whether to go or to abort the takeoff in case an engine fails after vmcg?

please forgive me if i'm wrong

john_tullamarine 21st Dec 2013 09:19

Since there is no such thing as "Vmca" for a single-engine aircraft

Not often considered but a large engine single aeroplane can have a situation similar to Vmca at low speed and high thrust. I understand that some OTE exercises in the military have considered this.

You won't stall/spin as soon as you slow below VMCA in a MEL

.. but you may be quite close to stall at book Vmca. Also, keep in mind ASI errors and the reduction in real world Vmca for most lighties as altitude increases.

Be careful .. for there be dragons .. best to stay right away from Vmca as there is little value in playing about with it.

even pilots apply full rudder they would still cant keep the aircraft on the centerline.

The aeroplane won't stay on centreline with a failure at low speed. Vmcg is defined in terms of a maximum deviation from centreline. As the failure speed increases, the deviation can be constrained to a smaller value.

the importance of vmcg is that it gives pilots time to decide whether to go or to abort the takeoff in case an engine fails after vmcg?

Vmcg is a certification thing which is used in the determination of numbers to be used by pilots. I suggest, presuming you are early in your career, that you don't worry too much about Vmcg at this stage.

barit1 21st Dec 2013 12:35


Not often considered but a large engine single aeroplane can have a situation similar to Vmca at low speed and high thrust. I understand that some OTE exercises in the military have considered this.
I hadn't thought of it in the Vmcg context, but this is very applicable for many prop singles, particularly taildraggers - e.g. Harvard, Mustang, Grummans, etc. Opening the throttle aggressively can result in a ride through the bush long before liftoff speed. And adverse crosswind can be a catalyst! :ouch:

Linktrained 21st Dec 2013 12:55

I was a "new " Captain on the Car Ferry, so my weather minima had 100ft added to the Company's ie for me it was 400ft.
The a/c ahead had landed a five minutes earlier. At 400ft I was still IFR, so I overshot. Whilst under training I had done a number of overshoots, both two engined and with one feathered.
On this occasion the Starboard propeller went into " Auto coarse" and was feathered.
My speed fell, as |I had started to climb. ( A two engine climb of course)
I had to trade height for speed and got down to 200ft before climbing. I cannot NOW recall my lowest speed.The following day the Chief Pilot said that I had reached Vmcg.
He said that he had not heard of this happening in flight before.
The auto coarsening had been added to the Car Ferry fleet to allow us to operate at 44,000lbs instead of 40,000lbs and had two Pitots to ensure that both engines worked equally on T/O.
I think he ( understandably?) blamed me.
A few months later a similar thing happened and people were killed.
The auto coarsen system was switched off, when not required, after that.

PS
Possibly my having learned and practiced low overshoots in gliders near Toulouse or having a large left foot may have helped. on my occasion.
I see that " engine failure on overshoot" may be practiced on a sim, nowadays. ( Not on a "single - engined "Link Trainer, then.)

TheChitterneFlyer 21st Dec 2013 16:00



The following day the Chief Pilot said that I had reached Vmcg.
I believe he meant to say Vmca and NOT Vmcg!

Linktrained 21st Dec 2013 18:13

TCF
You could be right... It was a while ago. ( His, or even my, memory could have slipped a letter !)
We diverted to Lympne, unloaded, had the aircraft checked by GEs and flew a further five trips ( 10 sectors ) with no further problems that day, the weather had improved.
There was no recording of individual flights, CVR etc. then.


I had an early WIREK wire recorder issued to me in the Spring of 1948, but that was heavy and not for an aviation use.

Old Fella 22nd Dec 2013 04:51

Vmca
 
Very sadly, those who know of the events leading to the loss of A20-103, a Boeing B707-300 operated by 33 Sqn RAAF, know very well the meaning and implications of Vmca.

Much comment, often misguided, has been on this forum and others over time. As pointed out by Pattern is Full Vmca is that speed below which directional control of the aircraft cannot be maintained with full rudder deflection. For some of we older folk things such as "Dutch Roll Recovery", "Demonstration of Vmca", "Stall Recovery" etc was demonstrated in the aircraft in the days when Simulators were little more than procedural training tools. The first "Simulator" I trained in, a C130A, was a fixed base model with no visual capability. Not so tough for me as a Flight Engineer, but pretty hard work for the pilots.

I have read somewhere that some items in the Qantas B707 FM had not been copied to the RAAF produced B707 FM. I cannot comment, other than to say that the only part of the RAAF B707 FM which was different to Qantas was the cover in the initial period of the aircraft's RAAF service. The publication was, in fact, the Qantas FM in a RAAF binder. Additionally, I have read elsewhere that two engines (double asymmetric) were SHUT DOWN. This, I do not believe. At no time during my association with the RAAF was an engine failure simulated by shutting down an engine. Engines were brought to idle, not closed down. The B707 rudder is the only hydraulically boosted flight control surface on the aircraft. At no time during my B707 experience was practice double asymmetric flight conducted, either in the aircraft or in the simulator. Vmca was demonstrated with one engine at idle, with and without rudder boost at FL150 over Bass Strait, likewise for Dutch Roll recovery.

HazelNuts39 22nd Dec 2013 15:25


The publication was, in fact, the Qantas FM in a RAAF binder.
Just for precision: You are probably referring to the Operating Manual (AOM or FCOM). The AFM is a certification document delivered with the airplane and is not operator-specific.

Bill Macgillivray 22nd Dec 2013 21:28

Never, ever, managed a low overshoot (or any other sort) in a glider! :hmm::hmm::hmm::hmm:

Linktrained 22nd Dec 2013 22:58

Glider low overshoots


Unusual, Uncommon, Agreed.


But at the French National Gliding Centre at Montaigne Noire this WAS a part of my gliding course.


The site was on the top of an E/W ridge with the hangar at the W end and student accommodation at the E. Most "endurance flying" used hill lift., along the ridge. Most landings were to the E. The Low overshoots were so that one could land on one or two fields at the bottom of the hill - unless one wished to continue.


We were also taught how to do a short down wind AND up a steep slope landing, where the glider could be turned around for short take off into the wind again.


It may have been an unusual site. They appeared to teach those who were not all novice pilots ( for whom a flit site might be better).



LT

Old Fella 23rd Dec 2013 00:56

Flight Manual v Operations Manual
 
Point taken HazelNuts39, however in the RAAF the C130H model Flight Manual was issued by Lockheed, titled "Flight Manual for RAAF C-130H Airplanes" with the "Lockheed Publication Number FM 382C-71D". This publication was our Operations Manual. So I guess it depends where you are, which type you fly or for whom you fly. The B747's I operated on came with Operations Manuals produced by Boeing, with the rider that in the event there were any differences between the Boeing Operations Manual and the FAA approved Flight Manual, the FM would take precedence.

Regardless of what the manual is called, the RAAF B707-338C publication used in the initial instance was simply the Qantas Operations/Flight Manual inserted into a RAAF binder. What transpired after I had left the RAAF I do not know.

Seasons Greetings.

OF


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