@Mad (Flt) Scientist

I'm awfully sorry to disagree. Like I already mentioned, my FCOM (A300) says

"Max. operating altitude for slat operation or flaps extended is 20 000 ft."

So it clearly distinguishes between slats extended and slats operation.

What do you think is the chart for (it is also of my FCOM and suggested if you fly for whatever reason with slats extended) ? Is there a doted or red line at 20k feet?

Kind regards

Consider this.
Most airplanes restrict available flap the higher elevation the airport.
At sea level, you've got gobs of flap to play with for takeoff or landing.
Go to some of them 10k+ airfields, and you're permitted very little, maybe slats only.
Why's that?
I figure it's because the denser air can press itself around the outer camber more easily and can stay laminar to a lower speed.
Get up into the thinner angel breath, and it's not so forgiving - you really have to coax those sparse molecules to stick with ya.
Thoughts?

Stubs400

@stubs400

99% of T/O in our route system are done with slats only (A300)


The point is: Am I limited to stay at or below 20k feet if slats are extended?

Concerning A300, I say "NO".

Regards

Why would you ever want to even think about extending flaps above 20,000'?


JD
:)

Why would you want to set autopilot on a CRJ200 at 40K on a repositioning flight?
Chuck Yeager syndrome?

Hi there,

Just been reading this thread and although explanations of very pertinent nature have been mentionned, I would like to humbly contribute, taking the risk of looking like a fool since my theory on principles of flight is many years old now.

The reason there is a MMO limit, say 0.82, is that beyond it, you will find some local areas on the wing that will reach or exceed Mach 1.
So I can easily see this local Mach value being largely exceeded if with the same speed, someone extends slats or flaps, increasing the camber of the wing, and having the airflow moving over the wing with higher velocity. The shockwave would be sufficient to disrupt, damage, or shear a component that wasn't designed to withstand such stress.

Feel free to correct if my statement is lacking accuracy, or has the wrong wording as english is not my native language.

Flex

In one aeroplane type, the maximum landing gear extension speed was 300KIAS.

The aeroplane wasn't fitted with speed brakes and one day a pilot decided that lowering the landing gear at 300 KIAS would increase drag and allow a more rapid rate of descent.

They were doing slightly more than 300, so he raised the nose slightly, saw the speed reduce to less than 300, then lowered the landing gear.......




At Mach 3.2! This was in an SR-71. Fortunately it all held together and they landed safely after rather a noisy descent. From then on, the -1 was amended to include an IMN limit as well as an IAS limit.

Intentional gear down at M3.2 is still the record, although an X-15 had an uncommanded nosegear extension at over Mach 4!

... I don't suppose anyone checked the tyre temperatures during that exercise ?

Puts exceedances in a totally different light for me.

Sorry, Mmo is not determined by the speed at which the local flow is transonic. That would be Mcrit, the speed at which the transonic drag rise starts (if we ignore low speed high lift effects). Mcrit is usually BELOW Mmo.

Mmo is set either by considerations of airframe loading (where it's called VC in the regulations, but there's a link between VC and Vmo, and thus indirectly to Mmo) or by considerations of aircraft handling (various criteria must be met at Mmo) or by considerations of various "upset" cases, which start at Vmo/Mmo and must not exceed VD/MD (or VDF/MDF as appropriate).

But your comments about shocks inducing loads on components that they were not designed to take is valid.

I think we are talking at slightly cross purposes.

The word "operating" related to operation of the aircraft. The word "operation" relates to activation of the slats. So indeed in your case, as worded, flight with "slats extended" is indeed permitted above 20k. (provided they remain fixed)

But the original poster's question was
And in that case (as in your FCOM text) the word 'operating' is an aircraft term, because the word "slat" (or flap, or anything else) isn't attached to it.

Also, logically, the slat(flap) operation envelope must be more restrictive than the slat(flap) extended envelope. So if the flap extended case is restricted below 20k, so must also be the flap operation, at least.

In passing, I'd say the FCOM statement is made clumsy by combining two different concepts. It should be:
"Max. altitude for slat operation is 20 000 ft.
Max. operating altitude for flaps extended is 20 000 ft."
to distinguish the two more clearly.

@Mad

Thanks for your clarification concerning operating/operation.

Kind regards

Hetfield, can you help me with reading the graph you posted, is this example right?

For zero wind, slats 15, at a speed of 250 kias or .55 IMN whichever comes first, at 130 tons weight, "optimum" altitude for maximum range is FL 280, minimum drag at FL 260, if flight at FL230 at 250/.55 then 4% loss in specific range .

But if 20 kts tailwind, then no loss in specific range for flight at FL 230.

But...what does the "maximum altitude" line represent?

@hawk

To be honest, I don't know.

Fortunately I never had to use that graph.;)

Greetings,

SLAPS, FLAPS, speeds are based on (E)TAS (equivalent True Airspeed)
at low altitude it is equal to IAS, however above 20000 ft, if you select your SLAT/FLAP using your IAS, you would exceed the limiting Speeds because the corresponding ETA would be much greater than the IAS. :}

Mad (FLT) Scientist is indeed correct. I raised the same question with my instructor at Alteon during initial. His response was that it was not deemed necessary to test the aircraft in any flap configuration above FL200. As such FL200 is the max alt with flap. Incidently I do recall during initial on the GIV that it was not considered safe to configure with flap above FL200 as it caused a disrupted airflow over the engines. FL200 being the limit on it as well. Given that, would it be fair to conclude that Gulfstream did test the aircraft in various configurations above FL200?

SP

Monom
 

Why would you ever want to extend flaps above FL200? I remember some years ago (in the sim) having progressive HYD failure in cruise, ending in total HYD loss. As it is essential to get stable at the lowest possible speed (probably F5 Vref40) asp, an emergency decent was initiated to get below 200 in order to extend flaps. So that's why!

That sounds pretty obscure, monom - what aircraft type was that ?


JD
:)

Monom
 

@JD
It was B757. Without any HYD, straight and level flight can be achieved at whatever speed total HYD loss occurs. Obviously the slower the better. It is quite hard to line up on finals at 260 IAS, so if it appears as if it might happen (and nearly did to me on the "Gripper"), get yourself into approach config asp. All this came out post the DC10 HYD loss.

Am doing PPL at mo and am studying IAS vs TAS at mo... Just trying to get it right in my head. Is mach similar to TAS in that as you go higher, depending on temp. and pressure alt., it will vary significantly to IAS? Like TAS being important for nav. high up for PPL Mach becomes important for both nav and op. limits(e.g. flaps) high up in commercial aircraft?

Thanks a mil...

flying_shortly


Greetings,
AGAIN......

SLAPS, FLAPS, speeds are based on (E)TAS (equivalent True Airspeed)
at low altitude it is equal to IAS, however above 20000 ft, if you select your SLAT/FLAP using your IAS, you would exceed the limiting Speeds because the corresponding (E)TAS would be much greater than the IAS. http://static.pprune.org/images/smilies/badteeth.gif