Inappropriate comments about RJ crash?

[PCL_128]

Here is a really good link that explains pitch vs. AOA

http://www.aerospaceweb.org/question/aerodynamics/q0165.shtml

If I am understanding this correctly, pitch mode would work just as Rez stated, if the RELATIVE WIND never changed. Relative wind is the key.

Yes, but relative wind changes as airspeed changes. As you slow down the AOA will become higher because the relative wind changes with drop in speed.

 

[rtmcfi]

Yes, but relative wind changes as airspeed changes. As you slow down the AOA will become higher because the relative wind changes with drop in speed.

Not necesarily. A plane is parked on the ramp, facing directly into a 20 kt headwind. Now the wind kicks up to 100 kts. Has the relative wind changed? Has the AOA changed? I'm not trying to be a smart a$$, just trying to work through this....

 

[Wasted]

Not necesarily. A plane is parked on the ramp, facing directly into a 20 kt headwind. Now the wind kicks up to 100 kts. Has the relative wind changed? Has the AOA changed? I'm not trying to be a smart a$$, just trying to work through this....

...and you're a cfi?

Was the Pinnacle plane sitting on the ramp when it crashed or was it FLYING? What an idiotic comparison. You are trying to make some kind of ill conceived aerodynamic argument by using the example of a plane parked on the ground?

Stop and back off before you stick your entire leg in your mouth.

 

[surplus1]

If I am understanding this correctly, pitch mode would work just as Rez stated, if the RELATIVE WIND never changed. Relative wind is the key.

As far as you've gone that is not "wrong", but you haven't gone far enough so you're not "right" either. If you don't take the concept all the way to its end, it will mislead you and get you into trouble.

It is also necessary to understand where the "relative wind" comes from; what generates it and what makes it change. Power available vs power required is the principle answer in steady state flight (whether climbing, descending or maintaining an altitude).

If you're just climbing (no turns) at a constant pitch attitude and airspeed, as altitude increases you will have to increse power to maintain the constant airspeed. In a climb, every time the power is less than required to hold the airspeed selected and the pitch remains unchanged, the "relative wind" will change and the AOA will increase. Eventually the aircraft will exceed the critical AOA and the wing will stop flying, i.e., stall. This reality isn't different in a "jet". It's the same in all aircraft.

It is true that the aerodynamics of a swept wing are different from those of a straight wing (to a certain extent) but that's irrelevant in what we are discussing. The principle remains the same. The source of power, i.e., jet vs recip vs turboprop doesn't really have anything to do with this principle. You can test it in a 150 if you want to or in a 747.

The CRJ certainly isn't the only "jet" that has experienced an upset. It's happened in just about all of them at one time or another. It has also happened in turboprops (like the Brasilia). Yes it happens more often in jets, but that's not due to the jet engine, it's due to the fact that they fly higher where the atmosphere is different and the power available doesn't exceed the power required by very much.

Airflow separation occurs differently on a swept wing than it does on a straight wing but by the time we get to that point, we've already gone past what we're discussing here. For example, the EMB120 has a straight wing but it still gets awful nasty if you stall it at a high altitude. It's happened more than once when the pilot elected to exceed the envelope. If you go back far enough, you'll find a lot of interesting "events" in airplanes like the DC-8, DC-9, BAC 111, B-707 series, CV 800 & 900, B-727, etc, Upsets at high altitude resulting in flame outs, structural damage or accidents. Not to mention numerous "hard landings" that put the undercarriage on top of the wing or high sink rates that put the airplane in the approach lights instead of on the runway. Over time we've learned a great deal, but not without a lot of hard knocks.

When these "large" jets came into service initially, there were just as many upsets caused by pilots that didn't understand high altitude operation and had transitioned from airplanes like the DC-6, L-1049, CV440 and such. This lack of understanding is by no means limited to "regional" pilots. The story was in fact worse when the "mainline" pilots first got their high altitude airplanes (jets).

Don't take my word for it but, it is truly important that you fully understand these aerodynamic relationships.

When you consider "relative wind" don't think of it as wind that's blowing, it has nothing to do with that. Realtive wind is created by the movement of the wing through the air mass. It's there whether the wind velocity is zero or 200 knots. A high wind velocity can add (or subtract) to the effect of the realitive wind depending on the direction from which it comes (this is why we have wind shear among other things) but it should not be confused with "relative wind".

Also, include in your analysis the difference between IAS and TAS. In reality, the wing knows nothing about IAS, it only understands TAS. We have learned how to calculate the difference and choose an IAS that produces the necessary TAS in a given atmosphere and flight condition.

At lower altitudes, the difference between the two is not great enough to cause serious concern. At altitudes above 20,000 feet the difference is great enough that it must be taken into consideration. This is why transport category aircraft do not have "red lines" on their airspeed indicators. The "red line" is depicted by a moveable "barber pole", thus ensuring that we do not exceed the maximum "true" speed (Vne or Vmo) at high altitudes.

Unfortunately, aircraft certified under Part 23 are not required to consider this reality and are not equipped with a "variabale red line equivalent". That wasn't a problem when the Reg was written because normally aspirated reciprocating engines didn't have the power to take the aircraft high enough. When the turbocharger was introduced, that changed but the regulation didn't. Today you have airplanes like the Malibu (not the only one by any means) that can fly above 30,000 feet, but they still have a meaningless "red line" on the airspeed indicator. The result is they often exceed "red line" in cruise flight, not in terms of indicated airspeed but in terms of true airspeed. Most pilots who fly them don't understand this as a result of which they often exceed the limitations (without knowing it) and the wings come off when they hit big bumps.

A similar scenario is the infamous "blue line" in light twins. Not a very useful piece of information and highly inaccurate. Transport category aircraft don't have "blue lines" because they're useless. They're just as useless in Navajos, but the government doesn't seem to think that pilots of those aircraft need to know this and the manufacturer of your turbocharged Piper, Cessana or Beech, don't want to pay for it. So they continue to paint these "lines" on airspeed indicators.

Please take the time to explore these factors on your own and avoid the pitfalls that are lurking out there.

 

[Rez O. Lewshun]

From a previous employers' CRJ flight manual

iv. PTCH- Pitch mode will allow the aircraft to climb at a set pitch attitude. The best pitch attitude usually falls around 2.5 to 3 degrees nose up. This mode allows for a smooth transiition from intermediate level off climb by simply sellecting the proper nose up pitch. There is also some "built in" stall protection because at 3 degrees nose up the aircraft will not stall, it will simply stop climbing. When using this mode, pitch selections using the control wheel must be done slowly, one at a time. Moving the wheel faster than this will cause passenger discomfort

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Thoughts.....???

 

[rtmcfi]

non-practicing CFI ;-)

I guess aerodynamics don't apply on the ground? Does the wing know if it is on the ground? I was trying to illustrate the concept of relative wind.

Relative wind has to do with angles and directions. It does not nesasarily have to do with speed. I put the airplane on the ground so as to "lock" the pitch angle. If the aiplane is on the ground, the chord line cannot change. If all I do is increase or decrease wind speed, you can see that the relative wind has not changed. On the ground, in this case, the wing is not "stalled" It is just not making enough lift to sustain flight. By doing this on the ground, I am eliminating the vertical wind component.

Now let's do this in the air. Set a pitch, and hold it. As the airplane slows down, you will reach a point where you lift equals weight. You can't climb, unless you can increase your speed. As long as you don't exceed the critical AOA, you won't stall, you just will stop climbing. If we continue to slow down to the point that you we are no longer maintaining lift, we sink. When we sink, we add a vertical component of wind. This vertical component of wind, added to the horizontal component of wind, gives you a resultant wind. This resultant wind is is at a different angle than the horizontal component by itself. This gives you a "new" relative wind. The angle of the relative wind has changed relative to the chord line. While your pitch never changed, you AOA did. If it changed too much, you will exceed the critical AOA, then you stall.

Now the above is an oversimplification. As we started slowing down, but not yet sinking, we were changing both the vertical and horizontal wind components. This whole concept is much easier to understand with a model plane in your hand than it is to type out. Constructive criticism and corrections welcome....

 

[Wasted]

Your initial statements were definitely oversimplified. I'm just glad to see your statement "If it changed too much, you will exceed the critical AOA, then you stall." in your expanded comments. That is all I am looking for. Your other post sounded a lot like you were agreeing with Rez. O Lewshen's statement that "No changes in PTCH means no change in AOA" which is blatantly wrong and shocking that anybody purpoting to be a professional or advanced pilot would say.

 

[Wasted]

From a previous employers' CRJ flight manual

iv. PTCH- Pitch mode will allow the aircraft to climb at a set pitch attitude. The best pitch attitude usually falls around 2.5 to 3 degrees nose up. This mode allows for a smooth transiition from intermediate level off climb by simply sellecting the proper nose up pitch. There is also some "built in" stall protection because at 3 degrees nose up the aircraft will not stall, it will simply stop climbing. When using this mode, pitch selections using the control wheel must be done slowly, one at a time. Moving the wheel faster than this will cause passenger discomfort




​

Thoughts.....???

Poorly worded and wrong. Any plane can stall at any nose attitude. I thought this kind of stuff got covered in Lesson #2 during your PPL rating.

I dare you, take a CRJ, set your 3 degrees nose up on the autopilot, disable your stall protection, and bring the power back to idle.....

 

[rtmcfi]

Pitch mode will allow the aircraft to climb at a set pitch attitude. The best pitch attitude usually falls around 2.5 to 3 degrees nose up. This mode allows for a smooth transiition from intermediate level off climb by simply sellecting the proper nose up pitch. There is also some "built in" stall protection because at 3 degrees nose up the aircraft will not stall, it will simply stop climbing.

At three degrees pitch up, the airplane simply runs out of climb. As you lose climb, you lose your vertical component of wind. You now have only a horizontal component. The 3 degree pitch up deck angle, combined with the angle of incidence is less than the wings critical angle of attack. Now if we were to set the pitch at 15 degrees, as we slowed down, and reduced our vertical component of wind, we would likely exceed the wings critical angle of attack and stall.

that's my take anyhow.

 

[Wasted]

At three degrees pitch up, the airplane simply runs out of climb. As you lose climb, you lose your vertical component of wind. You now have only a horizontal component. The 3 degree pitch up deck angle, combined with the angle of incidence is less than the wings critical angle of attack. Now if we were to set the pitch at 15 degrees, as we slowed down, and reduced our vertical component of wind, we would likely exceed the wings critical angle of attack and stall.

that's my take anyhow.

You guys are fixing to get yourselves hurt.