Inappropriate comments about RJ crash?

[surplus1]

PTCH is different in that it maintains the pitch angle the pilot sets. This is better than Vertical Speed or Speed mode because PTCH mode maintains a contant angle of attack. The pilot doesn't know what AoA he/she is flying, nonetheless it is constant.

Thoughts?

I have nothing against the use of pitch mode but please take a second look at what you said. I don't think pitch mode will maintain a "constant AOA" unless you also maintain a constant air speed. What you said may be true if you have enough power to maintain a constant AS at the same time and you use it.

Unless I'm mistaken, which is quite possible, when you set a given pitch attitude and airspeed the airplane "climbs" because you have more power than required for level flight. As the difference between pr and pa narrows, vertical speed will decrease. When you reach an altitude that requires all of the power either being used or available, the climb will stop. If the power is less than required to maintain that altitude, airspeed will decay and AOA will increase even though the pitch attitude hasn't changed.

Unless power available = power requiired (rather exactly) a steady state cannot be maintained and something will have to give.

 

[:-)]

I've got it. Why don't you CRJ people just hand fly to altitude? It sounds as if the airplane requires constant sheparding anyway, so just hand fly and relieve yourselves of the burden.

I think I'd rather just hand fly (act) instead of being forced to REACT to the actions of the autopilot/flight guidance system.

No kidding,
Hobbes

 

[TIS]

Why don't you CRJ people just hand fly to altitude? It sounds as if the airplane requires constant sheparding anyway, so just hand fly and relieve yourselves of the burden.

Well, with DRVSM that could get problematic. You're supposed to use the autopilot when in cruise in DRVSM airspace. It's not too much of a stretch to think that some FAA idiot would come along saying you have to use it for ALL operations in DRVSM airspace.

But that's speculative at best.

I do agree that if your jet doesn't do well in any automatic/pre-programmed mode such as those discussed, you should avoid using them in favor of simply setting a pitch and monitoring the climb for a reasonable rate of climb considering SAT/TAT and flight conditions. Most often it's the vertical modes that someone paid big dollars to get past the FAA certification group that cause the trouble. Lateral modes are generally pretty reliable and fly the plane well.

Just because a mode is there it doesn't mean it's necessarily the right thing to use and it certainly doesn't mean that it's always a good idea to use it. it's important to know your flight director controls and what they do. I saw a reference to a "click of NU" here. Understanding what that will do in a climb, a descent, and in altitude hold mode is important.

It's also important to understand how the AP interfaces with your LRN system. if you get your RNAV from an FMS, it's the FMS that actually commands the bank in order to give it control over intercept plots that it calculates.

Using an AP by rote because it's the way everyone else does it is fine as long as you're not left mystified as to what's happening. There's a book - probably online someplace. It's a good idea to read it at least once.

TIS

 

[Lear70]

The main issue with using roll mode is that you really haven't told the aircraft to do anything except hold a given bank angle.

Heading mode, used in conjunction with the TURB switch, when deviating around cells will give you a nice smooth roll rate and direct control over where you're going. Quite frankly, whenever I engage the autopilot, the TURB switch is right behind it - too many years of flying charter and corporate, I like a smooth ride.

 

[Rez O. Lewshun]

I have nothing against the use of pitch mode but please take a second look at what you said. I don't think pitch mode will maintain a "constant AOA" unless you also maintain a constant air speed. What you said may be true if you have enough power to maintain a constant AS at the same time and you use it.

Unless I'm mistaken, which is quite possible, when you set a given pitch attitude and airspeed the airplane "climbs" because you have more power than required for level flight. As the difference between pr and pa narrows, vertical speed will decrease. When you reach an altitude that requires all of the power either being used or available, the climb will stop. If the power is less than required to maintain that altitude, airspeed will decay and AOA will increase even though the pitch attitude hasn't changed.

Unless power available = power requiired (rather exactly) a steady state cannot be maintained and something will have to give.

Usually, the IAS stays the same, around 290/.70. It does start to bleed off once the jet gets to FL300+. (based on weight/ISA) It decreases, but I don't think the AOA changes too much, especially if one is operating the jet IAW with the flight release and performance charts, but then again, there is no AOA indicator to reference.

Speaking of performance charts. The CRJ chart reference climb capability that is given to pilots (usually in the QRH) to check if they can climb to any given altitude with a given weight/ISA is just one of many. It is for a specific %MAC and pack/bleed setting. IOW, it is a very generalized reference.

Lear70 indicated the same with a constant airspeed. AOA is elementry and paramount in aircraft control, yet "they" seem to keep us pilots from applying it.

I am wide open for a complete understanding... more info requested..... including links...

 

[liv'n_on_credit]

Rez, didn't you listen to your ground/sim instructor at Pinnacle? "Don't let the plane go into Pitch or Roll Mode!!!! You'll die!!!!!!!"

I think a big reason for the sim instructors not liking pitch or roll mode is that many newer people in the sim don't REALIZE that they are in that mode. I've had it happen to me a few times and seen it happen many times where you hit a certain mode and for some reason the A/P reverts to pitch/roll mode unintentionally. If you're not watching your FMA(mode annunciator), which many new people in the sim don't do, it could be a disaster. The sim instructors have probably seen it happen too many times. Just a guess though.

 

[PeanuckleCRJ]

Yeah in the sim there's really no reason to be in pitch or roll mode.... so if someone ends up in that more than a few seconds, they are probably wondering "what's it doing now and why?"

 

[surplus1]

I've got it. Why don't you CRJ people just hand fly to altitude? It sounds as if the airplane requires constant sheparding anyway, so just hand fly and relieve yourselves of the burden.

I think I'd rather just hand fly (act) instead of being forced to REACT to the actions of the autopilot/flight guidance system.

No kidding,
Hobbes

Speaking only for myself, the things that I post with regard to auto pilot modes and power available vs power required are NOT at all limited to the CRJ. They apply to all the aircraft I've personally flown (an I assure you that is not limited to CRJs and Cessnas). I've never flown and aircraft that did not require close monitoring when operating near the limits of its flight envelope.

I think monitoring the progress of your flight is the difference between being an aviator or just a pilot.

JMO

 

[surplus1]

Usually, the IAS stays the same, around 290/.70. It does start to bleed off once the jet gets to FL300+. (based on weight/ISA) It decreases, but I don't think the AOA changes too much, especially if one is operating the jet IAW with the flight release and performance charts, but then again, there is no AOA indicator to reference.

I would agree with you that the change is AOA when climbing in pitch mode is negligible when the aircraft is operating more or less in the middle of the flight envelope. In those regimes you have plenty of excess power available and can increase it as necessary to maintain a constant airspeed. It is only when you approach the extremes of the flight envelope that close monitoring is required.

In my opinion, close monitoring is required when operating near the extremes of the preformance envelope no matter what you may be doing, and regardless of whether you choose pitch mode, VS mode or altitude hold.

If you choose IAS/Mach mode for climb you won't get behind the power curve (unless of course you select an AS that is lower than the proscribed minimum); the airplane will just stop climbing and eventually descend to maintain the selected AS. The IAS/Mach mode is just "uncomfortable" because of the tendency to oscillate as the AFCS responds to airspeed trends.

Speaking of performance charts. The CRJ chart reference climb capability that is given to pilots (usually in the QRH) to check if they can climb to any given altitude with a given weight/ISA is just one of many. It is for a specific %MAC and pack/bleed setting. IOW, it is a very generalized reference.

I agree that the charts could be better (not sure who you work for or what they give you) but also think they are typical of what's provided in most aircraft. In the CRJ specifically, I wish that Collins would correct the errors in the FMS and make the information it provides reliable and useable in this regime of flight. But, I don't expect that to happen.

I am wide open for a complete understanding... more info requested..... including links...

Sorry, I can't provide you with "links". What I write is based on my personal experiences, not books or internet sources. I try to stay within the envelope of my limited experience.

The only book I can think of off hand is an older volume called "Flying the Big Jets", which I believe is out of print. If memory serves me correctly, I think it was written by a BA captain and contained many good tips related to energy management and big airplanes (nothing as small as a CRJ).

Over the years I've developed a couple of ideas. One is that there are 3 ways to fly any airplane: my way, your way, and the right way. When I know the right way I choose to follow it. The other two ways are just a matter of opinion; my way is no better than your way. The moral is simple: there is no substitute for knowing the right way.

The second is also fairly simple and in two parts: A) Before taking your seat don't ever forget to remove hat (the one with the thunder and lightning) and place it on the hat hook (usually behind your seat); then select the PRIDE switch to the OFF position. B) After setting the parking brake at the end of your flight and getting out of your seat, don hat, then select PRIDE switch to the ON position before exiting cockpit. You'll find the PRIDE switch just below the hat hook. (There are 2 in every two-man cockpit and 3 in aircraft with FE stations).

[Note: For those of you that no longer wear "hats", you can substitute the leather jacket or skip that part of the procedure. However, the PRIDE switch remains in the same location and must still be used as indicated].

The moral is as simple as the first example: egos and cockpits are incompatible with each other.

Tailwinds

PS. For those ancient aircraft that still carry a navigator - there is no PRIDE switch for the navigator. That is because navigator's have trouble locating things and too many flights were delayed while they looked for their switch.

 

[Rez O. Lewshun]

I would agree with you that the change is AOA when climbing in pitch mode is negligible when the aircraft is operating more or less in the middle of the flight envelope. In those regimes you have plenty of excess power available and can increase it as necessary to maintain a constant airspeed. It is only when you approach the extremes of the flight envelope that close monitoring is required.

If you choose IAS/Mach mode for climb you won't get behind the power curve (unless of course you select an AS that is lower than the proscribed minimum); the airplane will just stop climbing and eventually descend to maintain the selected AS. The IAS/Mach mode is just "uncomfortable" because of the tendency to oscillate as the AFCS responds to airspeed trends.

>If you choose IAS/Mach mode for climb you won't get behind the power curve

Agreed. The same applies to PTCH mode during autoflight. If the pilot sets 2.5 to 3 degrees on the CRJ, as it climbs toward the edge of the performance envelope it will want to increase AOA, to increase lift, to keep climbing, because excess thrust is not available. But the AOA cannot increase because the PTCH attitude is fixed. Like you describe in IAS/MACH the airplane will stop climbing and settle in at a FL.

No changes in PTCH means no change in AOA. (although the pilot does not know what the AOA is). AOA is controlled by the yoke, or the PTCH/VS wheel.

(my repsonse is discussion, not absolute)

 

[Carl_Spackler]

Rez, didn't you listen to your ground/sim instructor at Pinnacle? "Don't let the plane go into Pitch or Roll Mode!!!! You'll die!!!!!!!"

That and not selecting auto tune during a missed approach

 

[Wasted]

>If you choose IAS/Mach mode for climb you won't get behind the power curve

But the AOA cannot increase because the PTCH attitude is fixed. Like you describe in IAS/MACH the airplane will stop climbing and settle in at a FL.

No changes in PTCH means no change in AOA. (although the pilot does not know what the AOA is). AOA is controlled by the yoke, or the PTCH/VS wheel.

(my repsonse is discussion, not absolute)

Whoa dude. If you hold any particular nose pitch attitude while you bleed off speed, your angle of attack will increase. Don't confuse pitch attitude with angle of attack. They are different things.

 

[PCL_128]

No changes in PTCH means no change in AOA. (although the pilot does not know what the AOA is). AOA is controlled by the yoke, or the PTCH/VS wheel.

Maybe I'm just misunderstanding you here, but I'm not sure that I agree with the above. If you were to set a 5 degree pitch in PTCH mode and left it there, then the speed would start to bleed off as you climb higher. The slower the forward speed, the higher the AOA at a given deck angle (pitch). If you simply maintain the same pitch throughout the climb, then the AOA should continue to increase as the speed bleeds off.

 

[Rogue5]

PTCH is different in that it maintains the pitch angle the pilot sets. This is better than Vertical Speed or Speed mode because PTCH mode maintains a contant angle of attack. The pilot doesn't know what AoA he/she is flying, nonetheless it is constant.

Constant Angle of Attack provides a stable, steady climb up to your flight planned atltitude. There are no oscilations and thus wasted energy. Set the CRJ 200 at 2.5 degrees NU and the aircraft will stop climbing before anything else happens. It can't stall at 2.5 NU. In Speed mode or VS mode you run the risk of exceeding the critical angle of attack if no changes are made.

Thoughts?

I am without words to express my amazement that you still believe this. You may a recall an earlier thread when this theory was addressed:

http://forums.flightinfo.com/showthread.php?t=42858&page=3&pp=40

Responses to your quote are mine.

Quote:
Originally Posted by Rez O. Lewshun
When you use PTCH mode in the CRJ, (I know no other jet) you are setting a specific AOA.

Um, well... Whipping out the old CRJ 200 PRM on page 2-25 it says "Pitch mode will maintain pitch angle sensed at the time of autopilot engagement." Pitch angle, in other words attitude referenced to the horizon, not Angle of Attack, or attitude referenced to the relative wind. This is why when climbing in PTCH mode in any kind of wave activity airspeed will increase or decrease while attitude (say 5 degrees) will be maintained. Climb up too high in a constant pitch, airspeed will decrease as angle of attack increases and you will stall the wing.

Going back to my "Aerodynamics fro Naval Aviators" knowledge I remember it being hammered home that you climb due to excess thrust, not lift. So if you have the excess thrust to push you higher, and fix an attitude referenced to the horizon, you can be pushed high enough to exceed the critical angle of attack.

Think "Power-on" or "departure" stall: Full power, fixed pitch attitude to the horizon. Airspeed decreases, AOA increases to beyond the critical, you're now looking at the ground...

and:

As for the airplane just levelling off in PTCH mode and not stalling, think of this:

Calm, cool day, taking off empty with minimal fuel. Rotate, pitch up, and clean up. How many degrees do you think it could hold in a climb? Say 15 degrees pitch attitude (conservatively). "Auto on" and push the PTCH button.

Now if you think that the aircraft will just climb until it is unable and then level off while maintaining that pitch, you are attempting to claim that this swept wing, or any aircraft for that matter, will now be able to maintain in level flight with that 15 degrees pitch attitude. No way.

Same thread, Lear70:

Quote:
Originally Posted by Rez O. Lewshun
If pilots can't control AOA, we're in big trouble (in general, NOT to this specific thread title). If the critical AOA was exceeded, how would it be reduced? Pitch control...

That's about the only thing you said in this posting that's correct. Difference is, the autopilot doesn't intrinsically KNOW to reduce the pitch if the speed bleeds off.

Quote:
When you use PTCH mode in the CRJ, (I know no other jet) you are setting a specific AOA. This AOA is maintained all the up to the max weight altitude the aircraft can maintain. In addition, this AOA is less than critical so the aircraft will never stall. It may stop climbing, or even settle (decend) but the wing won't stall. That is the beauty of it. Set the PTCH or AOA and work on your monthly bid....

JUST DEAD WRONG. You are NOT setting an Angle Of Attack. If anyone that doesn't understand swept-wing aerodynamics is reading this, DO NOT LISTEN TO WHAT THIS PERSON JUST SAID!

Your AOA is dependent on several factors, ONE of which is Pitch, but your aircraft's Relative Airspeed, bank angle, and other factors all play a role in determining AOA. This is why pitch mode will NOT work unmonitored, or at least not without finding out where the shaker limit is at (or where the aircraft is trimmed to when the autopilot kicks off with the shaker).

If you set the aircraft for a 7 degree nose-up pitch climbing through 10,000 feet and "sat back and did your monthly bids", somewhere climbing through about FL 25,0 the shaker would go off. Why? VMD, otherwise known as L/D Max or Minimum Drag speed or, more simply, the speed below which induced drag increases faster than induced lift. As your "fixed pitch" remains the same, total thrust decreases as altitude increases (thinner air), and airspeed resultantly decays, you eventually wind up "behind the curve" or a speed less than VMD. Pitch mode keeps trying to hold 7 degrees and all the while your airspeed just keeps bleeding off and even though you start descending, that pitch is just too high to keep the airspeed from decaying to the point of stall.

Pitch mode has its uses, but ceasing to monitor your aircraft while left in ANY mode is nearly criminally negligent. And there are several other corporate aircraft that have pitch mode as an option, I used to fly the Lear 31 that way, set it about 2 deg and leave it alone unless the aircraft ran out of energy, but I sure as hell didn't just "sit back and read my paper".

 

[rtmcfi]

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.