Pitch. Power. Trim.

[moxiepilot]

You may want to look into a common aero book. I believe it was Dole who wrote Aerodynamics for Aviators. I know the Author's name is Dole, but I'm not at home right now to get the title right.

It may help you from more of a scientific/equation point of view

 

[mshunter]

Any speed change you get from power adjustment is all due to secondary effects. An increased propeller slipstream on the horizontal stabilizer will retrim the aircraft to a different AoA, often a higher one, which will decrease airspeed. Increasing thrust in jets may cause either an increase or decrease in airspeed due to the thrust line being above or below the center of gravity. This will retrim the aircraft for a different angle of attack just as if you moved the yoke or adjusted the trim wheel. Trim is trim. In all instances, however, there is an AoA change that results in the new airspeed.

No, you don't need to touch power, as long as you're willing to accept a change in your flight path. You need to adjust power only if you want to preserve altitude while maintaining the new airspeed. This increased power is necessary because the power requirements for the increased airspeed are higher than at the lower airspeed (if you're on the front side of the power curve). If you fail to increase power, you're running a power deficit, which is synonymous with being in a descent.

The yoke and throttle do very different things and you need to understand what each one does before you can mix and match them to achieve your desired results. Skipping that step and just telling people that they need to adjust both controls in whatever way works is insufficient guidance, in my view, because it doesn't give them tools to predict behavior.

Next time before posting with a quote, I recomend reading both posts.

 

[Cessna414JJB]

I don't see where the quality of this thread has suffered. Blackhawk pointed towards a misconception, that, if taught like this, is directly contrary to a succesful learning outcome and correlation. The few times I have had the opportunity to watch and observe pilots flying behind the power curve I was surprised about the heavily mechanical response, lacking any true understanding and feel for what the airplane was truly capable off. In more than one situation the old glider junky came out and I had to use both hands to push against a pilots believe that trees truly get smaller if you pull on the yoke. This only holds true as long as there is sufficient power available.

The discussion 'had' to vane off towards the fundamental difference in how people teach flying. However, applying the systematic approach and scientific research to everything, will, at least in the long run, not yield the desired results for OP. A 152 is not a Jet. The quality of discussion will be high but I don't see much being gained.

If this thread shows anything to me, it is that there are two different kinds of pilots and flight instructors available to teach one about flying.
Both have to be heared and both have something to teach, it's just a question of "what basics we put underneath" what is to come.

 

[tgrayson]

Yes, induced drag increases with an increase in the Cl. But it does not necessarily follow that the decrease in lift will still be = to weight unless, perhaps, in a 1G stall.

It doesn't follow from your statement, but it follows that vertical forces are in equlibrium in a steady descent. The lack of vertical acceleration indicates there are no unbalanced forces. Only two possible forces can counter weight: lift and drag.

How much lift exists? Back of the envelope calcualtions: stalled at 40 knots, 500 fpm descent rate, I show a descent angle of about 7 degrees. And since the lift is about equal to weight * cos(descent angle), I get that lift is about 99% of level flight quantity.

Even if you assume a 1,000 fpm descent, you get lift is still about 97% of level flight values.

Not worry about lift??? Probably why we have pilots crash in high DAs each year.

Generally a drag/thrust issue as well. Fly proper airspeeds and the lift will be there. Now, if you fail to rotate, then you have a lift problem.

 

[tgrayson]

I'm going to revise the way I explain the lift equation.

Blackhawk's objection is, as I said before, a red herring just to be argumentative. Cl is directly proportional to AOA via the lift slope equation. You will often see this written as (alpha)(a), where a is the lift slope. It's a constant for a particular airfoil. That formulation does assume, however, that alpha is given as an absolute AoA, rather than in reference to the chordline.

Likewise, devices like flaps only change Cl at a particular AoA. At any particular airspeed, only one Cl will do. If you drop flaps, you're going to lower your AoA to maintain the same Cl.

 

[richarms]

Hmmmmm.

A 152 is not a Jet.

Thanks everyone for the discussions. Always good to discuss theory and practice.

BTW, does anyone know where I can get a Cl indicator? All I can see in the cockpit are these AOA ones.

 

[tgrayson]

that AOA is in fact relative to Lift - for only the purposes of those angles below the stall angle .

I'm not sure what you mean by "relative", but it's true the linear relationship continues up to the stall. In fact, an airfoil is considered to be stalled after the max lift coefficient is reached. At higher AOA's the lift coefficient will decrease, but then it may well increase again at higher AOA's. You typically don't have to data to know for sure, but it's just not that relevant. The drag is likely to be such you won't be able to stay in the air very long.

The lift equation is useful because you can solve for V, which shows the dependence on lift coefficient, and via the lift slope, AoA.

 

[tgrayson]

Next time before posting with a quote, I recomend reading both posts.

You're welcome.

 

[Approach Control]

I'm not sure how you're envisioning trim, but I'll try to make it simpler.

I'm ok with understanding trim.


YOU SAID:

Pitch attitude and AoA are completely independent of each other.

THEN YOU SAID:

You want to know how to control AoA? It's strictly and purely from the physical position of the yoke. Move the yoke back and AoA increases. Move the yoke forward and AoA decreases. The reason for this is because you're changing the position of the tail. Simple as that.

Ok, I was with you on AOA until I hit this little snare. You say Pitch <> AOA. You then say AOA can be increased through Pitching the aircraft's [moving the stick back] nose UP using Elevator, which by definition is using Pitch. Can you clarify this for me? I'm stuck here as this seems to be a physical contradiction.


ONE:

Remember, power from the engine is what ultimately keeps us in the air.

TWO:

Add a little power and the plane won't sink quite so much. Add a little more power and it will be able to maintain level flight. Add a little more and it will start climbing a little. Add a lot of power and it will climb a lot.


Ok, here we go.

Taken from: The Proficient Pilot, Volume I, Barry Schiff.

Page 41 - Chapter 6: Flying Behind the Power Curve

Barry, tells a short story of a pilot on a short final. That pilot has a lot of experience with short-field landings. Initial airspeed was 65 kts and stall speed was 51 kts. Half mile from the numbers, the pilot sensed that he was too low, so he slightly raised the nose. The sink rate increased and he lost 5 kts airspeed.

Then, the pilot added more power and more back pressure and the sink rate increased and he lost more airspeed. So, he adds even more power and his airspeed drops to 56 kts. Desperate, he slammed the throttle into the firewall but it was too late. He crash landed short of the runway. He was able to walk away [this time].

Remember the purpose of this thread: Do I [as a student] obtain Pitch/Power/Trim settings for my training aircraft, from my Instructor, in order to optimize my training going forward by being able to efficiently manage the aircraft through each of the six (6) major segments of flight: T/O, climb, cruise, descent, approach and landing.

Barry's subject pilot tried both of the tactics talked about by many Instructors in this thread: using Power / using Pitch. Yet, that pilot still ended up crash landing.

Barry goes on to talk about two (2) primary causes for the mishandling of the aircraft, that the pilot in his story was simply not aware of: Parasite Drag and Induced Drag, but he focuses on Induced Drag as the culprit for this particular pilot's problem. He says that induced drage varies inversely with the square of airspeed. Therefore, cut airspeed in half and induced drag actually increases 400%.

He then combines both the Parasite and Induced drag curves into one "Total Drag" curve and then superimposes that curve on a chart to geometrically locate the Minimum Drag Airspeed [at a given gross weight], for any particular aircraft [using IAS]. What's interesting about this, is that if you know the Minimum Drag Airspeed, then you by definition know the airspeed at which the aircraft operates most efficiently and that equates to the speed that will yield the greatest gliding distance, as well.

Ironically, and what I found left out of the debate here, is this:

a) Allow the airspeed to drop below Minimum Drag Airspeed and the required power to maintain altitude, increases - because of the increase in the parasite drag curve. [The Region of Reverse Command]

b) Allow the airspeed to move above Minimum Drag Airspeed and the required power to maintain altitude, increases - because of the increase in the induced drag curve. [The Region of Normal Command]

So, my question is this:

If I can find the Induced and Parasite Drag values and produce a Power Curve for my training aircraft for any aircraft I fly, won't it be possible to locate the exact region [range] of throttle positions for all of the six (6) phases of flight that are optimal for that particular aircraft? And, if I can do that, won't that give me an advantage over this pilot who ended up crash landing short of the runway because he either forgot or never knew what the power requirements were for that particular segment of his flight [the Approach and Landing]?

In my mind, I don't yet see a compelling enough argument for merely "guessing" at these critical operational numbers. Yes, a gust of wind here and there while on Final, or a downdraft, or all of the smaller details of unstable air masses that will impact the aircraft while on Final, will be at play. But, if I have a range of values [high through low] for the Power setting based upon the Pitch attitude of the aircraft, does that not put me light years ahead of most brand new students? If not, why?

Please correct me if I am wrong, but my reading of Barry tells me that Positive Dynamic Stability works ONLY when the aircraft is being operated within the Region of Normal Command - or - the Front Side of the Power Curve. But, if I let the aircraft's speed drop below the "Minimum Drag Airspeed" [remember] into the Region of Reverse Command, I cannot rely on Positive Dynamic Stability to "hunt" a stable flight attitude. Does that sound about right? If not, why not?

If I get this stuff set-up in my head correctly now, I think I'll make a better student once I select my Instructor and begin the dual training.

Thanks, again!

 

[moxiepilot]

AC - just FYI, you can email barry directly as well. He usually responds within a day. Good series - if you havent read books 2 & 3, they are just as good as the first one

 

[Cessna414JJB]

Thanks everyone for the discussions. Always good to discuss theory and practice.

BTW, does anyone know where I can get a Cl indicator? All I can see in the cockpit are these AOA ones.

Sometimes I really wonder why airplanes fly.
Your C(L) indicator is in your hands, comes from the factory, not optional equipment. I'm sure there have been moments in history where people stared at their expensive AoA indicator while mumbling the most favorite famous last words:

"Why the hell is it doing that...?"
(the final comment comonly involves the shouting a four letter profanity also known as fecal matters, usually expelled by living things)​

If aerodynamics where truly so complicated, and full of formula and only result of function based on numbers and (IF/THEN/ ELSE), we could never witness a Extra 300, or a Pitts or a Decathlon for that matter fly the way they do.​

I would love to invite the writer of this:​

Cl is directly proportional to AOA via the lift slope equation.

and that...​

You will often see this written as (alpha)(a), where a is the lift slope. It's a constant for a particular airfoil. That formulation does assume, however, that alpha is given as an absolute AoA, rather than in reference to the chordline.

to a surprisingly humbling aerobatic experience. I got one early on in live and realized that all the scientific papers and Barry Schiffs and Mr. Kerschner's would either be thrown out of the cockpit, or covered in vomit ........ Yes, it is science, but no you don't need a PhD to get a clue.​

OP is trying to understand what he needs to "feel" first.
Thats not a bad thing, but neither is Blackhawk

a red herring just to be argumentative.

.... I can't speak for him, but I simply do not subscribe to the method of "simple equation's".​

If I can find the Induced and Parasite Drag values and produce a Power Curve for my training aircraft for any aircraft I fly, won't it be possible to locate the exact region [range] of throttle positions for all of the six (6) phases of flight that are optimal for that particular aircraft? And, if I can do that, won't that give me an advantage over this pilot who ended up crash landing short of the runway because he either forgot or never knew what the power requirements were for that particular segment of his flight [the Approach and Landing]?

Finding these settings, values and numbers would be a incredibly tiring act. By the time you would be done, you may hit turbulence, wind shear or a simple change in wind and nothing was where it 'belonged'. Once you are off track, thats that.​

In my mind, I don't yet see a compelling enough argument for merely "guessing" at these critical operational numbers. Yes, a gust of wind here and there while on Final, or a downdraft, or all of the smaller details of unstable air masses that will impact the aircraft while on Final, will be at play. But, if I have a range of values [high through low] for the Power setting based upon the Pitch attitude of the aircraft, does that not put me light years ahead of most brand new students? If not, why?

Guessing is a very powerful tool in the bag of every good pilot. If you have such scietific settings in your mind while you fly, your brain will be occupied trying to distinqish between all the variables rather than flying the airplane based on correlation. You would be in a 'limited capacity' as to controlling your aircraft when things actually got out of whack. They do, believe me.​

Please correct me if I am wrong, but my reading of Barry tells me that Positive Dynamic Stability works ONLY when the aircraft is being operated within the Region of Normal Command - or - the Front Side of the Power Curve. But, if I let the aircraft's speed drop below the "Minimum Drag Airspeed" [remember] into the Region of Reverse Command, I cannot rely on Positive Dynamic Stability to "hunt" a stable flight attitude. Does that sound about right? If not, why not?

Barry Schiff has forgotten more about flying than most of us will ever learn. Barry is well known for sharing his wisdoms and is, like every writer in aviation always playing it safe. None of them is wrong, but their subject is "knowledge" which needs to be converted into Applicaton and Correlation before we are looking at a sucessful pilot. Is it safe to fly any aircraft within the region of reverse command, or behind the power curve? No! Is it adviseable? Noooo! Is it done anyways... You bet!
In fact it is done safely everywhere on this planet and the airplanes are perfectly capable of handling the results of it. It's us pilots who make this part of flying dangerous, either by freaking out or simply by doing the wrong thing at the wrong time. A good pilot knows and feels what he can ask form the plane. It's a mixture. Never set in stone.​

If I get this stuff set-up in my head correctly now, I think I'll make a better student once I select my Instructor and begin the dual training.

You are already and will become a darn good student, because you ask 'why'. You are not likely to crash and die based on missing knowledge, nor will you answer the FAA "because John said so". That gives you an advantage, but can also be an obtstacle to learning this from the ground up. You would hate me and probably never hire my services as your instructor, but if you started such a discussion with me I would feel compelled to advise my client about the fact that by aerodynamic definition a Bumblebee CANNOT possibly fly. But.... the Bumblebee does not know, and therefore flies off. Take it easy. It will all get so much more than reading.​

 

[Approach Control]

AC - just FYI, you can email barry directly as well. He usually responds within a day. Good series - if you havent read books 2 & 3, they are just as good as the first one

Yes, I did one time, but it was on another subject.

I figured that on a forum like this, there would be more brains able to engage in helping me hash things out - instead of bombing Barry with a ton of questions - but, yes - he did actually respond. [pretty cool, actually.]

I'm currently working my way through several books: The Advanced Pilots Flight Manual [Kershner], FARs, AIM, AC 61-23, Jeppesen/King/Sporty DVDs, Proficient Pilot I [Schiff] and The Complete Guide to Flight Instruction [Penglis]. I plan to get the other Volumes as well.

I like the way Barry is able to encapsulate the substance of a topic and deliver a solution-set that seems to make a lot of sense. The more I read, the more his experience really comes to light. He just seems to really "get it."

After further review Moxiepilot, this forum seems to be no different than other types of forums where some people let their ego drive their dialog to the point of misunderstanding the essence of a topic or question. I've received some great input [constructive] from most on this forum, but it only takes one or two bad apples to spoil it for everyone else and that has unfortunately happened here.

Of course, actual flight training is critical. Of course, reading books is critical. But, so too is communicating with other experienced pilots and that is what these types of forums "could" be used for. Instead, forums tend to get reduced to the lowest common denominator, ego and pride. And, as the saying goes: Pride goeth before the fall.

For some odd reason, some people just can't find a way to "commune" with each other. I'm not knocking everyone here, but I have very little bandwidth for negativity in my attempt to understand what my role will be in the world of aviation.

A wasted opportunity - these aviation forums could be used for a much higher purpose. I suspect that there are plenty of newbies out there who lurk, but don't ever post, simply because they don't want the hassle of dealing with over-broad egos.

I'm just a guy, trying to get up to speed, so that I can handle the aircraft in my future with mastery and confidence - not ego and ruinous results.

I've taught people how to make millions in the markets individually and I never once felt the need to exort my ego in the process - just because I was the guy with the knowledge. That's just stupid, IMO.

I hope my flying career leads me in the path of meeting with and coming in contact with rock solid [humble] human beings, not ego driven tyrrants.

Thanks for the tip on Barry, Moxie!

 

[ppragman]

Look, if you need airspeed you can lower the AoA or add power or both. Those are the only combinations.

Lower the AoA:
Great for quickly converting your PE to KE (as mentioned above) you'll get the fastest increase in speed.

Add Power:
Great for increasing your speed without lowering your altitude over long periods of time, as less KE is generated in this way, plus the time it takes for your motor to convert the chemical PE of fuel to KE is a much longer period of time than gravity takes to convert weight to velocity.

Add Power and Lower AoA:
Best of both worlds, now you're adding velocity almost instantly due to gravity, plus you're adding airspeed due to the less instantaneous/powerful process of the engine.

Now, if you want altitude a similar process is in play, you have again three choices, increase AoA, increase Power, increase AoA and Power.

Increase AoA:
You convert the KE of forward flight to PE and climb, unfortunately as KE decreases so does your velocity. Trade Speed for Altitude.

Increase Power:
The engine converts chemical PE to an increase in KE. Increased KE, implies increased velocity (because the mass is roughly constant) thus lift increase, up we go with the same AoA.

Increase Power and AoA:
This is what most of us actually do. Add a little power, and pitch a little bit, and up we go, we get the advantage of the nearly instantaneous conversion of KE to PE of raising the nose, and we sustain the lower velocity with thrust from the engine.

Clear as Mud?

What does this mean? In real life it means a lot. Down low and slow (coming into land) we are particularly vulnerable to changes in airspeed due to windshear, being behind the airplane, etc. How do we combat this? Simple:

If you recognize that you're in deep kimchi early enough you simply want to arrest your glide and get back on glide path. If you have sufficient airspeed you can do this with any of the three gaining altitude methods. You're a mile out and you go to "red over red" this is what any pilot does, pitches up a little and trades his airspeed for now, adds a little power, or both.

If you're in close to the trees and this happens, and you have seconds to react the problem is a little more complicated. You have to be able to maintain your glidepath (read altitude) so you don't impact the ground, and you have to be able to maintain or increase your airspeed (read don't stall). You can't necessarily lower the nose because you'll crash short, and you can't really pitch up because you'll stall. It sounds like a lose-lose proposition.

Its not really though, because you can always lower the AoA a little bit, and add a short burst of a lot of power to get out of it. You need that airspeed yes, but you can't crash so you have to do both. Add power and slightly reduce your AoA. This is where finesse comes in.

If you're in the region of reverse command (dragging it in with power) you have to have your power set and be ready to instantly respond to changes in altitude and airspeed. In short you have to be dead nuts on, and not try to salvage a landing that doesn't go perfectly, if it doesn't go perfectly throw the whips to it, slightly lower the nose and go around.

What that really means is that there is a point at which you're commited to setting the mains down, whether you want to or not every landing. There is a point at which full power and any change in pitch, or increase/decrease in angle of attack will not arrest your decent in time to prevent touching down. That's part of that buffer you built into your landing distance calculations right? That's why setting down in the first inch of the runway, though cool, and impressive that you can do it, isn't the safest thing to do, because even if you've given yourself an adequate energy budget to make the runway in the even of an engine failure, you have not adequately planned for mechanical turbulence, windshear, or your hangover/divorce/medication skewing your ability to judge speed and distance close to the ground. The numbers is a good target, as is the start of the first centerline marking, or, if you have a displaced threshold, even the start of the runway proper, but make sure there will be something under your tires even if things don't go according to plan.

 

[Approach Control]

...Barry Schiff has forgotten more about flying than most of us will ever learn....

...A good pilot knows and feels what he can ask form the plane. It's a mixture. Never set in stone.​

I just want to be optimal, efficient and safe. Having fun with flying is a distant fourth. If I can get it from Barry or You, I'll take it, LOL! I just need to make sure that what I'm 'getting' is the truth, the whole truth and nothing but the truth.

When I read about a Former F-18 Hornet pilot, or someone with thousands of hours of flight experience, ripping a new hole in the ground, it causes me as a newbie to stop and pause long enough to ask myself the question: What the heck just happened?

I read NTSB reports. That may surprise you. But, I read them to find out as much as I can about WHY aircraft continually hit the ground with perfectly healthy pilots at the helm. I see things like people leaving gas caps off after refueling on the ground, or never setting the fuel selector switch to BOTH, or departing in VFR conditions, only to fly themselves directly into IMC conditions without ever once turning the aircraft around for a safe landing...etc. I look at all of this stuff and I have to wonder: Could this ever happen to me. What can I do NOW to prevent this from happening.

In short, I'm trying to do everything I can up-front BEFORE I launch into full-blown flight training, to prevent the errors of omission and greatly reduce the errors of co-mission.
​

You would hate me and probably never hire my services as your instructor, but if you started such a discussion with me I would feel compelled to advise my client about the fact that by aerodynamic definition a Bumblebee CANNOT possibly fly. But.... the Bumblebee does not know, and therefore flies off. Take it easy. It will all get so much more than reading.​

I don't hate anyone - hate is a strong word. But, I loath arrogance and over-blown ego. I don't place you in that category, but if you just browse the forum, you see it in many different threads.

People should just learn how to take their knowledge and engage in intelligent dialog, without all the bravado or injecting huge doses of ego into the dialectic equation. Nothing wrong with a heated debate, I think that is a good thing. But, people [all of us] should do so with tact and respect.

I believe in tools and skill-sets. I believe in fundamentals and organized thought. I believe in strategic planning and tactical implementation of those plans. I believe in getting a lock on the bigger picture before launching out and then monitoring the smaller details along the way, looking for change that will adversely impact my plans. And, when a problem does arise, I believe in applying the tools and skills developed over time, to remedy the problem.

So, of course [lol], I'm going to at least want to know whether or not I should obtain performance settings from my Instructor for all phases of normal flight for the aircraft I'm operating. That's just how my brain works - to me, it seems like a slam dunk question, lol!

Anyway, I hear what you are saying. I'm a very intense Man and sometimes that is not fairly appreciated in many circles. I think it is a cultural thing at this point. I can work 36hrs back to back and barely feel it. We just don't live in that culture anymore. My intensity/focus is often times misunderstood and misplaced.

Thanks, again!

 

[Cessna414JJB]

I hope my flying career leads me in the path of meeting with and coming in contact with rock solid [humble] human beings, not ego driven tyrrants.

I'm absolutely sure you will. Online communication is one of the hardest ways of communication there is, as it is missing every aspect of 'good' communication tools. The funny thing with these types of forums is that we can run into each other on the ramp tomorrow, and you would never think that you just met the guy/gal who always comes accross like a jerk to you on the forum.


<--- Almost retired from this thread, because I got a call to go on a three day trip with lots of ice, bad weather. Love it! Then I returned and saw your response. So - editing mine to reflect that too.

I just want to be optimal, efficient and safe. Having fun with flying is a distant fourth. If I can get it from Barry or You, I'll take it, LOL! I just need to make sure that what I'm 'getting' is the truth, the whole truth and nothing but the truth.

When I read about a Former F-18 Hornet pilot, or someone with thousands of hours of flight experience, ripping a new hole in the ground, it causes me as a newbie to stop and pause long enough to ask myself the question: What the heck just happened?

I read NTSB reports. That may surprise you. But, I read them to find out as much as I can about WHY aircraft continually hit the ground with perfectly healthy pilots at the helm. I see things like people leaving gas caps off after refueling on the ground, or never setting the fuel selector switch to BOTH, or departing in VFR conditions, only to fly themselves directly into IMC conditions without ever once turning the aircraft around for a safe landing...etc. I look at all of this stuff and I have to wonder: Could this ever happen to me. What can I do NOW to prevent this from happening.

In short, I'm trying to do everything I can up-front BEFORE I launch into full-blown flight training, to prevent the errors of omission and greatly reduce the errors of co-mission.

Hate was a wrong choice of word. Apologies!
I don't know a single pilot who does not read NTSB reports. Why, because we can learn so many things from the mistakes of others, while being constantly reminded that it can happen to us. We all slow down and look at how we fly when we read about someone having had a bad hair day. I believe that you are asking a bunch of very very advanced questions, because you are in an advanced state considering your goals. What you want to do requires commitment and discipline. Lots of it.

What we (or I) are trying to convey to you is that there is barely ever a 'one size fits all' method to go about things. What you read in Kerschners excellent books, or Barry Schiffs unbelievably interesting stories is the icing on the cake, when it comes to really getting behind what we do.

I would like to guarantee you a few things (!):
First: You will be taught to establish certain settings for certain desired outcomes.
Second: You will, during your intense instrument training to learn to establish what I call 'envelope figures" whereas a certain setting on pitch, power and trim will yield a certain result.
Third: You will come to enjoy both kinds of flying, develop a certain seat of the pants feeling for your airplane while getting 'rounded off' with the procedural and mechanical ability to fly and be successful at it..
Fourth: At some point during your flying career you will notice that you know a lot, can do a lot and have developed a feel for what you can ask your airplane to do. At this point the numbers game will leave you for a while.

There is no 'true' example of arrogance here, there are simply a bunch of guys trying to keep the basics in check.

 

[tgrayson]

Then, the pilot added more power and more back pressure and the sink rate increased and he lost more airspeed. So, he adds even more power and his airspeed drops to 56 kts. Desperate, he slammed the throttle into the firewall but it was too late. He crash landed short of the runway. He was able to walk away [this time].

This is my point. Midlifeflyer, among others, say that pitching for altitude and powering for airspeed works in this regime; this clearly shows that it doesn't. The proper recovery would have been to add full power and push forward on the yoke. Note that Barry, on page 48, says "It may seem confusing that lowering the nose causes an airplane to climb, but that is the way things work on the back side of the power curve."

If I can find the Induced and Parasite Drag values and produce a Power Curve for my training aircraft for any aircraft I fly, won't it be possible to locate the exact region [range] of throttle positions for all of the six (6) phases of flight that are optimal for that particular aircraft? And, if I can do that, won't that give me an advantage over this pilot who ended up crash landing short of the runway because he either forgot or never knew what the power requirements were for that particular segment of his flight [the Approach and Landing]?

Not in my view. If you accept that AoA controls airspeed, and that throttle should be the *primary* control of altitude, the front and back sides of the curve are identical.

Please correct me if I am wrong, but my reading of Barry tells me that Positive Dynamic Stability works ONLY when the aircraft is being operated within the Region of Normal Command - or - the Front Side of the Power Curve.

Unless you have a direct quote from Barry, I think that's a misinterpretation of what he said. He might have made some comment about the lack of speed stability, which is different and works at cross purposes with the longitudinal stability of the airplane.

 

[MNFlyGuy]

Looks like I missed one heck of a discussion today! I will give you a couple thoughts from a new CFI. I have a backround in engineering, I am guessing you may as well. I will say for all my love of equations and theory I dont give much thought as to the "whys" during a flight. During a flight you will learn to rely on your training. Training that will teach you to protect your airspeed on final, and what adjustments are proper to make when changes occur.

AC Said: Remember the purpose of this thread: Do I [as a student] obtain Pitch/Power/Trim settings for my training aircraft, from my Instructor, in order to optimize my training going forward by being able to efficiently manage the aircraft through each of the six (6) major segments of flight: T/O, climb, cruise, descent, approach and landing.

Let me give you my humble opinion, no you should not expect this from your instructor. The CFI that I did my initial CFI certification with called this "monkey see, monkey do" method of training. I can tell you that in a C172 1800 RPM with 10 20 and 30 deg of flaps as you are on downwind, base and final will yield a stablized approach. This is all great until you are landing with a strong headwind, maybe a light tailwind, another aircraft gets in your way and you need to extend your downwind. Basic flying can not be broken down into a pitch power airspeed cheat sheet.

Your instructor will have you explore aircraft performance with requests like, put me in a 500 ft / min descent at 70 kts. You will develop the feel for how the aircraft performs. It is one thing to read that if you keep adding backpressure on final, even with power additions the plane may continue to descend. Even better is to see it happen in the aircraft. Your instructor will show you, at a safe altitude, how this happens, and how to recover.

Do not try to skip this step, it is a critical base of skill for getting a feel for the airplane and how it reacts to your inputs. By gaining these insights you will be a safer pilots. You will go through the same process when you start your inst. training.

AC Said: so that I don't waste precious dual-time continually going over the mundane basics of trying to remember the proper control inputs in order to "put" the aircraft into a particular flight attitude at will when asked by my instructor to do so.

Mastery of these basics will help make you a safe pilot.

 

[jrh]

Blackhawk's objection is, as I said before, a red herring just to be argumentative. Cl is directly proportional to AOA via the lift slope equation. You will often see this written as (alpha)(a), where a is the lift slope. It's a constant for a particular airfoil. That formulation does assume, however, that alpha is given as an absolute AoA, rather than in reference to the chordline.

Likewise, devices like flaps only change Cl at a particular AoA. At any particular airspeed, only one Cl will do. If you drop flaps, you're going to lower your AoA to maintain the same Cl.

Maybe it's just been a long day, but I don't understand what you just wrote.



All I can say is this: The reason I now think using Cl is better than AoA is because Cl incorporates factors such as flaps, wing surface area, camber, etc. that are all very important to producing lift, yet have no place in the lift equation if AoA is used by itself.

If AoA is used by itself, there is no explanation for the differences between a jet's wing and a Citabria's wing. Cl is what bridges this gap.

AoA doesn't have to be ignored when talking about Cl, either--in fact, it goes hand in hand with Cl quite nicely. A person could say that in the non-stalling envelope of operations, AoA is primarily what determines Cl.

 

[Roger, Roger]

All's I can say is, I know that there are about 4 pitch and power combinations that I use every day, can use without so much as a peek at the flight instruments, and that get me close enough for certain conditions of flight.
Vy climb.
Normal cruise at 2200 RPM (can be set within 50 RPM by sound)
65 knot glide.
85/75/65 for downwind/base/final (same pitch attitude and power setting, different flap settings)

This doesn't really pertain to the extended discussion, but maybe addresses the OP's question. Note where I said that these can (and SHOULD) be set completely via outside references (then verified with the gages).

Edit: I also have certain pitch/powers that I use for IFR in the planes I fly.

 

[jrh]

Ok, I was with you on AOA until I hit this little snare. You say Pitch <> AOA. You then say AOA can be increased through Pitching the aircraft's [moving the stick back] nose UP using Elevator, which by definition is using Pitch. Can you clarify this for me? I'm stuck here as this seems to be a physical contradiction.

Ahh, I see where you got confused. It all comes down to wording.

"Pitching" is a verb. It means "moving in a vertical motion." So "pitching the nose" is like saying, "Moving the nose up or down."

"Pitch attitude" is an adjective used to describe the position of the nose relative to the earth's horizon. A "nose low pitch attitude" means the nose is pointed towards the earth. A "nose high pitch attitude" means the nose is pointed towards the sky.

I said *pitch attitude* does not equal AoA.

I also said moving the stick back increases AoA. But just because you're pulling the stick back does not mean you are moving the nose up.

Think about the possibilities when doing aerobatics. You could be coming down the back side of a loop. The nose could have a low pitch attitude (aimed below the horizon at the ground), and the pilot could be pulling back on the stick, making the nose drop even lower.

In such a case, the aircraft has a nose low pitch attitude yet a high AoA.

Does that clarify things at all?

Add a little power and the plane won't sink quite so much. Add a little more power and it will be able to maintain level flight. Add a little more and it will start climbing a little. Add a lot of power and it will climb a lot.

Ok, I tried to over simplify things too much and you caught me on it.

What I was trying to explain is how excess power determines climb performance and a lack of power determines rate of descent.

I'm glad you looked at the total drag curve.

This curve represents exactly how much power it will take to maintain level flight at a given airspeed. This is because thrust from the engine must equal total drag if the pilot wants to maintain straight and level, unaccelerated flight.

If you apply more power than the amount of drag for a given airspeed, the plane must do one of two things--speed up, or begin climbing and gain altitude. If you apply a lot of extra power, it will either speed up a lot, or gain altitude...a lot.

If you decrease the power to be less than the amount of drag, the plane must do one of two things--slow down, or lose altitude.

This is where the concept of "power equals altitude" comes from.

In the story you quoted from Barry Schiff, the pilot was simply one step behind himself the whole time. As he slowed down, he added power, but by the time he added the power, he had already gotten slower because of the extra drag...and since he was slower, he had more drag, which made him slow down more, which made him get more drag, which...see how this leads to a vicious cycle?

The pilot kept reacting to the problem he had 5 seconds ago, so he's perpetually one step behind where he needs to be with the power--which is why he kept sinking. At no point did he give it enough power to equal the amount of drag he had, at that moment.

Two actions could have prevented this.

1) Releasing back pressure on the yoke would have reduced his AoA and increased his airspeed, which would have therefore reduced his total drag (since he was flying on the "back side" of the power curve), and with less drag, he would have not needed as much power to maintain level flight.

2) He could have been more aggressive with the power and added lots of power from the start. This would have stopped his descent (if power = total drag) and would have prevented him from "sliding off" the back side of the power curve.

Or, he could do a combination of #1 and #2, which is what I always teach. But either one also works individually if the aircraft has the excess altitude available for #1 or the excess power available for #2.

So, my question is this:

If I can find the Induced and Parasite Drag values and produce a Power Curve for my training aircraft for any aircraft I fly, won't it be possible to locate the exact region [range] of throttle positions for all of the six (6) phases of flight that are optimal for that particular aircraft? And, if I can do that, won't that give me an advantage over this pilot who ended up crash landing short of the runway because he either forgot or never knew what the power requirements were for that particular segment of his flight [the Approach and Landing]?

In my mind, I don't yet see a compelling enough argument for merely "guessing" at these critical operational numbers. Yes, a gust of wind here and there while on Final, or a downdraft, or all of the smaller details of unstable air masses that will impact the aircraft while on Final, will be at play. But, if I have a range of values [high through low] for the Power setting based upon the Pitch attitude of the aircraft, does that not put me light years ahead of most brand new students? If not, why?

Here's why "guessing" is the best way to do it: there are *far* too many combinations of situations to make memorizing a list of specific pitch and power settings practical. I mean, I'm talking about literally thousands of combinations of aircraft weight, air temperature, wind speeds, distances from the runway, etc.

If you are driving down the freeway and the car ahead of you slams on his brakes, do you think to yourself, "Ok, we're on level, dry pavement and it looks like he's about 47 feet ahead of me and decelerating at a rate of 4.5 ft/sec, and since I'm going 72 mph I need to..."? Heck no, you just slam on your brakes, too, and slow down enough to keep from hitting the guy! You intellectually understand the concepts of friction coefficients with the road, kinetic energy, momentum, etc., but when it comes down to operating your vehicle in an everyday situation, you do it primarily through sight and feel. Does knowing the nitty gritty physics of driving make you a better driver? To some degree, yes. But when it comes time to apply knowledge, seeing and feeling flying is much more practical.

If flying were as simple as memorizing six numbers, why do you think that guy crashed? If that's all there was too it, we would have been teaching it differently by now.

Six numbers would not have saved him. Having a better feel for the aircraft, as well as a deeper conceptual understanding of what was happening, might have prevented it though.

Flying is a cross between art and science. I'm not sure how else to express it.


Hope this helps!