Low altitude steep descending turns...
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MAKG1
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MAKG
Huh?
Short final should certainly be "uniform," but the pattern involves several turns, power reductions, flap deployments, and gear deployments, all of which involve accelerations.
dtuuri
Final Approach
Here's what the OP said: "When turning in the pattern, usually to final, sometimes the wind is such that I want/need to turn steeper."
Pilots use every tool they have to make nice "uniform" flight. You make a power reduction, you add back pressure, so the passengers don't drop. When you turn you do it smoothly. Put down the flaps? Do it so the passengers can't tell. Now, Ernest Gann had to use the flaps to create un-uniform flight in order to save the Taj Mahal, but that was an exceptional event:
dtuuri
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Hank S
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^^^ What, you couldn't find the section so you searched for "the" because it occurs so few times in the rest if the book???
Good story, though. I need to get a copy of this book!
Good story, though. I need to get a copy of this book!
Everskyward
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Here's what the OP said: "When turning in the pattern, usually to final, sometimes the wind is such that I want/need to turn steeper."
Pilots use every tool they have to make nice "uniform" flight. You make a power reduction, you add back pressure, so the passengers don't drop. When you turn you do it smoothly. Put down the flaps? Do it so the passengers can't tell. Now, Ernest Gann had to use the flaps to create un-uniform flight in order to save the Taj Mahal, but that was an exceptional event:
dtuuri
That is not the way your "cute" video defined "uniform". There's nothing uniform about flying the pattern as far as physics is concerned, no matter how smoothly you do it.
denverpilot
Tied Down
dtuuri
Final Approach
dtuuri
Final Approach
The OP also said, "When around 75 kts how close are you getting to a stall condition at 30 degrees, at 45 degrees, at 60 degrees?"
The video said, and I paste, "UNIFORM MOTION AND NON-UNIFORM MOTION:A body is said to be in uniform motion, if it travels equal distances in equal intervals of time.A body is said to have non-uniform motion, if it travels unequal distances in equal intervals of time."
So... 75 kts seems to me to be "uniform". Now, if he said (btw, is he a he?), "When passing through 75 kts..." you may have a point.
dtuuri
denverpilot
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And you'd be wrong. Apparently you used it as an answer earlier, without understanding it at all.
Everskyward
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You would need to pass through 75 knots to some slower speed at some point or you aren't landing in a 172. Not to mention the fact that you need to turn in the pattern which introduces acceleration.
MAKG1
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You're confusing "uniform" with "smooth."
Uniform motion is always smooth, but the reverse is not true.
Using the layperson's definition of smooth (negligible 3rd and 4th derivative).
dtuuri
Final Approach
I understand it just fine: constant speed = same distances in same time intervals. Doesn't have to be in a straight line. Note the airplane in the drawings: http://www.physics.ohio-state.edu/~humanic/p111_lecture10.pdf
dtuuri
dtuuri
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MAKG1
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No. Constant velocity.
And it does have to be in a straight line unless you want to claim turning flight is exactly like straight flight.
You do seem to like to pile up the non sequiturs.
dtuuri
Final Approach
"Uniform circular motion" with a model airplane on a string as an example and you want to change the subject to "velocity", a term, if I remember my high school physics, that includes a vector--otherwise, I'm right and you know it. Go ahead, change the goal posts. I'm going to bed. G'nite.
dtuuri
MAKG1
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Tell us, in one sentence of your own words, what "uniform circular motion" has to do with anything in this thread.
azure
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Uniform circular motion and uniform motion may have the word "uniform" in common, but they are not the same thing and uniform circular motion is not uniform motion. In physics, uniform motion is motion at constant velocity. Neither speed nor direction of motion changes.
2Airtime2
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No free lunch, not without consequences. Why would you assume that? I specifically said "descending". That is the consequence of the steep turn while trying to stay away from a stall condition. I suspected this but wanted to get validation. I understand physics too (you are not that special). I guess I could have thought about the airplanes proximity to the airflow while in the attitude I was thinking about but I'm kinda lazy so I asked here. :wink2:
dtuuri
Final Approach
Because it's a common misconception that "unloading the wing" solves the problem of stalling when banking steeply to line up with the runway. You might solve the stall problem, but you make the line up even worse.
If I understand you, "descending" is not a result of a steep turn, it's the result of insufficient power. Nor is it a result of trying to stay away from a stall, since you can do that while climbing out after takeoff just as well without descending.
Then there was no need to ask.
dtuuri
dtuuri
Final Approach
No, you tell "us" what is the relevance of all this picayune focus of attention on the word "uniform".
dtuuri
MAKG1
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Why? It's not my choice.
dtuuri
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IIRC, you taught physics, right?
I used the word "uniform" as a surrogate for both, since a traffic pattern includes both straight lines and curves.dtuuri
MAKG1
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IIRC, you taught physics, right?
dtuuri
Honestly, you would do a lot better to admit you stumbled over a formal terminology trap, than to try to dig your hole deeper. It's pretty obvious that's what happened. And it's a hazard when depending on Google for your information.
There is no such thing as "uniform circular motion" in the pattern. Not even when Tower tells you to do a 360 (unless the wind just happens to be totally calm and the 360 is entered and exited instantaneously and executed perfectly, and of course there isn't any traffic you're trying to keep an eye on -- and you wouldn't be asked to do a 360 if there weren't).
Those of us who model physics professionally avoid the word uniform for more precise terminology like "unaccelerated" or "coasting."
dtuuri
Final Approach
This is BS.
This is the crux of your problem. You'd rather use nuanced technical words nobody else appreciates unless they're an egghead too. I've conveyed the essential information with enough physics accuracy to make the point you don't seem to get despite your high-brow elitism, namely: There is no practical difference in stall speed in a descent compared with holding altitude (exceptions previously noted for prop blast and thrust component). Go on in this if you wish, but I'm not playing this "gotcha game" with you. You didn't.
dtuuri
MAKG1
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There are several other people in this thread, some outside the field, who understood it just fine. "Uniform" (or unaccelerated or whatever) motion is hardly an obscure part of the field; it's taught in high school physics and sometimes even earlier. Heck, it even used to be taught in Saturday morning cartoons (remember Schoolhouse Rock?). You've missed the context, something you can't get easily from Google.
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dtuuri
Final Approach
Saying there's no difference in stalling speed in a descent vs. level flight as long as the plane is in uniform motion is meaningful, based in physics and is a correct statement. If the word "uniform" throws you (or anybody), I'd have to say they've lost sight of the forest for the trees. Btw, that Mari is a troublemaker with a capital "T". I knew what she was doing, so I flipped the tables with that video. I keep a college-level physics book within arm's reach on my night stand. I checked it this morning. The salient word in all types of motion is "uniform". Everybody knows what it means. So I used it. Shoot me.
dtuuri
Everskyward
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You hung yourself with that video because anyone can tell that is not the state of an airplane when flying the pattern.
dtuuri
Final Approach
Coriolis effect.
jaymark6655
Pre-takeoff checklist
LOL, I could see why someone would think that.
I am having trouble with the whole lift being the same in a climb as it is in level flight.
I thought the angle of attack was increased which at a constant airspeed means lift has to increase. Increased AOA means more drag, which is why you need to add throttle.
Not the propeller is pulling you up and AOA is the same in the climb, meaning same lift as level flight like the link says it is.
dtuuri
Final Approach
dtuuri
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You should read the article I linked to above to become familiar with the man and his renown. Then read his book. The lightbulbs will illuminate.
dtuuri
Dan Thomas
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The AoA is dependent on airspeed and load factor. The load factor in a straight-line climb is 1, so the AoA is not affected by that. However, the airspeed in the climb is lower, so the AoA is higher to generate the same lift as is generated at cruise speed and a lower AoA.
If the lift was higher than the weight, you'd have more than 1G and the airplane would be accelerating upward, seen as a constantly increasing climb rate. I wish...
jaymark6655
Pre-takeoff checklist
Thanks, that last sentence is what I was missing. An unopposed force causes acceleration, so a steady climb the forces would have to be equal or the rate of climb would be increasing.
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RotorDude
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I agree with "AoA is dependent on airspeed and load factor", however in a climb your flight path is inclined upwards, therefore (assuming constant airspeed) the lift produced is actually lower, since the thrust (engine) is actually bearing part of the load directly. In the extreme case, as a thought experiment, at a pitch angle near 90 degrees (vertical climb) the lift would be negligible, and the thrust alone would do all the "heavy lifting".
So clearly if there is less lift being generated by the wing (for the same airspeed), there is less AoA, and therefore more margin above the stall speed.
Again, in the extreme hypothetical (unless you are driving an F-15
), in a pure vertical climb you could climb at any speed above 0, and you wouldn't stall because your AoA would be zero (or negative, to counteract the "nuisance" lift).
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exncsurfer
Pattern Altitude
I wonder if the OP ever got his question answered, haha, Holy '7 pages of arguing' batman!
2Airtime2
Pre-takeoff checklist
I bought a Cherokee 180 the other day. Yesterday my cfi and I were going thru the logs, afm, and owners manual. We found a page that listed exact stall speed at different bank angles. Of course these figures are based on full load and holding altitude. I believe I found out in this thread that the stall speed will be lower if descending while banking.
Very good, because you're on the right track to stall is not determined by speed but by angle of attack.
RotorDude
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Regarding stall speed and climb/descent, beyond the reduced stall speed and AoA you get while climbing (as mentioned in my previous post), there is also a similar effect while descending (again, assuming a constant airspeed).
The point is really simple. As others have mentioned, your AoA is determined by your airspeed and load factor. Assuming the same airspeed throughout, the critical item is load factor. When flying straight and level, the lift force vector points up, countering the force of gravity which points down. The ratio between the lift and weight, or load factor, is one, which we call 1g.
Now if the nose points up (assuming constant airspeed), as I described in my previous post, the force of gravity perpendicular to the relative wind will be reduced (by half if you could climb at a 60 degree deck angle), since the engine starts carrying the plane's load directly (like a rocket flying upwards). This means that lift, which acts perpendicular to the relative wind by definition, is also down (to a half for 60 degrees), and load factor, which is lift divided by weight (which hasn't changed), is down (to 0.5g for 60 degrees), with a lower AoA and increased stall margin, as I mentioned above. Of course, in real life climbing at cruise speed is not normally feasible or practical, so we climb slower, necessitating a higher AoA to maintain lift, but the needed lift and load factor is still less than in straight and level flight.
When descending (again constant airspeed for simplicity), a similar effect takes place. The flight path is inclined downwards, gravity starts producing "thrust" (as it does most of the time in a glider), which means lift is lower. A hypothetical 60 degree nose down would reduce the lift (and load factor) to 0.5g, and therefore the AoA would be lower and stall margin higher.
This is why when descend we have an increased stall margin, all else being equal.
Again, in real life we are typically more concerned with stall speeds in the pattern, when we are flying slower, but the principle remains the same that inclined flight requires less lift.
So to summarize, stall speed depends on AoA, AoA depends on airspeed and load factor, load factor depends (among others) on the angle of climb or descent (reduced to half when the angle is 60, and down to 0 when the angle is vertical), so stall margin is increased (improved) when we climb or descend (all else being equal).
Comments welcome.
The point is really simple. As others have mentioned, your AoA is determined by your airspeed and load factor. Assuming the same airspeed throughout, the critical item is load factor. When flying straight and level, the lift force vector points up, countering the force of gravity which points down. The ratio between the lift and weight, or load factor, is one, which we call 1g.
Now if the nose points up (assuming constant airspeed), as I described in my previous post, the force of gravity perpendicular to the relative wind will be reduced (by half if you could climb at a 60 degree deck angle), since the engine starts carrying the plane's load directly (like a rocket flying upwards). This means that lift, which acts perpendicular to the relative wind by definition, is also down (to a half for 60 degrees), and load factor, which is lift divided by weight (which hasn't changed), is down (to 0.5g for 60 degrees), with a lower AoA and increased stall margin, as I mentioned above. Of course, in real life climbing at cruise speed is not normally feasible or practical, so we climb slower, necessitating a higher AoA to maintain lift, but the needed lift and load factor is still less than in straight and level flight.
When descending (again constant airspeed for simplicity), a similar effect takes place. The flight path is inclined downwards, gravity starts producing "thrust" (as it does most of the time in a glider), which means lift is lower. A hypothetical 60 degree nose down would reduce the lift (and load factor) to 0.5g, and therefore the AoA would be lower and stall margin higher.
This is why when descend we have an increased stall margin, all else being equal.
Again, in real life we are typically more concerned with stall speeds in the pattern, when we are flying slower, but the principle remains the same that inclined flight requires less lift.
So to summarize, stall speed depends on AoA, AoA depends on airspeed and load factor, load factor depends (among others) on the angle of climb or descent (reduced to half when the angle is 60, and down to 0 when the angle is vertical), so stall margin is increased (improved) when we climb or descend (all else being equal).
Comments welcome.