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Downwind turn Myth

Old 01-24-2014, 08:52 AM
  #1226  
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The link above uses an anology of a bus moving and running foward or backward in the bus, The person experiances the same forces of acceleration and speed as if he were on the ground. People have brought in gusts and that is not the same, it is the same as if the busdriver steps on the brakes during the expermenters jog.
Old 01-24-2014, 08:58 AM
  #1227  
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Originally Posted by BlueBus320
I'm sure you fly the governments UAV well inside of it's flight envelope, just like I fly my company's airbus, & every other aircraft I've been compensated to fly. As far as "microburst" here is an exact quote from my statement: "That is not linearly the same as our low energy theory, but it corroborates it."
Your claim neglects to address the low energy (close to stall) regime of flight. How has the manufacturer come up with the recommended approach speeds for you UAV? Why the buffer above stall?
In order for the original statement of this thread to remain true, you would need to be correct 100% of the time, but in order for it to be discredited, I would only need to be right once.
It is far to
definitive of a statement for aviation.
Approach speed is 43kts., stall is 37 kts. Wind limits are 35 kts. You do the math and see how close to stall we are operating. If the downwind turn myth were at all true, we'd fall out of the sky every time in the 35 kt. wind. Once again the micro burst analogy doesn't corroborate anything as they are two very different phenomena. Again, the telemetry files don't lie, they are right there in black and white. There is no change in IAS while turning in significant or any other wind for that matter.
Old 01-24-2014, 09:15 AM
  #1228  
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Truly amazing in an aviation forum.But a common misconception that is worth an explanation.Since 1632 and what is called "Galilean relativity" (no need for Einstein here), it is known that the laws of physics are the same in all inertial frames.This means that the measurements of interacting forces, accelerations, variations of speed, momentum changes remains unchanged when switching to another inertial framealthough measurements of distance, speed, kinetic energy are changing through frame switching.Let's look at this glider flying 20 kt in a 20 knot headwind and turning 180° .A turn always requires an acceleration ; this is the centripetal acceleration.In the frame of reference of the air, the glider turn changes its speed from +20kt to -20kt.The integral of the centripetal acceleration has completed a momentum change of -40kt (x the glider mass).In the ground frame of reference, the glider turn changes its speed from 0kt to -40kt.The centripetal acceleration has also completed a momentum change of -40kt.So yes, measurements of accelerations, momentum changes and forces give the same results in the 2 frames.And that's untrue for kinetic energy.Kinetic energy alone is irrelevant ; it can vary from zero to infinity just by changing the frame of reference.The actual meaning of the kinetic energy in a specific frame is that "it measures the work that the mobile object can do through interacting with a still object of the frame".It also measures the work necessary to give it its speed through an interaction with a still object of the frame.So kinetic energy is only relevant in the frame of reference of the objects that the mobile interacts with.The common misconception here is generated by these facts:1. the ground frame has a special meaning to humans since it is the frame of the objects our feet interact with.2. the concept of inertia is objectively handled in physics through the measurement of mass, but is subjectively felt in all day life as the work required for increasing the speed of a mobile object.3. the "inertial work" can only be measured in the frame of the interacting object, but humans tend to consider that it is an absolute value measurable in the ground frame of reference.Back to turning into head wind/down wind.In summary, one can state:1. In itself, turning into head wind or down wind makes no difference ; the airplane only interact with the air and so it is the frame of reference of the air that matters.2. Turning whilst crossing a windshear does make a difference ; turning into increasing relative wind increases the total energy of the plane (temporary increase of air speed or height gain),and turning into decreasing relative wind decreases the total energy of the plane (temporary decrease of air speed or height loss).A turn into decreasing relative wind is a potential hazard at low altitude.3. Flying perfect circles with reference to the ground makes irregular circles in the air (with non-zero wind). The rate of turn is lower when flying headwind and higher when flying downwind.Thus flying a ground pattern at low altitude and allowing very high rate of turn when turning downwind is also a hazard.

Luc



I found the above quote in another forum, Luc has articulated exactly what I'm saying much better than I could. In particular, his last sentence is the crux of this whole debate from my standpoint.

Last edited by hugger-4641; 01-24-2014 at 09:17 AM.
Old 01-24-2014, 10:03 AM
  #1229  
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Originally Posted by hugger-4641
Truly amazing in an aviation forum.But a common misconception that is worth an explanation.Since 1632 and what is called "Galilean relativity" (no need for Einstein here), it is known that the laws of physics are the same in all inertial frames.This means that the measurements of interacting forces, accelerations, variations of speed, momentum changes remains unchanged when switching to another inertial framealthough measurements of distance, speed, kinetic energy are changing through frame switching.Let's look at this glider flying 20 kt in a 20 knot headwind and turning 180° .A turn always requires an acceleration ; this is the centripetal acceleration.In the frame of reference of the air, the glider turn changes its speed from +20kt to -20kt.The integral of the centripetal acceleration has completed a momentum change of -40kt (x the glider mass).In the ground frame of reference, the glider turn changes its speed from 0kt to -40kt.The centripetal acceleration has also completed a momentum change of -40kt.So yes, measurements of accelerations, momentum changes and forces give the same results in the 2 frames.And that's untrue for kinetic energy.Kinetic energy alone is irrelevant ; it can vary from zero to infinity just by changing the frame of reference.The actual meaning of the kinetic energy in a specific frame is that "it measures the work that the mobile object can do through interacting with a still object of the frame".It also measures the work necessary to give it its speed through an interaction with a still object of the frame.So kinetic energy is only relevant in the frame of reference of the objects that the mobile interacts with.The common misconception here is generated by these facts:1. the ground frame has a special meaning to humans since it is the frame of the objects our feet interact with.2. the concept of inertia is objectively handled in physics through the measurement of mass, but is subjectively felt in all day life as the work required for increasing the speed of a mobile object.3. the "inertial work" can only be measured in the frame of the interacting object, but humans tend to consider that it is an absolute value measurable in the ground frame of reference.Back to turning into head wind/down wind.In summary, one can state:1. In itself, turning into head wind or down wind makes no difference ; the airplane only interact with the air and so it is the frame of reference of the air that matters.2. Turning whilst crossing a windshear does make a difference ; turning into increasing relative wind increases the total energy of the plane (temporary increase of air speed or height gain),and turning into decreasing relative wind decreases the total energy of the plane (temporary decrease of air speed or height loss).A turn into decreasing relative wind is a potential hazard at low altitude.3. Flying perfect circles with reference to the ground makes irregular circles in the air (with non-zero wind). The rate of turn is lower when flying headwind and higher when flying downwind.Thus flying a ground pattern at low altitude and allowing very high rate of turn when turning downwind is also a hazard.

Luc



I found the above quote in another forum, Luc has articulated exactly what I'm saying much better than I could. In particular, his last sentence is the crux of this whole debate from my standpoint.
He's saying flying with reference to the ground can be dangerous. Exactly the point that myself and numerous others in this thread have been trying to point out. When you fly from a ground reference (R/C pilot on the ground) and you try to make the turns look the same to you on the ground (upwind vs. down wind) you can get into trouble. The truth is that if both turns look the same to you, they are very different to the airplane. This is the crux of the issue and the point that you and others completely miss. There is no change from the airplanes perspective, only yours.
Old 01-24-2014, 01:29 PM
  #1230  
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GOOD GRIEF!!

HUGGER, this does not support the myth!! It DISPROVES the myth. Read your own argument. Carefully. Please.

1. In itself, turning into head wind or down wind makes no difference ; the airplane only interacts with the air and so it is the frame of reference of the air that matters.

2. Turning whilst crossing a windshear does make a difference ; turning into increasing relative wind increases the total energy* of the plane (temporary increase of air speed or height gain),and turning into decreasing relative wind decreases the total energy* of the plane (temporary decrease of air speed or height loss).A turn into decreasing relative wind is a potential hazard at low altitude.

3. Flying perfect circles with reference to the ground makes irregular circles in the air (with non-zero wind). The rate of turn** is lower when flying headwind and higher when flying downwind. Thus flying a ground pattern at low altitude and allowing very high rate of turn when turning downwind is also a hazard.

* notice that inertia only comes into play in a windshear, or changing wind.

** this is the rate of turn over the ground, if you are keeping your circle perfect.



Notice he says the turns relative to the wind MAKE NO DIFFERENCE. Yes, the wind shear DOES make a difference. His references to turns into an increasing wind and into decreasing wind are under his NO. 2 statement: WINDSHEAR!!

In No. 3 he is talking about trying to tighten your turn in order to maintain your ground track. Read it.

Not one of the high-time pilots or engineer "experts" responding in this thread would disagree with any of these statements.

Does a turn in a steady state wind affect airspeed? NO.

Does trying to fly your normal pattern in a high wind create a hazard? YES. YES!! BUT THAT IS NOT THE SCENARIO OF THE MYTH.

You can fly your traffic pattern (it probably won't be the exact same shape) using your normal inputs. You just have to adjust your timing. Start your turn to base early, normal bank, normal airspeed, normal elevator pressure. You will find yourself screaming across the ground, but your airspeed will not change from your normal pattern UNLESS YOU CHANGE IT.

You will have to turn more than 90° of turn if you want to fly your perpendicular base leg. Expect to find yourself on a longer final or at least a slower one.

IF YOU TRY TO TIGHTEN YOUR TURN OR SLOW THE AIRPLANE'S SPEED OVER THE GROUND YOU WILL DIE. NOT BECAUSE YOU TURNED DOWNWIND, BUT BECAUSE YOU MISHANDLED THE TURN.

Respectfully,

Steve.


Last edited by Sgt. Meyer; 01-24-2014 at 02:07 PM.
Old 01-24-2014, 02:30 PM
  #1231  
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Amazing thread. Like most of you I can't believe that it came back from the dead with a vengeance.

For those who want a little laugh I recommend this article from Flying magazine: http://www.flyingmag.com/pilots-plac...d-turns-really
Old 01-24-2014, 02:54 PM
  #1232  
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Unsubscribe. I just can't take it anymore. All you myth believers just keep on believing, if it will satisfy you.
Old 01-24-2014, 03:23 PM
  #1233  
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Originally Posted by littlera
Unsubscribe. I just can't take it anymore. All you myth believers just keep on believing, if it will satisfy you.
Unsubscribe NEVER this is just too funny and STUPID, not to watch. Supposedly grown and educated (some not too educated)Men fighting about weather a myth is real or not. When we gona get the boat in the river senerio, or did I miss that one?
Old 01-24-2014, 04:15 PM
  #1234  
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Originally Posted by HoundDog
Unsubscribe NEVER this is just too funny and STUPID, not to watch. Supposedly grown and educated (some not too educated)Men fighting about weather
I loved the pun.

Mike
Old 01-24-2014, 04:27 PM
  #1235  
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What about the plane taking off a conveyor belt? Some people never got that, swearing that Mythbusters faked it.

Last edited by Sport_Pilot; 01-24-2014 at 05:17 PM.
Old 01-24-2014, 04:59 PM
  #1236  
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Originally Posted by BaldEagel
I loved the pun.

Mike
Originally Posted by HoundDog
Unsubscribe NEVER this is just too funny and STUPID, not to watch. Supposedly grown and educated (some not too educated)Men fighting about weather a myth is real or not. When we gona get the boat in the river senerio, or did I miss that one?

My Spell checker is not cognoscente of syntax Sorry but it did turn out to be a good PUN nice catch.
Old 01-25-2014, 02:38 PM
  #1237  
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I fly F3A which has to be ground referenced, so unfortunately I have to deal with this whole moving airmass thing by flying my plane crooked and changing my airspeed all over the place.
Old 01-25-2014, 02:43 PM
  #1238  
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Congrats Guys,

You made it to 50 pages and still going strong. Somebody even brought up relativity. I'm impressed.....laughing at all this, but impressed.

Jim
Old 01-25-2014, 03:45 PM
  #1239  
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Originally Posted by rcjets_63
Congrats Guys,

You made it to 50 pages and still going strong. Somebody even brought up relativity. I'm impressed.....laughing at all this, but impressed.

Jim
Yeah, there's probably some alien race reading this and laughing their (multiple?) heads off, meanwhile they're arguing about whether turning into TIME or with TIME is real or a myth :-)

Last edited by bjr_93tz; 01-25-2014 at 03:47 PM.
Old 01-25-2014, 04:18 PM
  #1240  
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Originally Posted by bjr_93tz
I fly F3A which has to be ground referenced, so unfortunately I have to deal with this whole moving airmass thing by flying my plane crooked and changing my airspeed all over the place.
Everything we fly R/C is ground referenced, not just F3A though, but I'm sure you knew that. Trying to make your maneuvers look symmetrical is really the same illusion that gets the downwind turn myth guys. lol
Old 01-25-2014, 04:32 PM
  #1241  
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Originally Posted by Lownverted
Everything we fly R/C is ground referenced, not just F3A though, but I'm sure you knew that. Trying to make your maneuvers look symmetrical is really the same illusion that gets the downwind turn myth guys. lol
Wonder what it would be like to fly F3A (Pattern or IMAC) with a good FPV set up with head tracker?
That would be interesting how to get the camera to pivot left and right more that 180 degrees and tilt back more than 90 degrees.
Any one try FPV with Google Glasses yet? Watch the Plane while seeing out the coclpit.
Old 01-25-2014, 05:42 PM
  #1242  
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Originally Posted by bjr_93tz
Yeah, there's probably some alien race reading this and laughing their (multiple?) heads off, meanwhile they're arguing about whether turning into TIME or with TIME is real or a myth :-)
LMAO!!!!

For sure, someone on the alien thread has brought up relativity too! At least on that thread it would be applicable.

Jim
Old 01-25-2014, 06:19 PM
  #1243  
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Originally Posted by Lownverted
Everything we fly R/C is ground referenced, not just F3A though, but I'm sure you knew that. Trying to make your maneuvers look symmetrical is really the same illusion that gets the downwind turn myth guys. lol
Yep. it's just that we tend to aknowledge that we have to fly "turns" differently upwind or downwind to get them to look right. Quiet engines with an abundance of power, and smooth corrections for wind create the illusion that the airmass isn't moving around. Flying consecutive loops is a perfect way to look "down" (or up?) onto upwind and downwind "turns"

As for FPV for pattern, you'd need a GPS overlay as the plane isn't always travelling in the direction it's pointing on a windy day. Pulling 90deg into an vertical upline with a 20km/hr headwind will see the plane pointing straight up but your upline (model's flightpath) will be bent backwards by about 10deg. Same as with crosswinds.
Old 01-25-2014, 10:58 PM
  #1244  
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At least on that thread it would be applicable.
It's applicable here as well. As with the examples given about moving in the bus and train. Similar examples are given in Einstiens theory of relitivity and those examples adapted for his calculations for the speed of light and its effect on time and mass,
Old 01-26-2014, 12:02 AM
  #1245  
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I tell you one theory which has been debunked is evolution...
Old 01-26-2014, 05:41 AM
  #1246  
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And it is scenarios just like this that have women world-wide shaking their heads at men, laughing their asses off, and becoming lesbians.
Old 01-26-2014, 08:23 AM
  #1247  
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OK folks, I have the PROOF! I stayed up late last night making fun videos. The first one is foreplay, so you have to wait for Part 2 to get to the action. No not that kind of videos you perverts!
These should show up on You Tube soon. Here's the links. Enjoy.
I truly hope this helps dispel the Myth, at least among those who are on the fence and still savable from the mysterious power that the Myth seems to hold over its adherents. I believe these videos adequately answer the challenges that have been posted on this thread recently.

Part 1: http://youtu.be/PaPKLUdbqLU
Part 2: http://youtu.be/GdK3TzcFye4

Last edited by RZielin; 01-26-2014 at 10:51 AM.
Old 01-26-2014, 08:35 AM
  #1248  
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I just have one question. How do it know?
Old 01-26-2014, 10:14 AM
  #1249  
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Why don't you folks getting angry or continuing to mock others simply unsubscribe and do us all a favor, good lord! It's been said many times the issue is we track our planes' position from a static position, unlike a person IN a plane and in this instance, the wind from behind with a relatively quick change in direction from travelling into or perpendicular to it, will affect lift momentarily, how hard is this to understand really? Don't turn this into a full scale issue, I don't believe anyone is claiming a gentle turn inside a moving air mass affects lift...

Jack
Old 01-26-2014, 10:50 AM
  #1250  
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Yes they are, that's the problem. And I'm not sure what you mean about "a quick change in direction…. will affect lift momentarily". It will, but it will do it exactly the same turning upwind or crosswind as it does downwind. I think you get that, but others in this discussion do not.

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