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Downwind turn Myth

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Old 07-02-2011, 01:13 PM
  #1076
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Quote:
ORIGINAL: highhorse

Yet one more partially correct answer. AND way, way off topic besides.
Yep![:-]

No thread is complete until "someone" chimes in with great feats in British Aviation.......Ooooops! Did actually type that out loud?
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Old 07-02-2011, 02:55 PM
  #1077
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Quote:
ORIGINAL: m1morrow

Guys dont look on wikipedia.........

Straight and level flight Lift=Weight and thrust=drag.

During a climb Lift is momentarily greater than weight (causing an ecceleartion upward...... you feel gforce or load factor or whatever you want to call it) then once the plane is climbing constantly lift=weight......i know its kind of counter intuitive but its ture.
Don't you have something wrong here? The following makes sense to me:
Quote David Gladwin:

"The vertical component of 20 k pounds of thrust in a 45 degree climb is = 14, 000 pounds . A/c weight (mass) 30, 000 pounds , so 30k less 14 k = 16k pounds of wing lift required ! Gets less as climb angle increases !"

Therefore, shouldn't your statement be: "During a climb Lift is momentarily greater than weight ....... then once the plane is climbing constantly lift < weight (less by the amount of the vertical vector of thrust, which increases proportional to climb angle)."

Yes? No?

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Old 07-02-2011, 03:42 PM
  #1078
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Quote:
ORIGINAL: cactusflyer

No thread is complete until ''someone'' chimes in with great feats in British Aviation.......
..... OR, a sly mention of Weatronics products.
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Old 07-02-2011, 05:11 PM
  #1079
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Default RE: Downwind turn Myth

David,

Hes Coffin corner when you are talking about Critical mach and the plane stalling happens .  I understand that....I was just at 47,000 feet in the left seat of a Learjet 2 days ago.  :-)  You can see the red line on the Mach and the red line for the stall creep up.

But when you teach people how to fly some people refer to the turn from base to final as coffin corner also.  Because as you know many people get too slow and stall/spin during that turn.

And yes a rocket can use thrust to overcome weight. and climb away from the earth..  so thrust in that case is overcoming gravity and drag when the rocket is accelerating.

In a plane we overcome weight with the wings lift.......and yes you are right when the prop is angled away from the ground it is pulling you up and helping you need a little less lift from the wings to climb.

BUT you can still climb in a plane with the line of thrust perpendicular to the pull of gravity.  Especially if you have a wing like a cessna's wing.
I was just trying to make the Basic argument that during a established constant rate climb Lift=Weight Thrust=Drag.

Yes a F-15 can climb straight up and not loose speed for a few thousand feet because it has way more thrust than it weighs i get that. 


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Old 07-02-2011, 05:34 PM
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Quote:
ORIGINAL: m1morrow

BUT you can still climb in a plane with the line of thrust perpendicular to the pull of gravity. Especially if you have a wing like a cessna's wing.
I was just trying to make the Basic argument that during a established constant rate climb Lift=Weight Thrust=Drag.

Yes a F-15 can climb straight up and not loose speed for a few thousand feet because it has way more thrust than it weighs i get that.


I'm learning here, thanks for the mention about climbing with a high lift wing even when the thrust is perpendicular to gravity vector. However, I STILL think your math/geometry is a little off. If you're using the word "Lift" to refer to the work the wing does, then Lift may or may not = weight in a constant rate climb. As discussed a few posts above, if the plane is angled "up", the wing supplies lift LESS THAN weight, and if the plane is perpendicular to gravity (ie horizontal but climbing due to lift) then lift is greater than weight. I think.
At the extreme example of straight vertical climb, the wing is supplying zero lift.
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Old 07-02-2011, 06:11 PM
  #1081
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Quote:
ORIGINAL: cfircav8r
...or centripetal forces due to pitch changes and turns.
Thank you!! Yes, the force is "centripetal"; it is the "centrifugal" reaction to that force that we feel when turning, not a "centrifugal force."
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Old 07-02-2011, 07:39 PM
  #1082
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Default RE: Downwind turn Myth

Rezlin,

Yup your if your engine is angled up some thrust from it does help overcome weight.  But in a civilian aircraft you rarely pitch more than like 10-15 degrees up.  So there is not going to be much thrust pulling the plane up much.  (unless your Jim Leroy)  The wings are making you go up......I don't know the math equation but probably 99%..  Point I'm trying to make is that the plane is in a state of equilibrium during a constant climb.  Lift(from wings and possibly a tiny amount from the props thrust)=weight until you change something and level out or climb steeper.  :-)

Also when a plane is going straight up the wings are still making lift its just going horizontally.  So to make a f-15 it go straight up you would need to pitch back 80 degrees or something. 

This is a fun topic to discuss.
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Old 07-03-2011, 03:49 AM
  #1083
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Default RE: Downwind turn Myth

GA piston airplanes that I am familiar with have the engine mounted such that the thrust is angled slightly down and right (for a clockwise rotating prop as seen from the pilot's seat.)

Quote:
ORIGINAL: m1morrow
So to make a f-15 it go straight up you would need to pitch back 80 degrees or something.
Or bunt the stick to unload the wing if pure vertical
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Old 07-19-2011, 02:29 AM
  #1084
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Default RE: Downwind turn Myth

I hate dredging up old threads so please forgive me in advance.

Here is quite a cool experiment if, like me, you spend a fair amount of time in airports. I think it helps explain a few of the concepts of flight in wind and the observers position. I assume everyone has seen those horizontal travelators for people too lazy to walk.

Imagine that you are an aeroplane and your "stall speed" is a slow forward walking speed - so long as you are walking you have not stalled. The travelator represents the wind. Now walk along the travelator, still haven't stalled. As far as you are concerned you are going at normal speed. However the people sitting at the gates will see you moving faster than walking speed. Now turn around and walk against the direction of the travelator. You are still walking at the same speed but observers at the gate will see you moving slower or perhaps even backwards if the travelator is quite quick. Ok, I would imagine that no one has trouble relating this models flying downwind or upwind respectively.

Now walk forwards at the same rate for this whole exercise. Start by walking with the travelator and then slowly walk in circles on the travelator. As far as you are concerned you are walking at the same rate above "stall" speed. However the gate observers will see you moving "downwind" quicker and "upwind" slower. They will see you making elongated circles moving downwind. This represents constant airspeed circling.

Of course if you try to move in a circular motion with respect to the gate observers (model pilot) you would need to walk quicker when going against the travelator and slower with it. You can see that if you needed to slow down more than a walking pace minimum you have "stalled". Hence the downwind turn myth.

The travelator thought experiment can also describe wind shear and dynamic soaring. At the point that the travelator starts and finishes is a shear point. When stepping onto the travelator you sometimes have to take a half step to avoid falling over. Same with at the end you are moving with the wind and this is added to your speed and as you step off you sometimes feel like you need to be running.

In Hong Kong airport, and I would imagine others, there are travelators going in each direction. If you were walking along against one travelator and jumped across to the other one your speed adds. Now you are at a fast walk. turn on this travelator then jump back to the first and it adds again. Now you are running. Repeat over and over againand you find yourself not able to keep up. This experiment is a bit of a stretch but you can see how crossing the shear layer one way and then crossing it again going the opposite way incrementally adds speed.

With regard to the original post about stalling at the top of a loop (I think) you can see that if you did rolly-pollies on the travelator your airspeed is related to the travelator but gate observers would see a different shape loop depending on which way you were facing.

Cheers
Tarquin
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Old 04-26-2012, 06:18 AM
  #1085
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Default RE: Downwind turn Myth



Realized I bumped an old thread, nevermind.

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Old 05-24-2012, 12:16 PM
  #1086
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Default RE: Downwind turn Myth

totally unrelated, but I am looking for a rack to fit on top of my senior telemaster to carry a glider aloft. any help will be appreciated. Regards
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Old 05-24-2012, 12:36 PM
  #1087
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Default RE: Downwind turn Myth


Quote:
ORIGINAL: Superspook

totally unrelated, but I am looking for .........
Post in a jet forum? Novel approach to your search for sure.

Whatever you do - Dont turn downwind

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Old 05-24-2012, 06:10 PM
  #1088
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Quote:
ORIGINAL: Superspook

totally unrelated, but I am looking for a rack to fit on top of my senior telemaster to carry a glider aloft. any help will be appreciated. Regards
Seriously dude?

Shaz
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Old 01-14-2014, 02:19 PM
  #1089
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Charlie Precourt, you know - the astronaut and EAA Safety Committee Chair - published this article recently that explains pretty clearly that the "downwind turn" is not a myth for a couple reasons. One of which has been attempted to be explained several times here, only to be dismissed by the hoard (a rapid change of direction into and out of steady prevailing winds has the same effect as windshear on an airframe). I'm sure the OP and his fellow Deniers will skew the information or pick nits or try and explain how it doesn't apply to us. But it's here for everyone to interpret:

http://www.sportaviationonline.org/s...013?pg=14#pg14

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Old 01-14-2014, 04:18 PM
  #1090
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Quote:
Originally Posted by edh13 View Post
Charlie Precourt, you know - the astronaut and EAA Safety Committee Chair - published this article recently that explains pretty clearly that the "downwind turn" is not a myth for a couple reasons. One of which has been attempted to be explained several times here, only to be dismissed by the hoard (a rapid change of direction into and out of steady prevailing winds has the same effect as windshear on an airframe). I'm sure the OP and his fellow Deniers will skew the information or pick nits or try and explain how it doesn't apply to us. But it's here for everyone to interpret:

http://www.sportaviationonline.org/s...013?pg=14#pg14
No need to nit pick. This explanation, although obviously written from the perspective of a full scale pilot, is totally consistent with the more knowledgeable responses on this thread. The first section of the article observes there is no aerodynamic effect on the aircraft during "downwind" turns as long as ground track is ignored. However, when flying/turning in reference to a specific ground track (i.e. landing pattern), the "groundspeed change sensation" can cause a pilot to "erroneously respond to it" and cause an "undesired drop in indicated airspeed".

Makes sense to me. I think the "myth" part is that somehow the aerodynamics change in the downwind turn (which they don't) but the power/control responses do change to fly a specific ground track. Low altitude windshear is a different phenomenon altogether and is a danger regardless of ground track.

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Old 01-14-2014, 05:52 PM
  #1091
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Quote:
Originally Posted by CraigG View Post
No need to nit pick. This explanation, although obviously written from the perspective of a full scale pilot, is totally consistent with the more knowledgeable responses on this thread. The first section of the article observes there is no aerodynamic effect on the aircraft during "downwind" turns as long as ground track is ignored. However, when flying/turning in reference to a specific ground track (i.e. landing pattern), the "groundspeed change sensation" can cause a pilot to "erroneously respond to it" and cause an "undesired drop in indicated airspeed".

Makes sense to me. I think the "myth" part is that somehow the aerodynamics change in the downwind turn (which they don't) but the power/control responses do change to fly a specific ground track. Low altitude windshear is a different phenomenon altogether and is a danger regardless of ground track.

Craig
Well you didn't nit pick but you did cherry pick. The first section of the article does talk about the visual queues a full scale pilot uses while maneuvering near the ground being effected by changing winds relative to the acft. Obviously this has nothing to do with what we are talking about here. A large part of the rest of the article goes on to describe aerodynamic affects on the airframe from turning down wind that can contribute to dangerously low airspeed. I think he even uses words like 'push', 'inertia', 'acceleration'. Words that should not even exist in "the downwind turn is a myth" world. Well, here's a quote...

The other reality we face is windshear. This sudden change in windspeed or direction instantaneouslychanges our indicated speed.Instantaneous changes from head-to tailwind donít allow enough time for the wind to accelerate theaircraft (per the physics discussionabove) and will result in a drop ofindicated speed. So wind shear,rather than steady wind, is the killer.Combine the groundspeed changesensation with wind shear affectsand you have a handful.

In our yank-n-bank world of RC I'd say we experience this pretty much all the time.
Eric
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Old 01-14-2014, 06:40 PM
  #1092
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Well, After hibernating for 6 1/2 months it woke up !! It's ALIVE !!!

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Old 01-14-2014, 07:17 PM
  #1093
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Quote:
Originally Posted by edh13 View Post
Well you didn't nit pick but you did cherry pick. The first section of the article does talk about the visual queues a full scale pilot uses while maneuvering near the ground being effected by changing winds relative to the acft. Obviously this has nothing to do with what we are talking about here. A large part of the rest of the article goes on to describe aerodynamic affects on the airframe from turning down wind that can contribute to dangerously low airspeed. I think he even uses words like 'push', 'inertia', 'acceleration'. Words that should not even exist in "the downwind turn is a myth" world. Well, here's a quote...

The other reality we face is windshear. This sudden change in windspeed or direction instantaneouslychanges our indicated speed.Instantaneous changes from head-to tailwind don’t allow enough time for the wind to accelerate theaircraft (per the physics discussionabove) and will result in a drop ofindicated speed. So wind shear,rather than steady wind, is the killer.Combine the groundspeed changesensation with wind shear affectsand you have a handful.

In our yank-n-bank world of RC I'd say we experience this pretty much all the time.
Eric

Well, once again THE MYTH has generated comment from those who don't know their arses from a FEJ postmortem!

Craig is 100% correct. WINDSHEAR has nothing to do with THE MYTH...you have excerpted this quote that has no reverence to turning an aircraft..... WINDSHEAR is turbulence......period....if the guy driving the plane around the patch gets too slow while trying stay constant to a ground reference and gets into big time turb, then it's ass over teakettle time! It matters not if the reference is the pilot station or the sight picture of the runway. That is what the astronaut cum sport pilot is talking about.

Twiwinds,

John

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Old 01-14-2014, 07:18 PM
  #1094
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Yes!! Thread from the dead is back! And I see that the folks who still believe the myth live and breath. Glad I just bought a new box of popcorn....
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Old 01-14-2014, 07:20 PM
  #1095
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Quote:
Originally Posted by rcjetsaok View Post
Well, After hibernating for 6 1/2 months it woke up !! It's ALIVE !!!

More like a year and a half... And only because I saw this article that was written just a couple months ago.
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Old 01-14-2014, 07:29 PM
  #1096
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Quote:
Originally Posted by cactusflyer View Post
Well, once again THE MYTH has generated comment from those who don't know their arses from a FEJ postmortem!

Craig is 100% correct. WINDSHEAR has nothing to do with THE MYTH...you have excerpted this quote that has no reverence to turning an aircraft..... WINDSHEAR is turbulence......period....if the guy driving the plane around the patch gets too slow while trying stay constant to a ground reference and gets into big time turb, then it's ass over teakettle time! It matters not if the reference is the pilot station or the sight picture of the runway. That is what the astronaut cum sport pilot is talking about.

Twiwinds,

John
Wow... Did anybody actually read the whole article? And getting personal already?? The hubris on this board is mind boggling...
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Old 01-14-2014, 07:35 PM
  #1097
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Originally Posted by edh13 View Post
Wow... Did anybody actually read the whole article? And getting personal already?? The hubris on this board is mind boggling...
Your right !! 2012 , 2013... They all run together... My bad !!

D
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Old 01-14-2014, 07:59 PM
  #1098
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Originally Posted by edh13 View Post
Wow... Did anybody actually read the whole article? And getting personal already?? The hubris on this board is mind boggling...

Its not personal, it's wisdom.....THE MYTH us exactly that, a myth.....and this is coming from someone who crashed his first low wing r/c toy in a downwind turn 35 years ago. Luckily, my club was The McDonnell Douglas R/C Club which was chock full of aero engineers, electronics experts and physicists. It was hard to cry foul while expert onlookers analyzed. I was informed way back then that "the airplane has no idea which way the wind blows!" ...the same is true today no matter what article is written.

Tailwinds,

John
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Old 01-14-2014, 08:24 PM
  #1099
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Quote:
Originally Posted by edh13 View Post
Charlie Precourt, you know - the astronaut and EAA Safety Committee Chair - published this article recently that explains pretty clearly that the "downwind turn" is not a myth for a couple reasons. One of which has been attempted to be explained several times here, only to be dismissed by the hoard (a rapid change of direction into and out of steady prevailing winds has the same effect as windshear on an airframe). I'm sure the OP and his fellow Deniers will skew the information or pick nits or try and explain how it doesn't apply to us. But it's here for everyone to interpret:

http://www.sportaviationonline.org/s...013?pg=14#pg14
edh 13 The fact that downwind turns can be dangerous is no myth. Gusts and lulls and wind shear certainly make all turns dangerous. That's the gist of this article. This issue has been acknowledged in this thread long, long ago (see post #725). When some of us rail against "the myth", we're referring to something different. The article you site is "on our side", consistent with and in agreement with us nonbelievers in "the myth".

Nowhere in the article does he support the truly mythical belief that downwind turns are aerodynamically different from upwind turns. Dangerous due to confusing frame of reference issues with landmarks on the ground? Yes. Dangerous due to unexpected lulls causing sudden loss of airspeed? Yes. Dangerous due to an inherent aerodynamic loss of airspeed in downwind turns that is different from upwind turns or crosswind turns? NO! That is the part that we refer to as the "myth".
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Old 01-14-2014, 08:43 PM
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OMG it's back! I suspect this thread will be forever resurrected by those who just refuse to get it. It's about misperception; pilots misjudging airspeed because they are either on the ground looking at an R/C model in the air or are flying in a full scale plane and looking at the ground. In both cases, the misperception causes them to do the wrong thing with disasterous results.

This latest piece of "evidence" that supposedly supports the downwind turn myth actually does just the oppose. Please re-read the paragraph at the bottom of the first column on page 2.

Hopefully, I won't have to get the pictures of the pelicans out again.

Jim
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