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Flitetest join the downwind turn debate!

Old 11-09-2011, 04:08 PM
  #51  
JetPlaneFlyer
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Originally Posted by slipstick View Post
Them global worms are making a right mess of things aren't they .

Steve
yeah.. I blame spellcheck
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Old 11-30-2011, 01:00 PM
  #52  
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I have just read this thread all the way through and it really does surprise me how many people seek to explain the aerodynamic effect on a plane when turning 'down wind'.

If only RC pilots had plane mounted airspeed indicators it would become a non topic.
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Old 11-30-2011, 04:10 PM
  #53  
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I had some challenging downwind turns today, despite the throttle being set to a constant setting for downwind and upwind legs.

When you are heading downwind, just about to turn and the wind gusts and your airspeed goes to zilch, it's nice to have some altitude! Plane does look awfully funny, zipping along at 15 or 20mph, fully stalled...


Dave
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Old 11-30-2011, 06:17 PM
  #54  
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There is Airspeed and there is Ground speed.
Airspeed is relevant to the aircraft.
Ground speed is relevant to navigation.
Wind speed and direction affect ground speed and ground track only.
There is a stall and there is an accelerated stall. Both have to do with airspeed. One is wing level, one is wing in a bank.
Anybody besides me ever do "turns around a point" and "turns about a point" in a full size aircraft, single engine or multi engine ?

Bill
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Old 11-30-2011, 06:21 PM
  #55  
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Originally Posted by Dragonflyer View Post
There is Airspeed and there is Ground speed.
Airspeed is relevant to the aircraft.
Ground speed is relevant to navigation.
Wind speed and direction affect ground speed and ground track only.
There is a stall and there is an accelerated stall. Both have to do with airspeed. One is wing level, one is wing in a bank.
Anybody besides me ever do "turns around a point" and "turns about a point" in a full size aircraft, single engine or multi engine ?

Bill

Not in a loooong time...


Dave
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Old 11-30-2011, 06:32 PM
  #56  
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Originally Posted by CNY_Dave View Post
When you are heading downwind, just about to turn and the wind gusts and your airspeed goes to zilch, it's nice to have some altitude!
That's true, but as well as gusts there are lulls, and the lulls are just as big and just as regular as the gusts (must be otherwise the wind would get ever stronger).. When you are flying into the prevailing wind and you get a lull then that's every bit as bad.
Flying in gusty wind is harder (whichever direction you are flying) no arguments on that point.
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Old 11-30-2011, 06:34 PM
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True, but then I couldn't say 'downwind'...
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Old 11-30-2011, 06:53 PM
  #58  
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I've been saying this for a while but once again: Part of the problem could be that we're crabbing on the crosswind legs to maintain and orthogonal box pattern. This means our turns up/down wind will be considerably less or more than 90 deg.

i.e. If we're crabbing 15 deg on cross wind to keep from being blow down the field then our upwind turn would only be 75 deg. Adversely a turn downwind would be 105 deg. That's a delta of 30 deg and we're not taking it into consideration.

So in conclusion I'm saying the turn up/down wind are not the same but it's not for the reason everybody thinks, ground speed vs air speed but because of the deg turned are significantly different.
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Old 12-26-2011, 11:53 PM
  #59  
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While the principles of 'the downwind turn' have been thoroughly stated by JPF I think it's noting that in reality Wind Shear/Gradient can have a very noticeable effect on models that are climbing or descending. Even on a 'steady' wind day, the wind gradient is significant at lower heights, particularly at model sizes.

In this sense the earth does have a very real effect on the air and anyone descending into the wind below 50 feet or so will find airspeed reducing even at a constant groundspeed.

I think this effect is important enough to explain a lot of the 'downwind turn' handling behavior modellers report. The change in airspeed can be dramatic, as anyone who has flown the 'wrong way' through shear layers when Dynamic Soaring will know.

Jon

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Old 03-05-2015, 10:13 PM
  #60  
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Originally Posted by Octavius View Post
I've been saying this for a while but once again: Part of the problem could be that we're crabbing on the crosswind legs to maintain and orthogonal box pattern. This means our turns up/down wind will be considerably less or more than 90 deg.

i.e. If we're crabbing 15 deg on cross wind to keep from being blow down the field then our upwind turn would only be 75 deg. Adversely a turn downwind would be 105 deg. That's a delta of 30 deg and we're not taking it into consideration.

So in conclusion I'm saying the turn up/down wind are not the same but it's not for the reason everybody thinks, ground speed vs air speed but because of the deg turned are significantly different.
Someone who thinks like me!!!!!! You can test this theory by flying your plane on a perfectly calm day while in the car. Any affects you don't see then are purely coincidence of the turbulence in the wind, not the wind itself. Soon this will no longer be a problem!
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Old 03-05-2015, 11:52 PM
  #61  
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The way to see that the plane "doesn't care about wind" is to fly circles around yourself while you are in a hot air balloon.

You'd be moving with the wind at the same rate as the wind is moving over the ground. The circles would be similarly spiraling downwind, thus the airplane would "see" it as dead calm air. A constant rate of turn would keep the plane a constant radius from the balloon and no issues at all.

Driving in a car on a calm day would be changing it to simulate having wind and thus you'd need to continuously change bank angle/rate of turn in order to make "circles" with the car at the center, effectively simulating wind at the speed of the car's movement and you standing in place like we normally do when flying RC models.
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Old 03-06-2015, 12:08 AM
  #62  
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We are testing different things. I was talking about trying to isolate just the affect of a relative wind without any gusts, while your idea would have no relative wind but it would have gusts, so if we did both experiments we could figure out how much both gusts and relative wind contribute to the "windy day affect" as separate parts. They test completely different things
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Old 03-06-2015, 04:23 AM
  #63  
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Originally Posted by theapplepi3.14 View Post
Someone who thinks like me!!!!!! You can test this theory by flying your plane on a perfectly calm day while in the car. Any affects you don't see then are purely coincidence of the turbulence in the wind, not the wind itself. Soon this will no longer be a problem!
I don't follow. I do like FH's analogy though.
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Old 03-06-2015, 04:26 AM
  #64  
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The last sentence shouldn't make sense, but the previous ones should. I can't find an easy way to explain it without a diagram or a movie...
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