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Downwind Turns

Old 03-01-2009, 12:44 AM
  #26  
Sparky Paul
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Originally Posted by cbatters View Post
...

In order for the plane to fly with the wind with the same 20 MPH airspeed over the wing, the mass of the plane must be accelerated from 0 to 40 MPH which takes significant energy (e=mv^2) either from the engine or by concerting some of the stored energy (altitude) into kinetic energy (speed.) Which is why it is common to see airplanes lose altitude initially when they turn downwind.
...
I expect you're serious, but the plane has no idea what the wind speed is!
20 mph airspeed in any direction takes x amount of energy.
When referencing the airplane's flight to the -ground-, then the wind speed plus airspeed must be considered.
As far as the plane "knows", 20 mph into a 20 mph headwind, although the plane is stationary -relative to the ground-, is no different than 20 mph downwind, with the plane flying, as far as it "knows", 20 mph, while it's moving -relative to the ground- at 40 mph.
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Old 03-01-2009, 01:02 AM
  #27  
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I wonder if Bryce expected to generate this much interest...
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Old 03-01-2009, 01:47 AM
  #28  
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Lightbulb

Its not interest, its hard headedness. A refusal to accept the facts about flight, and a refusal to look it up for one's self and to instead continue to argue the point.
When in fact their point is absolutely wrong.

I say again and for the last time, look this all up for yourself if you cannot take mine or anyone else's word for it.
We aren't making it up.

For your own sake, please just spend a little less than 20 bucks and get yourself the facts, and let go of the falicies you are clinging to.
Stop thinking with "ground sense", and start thinking with "Air sense".

http://www.amazon.com/Stick-Rudder-E...871061&sr=11-1
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Old 03-01-2009, 03:15 AM
  #29  
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Thanks SabreHawk, but i dont need to look anything up. I haven't and I'm not about to argue with anyone here being back in the pecking order as i am... and quite freely will admit.. I have way back in post #6 if you would care to re-read accepted the "facts". My last post was a lighthearted comment rather than a "pot stirring" one. Perhaps some of us need to step back a minute. I was very simply speaking from my own experiences. " You can lead a horse to water" comes to mind somewhat... Cheers Darren..
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Old 03-01-2009, 04:16 AM
  #30  
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Originally Posted by Jaiwill View Post
I wonder if Bryce expected to generate this much interest...


Welll.......... I did know.....

but I wanted to Discuss it Politely

You perspective is good. You are a Self Confessed newB (like myself in many respects) and we can be told anything and we may tend to believe it.. The fascinating thing with being told something the first time and then believing it is that we tend to hold fast to the belief as "Gods Word". lol. this top has been likened to Religion and Politics. but it is not. but people are reluctant to change a Belief, and if no one has challenged it for a long time, then the belief can become so enrooted in a persons Psyche that they feel as if changing sides would be Sacrilegious...

I know that sounds hard. but what if I told you that WA was Crap and NSW is the best. (provided you have never seen or heard of NSW and you love WA) you may find it insulting to the core and begin defence without investigation, All based of feelings.

Now. this is what is and has been happening with this topic for a long while and I suspect SabreHawk has been on the front line of Debate/Argument and seen some serious denial from the "Downwind is Dangerous" "Downwind caused the crash" Clan.

Fear not. As you have already Opened you mind and Freely allowed the knowledge to enter. SabreHawk would probably be welcoming you with open arms as "One of US" (Currently I am un aware of any Welcoming ritual, and if there is on, Then I want mine ).

NE way. there is plenty of Material on the net and a Good book on the topic would only further you general and Technical Knowledge.

Just do a Google on "Downwind Turns" and you will find many a heated thread and many more Information pages....

I like you JaiWill. you are open minded. I also have compassion for SabreHawk

I would like to keep any conversation on the topic free of any insulting, degrading, inflammatory remarks (wouldn't any Forum Creator ?) and if anyone is feeling the need to add insult to their post. Please refrain, and just post the Points.
Wish me luck on that one

Bryce.
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Old 03-01-2009, 06:04 AM
  #31  
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Yes good luck Bryce. I feel you have opened the proverbial....
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Old 03-01-2009, 06:09 AM
  #32  
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My Planes fly so fast that the wind does not have a chance to catch up with them LOL , I Hope Everyone has their Boots on This thread is very interesting, Take care, Chellie
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Old 03-01-2009, 06:30 AM
  #33  
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Sorry Darren, it wasnt directed at you. Sometimes the written word doesnt indicate it's victim. I should have specified perhaps.
But I dont like singleing out individuals either, just those who arent following and accepting the facts in general.

I didnt think you you were in that group, nor did I think you take it that way.
My appoligies mate.
There are though so many in this hobby who have developed the wrong ideas about how a wing is flown, the ground based ideas having been so ingrained. It seems to me sometimes it requires sternness and shortness to get through.
And it can frustrate, especially when they continue to come back with "Well but, what if........." or "But that doesnt make sense, it cant be".
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Old 03-01-2009, 08:04 AM
  #34  
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No problems Sabrehawk. I don't know about anyone else but i like the ground to have as little as possible to do with my planes...Cheers all...
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Old 03-01-2009, 02:56 PM
  #35  
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Originally Posted by Jaiwill View Post
No problems Sabrehawk. I don't know about anyone else but i like the ground to have as little as possible to do with my planes...Cheers all...
Ahh hahahaaa! Now there's a statement I think everyone can agree with!
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Old 03-01-2009, 03:29 PM
  #36  
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Feel free to apologize to me as well.

I found no examples in the book at about airplanes with 120 knot stall speeds flying and turning in 120 knot winds.

Perhaps a video tape of you flying an underpowered MODEL plane in a high wind with downwind and upwind turns would settle this debate and open your mind.

The rest of us have noticed that when turning downwind, care must be taken to add more throttle and trade off altitude for airspeed lest we induce a stall. We have also noticed that when turning upwind, we do not lose any altitude and often have to push the nose down as it gains altitude.

<unsubscribing>


Clint

Originally Posted by Sabrehawk View Post
Sorry Darren, it wasnt directed at you. Sometimes the written word doesnt indicate it's victim. I should have specified perhaps.
But I dont like singleing out individuals either, just those who arent following and accepting the facts in general.

I didnt think you you were in that group, nor did I think you take it that way.
My appoligies mate.
There are though so many in this hobby who have developed the wrong ideas about how a wing is flown, the ground based ideas having been so ingrained. It seems to me sometimes it requires sternness and shortness to get through.
And it can frustrate, especially when they continue to come back with "Well but, what if........." or "But that doesnt make sense, it cant be".
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Old 03-01-2009, 03:43 PM
  #37  
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Originally Posted by Sparky Paul View Post
I expect you're serious, but the plane has no idea what the wind speed is!
20 mph airspeed in any direction takes x amount of energy.
When referencing the airplane's flight to the -ground-, then the wind speed plus airspeed must be considered.
As far as the plane "knows", 20 mph into a 20 mph headwind, although the plane is stationary -relative to the ground-, is no different than 20 mph downwind, with the plane flying, as far as it "knows", 20 mph, while it's moving -relative to the ground- at 40 mph.
I think cbatters is on the money here. Yes, the plane does not know the wind but the fact remains that it has to accelerate when making the turn. It might be better to think about this problem in terms of conservation of energy.

In your example the plane is travelling at 0 mph ground speed in the up wind direction and 40 mph ground speed on the down wind leg. Therefore there is a change in the planes energy state if you consider the kinetic energy (relative to the ground).

If KE = 1/2 m x V^2

lets assume the plane weight 1kg then

The in the up wind state KE = 1/2 x 1 x 0 = 0

In the down wind state th lane is travelling at a ground speed of 40 mph or 17.9 m/s

That means now the KE = 1/2 x 1 x 17.9^2 = 160 Jules

So where did this energy come from? The planes power was set to equal the drag at 20 mph IAS and this has not changed during the manoeuvre. There could be an exchange from the planes potential energy (as a result of altitude) to the planes KE which would explain a loss in height. The only other way you can balance the equation is to add power during the turn.
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Old 03-01-2009, 03:50 PM
  #38  
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You are a closed minded $^&^* idiot. Read the @#!$ book and stop misleading people on this forum. You are ignoring the $^# facts! Your ground based ideas are so ingrained and you ignore the truth.


Thx



Originally Posted by Buck Rogers View Post
I think cbatters is on the money here. Yes, the plane does not know the wind but the fact remains that it has to accelerate when making the turn. It might be better to think about this problem in terms of conservation of energy.

In your example the plane is travelling at 0 mph ground speed in the up wind direction and 40 mph ground speed on the down wind leg. Therefore there is a change in the planes energy state if you consider the kinetic energy.

If KE = 1/2 m x V^2

lets assume the plane weight 1kg then

The in the up wind state KE = 1/2 x 1 x 0 = 0

In the down wind state th lane is travelling at a ground speed of 40 mph or 17.9 m/s

That means now the KE = 1/2 x 1 x 17.9^2 = 160 Jules

So where did this energy come from? The planes power was set to equal the drag at 20 mph IAS and this has not changed during the manoeuvre. There could be an exchange from the planes potential energy (as a result of altitude) to the planes KE which would explain a loss in height. The only other way you can balance the equation is to add power during the turn.
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Old 03-01-2009, 04:04 PM
  #39  
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I should probably add that this isn't really a purely aerodynamics problem - I think that's is why there is so much misunderstanding.
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Old 03-01-2009, 04:13 PM
  #40  
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Originally Posted by Buck Rogers View Post
I should probably add that this isn't really an aerodynamics problem - I think that's is why there is so much misunderstanding.
You are still wrong and confusing the masses with your feeble attempts at obfuscating the truth with Newtonian math.

Very well done.


Clint
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Old 03-01-2009, 04:17 PM
  #41  
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Originally Posted by Sabrehawk View Post
"Well but, what if........." or "But that doesnt make sense, it cant be".

thats how people learn, by asking questions and questioning what they're are told. if we believed everything we are told without questioning it we'd all be sheeps.
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Old 03-01-2009, 04:19 PM
  #42  
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Originally Posted by cbatters View Post
You are still wrong and confusing the masses with your feeble attempts at obfuscating the truth with Newtonian math.

Very well done.


Clint
Yes, presumably I will be burnt at the stake for my heresy.
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Old 03-01-2009, 04:20 PM
  #43  
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Well I'll just have to disagree with those who would say that power needs to be increased or decreased due to wind. For is simply isnt true.

I dont need any formulas, nor references to kinetic energy or any other.

If those in opposition to this would simply go to the library and check out Wolfgang's "Stick and Rudder" you can read it all for yourself. Gosh no dont take mine or anyone else's word for it if you feel that strongly about it.
And if you do check out the book, refer to chapter 6 titled "Wind Drift".
Its all there in black & white.
I cant copy and paste any of it here,(Google books preview wont allow it, nor is that chapter in the preview.) and im not going to type it in from my copy of the book either. Im a terrible typist, and it would take me forever and give me a headache.

But a short trip to the library, and then and 30min. or so of reading will make it all clear.
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Old 03-01-2009, 04:30 PM
  #44  
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Originally Posted by Sabrehawk View Post
Well I'll just have to disagree with those who would say that power needs to be increased or decreased due to wind. For is simply isnt true.

I dont need any formulas, nor references to kinetic energy or any other.

If those in opposition to this would simply go to the library and check out Wolfgang's "Stick and Rudder" you can read it all for yourself. Gosh no dont take mine or anyone else's word for it if you feel that strongly about it.
And if you do check out the book, refer to chapter 6 titled "Wind Drift".
Its all there in black & white.
I cant copy and paste any of it here,(Google books preview wont allow it, nor is that chapter in the preview.) and im not going to type it in from my copy of the book either. Im a terrible typist, and it would take me forever and give me a headache.

But a short trip to the library, and then and 30min. or so of reading will make it all clear.

I don't think I'll bother with the library, I'll just trust my Masters Degree in Aerospace Engineering and the 10 years experience I've had since then as an Engineer.

Most likely the book you are referring to is talking about steady state flight - in that case you are correct in saying there is no extra power needed as the plane is unaware the body of air in which it i flying is moving.

But.......

As soon as you start doing manoeuvres you need to account for the planes mass and acceleration.
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Old 03-01-2009, 04:30 PM
  #45  
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Originally Posted by Buck Rogers View Post
Yes, presumably I will be burnt at the stake for my heresy.
LOL - Make sure there are two stakes available. Have a wonderful day.

(I may have to post a link to another heated debate where people were arguing about whether a dirty air filter in a moden car affected fuel economy. I ended up covering all but a 1 square inch opening on my TT air filter to prove that a clogged air filter was no different than throttle plate restriction when it comes to economy.)

[media]http://lancache.com/images/airfilter1.JPG[/media]

Sabrehawk - Free advise : Learning to argue a point without desparaging others in a public forum makes it a lot easier to say ""Oops, I was wrong and thanks for helping me see something differently."
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Old 03-01-2009, 04:52 PM
  #46  
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Originally Posted by cbatters View Post
LOL - Make sure there are two stakes available. Have a wonderful day.

(I may have to post a link to another heated debate where people were arguing about whether a dirty air filter in a moden car affected fuel economy. I ended up covering all but a 1 square inch opening on my TT air filter to prove that a clogged air filter was no different than throttle plate restriction when it comes to economy.)

[media]http://lancache.com/images/airfilter1.JPG[/media]

Sabrehawk - Free advise : Learning to argue a point without desparaging others in a public forum makes it a lot easier to say ""Oops, I was wrong and thanks for helping me see something differently."

Its a bit off topic but I have the answer to that one also. Its all about how the ECU measures the air going into the engine - there are two ways commonly in use today

1) Hot wire air flow meter - this measures the flow of air by measuring cooling the effect of the air flow over a hot wire

2) A Manifold Absolute Pressure (MAP) Sensor - this determines the speed of airflow by sensing the air pressure in the inlet manifold, a bit similar to a Pitot tube

If your car uses method 1 then blocking the air filter will not affect the air flow measurement therefore the fuel will be measured out correctly.

If your car uses method 2 a blocked air filter will cause a larger drop in pressure in the manifold and the air flow will be over estimated resulting in over-fuelling and poorer fuel economy.

I think the Hot Wire System has become more prolific these days so most newer cars will not be affected.
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Old 03-01-2009, 05:09 PM
  #47  
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We can take this to another thread but even in the case of MAP, the manifold pressure is identical with/without the air filter obstruction. You just have to open the throttle butterfly slighly more because the air filter is providing some of the restriction of air. A/F ratio and adiabatic pumping losses are identical.


Clint
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Old 03-01-2009, 05:21 PM
  #48  
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Lightbulb

Sorry, but I simply am not wrong friend. And wont appoligize for being right, only for being curt. And I've done that aready.
An engineering degree hasn't anything to with this.
There is no point to argue, it is all aviation fact.

Ok, im done. If you aren't willing to confirm what I've said, then I can help you no further.
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Old 03-01-2009, 05:25 PM
  #49  
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Originally Posted by Buck Rogers View Post
In your example the plane is travelling at 0 mph ground speed in the up wind direction and 40 mph ground speed on the down wind leg. Therefore there is a change in the planes energy state if you consider the kinetic energy (relative to the ground).
Now I have no trouble following your maths but there is one thing that's causing me a problem. Why on earth (or in the air) would I want to consider KE relative to the ground ? AFAICS neither the plane nor the air its flying in have any connection with the ground so can you please explain why you want to use a ground reference ?

If you use the airmass as the reference the answer comes out rather different. Airspeed starts at 20, after the turn it ends up at....oh look, still 20. No change in speed, no change in KE relative to the airmass and since the plane flies in the airmass not on the ground...

Steve
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Old 03-01-2009, 05:30 PM
  #50  
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Originally Posted by slipstick View Post
Now I have no trouble following your maths but there is one thing that's causing me a problem. Why on earth (or in the air) would I want to consider KE relative to the ground ? AFAICS neither the plane nor the air its flying in have any connection with the ground so can you please explain why you want to use a ground reference ?

If you use the airmass as the reference the answer comes out rather different. Airspeed starts at 20, after the turn it ends up at....oh look, still 20. No change in speed, no change in KE relative to the airmass and since the plane flies in the airmass not on the ground...

Steve
.
And that's all there is to it. KE -relative to the ground- isn't involved until the impact.
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