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 Tail wind carry distance is smaller than head wind distance? « View previous topic :: View next topic » 
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ksu45112
PostPosted: Tue Sep 30, 2008 2:48 pm    Post subject: Tail wind carry distance is smaller than head wind distance? Reply with quote

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Location: Seoul, South Korea

Mr. dtutelmam

I don't understand why carry distance of tail wind is smaller than that of no-wind carry distance?

ex, If ball speed is smaller than 120mph, at launch angle 11 deg, 3000rpm and wind speed 22.37mph(10m/s)

tail wind - carry distance 170.7 yds
no wind " 173.3
head wind " 159.2
or
if ball speed 80mph is under same condition
tail wind - carry distance 68 yds
no wind " 76.7
head wind " 81.8

Of course.
If ball speed is above 130mph, The carry distance of tail wind begins larger than head wind carry distance.

Thank you!
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dtutelman
PostPosted: Tue Sep 30, 2008 3:25 pm    Post subject: Reply with quote

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That's a great question and a good observation.

Yes it does work that way. I think I understand why; here's my take on it:

Distance is a balancing act between lift (which keeps the ball in the air) and drag (which slows the ball down).

At lower ball speeds, you need higher spin to keep the ball in the air. Because of the lower ball speed, there isn't that much drag, but you are depending on lift. A headwind increases the drag, but also increases the lift. A tailwind decreases both lift and drag.

Try this. Set up your 120mph example and vary the wind speed with the mouse's scroll wheel or the cursor keys. (Yes, you can do this with any numerical input; I learn a lot playing with TrajectoWare Drive that way.) As you increase the tailwind, the carry distance increases slightly to a maximum between 5mph and 8mph. Further increases in tailwind reduce the carry distance. This shows the tailwind helping just a little, until it reaches the point where the reduced lift hurts more than the decreased drag helps.

As you note, a big hitter (high ball speed) using the correct driver (lower spin) will get a lot more out of a tailwind. That's because, for this guy, lift is less of an issue (note the lower spin) and drag is much more of an issue (it increases with the square of airspeed, and a tailwind decreases the effective airspeed).

The results with the very low ball speed (80mph) defy my intuition as well as yours, but perhaps it is correct. OTOH, it may be a point where the effects are outside the equations we use in TrajectoWare Drive -- sorta' like the problem with spin over 4000rpm. I don't know, because I have no real-world data to compare.

BTW, now you know why sometimes your wedge shots get "knocked down" by a tailwind. You expect them to carry farther and they don't; they may even carry shorter. Shots with a short iron have a lot of spin, so their carry distance is very much dependent on the lift. A tailwind may reduce distance by reducing lift even more than its "pushing" increases distance. (Really the tailwind is just decreasing drag; it isn't really pushing the ball unless the wind speed is greater than the forward velocity of the ball.)

Hope this helps,
DaveT
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ksu45112
PostPosted: Wed Oct 01, 2008 2:47 am    Post subject: Reply with quote

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Really Thank you for your considerated explanations.

I really understand the Lift / Drag force of ball

Again

Thank you

Regards

Sun Ung Kim
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Anthony
PostPosted: Sun Oct 26, 2008 10:40 am    Post subject: Reply with quote

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Just read this thread. It's really interesting.

Anthony
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diamondrichb
PostPosted: Wed Dec 29, 2010 8:45 pm    Post subject: Tailwind carry shorter? Reply with quote

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Location: Hawaii

I found this forum a few days ago and find it very interesting. However, I can't quit thinking about this downwind carry info. I'm sorry, I just can't buy it. I guess my 35 plus years as a pilot just won't let me accept that a ball flying within in a moving air mass will not fly farther than a ball moving in a still air mass or an air mass moving towards the launch point. Nah, can't happen.

As far as that wedge shot getting knocked down, that's may be because the air mass is moving down also. Whether it's due to the wind coming over a small hill or trees the air mass can be 'tumbling', or moving towards the ground.

Just as an airplane with a constant airspeed moves faster over the ground in a downwind condition, so will the ball....all other conditions being the same. The spin/backspin whould be the same as when the ball flies in a calm wind. The air mass the ball is flying in will influence the distance the ball flies. I believe there may a fly in the ointment with the software in this particular case.

Interesting all the same. Thanks and Aloha
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dtutelman
PostPosted: Thu Dec 30, 2010 4:23 am    Post subject: Re: Tailwind carry shorter? Reply with quote

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diamondrichb wrote:
I found this forum a few days ago and find it very interesting. However, I can't quit thinking about this downwind carry info. I'm sorry, I just can't buy it. I guess my 35 plus years as a pilot just won't let me accept that a ball flying within in a moving air mass will not fly farther than a ball moving in a still air mass or an air mass moving towards the launch point. Nah, can't happen.

Faster does not necessarily mean farther. Not if it can't stay in the air.
Quote:
Just as an airplane with a constant airspeed moves faster over the ground in a downwind condition, so will the ball....all other conditions being the same. The spin/backspin whould be the same as when the ball flies in a calm wind. The air mass the ball is flying in will influence the distance the ball flies. I believe there may a fly in the ointment with the software in this particular case.

It is conceivable that there is a bug in the algorithm. Note: not the software, but the physics assumptions underlying it. But I doubt it; I trust the physics, even though the result is counterintuitive. (A LOT ABOUT GOLF IS COUNTERINTUITIVE.)

There is a serious problem with the airplane analogy. A golf ball is not self-propelled through the air. There is no reason to assume constant airspeed; the ball is launched from the ground at a constant groundspeed, and there is NOTHING to make the airspeed equalize. Unlike an airplane, there is no propulsion involved.

Since the ball's speed is really ground-referenced, let me suggest another analogy: a kite. Imagine flying a kite on a still day, by running with it. Say you run 10mph. That creates an apparent wind of 10mph, which lifts the kite. (I'm not sure you think in those terms. I'm not a pilot, but a sailboat racer.) Now a breeze picks up. You are now running in the same direction as a 7mph wind. So now the apparent wind is only 3mph. Might not be enough to keep the kite in the air.

A golf ball and a kite both depend on lift. If you drastically reduce the lift on the ball, you can significantly reduce the distance it flies -- even if you also reduce the drag. The details are in the numbers; it could work either way.

Thanks,
DaveT
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diamondrichb
PostPosted: Thu Dec 30, 2010 6:49 am    Post subject: Reply with quote

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Ok, interesting. This seem unfair, me a simple pilot and you actually knowing what you're talking about. :=)

While an airplane is propelled it is dependent on the air mass for it's lift, it must have lift from the wings to fly. Unless we're talking about the Space Shuttle all aircraft are dependent on lift. No lift, it's not leaving the ground and if it's in the air it can fall out of the sky. If the wind changes bad things can happen. Think well known airline landing in Little Rock many years ago.....crashed and people died (I think this was the one, might have been Dallas). Wind sheer practice for pilots in simulators was generated due to that accident and the wind sheer which caused it....the change in wind direction from head wind to tail wind took away the lift. An airplane when landing power off is dependent on the speed of the air mass being constant. That is, the speed of the air mass within which the airplane if flying. If the head wind decreases the pilot has to lower the nose or stand up the throttles or the airplane will fall out of the sky at some point because the speed of the air mass moving towards the airplane has decreased resulting in the loss of lift.

If we are talking about a change in the speed of the air mass within which the ball is moving then that is another ball of wax. If the speed of the air mass changes or the direction of the air mass changes than the speed of the ball will change.....all other aspects of the ball being normal.

What I am saying is that if the golf ball takes off in a tail wind (air mass moving towards the target) and the air mass is horizontal and constant, the golf ball is going to fly farther than a similar golf ball taking off and flying in a calm air mass. The air mass is moving. The golf ball will move with it. It has to. As far as I know this is what your software is simulating. I don't believe it is simulating a change in the speed of the air mass or a change in the lift of the ball. Once a ball takes off the change in lift will be the same as a ball in a calm air mass. Except the downwind air mass is moving towards the target at a higher rate of speed causing the ball to fly farther. IMHO of course. :=)

Thanks for your thoughts.
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Fran
PostPosted: Thu Dec 30, 2010 9:41 am    Post subject: Great debate Reply with quote

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Well as an engineer I fully agree with Mr. Tutelman.
The kite analogy is very intuitive as it is when you think of an airplane taking off with tail wind: it just needs more speed to reach the requested lift. It is all a matter of relativity (wind speed to airplane, not to grond)!

The golf ball, as very good explained, needs to reach a comprimise between lift and drag to fly longest, and therefore there must be an initial speed and spin rate in which tail wind is favorable and other combination for which tail wind will reduce so much the lift that even thaugh there is also a reduced drag, the ball just will fly shorter.

Regards!
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dtutelman
PostPosted: Thu Dec 30, 2010 2:54 pm    Post subject: Reply with quote

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diamondrichb wrote:
While an airplane is propelled it is dependent on the air mass for it's lift, it must have lift from the wings to fly... No lift, it's not leaving the ground and if it's in the air it can fall out of the sky. If the wind changes bad things can happen. Think well known airline landing in Little Rock many years ago.....crashed and people died (I think this was the one, might have been Dallas).....the change in wind direction from head wind to tail wind took away the lift. An airplane when landing power off is dependent on the speed of the air mass being constant. That is, the speed of the air mass within which the airplane if flying. If the head wind decreases the pilot has to lower the nose or stand up the throttles or the airplane will fall out of the sky at some point because the speed of the air mass moving towards the airplane has decreased resulting in the loss of lift.

OK, that's an analogy I can hang my hat on. Let's continue.

Quote:
If we are talking about a change in the speed of the air mass within which the ball is moving then that is another ball of wax. If the speed of the air mass changes or the direction of the air mass changes than the speed of the ball will change.....all other aspects of the ball being normal.

Strongly disagree! The ball doesn't know WHY it is suddenly in a different-speed air mass. It doesn't know whether it moved from one air mass to another or the whole speed of the air mass suddenly changed. All it knows it that the speed of the air at the ball itself has changed. If the wind suddenly changes, the ball's inertial speed is still the original ground speed immediately after the moment of the change.

That is pretty fundamental physics. If we can't agree on that, then we're going to have trouble agreeing on anything.

Quote:
What I am saying is that if the golf ball takes off in a tail wind (air mass moving towards the target) and the air mass is horizontal and constant, the golf ball is going to fly farther than a similar golf ball taking off and flying in a calm air mass. The air mass is moving. The golf ball will move with it. It has to.

OK, the ball is in my court, so to speak. And I'm an engineer, not a pilot, so I'm going to solve it as if I were in engineering school.

We'll start with your analogy of a plane landing without power. You run into wind shear, in the form of still air turning into a tailwind. The plane loses lift and drops like a rock.

The way an aeronautical engineer would analyze/simulate this is to start the analysis at the boundary of the air masses. He would assign the plane the ground speed it had in the still air, but run the simulation in the tailwind. If he did it right, the plane drops like a rock, starting right at the beginning of the simulation.

Are we still together on this? If so, let's continue...

TrajectoWare Drive works exactly like that. It is projecting the ball at a groundspeed into whatever air mass is there. If the air mass is moving with the ball, at a speed where lost lift is more important than reduced drag, then the ball will not go as far as it would have in still air. It's the same problem as the plane experiencing wind shear, as long as you set the initial conditions appropriately.

Lift and drag on a golf ball are funny things. Too much lift can be as damaging to distance as not enough. I have a chapter in my golf club tutorial on the subject. See http://www.tutelman.com/golf/design/swing3.php. There are a couple of graphs there that show how lift can help or hurt. Does the golf term "ballooning" sound familiar? It is what happens when there is too much lift. BTW, Later on that page, don't trust the numbers too much in the section labeled "Launch Space". The calculations were done with a few older trajectory programs that lose accuracy when dealing with Long-Drive class ball speeds or abnormally high launch angle and spin. In fact, those inaccuracies were exactly what motivated Frank and me to build TrajectoWare Drive.

Thanks for making me put on my thinking cap. Always a good way to start the day.

DaveT
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diamondrichb
PostPosted: Fri Jan 21, 2011 8:44 pm    Post subject: Reply with quote

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Wow, I can't believe it was last year when I last posted on this subject. It's not because I haven't thought about it. :=)

I understand the concept of loss of lift. I just don't agree with the ball not going farther in downwind conditions.

I feel a little foolish in that I didn't play around with the software more before I started this discussion. I just input my swing data and some tour average data and found out the downwind does increase carry distance, quite a bit in fact. I can't seem to duplicate the output you're talking about in the Sept 30 post in regard to the 5 to 8 mph and stronger wind decreasing carry.

I'm sorry, what the heck were we talking about? I was beginning to think all this time of playing in wind in Hawaii I was hallucinating. Now maybe I won't wake up in the morning thinking about this. :=)

Cool software by the way. Thanks.

Aloha
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dtutelman
PostPosted: Fri Jan 21, 2011 9:09 pm    Post subject: Reply with quote

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diamondrichb wrote:
I understand the concept of loss of lift. I just don't agree with the ball not going farther in downwind conditions.

I feel a little foolish in that I didn't play around with the software more before I started this discussion. I just input my swing data and some tour average data and found out the downwind does increase carry distance, quite a bit in fact. I can't seem to duplicate the output you're talking about in the Sept 30 post in regard to the 5 to 8 mph and stronger wind decreasing carry

OK, try this.

Bring up the program and start a new trajectory. The impact parameters are the defaults of 95mph clubhead speed, 0* AoA, and 10.5* loft.

Now click into the wind speed box, and use the scroll wheel on the mouse to vary the wind speed. When I do this:

  • With no wind, the carry distance is 210.6 yards.
  • Increasing the tailwind increases the carry distance. At 11mph wind speed, the carry distance is up to 213.3 yards.
  • Further increasing the tailwind does not increase the carry distance. In fact, at 15mph the distance starts to drop.

I believe this reflects the loss of lift from too much of a tailwind.

Cheers!
DaveT
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diamondrichb
PostPosted: Sat Jan 22, 2011 6:59 pm    Post subject: Reply with quote

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I really need to just play golf and quit making myself look so stupid. I don't know how I did it, but yesterday when I was putting data in the software it did not show a decrease in a downwind. I even showed my wife, so I'm pretty sure I wasn't imagining it.

When I put in your suggested values today, the software does indeed show a loss of carry when the down wind speed is above 15. I guess that shows why I have a hard time with the software results in that the wind here in Hawaii is usually 10 to 15 so I think the down wind always helps. Trying to recover some credibility here..... :=)

I am in contact with Titliest Test facility who is also talking to the Trackman tour rep, to see if I can get any data from them. They said they have not seen the down wind hurt to be true, but say it will depend on launch angle and spin rate. I clarified the question somewhat and asked for more input from them. Let's see what they say, if anything.

Not that I don't believe your software. :=)

Aloha
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dtutelman
PostPosted: Sat Jan 22, 2011 7:55 pm    Post subject: Reply with quote

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diamondrichb wrote:
I am in contact with Titliest Test facility who is also talking to the Trackman tour rep, to see if I can get any data from them.

I'll be very much interested in what Titleist comes up with.

DaveT
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dtutelman
PostPosted: Sun Feb 20, 2011 6:09 pm    Post subject: Reply with quote

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Just a related personal experience...

We've been suffering from "cabin fever" in New Jersey, so I jumped at the chance to get away to Ocean City, MD for a couple of days of golf. The forecast was warm enough, no snow (that by itself is reason enough to go), but a lot of wind. Yesterday was a steady 30mph, with gusts to 50mph easily. The strongest wind I've ever played in.

Now 50mph is a significant fraction of the ball speed. It should significantly reduce both drag and lift. If I had a Trackman with me (yeah, right!), I would have loved to actually measure what it did. I couldn't do that, but one shot in particular sticks in the mind.

The particular shot I want to mention was on a par-3. It was dead downwind, and the wind was definitely over 30mph. It was 160yd to carry a nasty greenfront bunker. I picked a 5-iron, my 160yd club. I felt (hoped, anyway; didn't think about this thread) that my 160 club should have no trouble carrying the bunker with that helping wind. I struck it well; it felt good and took off on a very nice trajectory. Then it fell out of the sky. It landed well short of the bunker, took three bounces and then rolled into the sand. Bill and I just looked at one another and shrugged; neither of us could believe how it just fell down, like it had lost all lift.

Not quantitative, and purely anecdotal. But another data point, FWIW.

DaveT
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