Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

Register Log in
  • Congratulations SSS148 on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Punted Football 5

Status
Not open for further replies.
GoldDredger

GoldDredger

Civil/Environmental
Jan 16, 2008
172
Yesterday I took a tour of the new Dallas Cowboy stadium and it is an engineering marvel. Above the field is a mammoth 4 sided scoreboard/screen, the bottom of which is 90 feet off the playing field. (Its length extends from 20 yard line to 20 yard line)

There is debate as to whether that is too low and may be hit by punts. I’ve read that the average hang time for an NFL punt is 4.6 seconds. To calculate the height I used the following reasoning, does this seem sound?

Discounting aerodynamics, a punted football will follow a parabolic arc, with exactly half it’s time traveling upwards, and the other half downward. That’s 2.3 seconds going up and 2.3 seconds going down.

Using the formula y= (0.5)(32.2 ft/s sq)(time squared). I calculate the average height based on average hang time is 85.2 feet. A hang time of 4.73 seconds and above translates toa punt 90 feet and higher height.

Does this seem correct?
 
Replies continue below

Recommended for you

Sort by date Sort by votes
launch angle and punting distance will certainly affect the height. It seems like you have ignored both. In addition, wind can change the flight path to something other than a parabola.
 
Upvote 0 Downvote
GoldDredger seems to have calculated the worst of all possible punts - straight up and straight down - no gain in yardage - fire the punter. Go Cowboys!!!
 
Upvote 0 Downvote
As cvg mentioned launch angle will affect the height dramatically. I'd try to model it as a ballistic trajectory and make some assumptions on the launch angle. You should be able to use the hang time to estimate an inital velocity.

I know it neglects friction and the aerodynamics of the football, but it would probably be a reasonable estimate of the flight path.
 
Upvote 0 Downvote
Take an long punt length, say 60 yards, and given the hang time as a trajectory as bpattengale noted, you should be able to get the height.
 
Upvote 0 Downvote
GoldDredger's calculation are exactly correct (for a vacuum, with an acceleration of 1 G). The X and Y components of motion are independent. The distance traveled will depend on the initial angle and velocity, but the altitude reached will be 85.2 feet for a hang time of 4.6 seconds.

[idea]
[r2d2]
 
Upvote 0 Downvote
When any free ball strikes an object above the field of play, including lighting, sound equipment, wires, etc. the down is replayed under rule. This rule was added to the rulebook years ago when punter Ray Guy hit the sound and scoreboard gondola on the ceiling of the Superdome. Guy became the only man to hit it with a punt that traveled roughly 180 feet in the air.

Initial velocity and launch angle determine the horizontal range and hang time of a punt, with a significant dependence on air resistance resulting from various spins on the ball. Air resistance reduced distances of punts by 24-33% and had a nearly negligible effect on hang times estimated from simple equations for projectile motion. The equations of motion provide a reasonable approximation for hang times, but need to include air drag factors to accurately model distances.

 
Upvote 0 Downvote
Gold Dredger -

Your assumption is a classic mistake made by engineers to make the calculations easier and eliminate the real world. Assumptions may lead you to the calculated result you expect.

Neglecting aerodynamics for an object traveling through the air is wrong, but it makes it fit idealized engineering formula if nothing else is considered. That is if the temperature is neglected.

It may be close for a round baseball (neglecting similitude and shape factors).

A football is a different shape and has different properties when propelled. The spin is one of the aerodynamic properties neglected in the interest of simplicity.

A football does not always travel in a smooth predictable path (according to equations) and it may even go end-over-end. Have you ever observed a punt "turning over" in its arc as its speed, orientation and aerodynamic properties change in an attempt to control the impact angle and the following roll.

A satellite is easy to predict because there is in an essential vacuum and only momentum and the gravity of surrounding masses.

For a football, you need a bigger computer and a more realistic parameters or just hire a punter to do everything he can do to provide some of the practical outer limits.
 
Upvote 0 Downvote
Sounds like a fun way to for ESPN the the Discovery Channel to chew up half an hour =)
 
Upvote 0 Downvote
Thanks for the posts guys.

bimr above found an actual study of punts, comparing equation predictions to real world results. They found that HORIZONTAL distances are 20-30% less than calculated, however the hang time values were not significantly affected. Presumably because drag affecting the accent would similarly act on the ball during decent, a wash if you will.

In the horizontal, drag affects the net flight entirely in the opposite direction of the flight, which may explain the reduced distances but not the hang times.

An important point is that hang times are real world results; ACTUAL recorded times from professional punts over many seasons of play. The study shows that hang time isn't affected as much by drag. I would speculate then that neither is vertical height of the punt.

The average professional punt hangtime of 4.6 seconds I believe results in height of around 85 feet, irregardless of velocity, angle or horizontal distance. Once punts pass the threshold of 4.73 seconds, we start seeing heights above 90 feet.

I am looking forward to football season this year. I guess we will see if punts regularly hit this thing or not. Remember that if this does become an issue, you heard it hear first, lol.





 
Upvote 0 Downvote
I drove by the construction site about a a year and half ago and remember actually stopping to admire and take a few pictures. Leave it to an engineer to stop by a site and do this.

I will certainly watch for this during football season. I hate the cold and dry desertlike feeling of the off-season. Lol. I really like footbal even though my team hasn't done that great in a while.
 
Upvote 0 Downvote
CPNG -

When you watch make sure you have your stop watch and a way to accurately determine the height. - The refs will take care of the distance.
 
Upvote 0 Downvote

The inside height of the Seahawks new practice building features a turf to rafters height of 95 feet, with another 17 feet from the rafters to the ceiling. The Seahawks claim the height is adequate to allow players to practice any football situation, including punts and kicks, without restraint.
 
Upvote 0 Downvote

Ya might wanna consider using an average of the ten longest punts of record-----------

At 74th year working on IR-One2 PhD from UHK - - -
 
Upvote 0 Downvote
bimr - as a punter (and place-kicker) I can say that no human can punt a ball 180 feet high on earth and in the atmosphere. The Superdome's board used to be at 90', but they raised it (to over 180') after Guy hit it.




If you "heard" it on the internet, it's guilty until proven innocent. - DCS

 
Upvote 0 Downvote
swearingen, you took the words out of my mouth. Living in N.O., I remember Ray Guy hitting the dome screen multiple times. (He was one the the best at what he does.) I think the Saints punter at the time hit it once.

Regardless of the math involved, if this screen is as low as the one in the Superdome used to be, then someone aught to be repremanded for not doing his homework. I hope this doesn't happen.
 
Upvote 0 Downvote
The post actually said "traveled roughly 180 feet in the air". Should have stated the vertical distance as well.

The screens were dropped from 100 feet above the field to 90. Then Oakland's Ray Guy hit the gondola with a punt during the Pro Bowl game.
 
Upvote 0 Downvote
Status
Not open for further replies.

Part and Inventory Search

Sponsor

Back
Top Bottom