wind speed effect on dragster

s/c 266 · Post by **s/c 266** » Wed Jan 31, 2007 8:00 pm

Has anyone collected actual wind speed data and made a table or graph to shows the effect on a mid 7 sec dragster?

I have seen the generic ones in the Jegs log book, but have this on my list of stuff to do better on in 2007.

I just purchased a hand held wind meter from the clearance area of Summit for $50.

I know the pricey weather station do this easy as pie, so no need for a commercial. Just looking for some actual data to get a jump start.

John Wallace · Post by **John Wallace** » Thu Feb 01, 2007 1:11 am

All I know is that at Joliet, with the wind from the South, and in the right lane as soon as you pass the grandstands, you're almost in the opposite lane.

s/c 266 · Post by **s/c 266** » Thu Feb 01, 2007 8:03 pm

Wow nobody know or nobody's sharing.
Guess I'll make my own,,,

BillyShope · Post by **BillyShope** » Fri Feb 02, 2007 5:03 am

s/c 266 wrote:Wow nobody know or nobody's sharing.
Guess I'll make my own,,,

Or, we might have problems figuring out exactly what you need. Do you want force required data? downforce from wings? movement of center of pressure? yaw torques? Or, when you start mentioning weather data, I'm wondering if you're concerned about engine performance effects. Maybe I'm the only one, but I'm totally confused. I'm not giving you a hard time; I'm just at a loss as to where to begin.

s/c 266 · Post by **s/c 266** » Fri Feb 02, 2007 8:47 am

This is not a Wing question.
In fact I do not need or run one.

What I'm looking for would be what you would get if you made 10 passes with head wind increasing by 1 or 2 MPH on each pass and what the 1/4 and 1/8 mile time slip would show for decreasing MPH and ET.

Was looking to jump start my own making of that X Y plot

thanks

John Wallace · Post by **John Wallace** » Fri Feb 02, 2007 12:01 pm

With a dragster, there isn't as much Cd as most bodied cars, so the effect isn't as much.

I never measured it, but it is negligible on my dragster.
Usually it will slow the MPH down some but the ET is usually about the same.

The problem I have is usually the side wind affect when pulling my chute.

BillyShope · Post by **BillyShope** » Sat Feb 03, 2007 5:55 am

I went into Page 2 of my blog:

http://home.earthlink.net/~whshope

and inserted reasonable figures for power, weight, etc. and got a dragster trap speed of 306.04 mph. I then went into the source code and added the ability to add a headwind. With a headwind of 10 mph, the speed decreased by 1.4 mph and the ET increased by 0.01 seconds.

In other words: Donworryaboudit!!

s/c 266 · Post by **s/c 266** » Sat Feb 03, 2007 8:15 am

In all do respect Billy, your spreadsheet has issues, if that's what it's set up to read.

I know for a fact that both MPH and ET effects are way more than that on a 7.5's 180mph bracket dragster based on 1st hand experience over many years.

I'll sort this out and post some actual data some time. A real curve.

I started this thread based on the observation in my racing for years now, but up till this year all I could do was guess at the wind speed and record that. I have seen as much as .05 off on the 1/4 mile and 3mph. Now I'll be measuring it and entering it into my DB.

BTW This information is known and it's built into most of the systems a racer can buy to predict ET that have weather stations. My little hand held TAG unit cranks in some factor at the end of a data entry for a run, but only let's you pick LOW or HIGH head or tail winds. I plan to take it to a different level.

The Jegs log book has a little predictor helper and they say for a dragster
HEAD WIND
1-5mph 0 to .02
6-10 up to .03

Tail Wind
1-5 0 to .03 gain
6-10 tail up to .05

this I'm sure is for a Bracket dragster not a TF dragster in your example

It's more with cars and a great deal more with roadsters

BillyShope · Post by **BillyShope** » Sat Feb 03, 2007 8:33 am

"Garbage in; garbage out" is an old saying among programmers. No, there's nothing wrong with the spreadsheet. It's simple "F=Ma" stuff. But, the answer is only as good as the input. I used the aero drag for a modern sedan. I thought this was reasonable. While the frontal area of the dragster would be less, the drag coefficient...what with the exposed tires and airfoils...would be much more. If what you and Jeg's are saying is correct (and I have no reason to suspect that it isn't), the aero drag of a dragster is much higher than I anticipated. I'm quite surprised that it's that high!

Edit: Went back and tried the same thing, but with a 170 mph dragster. The effect is more pronounced (this is due to aero drag being a higher percentage of the total force to be overcome), though still not as high as Jeg's would predict.

Then, I tried the spreadsheet sample with the same headwind. The speed dropped almost the same amount as with the 300+ dragster, but, percentage-wise, it amounts to almost 3 times as much of a change!

So, as would be expected, the slower the car, the greater the effect...percentage-wise...of a head or tailwind.

s/c 266 · Post by **s/c 266** » Sat Feb 03, 2007 9:49 am

I looked at a few of your calculators and will make this offer. If you want to true any of them up, using empirical data from my race car (I feel is pretty typical) I'd be glad to help you.

I looked at the ET predictor based on HP tire size and plugged mine in. Noticed you give more credit for smaller tire (less loss) than positive credit for improved traction. This may work for a Nat prepared track but heck the guys that run that don't need it anyway and most of race on a marginal tracks. My 236" 4 link 1900lb dragster with BBC and 17" is what I have now.

BTW
I have one I made to measure converter slip. It's based on data using eng rpm and drive shaft rpm.

The converter slip I read directly from the RPM's on my stuff but I used that to build in a correcting factor for tire growth based on advertised tire height and trap MPH so I can use it on any car with the easy variables. It's way better that the ones Ive seen.

Variables needed are
Trap MPH
gear ratio
Trap RPM
Tire diameter

I have to est tire growth on other cars and do that based on MPH

I see you live in Orlando. Do you race at OSW?

John Wallace · Post by **John Wallace** » Sat Feb 03, 2007 11:35 am

s/c 266, what is your numbers for the wind, ET of your car?

BillyShope · Post by **BillyShope** » Sat Feb 03, 2007 11:58 am

s/c 266 wrote:I looked at a few of your calculators and will make this offer. If you want to true any of them up, using empirical data from my race car (I feel is pretty typical) I'd be glad to help you.

I'd love to have additional input and I mean that sincerely. In a couple of my spreadsheets, I assume constant acceleration over the first 60 feet. While I consider that a good enough assumption for my purposes, I wouldn't object to a "fudge factor" based on empirical data.

I would particularly appreciate feedback on traction dyno results.

s/c 266 wrote:I looked at the ET predictor based on HP tire size and plugged mine in. Noticed you give more credit for smaller tire (less loss) than positive credit for improved traction. This may work for a Nat prepared track but heck the guys that run that don't need it anyway and most of race on a marginal tracks. My 236" 4 link 1900lb dragster with BBC and 17" is what I have now.

I don't have an "ET predictor" on my site, but perhaps you're referring to the quarter mile performance spreadsheet. If so, I think I warned that the ET values are to be used only for comparison purposes. I'm sure you realize why, but, for others following this thread, this is due to the many uncontrollable variable which can affect ET. Speed, on the other hand, can be calculated with a fair degree of accuracy.

s/c 266 wrote:BTW
I have one I made to measure converter slip. It's based on data using eng rpm and drive shaft rpm.

The converter slip I read directly from the RPM's on my stuff but I used that to build in a correcting factor for tire growth based on advertised tire height and trap MPH so I can use it on any car with the easy variables. It's way better that the ones Ive seen.

Variables needed are
Trap MPH
gear ratio
Trap RPM
Tire diameter

I have to est tire growth on other cars and do that based on MPH

I have no experience with radials. I've been told that radial growth with speed is negligible. With bias ply tires, however, the correction factor was, as I recall, -0.2 revolutions per mile per mile per hour. (In the late fifties, I sat at a mechanical Friden 8 hours a day making performance calculations. But, that was always with bias ply tires.)

s/c 266 wrote:I see you live in Orlando. Do you race at OSW?

My racing days are behind me. I was an original member of the Ramchargers, so you know I'm long of tooth. I'm 71, to be precise. I passed on the last opportunity to go down the strip. I used to live in Southern California and Steve Magnante offered me the chance to drive that 500 cube Chevette he built for Hot Rod. I could see this old man wrecking one of Hot Rod's project cars, so I passed.

If you're in the Orlando area, perhaps we can get together. I live up near Apopka.

Incidentally, with regard to that "garbage in/garbage out" business, I discovered that I had increased the headwind to 10 FEET PER SECOND and not 10 mph. Making that correction, I do now agree with Jeg's numbers. In fact, the 306 mph dragster gained more than 0.05 ET, so it now appears that the dragster aero drag is not as large as I thought.

Post by **maxracesoftware** » Sat Feb 03, 2007 12:33 pm

s/c 266 wrote:In all do respect Billy, your spreadsheet has issues, if that's what it's set up to read.

I know for a fact that both MPH and ET effects are way more than that on a 7.5's 180mph bracket dragster based on 1st hand experience over many years.

I'll sort this out and post some actual data some time. A real curve.

I started this thread based on the observation in my racing for years now, but up till this year all I could do was guess at the wind speed and record that. I have seen as much as .05 off on the 1/4 mile and 3mph. Now I'll be measuring it and entering it into my DB.

BTW This information is known and it's built into most of the systems a racer can buy to predict ET that have weather stations. My little hand held TAG unit cranks in some factor at the end of a data entry for a run, but only let's you pick LOW or HIGH head or tail winds. I plan to take it to a different level.

The Jegs log book has a little predictor helper and they say for a dragster
HEAD WIND
1-5mph 0 to .02
6-10 up to .03

Tail Wind
1-5 0 to .03 gain
6-10 tail up to .05

this I'm sure is for a Bracket dragster not a TF dragster in your example

It's more with cars and a great deal more with roadsters

i've been involved with 4 different NHRA Record holding C/ED's
years ago....tryout the C/ED example File in ETA
its close to your Times/MPH
7.560 ET 176.131 mph CED_1996_ETD file

then play around with Wind MPH and Angle

http://www.speedtalk.com/forum/viewtopi ... &highlight

The Jegs log book has a little predictor helper and they say for a dragster
HEAD WIND
1-5mph 0 to .02
6-10 up to .03

Tail Wind
1-5 0 to .03 gain
6-10 tail up to .05

5 MPH HeadWind= 7.590 ET @ 174.813
10 MPH HeadWind= 7.624 ET @ 173.414

5 MPH TailWind= 7.532 ET @ 177.368
10 MPH TailWind= 7.507 ET @ 178.529

some descrepencies might results from:

1-actual Torque Curve values like a D/ED V6 running 7.50's will not
run 176 MPH..and loose a little more MPH than C/ED or a B/ED,
also depends on the shape of TQ Curve.
another good example to look at would be effects on a F/ED vs B/ED
or A/ED with same HeadWind

2-also if its a "pure HeadWind", no side wind angle component

3-how Wide + Tall are the Slicks..and how much Slick is effectively
exposed and a Tire RPM effect of Slick's Cd
A spinning Tire has a different Cd than a static Tire.

4-what effect does a pure-HeadWind -vs- Cross-HeadWind have
on Ram-Air Scoop around 180's mph

5-the Lift Coefficient...anything other than pure-HeadWind will
affect the Lift Coefficient...sometimes enough to increase or
add to Aero Drag Lbs.

6-actual Cd and Frontal Area you use as Input values

just a few quick things i could think of to mention
in Modeling your Data.

s/c 266 · Post by **s/c 266** » Sat Feb 03, 2007 7:53 pm

John Wallace wrote:s/c 266, what is your numbers for the wind, ET of your car?

I don't have any wind data at all.

I just purchased a meter to measure and record wind speed. Dragster runs 7.5's at 178 or so

s/c 266 · Post by **s/c 266** » Sun Feb 04, 2007 4:52 pm

Billy, Here's a 1/8 mile pass of G force. I can do more if of interest.
The track was soft as the G force did not go to the typical 3 on the tire strike. It was also 1/8 mile, as that was what the ran at Moroso that night. It's accurate G force, just inverted as far as numbers. The Y scale is on the right and the channels with color are in the legend at bottom.
I blew it up so you could see it well.
My data collector does not have a viewer smoothing filter is this is what the G meter saw at 200Hz sample rate.

max software,
That's a very nice software tool. I spent the time to adjust the variable to match my results. Is there a switch for methanol fuel. They respond to the air conditions different than gas.