Tractor speed math problem

Has anyone a formula to calculate MPH using diameter of the rear wheel/distance traveled/length of time? Also, how about width of implement/distance traveled to get 1/10th of an acre? I changed the size of my spray tips and need to select a lower gear to get to my target rate of 18 GPA. Plus, the 28% may come out at a different rate than indicated on the tip chart. My deepest thanks, as I hate math to the 7th power.

Hard for me to understand your question.
High School physics.
Speed = distance/time. If you want MPH, measure distance in feet, time in seconds then use 60 mph = 88 ft/second. In simple terms, divide speed by 88 then multiply by 60.

Has nothing to do with rear tire size unless you have a tractor like my jubilee and you change tire size.

The tach on my Old Jubilee, shows speed in each gear for any engine RPM.

Too early for me to understand the rest of your question.

geo

Go to your cooperative extension office and get the CORE Pesticide Training Manual. There's a whole chapter on sprayer calibration.

Usually better to calibrate the sprayer by just spraying water for a known number of feet, and then see how much water it put out. Then just calculate your gallons per acre by dividing the gallons used by the acres covered. Acres covered is length traveled times sprayer width (all in feet) divided by 43,560 ft2/acre. Best results obtained the farther you travel such as a couple rounds in a field or a quarter mile down the lane.

If you dont like the gallons per acre, try a different gear or different pressure and try again.

Hello Fritz Maurer,

Here is the formula. R.P.M.'S X TIRE DIAMETER / GEAR RATIO X 336.
Gera ratio is the final gear ratio drive, while 336 is the constant,

Guido.

If you have access to a hand-held gps it will give you a very accurate mph.

Instead of driving and looking at how much water comes out. The better method is to start the sprayer with only water. Then with a measuring cup and a stop watch go to a nozzle and collect the water from it for 30 sec. Then you can figure out how much you are spraying total by multiplying the measurement by the number of tips and by 2 (to get the amount per minute). Then you can figure out what speed needed to get 18 gpa. Say you have 20 nozzles and 30 foot coverage and got 12.8 oz. in 30 seconds from one nozzle (just making up numbers). That means in 1 minute you pump out 512 oz. or 4 gallons.
That means you need to cover one acre in 4.5 minutes. Then you use the formula of Width * MPH * 5280 / 43560 = acres/hr. This example would be 30*X*5280/43560=13.3 (To cover an acre in 4.5 minutes you need to cover 13.3 acres per hour, 60/4.5) with the "X" being the unknown. That then changes to X=13.3*43560/5280/30. It then works out to 3.65 MPH.
Obviously the example is not a practical one as I had either the number of tips too high or the oz. per 30 sec. from one tip too much.

I was calculating the distance by tire circumference x number of revolutions. You lost me at "speed divided by 88". What number do I enter for speed?

This maybe a good time to brush up on your pesticide license test. Many states have online training classes.

www.certifiedtraininginstitute.com/pesticide/nebraska-pesticide-continuing-education-courses/?gclid=CNHe9_uvzNMCFQaQaQodRA4LZA

You will NOT get a accurate ground speed by calculating using tire diameter. The reason being you would need to be using the actual ROLLING radius of the tire, when loaded with the actual load and actual tire pressure. Then you also have wheel slippage which is usually 3-5%. Your making this much more difficult than you need to. Here is a much simpler way to find your ground speed.

1) Measure out a distance in the ground your going to be spraying on. Meaning if it is disked fluffy soil then measure out a 200-300 foot distance on that type of ground. Set two stakes marking your distance. Estimate what gear and engine speed you think will get you your targeted ground speed. With your sprayer half full of water, get up to speed and drive your measured distance. Use a stop watch or you cell phone to time how long it take you to drive the measured course. So just start your timer when you pass the first mark and stop the timer when you pass the second. You need to be moving at your set speed when you pass both the beginning and end of you distance.

Now the math. One MPH is 88 ft. in one minute. So if your targeted speed is 5 MPH then you would need to travel (5 x 88 =) 440 feet in one minute. Easiest way is to make your distance 220 feet and travel it in exactly 30 seconds and you will be traveling 5 MPH.

2) Gallons per acre. You will need a rate chart for your sprayer tip. Those will usually tell you the gallons per minute or Pressure you need for so many gallons per acre at a set speed. You can calculate it but it is involve and you say your not good at math so get a chart.

Now getting your gallons per minute for your sprayer tip. With what your going to be spraying in the sprayer. Meaning water or 28%. Without any chemicals. The reason being is the viscosity is different between the two. You need a higher pressure to get the same gallons per acre when using 28%.

You need your ground speed figured out. Then run your tractor at the engine speed you will be using when your traveling at your targeted speed. Example if your 5 MPH is at 1700 RPM is fifth gear then you would need to run your tractor at 1700 RPM so the PTO speed is what it will be when your spraying. Then set your sprayer pressure to what you need to get your gallons per acre. Again look at your nozzle chart. So if you need 35 PSI then set your sprayer at 35 PSI. Keep in mind the pressure needed is at the sprayer tip. So the pressure at your control valve will need to be a little higher because of line loss. This difference is higher with 28% too. Example 35 PSI at the nozzle maybe 38 PSI at the gauge on the control.

Start your sprayer running and catch the liquid at one nozzle for one minute in a container that you can measure ounces in. Take the ounces you catch in one minute and divided it by 128 to get gallons per minute. If your container will not hold what the sprayer puts out in one minute than use 30 seconds and divide by 64. example for 30 seconds: 48 ounces caught (48/64=) .75 gallons per minute.

With the gallons per minute and the speed you can use a nozzle chart to get your rate per acre. Usually I use the gallons per minute to find out the actual nozzle pressure. Then just use that and ground speed to find the gallons per acre. Most charts will tell you the gallons per minute flow a nozzle puts out at set pressures.


Actually most nozzle books have the way to calibrate your sprayer listed in them. It will be usually finding true ground speed and actual nozzle pressure. You only need the two things to set your sprayer.

And the old "Tee Jet" books had the formula in the back of them too...most smart phones will give an accurate ground speed..

(quoted from post at 04:42:38 04/30/17) Has anyone a formula to calculate MPH using diameter of the rear wheel/distance traveled/length of time? Also, how about width of implement/distance traveled to get 1/10th of an acre? I changed the size of my spray tips and need to select a lower gear to get to my target rate of 18 GPA. Plus, the 28% may come out at a different rate than indicated on the tip chart. My deepest thanks, as I hate math to the 7th power.

Click to expand...

Lots of good responses but it can get confusing. Here are answers to your specific questions.

Diameter of rear wheel like you asked: Measure axle to ground to get the radius. The distance traveled in one revolution is 2x3.14xradius (so 20 inches axle to ground is 2x3.14x20 or 125.6 inches traveled in one revolution). Then feet per minute speed will be distance (feet) divided by time (minutes). If you want miles per hour multiply by 88.

Distance to get 1/10 acre is 4,356 divided by the width. So if you spray 33 ft wide it takes 132 feet to cover 1/10 acre.

Now my advice, use a 100 ft tape and measure like JD said, 300 ft and set stakes. Then fill your tank to a good mark, on level ground. Then go to the field and spray your 300 ft line, starting at the first stake and finishing at the last stake. Go back to the house and park in the same spot you filled and refill to your mark with marked gallon jugs and measuring cups so you know exactly how much you sprayed in 300 ft. Acreage is width sprayed times 300 (length) divided by 43,560.

Of course you could do 1/10 acre but 2/10 will be more accurate.

One thing which hasn't been mentioned is dilution. If you are spraying too much per acre you can dilute you mixture to get what you want. For instance, you want to spray 18 GPA but the tractor gear you want to use is spraying 20 GPA. You just need to add 2 GPA of water mixed in before you start. If you are putting 250 gallons in a 300 gallon tank you wanted to spray 13.88 acres with the tank (250/18) but instead you will only get 12-1/2 acres (250/20). So to get 18 GPA you need to add 27.76 gallons of water (13.88 acres times 2 GPA) to the mix. Now you will spray 277.76 gallons over (275/20) over 13.88 acres. So the original 250 gallons of mix will spray over 13.88 acres (250/13.88=18 GPA). In reality you are never this accurate but if you shoot for accurate numbers you get closer.

GPS or smartphone. There are many apps you can get with gps or simple speedometer info. I have used the "android speedometer" app for various things, it even has a HUD function that you can sit on your dash and it will display/reflect on the windshield.