- -  AGRICULTURE CORE CURRICULUM - -

(CLF2000) Advanced Core Cluster: AGRICULTURE MECHANICS

 (CLF2900)  Unit Title: WORK AND POWER

____________________________________________________________________________
 (CLF2911)  Topic: WORK AND POWER             Time            Year(s) 
                     FORMULAS                 3 Hours       1 / 2 / 3 / 4
____________________________________________________________________________

          Topic Objectives: Upon completion of this lesson the student will 
                             be able to:

          Learning Outcome #:

          (S-2) - Demonstrate knowledge of energy, force, pressure, work,
                    and power, using applications of levers, gears, pulleys,
                    and shafts.

          (T-3) - Demonstrate knowledge of the transmission of power, 
                    using chains, belts, gears, and shafts.

          Special Materials and Equipment: None

          References: Jacobs, C. O., & Harrell, W. R. (1983).
                         AGRICULTURAL POWER AND MACHINERY. New York: 
                         McGraw-Hill.

                       Smith, H. P., & Lambert, H. W. (1976). FARM 
                         MACHINERY AND EQUIPMENT. (6th ed.) New York:
                         McGraw-Hill.

          Evaluation: Quiz by instructor and evaluation in discussion and
                       lab work.

TOPIC PRESENTATION: WORK AND POWER FORMULAS

A. Formulas

   1. Work

       a. Work (ft X lbs) = force applied (pounds) X distance moved (feet)

       b. Electrical Energy

           1) Work is moving electrical charges against resistance

           2) E = I X R

               Where,

               E = electrical energy (watt-hours or kilowatt-hours)

               I = electrical current (amperes)               R = electrical 
resistance (ohms)

       c. Heat Energy

           1) Q = (M)(C)(TF - TI)

               Where,

           Q = Amount of heat required to heat up a given amount of 
               matter (BTU's)

               M = Weight of the matter to be heated (lbs.)

               C = Constant (equals 1 for water)

               TF = Desired final temperature of the matter

               TI = Initial temperature of the matter

       d. Pump Energy

           1) The energy to pump irrigation water is given by the formula:

               KWH/ACFT = (1.024)(H)/E

               Where,

               KWH/ACFT = pump energy in kilowatt hours per acre foot of 
               water pumped

               H = total lift of the pump in feet

               E = pump efficiency as a decimal

   2. Power

       a. Fluid

           1) HHP = (F)(P)/1714

               Where,

               HHP = Hydraulic horsepower of pumped hydraulic oil

               F = Flow of the hydraulic oil pumped in gallons per minute

               P = Pressure of the pumped oil in pounds per square inch 
       b. Engine

           1) Drawbar Horsepower

               DBHP = (D)(W)(S)/375

               Where,

               DBHP = Drawbar horsepower

               D = Draft (lbs) = pull exerted on the implement by the 
               tractor (see chart on following page)

               W = Operating width of the implement (feet)

               S = Speed of the tractor (mph)

           2) PTO Horsepower (2-WD tractors ONLY)

               PTOHP = (K)(DBHP)

               Where,

               DBHP = Drawbar horsepower as calculated above

               K = factor depending upon soil condition, tire type, etc.

               (see following page for typical values)

           3) Rotary PTO Horsepower

               RPTOHP = (T)(R)/5252

               Where,

               RPTOHP = PTO horsepower from the PTO shaft

               T = Torque (lb-ft) provided by the PTO shaft

               R = Speed of rotation of the PTO shaft in revolutions per
                   minute

                             UNIT DRAFT REQUIREMENTS
                                      OF
                                FARM IMPLEMENTS


                  Implement Operation               Unit Draft (UD)*


                     Moldboard Plow 

                     light soil                     500 lbs/ft 

                     medium soil                    800 lbs/ft 

                     heavy soil                    ll00 lbs/ft 

                     Lister 

                        light soil                  400 lbs/ft 

                        medium soil                 600 lbs/ft 

                        heavy soil                  800 lbs/ft 

                     Field cultivator               290 lbs/ft 

                     Light disc harrow              250 lbs/ft

                     Medium disc harrow             600 lbs/ft 

                     Heavy disc harrow             l000 lbs/ft 

                     Row crop planter               l50 lbs/ft 

                     Grain drill                     70 lbs/ft

                     Spike tooth harrow              40 lbs/ft 

                     Roller                         l00 lbs/ft 

                     Subsoiler 

                        light soil     840 lbs per shank per foot of depth

                        medium soil   1200 lbs per shank per foot of depth

                        heavy soil    1920 lbs per shank per foot of depth

                     Landplane                      500 lbs/ft 

                     Chisel plow                    500 lbs/ft 

                     Spring-tooth harrow            l90 lbs/ft 

                     *pounds per foot of width unless otherwise noted.
_____________________________________________________________________________
                                  K FACTORS
                                      FOR
                           2-WHEEL DRIVE TRACTORS

                   Soil Conditon                 K-Factor

                   Concrete                        l.l4

                   Firm, untilled soil             l.50

                   Tilled, reasonably firm 
                            soil                   l.80

                   Freshly plowed soft soil        2.10

       c. Electrical

           1) P= I X E X pf

               Where,

               P = power in watts

               E = electrical energy (watt-hours or kilowatt-hours
                   = I X R

               pf = power factor encountered in AC power with inductive and 
                    capacitive loads,

               I = current flow (amperes)

           2) For DC applications

               P = I X E 

               P = I X (I X R)

                   2
               P= I X R

   3. Pressure

       a. Pressure (psi) is the force per unit area

       b. Formula:

           1) P = F divided by A

           Where,

           P = pressure (psi)

           F = force (lbs)

           A = area (square inches)
   4. Torque

       a. Torque is a twisting force applied about the center of rotation or
           fulcrum.

       b. Formula:

           Tq. (lbs. X ft) = Force (lbs.) X Distance (ft)

           or,

           Tq. (lbs. X in) = Force (lbs.) X Distance (in)

   5. Energy Efficiencies

       a. Mechanical Efficiency  -  takes into account all factors that 
           keep horsepower away from an engine, including friction H.P. loss
           to find mechanical efficiency:

           Brake H.P.
           ________________   X  100  =  Mechanical Efficiency (%)
           Indicated H.P.

       b. Volumetric Efficiency  -  the limiting factor in an engine's 
           maximum torque output.

          To find volumetric efficiency:

           Actual Air Inducted
           into Engine (cu. in.)
           _____________________________ X 100 = Volumetric Efficiency (%)
           Engine Cubic Inch Displacement

       c. Brake Thermal Efficiency  -  brake horsepower expressed in 
           BTU's, divided by the fuel heat input (BTU's), times 100

           Engine H.P. X 2545 (BTU's)
           __________________________   X 100 = B.T.E.(%)
           Fuel Burned / Hr.(BTU's)









7/23/91 YNJ/JWR/sg

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