Preventing Tractor Turnover
                          To The Rear

No one deliberately tries to roll his tractor over, yet approximately half of all deaths by tractor each year are the result of overturns. While only few upsets are to the rear, the chances of surviving a rear overturn are very slim

• 85% result in a death.

In a backward tip, a tractor can flip completely over in 1 1/2 seconds, but the point of no return can be reached in 3/4 of a second. This leaves little time to realize what is happening and take preventative action. Usually the tractor pivots beyond the point of no return before the operators are able to do anything to keep it from falling on them.

The causes of this type of accident vary but are usually the result of a combination of forces acting upon the tractor at the same time. One force affecting tractor stability is the pull which gravity exerts upon it. A tractor's center of gravity is the point at which all parts of the tractor exactly balance one another. The center of gravity on the average tractor is located about 2 feet in front of and 10 inches above the rear axle. When the center of gravity is maintained in this position the tractor cannot be upset. Rear overturns occur when other forces move the center of gravity back over the rear axle.

Another force is rear-axle torque. When the clutch is engaged, a twisting force is applied to the tractor's rear axle to rotate it and move the tractor forward. But if the axle is restrained in some way, and sufficient power supplied, something has to give. The front end lifts off the ground and rotates the tractor backward around the axle. The same thing happens if too much throd{tle is used too quickly. When the front end passes the point of no return, momentum takes over and completes the rearward flip.

The other important principle of rear overturn concerns the angle of leverage of the hitch. When a heavy load is being pulled, considerable force is exerted against the ground by the rear tires. At the same time, the load is pulling back and down against the forward movement of the tractor at the hitch. As these forces interact, the contact point between the wheels and the ground serve as a pivot point with the pulled load attempting to pivot the tractor, raising the front end.

Hitching above the drawbar increases the chances of a rear overturn dramatically. Tractors are designed so that loads can be pulled by the tractor's drawbar without upsetting. If you attach a load anywhere but where the tractor manufacturer recommends, you raise the angle of leverage and defeat the design of the tractor. This greatly enchnaces the chance of a rear overturn.

When pulling loads up a hill, both the slope and the pull on the drawbar combine to make the tractor less stable. Therefore, smooth operation of clutch and throttle is essential. Avoid stopping or shifting gears on a hill. Extra power is needed to start again and if the tractor drifts rearward, it's tempting to engage the clutch too quickly.

If you must take your tractor up a particularly steep grade, back it up the hill. Because nearly 70% of the tractor weight is on the rear wheels, the tractor will not be able to rear up and flip over. If this is impossible, use alternate routes or roads to approach the work area.

Jumping tractors out of mud holes and frozen ground result in rear overturns. Should your tractor become mired in mud or wedged in a ditch, attempt to dislodge it by backing out. This may require digging away mud or dirt from behind the rear wheels, unhitching and pulling away any towed load or machinery, or placing boards behind the wheels. You should never place boards or blocks in front of the wheels, or chain the rear wheels to a pole and attempt to move forward. If the wheels suddenly catch and stop turning, then the principle of rear axle torque comes into force and the tractor might tip backwards. When backing out is impossible, it is safer to use another tractor to pull you free.

When it comes to preventing deaths from overturning tractors, the roll over protective structure (ROPS) and accompanying seatbelt are the two most important safety features on the tractor. ROPS usually limit the degree of overturn and the seatbelt keeps you within the protective space of the ROPS. A totally enclosed ROPS is the safest type of tractor and should be used wherever there is a particularly high chance of overturn. Examples would be if the tractor is being operated by youth or new employees, or if it's being used in logging type operations or on steep terrains.

Because there is very little chance for the operator to either jump or be thrown clear of the tractor, 85% of rear overturns are fatal. So learn the rules of safe tractor operation and minimize your chances of becoming a statistic.

Keywords: ACCIDENT, AG-ENGINEERING, AGRICULTURAL-ENGINEERING, ENGINEERING, FARM,

          MACHINERY, MURPHY-DENNIS, OVERTURN, REFERENCE, ROLLOVER, SAFETY,
          TRACTOR

תתתתתתתתתתתתתתתתתתתתThe National Dairy Database (1992)תתתתתתתתתתתתתתתתתתתת תתתתתתתתתתתתתתתתתתתתתתתתתת\NDB\OCCSAFE\TEXT1\81תתתתתתתתתתתתתתתתתתתתתתתתתתת

%f TITLE;PREVENTING TRACTOR TURNOVER
%f COLLECTION;FARM AND OPERATOR SAFETY
%f ORIGIN;Pennsylvania
%f DATE_INCLUDED;June 1992