S-49
Safety Makes Sense: with farm machinery - demonstrations
by F. R. Willsey, Extension Safety Specialist, Agricultural Engineering Department
Here are some demonstrations that should help make people aware of potential dangers with farm machinery. Some of these demonstrations involve an element of risk to the demonstrators. Consider the hazards involved and do not use the demonstrations if you are unable or unwilling to take necessary precautions. There is no point in causing an accident while trying to prevent one.
Tractor Tipping Demonstration
Several effective demonstrations can be presented by using model tractors.
Side tipping. Start with two identical model tractors. In one of them, place a longer rear axle. Leave the front wheels the same (both wide front end or both narrow).
Place the tractors side-by-side a few inches apart on 12"x18" board which has been covered by emory cloth or sandpaper. The rough surface prevents the tractors from sliding off when the board is inclined. Gradually lift one end of the board until one tractor tips. Catch and remove that tractor and then continue to incline the board until the second one upsets. (The size of the board may be varied somewhat but the tractors should be placed so that the long dimension of the tractors is parallel to the short side of the board.)
Conclusion: The wider the rear wheel spacing the less is the chance of side tipping.
Note: To some extent the same principle is true concerning front wheels. However, on full-scale tractors the front axle is not rigid as it is in model tractors. The tractor frame tilts several degrees before it touches the axle. For this reason wide front ends do not reduce side tipping as much as it might seem.
Back tipping as a result of hitching too high.
Fasten a light-weight but rigid metal strip to the middle of the rear axle so that the strip hangs directly downward and almost touches the ground.
Provide a place near the lower end of this extension to fasten a string. This point represents the point of pull or traction of the tractor. It is near the ground level and half-way between the two wheels. Extend the string forward along the ground to a point directly in front of the tractor.
Fasten another string to the drawbar and extend it back from the tractor. Hold this string firmly to represent a load behind the tractor. Now pull forward on the other string at ground level. If the demonstration is done properly the front end of the tractor may raise slightly but should not tip backwards. (In actual practice the front wheels of a real tractor should not leave the ground if hitched to a standard drawbar on a level surface.) Next hitch at a higher level. Either hitch to the axle or arrange a higher-than-normal drawbar. Repeat the demonstration and notice the way the tractor tips backward.
Conclusion. High hitches can cause a tractor to upset backward. Hitch only to the drawbar.
Note: This demonstration can be varied to show that a tractor going up hill can tip backward even if the load is hitched at drawbar height. This situation places less weight on the front end and the tractor will complete its back-flip more easily.
Back tipping is influenced by wheel weights and front end weights.
By using the board that was prepared for the first demonstration and the tractor that was equipped for the second demonstration, it is possible to demonstrate the effect of adding weights to a farm tractor. With the board flat on a table, place the tractor on the board with the long dimension of the tractor parallel to the long side of the board. Take the loose end of the string that is fastened to the special metal strip and extend it forward as before to a position directly in front of the tractor. Press the string against the end of the board while raising that
Cooperative Extension Service, PURDUE UNIVERSITY, Lafayette, Indiana