When rally cars leap up into the air over so-called yumps, why don’t they land on their noses? NE.
Well, depending on the shape of the yump they do tend to land on the front wheels a lot more heavily than the rear ones, but rarely at such a steep angle that the bodywork hits the road before the wheels do.
Putting part of the physics simplistically, the forward momentum maintaining their speed, direction and relatively level posture is more powerful than the force of gravity pulling the whole vehicle back to earth.
And the fore-and-aft weight balance of rally cars is distributed as equally as possible, so any tilting force is relatively small compared with the other two forces.
Gravity exerts a downward accelerative force of about 10 metres per second. A car travelling at 160 kph has a forward momentum of 44 metres per second. That’s not the whole equation, but it is a key factor of the outcome.
In this context a clear distinction should be drawn between a large bump and a yump, including the angle of the road where the car takes off and where it lands.
With a sudden big bump, the angle of the road is usually the same (flat) before and after. The front wheels hit the bump first and the nose is thrown upwards...and thus the back is forced downwards.
Then the back wheels hit the bump, and the rear of the car is forced upwards...and the front is tipped downwards. In this position, it lands on a flat road and is much more likely to get a bloody nose.
A big (short) bump is much more likely to cause a nose-dive and/or end-over-end cartwheeling. Any serious suspension damage is likely to be caused at the start of the process.
With a yump, the whole car is pointing slightly uphill as it arrives at the crest (of what in effect is a small hill with an abrupt crest) and it is not “thrown” into the air - simply its forward momentum is so much greater than the force of gravity it maintains its existing upward trajectory while the road beyond the crest goes downhill. In a sense, the resultant gap between the road and the vehicle floor is caused as much by the land falling as by the car rising.
The car has probably not had its rear end flicked upwards; the back wheels are simply following the front at take-off. And if the vehicle does tilt forward slightly in flight, landing-ground allows a smoother touch-down, because is sloping downwards at much the same angle as the vehicle’s posture. Suspension damage is less likely and will happen only at the end of the process.
In this year’s Safari, the most photographed bump flung cars into the air. But what was a breath taking enough sight to exaggerate the imagination lifted the floor about two metres above the ground.
In the time it took gravity to close that gap, the car had “flown” forwards 20-30 metres and still had considerable forward momentum and the landing was downhill, so the meeting with terra firma was at a glancing angle, not a square-on collision.
Several cars suffered damage because the yump was not symmetrical, and it slightly tilted the transverse angle of the car. This, and a slight forward tilt, caused the brunt of landing force to be applied to just one front wheel (at least double the usually shared force). Some of them broke.
