Originally Posted by
fredswain
The biggest problem that I see with many people and jumps is that they hit them at full throttle, never letting off at all. In some instances this may be fine but watch motocross riders hit jumps. Often times they'll quickly let off and then blip the throttle on the ramp before the wheels leave the ground. This automatically gets them in a slight nose up orientation. Lowering the nose just requires a tap of the brakes.
One thing to remember, and I know it wasn't just mentioned here, is that vehicle layout has nothing to do with pitch while in the air. I've seen it stated elsewhere that a rear motor car will jump nose up and a mid motor will jump more level or nose down. That's a physics violation. Remember that a feather and a bowling ball will fall at exactly the same rate in a vacuum. It is only due to air resistance that this isn't so. We don't have that problem with an rc car. What this means is that it's either off balance spring rates, driver technique, or both.
I'm going to disagree with you a bit on both of these points. One of the main reasons motocross riders jump like they do is to get back down to ground as quickly as possible to be putting the power down and not sailing through the air. If you are in the air you are losing time compared to someone who is already on the ground and accelerating. The point is to minimize total flight time and still clear the jump(s). This is also the reason you see many guys "scrub" the jumps any time possible.
On the second point...the weight distribution does have an impact the car flight pitch once it is in the air. Think of the car like a teeter-totter once it is in the air. If you have a teeter-totter and take a 10 pound weight and put it 1 foot from the fulcrum you will create a torque force that will push that side of the teeter totter down. Now take that same 10 pound weight and put it 10 feet from the fulcrum. At this point we have now created a larger torque force that wants to push that side of the teeter totter down. The masses of the teeter totter and the weight added are the same in both instances, so M1 = M2. However F2 > F1....and we know F=MA (force = mass * acceleration)...therefor the increased force shows up as increased acceleration. Just like a teeter totter that is just out of balance will slowly drop to the side that weighs more, add weight to that side and the teeter totter will drop more quickly. So why does that matter? Well if the car is a teeter totter in the air, then a car more centralized mass will cause less pitch change in air than a car with all the weight far to one end or the other.
Geez after all that I think I may agree that weight distribution does not alter the pitch just after leaving the jump, however weight distribution will affect how the pitch changes while flying through the air.