Calculating Aircraft Performance

[hilltop170]

Richard
Does that work for the 195 also?
Another week we will be able to get back on the turf runway, I'll have to check it out. I'll have to make sure to get the nose wheel up right away..........
W.

W.- 70% takeoff speed at the 50% point works for any airplane but remember it's just a rule of thumb. It's not a law of physics.

Richard,
That works well for a level strip. With a sloped strip one's abort point may be just after releasing the brakes.

That is correct as you might not achieve 70% take off speed by the 50% point, but you would still have room to stop safely if it didn't. As long as the slope is constant it works. If the slope increases after the halfway point it won't apply and all bets are off. Also notice it does not say you will be able to clear obstacles after lift off, that is another topic of discussion.

On sloped strips take off downhill as long as there is no more than 10mph tailwind. If more than 10mph tailwind and you're not confident you can clear obstacles taking off uphill, DON'T take off. Wait for favorable conditions. Many planes have been wrecked in down wind take offs and trying to outclimb terrain. Never take off uphill if the plane will not easily outclimb the terrain. Obvious of course, but it's still something that must be deliberately considered.

[GAHorn]

Downwind operations are especially misleading. Think about it this way:
If a takeoff is dissected into it's components, it will be seen that distance is only one portion of the equation. Another is ...time...required for acceleration. Notice that the time expended versus speed (acceleration rate) is not linear....more time (and therefore distance) early in the takeoff run is devoted to acceleration than later in the takeoff run and that can be especially hurtful when operating with a tailwind. (Think of the amount of time spent attempting to accelerate just to the same speed as the tailwind.)
If it takes 10 seconds to accelerate to 10 mph....and if that ten seconds consumes 300 feet of runway (approx 30% of takeoff distance) ... then with a 10 mph tailwind, 300 feet of runway will be wasted simply to achieve a ZERO relative speed to the wind. It is actually worse than if one were to BEGIN the takeoff roll 300 feet down the runway instead of at the threshold.
The misleading thing about it is that the entire remainder of the takeoff is also performance-diminished, including the climb-angle to the obstacle!
Downwind operations have bit many an unsuspecting pilot.

[hilltop170]

All that is correct George. During the distance that the airspeed has not hit zero yet, the rudder effectiveness is dimished which can easily lead to loss of directional control.

And if the airspeed has not hit 70% of that required for takeoff at the 50% point on the runway, you better shut down immediately and stop on the last half of the runway.