## Subscriber question:

"When taking off from a sloped runway, which factor has a more significant effect on takeoff performance - runway slope or the wind?" - Adriano N.

**Wally:**

“The adjustment factors used by at least one manufacturer are as follows: Considering winds for takeoff, subtract 10% ground roll for each 12 knots of headwind. Add 10% ground roll for each 2 knots of tailwind up to 10 knots.

From this, you can see that tailwinds are evil. They hurt way more than headwinds help.

Now, considering runway slope on takeoff – an upslope of 1% causes a 22% increase in ground roll at sea level, while a 1% down slope only decreases the ground roll by 7%.

Here again, the upslope hurts a lot more than the downslope helps.

So given these figures, let’s look at a problem wherein we could either take off into the wind with a 1% upslope or downwind and a 1% downslope.

We learned that the upslope will cost us a 22% increase in ground roll and if we have a 6 knot head wind, we should get about 5% of that back for a total increase in our ground roll of 17%.

If we choose to take off downwind and downslope, we will get a decrease of 7% due to the slope, but an increase of 30% due to the tailwind. So we have a total penalty of 23%.

In this example, the upslope takeoff into the wind is the better choice from a ground roll standpoint. However, these calculations only consider the ground roll portion of the takeoff. If there is an obstacle involved then another calculation is needed and the effect of the wind reconsidered. Also, don’t forget that the condition of the runway and the aircraft can have a significant effect on the takeoff performance.

Remember, these numbers are for one type of general aviation aircraft and may not be applicable to any other aircraft. Always use the data from your POH and apply it very conservatively.”