I managed to get a short flight in over the weekend – only about 45 minutes but that was enough.
I wanted to fly on Saturday because a weak cold front was forecast to pass through on Sunday and to pick up the winds a bit (it did). A series of circumstances resulted in not getting into the air until about 2 pm.
There were no aircraft in the traffic pattern by that time of day so I listened to the AWOS to help in the runway choice decision. The winds as I taxied out were from 110 degrees at 9 knots. Hmm.
My airport has two runways 14-32 and 8-26. So, using runway 8 would have the wind 30 degrees right of the runway heading and using runway 14 would out it 30 degrees to the left. So, which would be better?
Anyone who had conducted a takeoff in a propeller-driven airplane (especially one with a tailwheel) has experienced the tendency of the aircraft to head for the weeds to the left of the runway. Torque, p-factor, gyroscopic effect, Coriolis effect, phase of the moon and the due date for your utility bill all seem to conspire to aim the aircraft to the left when you add power (and raise the tail) on takeoff.
If during the takeoff roll you have a crosswind from the left, which way will it cause the aircraft aim? Some will say that it would make the aircraft exit the right side of the runway and others will say the left side. Both are correct if you consider the complete takeoff operation.
Given the shape of the average aircraft fuselage the largest non-symmetrical side area for a wind force to work on is the vertical tail. As long as the wheels are on the ground a crosswind will have a tendency to push on the tail and yaw the nose around the main landing gear. A left crosswind would then have a tendency to yaw the nose to the left.
Once the main gear leave the runway surface there is no pivot point to anchor the yawing force. The wind will then start moving the entire aircraft ‘downwind.’ At that point the example left crosswind would move the aircraft toward the right side of the runway unless a crab is established to counteract the movement.
Unfortunately all takeoffs do not exhibit a clean transition from one phase to the other and the crosswind-induced forces can become coupled and complicated as the aircraft transitions to flying. It especially becomes complicated if crosswind aileron controls are not used or are ineffective and the upwind wing starts to raise. This can result in more weight being transferred to the downwind main landing gear causing a tendency to turn into the wind or it could reduce the wheel to runway friction enough that the crosswind causes the aircraft to skip sideways in the downwind direction. Takeoffs are always an exciting time.
Takeoffs are optional, landings are mandatory.unknown
So, with all this in mind I selected Runway 8 for my takeoff. With the aircraft’s natural tendency to turn left on takeoff a slight crosswind from the right would work against those forces while the aircraft was on the runway and reduce the work I would have to do to keep the plane moving straight down the centerline.
All that being said, the short flight to a practice area was uneventful – learning a little more about the operation of my relatively new engine analyzer.
Then there were more decisions when I returned to the airport. I’ll cover those next time.