Saturday, July 23, 2011

Hot Air!

As I taxied N631S away from its tie-down at KBDR last evening, the outside air temperature (OAT) gauge read 102°. Now, that's toasty! I was anxious to get off the ground and up a few thousand feet to where it might be a little bit cooler.

Of course, it wasn't going to be that easy. Half way to the runway, the ground controller said, "631 Sierra, for whatever reason, Approach has decided to modify your clearance...and it's a full-route clearance, so...advise ready to copy." I gave him a "Wilco" and pulled into a convenient spot for my run-up, then said, "31 Sierra is ready to copy."

I had filed for, and initially received, a clearance for what I've come to think of as "the usual route." It takes me west to Sparta (SAX) then south to Solberg (SBJ), then west again to Allentown and Reading, down to Lancaster, across Baltimore, and finally home to KVKX. The re-route was for a coastal flight path: Vectors to Deer Park (DPK) then airways over JFK and down past Atlantic City and Cape May, and across the DelMarVa peninsula toward home. Often, weather factors make this a desirable route but I usually have to beg and plead to get it. This time, it appeared spontaneously. Why? It's a mystery.

So I copied and read back the new clearance, did my run-up, then sat at the hold-short line for five or six minutes, quietly perspiring while awaiting IFR release. "Skylane 31 Sierra, cleared for takeoff" came at 2030Z.

As New York Approach cleared me to progressively higher altitudes, I kept the nose down and the speed up in an effort to keep the engine relatively cool. Instead of going for a good rate of climb, I kept the Vertical Speed Indicator (VSI) at 500 feet per minute. This allowed me to complete most of the climb up to 6,000 feet (my final altitude) at 100 knots indicated and kept my cylinder head temperatures around 400°F.

Level at 6,000 feet, the OAT was 73°. The "Top of Climb" checklist includes "Cowl Flaps – Close" but I left them wide open. Even so, with my normal cruise conditions set (throttle wide-open, 2350 RPM and 11.8 GPH fuel flow) the cylinder head temps were creeping up. Since I was operating on the lean side of peak exhaust gas temperatures, I knew that my power output was a simple function of fuel flow. I adjusted the mixture control for 11.4 GPH and watched with satisfaction as the temperatures of the hottest cylinder heads settled down to about 395°. I'd given up about 3 or 4 knots of true airspeed, but having a happy engine was more important.

With cruise conditions set, it was time to look ahead at the weather along the route. Before departure, radar had indicated some scattered thunderstorm activity and it would be prudent to see if any of that was scattered in places that N631S and I needed to go.

Just before New York Approach handed me off to McGuire Approach, I saw the picture at left on the weather display. Clearly, the cell just to the west of the Coyle VOR (CYN) would bear watching. Checking in with McGuire, I asked the controller what he was looking at down around Coyle and he said there was a cell west of the VOR, moving eastward with precipitation echoes up to Level 5 (that's mean stuff!)...and he might need to vector me around it. Of course, I concurred.
But as I watched, that storm cell dissipated as summer "popcorn" cells often will. By the time N631S and I got to CYN, it was just some light rain visible off to the right of the airway. False alarm, but better to be prepared.

The balance of the flight was warm but uneventful. Soon after crossing the Delaware Bay, Potomac Approach took me down to 4,000 feet where the OAT was 83°, and then (nearing the DC Class B airspace) down to 3,000 feet and an OAT of 88°. It was hazy, with a flight visibility of about five miles approaching KVKX, but I know where to look now and could report, "31 Sierra has the field in sight," in a timely way for the visual approach. The final controller cleared me for the visual and accepted my IFR cancellation. Now at 2,000 feet, the OAT was 95°. As some would say is normal, the DC area was full of hot air.

N631S and I were on the runway at 2238Z. The surface temperature was 93° – actually a bit cooler than it was 2,000 feet up. I promptly put the airplane to bed in the hangar and headed home in the convertible...with the top up and the air conditioning on.

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