Monday, December 7, 2009

The Two Humps

I strapped in with the 4-point harness while the instructor untied the rope, let it drop into the water, and patiently held on to the wing strut to keep the airplane from drifting away as I got myself set up. As far as casting off goes, this one would be fairly easy as there were no other seaplanes docked immediately next to us. The trick is to get the cockpit set up for engine start, so that when you cast off, you can jump immediately into the cockpit and start the engine. Until the engine's running, the seaplane is simply drifting and weathervaning, out of control. I learned that first-hand in a later lesson, when we were docked between two airplanes on a day with a 5-10kt wind. Complicating matters even more is that a seaplane does not have a very tight turn radius compared to a landplane. You don't have differential wheel brakes to help, so there's a special technique to get out of a tight space on a dock. More on that later.

Once I was ready, the instructor hopped in, I started the engine, and we were gone. It was surprising that we were moving probably 5kts even at idle, into a headwind. "This is going to be an interesting run-up," I thought. I did the after start checklist, closed the door, and headed out into the open lake. This was a warm sunny day, late afternoon, and many people had already gotten off work. It seemed that anybody who owned a boat all decided to come out the same time I decided to fly.

The run-up in a seaplane is decidedly different than one in a landplane. Sure all the same stuff gets checked: mags, carb heat, flight controls, and ammeter, but the fact that there are no brakes in a seaplane makes the run-up an order of magnitude more amusing. In a landplane, taxi into the run-up area, turn generally into the wind, set the parking brake, and occasionally look around during the procedure to ensure the brakes are holding and nobody is about to taxi into you. I never appreciated the wonderful simplicity of this procedure before. In a seaplane, while checking the mags at 1700rpm, carb heat, flight controls, and ammeter with one hand, the other hand is holding the stick all the way back to minimize water spray on the prop, the head is tilting left and right so that the eyeballs can look beyond the now very high nose, and the feet are responding to steer away from anything the eyeballs see. Oh, and don't forget to make sure the mag drop is within limits and smooth, but don't hit that jetski that just appeared out of nowhere!

With the run-up complete, two notches of flaps set, intentions announced over the radio, it was time for takeoff. Certainly the great thing about a seaplane is that without a clearly defined runway, it's up to the pilot to choose the preferred direction for takeoff, within reason. There are often restrictions due to noise abatement, boat traffic, terrain, and areas of rough water, but the float pilot still has more flexibility in taking off into the wind than a landplane pilot. For this takeoff, I had roughly 20-30 degrees of freedom. I pointed us more or less into the wind and raised the water rudders. This is a key point in the takeoff because once the water rudders are up, directional control is severely limited until takeoff power is applied so that the air rudder has sufficient control authority. Although the water rudders can always be quickly lowered again if you get into a bind, it's good practice to begin the takeoff roll as soon as possible after raising them, especially with a crosswind.

I held the control stick full aft again to raise the pitch attitude to minimize water spray on the prop, which causes significant erosion. I smoothly applied full power, and quite disconcertingly, the airplane immediately began to yaw left, even as I applied full right rudder. I was tempted to just pull the power to idle and end this madness, but my instructor assured me to keep applying power and I would quickly regain control. As I approached full power, the air rudder became effective and I was able to correct back to my original heading. Although it seemed like an eternity without any effective control authority, the airplane probably only turned about 10 degrees until I regained control, which in the middle of a fairly large lake seemed insignificant.

With full power, the Super Cub quickly accelerated to 15-20kts, and pitched up until the horizon was just visible above the glareshield, and then stabilized. This, I was told, was the first of two "humps". Following the instructions I was given in the briefing, I kept the stick full back, steering with the rudder, and waited for the airplane to accelerate more. After a few more seconds, the nose suddenly began pitching up even more until I had to lift my head up to still see the horizon, and then it stabilized again. This was the second "hump". I gently released some of the back pressure on the stick and allowed the nose to come down towards the horizon. "Lower....lower," was the guidance from the back seat. I very briefly had a flashback of a video in which I saw a amphibious floatplane land with its gear down, and violently flipped over onto its back. I wondered if pushing the nose too far down would have the same effect?

"You might have to push a bit....a little lower.....that's it....hold it right there," the instruction continued. What I saw now was similar to what I saw sitting in the airplane tied to the dock. Nearly level pitch attitude, maybe a couple degrees nose up. There was a noticeable increase in the acceleration rate as the nose came down into this "step attitude", which is the attitude that provides minimum water drag. The plane was more like a speedboat now, with the two floats barely skimming on top of the water, with very little metal actually in the water. I held the step attitude, and waited. Eventually, the ride smoothed out as the floats lifted free of the water and we climbed away.

I pitched for our climb speed, looked down and behind us at the water trailing off the float, the ropes flailing in the slipstream, and the wake we left behind. "This is going to be an adventure" I thought to myself.