Lesson Seven – Tune for the step
Lesson Seven - Tune for the step
This exercise more than any other will quantify immediately your understanding and awareness of the dynamics involved with what really is happening during the float plane take off. It is imperative that you understand the four distinct phases of a float plane
- Step or the Planning/Acceleration Phase,
- Liftoff. (See FAA Handbook, FAA-H-8083-23 Page 4-10.)
For this discussion, we are only going to deal with the step or planning/acceleration phase. Why? This is where it all happens during the seaplane takeoff. Referring to the step phase as the planning/acceleration phase should call your attention to the fact that things are happening here. You NEED and MUST be aware and KNOW what to expect and what to DO in order to make it happen as efficiently as possible, especially when dealing with short distances and heavy loads.
What is needed to practice this exercise?
A float plane. 🙂
A long lake, like Upper Trail Lake at my base in Moose Pass on the Kenai Peninsula, where I am located, “0” minutes flying time. Or Figure 8 Lake 20 miles west of Lake Hood, 40 miles to and from, 30 minutes round trip in a Cub or T-craft. (Read my “Important Message to Alaska Pilots regarding Lake Hood” on this web site.)
Light winds, 5 to 10 Knots, not glassy water.
Preferably an instructor familiar with this exercise.
The exercise: Each phase of this exercise is important. Do every part and memorize the attitudes. Mark them on the windscreen if need be.
As you are slow taxiing for takeoff in the “displacement phase” carefully note the exact relationship of the top of the cowling and the far shoreline. Label this relationship as the “D” attitude. “D” is for displacement or “D” for death, which could happen if you ever touchdown in this attitude.
Next, assuming you made it to your long lake, start your takeoff run, carefully noting the cowling attitude in the displacement mode. Stick or yoke full back to start the Hump phase of the takeoff.
In most airplanes you will have a two-step rise. (Why? You answer that.) As the nose of the aircraft or top of the cowling starts the second rise, begin to neutralize the elevator and allow the nose to rise and go over the hump to the step attitude (planning/acceleration phase).
So you say, “I thought this was what you’re going to teach me to do.” And right you are. So this first time just go to where you think the attitude of the “optimal planning angle is,” i.e. the step attitude, and reduce the power back to the minimal power that will keep you on the step. Note what this power setting is, make a mental note of it and remember it. We know that at full power we can accelerate to lift-off speed even if you are sloppy.
On the Step — Planing/Acceleration Phase
Establish a nice step taxi, into the wind and carefully note the exact attitude or relationship of the top of the cowling and the far shoreline. Make a mental note of that relationship. Now think of the far shoreline as the “front sight” on a rifle; think of the top of the cowling closest to the prop as the rear or back sight on a rifle. There-in the name of this exercise, “gunsight method of step identification.”
Note the feeling of the vibrations coming from the floats caused by the small wavelets on the lake’s surface. This is important because we will “tune for the step” from these riffles.
OK! Be sure you have lots of lake ahead; set your flaps to takeoff position (which you know from your airplanes POH). Slowly start adding 1″ manifold pressure or 100 RPM at a time. From this point on you are attempting to make the airplane fly. You should have set your flaps for takeoff. Remember that for step taxiing you do not use flaps. As you add the power at each increase, note the nose attitude from the far shoreline as the power is added, drag on the floats increase causing the nose to pitch down. Note the effect of the increase speed when you do not make any elevator adjustments. Then with small tiny adjustments of the elevator note these changes, accelerating air speed, vibration from the floats on the wavelets, and the aircraft getting lighter. Ask yourself, what is happening? Don’t be afraid to make crude adjustments of the elevator. You are attempting to note the changes and effects of these changes from the feeling in the seat of your pants to the indication of the airspeed indicator. Are you paying attention to the acceleration difference from these changes? Do you note what effects the hydrodynamic drag differences cause on the floats and what happens from changing the angle of the floats contacting with the water surface? You should be feeling the differences in the drag and the acceleration caused by these changes.
Take your time doing this exercise. Pay very close attention to your cylinder head temperatures. If rising, I make it a habit to takeoff and cool the temps down before attempting another go at it. After each power change you are attempting to make the airplane fly. Play with the step and have fun with it. It is important to have patience after each power change. Somewhere around 20″ to 21″ manifold pressure or 2000 or 2100 RPM, depending on weight, you should be able to fly. It could take a little more if it is warm or you are heavy. The point is we are “tuning for the step.”
As you liftoff the water, note exactly where the cowling attitude relationship is with the shoreline. REMEMBER this relationship. This is your “optimal planing angle.” You now know the gunsight method of step identification.
Maintain this liftoff attitude. Increase your power to max takeoff power. Note the pitch changes as you add power to accelerate. Do not let the nose rise from the liftoff attitude. Keep the ball in the center as your airplane accelerates to Vx. Even small deflections cause significant reduction in climb performance. Note the
elevator adjustments needed as you raise the flaps. With these small elevator adjustments you should be maintaining the liftoff attitude and accelerate to Vy. After Vy, adjust your power to max climb power and get set up to do the exercise again.
You now know the exact relationship with the shoreline and the top of your cowling that produces the most efficient, fastest, “optimal planing angle” using the gunsight method of step identification. This method will quickly get you into the air. It saves wear and tear on your engine, floats, and airplane. It could even save your life.
Always use this method for takeoff and remember this attitude or relationship with the far shoreline for landing. NEVER let the nose attitude be lower than this for landings. Slightly higher is OK. Never lower.
My four rules for float flying are:
- Always keep the nose up,
- Never drop the airplane,
- You cannot see glassy water,
- Never make descending turns over glassy water without a positive reference.
Practice, Practice, Practice.
See you on the water.