At first I thought I would never really get the hang of it. I tried to read on the internet, but there is not much to be found on the topic. Also, there are not many books that go into great detail on the subject of how to get into the air in high density altitude with a heavy seaplane. Tried to talk with other pilots (at least here in Europe there are not many people with experiences on that stuff) and I was extremely lucky to be able to experiment a few seasons under the watchful eyes of Bjørn Horne, one of Europes last remaining expert seaplane pilots.  (he is way too humble to agree to this statement) 

I believe that now I might have found a rather suitable way on how to do it. I am writing this down in order to remind myself one day, and also to maybe preserve some rare knowledge that might be useful for another seaplane pilot´s bag of tricks in the future.

Maybe it is also a good starting point for a fruitful discussion among really expert seaplane pilots, which will hopefully reveal much better techniques. 

My only seaplane experience so far is a few hundred hours on Cessna 206 with extended wingtips and vortex generators. These are equipped with EDO 3430 straight floats.

So you are tasked to take off with a non-turbo Cessna 206 in a lake with 4000ft MSL elevation and it is a nice summer day with about 20 degrees celsius. 

The density altitude would be something around 5500 ft, which is quite high for a normally aspirated airplane. Not much wind to be expected today.

First thing that I would recommend is to take a good look at your available takeoff length and the flightpath that you will chose after liftoff. Be sure to have either flat area straight ahead where you can safely accelerate, or enough space in one direction to turn after liftoff. Anyway, you will most certainly need some distance straight ahead before you can really make a good turn. If surrounding terrain is close, have a good idea about updrafts and downdrafts from the wind, if you have wind. Hopefully, you have wind! Plan your flightpath after takeoff to use updrafts, and by all means avoid downdrafts. Even a very small downdraft will eat up all your excess power and you will not accelerate after liftoff. Or it will put you back down into the water, which would really be undesirable if this happens after you have already passed your abort point and you will be left with not enough water ahead to stop safely. 

Next, take a look at the performance charts, not because they give you the exact numbers, but just to get a general idea wether you will need one mile or two miles takeoff distance. You will notice how big difference an increase in weight makes, so first thing to work on is to be as light as possible. Same as with all mountain flying- do not take unnecessary stuff on board and spend some time on a reasonable fuel calculation. But this is not supposed to become a guide on how to fly in the mountains. Glider pilots with mountain experience have a distinct advantage, so I would really recommend such experience as a prerequisite for flying low powered airplanes at slow speeds very close to the terrain. 

In this article I am trying to explain as much as I know about how to get the plane out of the water at all, which is not always a „no brainer“.

Where were we at? Yes, about the weight. Keep it light. 

Remember to pump the floats if they are leaky. Also, arrange the ropes so they will not drag in the water during takeoff. (I can hear Bjørn laughing, this is indeed a very nitpicky detail…)

Your load distribution is absolutely essential. The center of gravity must be as far forward, as possible. All seats forward as much as possible, heavy items under the front seats, and have your passengers lean forward during takeoff. I have heard about pilots who have their passengers hold heavy bags on their laps during takeoff… The heaviest guy sits in the front seat, even if his girlfriend looks and smells better. No stuff in the back of the cabin, stack the bags up as far forward as possible. This will be necessary in order to get the airplane on the step quickly, so you do not waste any of your precious takeoff distance while ploughing through the lake. 

Be sure to use every little wind that is there. Ignoring a 3 knot wind for the convenience of not having to taxi to the other side of the lake may make the difference. After all, the difference of speed relative to the water surface will be 6 knots wich is some 10% of the total liftoff speed. Especially in smooth water surfaces, as it often is the case in light wind, the water really sticks to the floats and you may just not be able to lift off. More on this later.

While preparing for the takeoff, find a distinct point where at the latest you want to either be safely flying, or, if not, abort the takeoff. This can be some feature on the shore, an island, or a larger rock. I use the published numbers for the water run from the landing charts as a guide on how much distance is needed to stop. (A method to stop quickly is to push forward on the elevator, a dirty little secret) 

Also consider the distance you might need after liftoff, because you will not climb very steeply the first seconds after leaving the water. I prefer to have some distance to accelerate in ground effect and reduce the flaps.

The most important point is to know when it is time to stop, much more important than the numbers from the book. Think about this!

Use the entire available surface, if takeoff distance is a limited resource. Really use all of it. Be completely ready to advance the throttle when you have turned around.

You know that you can set the proper fuel flow according to the density altitude, do you? Not much to say about this except: Please be nice to your engine. Do not heat it up in step taxi or by repeated takeoff attempts when you are too heavy. Do not reduce fuel flow to below the placard for takeoff power in the respective altitude. Always have the cowl flaps open on takeoff. Hot engines at high power settings and too lean mixtures are susceptible to detonation which can drastically reduce power, burn holes in pistons and thus, in more than one way, can ruin your day.

How much flaps? So many different opinions on this… For me it makes sense to make the choice, which flaps I use during the initial stage of the takeoff depending on the headwind I have. We always consider a max performance takeoff here. If you have distance to spare, it is not so important. 

If I have some considerable headwind, say 10 kts, then I would like takeoff flaps from the beginning. The lift from the flaps in the propeller slipstream seems to help a little bit with raising the airplane on the step. 

If there is no or only a very light headwind, I find it useful to begin the takeoff without flaps. The slipstream is not deflected and the thrust is straight. The elevator is able to produce a larger nose up force which brings the float bows higher, and the plane seems to just accelerate and climb on the bow wave a little better until the point where the nose stops rising. This point where the plane is as high as it can get on the bow wave, seems to be a little higher when initially accelerating without using flaps, too. 

Now, if the plane is heavy and has a rather aft CG, without action by the pilot, nothing would happen after this point, anymore. Or it would happen so slowly that we waste a lot of distance, which we try to avoid. 

At this point I lower the flaps (on the 206, they are electric and take their time) to full and at the same time initiate a slight rocking motion with the elevator. Just 2-3 rocks should do to get the bow wave, which will be our pivot point to get onto the step) a bit further aft, so the plane will have it easier to drag itself onto the step into planing attitude. The flaps 30 will now help us by lifting the airplanes rear due to the increased lift over the flaps, which are behind the pivot point (bow wave).

Pushing the elevator would not have the same effect- not much lift but a lot of pivoting force, so we would push the bows of the floats down again and the bow wave would move forward again. Not desirable. A little bit of push can be ok but just to help lifting the tail up.

So as soon as the airplane attains the planing attitude we can reduce flaps back to the takeoff setting. Please check the indication to make sure they are set correctly.

This flap working in the takeoff needs some practise and it bears the risk of forgetting the flaps, or putting them to the wrong setting for the takeoff. Also, when you chose to begin with flaps up, make sure you check that the flaps will work. Sometimes the rear door on a 206 can be forgotten or mishandled, leading to an open flap microswitch disabling the flap circuit. 

So a lot of work, but you get on the step earlier. 

Now as we accelerate on the step, the sweet spot will slightly move. We must constantly optimize our pitch attitude for minimum drag. I find, the higher the speed, the higher the pitch for best acceleration, but this is very minor variations. Use the elevator trim for more precise pitch control.

In this high density altitude scenario we will have higher ground speeds, so hydrodynamic drag is really high at takeoff airspeeds. I do not want to waste any time on two floats.

Therefor, when it is the correct time to raise one float, how do I notice, and which one should be raised? The easy part first:

I feel that in zero crosswind I prefer to raise the left one. Then I can relax some right rudder which was needed to counteract the slipstream effect. Again, less drag.

In crosswind, I raise the upwind float. The upwind wing will be much easier to raise, so it can be done at much less speed. Additionally, the down aileron needed on the downwind wing will act as an additional flap, helping to break out the remaining float later, when it is time to fly.

Until now we are still partially supported by hydrodynamic forces, the wing can not yet lift us out of the water. With one float up, if no obstacles in the water, accept the slight turn instead of deflecting the rudder.

Now about the when. When are we fast enough to be able to break out the first float? This depends on so many variables, I can only say that the airspeed indicator may help. But sometimes, the indication is different depending on which side the wind comes from. Also, if there are waves, much less force is needed to pull the float from the surface… (By the way- if there are considerable waves, avoid the one float technique because the asymmetric beating will be quite hard on the airframe) 

I am afraid you must practise to find out how it feels by yourself. If you use full aileron too early you will just push one float deeper into the water and also create drag from the unnecessarily deflected ailerons. If you wait too long, it is generally not so bad, but of course not optimal. Acceleration really suffers on two floats so I find it important to try to find the correct point.

In glassy water it helps to combine the aileron input with a quick jerk on the elevator, and sometimes even some rudder opposite the aileron, just to break the suction force and lift the first float out. 

Then get back to the correct pitch and ride on the sweet spot, as the aircraft accelerates further to flying speed. Now be patient. Keep your abort point in mind and be prepared to stop if you have to. Be aware that it is easy to get too focussed on trying to get it in the air, since you are so close to flying… Be stop minded until both floats are out of the water.

So now we have accelerated to what looks and feels like flying speed. If we have some waves, the plane will lift off with just a very little tug on the Elevator, if any. 

If we have no waves and the suction and additional drag has reduced acceleration to nil, we have to act again.

Simply jerking the elevator may work, but if the end of the float digs into the water, this will kill a few knots and can cost you hundreds of meters to regain the speed.

One option is to pop the flaps to full. Popping electrical flaps is not so poppy, and it creates more drag than lift. Also hanging there above the surface with full flaps at minimum speed is not exactly the way to accelerate after takeoff in thin air with little excess power. But it works.

A combination of aileron and a well timed gentle jerk on the elevator is my favourite solution. If we do it correctly and not dig the heel of the float into the water, we are now flying and can accelerate to a safe speed in ground effect. 

What you can do is to practise your takeoffs at sea level at reduced power. You will be amazed on how little power you can get away with when using the correct technique.

Have fun and be safe!

Christian