skimmerone wrote:During training in the Lake amphibian we generally get to do a downwind take off and landing...very carefully. The wind is probably not more than 5 knots. It is done to demonstrate the extra distance that is needed and the extra water speed that is needed to lift off, plus the lowered climb angle needed to clear an obstacle. We discuss it at length beforehand. We like a steady breeze without gusts if possible and the instructor (me) stays right on top of the situation. The proper attitude is critical to a safe lift off and climb out and also on the landing. Not recommended unless the wind is very light. Under upwind conditions, the Lake is capable of 1.5 foot waves, but it is governed by the proficiency of the pilot. The Lake Renegade is more comfortable in even bigger waves due to its stretched hull, a slightly deeper V, and its heavier weight.
de Haviman wrote:For most bodies of water, the question of wave height for downwind takeoff is a moot point. Generally speaking, the amount of wind required to generate a wave of any consequence is strong enough to negate the notion of taking off downwind.
Float Pilot wrote:There is a formula that says:
Take 20% of your floats overall length.
That is the danger point for waves if that height is measured from the bottom of the trough to the peak wave height.
So my PK-2300s are 16.8 feet long. So in theory a 3.4 foot wave is the dangerous. ( remember it is from the trough to the crest, so 1.7 feet above the regular level and 1.7 feet below )
I was able to get a Super Cub off of Tustumena Lake with swells and waves that were pretty high. I only did so because I had totally goofed up and had the plane in an unsheltered beach when the waves came up. I almost did not make it out of there. Every time I would think I was doing OK, the next wave would toss me into the air and I would stall because I was not going fast enough. Then I would slam into the next wave and take water into the air intake and into the prop. After a mile of smashing the plane over the swells I was able to catch a good wave and get the heck out of there.
As for a tail wind, in some underpowered light planes it is darn near impossible to get up on the step with anything over a 3-4 knot tail wind.
Even in a plane like a Beaver, a 5-6 knot-tail wind can double your water run distance.
There are more than a few lakes along the coastal mountains which are surrounded by mountains on three sides. Depending on the time of day, there is a good chance that either your take-off run or landing will be with a tail-wind.
In a plane like a PA-11, J3 or Cessna 172, I try to get up on the step into the wind and then step-turn towards down-wind for my escape take-off.
Float Pilot wrote:In a plane like a PA-11, J3 or Cessna 172, I try to get up on the step into the wind and then step-turn towards down-wind for my escape take-off.
That's better than going the other way where you'd have centrifugal force AND the wind trying to turn you over.
I've also heard formula variations based on vertical float height at the step.
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