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Glassy Water Takeoff Tips/Tricks

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Glassy Water Takeoff Tips/Tricks

Unread postby sportsman » Tue Sep 16, 2014 5:12 pm

Anybody want to share some tips for glassy water takeoffs? I was in British Columbia last weekend and had no problem at all getting on step and flying out of a lake at 3080 MSL at full gross when there was a good ripple on the surface both Friday and Saturday afternoons. I even made a downwind takeoff with about a 10 knot breeze, just to see if I could. But on Sunday, at about 50 pounds below gross, with morning temperatures about 20 degrees cooler than the previous two afternoons, I couldn't get on step. The plane just plowed water regardless of what I did with the stick or the flaps (I've got 40 degree large fowler flaps that add a lot of lift and tried both half and full flaps). Ultimately, I had a 250 pound passenger exit the plane and get a ride to a paved runway and my amphib happily got off the water at 300 pounds under its gross weight of 2650. So, does anybody have any tips/tricks they want to share? I had everything to the stops -- would leaning the mixture help? What about pulling the prop control out a bit, thereby decreasing horsepower, but increasing torque? Taxiing in circles was of no use, as the plane never got going more than about 15 knots, so wakes were useless and the water was ideal for one of those pictures that you can turn over and over and never figure out which end is up because the mirrored surface is so perfect. I didn't try messing with the prop or mixture, but I'm wondering if it would help, or am I just stuck with reducing weight or having a more powerful engine (currently a Lyc IO-390 with 270HP)?
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Re: Glassy Water Takeoff Tips/Tricks

Unread postby skimmerone » Tue Sep 16, 2014 7:41 pm

Never take anyone for a ride over 200 pounds. Leaning the mixture at that altitude should help.
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Re: Glassy Water Takeoff Tips/Tricks

Unread postby cubdriver2 » Wed Sep 17, 2014 10:22 am

skimmerone wrote:Never take anyone for a ride over 200 pounds. Leaning the mixture at that altitude should help.


Now you tell me. You should have seen CC Joe ( 260 ) and me trying to get off in my J4 on Chesuncook 2 weeks ago.

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Re: Glassy Water Takeoff Tips/Tricks

Unread postby Tim McCormack » Wed Sep 17, 2014 8:29 pm

Sportsman, that doesn't sound like a "glassy water" problem. In my experience, getting on the step isn't related to how smooth or rough the water is. If sufficient power is available, you should be able to get on the step regardless of the water surface. I've heard of "suction" on the surface of the water keeping the floats from wanting to leave, but even that can usually be broken by lifting one float first after you reach take-off speed.

Yours sounds like more of a power loss situation. I suppose the humidity may have been higher on the second day, even though the temperature was lower. This would make the air less dense and adversely affect performance of the engine, wing, and prop. You may have been right on the edge the day before and the slight difference on the second day could have been just enough to keep you on the water.

Leaning may have been enough to make the difference. I sometimes do it on the take-off run when I want a little more umph.

I have very limited experience with a constant speed prop. I tried one on my plane for one year hoping for improved take-off performance. I got just the opposite so I went back to my fixed pitch. But I do remember that for take-off you firewall the control. If you back it out any you won't "increase the torque" as you suggested, but rather decrease the pitch and thereby reduce the bite of the prop. I'm sure someone with more experience than I can give you a better explanation.
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Re: Glassy Water Takeoff Tips/Tricks

Unread postby RKittine » Thu Sep 18, 2014 8:02 am

A constant speed prop in High RPM, take off position, is a flatter pitch to get higher RPM and hence more horsepower. Backing it out will give a rougher pitch with lower rpm.
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Re: Glassy Water Takeoff Tips/Tricks

Unread postby Tim McCormack » Fri Sep 19, 2014 7:38 am

See.... That's what I mean. I said that backwards. I agree with Bob. :headbang: The results are the same though. Poorer take-off performance.
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Re: Glassy Water Takeoff Tips/Tricks

Unread postby RKittine » Sat Sep 20, 2014 7:37 am

Yep, Lower RPM, less horsepower developed. Have no clue how it would work on this plane, but when I had the Chief, I found when heavy, if I did the Full Back Stick thing for takeoff, I might mush for a long time or ever, but if I put some down elevator trim in and only held the stick back about 1/2 way, I would get up on the step every time and much quicker. It became my procedure for all take offs in the Chief.

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Re: Glassy Water Takeoff Tips/Tricks

Unread postby skimmerone » Sat Sep 20, 2014 9:07 am

Works the same with the Lake Amphibian. If you hold the nose up as far as it will go, then you have to get it back down to the step or planning attitude which can take forever and needs all the power you can get and more, especially with a load on board. However, if you start with full up elevator and watch the bow wave, as soon as it gets past the nose gear doors, go full forward with the yoke and you will rise onto the step quite nicely, then back to neutral with the yoke before porpoises and away you go, in half the time and distance. Getting on the step requires power that most seaplanes lack, so using the Vee of the hull (s) helps a lot. With the pusher engine it helps to ease the power in slowly and the go to full power as you relax the yoke. It keeps the spray down at the start of the takeoff. The pusher also helps get on the step by pressing the Vee hull into the water. It also helps with the eventual lift off if you reduce power just slightly at that point where you think you are never going to fly. The lack of nosedown thrust results in an immediate takeoff with little or no effort from the pilot. Once airborne, full power is added slowly and a climb commenced. Can't do it with a tractor configuration, though.
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Re: Glassy Water Takeoff Tips/Tricks

Unread postby KeithSmith » Tue Sep 23, 2014 8:54 am

sportsman wrote:Anybody want to share some tips for glassy water takeoffs?


This is from the FAA's Seaplane Handbook (FAA-H-8083-23) and gives three techniques that may help:

GLASSY WATER TAKEOFFS

Glassy water makes takeoff more difficult in two ways. The smoothness of the surface has the effect of increasing drag, making acceleration and lift-off more difficult. This can feel as if there is suction between the water and the floats. A little surface roughness actually helps break the contact between the floats and the water by introducing turbulence and air bubbles between water and the float bottoms. The intermittent contact between floats and water at the moment of lift-off cuts drag and allows the seaplane to accelerate while still obtaining some hydrodynamic lift, but glassy water maintains a continuous drag force. Once airborne, the lack of visual cues to the seaplane’s height above the water can create a potentially dangerous situation unless a positive rate of climb is maintained.

The takeoff technique is identical to a normal takeoff until the seaplane is on the step and nearly at flying speed. At this point, the water drag may prevent the seaplane from accelerating the last few knots to lift-off speed. To reduce float drag and break the grip of the water, the pilot applies enough aileron pressure to lift one float just out of the water and allows the seaplane to continue to accelerate on the step of the other float until lift-off. By allowing the seaplane to turn slightly in the direction the aileron is being held rather than holding opposite rudder to maintain a straight course, considerable aerodynamic drag is eliminated, aiding acceleration and lift-off. When using this technique, be careful not to lift the wing so much that the opposite wing contacts the water. Obviously, this would have serious consequences. Once the seaplane lifts off, establish a positive rate of climb to prevent inadvertently flying back into the water.

Another technique that aids glassy water takeoffs entails roughening the surface a little. By taxiing around in a circle, the wake of the seaplane spreads and reflects from shorelines, creating a slightly rougher surface that can provide some visual depth and help the floats break free during takeoff.

Occasionally a pilot may have difficulty getting the seaplane onto the step during a glassy water takeoff, particularly if the seaplane is loaded to its maximum authorized weight. The floats support additional weight by displacing more water; they sink deeper into the water when at rest. Naturally, this wets more surface area, which equates to increased water drag when the seaplane begins moving, compared to a lightly loaded situation. Under these conditions the seaplane may assume a plowing position when full power is applied, but may not develop sufficient hydrodynamic lift to get on the step due to the additional water drag. The careful seaplane pilot always plans ahead and considers the possibility of aborting the takeoff.

Nonetheless, if these conditions are not too excessive, the takeoff often can be accomplished using the following technique.

After the nose rises to the highest point in the plowing position with full back elevator pressure, decrease back pressure somewhat. The nose will drop if the seaplane has attained enough speed to be on the verge of attaining the step position. After a few seconds, the nose will rise again. At the instant it starts to rise, reinforce the rise by again applying firm back pressure. As soon as the nose reaches its maximum height, repeat the entire routine. After several repetitions, the nose attains greater height and speed increases. If the elevator control is then pushed well forward and held there, the seaplane will slowly flatten out on the step and the controls may then be eased back to the neutral position. Once on the step, the remainder of the takeoff run follows the usual glassy water procedure.


Here is one of the sites that sells that handbook:

http://www.skygeek.com/asa-8083-23.html?utm_source=googlebase&utm_medium=shoppingengine&utm_content=asa-8083-23&utm_campaign=froogle&gclid=CL_O2LOw98ACFQGRaQod2UoAYg
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Re: Glassy Water Takeoff Tips/Tricks

Unread postby RKittine » Thu Sep 25, 2014 5:40 am

That last paragraph is great if you have enough space. Not sure if you would have enough room at Island Bob's taking off from the Channel, but at Gurney's with 12,000 feet and plenty of water before and after that, might be another alternative.

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Re: Glassy Water Takeoff Tips/Tricks

Unread postby cubdriver2 » Thu Sep 25, 2014 11:18 am

Yup shorter is more challenging on both take off and landing when glassy. I have 3000' tree to tree so do what works. On TO I chew it up and try to leave a bow wave where I think I'll rotate, and then have to decide in the next 3 seconds if it's going to keep climbing at 45 mph or put it back down. Gets really exciting when I screw up and get back after dark and it's glassy.

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Re: Glassy Water Takeoff Tips/Tricks

Unread postby CFII » Tue Sep 30, 2014 1:40 am

Isn't it SOP to lean Lycomings above 3000'? I do at any elevation to get max rpm for demanding takeoffs, after obstacles are cleared adjusting as needed per POH.

Without an EGT, the max RPM check might still be done while plow taxiing, and I prefer it over the EGT method anyway since it tells you what you really have at the business end.
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Re: Glassy Water Takeoff Tips/Tricks

Unread postby snoboy58 » Tue Sep 13, 2016 12:02 am

My question would be were you actually making full RPM on day 2? I mean were you 50 RPM shy or right at max RPM? If you weren't at max RPM then leaning should help. Max RPM is max hp. On the 172 I fly I start with mixture rich, full RPM and full throttle. Once the plane pitches back into a plow I roll the mixture out to 17 GPH per the POH and Isham STC. Forgetting to lean the mixture on the takeoff roll can be fairly significant dependent on other environmental issues. If I'm already on the step and not really accelerating like I'd like leaning the mixture seems to always be the remedy. BTW this is for sea level. The fuel flow is reduced by 1/4 GPH every 1000' of elevation for full throttle operations.
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Re: Glassy Water Takeoff Tips/Tricks

Unread postby gear » Tue Sep 13, 2016 11:13 pm

My opinion this has nothing to do with glassy water. If you have 270 HP under the hood and can't get past 15 knots it's something else. What type of aircraft is it and what type of floats do you have on it? Although I think your issue is something else, when you are having trouble getting off the water, a lot of guys accelerate with 0 flap till rotate speed and then "pop" the flaps on. I have a 182 so the flaps are electric. I still use this technique - I get to 60 mph, hit the flaps to 20 and I'm off the water right away.

Do you happen to know what the density altitude was that day? Even at 3500 feet, I still don't understand only getting to 15 knots. Did you have a lot of weight in the very back?

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Re: Glassy Water Takeoff Tips/Tricks

Unread postby cubdriver2 » Wed Sep 14, 2016 10:39 am

Wipline had their Boss 270hp amphip 182 on the seaplane ramp at Greenville this year. Friday morning they were going to hop some rides. After two tries it failed to get up on step. Someone got on the radio and suggest that they retract the gear, took right off after that. :lol:

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Re: Glassy Water Takeoff Tips/Tricks

Unread postby gear » Wed Sep 14, 2016 6:09 pm

cubdriver2 wrote:Wipline had their Boss 270hp amphip 182 on the seaplane ramp at Greenville this year.

Glenn

If its their "Boss" 182, it supposedly is 340 HP, not that this would help if the wheels were down,... :anonymous:
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Re: Glassy Water Takeoff Tips/Tricks

Unread postby jjbaker » Thu Sep 15, 2016 12:47 am

Couple years ago, some lady did that with a van in Greenville, too...
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