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Old Nov 17, 2015, 01:05 AM
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Zen in the art of foam
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My Icon A5 won't take off from water

It does very well taking off the grass but not so from water.
It's shape is the nearly same as the original and 46" span.
Looks like its nose creates a wave that it can't overcome.
Any ideas?

Icon2 failed takeoffs, slomo (0 min 58 sec)

Scratchbuilt Icon A5 flying great with pitch stabilizer (3 min 7 sec)
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Old Nov 17, 2015, 06:07 AM
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How is the Step .... on the bottom ... ?
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Old Nov 17, 2015, 07:24 AM
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Where did you get the plans for this ?
Or did you design it?
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Old Nov 17, 2015, 08:20 AM
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Quote:
Originally Posted by Aussieflyer View Post
Where did you get the plans for this ?
Or did you design it?
http://www.rcgroups.com/forums/showthread.php?t=1606211
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Old Nov 17, 2015, 08:29 AM
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move Cg back a bit . also noticed left wing is dragging trim ailerons at takeoff to lift that wing
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Old Nov 17, 2015, 11:48 AM
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gpw, I'll make sure the step is more pronounced.
I designed it. This is my second attempt.
The left wing drags because of prop torque. I put a small weight (a quarter) on the tip of the right wing to kind of counteract the prop torque. I'll move the CG back a bit.

Thanks for the feedback!
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Old Nov 17, 2015, 12:04 PM
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Just guessing based on the videos. The skid plate on the bottom of the fuse looks like it needs to curl up more in the front and be much narrower in the mid and back sections. It looks like the skid plate is actually under water. If it had more curl-up in the front and less drag (narrower) farther back I think it would make it. Of course more power would also help. Maybe add one cell to the battery pack. Oh yeah, reducing the mAh rating to reduce weight could also help.

I fly a frog with a narrower skid plate. It has about a 3/8" step about 1/2 " behind the CG.

Post pictures of the skid plate and step area and post with the next video.
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Old Nov 17, 2015, 02:18 PM
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Great looking and flying model!!

+1 to bz1mcr above…

I designed an A5 a while ago and experienced some of the same issues with the first prototype. The nose digging is a result of the nose being low and narrow. I even noticed the same on many videos of the park zone model as I was doing research. The remedy was to make the nose a bit wider and deeper. At "rest", the airframe needs to "lean back". When on water, the motor is up top, and all the drag is on the bottom so it naturally wants to dip the nose. A bit of up elevator may help - careful though -- too much will tip stall her on takeoff! Flaps help too, but again, the best thing is reshaping the nose a bit.

I would also remove the quarter to counteract torque. That is just unnecessary weight. This airframe needs to be "flown" on the ground. Use the ailerons to lean into turns and keep the fuse upright on straightaways. Accelerate gradually from a stop and you will find once she gets to a good speed, she will sail upright.

Also, this airframe needs a lot of power to overcome all the friction from the water to get enough speed to take off. I would definitely suggest a higher KV motor and a smaller prop - think park jet power plant.

Great job! I know this is a tough model to undertake! It's a lot of fun to fly as you will never be bored! I ended up adding leading edge droops to a larger one I built (52") to help ward off tip stalls. The full size one also has these droops to prevent spins/stalls.

I have pics/vids of my version here:http://www.rcgroups.com/forums/showthread.php?t=1606211

Best of luck!
SNice
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Old Nov 17, 2015, 02:25 PM
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Add some anti-spray strakes to the bottom corners of the hull ? (Not sure what the Icon A5 hull looks like).

The amount of water coming up over the nose is just too much. I added some strakes to a Catalina that solved that problem.

Ray.
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Old Nov 17, 2015, 04:24 PM
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bz1: Yes, I need to minimize the drag on the fuse and skids. The prop has a large moment arm above the water and tends to drive the bow into the water.
The pic below showing the skid mod is what you mean, right?

SNice: I've referred to your design quite a bit while working on mine.
I'll consider a higher KV motor and smaller prop. That might reduce prop torque.
You wrote: "A bit of up elevator may help - careful though -- too much will tip stall her on takeoff!"
Is this what you mean? ;-)
Icon2 stall and crash too much elevator (0 min 35 sec)


Ray, I was going to add strakes in front as you suggested (pic below).
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Old Nov 18, 2015, 07:30 AM
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Start the takeoff run with full up elevator and be ready to come forward on the stick as the plane gets on the step and particularly as it pops off the water.
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Old Nov 18, 2015, 12:41 PM
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Will do.
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Old Nov 18, 2015, 03:51 PM
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OK, I moved the CG a bit back, trimmed the skid plates a bit, put some up elevator at take-off, and added a strake on the bow, but it still won't get off the water.
Next I'll try SNice suggestion and use a smaller prop. I can't install a higher KV motor because all the motor lines are inaccessible. Could I use a 4S battery with a smaller prop instead of 3S, but not give it full throttle?
Maybe I cannot reach take-off speed because water is hitting the prop and slowing it down.
I went straight from the pond to the park where it flew nicely.

Icon2 still water bound (4 min 2 sec)

Icon2 straight from the pond to the park (3 min 58 sec)


The last video is off a rescue airboat I built just in case a plane ends up stalled in the water. I used a 20A DPDT switch to reverse the motor in case I need to back up. The reverse thrust is about 30% of the forward thrust, and that's just enough for reversing.
The motor/prop is thrust vectored.

Airboat Testing (5 min 22 sec)
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Old Nov 18, 2015, 05:20 PM
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Cool rescue boat!
From the motor sound on the videos, you use more throttle on the land takeoff than you do on the water attempts. And, it takes more power to lift off water.

It seemed like when you approached full throttle water was hitting the prop. That needs to be fixed, but I can't tell from the videos what is directing the water to the prop area. I hope you can watch carefully and see what needs to be changed or added.

It does seem like you have trouble leveling the wings. My frog always has a low wing with one wing float on the water at low speeds. In calm conditions it is pretty easy to level the wings as speed is increased, but with winds above about 5 MPH the wings can only be leveled when headed directly into the wind. Any cross wind will lower the down wind wing and the float drag in the water will hold the speed down and prevent takeoff.

I think a smaller prop is going in the wrong direction. You can go to 4S and keep the same prop. Just do not hold full throttle for long time periods.
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Old Nov 18, 2015, 05:44 PM
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Thanks!
I installed a 6x4 prop on it and it wouldn't even move on the grass. Went back to the 7x4.
Yes, I'll have to figure out what is guiding the water towards the prop area.
The left wing dips down because of prop torque. Once enough speed is achieved, ground effect levels out the wings. Also aileron function is established.
And you're right about side winds rolling the plane to one side.
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