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Old Apr 19, 2011, 11:46 AM
Registered User
United States, WI, Platteville
Joined Jul 2007
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Build Log
Dynam Hawk Sky Flying Boat

I bought a Dynam Hawk Sky from graysonhobby.com. I intend to convert it to a flying boat by building up a foam float that will attach into the landing gear slot and convert the bottom of the fuse into a flying boat hull. I'm also going to attach a water rudder to the air rudder that it currently has.

I've seen threads on various forums of people putting 300 grams worth of floats on this 600g plane, and it makes no sense to me at all. I plan to add maybe a square foot of foam from meat trays at the most. I don't see any reason to add more weight than that.

Based on what I've read in this forum, the step should be about an inch behind the CG. Can I leave the bottom of the fuse behind the step alone and just add on the boat hull?

EDIT:

On a side note, the weight in the front actually needs to be there. I figured I could just slide the battery farther forward, but the nose isn't deep enough for that. I cut a slot in the nose for the weight and filled it with gorilla glue.
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Old Apr 19, 2011, 01:32 PM
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If it were me, I would just add the planing surface ahead of the step. Probably half-inch thick, and curved upwards toward the nose. Maybe even split the difference and remove some of the bottom of the fuse behind the step.

Attach a piece of credit-card plastic to the water rudder to dip into the water a half-inch deep behind the tail.
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Old Apr 19, 2011, 03:31 PM
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This plane has such a long fuselage and low H-stab that you might need more than just a forward planing surface... you need enough height at the step so the plane can rotate back for take-off without dunking the tail or have WIG-effect on the H-stab, thus pushing the nose back down. 5-8 degrees of rotation is typical.

You might be able to use just the plastic bottom of a single GWS float and glue it directly to your fuselage, or make a foam (FFF) cradle that fits inside the GWS shell that mates to your fuselage and hooks on with rubber bands.
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Old Apr 19, 2011, 04:23 PM
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United States, WI, Platteville
Joined Jul 2007
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The angle of incidence is already 5 degrees. Is the 5-8 deg the angle of attack or is it the angle of the fuse wrt level?

From the hinge of the H-stab to the cg is about 55 cm, so if we play it safe and call it 10 deg, the bottom of the step needs to be 10 cm below the centerline, or about 8 cm below the fuse. At that point, it would look so silly that the purpose of a flying boat would be defeated.

Anything I build will be detachable, so I can just build the hull with a 3 cm step and see if it works.

The tail drags on the ground on during ROG, but the landing gear give the 8 deg extra angle of attack.

If I really want to make a lot of work for myself, I could cut off the H-stab and make a T-tail. Not sure I have the fabrication skillz for that, though.
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Old Apr 19, 2011, 05:13 PM
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The 5-8 degrees is not referring to the wing angle of attack, it is the "fuselage rotation from level flight". You need this rotation at two times during ROW: First, you need a bit of rotation in order to plow up over the bow wake. You can do this without rotating if you have loads of thrust or a very shallow draught, otherwise it is easier to give full up-elevator to get the nose up over the water and prevent "submarining". The second time you need to rotate is at lift-off. In order for the plane to climb, you have to either go really fast for the wing to create enough lift, or you need to pull up on the elevator. When you pull up on the elevator, that pushes the tail down. If you push the tail down into the water, (A) the water will buoy the tail back up make for some bouncy skipping and hopping, and/or (B) you will lose a lot of airspeed from the drag... which could result in stalled take-offs.

I think the style of mid-wing plane you have will require at least 2" of additional height at the step just to keep the wings and tail from dipping into the water. If you want something that is easily removable, then why not just make a pair of floats, or use GWS floats? Maybe you could use the parkflyerplastics Twinstar kit and modify it to fit.

My 2cents.
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Old Apr 21, 2011, 11:19 AM
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United States, WI, Platteville
Joined Jul 2007
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Before I even think about converting this into a waterplane, I will need to come up with a system to attach the wings firmly and detachably. When my trainer flew it, he did a loop and the wings fell out. The obvious solution is hot glue, but that's out of the question because I need to fit it in my car.

There is a 1/4" diameter carbon fiber rod that goes about 10" into each wing, so I think I might cut a hole out of each wing and make something that would be firmly attached to the foam of the wing, and that could clamp on to the rod with friction. Any ideas?
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Old Apr 21, 2011, 07:41 PM
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Here is my idea: Mark each wing root so the surgery will match. Plunge your soldering iron into the wing root (quickly-the hole continues to grow.)
Do this to make a hole around 1 1/2" deep, 3/8 diameter. then glue (Gorilla Glue) 3/8" dowels into each hole. Drill pilot holes lest you split the dowels, then screw a cuphook into each dowel. Stretch a small rubber band between the hooks when installing the wing.

If you can't put the dowels into the wing root, then insert them into the top of the wing with just a screw-head protruding, and stretch the rubber band across the top.
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Old Apr 22, 2011, 11:24 PM
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lupy's Avatar
Renton WA
Joined Oct 2001
825 Posts
unless you do something to the tail, you will drag the horiz stab in the water and make taking off very tricky. I did almost exactly what you are talking about with an easystar, and finally took it back off. The stab would drag back and forth. Very tricky to get enough speed up to take off. I only used about 1" of hight, so if you went with 2" or more as Warhead said, and then cut it down a little, you might make something work.

There was also a plane I saw, think it was the shearwind, that had a single water ski like skid on the bottom, that went from flush with the hull at the front, to enough height at the rear to pivot off of for take off. You will need enough power though to go forward fast enough to have the ski lift the fuse out of the water.
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Old Apr 23, 2011, 06:44 AM
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One thing: This plane has a glider-like high-aspect-ratio wing, and will need less AOA to get airborne.
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Old Apr 23, 2011, 07:28 PM
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Blacksburg, VA 24060 USA
Joined Feb 2000
3,205 Posts
There's also the question of proper thrust line on the motor. As a handlaunched airplane, it needs less than full throttle, fortunately. At full throttle, the high thrust line will dive the airplane.

So you may have to fiddle with that thrust line, so the nose won't plow into the water.

Jim R.
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Old May 06, 2011, 05:11 PM
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United States, WI, Platteville
Joined Jul 2007
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I fixed the wing problem with an elastic band that goes through the CF rod spar, with a knot tied at each end that slides into a slotted square of balsa plywood. It won't pull the wings back together if they separate by an inch, but it does keep them in the slot so the plane still flies.

I went flying today - or should I say crashing. The wind was fairly strong and gusty. That combined with my complete inexperience in trimming, flying, finding the CG, etc, caused quite a few crashes. I must say I'm impressed, though: the only things that were even remotely broken were the nose and one of the ailerons that fell off. For six or seven crashes straight into the ground, followed by crashing into a tree and having sticks and rocks thrown at it for a good half an hour, this thing held up pretty amazingly.
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Old May 23, 2012, 10:50 PM
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United States, TN, Farragut
Joined Dec 2011
15 Posts
Did you ever Create the Flying Boat

Knox,

If you did create the boat please share some pictures......
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Old Nov 15, 2012, 06:36 AM
Teddy Ong
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Joined Nov 2012
580 Posts
Your boat sounds fun! although a watercraft is not easy to fly. Try it on any simulator and you would nose into the water/flip over for the first few times. borrowing a sim or buying one and spending sometime on it will help. I have no experience in water planes, but you need to tweak the motor mount a little or increase wing area to help. from what you described, i would prefer that you replace the foam hinges with at least tape hinges. hope that will help!
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