I was inspired by a video posted recently from rcflyboynj. I have flown a PBF for a long time and love it. The video showed a similar type of PBF flying off water, so I decided to modify mine, actually the original is LeadFeathers design on RCgroups, to include floats and a new fuse to support the motor for water purposes.

So anyway, this is just a preview of what I am working on.

I plan on using my Phlatformer to create plastic covers for the floats.

This all assumes of course that it flies decently and can takeoff and land from water.

I named it the Rubber Ducky cause it just reminded me of one...

Once it is complete and if it flys well, I will post the build files. Attached files

 

Flash, I like it,
one suggestion- extend the rudder slightly below the trailing edge of the elevons. that way it will not hit the ground, but when in the water, as the "boat" squats on the back,(because of the larger displacement up front), it will act as a water rudder and give it much more positive steering in the water. I tried one similar to this and it was real squirly when trying to turn at low speeds without the wet rudder. you may also want to move the motor mount back just enough to accommodate whatever size motor you plan to use. this will help push the CG back and make it fly more like a Pizza Box.

Looks good, I noticed you are using steps on the sponsors. Very nice , try to lay it out so that the step is on the CG or just forward of it, it will come up an plane very nice in the water that way.

Ross

 

Thanks for the suggestions. I just finished putting it together and did a quick pool float test.

Looks like I may have to move my battery back to around the center of the board to get the CG where it belongs.

The motor I picked is a heavier motor (BP 2212-13) than my old pizza box. I may have to reconsider this and go with the lighter 17g Lazertoyz Blue Wonder motor. I just wasn't sure if would have enough kick to ROW.

Will know more tomorrow... Getting late and time to call it a day.

Edit: I think you are exactly right... The motor mount needs to go back, probably 4 inches. My CG is way too far forward. Even moving the battery back wasn't enough. Fortunately, the glue wasn't completely set and I was able to get it off.

Attached files

 

Flash,
it looks better. I would back way off on the wet rudder though. Water is much harder than air and you don't need that much. I would try about 1/2" bellow the rear step. as I said before, as you increase throttle/forward movement, the "boat" should squat pushing the rudder deeper in the water. The hydraulic effect on the front sponsons give them much more "lift" than the rear one pushing the back down. That actually helps for take off on water as it creates a tunnel hull effect.

Remember that the distance from the pivot of the rudder has a huge effect as well, with that much rudder, at speed, it would put a great deal of strain on a 9 gram servo and if you landed back on the water with just a bit of rudder in, I think it might flip the boat.

I also noticed that you KF airfoil is a bit far back. Most I have seen are around 1/3 to 1/2 the OAL. If you are looking for added stregth, try something like this. I would move it to right over your step.



it acts as somewhat of a keel in the water and adds some sudo-dihedral in the air.

Also, after you try it out in the water, if you notice it wanting to nose dive, add about 5-10 deg. of up thrust to the motor. It really helped a few of my designs.

Hope this helps. Keep up the good work
Ross Attached files

 

Great Advice! Here is a revised drawing... I was a bit concerned about the KF foil. I needed the extra length to mount the sponsons. Adding a 3rd layer solves that problem. I set it to 8 inches like the original LeadFeather design had it. This adds even more strength which is perfect.

And I reworked the rudder per your suggestion.

Attached files

 

now that is looking like something that will get along. I don't think you need the third layer. just notch the sponsons accordingly. That extra layer will add quite a bit of weight.

When she is ready to go, be sure to keep the trailing edges of the sponsons and rudder sharp. you can round the leading edges but keep the backs sharp. this makes for much better wet performance. it will help break the adhesion of the water and let the "boat" take off.

The revised rudder looks great. I would run the keel strip all the way back to the rear sponson.

 

Well, this is one duck that don't take to water very well. Keeps wanting to drink from the pond!

Even with 15 degrees thrust angle on the motor, it still wants to dive looking for fish or whatever ducks eat.

I see now why they used 45 degree angle sponsons!

Oh well, my Phlatprinter will be here soon (rescheduled for Monday delivery) and I will have enough to do to keep me busy.

Think I may give up on this project at least for the time being.

 

In all the wing only planes that I've built I had to make the nose gear high so that the plane had an angle of attack just sitting there on the runway. I was told that you have to break the suction that is created under the wing. It's the venturi effect, I think. Maybe that's what ailing your plane? I think giving it an angle of attack will help or making the plane sitting on the pontoons way higher.

 

I put a BIG angle of attack on it and could not overcome it.

I have a new one on the drawing board now... Just finished gluing the parts together. Next step is mount the electronics and see how it performs.

This one will have much taller sponsons, motor lowered and CG moved back a bit.

The great thing about having a Phlatprinter is that you can easily try something new if at first your creation doesn't work out...

We'll see....

 

After 3 attempts, I think I am getting close. The duck isn't looking so ducky now, but maybe it will stand a better chance of flying.

A pool test of my 2nd version was much better. It showed me what I needed to do to this version. While version 3 is still under construction waiting for glue to dry, I hope to finish it by tomorrow and pool test it, maybe even get in a maiden flight.

I had to do away with the normal sponsons. After all, it's not a normal plane and abnormality begets strange bedfellows.

I have lowered the motor since the new sponsons get the nose up out of the water and give the plane a high angle of attack which should allow ROW easily.

I will be able to experiment with the fuse component once assembled to see where battery placement and motor will produce the proper CG, so it might change a bit more before its all over.

Thanks to everyone for your comments. I think I have most of them incorporated into this version and the initial testing of version 2 looked promising. Attached files