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Old 01-21-2013, 04:17 AM   #1
Alf_Geiger
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Default Converting Ducted Fan Jet to Seaplane

I now live on the water and am in the process of converting all my planes with floats, been pretty good converting over the prop planes with floats but am struggling a bit with the ducted fan jets.

The fuselage on jets is quite long, using the guidelines for floats doesn't seem to work as the 75% length of the fuselage doesn't put the front of the float much past the "long" nose found on most jets.

Anyone crack the code on converting ducted fan jets to seaplane? I am on my fourth modification of floats on a BD-5 (70mm motor) and am starting to doubt that this will ROW.
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Old 01-21-2013, 04:26 AM   #2
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Originally Posted by Alf_Geiger View Post
I now live on the water and am in the process of converting all my planes with floats, been pretty good converting over the prop planes with floats but am struggling a bit with the ducted fan jets.

The fuselage on jets is quite long, using the guidelines for floats doesn't seem to work as the 75% length of the fuselage doesn't put the front of the float much past the "long" nose found on most jets.

Anyone crack the code on converting ducted fan jets to seaplane? I am on my fourth modification of floats on a BD-5 (70mm motor) and am starting to doubt that this will ROW.
Hi IMHO EDFs dont have enought thrust to get a plane/jet Airborn from water, just to much water drag on the floats. and a BD-5 does not have very much wing area for lift off of water.

I may be getting Older, But I Refuse to grow Up I am Having to much Fun to Grow Up LOL
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Old 01-21-2013, 04:33 AM   #3
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I already have flights on my flying W / Capricorn with a 70mm EDF, ROW in about 10 ft. I think this can be done with many of the ducted fan jets like the Habu, Twister....anyone ever have any luck? I just have about 20 jets and plenty of water in my backyard (not much open fields)

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Old 01-21-2013, 04:38 AM   #4
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What might work, is to have one single float under the fuselage, and have the sides Tappered in steps so the drag is less as it lifts off

and have wing tip floats to balance out the plane, so with one float rather than 2 and small wing tip Floats for balance, it may work.


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Old 01-21-2013, 04:39 AM   #5
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Default BD-5

Here's what I have so far, pretty long float....


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Old 01-21-2013, 04:40 AM   #6
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Originally Posted by Alf_Geiger View Post
I already have flights on my flying W / Capricorn with a 70mm EDF, ROW in about 10 ft. I think this can be done with many of the ducted fan jets like the Habu, Twister....anyone ever have any luck? I just have about 20 jets and plenty of water in my backyard (not much open fields)

The Capricorn has a Huge wing area, so it will work on that, but jets dont have the Square inches in wing surface needed to lift off on water

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Old 01-21-2013, 04:44 AM   #7
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Default One float

That is a great idea Chellie, as you can see i already put the wingtip floats on (though I may have to make them a bit taller if I go with a single float.

I will try this one more time tomorrow with my two float mod and if that doesnt work will try the single....THANKS!

Maybe I should have tried this on my F-16 first, that jet is has a great fuselage (lifting body), very floaty. The BD-5 was picked because it was both an EDF and a glider kit, so I thought that the wingspan would give me some good lift.
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Old 01-21-2013, 04:45 AM   #8
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Originally Posted by Alf_Geiger View Post
That is a great idea Chellie, as you can see i already put the wingtip floats on (though I may have to make them a bit taller if I go with a single float.

I will try this one more time tomorrow with my two float mod and if that doesnt work will try the single....THANKS!
Good Luck to you Take care and have fun, Chellie

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Old 01-21-2013, 12:27 PM   #9
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Good luck with it but I suspect it will be a hard challenge because these very small EDF's tend to be quite marginal on thrust at the best of times. Adding extra drag/weight of floats then expecting the plane to RoW is a big ask... but I hope you pull it off.

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Old 01-22-2013, 01:02 AM   #10
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Alf, a few thoughts:
-Your floats appear to be mounted at a lower incidence than the currently favored guideline of 2-3 degrees positive wing incidence to the top of the float.
-The floats are subject to improvement in the shape of the bottom. A gentle curve will generate less drag in both wet and dry modes than the somewhat abrupt transition yours seem to have from nose to planing surface.
-looking down on each float, they will be less draggy if they are torpedo-shaped.
-another post suggested tapering in the sides.
-From the photo, I can't tell where your step is, but under a point at 40% of the mean Aerodynamic Chord has always worked well.
-making the bottom as slick as possible is a good plan. Sand it gently with a sanding block and 120 grit or finer sandpaper. You can get foam as smooth as the proverbial baby's butt. Then give it a glossy coat with epoxy or water-based polyurethane. A layer or 2 of 3/4 oz glass cloth will make it last a lot longer. Apply the WBPU with a roller and it will not be so prone to drag the cloth. Keep the step and the edges of the planing surface as sharp as you possibly can.
-some recommend toe-in to the floats, but my opinion is that anything other than parallel floats will increase drag.
-Watch the air inlets and be sure no water spray is getting into the fan. Water slows the fan and kills your thrust, right when you need it. I have not seen the BD5J model but I suspect there is a cheater duct in the bottom of the fuselage. If needed, Spray deflectors (chines) at the edges of the floats' bottoms will keep spray down AND they will add lift to the floats when you need it.
-Don't worry too much about the 75% rule for float length. That's for planes with tractor props and the most critical advantage that it provides is keeping the prop protected when beaching. Otherwise if the float is long enough to provide stable operation and each float is large enough to float the airplane you're good. If you choose to make 75% floats and put the steps of the floats at 50% of the floats' length and scoot the floats back so the step is in the right place, the plane will balance with less if any ballast and will also be more stable with less side area in front of the CG.
-Conventional airplanes have propblast over the control surfaces, so you can manipulate the plane's attitude from zero ground(water) speed. I suspect the BD5J is less sensitive to elevator initially but you may still gain some performance by starting the takeoff run with full up elevator. That tilts the thrustline and the wing incidence up, and any additional lift you can get helps the plane pop up on the step. Once the plane "humps" (technical word) over, relax the elevator and let the plane gain speed. Then gently ease the stick back for a takeoff.

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Old 01-22-2013, 01:32 AM   #11
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Excellent info, lots of tweaks to do, many thanks!
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Old 01-25-2013, 07:17 PM   #12
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Here ya go Alf . joe
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Old 01-25-2013, 11:48 PM   #13
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Thx for sharing the videos Joe! I bet they had to wash the heck out of that Sea Dart after flights to keep it from rusting!
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Old 01-25-2013, 11:55 PM   #14
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Originally Posted by Alf_Geiger View Post
Thx for sharing the videos Joe! I bet they had to wash the heck out of that Sea Dart after flights to keep it from rusting!
Yea alot of water flying up while he tried to get it on step with those skies.lol joe
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Old 01-26-2013, 01:29 AM   #15
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I got a great book on the Sea dart that includes a pilot's report on flying it. he said in the right water conditions at take off or landing, the vibrations transmitted up through the skis were so bad it was impossible to read the instruments!
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Old 01-26-2013, 01:39 AM   #16
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Originally Posted by Alf_Geiger View Post
I now live on the water and am in the process of converting all my planes with floats, been pretty good converting over the prop planes with floats but am struggling a bit with the ducted fan jets.

The fuselage on jets is quite long, using the guidelines for floats doesn't seem to work as the 75% length of the fuselage doesn't put the front of the float much past the "long" nose found on most jets.

Anyone crack the code on converting ducted fan jets to seaplane? I am on my fourth modification of floats on a BD-5 (70mm motor) and am starting to doubt that this will ROW.
Wonder what a shot of water will do to a plastic fan turning over at 35-40K RPM?

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Old 01-26-2013, 01:41 AM   #17
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Mine is coming along! Has anyone ever tried this with a ducted fan?
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Old 01-26-2013, 01:45 AM   #18
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Pic, I think I could mount a 64mm in there


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Old 01-26-2013, 01:46 AM   #19
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Originally Posted by Alf_Geiger View Post
Mine is coming along! Has anyone ever tried this with a ducted fan?
Have you considered a "Bungee" launch over the water? One of my club members made a bungee launcher with some PVC pipe, and a length of bungee cord. This thing really works well, and most club members are now using it, rather than hand launching those electric jets.

This thing will launch an electric jet for well over 100 feet, if you forget to turn on the motor.


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Old 01-26-2013, 01:48 AM   #20
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Kyle most of it would bypass the motor, I have dunked a few brushless motors in my brackish creek and they are still kicking! I also now put all my esc's and receivers in balloons after a small fire.

I like to have them take off from the water. I could likely hand launch them but that wouldn't be as much fun!
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Old 01-26-2013, 01:53 AM   #21
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Originally Posted by Alf_Geiger View Post
Kyle most of it would bypass the motor, I have dunked a few brushless motors in my brackish creek and they are still kicking! I also now put all my esc's and receivers in balloons after a small fire.

I like to have them take off from the water. I could likely hand launch them but that wouldn't be as much fun!
Never thought of a balloon for protecting the $$$$ electric stuff.

As you indicate, most quality motors can handle getting wet, if they are dried off quickly before you get rust. Running up the motor will dry it off very quickly.

The only concern is the quality of the ball bearing shaft seals.

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Old 01-27-2013, 05:27 PM   #22
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http://www.flyrc.com/index.php/category/plans/ The new moon is not a seaplane but it could be turned into one . The sea dart is here also both for another free download. joe
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Old 01-27-2013, 09:30 PM   #23
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Thanks RK, That new moon servo setup may not be too water friendly, that is one thing I didn't like about the Polaris as water can get in where the control rod goes into the fuselage (hull).

Painted my sea dart today in 30F weather, looks pretty lousy, I knew I should've painted it in the house! Bottom line, once it the air won't really be able to tell. This sea dart is going to be a prop, my next one I will try it as a ducted fan.
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Old 01-27-2013, 10:18 PM   #24
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Originally Posted by Alf_Geiger View Post
Thanks RK, That new moon servo setup may not be too water friendly, that is one thing I didn't like about the Polaris as water can get in where the control rod goes into the fuselage (hull).

Painted my sea dart today in 30F weather, looks pretty lousy, I knew I should've painted it in the house! Bottom line, once it the air won't really be able to tell. This sea dart is going to be a prop, my next one I will try it as a ducted fan.
The oringal polaris plans had the control rods inside the fuse but it was a pain in the ars with the ail tork rods so close together so he changed them for the kit. I built two of them the oringal way . Servos and control rods could be moved on the moon but dont get me started or i will build it myself. lol I have three scratch build's that i started and never finished waiting their turns while i put together a funcub they bought me for x-mas . joe
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Old 01-29-2013, 01:00 AM   #25
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My buddy Warren put a 70mm ducted fan on a little polaris. It went so fast it ripped the wings off. He rebuilt it in balsa-as a true delta, and it's an amazing airplane.

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