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A boat that flies!!

The original Hydro-Foam

by Michael Connally



I've built my own version. It's called a 'Hydro-Fly',
since Mike Connally, the originator of
this idea calls his creation a 'Hydro-Foam'

I guy in the Netherlands (Prop-er) came up with a free plan

The PDF-file can be downloaded here

And here it is in DXF format


3mm Depron now available
in South Africa from:




Suppliers of Hydro Kits

South Africa Mad Models Sells the Jomari Hydro
USA Hangar One Hobbies Sells the Miss Hangar One Hydro
United Kingdom Robotbirds.com Sells the Piranha Hydro
Germany Jomari Manufactures the Jomari Hydro


Scroll down, to see what my own
Hydroplane looks like...


When I build my next Hydro...
I'll make the following changes
Make the deck longer. The width is ok, but I'll extend the deck forward about 50 - 60mm.
Maybe make the sponsons (floats) a little shallower.
Move the fins closer together in order to get more propwash over them. Increase the size of the rudders and possibly install a central fin and rudder. This would make the linkages easier too, as you could link the 2 side rudders from the middle one.
 Add diagonal bracing to the fins (2mm carbon rod). This is essential. Increase the lower elevon width to approx. 55 - 60mm. Use Kokam 740HD LiPo's. They are 20C (14.8A) cells and a 3S pack weighs only 60g.


Important points + hints & tips
The CG is about 60mm from the LE on the free plan. That's only 16% of the chord and is probably due to the sponsons acting as lifting surfaces.
The motor should have zero-zero thrust angles.
Do not fly with the lower elevons alone. The deflections needed are too severe then.
With dual-elevons (top and bottom), the control surface movements should be minimal otherwise they are much too sensitive (use lots of exponential). Found that out the hard way (crunch).
It's best to use 1.5mm or 2mm carbon rod with heat shrink tubing for the hinges when inter-connecting the rudders and elevons.


Specifications of the original Hydro-Foam (Red one in the video)
Length: Approx. 660mm (10% bigger than the free plan)
Weight: 270g
Thrust: 396g with 7x3.5 GWS prop @ 10 - 12A
Motor: DIY CD-ROM motor - 22.7mm stator, 12 turns 0.5mm wire, N50 5x5x1 magnets
Battery: Etec 700mA/h LiPo, 3S pack
ESC: Castle Creations Phoenix 10A with max. timing
Servo's: 6 Gram, 2 for elevons, 1 for rudder

I built my hydro from the free plan.
This is how it came together...

Friday, 24 June 2005

The starboard sponson built, with
the parts of the port sponson shown
in the background.

The second sponson half built.

With both sponsons completed,
the weight is 58g.
The black lines are carbon fibre
strips epoxied top and bottom to
stop flexing of the 2.7mm Depron.

The intended power source -
a CD-ROM motor (20mm)
with 3-cell 700mA/h LiPo pack.
With the Gunther prop it gives 
300g thrust at 8A.

Saturday, 25 June 2005

The canopy top added.
Canopy still needs splash proof
bottom half where the battery
and electronics will be housed.

The canopy was hollowed
out to save weight. The front
part was left solid - that's
where the battery sits.

Saturday, 2 July 2005

The sponsons were painted with
Testors enamel spray. It doesn't
damage the Depron and has a
nice, smooth finish.

Surprisingly, the enamel spray
added only 4g to the total weight.
This view also shows the 20mm
CD-ROM motor, 10A Hyperion ESC
and 7x3 GWS prop.

The control linkages are 1mm
piano wire running in thin
Graupner plastic sleeving.

The motor mount was made
from 2mm ply. It is recessed
into the solid foam canopy.

Sunday, 3 July 2005

Almost finished - just needs
some paint on top and a splash
guard underneath, but since it's
my flying day, that can wait.

She flies!  I went to White Hills Radio Flyers today and flew it off the grass. There is a tendency to turn left (same as a full scale hydro plane, I believe).

As I put the Hydro-Fly down onto the grass,
I got a few puzzled stares from fellow club members. I just smiled and opened the throttle. She jumped forward. Picking up speed easily, my boat skimmed the short grass and with a little bit of elevator she was airborne...

...and this is what a full size hydroplane looks like

A really nice picture.
I just had to share it.

A full size hydro at speed.
If it flies any higher than this, the
pilot starts sweating a lot more
than usual.

Even the big ones get damaged.
See the interesting sponson design.
It's a lot shallower than on the model.

This view shows how thin those
sponsons really are.





I post as Skylar on RCGroups.com
and also on


  E-mail: Christo van der Merwe   ---   Skype name: Christo1636