Scratchbuilt Canard Hydro

[VeloceHydro]

Hi everyone,
I'm new to this forum, and I've just recently finished building my own design canard hydro,
so I thought some of you might be interested in having a look.
Its an idea I've been toying with for some time, as there are not that many canards out there,
and I'm just fascinated with the challenges that arise in trying to get them to run properly.
I believe these designs have a lot of potential if they can be setup and tweaked correctly.
I know there has been a couple of other experienced builders on this forum, and others,
that have tried going down the canard hydro route in the past, with varying degrees of success.
I only wish I had read all their posts before I started building this design...It would've saved me
some serious head-scratching on certain aspects of the hydro-dynamics involved in trying to push a rear-sponsoned, twitchy, loose-running lump of ply, balsa and foam fast across the water!!
I'll list the basic specs of the boat first, then I'll go into some of the little ideosyncrasies it has
shown when asked to do some fundamental boat-like things such as...turning left or right!

Length - 27''
Beam - 18''
Weight - 2kg
Hull material - Lite-ply, balsa, foam, carbon tube, solid pine, Depron.
Sponson angles - 4 deg on rear with 5mm step halfway and 2.5 deg deadrise. 3 deg on front with shallow V with flush water pick-up incorporated in ride pad.
Motor - 3674 540XL 2770kv (cheapo Chinese type)
ESC - Hobbywing Pentium 80 - 100 amp (with home-made water-cooled ally plate).
Lipo - 3S 4500mAh Turnigy Nano-Tech (with 4mm bullets).
Driveline - 1/16'' (0.062'') piano wire thro solid brass stuffing tube, turning a 4mm threaded steel
propshaft, running in 2 off 4mm x 8mm x 8mm needle races in the strut.
Props - various, from 35mm plastic Graupners up to PropShop 3714/3 and 4014 and 3816/3
bronze/beryliums....still experimenting of course.
Speed - early to mid 40's depending on prop...tho' these are 'guesstimates' as I have no gps.

This canard hydro...I've named it 'Cyclops' by the way...had it's maiden outing on Ruislip Lido
a couple of weeks back....flat calm water inshore...bit choppier further out where the wind was.
I didn't know what to expect with this scratch-built, so I started with a 35mm plastic prop to give myself and the motor/esc/Lipo, an easy time of it till I saw how it handled.
Well, I was pleasantly suprised when it immediately got up on the plane and shot off like that
stuff that comes off a chrome shovel! Before I knew it, It was screaming halfway across the Lido and out into the choppier water I initially wanted to stay clear of. So I backed off the throttle a bit and fed in some right rudder to bring it back...it didn't like that at all!...loads of cavitation, very reluctant to turn, bled a lot of speed off and came off the plane. Managed to turn it round in displacement mode by jigging the throttle with full rudder till it was pointing back at me...then I wellied it again...it snapped up on the plane once more and I let it run towards me, I noticed then
a bit of prop-walk happening with a slight, general veer to the right, and a high rate of what I would call 'chattering' or bouncing at the rear sponsons, as if the prop was trying to find a good 'bite' with the water. Prop needs some more depth I thought...or a bigger prop. To cut a long story
short, this canard hydro loves to go fast in a straight line...it will only turn (left or right) when at full wot, and then only in a wide scary arc. I figured the rudder area was too small,
so I knocked up a larger, deeper one from some aircraft grade ally sheet and tried that...the original rudder hardware I made was the central in-line type like you find on cats...this larger one worked a bit better with turning a bit more positive than before, but any more than 10 deg either way caused loads of cavitation and consequent loss of drive and speed. I finally had to redesign the rudder to a twin setup when, one time I was giving it wot with the 37mm prop on mirror flat calm when the rear lifted right up and in the blink of an eye, it submarined completely, reappearing about 7 feet away inverted!
When I retrieved it, I found the rudder had bent to such an angle, it had acted like a foil and
lifted the whole rear end when I had tried to turn it. I obviously had completely underestimated
the force a medium such as water has on something like a rudder, when it's travelling through it
at 40 mph+. If you take a look at the pics, you can see I've gone a bit on the...'erm... 'agricultural' side when fitting the new twin rudder design! I haven't tested these twin rudders yet...my thinking was to get the rudder out of way of the prop wash/rooster tail and hopefully stop or minimise the cavitation when turning. The original in-line rudder was quite close to the prop
anyway...and I believe this was part of the problem, 'sprayback' from the rudder face interfering with the 'cone' from the prop. This happens regardless the size of prop I put on, or what depth or angle I set the strut at.
If anyone has any ideas I could try out, I would welcome any comments, suggestions or advice.
Many thanks for reading...sorry it's a bit long and rambling for a first post!

VeloceHydro

[drwayne]

Hydros without turn fins have equally poor turning
Use a single rhs offset rudder, and place a turn fin on the inside front edge the RHS sponson. ( when facing fwd )
Works well on mine

I do enjoy scratch builds with a difference.. out of the box thinking.

W

[VeloceHydro]

Thanks drwayne,
Funny you should say that, I've got a couple of turn fins made up already from ally sheet, ready to go on the inside of each rear sponson if they are really needed. I was hoping that my new bigger, deeper running twin fins might obviate the need for dedicated turnfins that will no doubt create more drag.
As this boat is more of a 'prototype/proof-of-concept' experimental, sporty runabout kinda thing,
and not for racing competition, I'm just looking for equal ability in turning left or right.
I'm actually getting to quite like the cool way it 'drifts' like a rally car at max throttle when
I ask it to change direction... a bit un-nerving though!

[Fluid]

Part of the problem is the choice of prop. My canards did not like lifting props, exhibiting the "chattering" you describe. I had to de-lift them or better yet use Octura "X" series or Prather props. These settled the boat down, helped turning and increased the speed once I settled on the prop the boat/motor liked.

Properly designed canards do not need a turn fin. They rely on the front sponson to provide the pivot on which to turn. Your front sponson is too large and flat bottomed, floating over the water in a turn rather than digging in. Put the turn fin on the front sponson, or re-configure the latter with some side resistance. A bottom mod like on the canard below would be easy.

[Larger]

@ Fluid, can you post more pics from your Canard?

Heiko

[VeloceHydro]

Hi Fluid,
Yes, I see in your pic that there is now a 'ramp' over your front V, giving I guess, around 5 or 6mm sides or 'strakes' that can
get purchase on the water in a turn. This could be done quite easily. I've been talking with a couple of the regulars over
on RCG who have built and run their own canards, and they say the same thing. The front sponson should be very light on the
straights, almost in the air and hardly touching the water at all, then it comes down wet in the turn, helping to 'hook' the boat round,
and then back up in the air for the straight again....and I'm thinking...that's exactly what a tunnel hull does in a circuit round the bouys!
They must be very similar in setup...canard hydros and tunnel hulls. Both have a rearward CoG, and the prop situated close between
the two rear weight- bearing sponsons. Just a thought!
I agree with you on the correct prop choice. A non-lifting prop I think would be essential...having a large wing at the rear like I have on my canard, it would be contributing a substantial amount of lift on it's own at full wot, without making matters worse getting the extra lift as well from a heavily cupped hydro prop...it would probably just take off and become an airplane!

Mucho Regards,
VH

[Larger]

i think, a canard must run on the frontsponson and straighjt, the rearsponsons are in air. Only in an turn, the inside sponson have contact with water . This canard is 45cm long, ruins with 3s Lipo 2200mAh and a little Lehner with 4900U/V, and a Octura X431 86km/h at the german saw 2010

Heiko