Canard design discussion.

[Simon.O.]

O.k here is the plan.
I want to build something a little different, as some of you know I like to do it a little differently anyway.
I have been looking at the idea of a canard and like it for a number of reasons.
Looks weird
Looks fast
Would be a nice challenge to design and build
Would be a real challenge to get it running well.
An inspiration for design is this one

http://www.hydromarine.de/hm_20895.htm

obviously mine will be “a little different”

Given the limited reading material that I have been able to find I see there seems to be two different ways of running these hulls.
It appears that the American approach it to run the front dry and the Europeans seem to load the front a little and fly the rear.
Have I got this right?

I am keen to go for a front on the water and fly the rear.
Basically I know that I can generate enough lift to easily fly 6-7 cells + 05 motor and associated bits. This is from the hydro that I have built, basically copy the front of the hydro to build the rear of the canard, then have a long slender body forward to a front riding surface.

Performance requirements:
Must float !! always a good start.
Must get up on its air cushion !!
Must go fast!! Yeah about that quick will be fine.

Am I nuts or is this a viable project.

[ED66677]

what looks strange on the H&M canard is the flat front of the hull, I would keep a very deep V style for the front as well as for the sponsons and use an airfoil between for lifting the back, using very deep V style would make it very penetrating and very efficient in rough water and the wings might help to regain some aerial comportment. just my thought
there's been a project for a world tour with such a hull design and someone posted a link about it here on OSE forum just the time for me to look for it...http://forums.offshoreelectrics.com/...ight=earthrace and web site is here http://www.earthrace.net

nice challenge though!

[Simon.O.]

Thanks for reply.
I agree that the H&M t'bolt looks a little flat in the nose and am looking at placing more volume in the bow area to prevent it digging in if any pitching occurs.
With the vee profiles, I found some pics of some big gas canards on the dutch forum and it appears that the sponson have a 30-40deg vee for the sponsons and a flat ride pad up front with 45 deg sides.

My initial thoughts are that as this is in effect a backwards rigger I see the rear sponsons hving a similar profile to my Cat with a shallow vee and flat ride pads and up the front to do a pad with angled sides like the big euro gassers.

I would like more pics of sucessfull euro canards particularly the bottoms if anyone has these.

More research, more sketching, more thinking.

Thanks.

[Tommy]

I would like more pics of sucessfull euro canards particularly the bottoms if anyone has these.

I think we'd all like to see more pics of euro bottoms.

Actually, I'd like to see pics of the bottom of canards, too. I've been toying around with building something similar for years now, and that's the part of the design that has foiled me thus far.

[G Doggett]

Great idea for a challenging project Simon.
The little info I have on canards points to the fact they must be as light as possible or they will not get up on plane.
The full size Circus Circus canard was a complete flop because it could never get going properly even with the same power as conventional hydros at the time, and many years ago one of our club members built the Circus canard as a 1/8 scale hydro and like its full size counterpart we could never get it to get up on plane.
It would go OK for a short while if it was given a throw launch, but if it slowed for any reason it would come off plane and bog down.
You might need the power of a brushless motor and the light weight of lipos.
Keep thinking outside the box mate !!!!
Graham.

[G Doggett]

[QUOTE=Tommy;43507]I think we'd all like to see more pics of euro bottoms.

but we might be on the wrong forum

Graham

[Simon.O.]

It appears that I will need a lot of lift to get this one to run right.
Fine ! That can be done.

Here is my take on the whole lift thing.
There are 3 types. Hydrodynamic, Aerodynamic, Pressure.

Hydrodynamic lift (HL)we are all familiar with and this should not need too much discussion.

Aerodynamic lift. (AL) To me this is the lift produced by a true wing such as on an aeroplane. The airfoil shape produces a lower pressure region on the upper surface and therefore the wing lifts. I am aware of something called wing in ground effect WIGE, but know little about it.

Pressure lift. (PL)
To me the difference between this one and AL is the way that the high pressure region is produced.
Take the typical tunnel / cat hull. Here we have a larger opening at the front than at the rear, as speed increases air is packed into the tunnel pressure increases and the hull is pushed upwards.

From here we can see why the traditional full bodied hydro has speed limitations and here the rigger takes over. Too much air into the tunnel due to speed will cause too much lift.

Here is where the whole thing can get a bit mixed up.
To get the pressure lift we need speed.
To get speed we need the hull up on the plane.
To get up on the plane we need lift.

This lift to get on the plane has to come from Hydrodynamic lift.
The front of my hydro has demonstrated this process for me.
Out of the hole the sponsons are very wet but air out as soon as the tunnel gets an airflow of say 20kmh. (an approximate figure ) It is very easy to see that the front of this boat is supported not just by the sponsons ride area but by the PL of the tunnel, easily shown by damming the tunnel.

So for a canard I need lots of lift ?
I intend to produce a lot of pressure lift by having the sponsons quite far apart. This will be a similar length to width ratio as a rigger but naturally the gap between the tub and sponsons will be a big tunnel roof.
I can supplement this by making this part of the boat an airfoil section to generate some true AL ( maybe ) I need to find out more about WIGE.

That will do for now, my brain hurts and I need more coffee.

[Simon.O.]

Over the last few days I have done a pile of test runs with my rigger and the shovel hydro.
I have spent hours reading about WIG, lift functions, drag profiles, thrust vectors, I have spent hours deriving my own formulae to work out lift functions.
My brain hurts

Enough !!

I have now decided to design and build one and run it to see what happens.

Here are a few pics of progress.

This is the closest that you will get to plans for my first Canard.
I have a few design keys to work off and then it is fill in the curves and lines.

I have cut out of card a couple of shapes to inspire the work, they are hung in the dark end of the workshop as silhouettes.

Pics of plans and cutouts.

[Tommy]

Looks like you're off to a great start. Keep us updated!

[Simon.O.]

The design is not set in concrete yet.
Here are some of the factors that are going into it.

My OB powered F1 tunnel produces enough lift to fly the whole hull such that it dances on the rear of the sponsons,
My hydro does the same with the sponsons only they are at the other end of the hull so to speak.
My Cat gets up and runs quite dry with a nice nose lift. Out of the hole is great and about 5-10m it will settle with the nose up running 20% of the sponson length on the water.
All 3 of these boats will do this with the 23t motor on 6 good cells and a 531 prop.
This prop gives very little lift if set neutral.

So where to we go from here.
I have measured the tunnels of each of these boats and taken a look at the tunnel entrance too.
No surprise that the Tunnel has the largest area of tunnel roof and the cat has the least.
This area is what the pressure lift acts upon to lift the hull to its riding position.

The proposed tunnel design for the canard has a greater surface area than the other boats and it is intended to have the same power system. This in theory will give me more lift. I do appreciate that lift induces drag but that is a small price to pay.
Given that I want it to fly the rear almost entirely dry and to run the front sponson in contact with the water I feel I am on the right track.

I have the ability to shift weight to get a CoB where it is needed. Where that is I am not sure yet thus the need for adjustment.
I have played with tunnel dams on the hydro so I know that I can reduce lift during development if necessary, I can remove this lift later if needed.

The wing section will go from tub to sponson with 1 or 2 degrees angle of incidence.
This will give me the AoA on the tunnel roof to produce the pressure lift.
It will be semi-symetrical in profile. My reason for this is that I need the slightly aggressive ramp at the front to assist packing the air into the tunnel.

I have taken Christian's advice and will ensure that the sponsons produce lift too.
My rigger sponsons are a proven design so many of their features will be used here.

[ED66677]

be carrefull if you play with airfoil between rear sponsons!!!
what speed will you try to achieve?
I'm not sure you really want to create lift with an airfoil (fly), airfoil lift is a negative pressure on the extrados (top) of a wing, the shape of the airfoil you will use, its angle and the speed will considerably affect lift and stability, if you use a semi-symetrical airfoil, it will certainly generate lift even at 0° angle, some well known airfoil like Clark Y still generate lift at -1 or -2° angle, the problem I'm seing here is that, assuming you will luckily choose the best airfoil for this particular application, as the airfoil generates lift, sponson's drag will reduce, speed will then increase, the result is that the airfoil will then generate more lift!!!

[Simon.O.]

ED your input is very valuable.
I like the idea of unloading the sponsons and the corresponding increase in speed.
Now as far as speed goes 30mph, 50kmh will be the target.
If I get that I will be very happy. Remember this is brushed and Ni cells power !!

IF there is too much wing lift either from the true Aerodynamic function or the forced pressure underneath then there are ways of reducing that lift without introducing more drag.
At this point I want to design in more lift than I think will be necessary.

This will most likely go the same way as my Hydro project. I built a prototype to use as a development test rig and worked from there.

I am confident that I now have enough information to begin a final design and indeed to start a build.

Keep the input coming guys. This is my most ambitious project so far !! but not the most ambitious I plan to do

[smm_cbf]

damn, thats mean lookin , great work so far

[ED66677]

use a very thin symetric airfoil (NACA) then, those used for airplane rudder or elevator don't really "fly" and this might be easier to generate pressure without any perturbating fly effect lift... just my 25 years in RC planes talking here!

[Simon.O.]

use a very thin symetric airfoil (NACA) then, those used for airplane rudder or elevator don't really "fly" and this might be easier to generate pressure without any perturbating fly effect lift...

After a day of researching foil shapes I do agree with your reasons here

just my 25 years in RC planes talking here!

I can not argue with that sort of experience !!

I have another idea.
Any excessive lift in the rear will be self regulating in that if the rear flies too high the prop will lose thrust and speed will come off. Naturally this would be a cyclic motion much the same as a rigger or hydro with too much positive set on the shaft angle causing tail skip, I have been there too, no fun !!

Given that any unusual pitch moments caused by this cyclic lift and fall will have all kinds of consequences on handling I think that it is best that I go for only a little too much lift and retain the ability to remove or reduce it as necessary.
I think that excessive lift designed in is going to cause too many headaches.

I am working on wing construction and attachment options at the moment so I am still a little away from begining a build. With the weather the way it is at the moment I think that there will be a lot of build time soon.........Excellent !!!