Simon's Canard.

[ED66677]

you have it now DXF1-400 and DXF2-400

[Simon.O.]

I had the Canard out again today. The “Spanish Armada” (Swans) was at the far end of the pond so I got a bit of peace and quiet to be able to run a few boats.
Further back you will recall that I had some issues with tracking straight and a little bit of high speed tail hop that looked liked vibration.
The “vibration” was established as being the prop releasing as lift became too high then biting again then releasing……….very fast.
This was sorted by placing the prop lower. How and why that worked I am still not 100% on and will not bore you all with a very long theory that I have.
At the same time the tracking has straightened up and the is now no longer a need for fins at the rear thus less drag = good !

I set the strut with a little up angle at the rear to loosen the front step.
It did !!!………………..but………………now this thing has an amazing motion at top speed that I will describe as a shimmy. It is a very fast oscillation of the bow left to right. It is only a small movement but it looks very weird and must be causing some performance loss.
I will attempt to overcome this by placing a small fin on the back of the front step to see if this dampens the motion. It will also assist in turns as at the moment it is a like a drift car when the power is on.
I have attached a small diagram to illustrate and summarise my findings so far.

[ED66677]

Simon any vid's one of these days?
It sounds like we may want to have a little V on the front step instead of a flat bottom, as well as sponsons bottom angle should be increased by 1 or 2° so that drift would be less sensitive to prop immersion level.
the drift you see is certainly the prop walk effect, having the prop deeper reduces the prop walk and everything you describe seems logical to me.
BTW an important point I noticed on your drafts and on the pictures you posted, the rear of the sponson may have a negative impact on the overall boat behavior, the angle shoud be pointing forward, that is the principle of the front step witch is at 90°, the angle you have tend to pull the sponson downward because of the way water flow, water has to brutaly separate from the sponson's bottom, that is something I modified on my drawings!

[Simon.O.]

Vids are a bit hard to get as I have enough dificulty driving and not hitting stuff without having to work a camera too. I can try with the camera sitting still. I'll have a go in the next few days and see what I can do.

The vee profile on the front step sound like a grand idea. I will temp fit a small fin and if this reduces or eliminates the shimmy effect then we will know that a fin is needed or a v profile.

Regarding the transom angle and water break-off. I took this design cue from the H&M Thunderbolt as to me it looks neat. Any pulling down effect that the water may have on this area I would imagine to be negligible, considering the demonstrated amount of lift from the wing and sponsons. Your point is noted however for my reference folder.

Again I believe that a small fin on the front step will 'kill two birds with one stone'.
Those being the drift and the shimmy, really this high speed wobble is quite funny to watch.

[ED66677]

Get a helmet and stick the cam to it!
I would not go for fins on the front step, because they would face the prop and generate perturbation inducing prop efficiency loss! just an idea!
What I also noticed is the strong curved surface on top of sponson, this may, at certain speed, generate aerodynamic lift, the more is it curved the more lift it generates at lower speed, this added to the wing angle, that may also generate aerodynamic lift can cause some sort of instability, I think avoiding aerodynamic lift creating ground effect is the key!

[Simon.O.]

Another day and another finding.
I tried a small fin on the rear of the front step in a effort to reduce or eliminate the high frequency yaw oscillations that occur.
This was not a success !
It appears that with the existing setup the hull runs on the back of the rear sponsons and the prop only, given that these are in very close proximity in a fore-aft dimension this is no surprise as there is very little longitudinal stability.

Take a look at a rigger. Front supporting sponsons and the prop 10”minimum aft of there.
Take a Canard with the front step running dry, the supporting sponsons and the prop are nearly in a line that is perpendicular to the direction of travel. With the front step on or out of the water there is no longitudinal yaw stability as with the rigger.

There are a numbers of ways to offset this effect. A fin on the front step may work, it did not for me.
Moving the prop aft will help but how far it needs to go is not something I am about to find out on this hull ! There may be another one coming
A vee profile on the front step in lieu of a fin to reduce yaw oscillation is in my opinion much the same thing: Drag generation to offset something that can be fixed elsewhere.
This is not a viable solution for me at this time.

I have now reset the strut to a previously untried position and will trial it in the next few days if the weather holds out.
It is very wet here at the moment and boating has to be a dash to the pond while a fine spell is upon us.

[ED66677]

how big was the fin on the front step?
on a rigger there are only 3 points, 2 sponsons and the prop while you have 4 on a canard, general mecanic basics says that for a proper stability 3 point is sufficient, 4 may be too much in certain case, now we are talking about something moving, dynamics here, and one important thing in general dynamics is the center of thrust COT as opposed to the center of gravity COG, I'm trying to make a parallel with rockets, I make water rocket myself, and the COT is far behind the COG, on a rocket if the COT is too close to the COG it gets unstable, if the COT is in front of the COG it gets over-stable, remove weight from the rocket's noze and the thing becomes really unstable, and trajectory is un predictable and might not even be straight!
Back to the canard, move the prop 80-100mm AFT, we're back at 10-12% that is commonly used on a mono!

[Simon.O.]

I understand that you have a very strong and demostrated engineering background. That will help us all.
I agree that 4 points of contact, unless balanced perfectly can be unstable. Look at a chair with one uneven leg for example. That is where where my canard is at the moment.

3 points of contact CAN be stable but there are issues with cornering as demonstrated by tricycle type vehicles. CoB comes in here too. I will leave the CoB issue alone as in regard to boats in general the CoB is more of a fore-aft measurement as opposed to a 3D vector that produces all kinds of handling issues for many other vehicles.

I think that to get the 4 points perfectly balanced would acheive amazing stability and speed, however given that the surface of the water is a moving fluid, this is going to be difficult.

I will aim for 3 points of hull in contact and then feed in a thrust vector that will naturally become a contact point and then we head back to the 4 point problem.

It all depends on which points the chair rocks on.

I will continue to push this Canard and will achieve something great:
Knowledge of how a Canard works and why or why not it is the greatest hull form to date.

Ingo Grimminger had one in mind when he went to the German SAW 2008

[ED66677]

I agree that 4 points of contact, unless balanced perfectly can be unstable. Look at a chair with one uneven leg for example. That is where where my canard is at the moment.

not really a chair is not moving, that's where Center of Thrust comes, IMHO it is too closed to you COG!

3 points of contact CAN be stable but there are issues with cornering as demonstrated by tricycle type vehicles

yes but COG is very high compared to a rigger, so it tend to flip on the ouside of a turn!

Give it a try, move the prop 80mm in the back!

[ED66677]

Simons,
look at this one a french guy who did it, he got to the conclusion that above 80Km/h such a boat do not need wings, at least with very few lift or it tend to be unstable!
this one is German

[Simon.O.]

ED that first one is an Australian one if I am not mistaken. He is 785Boats from RCG. I have seen that one before and it gave me a few good design clues.
Here http://www.rcgroups.com/forums/showthread.php?t=789287
The German one is nothing less than beautiful.
It is interesting to note that both have their prop close to the rear spnson line.

In saying that I do tend to agree with you that it is worth setting the prop back to seek more stability. This will also stop the boat going nose up when I hit the power from a standstill, which actually looks realy good. !!

I will trial a few more prop positions tomorrow as we have a storm here today.
While it is a workshop day I will make a new strut that will put the prop further back.

This is deffo the most challenging hull to setup so far. In comparison riggers are easy.

[Dr. Jet]

Keep working away on it Simon. I have a BBY MTH to build, and by the time that is done, you should have all the major issues worked out. Then we can talk about the 400 mm version. Ed's drawings are a good start.

[peells]

So have you tried putting turn fins at the back of the sponsons? or maybe a skeg somewhere at the lower 1/2 of the main body? Is your prop balanced? try a slight down angle on your prop and easing the throttle on.

[peells]

I just thought of something else, your battery position, try moving it forward or back, I found that by having someone video your run you can try and drive some laps and then watch the videos closely to see what is actually happening rather than try and analyze while your driving, just start by taking some easy laps then go faster until you get to top speed I hope this helps.

[Simon.O.]

So have you tried putting turn fins at the back of the sponsons? or maybe a skeg somewhere at the lower 1/2 of the main body?

I have had fins on the sponson rears that did have an effect. The front mounted one was not the best. I now know why.

Is your prop balanced? try a slight down angle on your prop and easing the throttle on.

Balanced ?? It is a plastic Octura 531 that I beleive needs no balancing. Down thrust at the strut is a hoot as the back end gets real lively.

I just thought of something else, your battery position, try moving it forward or back, just start by taking some easy laps then go faster until you get to top speed I hope this helps.

There is very little room to move the pack in this hull. I am very lucky that the CoB appears to be in the right place so far. I have one other isssue that needs to be addressed first.
Easy laps ???? Where is the fun in that??? for me it is Wot or not !!!

Don't panic Peter, I do take your advice seriously and hope to get this thing really screaming soon.

I just need to get a FM radio now.