New High Performance Monofoilers

[bistros]

Originally Posted by Doug Lord

Thanks,Rick. I just can't get the picture in my head of what he is actually doing. The only picture there is of his intial testing doesn't seem to show a forward rudder. Seems to show a "conventional" Moth configuration with a bow wand:

Jeez, Doug how about writing a letter to Julian Bethwaite and asking? His email address is really easy to find - took me all of three seconds.

You aren't going to have much success trying to get him to respond on web forums, as he doesn't actively participate. Julian tends to only post to quiet rumors and misinformation.

Julian came up to the Ottawa Skiff Grand Prix three or four years ago - he was a really nice approachable guy. I expect he'd respond if you are polite and to the point with your request.

Cheers,

Bill

I'm hoping he might respond here( I PM'd him on SA) as he already is posting on Sailing Anarchy.

PM received from Julian today:
"Doug,
Your welcome to quote me

Re Moths, I find them frustrating and fascinating.

If you go to any high end models where they have been at this for the last 100 years you find the majority are Tractors (control surface behind the main lift surface) and the control surface is quite small, 28-29% of the main surface.

With the moth, not only do you have the control surface as the main lifting surface, but you have a huge stabilising surface, aft, upwards of 70% of the main lifting surface.

Its pretty easy to do the sums so we know the CoL they are running and the load they are running.

We would like to tow them full size and get some real CoD numbers and may do that very shortly. Scott Babage is a very old friend as in John Harris, both of their boats are within 200m of my office.

Hencce my comment that they are quasi Canards!

We have progressed 150 pages of data and probably 10 variants since the SeaHorse photos.

We are now busy getting a sailing variant ready for a run.

if you tell me how to do it I will attach a photo,

Julian "

[markdrela]

Originally Posted by Doug Lord

A guy who races Moths(Bora Buglari) said ,on SA, that he sails with up to 70% of the all up weight on the rear foil and also called the Moth a "canard" configuration. His comments were contradicted by another experienced Mothie.
The Main foil on the Moth is larger than the rudder foil(elevator)-is there anyway to define that configuration as a canard?

This is an argument only about labels and definitions. In airplanes, there is no sharp boundary between a conventional, tandem, and canard configuration. See the attached PDF. The configuration smoothly morphs from tailless, to conventional, to tandem, to canard, and back to the tailless.

To first order, the main requirement for pitch stability is that the front surface must have a larger CL than the rear surface, so a "conventional" configuration can easily have an upward load on the tail and still be stable, provided the tail is big enough (say at S_rear/S_front = 0.3 on the plot), and the airfoil Cm is not too negative.

This simple surface-CL stability rule doesn't apply to a hydrofoil with one or more wand-controlled surfaces. But the issue of whether a configuration is a canard or not is still just a matter of labeling.

Thanks very much,Mark-helps a lot.

[alans]

Originally Posted by markdrela

This is an argument only about labels and definitions. In airplanes, there is no sharp boundary between a conventional, tandem, and canard configuration. See the attached PDF. The configuration smoothly morphs from tailless, to conventional, to tandem, to canard, and back to the tailless.

To first order, the main requirement for pitch stability is that the front surface must have a larger CL than the rear surface, so a "conventional" configuration can easily have an upward load on the tail and still be stable, provided the tail is big enough (say at S_rear/S_front = 0.3 on the plot), and the airfoil Cm is not too negative.

This simple surface-CL stability rule doesn't apply to a hydrofoil with one or more wand-controlled surfaces. But the issue of whether a configuration is a canard or not is still just a matter of labeling.

Mark your statements are true for aircraft that do not have their stability augmented with "auto pilot" gearings. The static margin analogy would apply to a foiler were the centre of thrust close to the centre of drag. The large bow down monent created by the sail CofP being well seperated from the foils necessitates the CofG being well aft of the nuetral point (NP as shown in your PDF). Stability can be reestablished, as demonstrated, by the helmsman throught an elevator as we did with David Lugg's int 14 or with a mechanical autopilot likage from a wand to flap. This latter proves to be extremely effective as this stability augmention improves the effective static margin by about 6 or 7 feet. It seems that at high speeds it is acceptable (stability wise) to move the CofG that far aft that you are sailing with a cL on the rear foil 3 times that of the front foil. However best performance will usually be achieved when the cL's of both foils are equal.

alan

[alans]

Originally Posted by Doug Lord

PM received from Julian today:
"Doug,
Your welcome to quote me

Re Moths, I find them frustrating and fascinating.

If you go to any high end models where they have been at this for the last 100 years you find the majority are Tractors (control surface behind the main lift surface) and the control surface is quite small, 28-29% of the main surface.

With the moth, not only do you have the control surface as the main lifting surface, but you have a huge stabilising surface, aft, upwards of 70% of the main lifting surface.

Its pretty easy to do the sums so we know the CoL they are running and the load they are running.

We would like to tow them full size and get some real CoD numbers and may do that very shortly. Scott Babage is a very old friend as in John Harris, both of their boats are within 200m of my office.

Hencce my comment that they are quasi Canards!

We have progressed 150 pages of data and probably 10 variants since the SeaHorse photos.

We are now busy getting a sailing variant ready for a run.

if you tell me how to do it I will attach a photo,

Julian "

Canard will work OK the 11 foot model in the attached video is being towed from the top of the mast at about 60 degrees from its track

Alan, what caused the pitch up toward the end of the video? Have you done a RC version with a rig? Damn good looking boat!

[alans]

Doug

As soon as the tow line is released the bow rises before the front foil can respond and then with the drop in speed she sinks back into the water. No we are yet to sail her. The towing tests were the main aim of the test program to demonstrate that splayed main foils (30 degrees) worked without lateral problems. The configuration makes vertually no leeway and therefore minimizes ventilation problems.

alan

[bgulari]

Bora Gulari

Here is video of sailing at the back of the bus with the main trimmed in hard

http://www.youtube.com/watch?v=QH9iXgh3fpA

Sorry about that! Corrected...

[alans]

Originally Posted by bgulari

Bora Gulari

Here is video of sailing at the back of the bus with the main trimmed in hard

http://www.youtube.com/watch?v=QH9iXgh3fpA

Bora

A great bit of footage. I sailed 14's from the "rock" for nearly 20 years and we used to sail that same track many time just for fun, some times at 20 knots. I guess you were doing about 25. Do you know what speed you were actually doing? Having watched your video across water I know like the back of my hand I think the two man boat two on trap was more challenging and more fun!

[sigurd]

Ancient Kayaker:

I got to admit I was as confused as S2 was. I guess if the real monofoiler ever shows up we will just have to call it the unifoiler. Of course it might turn out to have a perfectly good French name!

Jon Howes has made something he calls a monofoil. It has only one foil in the water. Very nice craft. I agree with you it could become confusing to call a monohull bifoiler a monofoiler.

When a thread gets to this point I just quit.

'bye

In case you are still reading: I hear you can put particular members on "ignore" in this forum - I have not tried it, I usually just scroll past the posts written by members who are always just antagonising.
edit: no, sorry, I cannot find any such "ignore" function. anyway the scrolling works fine for me

[bistros]

Originally Posted by sigurd

Ancient Kayaker:
In case you are still reading: I hear you can put particular members on "ignore" in this forum - I have not tried it, I usually just scroll past the posts written by members who are always just antagonising.
edit: no, sorry, I cannot find any such "ignore" function. anyway the scrolling works fine for me

If you go into the Member's List area above, search for a member and select their profile, there will be two options in about the middle of your screen - Add to Your Buddy List - and - Add this user to your Ignore List.

Just click on the "Ignore List" option and then click on "Save List". Presto - their posts will be marked: "You have chosen to ignore <username>".

Click here to ignore me. Once you have a URL to ignore someone, you can use the URL like any other link.

--
Bill

[sigurd]

thanks!