Space frames for main beams

[robherc]

Originally Posted by Gary Baigent

Chris, those high powered boats (cats/hydroplanes?) are really wing in ground effect designs (WIIG)

Are you sure, WIIG uses a LIFTING airfoil, but last I heard these thing use DOWNTHRUST airfoils, to keep the "boats" from flying up & doing flips. (similar to the F1 cars mentioned earlier in this thread)

Originally Posted by Petros

BDW,

Why would putting the mast forward increase the chance of pitch-poling? Pitch-poling is a function of the height of the aerodynamic center (or as sailer's call it, the center of effort) above the water, and volume of the bows, and your counterbalancing load (size and location). The location of the mast does not enter into it unless you have an especially heavy rig (which I do not). I intend to the have crew compartments in the hulls as far aft as possible to counter balance the pitch-pole tendency, and with the foil planes up front the bows should not dive.

Freenacin,

Space frames may not be cheaper, in fact they could be one of the most costly way to build a structure, what they do is save material costs. Many production aircraft abandon it because of the very high labor costs, and as you know many production compromises are made to save manufacturing cost (though there are many sub-assemblies where they are used, like in engine mounts, landing gear, etc.) But you still see it used in in ultralight and other homebuilt aircraft, and in many modern aerobatic aircraft (hand built), and in building structures such as roof and floor trusses (where assembly jigs save labor), and also you saw them in the Gossamer Albatross and Condor, where extreme weight savings was critical. You will see them used in tower structures and bridges (though in highway bridges recent regulations have made them no longer economically viable). You also see them used in modern folding kayaks since a frame will fold down to a much smaller package.

Besides, in boats, cars and aircraft you need a smooth outer skin of a certain shape, and if the shape carries loads as in a hull, the weight savings become somewhat less, you may be as well off with a rigid structural skin.

====================
Have you heard of Mirabaud? It is a monohull foiler with the entire structure made of carbon tubes. The 26' hull was cut from a cat hull and is just a shell.
I've talked to Thomas Jundt,the developer and one thing they have considered is fabric skins down the line.
As to foils: the boat has to be very carefully designed or there will be little if any gain. Cats,so far, have not been ideal foil platforms for sailing -monohulls and tri's seem better suited.
http://www2.jundt.ch/blog/

[Chris Ostlind]

Originally Posted by robherc

... I don't know about the "efficiency" of a planing surface at those speeds, but I am quite sure that a planing surface with as little surface area as those foils would be too unstable to manage. (and one with 1/2 the wetted surface would be nothing short of suicidal)

Above is the portion of the post to which I was responding. There are very clear examples of planing craft (and these are planing craft whenever their hulls touch the surface at any speed beyond a slow crawl) in response to the posted comment.

I used to photograph these boats as a part of my photography career back in the seventies along with cars and motorcycles and have spent a very long time watching how they work at different speeds around a course. I get that they utilize WIIG technology for a good deal of their ability to attain such high velocities, but at much of the lower speeds, which they do see frequently in a race, they are purely planing.

The foil in the water from the port hull form is specifically to hold the boat when they turn left. Without the fin, they would quickly skate away into the bank of the river, or do a rather spectacular capsize flip as the starboard hull caught an edge. When you see great amounts of spray off the transom, it's all because that part of the boat is riding on the surface. If they were totally supported as WIIG craft, then the disturbance would be limited to pure prop effect and nothing more.

When they are doing their taxi out to and back from the course, there is a lot of wetted surface, as has been suggested. However, the same is true for Hydrop whenever it is off the foils, so I truly do not see the point of that particular comment.

The photos illustrate that absolute minimal planing surface contact at quite outrageous speeds is not only safe, but it is well within the realm of a properly handled craft. Not only do they go in straight lines, but they make 180 degree turns on a race course while changing lines for competitive purposes. You can’t maintain that kind of handling at speed from a relentlessly evil boat.

The underbody provides the lift on these boats in the fashion that Gary indicated and they do have downforce surfaces in order to keep the boat in balance while under way. The downforce foils (especially the forward surface in front of the cockpit) on many of the boats can be tuned while underway in order to adjust the proper force for different speeds. These are very complex craft to operate, much like Hydrop. The reward, just like Hydrop, is a maximization of available power when compared to the minimization of the drag signature.

Perhaps a relaxing of the thoughts on the topic would allow for the consideration of the technology as it applies to the conversation. I get that engine driven boats are not for everyone and these are particularly powerful engines, but many of the same issues are present, albeit at much greater speeds.

There's a reason why they are called "HYDROPLANES" and not HydroWIIG's, or Hydrofoils.

And yes, Rob.... they do occasionally crash, as does Hydrop and all high end racing machines of every kind. Sadly, it's really the only way to find out just where the limits exist for any particular setup and the boys (and some gals) are pushing the envelope whenever they can. There's no such thing as a successful race driver who practices consistent, conservative tactics. If taking it slow is one's MO, then that driver is quickly shown the door and thanked for their time.

Originally Posted by robherc

The end result of this thinking (so far) is embodied in the "ladder foil"design, which is used in l'Hydroptere; with multiple, small foils mounted at different heights along a trunk, you get a good balance of lift/speed. Once you reach a high enough speed that your foils are producing to much lift, one or more foil sections get flown out of the water, and the rest below them are now providing just the right amount of lift. I'm not saying that ladder-foils are perfect, though, just trying to illustrate the technology as it stands today; there is ALWAYS room for visionaries to advance the science!

==================
Just a heads up: Hydroptere uses two surface piercing foils forward and an inverted T foil on the rudder. The two main(surface piercing) foils are not "ladder foils" but are single tapered foils with fences along the span to prevent ventilation.
-See the picture below of the Baker/Navy Monitor-the first sailing monofoiler. Note that it has ladder foils.

[robherc]

Interesting Doug..I hadn't translated the site yet (my French is a bit fuzzy), and was going based on visual observation of the foils & the craft in motion...looked like ladder-foils to me (and yes, I did notice that they were angled like surface-piercers, and I saw that the rudder was an inverted "T" as well, but it doesn't seem to be suppoerting much weight...primarily just steering & maintaining attitude, I think.

[Chris Ostlind]

Originally Posted by robherc

... and I saw that the rudder was an inverted "T" as well, but it doesn't seem to be supporting much weight...primarily just steering & maintaining attitude, I think.

When you look at this photo below, how much of the weight do you think it supports, considering that the entire starboard foil is clear of the water?

Lots to learn here, to be sure.

[sailor2]

Originally Posted by robherc

I think you're missing the increased lower-surface pressure on the foil due to deflection (i.e. Angle of Attack) forcing the water beneath the foil down. Hydrofoils don't ONLY generate force through Bernouli's principle, they also develop force through deflection, similarly to the planing hull.

First all the lift created is due to pressure difference due to Bernoulli principle AND at the same time all the lift is due to deflecting mass of water (or air) down as Newton's laws require.
These are just 2 different ways to discribe it, you cannot add those effects up.
Also the high pressure on lower surface is limited by sum of ambient pressure at some depth below surface + dynamic pressure. This is equally valid for both foils and planing surfaces. At the max pressure the speed of water flow is brought down to zero related to the surface, also called as stagnation pressure. There is no way to exceed that limit. And at high speeds both foils and planing surface can be reasonably close to that condition. (less than 50% off at average pressure on lower surface) That means same platform areas produce same max force on lower surface. No advantages on either foils or planing surfaces. But since planing surface has less than 50% wetted area, the foil would need same pressure difference between ambient preesure and upper surface pressure to compensate. This is not possible at high speeds when it requires negative absolute pressures. Therefore max CL available drops in those conditions as cavitation limit hits in.
When a foil is operating at low speeds and optimum L/D the suction side has typically 2-times the pressure difference related to ambient compared to the high pressure side (=lower surface on foils) At high speeds the cavitation pressure limit reverses the situation and L/D drops.

Lets try an example:
speed 50 m/s, dynamic pressure=1275 kiloPascals = 13 atm.
If the foil is just 1m below surface the ambient pressure is 1.1 atm
Max pressure at stagnation is 14.1 atm and minimum practical pressure near cavitation 0.1 atm. Max peak pressure difference for foil is therefore 14 atm.
High pressure side produces 13 atm and low pressure side (top surface) just 1 atm or just 7% of total. Clearly much less than typical 67% at slower speeds.
If the average pressure difference for the foil is 10 atm, then Cl can be calculated as 10atm/13atm = 0.77 To produce the same lift force the planing surface with twice the planform area only would need 5atm pressure difference over ambient 1atm at the surface. In practise it can have at least 8atm allowing less area and less wetted area as a result.

Originally Posted by robherc

Therefore, as long as the foil is deep enough in the water that no air is trailing down to it and enigneered/adjusted so that it isn't vac-boiling the water (thus creating its own cavitation & stalling), I still think they can develop more lift/area AND more lift/drag than a planing hull.

If you meant planform area then no problems with L/area at those assumptions (=below speeds cavitation effects take place) however if you meant wetted area, you need more than double Cl due to less than double planform area. That's possible with limited range of speeds above low RE-numbers and below cavitation limits, but there are no guarentees on that. Also better L/D at the same time is a lot to ask for, not too sure that's possible but can't prove otherwise either.
Skip the lift/area requirement and only use beter L/D and it becomes much easier task for the foil at the same limited range of speeds.

Originally Posted by robherc

Question:
If, by your explanation above, all foils at <10m depth will experience cavitation issues at or near 20m/s, how then do you explain l'Hydroptere's ability to use VERY shallow (less than 2m when flying) foils to maintain lift/stability while traveling at 60+ knots (39+ m/s)?

Because they don't try to use max Cl for minimum area to produce required lift force. As a result they have more wetted area than optimum planing surface would have. Instead they consentrate on best L/D and select areas whatever is most suitable for that taking cavitation issues very seriously.
Further more old YPE (Yellow pages Endevour) used planing surfaces and acheaved beter Vboat / Truewind ratios than hydroptere does. Same for the newer version. That's a good indication on L/D differencies.

Like I alredy said the real advantage of foils over planing is when they have to cope with some seaway. No sailing planing craft is likely to compete with Hydroptere in such case succesfully.
Hydroptere also adjusts it wetted area with different speeds and is closer to optimum than planing surface is likely to have with same requirements on wide speed range. But at optimum operating point it loses on optimized planing craft like YPE on L/D.

[robherc]

Originally Posted by Chris Ostlind

When you look at this photo below, how much of the weight do you think it supports, considering that the entire starboard foil is clear of the water?

Lots to learn here, to be sure.

I'd say (in that picture, at least) that the vast majority of l'Hydroptere's weight appears to be supported by the larger-immersed section of the port foil. Considering the forward-high (bows down, stern up) moment of the sails & the lack of excessive trim, I don't think the rudder foil could be supporting a very high percentage of all-up weight, without causing the whole craft to pitchpole. It could be supporting more weight than I'm realizing, though, but I'm betting that the vast majority of lift (and ALL of the compensation for the lifted starboard foil) is coming from that deeply immersed port foil.
If the rudder foil were supporting any more weight with the starboard foil flying than with both forward foils immersed, then there would be a notable difference in the craft's pitch when this happens, and I haven't seen that happen in any of their videos, nor in this picture (think of the balance issues that would cause).

[robherc]

Originally Posted by sailor2

First all the lift created is due to pressure difference due to Bernoulli principle AND at the same time all the lift is due to deflecting mass of water (or air) down as Newton's laws require.
These are just 2 different ways to discribe it, you cannot add those effects up.

Bernoulli principle: Moving fluid (air/water/whatever) exerts less pressure
Deflected mass: Inertia from watermass imparted to foil as lift when water is deflected downwards

These are two VERY SEPARATE forms of lift, please try not to confuse them as they will MOST DEFINITELY affect the accuracy of your equations if you leave one out. The difference between these two forces is the difference between flying a flat plane, and flying an airfoil....otherwise aircraft wouldn't use airfoil-shaped wings, as the exact same effect could be had without the design constraints needed to take advantage of Bernoulli's principle.

robherc, another picture of the "space frame" foiler above(from the Mirabaud thread under "sailboats"). This thing has the same W(weight in pounds)/SA(in sq.ft.) as the 11' Moth! :

[sailor2]

Originally Posted by robherc

Bernoulli principle: Moving fluid (air/water/whatever) exerts less pressure
Deflected mass: Inertia from watermass imparted to foil as lift when water is deflected downwards

These are two VERY SEPARATE forms of lift,

Every fluid dynamicist can tell you you are absolutely wrong, just ask any of them. Read any book about fluid dynamics and the result is the same.
If you were correct Newton's law would not apply to foils, the idea is obviously completely wrong. Same for Bernoullis law. Same for principle known as conservation of momentum.

Originally Posted by robherc

please try not to confuse them as they will MOST DEFINITELY affect the accuracy of your equations if you leave one out. The difference between these two forces is the difference between flying a flat plane, and flying an airfoil....otherwise aircraft wouldn't use airfoil-shaped wings, as the exact same effect could be had without the design constraints needed to take advantage of Bernoulli's principle.

The difference between flat plate at aoa and an airfoil with some, but not the same, aoa when both provide the same lift force is significant difference in drag, airfoil has the advantage. Another difference is that airfoil can have greater Cl before stalling than flat plate. Airplanes can fly upside down just fine provided the pilot knows what he/she is doing.
Having any accuracy in lift calcs requires Bernoullis law and newtons law to have exactly the same lift as a result.