V-44 Albatross World Speed Sailing Contender

[RHough]

Originally Posted by Doug Lord

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This isn't an answer but its-maybe the begining of an answer. I looked in Darrol Stinton's "Design of the Airplane" for his remarks on forward sweep.
1) " forward sweep avoids premature tip stall, because the root stalls first. Ailerons tend to remain effective, but pitch up still occurs. However, forward sweep has an adverse effect upon directional stability.........."
2) " Forward sweep causes vortices outboard to be shed ahead of those inboard. Tip stalling is suppressed by off-loading outboard sections. The spanwise lift distribution of a forward swept wing is nearly elliptic and further forward than for one swept back. This, with root losses helps to shift the aerodynamic center 7 percent to 10 percent further forward than for a swept back wing."

Tip stall should not be a concern. "Adverse effect on directional stability" is.

One of the issues with forward sweep is flutter. Forward sweep of the aerodynamic centre usually requires a wing much stiffer in torsion than aft sweep.

One of the reasons the F-29 was designed with forward sweep is because the inherent instability allows it to change direction faster. This is good for a fighter. The pilot cannot control the aircraft without the active stabilization from the computers.

The V-39 cannot use powered active stabilization so the limit is the skill of the pilot.

R

[P Flados]

The concept has a lot to like. I love the basic layout, it is the reverse of the early flip tackers. Early flip tacker were looking for the "inherent roll stability" that kiters and boats like Sailrocket have. This one puts the weight of the vertical wing above the main hull. This is much more efficient, but it does require active roll stability considerations.

Given that the root sections of the wings are well to windward, you get to use really robust components to provide strength. Since they expect to have to add ballast on this side of the boat, the weight just does not matter like it normally would.

Most of these wonderfully weird concepts (YPE, MI, Sailrocket, Wot rocket) have some sort of cross beam. With this design the cross beam function is provided by a two section airfoil that can provide lift and roll stability control.

One item of concern I would have is with implementation of the very aggressive sounding multi axis control scheme. Each of the 4 wing segments are described as freely rotating with a flap that determines the angle of attack on the segment. For stability control, you want positive and fast acting control surfaces. Modulating a flap that then results in wing rotation might work, but I am not convinced yet. Also not sure of what kind of control scheme is planned, I saw no feelers dragging the surface. Ultrasonic sensors work, but are they worth the added complexity.

The other concern I have about this configuration is wing lift and efficiency. For example, say you need max lift on the outboard segment of the horizontal (leeward) segment. You have to rotate the flap up to cause positive rotation of the overall wing for an increase in angle of attack. This result in a flap that is displaced in opposite direction that will give maximum lift for the overall wing. At the same time, while producing high lift with a flap deflected in the wrong way, drag has to go up.

They argue that stuff like this does not matter as max speed will only be limited by keel (a.k.a. main foil or dagger board) cavitation. As I recall onset of cavitation is a function of both speed an load applied. Anything that decreases efficiency and/or increases overall craft drag will increase the loading on the main foil. I like the rotating segments, but again I am not convinced that their chosen method of getting the desired angle of attack is optimum.

For craft like this, it would seem that an initial build of a less expensive (more glass than carbon) prototype might be worth considering. After you get some of the bugs worked out, upgrading parts should be easy builds (you already did it one & you save any molds). With anything as radical as this, much will be learned in early prototype runs.

Regardless of anything that looks iffy to us, I just hope they go ahead and push forward.

[Doug Lord]

Originally Posted by P Flados

For craft like this, it would seem that an initial build of a less expensive (more glass than carbon) prototype might be worth considering. After you get some of the bugs worked out, upgrading parts should be easy builds (you already did it one & you save any molds). With anything as radical as this, much will be learned in early prototype runs.

Regardless of anything that looks iffy to us, I just hope they go ahead and push forward.

===================
I agree but I think an 8-10'LOA RC model might be a good way to begin. Hydroptere started as an rc model and many other fast boats have had control systems tested this way.
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Just a gut feeling: I'd bet a controllable lifting foil on the daggerboard would be worthwhile....

[RHough]

Originally Posted by P Flados

... but it does require active roll stability considerations.

Given that the root sections of the wings are well to windward, you get to use really robust components to provide strength. Since they expect to have to add ballast on this side of the boat, the weight just does not matter like it normally would.

I agree, yet they state:

There seems to be some contradiction in the above ..?

One item of concern I would have is with implementation of the very aggressive sounding multi axis control scheme. Each of the 4 wing segments are described as freely rotating with a flap that determines the angle of attack on the segment. For stability control, you want positive and fast acting control surfaces. Modulating a flap that then results in wing rotation might work, but I am not convinced yet. Also not sure of what kind of control scheme is planned, I saw no feelers dragging the surface. Ultrasonic sensors work, but are they worth the added complexity.

The other concern I have about this configuration is wing lift and efficiency. For example, say you need max lift on the outboard segment of the horizontal (leeward) segment. You have to rotate the flap up to cause positive rotation of the overall wing for an increase in angle of attack. This result in a flap that is displaced in opposite direction that will give maximum lift for the overall wing. At the same time, while producing high lift with a flap deflected in the wrong way, drag has to go up.

This the underlying reason that flying wings don't make great gliders. There is a wealth of information on flying wings and reflexed airfoils.

They argue that stuff like this does not matter as max speed will only be limited by keel (a.k.a. main foil or dagger board) cavitation. As I recall onset of cavitation is a function of both speed an load applied. Anything that decreases efficiency and/or increases overall craft drag will increase the loading on the main foil. I like the rotating segments, but again I am not convinced that their chosen method of getting the desired angle of attack is optimum.

I agree, just the split at the "planks" will shed a vortex and add drag anytime the AoA of the adjacent sections is not the same. To get the lift distribution they want it looks like that will be the case 100% of the time?

For craft like this, it would seem that an initial build of a less expensive (more glass than carbon) prototype might be worth considering. After you get some of the bugs worked out, upgrading parts should be easy builds (you already did it one & you save any molds). With anything as radical as this, much will be learned in early prototype runs.

Regardless of anything that looks iffy to us, I just hope they go ahead and push forward.

If ever a project screamed for proof of concept modeling this is it.

At least two members of the team have model building experience. All it would take is a 6 channel programmable helicopter radio, a few rate gyros, blue foam, glass, epoxy and a hot wire cutter and you could have a working model in a week or two. For under $1000.

Once the design proves controllable with the rate gyros turned off you will have proof of concept and a real world flight simulator for pilot training.

All of the wingnut ... er ... wonderfully weird programs including hydroptre have had some spectacular control or structural issues that have resulted in crashes, damage, and down time.

Rather than build a prototype at full scale, a series of models to finalize the design would be much more cost effective.

I'll bet there are people with some mad modeling and flying skills in the UK that would love to join the team.

This guy is from the UK: Duncan Osbourn flying 3D

If anyone can fly an unstable vehicle ...

(I have hundreds of hours flying fixed wing RC and can barely hover my RC Helicopter)

[tspeer]

Originally Posted by RHough

Tom, have you looked at the pitch stability information they posted? I'm struggling with how that is going to work. It looks more like a pitch instabilty system me?

R

I've not tried to work out their pitch stability. Their website talks about pitch trim, but I didn't see anything that actually addressed stability.

Similarly, the spanwise lift distributions they show do not include the effects of the discontinuity at the junction between the panels, so I suspect they are notional and not actually computed. I don't see a diagram showing the sum of forces and moments in the horizontal plane, and that's the real essence of sailing performance.

The section shapes they show would still have a negative moment with the flap at zero deflection, making the section trim at a negative angle of attack, but there will be some flap deflection at which the panel will trim for zero lift. The damping will be very low, however. I think a tail would be a very valuable addition to the panels, as was used for Greenbird and for Harborwing.

The business about regulating height to regulate speed doesn't make much sense to me - this is a record-breaking yacht, and the whole point is to go as fast as possible. Their stated objective of speeds >60 kt will be very difficult to achieve with subcavitating foils. The foils must be thin (5% or less) and will have only a narrow range of lift coefficients at which they can be subcavitating. Outside of that range, they will form a leading edge suction peak on one side or the other, causing cavitation.

The Eppler E817 scaled down to 5% thickness in the plot below is probably typical of what they will need to use, except that the keel foil will have to be symmetrical, shifting the subcavitating lift range to the left to be centered on zero lift. That means the keel will have to be lightly loaded - maybe 20 - 30 kN/m^2 (500 - 600 lb/ft^2).


What does make more sense to me is to regulate the amount of immersion of the foils to keep the foil loading within the subcavitating range for the section selected. For example, at 20 kt, the foil loading may have to be under 10kN/m^2 (200 lb/ft^2) to avoid cavitation. It may amount to the same action, but for a different reason than they state.

It may be they've worked things out quantitatively better than they've shown in their website. I hope so.

[RHough]

Originally Posted by tspeer

I've not tried to work out their pitch stability. Their website talks about pitch trim, but I didn't see anything that actually addressed stability.

They balance pitch up with aft CG and T foil. Active trim in pitch is the T foil.

The Eppler E817 scaled down to 5% thickness in the plot below is probably typical of what they will need to use, except that the keel foil will have to be symmetrical, shifting the subcavitating lift range to the left to be centered on zero lift. That means the keel will have to be lightly loaded - maybe 20 - 30 kN/m^2 (500 - 600 lb/ft^2).

V-39 has two keel foils and two rudders. They have a set for each tack so they can use a cambered foil in both locations.

What does make more sense to me is to regulate the amount of immersion of the foils to keep the foil loading within the subcavitating range for the section selected. For example, at 20 kt, the foil loading may have to be under 10kN/m^2 (200 lb/ft^2) to avoid cavitation. It may amount to the same action, but for a different reason than they state.

It may be they've worked things out quantitatively better than they've shown in their website. I hope so.

They are doing what you describe for the same reasons. They control foil immersion with altitude, hence the height/speed relationship.

It is a very young project.

Do you have an opinion on the design tools they are using?
Dassault Systemes Abaqus Unified FEA for structural design and analysis and SolidWorks Premium for 3D modeling and product data management.
Capvidia FlowVision HPC for CFD and Multiphysics simulations.
and of course XFoil.

Thanks for taking time to look.

Randy

[tspeer]

You're right about the two keel foils. Somehow I'd missed that. I saw the two rudders but not the two keels.

[masrapido]

If assimetry were good, it would have been default in the nature. These Australians had proved how fragile is such a hydro-aero/dynamical set-up:

http://www.wotrocket.com/news.html

I cannot wait for Albatross to hit a small wave and fly away just like Wot Rocket did. Such sailing boats are trying to balance two different environments with different challenges.

From my 17 years of open sea navigation I think that the only favourable (meaning safe for the crew) conditions are flat seas with the wind and (small, if any) waves going in the same direction.

And how often that happens...?

I wonder if there is a way to fly completely above the water, with the sails as the only power. There is a (surprise...) French guy who is/was working on a WIG sailing boat.

I think that if that could be made to work, that would have to be the way to go.

[RHough]

Progress?

You may have noticed a slight name change to ‘v-44’ along with some changes to the layout of the boat. Firstly, the change to ‘v-44’ is simply to reflect the fact that the overall length has increased to 44’. We have developed a new main hull configuration where the entire hull remains upright (as opposed to only the forward section). This new hull layout has a cockpit located behind the wing-sails, above the waterline. The hull has an increased slenderness ratio and since it remains upright, it now has a more classical shape for low wave drag. The two wing-sails and keels are rigidly connected through the hull centre section. The pilot retracts a fairing which covers this section, allowing the wing-sails and keels to rotate through 90 degrees as the boat tacks.

A second crew member will be stationed on the windward outrigger of two additional fixed outriggers. The second crew member / fixed outrigger combination will assist with the tacking process and benefit the overall boat centre of gravity position. The cross member supporting the two fixed outriggers is streamlined. Two full length trailing edge flaps acting as ailerons have been introduced to the cross member to give an additional rolling moment boost (opposing the heeling moment from the vertical wing-sail). This additional moment will increase with speed and compensates the increasing heeling moment as the boat rides higher at high speed.

Now they have a crew that walks/crawls from outrigger to outrigger during tacks ...

I think they may be channeling Rube Goldberg?



v-44

[Doug Lord]

Hey, Randy! Thanks for reminding me about this project-I had let it slip by...

[Doug Lord]

I want to thank Jeff for changing the thread name to reflect the new name of the project!

[Doug Lord]

Specs from the site:

Specifications

Velocity not to exceed: 70 knots (80.5 mph, 129.6 km/h)
Target lift / drag ratio: 2.3:1 ( design wind speed 30 kts )
Length overall: 44.2 feet (13.5 metres)
Sail area: 26 m2( 279.8 sq.ft.) (52 m2/ 559.6 sq.ft. for both wing-sails)
Weight empty: 520 kg / 1144lb
Weight all up: 670 kg / 1474lb

[Verney]

We've dropped the second crew and have replaced him with an internal moving mass system. The fixed wing now passes in front of the cockpit. A closed loop rope/pulley system with a few meters of slack will be accessible ahead of the cockpit to move the mass.

Before tacking, the skipper has a short checklist: move mass to centre; retract centre hull fairing (to allow wing-sails to rotate).

Post tack checklist: move mass to windward; close fairing; reverse position of fixed wing trailing edge flaps.

Once established on a new tack, the principle controls are the stick and rudder.

A couple of points, due to the weathervane nature of the wing-sails (as used by Greenbird) the aerodynamics are partially decoupled from the hydrodynamics. For example, the lift is fairly independent of the pitching of the main hull.

With pitch, the rudder hydrofoil gives you all back which you lose when the hulls lift out of the water. There's a nice cross over between the two as the v-44 speed up (similar to Hydroptere).

Regarding aero-elasticity problems with forward swept wings, i.e. increased bending gives increased incidence at the tip, this is not applicable since our wing-sails freely rotate. The problem we do have however is that the close coupled stability of the tailless approach we are taking gives us some unusual structural requirements to meet. There must be, structurally speaking, no preferred orientation when the wing-sails are subjected to bending. We have simulated a structure in Abaqus which adopts this behaviour.

[tspeer]

I think you'll find the tailless approach may not be the best way to go. There is a significant increase in trimmed profile drag compared to the sections you could use with a tail. The tail should pay for itself in reduced parasite drag compared to the tailless approach.

Aerodynamic damping goes up with the square of the tail length when the static stability is held constant. The tailless panels have a short effective tail length, and low damping. Small tails on comparatively long arms will add a lot of damping and minimize the added weight and wetted area.

I don't know why you've put the mass balance arms at the inboard ends of the wing panels. They would be much more effective at preventing flutter if they were placed at the outboard ends of each panel. That is where the linear acceleration will be greatest and therefore where the favorable coupling of the ballast between linear acceleration and panel rotation will be most effective.

Also, a small ballast weight on a long arm saves weight, but the moment of inertia is higher than for a heavy weight on a short arm. Since you want the panels to track the apparent wind, the extra inertia of the longer ballast arms may be counterproductive because it lowers the natural frequency and adds to the lag of the panels' response.

The combination of low natural frequency due to small static margin and high inertia, combined with low aerodynamic damping, is going to make it difficult for the wings to track the dynamically changing wind. You haven't mentioned how the natural frequency of the wing panels compares to the frequency content of the apparent wind they will encounter. If you haven't looked at this issue, you ought to identify the frequency range of interest in the apparent wind and then use that to define a minimum natural frequency requirement for the wing panels, along with a minimum damping ratio. Those requirements will then drive what you have to do with regard to wing panel design for static margin and aerodynamic damping.

[Verney]

This is a hot topic for us so it's good to read your post. Good point regarding the length of the mass balance arms. I guess we need to get the mass / inertia trade off as best as we can! One thing in our favour is the wing-sail inertia at the rotation axis is a lot lower without the tail and additional tail mass balancing.

If we employed a Greedbird http://www.greenbird.co.uk/ tail, we would need four of them with significant additional mass balancing. This will give a poor boat CG and will not allow overall roll balance of the boat. Each mass balance is to place the plank CG on the axis of rotation; we put them inboard to help overall CG placement of the boat.

Regarding zero CM airfoils, they are nice and fast (very good speed range). Sure they have their drawbacks, i.e. reduced CL max and limited laminar flow. No good for a L/D 50:1 sailplane, but we will be doing well to achieve 2.3:1. Our build accuracy will not give us long laminar runs anyway. We are aiming well up the cavitation drag curve giving us a relatively massive keel wetted area with extremely low keel loading. This is such a dominant source of drag that it often puts other sources into perspective.