Welcome back to another episode of One Wingspan Above where we discuss anything to do with Ground Effect..
In this episode we will try to do a deep dive into Regent’s first Seaglider called the Viceroy. This is the Viceroy right here.
We have reached out to CEO of REGENT Billy Thalheimer. And also Shah Aslam as he will be bringing the Seaglider to New Zealand, under his OceanFlyer brand. We wanted to get some first hand information from them for this video. But both have not responded. So all that is shared here is all our own interpretation of publicly available information. Most of it is from the Regent website combined with information from more updated images from the full scale mockup reveal and recent news snippets.
So let’s start with the general info we know for the Regent Viceroy.
The Viceroy is a 12 seater Seaglider. Regent call their type of craft Seagliders. It operates exclusively over water, traversing the sea in one of three modes: hull, hydrofoil, or flight in ground effect. They mention that Full-scale prototypes will begin human flight trials by 2024.
Before we get into details. We would love to compare the Viceroy to other existing Skimmachines. But there are not many examples of ready-built ones that we have actual proven specs on. There are similar capacity Chinese and Russian Skimmachines and but they only have been built as prototypes and details are limited.
So we will compare the Viceroy to the Airfish 8 which at the moment is the closest comparable ground effect machine. Even though the Airfish can only carry 8 passengers plus 2 crew, it seems to be a vehicle with the most flown hours available. We will also compare the Viceroy to a comparable airplane as well. In particular a Pilatus PC12. This is a highly reliable passenger airplane that has been flying since 1991. Capable of carrying 9 passengers plus 2 crew it is along the same lines as the Airfish for easy comparison. We will also compare the Viceroy with a 12 passenger taxi boat, the TEJUS-1 for completeness.
Main dimension.
The main dimension of the Viceroy is the wing span of 19.8 metres. The wingspan of the Airfish 8 is 15m and of the Pilatus is 16.28m. Needless to say, our boat, the TEJUS-1, does not have wings.
But since the vehicles are different sizes, the best comparison figure would be wing loading. The wing loading specifies how much load in kgs is carried by each square meter of wing.
Regent gives the Viceroy wing loading as 264 kg per m2 which is massive!
The Pilatus wing loading for comparison is about 4740/25.81 = 183 kg per m2
And the estimated wing loading for an Airfish is about 5550kg/105m2 = 52.8kg per m2
This gives the Viceroy by far the highest wing loading of the three even though its wing has the highest aspect ratio or in other words has the skinniest wing. This means that the wing would have to be stronger so it wouldn’t break. The distributed motors on the wing would spread out that load over the whole wing which might help.
Generally a high wing load indicates a longer take off, but since the Viceroy gets up on its foils first before flying, this might be negated. An advantage of a higher wing load would be a more stable flight as it would not bounce around as much.
Speed and range
The Viceroy is noted to cruise at 300 kph and has a range of 300km.
The Pilatus airplane cruises almost two times faster at 537 kph and the range is about 10 times more at 3417 km.
The Airfish skimmachine cruises slower at about 167 km per hour but has almost twice the range at 556 km. This is probably due to the fact that it burns petrol rather than running on battery power.
The water taxi goes at a leisurely 28km/h and reaches about 196km.
When compared with an airplane, the speed and range of both the Skimmachines are pretty pathetic. Despite its high wing load and low ground effect drag, the Seaglider still trailing behind the Pilatus with regards to speed and range. Of course it blows the water taxi out of the water in both range and speed.
Efficiency
It gets interesting though when fuel efficiency is compared.
There are no numbers available for the Viceroy, but..
The Pilatus has a listed fuel usage of 250 L/h and the Airfish is noted to use 70 L/h.
If we recalculate this we get..
Pilatus = 6.3hrs => 1575L /3417km => 0.46L/km
Airfish = 3.3hrs => 231L /556km => 0.41L/km
TEJUS-1 => 0.64L/km
This oddly puts the plane and the Skimmachine almost at similar levels, with the Airfish only slightly better economics despite skimmachines being known to have less drag due to the ground effect. The water taxi consumes the most by far.
The Viceroy is powered by electricity and so will be hard to directly compare the Seaglider with these numbers. Regent also doesn’t list any numbers at all with regards to energy usage apart from the 120kW rating of the motors. But it is assumed that the cost per kilometer would be well under that of the Airfish as the Airfish used a V8 500HP combustion engine, which would translate to about 370kW.
Fun fact. A Nissan minivan which seats 15 would have a similar range as the Viceroy. It would burn just 0.08L/km so that’s a nice number to aim for. I wouldn’t recommend driving the minivan at 300km/h though.
What type?
Since we are comparing, the Seagliders fall in between the water taxi and the plane as a mode of transport.
A Skimmachine is actually certified under the IMO, the International Maritime Organization and is a maritime vessel. The IMO states that these craft are supported in their main operational mode solely by aerodynamic forces which enable them to operate at low altitude above the sea surface but out of direct contact with that surface.
The IMO and ICAO (International Civil Aviation Organisation) have agreed that any WIG craft capable of flying outside the influence of ground effect at an altitude of more than 150 m, typically referred to as type C craft, should in such a flight be subject to the rules and regulations of ICAO. Other craft, including those with limited “fly-over” capability, should be covered only by the maritime regulatory regime.
In the case of Ground Effect, IMO recognizes three types of Skimmachine: A, B and C.
Type A: a craft which is certified for operation only in ground effect. Within prescribed operational limitations, the structure and/or the equipment of such a craft should exclude any technical possibility to exceed the flight altitude over the maximum vertical extent of ground effect. The IMO has a certain formula it applies to determine this vertical extent which links to the aerodynamic properties of the craft.
Type B: a craft which is certified for main operation in ground effect and to temporarily increase its altitude outside ground effect to a limited height, but not exceeding 150 m above the surface, in case of emergency and for overcoming obstacles
Type C: a craft which is certified for the same operation as type B; and also for limited operation at altitude exceeding 150 m above the surface, in case of emergency and for overcoming obstacles.
So what type of craft is the Viceroy likely going to be certified as if it wants to gain all the benefits from being registered as a boat? WIth a wing span of 19m it would generally be operating inside that vertical envelope which is below 150m. The quarter scale model operates at the top end of the ground effect envelope. The wing is slender and even though the wing loading is quite high, the design looks like there would be no reason that it wouldn’t be able to exceed this height and escape ground effect since it is essentially an aircraft based on its geometry.
As we covered in previous videos, the flight above the surface for the Seagliders is fully computer controlled and stabilised. As described in multiple instances by Regent, the captain of the ship would have no direct way to increase height above the surface.
This would slot the Viceroy into certification as a type A skimmachine.
However, if the control system was ever to be disturbed by, say a rogue wave, air disturbance or computer malfunction, the craft would easily gain height above the vertical extent limited by the Type A classification. This would enter the type B or even the type C classification depending on height gained. Once it jumps out of this region, the craft would have no problem flying outside of ground effect. It doesn’t seem to be dependent on it.
And perhaps Regent will opt to give the captain the controls to do a temporary height increase to allow the Viceroy to jump obstacles it cannot evade in time by banking. This would then mean it would be automatically classified as type B at least.
It turns out that recently the OceanFlyer company, the company that are bringing the SeaGliders to New Zealand, stated in a zoom meeting that in fact the Seaglider would be certified as Type B. This is not publicly confirmed by Regent as far as we know but we’re assuming that Oceanflyer has the correct information.
Currently Regent are stating as per Billy Thalheimer’s interview on the Vertical Space podcast that the US coast guard are Regent’s certification authority. And that Regent are working towards design basis agreement with them and that they have been in contact with Bureau Veritas. This is a French company specialized in testing, inspection and certification founded in 1828 and well known to assist manufacturers to certify their vessels.
Would the IMO accept the Viceroy as a ground effect boat? It is only limited in height by a computer system that could be overridden or faulted It is not a vessel that is bound to ground effect by its design outright.
The Viceroy is essentially an airplane that is bound to ground effect only by its control system rather than a skimmachine incapable of flying outside ground effect. It would be fully capable of flying outside it if ordered to do so, making it an aircraft.
Stability
In previous videos we have discovered that the Viceroy geometry is unstable in ground effect. This had been confirmed by Billy Thalheimer in emails to us. And as such it would be impossible to fly by a human. Regent are getting around this by having a computer control the craft. This means that the captain only inputs left/right, power and the mode the craft needs to travel in, float, foil or fly.
This is all well and good. A computer control system would definitely take the strain off the captain as constantly adjusting for height has been discovered by the Russian ekranoplan developers to be a major pain. Even James Greenberger who flies his Mudskipper in Australia mentions the need for constant height input.
A modern airliner would also be computer controlled, however it would be stable in flight when the computer fails and would be controllable by a pilot giving manual inputs if needed. There is also no hard surface nearby to crash into straight away.
Of course, nowadays computer systems are reliable and they are made redundant. Some are even referring to the VTOL designs that are being readied to transport people.
And sure, if for some reason the system fails, for a Seaglider, the landing strip is always under it.
Unfortunately though, if the captain cannot control the craft without the computer stabilising it, it has a high chance to either crash right into the water. Which at 300 km/h would be unforgiving. Or it would pop up like the Orion 20 did and crash land from a fair height onto that same unforgiving water surface.
I think that is asking for trouble. I liken it to making a deep sea sub out of carbon fibre and then installing an acoustic system in it to warn you when it’s failing..
Box tail
Let’s just talk about the elephant in the room, the box tail that is now evident in the latest renders from Regent and on the full size mockup. The original renders still shown on the Regent website still show the original high tail configuration.
A box wing, normally suggested for the main wing of aircraft, would be chosen to reduce induced drag. The Seaglider has it as a tail so it is less likely picked for the reason to reduce drag.
At a guess the function of this tail could be to avoid tail stall. In ground effect the stall angle of a wing is lower. This means that a wing stalls or loses lift at a lower angle of attack. Once it does that, the wing sheds a turbulent wake behind it. With the original high tail of the seaglider, if the wingstalls, it sheds turbulence over the tail and the lift of the tail will dissipate and with it any longitudinal control you have over the craft, whether it is computer controlled or not. In the case of the new renders, the top section of the box tail might be right behind the main wing if it stalls. The lower section could then avoid the stalled wing turbulence. The added surface on the bottom of the boxed tail might help avoid a totally stalled tail section.
What the box section tail also does is it adds directional stability as you effectively have three vertical surfaces instead of just the one. Think of increasing the surface area on a weather vane.
It turns out though from a recent post on LinkedIn and a deleted post on Twitter from Oceanflyer that the main reason for the box tail is to actually reduce the weather vane effect during low speeds.
At low speeds the quarter scale test model must have had a tendency to put its nose into the wind even though the captain would not have wanted to go that way. They explain rather awkwardly that the vertical tail surface exposed to the wind is less in a box tail arrangement. They mentioned the two horizontal tail surfaces as the reason for this but they would actually mean the fact that the main vertical surface has been divided up into 3 smaller surfaces which reduces the area exposed to crosswinds.
Observing the test flight video there seems to be a crazy amount of negative lift from the tai. The horizontal tail surface seems to be angled upwards quite considerably, creating downwards force. The reason for this might be that it is canceling out the moment that the water foil drag creates. An observation is that the test craft has got quite large flaps. Probably to divert the prop wash down to create lift for the take off effort. This would also need a tail creating an opposite moment to counter this.
Generally a skimmachine would have positive lift to make sure it is stable in ground effect. A negative lift or a downward lift of the tail is common in conventional aircraft.
The angle of the tail surface comes down as soon as the hydrofoils come out of the water. This might indicate that indeed the tail cancels out the drag force moment of the water foils.
Foiling
Essentially all other skimmachines that have had hydrofoils have used them solely to make the transition from boat to ground effect as easy as possible. But the Seaglider is deemed different as it can foil as an extra mode of transport and so is able to foil in the water for longer amounts of time. This is especially convenient in areas like harbor inlets where low wakes are desirable.
In the past, the X114, the predecessor of the Airfish, had hydrofoils attached to decrease the takeoff efforts. But it actually had the opposite effect as it decreased the RAM effect by lifting the craft out of the water, essentially leaking air from under the wing. It also were these hydrofoils that made the X-114 crash as the hydrofoils dug into the water and pulled it down.
The Viceroy will be equipped with retractable hydrofoils, but the same thing could be imagined to happen.
From footage with the quarter scale model, the hydrofoils seem to be ‘popping’ the craft up from the water when the speed is up to a certain number. This would be a result of trying to breach the hydrofoils out of the water as safely as possible. It doesn’t look very comfortable from a passenger perspective, but it works for boats like the SailGP yachts with its daggers.
When a foil enters the water on landing it would instantly add drag, which is like stepping on the brakes. If the foil comes out of the water for take off, the moment around the CG changes dramatically the other way round and the craft needs to adjust for this in a split second with its aerodynamic surfaces before it is too late and the craft flips over.
The foils need to leave and enter the water at perfect angles. Even when computer controlled this might be a challenge to do this consistently.
The landing would probably be done with the foils still retracted. As it would be dangerous to do with the foils out. But looking at the latest model, the foils would still enter the water before the hull does even when they are retracted.
Batteries and electric motors.
It makes total sense to go electric. And skimmachines, with their theoretical decrease in drag and increase in lift are the perfect foot in the door for electric aviation. Battery weight and power ratio is not quite there yet in general aviation, but in ground effect this might just be the ticket to green transport.
Other differences from first renders
FIrst of all there is the increase in the amount of motors from the original design. The original render had 8 motors, but the new render has 12 motors. The props on these motors seem to be smaller in the new configuration.
They might have decided they needed more power based on the quarter scale tests. Or a more distributed power over the wing. Or even more redundancy over the already 8 motors which seems unlikely.
We can see that the wing has got a drooping down of the wing tips. Or what is called an anhedral. This is a difference between the first and the current render but the quarter scale version already had this.
It allows Regent to put floats on the tips of the wings for stability during Floating, much like flying boats from yesteryear.
It would also help build the ground effect more, by keeping it the higher pressure air under the wing and to keep it from escaping from the tips.
It would probably even help with keeping the craft stable in ground effect because of a stabilising moment that is created.
Then they have done away with the struts that were holding the wings down at the start. They always looked a bit strange as at the start they were connected to the retractable hydrofoils and the whole wing seemed to move up when the hydrofoils were retracted. I am assuming that these struts now are a thing of the past and they have found a way to make these very thin wings stay in shape on their own.
Conclusion
On the face of it the Seaglider seems to be a logical and sane concept.
But it still essentially is an airplane that flies low. And it has an unstable airframe in ground effect that is made stable with a computer system.
Even with enough redundancy I am not sure if the IMO will fall for this. To certify an airplane as a boat just because it is limited to a certain height by a computer seems like a big risk.
The foiling as an extra mode of transport between floating and flying is appealing for harbour work and if we look at the foiling taking place in the racing boats, very doable, but as a passenger transport it does add a very real risk. And again, just adding computer control to it only paints over the top of the problem.
The numbers at the moment do not give it an edge with regards to speed and range over existing planes. They certainly beat any boat by any measure which is the whole point. These are fast boats in the shape of an airplane only without the costly maintenance and running cost of an airplane.
I want to believe in the Seaglider. And the team that are behind it, seem to be the first ones capable of actually getting skimmachines into the mainstream public transport. In the past there have historically been two camps. The money grabbing schemes that never made it past the drawing board. There are still a few out there. Or there were projects that were led by a technical team that were never able to market it properly.
Regent seem to have the best of both worlds and they seized on the opportunity to sell the advantage of a skimmachine to start developing electric propulsion for.
I just hope that Regent are approaching this very carefully as one small accident with any of their prototypes or any of their first production craft will not only set their own efforts back many years. But it will also be used as an excuse for ground effect boats to be shelved right next to the Hindenburg airship, flying cars and jet packs.
For now.. thank you for watching. Keep in the loop by hitting the subscribe button and we’ll see you here for the next episode of One Wingspan Above.
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