The craft rapidly accelerates to settle smoothly on an air cushion generated by the effect of forward air caught by a wing shaped like a baseball glove and the water surface.
WIG: wing in ground effect
reverse delta: triangle pointed backwards
ram: forced air
I think it combines the worst characteristics of helicopter, WIG, and multihull.
Rotary wings are complex, require large amounts of maintenance, and cause high levels of vibration. Their only virtue is they are unbeatable for efficiency in the hover. If you're in the hover, there's no WIG cushion. The "weighted, prerotated" rotor means it's an autogyro capable of a jump takeoff. Since the rotor is sized to carry the whole weight, why WIG? In forward flight, the rotor has far more drag than a fixed wing, so the speed is limited and the fuel consumption is high.
A WIG needs a very robust structure because it operates at low level and must operate off the water. This adds weight that has to be lifted by the rotor. This autogyro will be able to fly well above ground effect once it transitions to forward flight. Once at altitude it will be away from the hazards of operating near the surface. Fixed wings would be useful to offload the rotor, making it a compound autogyro. But to be efficient, they need more span than shown. Otherwise they are just weight and drag.
"Wave piercing" hulls mean "under water" as the waves pass by. The reason for wave piercing is to have low heave stiffness for better ride quality in a seaway. But this craft should be flying above the waves, not plowing through them. Going through the waves adds lots of stresses as the waves squeeze the hulls together or try to split them apart. Being deeply submerged when the crest of the wave passes with its horizontal orbital currents means one hull resists the motion of the other hull under the influence of the wave. This requires a beefy structrure to resist - just look at Team Phillips breaking her bows off. More weight and bad news for a flying craft.
This is what you get when an artist sticks together trendy buzzwords to make a pretty picture with no understanding of the engineering behind the concepts, or of the design requirements for the intended mission.
Hey, you asked the question!
Perhaps it was my mistake. The link posted above goes to a basic introductory page at the Worlds Most Radical Boat Designs, and it would be a mistake to base conclusions upon only the information on that page. To get a full understanding of the HF concept one should go to the home website for the concept to fully understand how it works and the advantages offered >
Although any rotor at higher speeds is much draggier than wings. The CAT rotor however, slows down at cruise to stay out of the exponential part of the drag curve. An understanding of this specialized rotor can be found at Carter Technologies > [ this page explains the rotor as applied to an aircraft, not to Type B WIG (Aerofoil Boat) applications ]
As I view it, the craft is not just simply a combination of three very different concepts, it is a transitioning craft designed to operate to best advantage in each of the three modes of operation, while minimizing the disadvantages of each.
Thanks for your input. Just out of curiosity, what is your WIG experience? (Not trying to be 'confrontational', just interested in your involvement with WIG projects).
Thank you for reviewing the HeliFerry. I have been most impressed by the content of your messages in this forum and I secretly hoped for your comments in this thread. Now, I am even more impressed, as you are the first person with cogent comments on each of the three very distinct technologies used in the HeliFerry. Although, every single statement of yours is correct, I hope to change your mind on your conclusion.
First of all, the HF is STOL not VTOL. It does not have a sustained hover capability. That would take too much power that would not be needed in cruise. Also, the HF cannot do jump take-off . With so little power, that would take too much tip weight and require an axle of a material of impossible strength. The HG does prerotation just to shorten the take-off run. The rotor is not very complex thanks to the patented torsion based collective. Also it is a two-blade teetered rotor: the most simple you can get. During cruise the rotor is offloaded and slowed down to minimize drag. Then, the tip weights keep the blades straight and stiff despite the low rpm.
The low wing WIG only provides significant lift in the higher speed regimens when it takes over from the rotor. Therefore, it can be kept simple and much smaller and thus lighter. The WIG does not need flaps or other takeoff devices that are failure prone and add weight.
The small high wing on the HF is just to carry the propellers and to be a conduit for driving the props and rotor from the engines. The wing is extended somewhat to provide ailerons for roll control. There is no intent to make a compound aircraft and fly out of ground effect in a sustained fashion.
The wave piercing hulls are only meant to be in the water and under stress during the take off run in more rough waters than planing flying boats would be able to handle. This take off run is kept relatively short with the overrotated rotor. From then on the hulls should never touch the water until landing. The rotor provides a nimble control of the height where other WIGs have to control with throttle instead. Furthermore, the configuration of the hulls is more of a monohull with side pontoons, than a real trimaran. Stresses between hulls should be a fraction of those seen in the racing catamarans. During takeoff, the side pontoons hardly touch the water, in particular at speed. Operators in consistenly still waters should replace them with less conspicuous hulls.
Please note that beyond the particular combination of technologies, the only true innovation of the HF lies in the Carter rotor. Just as it will revolutionize general aviation, it also frees WIG craft from the haunted hump drag.
If you have any more reservations, questions or comments I would be more than happy to provide you all the background information needed.
I readily admit to being no expert on WIG's. My WIG experience is pretty much limited to post-lecture conversations with Alexander Lippisch and a NASA engineer (whose name escapes me at the moment) that went to Russia for NASA-sponsored flight tests of their WIG's on the Caspian Sea. Other than that, I have to fall back on general engineering principles learned getting my Masters' in aeronautical engineering, completing the Air Force Test Pilot School as a Distinguished Graduate of the Flight Test Engineering Course, and flying several hundred hours of flight test missions on all types of aircraft from helicopters to fighters to the Goodyear Blimp. And almost three decades of engineering experience.
It still looks ridiculous to me. But I'm willing to be convinced if they'd publish some real engineering info on their site, instead of drawing circles in cartoons and handwaving. Show me the data!
Dynamics & WIG
be grasping this concept. Usually, those who have extensive backgrounds
in aeronautical design, engineering, and theory fail to fully understand
Aerofoil Boat (WIG) design. My opinion is that this is due to an overload
of mathematical theories all related to aircraft design, most of which
have no relevance to Aerofoil Boat operation.
An exception was Dr. Alexander Lippisch, whose background was founded in
aircraft design (mostly centred around 'delta wings')... hence his great
contribution to WIG design through the development of the anhedral reversed
delta platform. Lippischs' experimental prototypes ( X-113 and X-114 )
were concentrated more on developing Type C WIG, and in these craft
aeronautical design does play a significant role.
However, even before Lippisch began thinking about wing-in-ground-effect
as applied to 'boat' design, the Russian shipbuiler Rostislav Alexeiev
began to design ships (from a naval engineering viewpoint) which employed
WIG principles in his designs. This came from his understanding that
hydrofoils had certain design speed limitations, and he reasoned that if
the foil could be lifted clear of the water, these speed limiting factors
could be eliminated. Although Dr. Lippisch (and his student Hanno Fisher)
are highly regarded as pioneers of WIG, Alexieve must surely be regarded
as the 'father' of WIG / Aerofoil Boat design building pre-cursors to the KM
long before 'the west' was even considering such advanced boat designs.
The differences between the background of these two designers
illustrate that one approached the 'problem' from an aeronautical
viewpoint, whereas the other approached it from a hydrodynamic
viewpoint. If the 'problem' is approached from a strictly aerodynamic
perspective, then I would have to agree with you that the HF concept
would be an ineffecient aircraft, However the craft is not meant to be
an 'aeroplane', but rather a highly effecient 'boat' (Aerofoil Boat / Type B WIG).
In an attempt to explain further the differences, there are a few Aerofoil Boat
designers who have abandoned the wing-foil shape completely and are
experimenting with flat surfaces to create the ram cushion, and apparently
with great success... suddenly even more 'aerodynamic principles, math
and theory' disintegrate into irrelevance. It's a bit like an aerodynamic
engineer trying to prove (through reams of data) why a paper aircraft
cannot fly, as a kid folds one and sends it 'flying' across a field.
A 'WIG' (Type B WIG / Aerofoil Boat) is a BOAT, not an 'aircraft', it is
not an attempt to create an aircraft, and does not operate in the
design parameters of aircraft (3 axis control). WIG in fact, are more
closely related to advanced tunnel-hull, advanced hydroplanes, and advanced
hovercraft in their operating parameters. Actually, the Chinese 'SWAN'
Aerofoil Boat (see photo below), is almost capable of 'hovering' and VTOL utilizing 'PAR' (power assisted ram).
I also think you could 'tone down' your 'hard' criticisms of the concept
through such terms as ... "This is what you get when an artist sticks together trendy buzzwords to make a pretty picture with no understanding of the engineering behind the concepts, or of the design requirements for the intended mission... cartoons" ...."
We get the point that, (in your opinion) the concept has no validity. Thanks for your observations - obviously everyone is entitled to their own opinions. I guess the 'proof will be in the pudding', and we will have to wait to see the final testing to actually determine whether the concept is valid or not. Most aeronautical engineers believed the 'Swan' was a ridiculous concept when first proposed also, but it has been successfully operating as a 12 passenger ferry on a Chinese lake since the late 1990's.
Last edited by foxxaero : 08-22-2004 at 01:45 PM. Reason: add link
As already mentioned, the enabling technology in the HF is the unique overhead rotor. It is it the core of an effort to fly a rotor at mu>1, this is, as you know, where the forward speed generates a reverse airflow over the full length of the retreating blade. Although
Carter has not reached this magic limit yet, their test flights have reached mu=0.87, apparently a rotorcraft record already. You can find engineering data on their web site
As the cruise speed of the HF is "only" around 120 knots, the results from Carter tests cover already the reduced operational requirements of the HF.
The wing in ground effect
The same for the WIG wing. With traditional WIGs there are at least two problems:
1. The center of lift travels from about 45% till 25% of chord going from extreme ground effect to out of ground effect
2. The power required to overcome the hump drag needs to be cut very rapidly once the hump is conquered
To keep pitch stability WIGs:
1. need a very large horizontal stab
2. cruise at speeds that are barely over take-off speed
The tip weighted rotor as "take-off aid" eliminates both problems as the WIG of the HF:
1. only has to provide significant lift in the upper third of the speed range, as the rotor takes care of the middle third
2. cruise speed can be extended to about three times the take-off speed.
Again, there are few if any remaining engineering challenges in downgrading WIG wings to such markedly reduced operational requirements and simplicity of design.
This is not to say that the HF is without engineering issues: one is the effect of the rotor down wash on the performance of the low WIG wing. This is being studied at the School of Mechanical and Manufacturing Engineering of The University of New South Wales in Australia, one of the few academic institutions where ground effect is being studied intensively.
In this sense I believe the HF is very much an engineering effort, in particular, one that tries to optimize three modes of lift across the speed range for the sake of efficiency and economy of operation within the transportation niche between high speed ferries and short range aircraft.
But the proof of the pudding remains in the eating.
Thank you for your continued interest.
WIGS do physics too
I admire your enthusiasm for WIGs. However, classifying them as boats does not absolve them from the general engineering principles of flying. I have not read the report Tom mentions nor do I know anybody who did, but in WIG circles this report is famous for keeping the USA institutions out of the WIG race (for as much as there was one). All in all, the experts did understand the problems WIGs were faced with and I can sympathize with their conclusions that there were more established technologies to fill the missions that the Russians were trying to fill with the big Ekranoplans. Furthermore, I strongly doubt that those who apparently are successful in testing flat surfaces instead of wing foils are a threat to "aerodynamic principles, math and theory". I am not saying that there is nothing new to be learned, possibly even from the behavior of flat surfaces in ground effect, but it is a pity that those who claim to find striking exceptions to the general laws do not have the necessary background to be able to formulate and validate the purported updates to those laws.
I appreciate your efforts to tone down criticisms, but I also understand the frustration of separating the internet bazaar of the bizarre from the pearls of the radical ;-)
Furthermore, the HeliFerry web site was only meant to be an introduction to the concept for ferry operators. It is only normal that an engineer would not be satisfied with this shallow level of discourse.
Thank you for taking the time to provide all this historic background on WIGs.
Empirical vs Theoretical
The 'flat' surfaces references were thrown in sort of 'tongue in cheek' and I agree that the 'flat surface' proponents do not represent a serious threat to 'aerodynamic principles, theory, and math', however I feel the experiments are 'interesting' nevertheless.
According to my understanding there are two types of 'knowledge' ...
empirical & theoretical. There are some who propose that 'theoretical'
knowledge is the 'be-all & end-all' [only true form of knowledge] while
others propose the opposite. In my view, the 'truth' lies somewhere in
Here is an example ...
Three teams are currently developing boats for the outright WWSR
(World Water Speed Record). The 'Quicksilver' (UK team) and the
'American Challenge' (US team) are both heavily reliant on
computational & aerodynamical studies in developing their craft.
Opposed to these teams is Ken Warby... (current holder of the
outright world water speed record set in 1978 - 317.6 mph), and who
has prepared a new boat, 'Aussie Spirit' to break his own record
some 27 years later. Like his last boat design, this was built in
his garage ... no computers ... no theory... no math - just 'gut
instinct' based upon empirical knowledge.
Now, Ken Warby has no experience whatsoever in 'theoretical'
knowledge ... has no understanding of aerodynamic math & theories...
has no back-up from giant corporations - and yet, based upon
'empirical knowledge' alone has held the outright WWSR for over
25 years! Other attempts (based upon 'theoretical' design) to
overcome his record, have ended in catastrophic life-terminating
What is the point of this story? ... Simply, that I do not accept that
one form of knowledge supercedes another.
Just my .02 cents worth (again). Now, I think I will retire from this
conversation, but please continue this discussion which i will follow with great interest, because I know little, but I like to learn.
There is no contradiction here. The core of science is experimentation. The purpose of science is repeatability. Mathematics is just a language of science. A theory is just a consistent set of laws. There is nothing more practical than a good theory. In aerodynamics plenty is covered with good theories, but there is also plenty not covered well. Yet. Then there is the problem of computability. There is little use of a theory for which a computer as big as the universe is not large enough to work out a solution. Many aspects of aerodynamics are not yet covered by such a useful theory, no matter how many mathematicians are put to the problem.
So, Ken Warby is an experimenter and is apparently very good at it. He is not a scientist as he probably has no desire to communicate his findings as to keep the records in his name. His exploits do not defy the laws of nature, most likely do not defy present theories of hydro- and aerodynamics (which are just the best current approximations of the laws of nature). They just defy a couple of teams of learned engineers in a domain of application that is only partially covered by current theories.
By the way, the tale about the theory of aerodynamics (as if there is only one) proves that bumble bees (or replace by any other flying creature) cannot fly is an urban myth.
Wacky Heliferry from 1930
From the covers of Popular Mechanics magazines
Although not very 'reasonable', I guess it just goes to show there is 'nothing new under the sun'... (although, I don't think you have any competition here, Luc ... :-)
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