Wing in ground effect boat

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
6,728
Location
Saline Michigan
When you say "mechanical surface follower", I assume you mean a small gadget that is bouyant to prevent sinking at rest and planes on the surface at anything above taxi speeds, and is connected to the elevator or to a servo tab that drives the elevator.


WIG watercraft face some significant challenges on anything except flat seas. The biggest issues involve flying along swells, waves, and wakes. If you have a deep water swell of 2 feet running 300 feet between crests, and you are going 67 mph, the water beneath you is about going up and down 2 feet every three seconds. And you are asking the craft to try to follow that. Make it a shallow lake chop like we deal with on Lake St. Clair and Lake Huron, and it is more like two feet every 60 feet. Ok, inland lakes with four inch chop on a several foot spacing. You are still trying to follow a surface that moves up and down at accelerations that will be more than just uncomfortable.


To run successfully on big water, you need to fly above the crests, be able to average the surface movement, and be able to correct upward for an impending big wave. That really says radar/ultrasound/laser sensing of the seas state ahead, digital processing to figure out what the craft needs to do, and fast servo control of the elevator, and fast elevation response of the craft.


Surface followers have several issues, but the biggest one will be lag. The planing gadget runs into water of increasing height, pushes upward on the linkage, which moves the elevator, which generates extra lift on the canard, which pitches the craft nose up, and both wings make more lift, which accelerates the craft upward. Each step requires some small but finite time to achieve. If the total response time is longer than the time available between trough and crest, you have just clipped the crest.


Next the surface follower does not know anything about how quickly it is being moved upwards, only about how high it is. So it does not know if the wave front is shallow or steep. And it does not know if the the trough it is following and causing negative vertical velocity is followed by a steep rise in water height...


Next problem is with with mechanics. It has to float when stationary, and plane when moving, but it also has drag which is a function of vertical load and water speed (not airspeesd). It can be on a mast, a leading arm, a trailing arm...The mast can be bound from the drag of the sensor planing over the surface, the leading arm has downward moment added to the primary moment, and the trailing are has arising moment. Muddy signal to drive the elevator... Oh, and the arm the sensor is running on has aero drag too.



Billski
 

Starman

Well-Known Member
Joined
May 16, 2009
Messages
2,011
Location
High in the Andes Mountains
Those are good points Billski and the system I was thinking of addresses them to some extent and I realize it may not be sufficient.

First of all the surface follower won't float, it will be quite heavy and fairly thin so it can iron out some of the smaller surface irregularities, plowing through ripples and low waves, but that will make it take longer to respond to bigger waves.

The method uses a trailing arm pivoting near the nose so that it won't tend to catch or get broken off if it hits a solid object in the water. Due to the geometry a trailing arm will react with more authority, or power to move the elevator, to a rising surface than a leading arm would (kind of like a mast that angles forward)

Also, as I mentioned in the previous post, the follower will be able to be trimmed and overridden by the pilot, who will have 100% elevator control. This is needed partly to keep the follower from sinking (causing nose down pitching) during the takeoff run. I envision some kind of stiff spring in the system and it also may need to have a hydraulic damper which slows the extension of the follower after it has been pushed upwards in order to reduce the workload for the pilot.

After all is said and done, the best surface follower is no doubt and air cushion at the nose generated by the front wing and the mechanical follower is more like and adjuster or trimmer of that.

I've been contemplating multiple wings, like three or even more. With three a center wing can be a fuel tank. In a plane the downwash from the front wing affects the rear wing whether it is a canard or conventional but on a WIG there is no downwash so it seems there would be less of a penalty from using multiple wings.
 
Last edited:

orion

Well-Known Member
Joined
Mar 2, 2003
Messages
5,800
Location
Western Washington
Actually there is an effect similar to downwash in WIGs and it's something that has given the Jorg craft some problems, especially early on. While the presence of the surface does mitigate the downwash field, it is not total due to the close proximity of the wings to each other. And of course the other issue that has to be dealt with is the variability of this effect (and others) with height so trim functions can get "interesting".
 

Starman

Well-Known Member
Joined
May 16, 2009
Messages
2,011
Location
High in the Andes Mountains
I had the idea of using longer spans, which would allow the aircraft to fly out of ground effect, but using only a water drive to make it qualify legally as a boat. A low power high efficiency water prop for cruise with the addition of a high power inefficient prop for takeoff.

This is probably a long shot, but does anyone know what the relative efficiencies are of water props vs. air props when both are optimized for efficiency? :)

I think that even if the efficiencies are similar that the requirement to have automatic surface following will cause excessive drag for the water prop setup and make the efficiency unacceptable for long range.
 
Last edited:

Starman

Well-Known Member
Joined
May 16, 2009
Messages
2,011
Location
High in the Andes Mountains
OK, I invaded a boating design forum and found out that water props aren't as efficient as air props, so scratch that idea.

I guess it's time to build a model now so I can do the juggling in 3D.

What's the easiest, quickest way to build a model that won't get waterlogged? Styrofoam?
 
Last edited:

orion

Well-Known Member
Joined
Mar 2, 2003
Messages
5,800
Location
Western Washington
Water props are nowhere near as efficient as air however, they do operate in a liquid that's 800 times as dense as air so even with low efficiency they can generate sizable thrust numbers. But whether to use them versus an air drive does require a bit of analysis so an off the cuff answer is pretty much impossible.
 

Starman

Well-Known Member
Joined
May 16, 2009
Messages
2,011
Location
High in the Andes Mountains
Re: Wing in ground effect

Water props are nowhere near as efficient as air however, they do operate in a liquid that's 800 times as dense as air so even with low efficiency they can generate sizable thrust numbers. But whether to use them versus an air drive does require a bit of analysis so an off the cuff answer is pretty much impossible.
I found out what I needed to know on the boat design forum. A slow turning large diameter submerged water prop, that looks like an airplane prop, can get up to 80% efficiency, but that's for slow boats, and then they also have the drag of the prop supports.

For fast boats a surface prop is better, and the best of those gets 70% efficiency. The experts there agreed with what you said, that larger slower turning props are more efficient for surface props as well. I would have been willing to use a water drive on the cruise engine if it was high efficiency but it's not worth the trouble, plus a water drive can become damaged easily.

I'm aiming for a cruise of around 90 - 100 mph and a cruise power of about a 100hp engine running at say, 70% or so, or less hopefully. In order to get maximum efficiency there will be no limits as to prop diameter and rpm, so it can be a big prop, say 8 ft.

Is it reasonable to expect an efficiency of 80% with an optimized air propeller?
 
Last edited:

Jan Carlsson

Well-Known Member
Joined
Jan 11, 2009
Messages
1,860
Location
Sweden
Starman, calculate with an efficiency of 75- 80% depending on speed and prop diam/RPM (6-8´)

Jan
 

lurker

Well-Known Member
Joined
Apr 13, 2010
Messages
385
Location
salisbury, NC
Re: Wing in ground effect

you are of course correct. i posted the airboat link because i don't really understand why the discussion went to props in water, when there are boats (and GEVs) that operate fine without them, and without the added complexity and weight, which appear to my uninformed eye to increase the more you look at it..

maybe i need to re-read the thread?:ponder:
 

Starman

Well-Known Member
Joined
May 16, 2009
Messages
2,011
Location
High in the Andes Mountains
Re: Wing in ground effect

Starman, calculate with an efficiency of 75- 80% depending on speed and prop diam/RPM (6-8´)
Thanks Jan, so far I'm allowing for an 8 foot prop as I think that for optimum efficiency at 100mph it will not need to be larger than that. If it can be smaller and still optimum that would be good because it can lower the thrust line. Could you please make a rough guess as to optimum diameter for 100mph @ 100hp to get me in the ballpark.
 
Last edited:

Starman

Well-Known Member
Joined
May 16, 2009
Messages
2,011
Location
High in the Andes Mountains
Re: Wing in ground effect

you are of course correct. i posted the airboat link because i don't really understand why the discussion went to props in water, when there are boats (and GEVs) that operate fine without them, and without the added complexity and weight, which appear to my uninformed eye to increase the more you look at it..

maybe i need to re-read the thread?:ponder:
Sorry, I've given away some valuable ideas to the public before but I'm not ready to give this one away yet.

Besides, it probably won't work, it's just a stupid idea from a, like, totally crazy dude. :gig:
 
Last edited:

bmcj

Well-Known Member
HBA Supporter
Joined
Apr 10, 2007
Messages
13,358
Location
Fresno, California
Here's a link to a WIG craft by the Universal Hovercraft guys. It appears to use a industrial v-twin and belt redrive. From the site, each prop can be decoupled via belt tension to add slow speed maneuverability. Pretty neat machine.

~Bill

I thought this one was pretty neat too. It says "radio control", but it looks full-sized to me.

[video=youtube_share;gyLwK7Akx2I]http://youtu.be/gyLwK7Akx2I[/video]

Bruce :)
 

orion

Well-Known Member
Joined
Mar 2, 2003
Messages
5,800
Location
Western Washington
No, it is a model (the boat in the video is the chase boat with the radio operator in it). Furthermore, it is a model made out of very light styrofoam artboard sheets and as such, it has totally unrealistic behavior and performance, scale or otherwise. Also, when it comes to ground effect flight, canards tend to be very destabilizing except in extreme ground effect craft such as the tandem wing concept developed by Jorg.
 

FlyOver

Member
Joined
Jun 14, 2012
Messages
5
Location
Munich
Hi, I am new to this forum but I have a special interest for Ground Effect Craft.
Lately I hear that Mr Fischer is building the Hoverwing 20 and he said that Hoverwing 50 is already built. It is currently being tested in Korea. Anybody have heard about this?
 

orion

Well-Known Member
Joined
Mar 2, 2003
Messages
5,800
Location
Western Washington
The twenty seater I believe is an outgrowth of the Airfish 8. The program started up in Australia, moved to Malaysia after accounting discrepancies were discovered, was sold to an investment group in Turkey and as of a couple of years ago, the whole thing was again sold to Singapore. Although it started certification, I don't think it ever completed the process (International Maritime Organization and Lloyds) - the Singapore government was going to certify it themselves, but only for their waters. According to one of my sources, the craft has some stability / trim issues so we're not sure if it will succeed in its current form or not.

The HW50 is apparently being developed in Korea but outside of some published hype, I don't think there has been anything of substance published, as far as I know.

In the past the most current information was published at the WIG page (The WIG Page - information about Ekranoplan and Wing-In-Ground effect craft), although it seems the last page registration was in 2008. I don't know if Edwin is keeping up with it or not. The site also had a discussion board (I was one of the technical moderators for a while) but I don't know if it's active today or not.
 
2
Top