Wing in ground effect boat

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

Cardmarc

Well-Known Member
Joined
Jun 16, 2021
Messages
100
Modify a Seawind 3000 kit with a lower hp engine for WIG? The 3000 we are finishing building has an io550 and is expected to cruise ~200 mph. One guy is using a diesel and expects it to be able to go trans-pacific easily. And no have to deal with choppy seas affected a wig. Thoughts?
 

nestofdragons

Well-Known Member
Joined
Jun 8, 2016
Messages
809
Location
Near Antwerp, Belgium
The Seawind missing the chance to blow prop air under the wing. By doing so, it would gain increase of pressure under the wing and get a quicker rise out of the water which results in less drag and higher speeds.
Airfish 8 has a rather long run before it gets out of the water.

If i would generate a WIG i would go for a Power Augmentation Ram (like they call it for the Russian Ekranoplans) and place the props in front of the wing. Examples: Wolga-2, Aquaglide, TW-1, Ivolga, Kaien. Last one is a huge RC-model. If you don't know these.



 

Dan Thomas

Well-Known Member
Joined
Sep 17, 2008
Messages
7,470
The Seawind missing the chance to blow prop air under the wing. By doing so, it would gain increase of pressure under the wing and get a quicker rise out of the water which results in less drag and higher speeds.
I don't think so. It would work against you. Accelerating air between two surfaces lowers the pressure there. It doesn't raise it. It's what makes a venturi work. Hovercraft raise the pressure by trapping air underneath with a skirt. Very little air movement.

1668618011245.png

1668618033786.png

This is the same reason that some aircraft direct the blast over the top of the wing. It lowers the pressure and increases the lift.

Sometimes the laws of physics are not intuitive. A WIG generates its lift the same way an airplane does, with ground effect defeating drag-making and lift-losing wingtip vortices, and by reducing the upflow at the leading edge. Lift is generated over the top.
 

jedi

Well-Known Member
Joined
Aug 8, 2009
Messages
3,470
Location
Sahuarita Arizona, Renton Washington, USA
I don't think so. It would work against you. Accelerating air between two surfaces lowers the pressure there. It doesn't raise it. It's what makes a venturi work. Hovercraft raise the pressure by trapping air underneath with a skirt. Very little air movement.

View attachment 131809

View attachment 131810

This is the same reason that some aircraft direct the blast over the top of the wing. It lowers the pressure and increases the lift.

Sometimes the laws of physics are not intuitive. A WIG generates its lift the same way an airplane does, with ground effect defeating drag-making and lift-losing wingtip vortices, and by reducing the upflow at the leading edge. Lift is generated over the top.

There is more to the story than the above implies.

The examples given demonstrate the conservation of energy. Add mechanical energy to the system and the variables, pressure and velocity, change to represent the energy added. Adding energy as heat is a different story.

A propeller, fan or compressor adds energy (sometimes) resulting in a higher pressure or velocity. A turbine (or windmill) extracts energy. reducing pressure or velocity.

Nuff said?
 
Last edited:

Dan Thomas

Well-Known Member
Joined
Sep 17, 2008
Messages
7,470
Nuff said?
Probably. So someone needs to build it and prove it one way or another, but converging and diverging duct theory doesn't care about added energy. Just study the turbine engine.
 

nestofdragons

Well-Known Member
Joined
Jun 8, 2016
Messages
809
Location
Near Antwerp, Belgium
I like this discussion as i see that many doubt about how a WIG works.
I am really puzzled by the reverse delta of Lippisch. I read that it is a help to gain better transit from ground effect to flight. But ... how? In a delta the main chord is closer to the centerline of the airplane. So ... main chord is longer. So ... distance between AC (aerodynamic center) in flight (at about 25% main chord) and AC in ground effect (much more backwards, not sure at which percentage of main chord) must be larger. And i think that makes it just more difficult to transit from ground effect to flight. Or ... am i missing some large other item that explains it???
 

cluttonfred

Well-Known Member
Supporting Member
Joined
Feb 13, 2010
Messages
9,726
Location
World traveler
I like this discussion as i see that many doubt about how a WIG works.
I am really puzzled by the reverse delta of Lippisch. I read that it is a help to gain better transit from ground effect to flight. But ... how? In a delta the main chord is closer to the centerline of the airplane. So ... main chord is longer. So ... distance between AC (aerodynamic center) in flight (at about 25% main chord) and AC in ground effect (much more backwards, not sure at which percentage of main chord) must be larger. And i think that makes it just more difficult to transit from ground effect to flight. Or ... am i missing some large other item that explains it???

1668782866307.png
If I had to guess I would say that the reverse delta planform and anhedral of the Lippisch type of WIG acts as a triangular scoop when the tail is down and therefor helps with the initial transition from floating on the water to flying on a cushion of air.
 

addaon

Well-Known Member
Supporting Member
Joined
Feb 24, 2008
Messages
2,293
Location
Kanab, UT
As so often, AVL is a great tool for quickly gaining an intuition on the impact of ground effect on flight dynamics. It’s not full CFD, and in this case that means that it can’t model a “ground” at an angle to the coordinate system, so it can’t capture e.g. the effect of AoA putting the back or an airfoil closer to the ground than the front; but (a) you can get pretty far without that and (b) it can handle a tandem wing where you add that effect manually.

Recommended, as always.
 

nestofdragons

Well-Known Member
Joined
Jun 8, 2016
Messages
809
Location
Near Antwerp, Belgium
As so often, AVL is a great tool for quickly gaining an intuition on the impact of ground effect on flight dynamics. It’s not full CFD, and in this case that means that it can’t model a “ground” at an angle to the coordinate system, so it can’t capture e.g. the effect of AoA putting the back or an airfoil closer to the ground than the front; but (a) you can get pretty far without that and (b) it can handle a tandem wing where you add that effect manually.

Recommended, as always.
I read that if you want to have calculations of a WIG in some software, you need to mirror the same vehicle upside down with the ground as mirror-line.
 

nestofdragons

Well-Known Member
Joined
Jun 8, 2016
Messages
809
Location
Near Antwerp, Belgium
This video Aron-7 Wing-in-Ground-Effect (WIG) Seaplane Video shows the Korean Aron 7 taking off from relatively rough water at one point (40 seconds). It also looks like it is underpowered and requires a long time to take off.
Starman, please, do not make the same mistake as they did with that American reverse delta (sorry, forgot its name). Story goes that they knew about the Airfish 8, but they wanted a USA-edition. So ... they put a much larger engine in it. Seems like they want always at least a V-8 in what ever they ride, fly, float. 🙄
I guess it was Orion who already mentioned that it had a bad history.
About a long run before take off, it seems they all have that. I saw a Airfish 8 take off video that demonstrate it too. Took some time before it got in the air.
I have heard about people trying to add hydrofoils to get it quickly out of the water. They did that in France, but i cannot find a video of it taking off from water. The video i found tells that it took 10 years to get the hydrofoil right. 😯
Most promising videos i saw had their props in front of the wing and were directable to blow under the wing.
 
Last edited:

jedi

Well-Known Member
Joined
Aug 8, 2009
Messages
3,470
Location
Sahuarita Arizona, Renton Washington, USA
I like this discussion as i see that many doubt about how a WIG works.
I am really puzzled by the reverse delta of Lippisch. I read that it is a help to gain better transit from ground effect to flight. But ... how? In a delta the main chord is closer to the centerline of the airplane. So ... main chord is longer. So ... distance between AC (aerodynamic center) in flight (at about 25% main chord) and AC in ground effect (much more backwards, not sure at which percentage of main chord) must be larger. And i think that makes it just more difficult to transit from ground effect to flight. Or ... am i missing some large other item that explains it???

I will not verify or dispute the premise but can suggest a possible explanation.

In ground effect the loss of lift due to tip losses is reduced therefore the CP (center of pressure or effective center of lift) moves outboard and forward with the reverse delta when in ground effect. This counters the CP shift from the transition of the CP from 50% to 25% MAC as the aircraft climbs out of ground effect.

This characteristic is amplified with the anhedrial and tip plate effect of the floats in the Lipish configuration.
 
Last edited:

nestofdragons

Well-Known Member
Joined
Jun 8, 2016
Messages
809
Location
Near Antwerp, Belgium
I will not verify or dispute the premise but can suggest a possible explanation.

In ground effect the loss of lift due to tip losses is reduced therefore the CP (center of pressure or effective center of lift) moves outboard and forward with the reverse delta when in ground effect. This counters the CP shift from the transition of the CP from 50% to 25% MAC as the aircraft climbs out of ground effect.

This characteristic is amplified with the anhedrial and tip plate effect of the floats in the Lipish configuration.
Now that explains a lot. As the CP shifts outwards the chord gets shorter and the distance between AC in flight and in ground effect gets smaller. Yep, that might be a great new insight. I will try to generate a drawing that explains this thinking.

Step by step we might get closer to the why and how of that Lippisch design.

Thanks, Jedi. You helped a lot.
 

Tiger Tim

Well-Known Member
Joined
Apr 26, 2013
Messages
5,058
Location
Thunder Bay
View attachment 131869
If I had to guess I would say that the reverse delta planform and anhedral of the Lippisch type of WIG acts as a triangular scoop when the tail is down and therefor helps with the initial transition from floating on the water to flying on a cushion of air.
Maximizing wing area while holding the floats down low and floating with a nose up attitude without dragging too much below the waterline also brings you to a reverse delta.
 

jedi

Well-Known Member
Joined
Aug 8, 2009
Messages
3,470
Location
Sahuarita Arizona, Renton Washington, USA
In my opinion the biggest advantage of the Lipish reverse delta is the ability to have a very small ground clearance at the trailing edge of the wing while the leading edge is high enough to clear any significant but reasonable waves in overwater operations. This allows operations at an efficient cruising height that can be controlled to an optimum depending on the sea state for overwater operations.

In addition having a stable translation from “ground” to flight mode allows it to skip from crest to crest, an important quality for the transition. This helps minimize, but does not eliminate, the multitude of WIG issues.

I look as it as a super air boat or the ultimate Bass boat.
 
Top