Soviet Union's Giant Ekranoplane (Ground Effect Vehicle)

[hyo silver]

Just out of curiosity, what percentage of total thrust would typically be used to generate the necessary lift? Is the percentage higher for a larger plane?

[mbartley]

How do these turn? All the video clips I've found of these (modern ground effect planes, as well as the Caspian sea monsters) show them in straight and level flight. It looks like if they banked more than a few degrees, a wing would hit the water and they'd crash.

Although, I saw a brief (a few seconds) clip of a smaller ekranoplan descending from an an altitude high enough to safely bank. I also saw a clip of one with wingtip fuel tanks which occasionally did hit the water. I don't know how fast that was moving though. I can't see surviving this at 300 knots.

[qbee42]

Originally Posted by hyo silver

Just out of curiosity, what percentage of total thrust would typically be used to generate the necessary lift? Is the percentage higher for a larger plane?

The lower the speed, the higher the percentage of thrust that is used to create lift. Looking at it the other way around, high speed creates more aerodynamic drag, so when you go fast you have to devote a lot of thrust to overcome the drag. A hovering helicopter devotes 100% of it's thrust to creating lift.

Originally Posted by mbartley

How do these turn? All the video clips I've found of these (modern ground effect planes, as well as the Caspian sea monsters) show them in straight and level flight. It looks like if they banked more than a few degrees, a wing would hit the water and they'd crash.

Although, I saw a brief (a few seconds) clip of a smaller ekranoplan descending from an an altitude high enough to safely bank. I also saw a clip of one with wingtip fuel tanks which occasionally did hit the water. I don't know how fast that was moving though. I can't see surviving this at 300 knots.

Banking is not necessary to turn an aircraft. Normally we bank aircraft to keep the G forces perpendicular to the floor of the aircraft. This is more comfortable for the occupants and keeps the lifting surfaces equally loaded. However, you can use the rudder to skid an aircraft around a turn, just like a car steering around an unbanked turn.

Tom

[cnschult]

In aviation we have a saying:
If its weird its French, if its ugly its British, and if its weird and ugly its made in Russia

The ailerons control roll, elevators control pitch, and rudders control yaw. The ailerons, elevators and rudders are called control surfaces. While you can turn using just the rudder, when you turn using both ailerons and the rudder it is called a coordinated turn, which allows the pilot to overcome adverse yaw so that the nose of the aircraft remains pointing directly into the relative wind as the flight path begins to curve. This is basic flight school stuff even taught to ATC who may never set foot in a cockpit.

Vehicle stability control systems are designed to prevent understeer (FWD) and oversteer (RWD), if someone says VSCs are designed to keep your car from losing control of yaw it means they are in aviation and that's just how we think of things.

[cnschult]

To answer hyo_silver's question about what percentage of thrust goes to keeping it afloat as opposed to moving forward.

This is not something we consider in aviation. Instead we consider something called stall speed, as air moves past a wing it flies faster over the wing, the decrease in pressure over the wing creates lift. This is Bernoulli's principle, obviously he used liquid fluids when he discovered this phenomenon hundreds of years ago, but air is a gas fluid so it applies to air as well.

Back to stall speed, which is the speed in which an aircrafts wings can no longer create enough lift to overcome weight (4 forces on aircraft are lift, weight, thrust & drag). The stall speed for every aircraft is different, the most powerful aircraft have a higher stall speed, which is why in certain controlled airspace jets are often allowed to exceed the speed limit for safety reasons.

At lower speeds the pilot can extend the wings (flaps) to create more lift which thus lowers his stall speed for landing and takeoff but they cannot be extended at higher speeds. As I said the stall speed for every aircraft is different, the stall speed for a cessna or piper is well under a hundred knots, whereas the stall speed of a fighter jet may be much higher. So the Air Force would typically send 2 jets to intercept a small plane or helicopter that is suspected of smuggling drugs because a plane or helicopter can safely fly much much slower than the fighter jet, so the fighters have to take turns flying tandem circles around the smaller aircraft in order to have the suspected aircraft in constant visual contact, otherwise a defense attorney would be able to get the smugglers off if there was only one fighter claiming that the fighter lost visual contact with the suspect while circling around.

Back to the giant Russian beast. Unlike Boeing or Airbus, the Russians don't give a hoot about aesthetics in their aircraft, they are purely functional machines, as i said if its weird its French, if its ugly its British and if its weird and ugly its Russian. Don't confuse ugly & weird with unsafe, the principles of flight are not that difficult, I wouldn't mind riding in an aircraft like that once in my life just for fun.

Needless to say the stall speed on that thing is going to be pretty high (around 200mph without flaps), and its going to require at least a 2 mile runway, and if it were to land at high altitude it may require a much much longer runway. I've heard a 727 will use pretty much the entire runway when taking off from Denver in the summer.

Another thing to consider is the glide ratio, a typical glide ratio is 11:1 (meaning if the engines fail it will glide 11 feet forward for every 1 foot in elevation it loses), this is very important as it is what allowed Captain Sully to fly for miles to land his craft in the Hudson. Obviously the glide ratio goes to almost zero once stall speed is reached, but I'm willing to bet the glide ratio of the Russian beast is much much less than 11:1.

[Rokeby]

There are special considerations and economies for aircraft specifically
designed to fly close to a hard surface, the ground or water:

Ground Effect in Aircraft

WIG - Wing in Ground Effect - YouTube

WIG - Wing in Ground Effect - YouTube

Ground Effect Vehicles; Damn Interesting

A long time ago, I soloed in sailplanes, frequently but incorrectly
called "gliders." At the time the typical L/D (Lift over Drag or glide ratio)
for a trainer might be 15-20/1. IIRC, competition sailplanes were 50/1
which has since been extended to 60:1 and perhaps more.



At any rate, sailplanes typically aren't very tall and on landing the wing
is low enough to be flying in ground effect. The practical result is lift is
increased, the 'plane wants to ballon upward which is countered with
down stick which increases speed. The problem is how to stop the thing
before you run out of runway. For this, sailplanes typically have "spoilers"
on their wings, vertical surfaces that can be raised just behind the thickest
part of the wing -- good thing too, that's where the wing spar is typically
located -- to grossly disturb the flow and kill the lift. Spoilers properly
deployed have you dropping slowly through a foot or so and "greasing"
the landing with hardly a bump or jolt. Only then do you apply the brake
or drop the nose onto the skid to shorten the roll-out.



My instructor said, "Any landing you can walk away from is a good one."

[qbee42]

Originally Posted by cnschult

To answer hyo_silver's question about what percentage of thrust goes to keeping it afloat as opposed to moving forward.

This is not something we consider in aviation.

<snip>

It may not be something that pilots consider, but aeronautical engineers spend a great deal of time an effort understanding just such things. The word "aviation" in the above statement is too broad.

Tom

[cnschult]

yes i was just referring to the airmen and the ATCs who (attempt) to control them. I mean no disrespect to aeronautical engineers; after all, I think the lowest quality aircraft built in the U.S. is probably built way better than a Lexus, as aeronautical engineers often build redundant, double and even triple redundant systems into their aircraft. This makes airplanes very expensive to own and maintain, my neighbor just sold his mooney in favor for a 1/5 share in a twin cessna. Needless to say it was the smart move as he was able to buy a new corvette and volt with the proceeds. I've taken it up a few times but it'll be awhile before I make the transition from right to left seat. (Don't you just hate movies where the "pilot" is sitting on the right instead of the left? . . . as though I'm ever going to allow anyone to make right hands turns in my airspace)

But I'm pretty sure that job number one of an aeronautical engineer these days is fuel economy, not stall speed (even though type A jet fuel and 100 low lead fuel are both much cheaper than gasoline or diesel). Nowadays if you design an aircraft and are considering 2 engines, say a rolls royce or a G.E. If one saves you 2% fuel over the other but raises your stall speed by 2 knots, I'm pretty sure the engine you're gonna go with is the more efficient one. That's just my opinion, I could wrong.

[airportkid]

WIG is a concept that's been explored for more than half a century, with, as shown in this thread, some serious development money devoted to it. But WIG has NEVER been developed beyond prototypes - it's never made it to practical application and production. Efforts are still underway right now to try to do so; the effort has been more or less continuous all along, and I expect it'll keep going for decades more.

But if it can't be made to fly after more than fifty years of dedicated attention, it probably never will. Some of its problems may be insuperable. One enormous problem is swell. Anything greater than about 12 inches of swell knocks these things right back into the water.

Another problem is air density. WIG craft operate at the most expensive layer of the atmosphere, where it's thickest, at sea level, and are thus overcoming the greatest drag. Their fuel consumption per horsepower would be higher than that of any airplane, and they'd need enormous horsepower on top of it. Those Caspian Sea Monsters needed twelve (twelve!) engines for a reason. The Airbus 380 only needs four (albeit the 380's engines are considerably superior to the 60's technology of the Sea Monsters, but a 1960's Boeing 747 only needed four engines too).

By far the largest problem, however, is relative cost effectiveness. You have to build a WIG craft to aircraft standards, and if you're going to all the expense and trouble to build an airplane, build an airplane, not half of one that can only do half of what an airplane can do. Essentially, an amphibious airplane can do anything a WIG craft can do, plus a good deal more, so the airplane makes more sense for the same investment.

If you could build a WIG craft for a third the investment an airplane requires, in engineering, fabrication, training or operation, the concept might start to be feasible. But that hasn't been possible after 60 years of trying.

[Maine Pilot]

Here's still a different link, (English-Russia): http://englishrussia.com/2007/06/21/ekranoplans/

Great pictures.