Wing-in-ground-effect aircraft question

[H. Meyer]

Hello, I'm looking for an answer to a question relating to the performance of a WIGE aircraft at high altitude (between 5,000 and 10,000 ft.).

To clarify, I play a (unrealistic) table-top wargame in which wing-in-ground-effect aircraft have recently been introduced. I'm a member of a group trying to establish roles for these vehicles besides the large cargo carrier, and a question about deployment at high altitude was asked. Ideally, the aircraft would be 'dropped' or 'launched' from a large inter-planetary aerodyne (termed a 'DropShip'), and be able to maneuver (possibly dogfight against opposing fighters without radar-guided or heat-seeking missiles) before successfully descending to low altitude and sustained flight using the WIGE principle.

Available rules for the WIGE vehicles allow a controlled descent of 1 level of altitude per 'hex' travelled, roughly 6 meters vertical per 30 meters horizontal, with no allowance for climbing to higher altitude. (For example, a WIGE aircraft might fly off a 60-meter cliff and descend safely to its normal altitude, or maintain its altitude for a penalty in distance traveled until the end of its movement, at which time it is unable to sustain the altitude and descends safely. The WIGE aircraft is also unable to trade height for speed, 'bunny-hopping' over obstaces such as trees and low buildings.)

So, we have these questions;

1. What kind of drop rate might be expected at 10,000 ft? At 5,000 ft? Would the aircraft simply drop so steeply it resembles a lawn-dart?

2. What kind of maneuverability would such an aircraft have between 10,000 and 5,000 ft, or 5,000 ft and low enough to allow the ground effect to support it?

3. WIGE aircraft might include some form of generic 'STOVL' equipment (the ability to redirect thrust, hydraulics to change wing pitch similar to a Korean war-era U.S. jet bomber - can't remember its name, sorry.), be provided with a 'swept-wing' concept to increase the amount of surface area of the wing, or other gimmick justified in the description of the vehicle (referred to as 'fluff'). Would that assist in high-altitude flight? What kind of trade-offs would be realistic in such a situation?

We would appreciate any assistance, since we insist realism in the capabilty of such an aircraft be considered before any 'house rule' on the performance of a WIGE aircraft be created, and frankly, none of us are engineers. Thank you in advance.

 

[Filip Larsen]

The ground effect is usually considered relevant only at heights above the ground that are comparable to the wingspan, so traditionally the ground effect is usually only considered in scenarios involving landing and take-off. For a plane to utilize the effect to, say, save fuel, it has to fly very close to the ground or the water surface.

So to answer your first two questions as I understand them: Ground effect has no effect at 5k-10k ft and any aerodynamic vehicle would "have to" fly without it. Building a (fixed geometry) plane to utilize the ground effect would probably mean it has to have large wing surface so it should have no problem generating lift at those altitudes. However, if you go for very large wings it may have trouble with fluttering at high altitudes, meaning that it realistically would not be able to fly fast enough to generate lift without either stalling or beginning to have wing flutter. Of course, in your game you could just introduce the notion of some advance wing design that removes flutter.

As to your third question, it would almost surely be an advantage if you had a vehicle with morphing (or variable-geometry) wings that could adjust its shape to give optimal conditions for the given airspeed and altitude. Especially so if it is to be a re-entry space plane that use aerodynamic drag to slow down from orbital velocities (involving a lot of heat and high stresses).

And the term you are looking for is probably thrust vectoring.

 

[rcgldr]

I assume you mean ekranoplan type aircraft which have wings with long chord and short wing span, and perhaps some tunnel effect.

http://en.wikipedia.org/wiki/Ground_effect_vehicle

If released at moderate altititude, 5,000 to 10,000 feet, the issue would be it's glide ratio and structural limitations on speed when out of ground effects to control the descent rate. The mass to drag ratio seems fairly high, which could result in a lot of speed, possibly exceeding the structural strength of the aircraft. If the aircraft was strong enough to handle higher speeds, then it would be able to dive down to gain speed, then climb for a short period of time. Given suffient speed and angle of attack, a brick will climb.

Another issue would be an enhanced requirement for roll (aileron) and pitch (elevator) control when out of ground effect.

 

[vibjwb]

The space shuttle is a glider that uses ground effects when landing.
Most delta wings use ground effects when landing

 

[H. Meyer]

Thank you all for your interest!

We are assuming a fixed-wing aircraft designed to operate solely at low altitude with the wing-in-ground effect and a fairly low maximum airspeed. Would such an aircraft be able to control its descent? Variable-geometry wings, swept forward to espose more wing area, could be swept back to allow for an airframe designed to move at a higher speed, but according to game rules maintains the same structural strength as a slow moving aircraft. So, it cannot move faster than its 'flank', or top speed.

Really, we are looking for generalities; would (a slow, fixed-wing WIGE aircraft) enter a steep dive, unable to provide enough lift to support a controlled descent to low altitude (let alone fairly violent maneuvers, intended to evade weapons fired from another aircraft) and either be torn apart or loose control, or be able to generate enough lift at its maximum airspeed to approach level flight and control its descent?

I suspect a design such as the 'Caspian sea monster' (ekranoplan-type aircraft) would simply loose control, in which case I'm afraid the concept of a WIGE aircraft capable of flight outside the maximum height of the ground effect is fairly absurd. Hopefully this is not the case, but we rely on your opinions in this matter.

 

[rcgldr]

Would a WIGE aircraft enter a steep dive, unable to provide enough lift to support a controlled descent to low altitude.

Well it's going to reach a terminal velocity (magnitude and direction) no matter what. It may not do this while still in one piece though, and the resultant direction could be nearly vertical.

Assuming the aircraft doesn't break up, then the issue is if the vertical rate of descent results in impact with the ground before the aircraft can pull out of the dive.

Note the wiki article includes "Type C" WIGE's which are considered to be true aircraft that also operate efficiently in ground effect mode. These would be able to make the transition without issue.

I doubt that a large cargo WIGE could survive a drop from a few hundred feet, much less thousands of feet. Part of the design goal for WIGE's is to create a very strong tendency to target a specific ground effect altitude, despite any gusting wind effects. I don't know how relatively fragile the large transport type WIGE "ships" are made.

 

[mugaliens]

http://www.vincelewis.net/ekranoplan.html", great story, tons of pics and awsome videos!