Can fighter aircraft glide?

Question

In case of engine failure, do the fighter jets have such a stable airframe so that they can glide their way through to the nearest landing strip (As it happened in the case of Gimli glider)?

Answer 1

All airplanes can glide, if they couldn't they wouldn't be able to fly in the first place. When you glide an aircraft you are converting height into airspeed, which you can use to move across the ground. How far you can go across the ground for height lost is called the glide ratio for the aircraft. Gliders have a very high glide ratio as their wings are designed to provide lots of lift at low speeds, fighters have a very low glide ratio as they are designed to provide lift at a much higher speed enabling the fighter to achieve high airspeeds efficiently.

So a fighter will glide, it just won't be able to glide that far over the ground. If a fighter has enough altitude to trade for speed and a strip close enough by it can be done (and has been done in the past) by a skilled pilot.

Answer 2

All airplanes can glide. Some glide better than others.

A very old reference I read talked about engine-out landings in military aircraft. Their procedure was arrive at the airfield at X feet, circle once and land. Trainers like the T-33 needed 2,500 feet, other aircraft needed 3,500-5,000 feet.

An F-104, which is basically an engine with fins, needed 20,000 feet for the landing loop. So unless you have a flameout in the stratosphere (or directly overtop an airport) you would simply point it at an empty space on the ground and eject.

Answer 3

Yes, all aircraft have a glide ratio. On many of the higher-performance fighters, it's 1:1 at best (1 foot altitude traded for one foot forward gliding).

Many of the newer fighter aircraft are intentionally unstable. They aren't really flown by the pilot; they're flown by a Flight Control Computer System (FLCCS) which depends on electrical and hydraulic power; the pilot tells the FLCCS what they want to do and the FLCCS uses electrical signals and hydraulics to move the flight controls. Electricity and hydraulic power are provided by generators and pumps on a gearbox driven by the engine. Ergo, engine-out (especially on a single-engine bird) means they can lose the FLCCS which means they are, effectively, giant "lawn darts."

I spent multiple years as a Crew Chief on F-16's with Uncle Sam's Air Force. As a single-engine plane, we jokingly said that, when the engine went out, it was in "lawn dart mode."

The F-16 does have backup systems. The aircraft battery will supply power for a couple minutes, depending on what all you're using. The hydraulic accumulators will provide hydraulic power for a minute or two, assuming you don't get too crazy. And the Emergency Power Unit (a small, monopropellant turbine in the right strake of the aircraft) will start promptly after losing the engine, providing electricity and hydraulic power for several minutes as necessary (the battery and accumulators keep you under control while it spins up). Ergo, if you lose the engine, you lose propulsion but you still have electricity and hydraulic power. So you can still maintain control of the airplane.

We had more than one occasion, in my time, where we had an F-16 engine conk out (we were playing with brand spankin' new Block 50s with a new model of engine) and the pilot managed to glide the plane in without injury or damage to the aircraft. They were near the base when it happened, the EPU fired (so they were able to maintain control of the aircraft), the glide ratio was sufficient to reach the runway and the tailhook (yes, Air Force birds have 'em) caught the cable and stopped them safely.

So, the short answer is yes, modern fighter planes can glide. Different planes have different ratios, some of them little better than a rock thrown at altitude. And, even if they're designed to be inherently unstable, they have backup systems such that the pilot can maintain control in an engine-out situation.

Answer 4

If the shuttle can glide to a landing, so can a fighter aircraft. Gliders have speed brakes to control the glide path angle, and the fighter can vary the angle of attack, which works in much the same way. Also, it can slalom towards the field, so if the pilot picks a landing site close and long enough, the landing is no big problem. Landing gears are normally designed to fall out with gravity alone if the locking mechanism is unlocked. However, I doubt the pilot will be able to deploy all the high lift devices, so the touchdown speed will be rather high.

On modern fighter aircraft with artificial stability, the avionics and hydraulic pumps need to work, or the aircraft will not be controllable by a human pilot. In that case, ejection is probably the safest option if all engines fail. If the glide takes more than only a few minutes, hydraulic pressure will have been lost shortly after the engine(s) and any auxiliary power unit (EPU) stop running, and even if the battery-powered flight computer still gives the correct commands, the actuators will not work anymore. Fighters need to be light, so running times of EPUs are only a few minutes, mostly.

For a successful flare, an aircraft needs a minimum L/D of approximately 5, so it will fly even if no more altitude can be spent during the landing rotation. The only aircraft I ever "met" which did not fulfill this criterium was the European return vehicle project "Hermes" before it got winglets. They were added to make the transition between final approach and touchdown flyable. Hermes was never built, so all these landings happened purely in a computer.

Answer 5

Descent Characteristics of the A7-E

The A7-E, which has been retired for a while, was a single-seat, light-attack jet. The glide ratio of this aircraft is about 12:1. This is calculated for a windmilling engine (2-3 %rpm), aircraft gross weight at 23,000 pounds, drag count of 30, and no wind. With an initial altitude of 35,000 feet (5.76 nm), and a maximum range descent speed of 209 KCAS, the aircraft will travel 69 nautical miles. This performance will be worse if the engine is seized.

Without an engine the A7-E didn't fly very well, and dead stick landings were prohibited. If I remember correctly this was true for 2 reasons:

1. Hydraulics on the Emergency Power Package were not optimal, and quick movements of the controls could freeze them.
2. In an engine off approach it would be very difficult to stay within the ejection seat envelope, and towards the end of the approach the pilot would actually find themselves outside the ejection seat capability.

Flameout Approach and Landing

If flameout occurs below 1,500 feet and below 250 KIAS, no restart was to be attempted and the pilot was to eject. If airspeed was above 250 KIAS, the excess speed could be converted into altitude, and a restart of the engine attempted. Again, if the restart was unsuccessful procedures dictated the pilot eject. The approach is aggressive.

The flameout approach and landing is a procedure to be used only if the pilot cannot eject from the aircraft. All external stores are jettisoned to reduce drag as much as possible. In this configuration the aircraft will lose 5,000 feet in a 360 degree 30 degree turn. The "high key position" is at 175 KIAS and 5,000 feet with gear down, coming in perpendicular to the runway.

Low key position is 3,200 feet and 175 KIAS, transitioning to the 90 degree position of 1,500 feet and 175 KIAS. Final is at 500 feet and 175 knots, and the aircraft is flared at 50 feet. Touchdown 3,000 feet from approach end at 155 KIAS. The Emergency Power Package will not supply adequate flight control pressure below 125 KIAS.

Normal Carrier Approach

The normal approach for us was the 180 position with gear and flaps down at 600 feet at approximately 125 knots. For situations such as engine oil pressure low, critically low fuel, engine fire, or in other words possible engine failure, a precautionary approach was required. It will keep the pilot within the ejection seat envelope throughout the approach.

Precautionary Approach

The precautionary approach had the aircraft at the normal distance abeam, 180 degree position at 2,000 feet with the gear and flaps down. The Emergency Power Unit would be deployed. This provided limited hydraulic power in the advent of power loss, as well as basic electrical power. The speed brake might be needed to manage airspeed in the descent to the field. The power was set at 75% and the aircraft airspeed at 150 knots. The normal 90 degree position would be hit at 1,000 feet, instead of the normal 450 feet. At the 45 degree position and runway made, gear down, reduce power to flared landing.

I remember doing the Precautionary Approach after taking a bird strike near the intake at the target. Only touched the power a few times, minimized g-loading. Out of the target set the maximum range climb rate, called an emergency with ATC, planned the descent. Came in high and fast to hit the 180 at 150 knots and 2,000 feet. It was quite a ride compared to the sedate carrier landing pattern.

If the engine flames out roll wings level, stop descent, using excess airspeed, and EJECT.

Answer 6

One of the most important things I learned ( in my opinion) when I played around with flight simulators is that all planes can glide. Every aircraft has a "glide plane" which is basically an angle of approach to the ground where you won't stall. The angle depends on the physical characteristics of the plane (wings, etc.). So if you lose power, you can always glide to the ground. The problem is whether your glide plane is wide enough to allow you to reach an airport. You can think of the glide plane as basically telling you that you will drop X feet every Y minutes. So if you want to land at airport you have to time it right (you can also point the nose down to increase speed and approach the ground faster, if you don't have enough glide path left to circle the airport completely.)

Answer 7

To help put the discussion of a dead stick landing in perspective here is the ejection seat envelope for a fighter jet.

Thought I would provide the ejection emergency procedure for the A7-E. There are several factors that go into the ejection envelope, e.g. pilot reaction time of 2 seconds. But you can see from the documentation that the last 40 feet of the approach are outside the envelope, unless you can stop the descent. When you stop the descent then you would be at positive altitude and zero airspeed, which is better than zero-zero. At that point of a standard approach one must be careful because you are at the edge of the envelope. At the edge means something like one swing in the shoot before hitting the ground.

The procedure for the dead stick landing is EJECT. If you can't eject and have to land with a windmilling engine you will not be inside the ejection envelope for the last part of the descent. The dead stick approach has very high rates of descent. Another consideration that makes this approach so dangerous is that as airspeed decreases, emergency hydraulics have limited effectiveness. One can't juts yank the stick to stop your descent. The stick will freeze. The comment in the manual is "You better be an exceptional pilot to attempt this!"

I would bail out before I would take a dead stick landing.It is like why they give old-timers a zero visibility and zero cloud ceiling height clearance to take off. They know these pilots would never use it.

Here is another look at the envelope given dive angle and airspeed. You will see that there is no safe ejection at zero-zero for any dive angle. The closer you approach a zero degree dive the closer you are being in the envelope, but nonetheless you are still just a bit outside.

Again "zero airspeed and zero altitude" means that. If you are at zero altitude and have any descent you are outside the ejection envelope. If you are at zero altitude and have any rate of climb you are inside the ejection seat capabilities. Judging exactly where you are when close to the boundary is a very dangerous decision that probably should have been made earlier.