The F-117 Nighthawk... ???

Question

Is it true that the F-117 Nighthawk is aerodynamically unbalanced under certain conditions? If so, what r the conditions n why is it unbalanced??? Details welcome.

Answer 1

The concept is called Relaxed Static Stability (RSS) or Negative Static Stability.

A stable aircraft tends to return to its original attitude when aerodynamic changes (intentional or otherwise) causes disturbances. Though this is good from the design point of view, it also means that there is a latency in response to a control surface deflection (aileron/rudder/elevators) as the aircraft tends to maintain its stable attitude or in other words it hinders maneuverability. An unstable aircraft doesnt have the tendency to return to level attitude and is more responsive to control surface movements. The trouble is, its a pain to fly as it needs constant attention from the pilot to keep it level. In the RSS aircrafts there will be dedicated onboard computers that constantly trim the aircraft without instructions from the pilot. The computing power required is significant and so only the modern aircrafts have the RSS design and they obviously need Fly-By-Wire controls.

The F-117 is unstable in all the three axes at all times. There is no case of special conditions, it was designed to be unstable.

Answer 2

Well different missions really, the F-117 is an Attack/Bomber type aircraft, designed to fly at night, and be undetectable by radar carries all weapons internally. Although the A/C was developed in the mid-late 70's, it has an advanced computer fly-by- wire controls, modern glass cockpit and systems. It will easily stay in service for the next 5-10 years as a front-line aircraft. It also had a fantastic service/sortie rate (85/90%) during the first Gulf War. The F-22 is designed as a All weather Fighter/Attack, steallthy (more so than the F-117), but is also a supersonic (the first A/C to cruise supersonic without using afterburner) FIGHTER first, designed to defeat any opposing aircraft, an "Air Superority fighter". Its expensive, and will take several years to be fully intergrated into service. Yes, its a replacement for the F-117, but look for a later mark say a F-22 D/E model, with adjustments/modifications in the airframe (extra seat most likely) that will replace (and retire) the F-117 . After all look how long the F-15-16's have been in service

Answer 3

Aerodynamically, the F-117A is a nightmare.
The plane was built with one purpose in mind, to be stealthy. Everything else was secondary. All the facets (flat plates) on the surface make aerodynamic hash (turbulence) out of the airstream around the aircraft. Normally, aircraft want to have as smooth (laminar) airflow around the body as possible.

In fact, the first flight took place with the engineers unsure if the plane would actually get off the ground.

The reason the F-117 is able to fly at all is because of computers and fly-by-wire flight control systems. The aircraft is inherently unstable in all three axes of flight (pitch, roll, and yaw). For fighter aircraft, this is actually an advantage. An unstable aircraft is a responsive aircraft. Some of the most unstable aircraft out there are the most maneuverable aircrafft. They WANT to turn, loop, and roll.

On old aircraft, the limiting factor was always the pilot. The pilot had a direct, mechanical (or hydraulic) connection between the flight controls and the flight control surfaces. The pilot's reactions and skill had to be great enough to keep the unstable aircraft in the air. If it was TOO unstable, the pilot would crash.

Fly-by-wire systems have changed that. The pilot's controls fed information into a computer, and then the computer moved the flight controls to do what it thought the pilot wanted. The advantage is that the computer also took information about how the aircraft was flying, and used that information to keep the plane flying straight and level.
So, aircraft could be made much more unstable, because the computer could keep an unstable plane flying straight and level much better than a pilot can. In fact, there are many stories of fly-by-wire aircraft getting the pilots home even though they were missing big chunks. One early F-117 lost it's entire tail, and the pilot did not notice until his chase plane asked him if he noticed the plane acting strangely. The computer was able to use the remaining flight control surfaces to keep the plane flying even though the tail was gone. The tail was redesigned.
Other stories of F/A-18's and F-16's landing with missing wings are factual.

Answer 4

Unbalanced? I'll say, it is definitely unbalanced. It takes a very complicated computer system just to keep it in the air. It is a fly by wire aircraft in that the flight controls are electrically operated, not by hydraulics as hydraulics respond too slow. The pilot determines the attitude the plane is to fly in and the computer maintains that attitude by making dozens if not hundreds of corrections per second to the flight controls. That is something the pilot cannot do.

I saw a 117A do a fly-by at an airshow one time and the pilot waved the wings to the crowd. In the process he almost lost the plane, at least it looked that way to me. It was very erratic. The 117A is a stealth aircraft, not an acrobatic aircraft. It was designed more for ground attacks at night, rather than a fighter.

Answer 5

That planes is unbalanced in all flying conditions and requires a computer to fly without it it will crash. The imbalance is caused by the squared shaped body. It is rumored the planes high operating cost have put it on the chopping block to be replaced by the F-35.

Answer 6

correction : the jet is unstable like all the new generation jet fighters so it can have better maneuverability like the F16 , but that doesn't have to do with any condition .the super computers are assigned to detect every move and feed the aircraft with the co-ordinations to balance the jet automatically . just think about it . if jet fighter is aerodynamically unstable its going to be unstable under any condition .
some information u might like on the F117 :
*1st jet aircraft to be completely stealth
*maximum speed : 702 mph 1130 km/h (just below Mach 1)
*only operates at night and the pilot shuts down any radio transmitions to overcome any risk to get caught)
*Laser guided missiles feature
*cant operate without its computers
*costs 45 million dollars each
* maiden flight was in june 18th 1981

Answer 7

I just read that the F-117 is standing down. This basically means that the entire fleet is about to be retired.
It's funding is being moved to the F-22 Raptor program.

Answer 8

To answer the other asker's question of why it's called a fighter ... the START/SALT series of nuclear arms treaties limits the number of bombers we and the russians could have. Therefore, since the F-117 wasn't a nuclear capable bomber, it was designated a fighter so that it wouldn't rack up numbers against the limit of bombers.

Answer 9

The Air Force's F-117 fighter uses aerodynamics discovered during research into how bumblebees fly

Answer 10

The more stable the aircraft, the less maneuverable it is.