[Sergio]

I will be in and out so please excuse any delays in replying to posts. Thanks in advance for everyones expertise and sense of humor.

[ImJustAnotherOkie]

The F117 was unstable and un-flyable without computers but I never heard of that associated with the F16.

[Rennes Templar]

Heck, build it a little bigger and you can hop in and take a spin!

[SJSAMPLE]

I think the “too unstable” stigma was originally given to the F-117 “Wobbly Goblin” stealth “fighter”. I believe pilots have dispelled that rumor.

The F-16 was the first production fly-by-wire aircraft, but that was because the unique control configuration and the desired performance envelope.

[MtnClimber]

It is not just how the model looks. I believe the real F-16 has the center of mass behind the center of drag so it would tend to swap ends if not for the computer controls. The model would only need weight distribution to move the center of mass in front of the center of drag. The tail even increases the drag behind the center of mass if the model starts turning a bit sideways.

[Steely Tom]

I never heard anything about the F-16 being inherently unstable.

F-16 was developed in the early 1970s, with first flight in January 1974 (according to Wikipedia). This was several years before the first active computerized fly-by-wire aircraft were demonstrated; if I recall correctly, the first such aircraft to carry a human pilot was the Grumman X-29.

[DCBryan1]

Everyone knows that if you put a big enough engine on ANYTHING, it will fly. Exhibit A: The F4 Phantom

[driftdiver]

The F117 required computers to fly as it would depart from normal flight if the computers went down. This is called negative stability.

I don’t think the F16 has that problem. It requires computers to fly but will stay in the attitude it was when the computers were lost (neutral stability). Its more complex than that but there are definately model F16s that fly.

Do a search on “airplane stability” and you will find some good sources.

[skinkinthegrass]

absolutely Awesome, w/o icc.
didn't know turbojets engine are that small.

[blueunicorn6]

The F-16 was unstable, but after four years of intense psychotherapy, and lots of mood-altering drugs, it worked through all the issues.

[SpeakerToAnimals]

It is called relaxed static stability. Move the CG far enough aft and the plane is unstable. But it turns much more responsibly. That is what GD did to me the F-16 so maneurable. The model has the CG further forward and is stable.

[USNA74]

Not certain of the real answer, but the fact that the Blue Angels flight demonstration team flys them for that purpose means they must be pretty darn stable.

[DJ MacWoW]

Did You Know?

The Current FReepathon Pays For The Current Quarter's Expenses?

Now That You Do, Donate And Keep FR Running

[Mat_Helm]

Because a model does not have the same weight, thrust, CG, aerodynamic forces involved. The model may look like an F-16 in dimensions and wing sweep, but does not have the same wing profile for supersonic flight, slats and flaps, fuel cell transfer system to maintain specific CG during flight, and other factors. Control surface dampening and computers prevent pilot induced oscillation (PIO) and require functioning AOA sensors along with the flight control computers. If you lose all the AOA sensors the plane is equally difficult to control. As the nose departs one direction and the pilot corrects it departs again in another direction and or over corrections by the pilot until he is chasing it to the point of complete departure. F/A-18 Hornets have the same problem if you lose the AOA sensors. The flight computers are continuously making small trim corrections to maintain 1G flight with hands of the stick. Even with pilot inputs to the controls the computers chose the best assortment of control surface deflections to accomplish the directional change input by the pilot as programmed and with design limitations for allowed positive and negative G forces. Flight test pilots take the test aircraft to departure limits in the design phase with unlimited and dangerous control and from subsequent tests software engineers create the code that than limits flight control movement to prevent loss of flight control. That is why flight testing is dangerous business and flown under strictly scripted maneuvers over time and testing departure limits beyond the wind tunnel and computer modeling.

[longfellow]

Can’t help but think about the Jimmy Stewart movie flight of the Phoenix.

[SolidRedState]

I've been flying crashing RC planes for some time. Never anything that large. That is one slick little model.

[Phlyer]

Some of the other posters are getting close to the right answer, but I'll take my shot at it, too.

The F-16 (including YF-16) is unstable in pitch. That is caused when the center of gravity (CG) is behind the aerodynamic center (AC, also sometimes called the center of lift - not drag). You can make it stable either by moving the aerodynamic center aft (which happens inherently in supersonic flight - so the F-16 is stable in pitch when supersonic) or by moving the CG forward (which is what models do), or by adding area aft in the planform (bigger horizontal tails) which also moves the AC aft.

Being unstable in pitch has two advantages. First, since you have to work to keep the nose from pitching up, it's very easy to get it to pitch up when you do want it to - so it's very quick to increase pitch/angle of attack/g-level. In fact, unlike the F-4 and other prior fighters, you can increase g so fast in an F-16 that the pilot can pass out (G-LOC, or g-induced loss of consciousness) so fast that he never knows he's losing it until he's unconscious. In other fighters, there's generally a tunnel vision, then gray-out as warning signs. So they had to add automatic recovery modes to the F-16.

The second advantage is that traditional aircraft, when they pitch up, require a down-load on the tail to keep the stable aircraft from pitching back down. A statically-unstable (in pitch) aircraft requires an up-load on the tail to keep it from pitching up even further. This adds to net lift. This is particularly helpful on tail-less aircraft like the Mirage 2000 (also statically unstable in pitch) where the trailing edge surfaces can now be used like flaps to increase total lift rather than like spoilers as an unwanted effect to go with their pitch effect.

There is an additional benefit for supersonic aircraft in that the transition from statically unstable (subsonically) to statically stable (supersonically) does not result in the aircraft becoming so stable supersonically that it's hard to maneuver at all.

The flight control computers take care of all of this without direct pilot intervention, so the aircraft flies as though it were stable in all flight regimes.

Once the F-16 proved it could be done, all subsequent advanced fighters (e.g. F-22, F-35) have been statically unstable in subsonic flight.

[tcrlaf]

“So my question is; “How is the unstable F-16 model can fly so well without its flight computers?””

“If you put enough power on a door, it will fly”. Something my first flight instructor told me, many years ago.

The relative power curve is probably higher on the model, than on the real thing. Just my guess.

[bunkerhill7]

F-16 jocks do low pass stuff over my farm all the time and the horses try to jump the doors n` run out of the stable.

F-16 was an inherently unstable aircraft coz it unstables the horses.

[BikerTrash]

I built a ducted fan F-16 radio control model back in the mid-80s, the first one anybody ever seen around my neck of the woods. It most assuredly did not have a flight control computer. It flew great.

I was not the pilot, just the builder. That had a lot to do with why it flew so well.

[Half Vast Conspiracy]

Former F-16 “B-shop” Flight Control Systems Specialist here. Yes, the F-16 was designed with relaxed static stability. The all-electronic fly-by-wire flight control system instead of a conventional hydromechanical system with linkages and cables made this design possible.

F-16 Design Origins

Since a model is…well, a model…is doesn’t necessarily have the same characteristics of the real F-16. In the model, you could easily adjust he center of gravity for optimum stability.