Awesome RC Model Plane (Vanity)

YouTube ^ | 08-27-2014 | Self

[Sergio]

A question for the aviation buffs on this forum. I was told at one time, that the F-16 was an inherently unstable aircraft, and that without assistance from it computers, no human pilot would be able to fly the aircraft.

Then I saw this video, (see link below), of a quarter scale, radio controlled F-16, in the colors of the Royal Dutch Air Force demonstration team.

I would think that there is not enough room in the model or money in the owner’s bank account to include flight control computers. So my question is; “How is the unstable F-16 model can fly so well without its flight computers?”

https://www.youtube.com/watch?v=qQ9dSrrBN28

[USNA74]

Yep, good catch, my bad. The Thunderbirds.

[longfellow]

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

[ontap]

It’s also deified in Israel!!

[SolidRedState]

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

[Mat_Helm]

Paul Mantz was a great pilot. He died flying the Tallmantz Phoenix P-1. It was not made of parts from the Flying Boxcar Fairchild C-82. It was:

North American T-6 Texan engine, cowling, propeller, undercarriage wheels and cockpit controls Beechcraft C-45 Expeditor wings, North American L-17 Navion wheel used as the P-1's tailwheel. Tallmantz-designed and constructed fuselage, wing roots and skids.

"During filming on 8 July 1965, Mantz tried to simulate a takeoff by making a "touch-and-go". As Mantz came in for another low camera pass, his rate of descent at 90 mph exceeded the plane's structural capacity. The modest impact of the touchdown, coupled with the sudden drag caused by the aircraft's cobbled skid/wheel landing gear, caused the boom section behind the wings to fail, propelling the nose section forward, with the P-1 breaking up violently, killing Paul Mantz instantly.[2] Stuntman Billy Rose, also on board, was thrown clear and survived with a broken shoulder and pelvis."

[tanknetter]

Depends on the configuration of the aircraft as well. Had an F-22 tell me once that the Raptor is stable in take off and landing configuration (gear and flaps down) but unstable in flight config.

[uncle fenders]

I have been flying model planes for years.. and while most models aren’t truly dead on scale the F16 is considered one of the best flying models of jets..It flies fine without any complicated gyros on board... the fuselage provides a lot of the lift and stability.

[Sergio]

Thanks Mat, I had no idea that it all revolves around the relationship between CG and CL. Makes perfect sense once explained, but in my mind, the whole instability thing was much more complicated than that. I thought it was all structural design features and black magic.

Thanks for the very educational post.

[Sergio]

Good to know...so I’m a putz...at least we got to talk about some cool airplanes and models. LOL! Thanks for the post.

[GBA]

You're not ready for a Memory Care Unit yet.

You are correct about the F-16's inherent instability and this instability is desirable for an aerobatic airplane like a fighter. From Wiki:

Negative stability and fly-by-wire

The F-16 was the first production fighter aircraft intentionally designed to be slightly aerodynamically unstable, also known as "relaxed static stability" (RSS), to improve maneuverability. Most aircraft are designed with positive static stability, which induces aircraft to return to straight and level flight attitude if the pilot releases the controls; this reduces maneuverability as the inherent stability has to be overcome. Aircraft with negative stability are designed to deviate from controlled flight and thus be more maneuverable. At supersonic speeds the F-16 gains stability (eventually positive) due to aerodynamic changes.

To counter the tendency to depart from controlled flight—and avoid the need for constant trim inputs by the pilot, the F-16 has a quadruplex (four-channel) fly-by-wire (FBW) flight control system (FLCS).

The electric jet/lawn dart F-16 was a huge step, an honest technological leap actually, beyond the F-4 or anything the Soviets or anyone else were flying at the time.

[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.

[MtnClimber]

Yes, I can see that. Flap settings could change staability too.

[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.

[GBA]

Stability also comes from the angle of the wings to the fuselage, with the greater the angle (more V shape as viewed from head-on), the greater the stability and self-leveling as opposed to no angle/greater instability as with a fighter.

Boats, V-hulls and flying wings are similar.

[DainBramage]

Blue angels fly 18s

[TruthBeforeAll]

Don’t know if he is using them, but the miniature gyros available for model planes and helis are quite amazing. You can set them up to correct for unwanted pitch, roll, or yaw. They sense deviations in position not initiated by the transmitter (pilot) and automatically move the servos controlling the flight surfaces to try to correct for it. If the movements coincide with what the pilot is doing with the transmitter, they allow movement proportional to the amount of stick input. They are not perfect, but they make flying unstable RC aircraft much easier. Especially helicopters.

[Sergio]

I’m cured! I’m cured! Thanks for the information GBA.

[Sergio]

Thank you Phlyer. Cool and educational.

[Sergio]

LOL! Poor horsies.