Forum: F-16 Procedures

What Gums said about F-18 not having full fly-by-wire is still true. It has a mechanical back up, and that's not full FBW. I may be wrong, but I believe the F-18 also does not have relaxed static stability (aft CG) to take advantage of FBW capability. About controlling roll with leading edge flaps - the Navy found out very early in the game that the F-18 could not roll fast enough at low altitude high speed conditions. Something about a wimpy wing tending toward aileron reversal. The wing was redesigned for greater torsional stiffness and the LEF was programmed to help roll the airplane.

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Salute

Contrary to many references, the Hornet was not the first plane to have fly-by-wire, much less full fly-by-wire [FBW]. It still does not have full FBW. And the aero design is statically stable, unlike the Viper.

Many misconceptions are out there, and this is the place to find the "truth".

And by the way, the whole discussion should be on another thread.

I expect John-boy, Snakehandler, Outlaw, Snake-one, Roscoe, JR and others to help me here.

I refer to a recent article in Popular Mechanics by a techno-dude I had respected. He looked at or talked with an "expert", and the outcome was not all that accurate.

http://www.origin.popularmechanics.com/ ... 95240.html

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a] "touch"

Since the early fifties, no advanced U.S. jet fighter had feedback on the stick from the control surfaces. Some of the Migs had it and those pilots can tell you what it was like pulling hard at high speed. Try the Fresco, for one.

All of the jets used hydraulics to move the ailerons, rudder and elevators.

You can not "feel" the air on those control surfaces. All you can "feel" is the reaction of the jet to your inputs. I flew one jet in combat, and for another thousand hours, that allowed you to actually "feel" the air. It was the Dragonfly.

So let's get this "feedback" crapola off the table, huh?

b] Most every jet I flew had electric or mechanical or pneumatic "helpers" for dampening. Even the Dragonfly, but not the original "Tweet" version.

Some even had "limiters" such as the Viper. Primarily the VooDoo, which had several layers of "help" to keep the pointy end forward.

The SLUF had a doofer called "control aug" that used force transducers on the stick to "help". In fact, if you commanded small movements, the physical movement of the stick was negligible. On FCF's we would keep the control column stationary and use only the stick grip to command maneuvers. The grip had transducers similar to the Viper to provide hydraulic commands to the control surfaces.

c] The "expert" from Global Security doesn't realize that the update rates for the Viper's new digital FLCS is faster than forty hertz.

The digital FLCS is slower than the original analog FBW system used by the Vipers I flew. The analog hardware had "zero" lag, as it didn't have a "frame rate" and the basic capacitors, resistors and inductors operated at the speed of light [ or electrons].

d] One thing the "expert" got right was the battle damage aspect of the Viper's FLCS. My leading-edge-flap recovery would have been impossible without that neat FBW system.

The Viper's FLCS uses every control surface there is to get you where you "command".

I will take that any day versus my pilot skill keeping the plane flying.

e] The Viper was the first operational jet with full FBW and zero mechanical backup. I stand by that.

There were other "x-planes" and such that needed full FBW, and some prolly flew outta Groom Lake, but that's another thread.

The shuttle is also full FBW, and it's frame rate was fifty hertz or so, not forty as the Global Security expert alleges.

In the Viper, there is no control stick connected to any hydraulic valves or anything. The stick grip has about an eighth of an inch movement to help formation and small corrections [ I didn't find it helped in the Block Five and later, but what the hell].

The Hornet actually physically moves a hydraulic valve for pitch commands when the electrons go to lunch. Tell me I am wrong.

f] Does the Hornet have a RAT? Can it have hydraulic and electrons if both motors go offline?

I don't think so.

The Viper has an EPU that works no matter what. It will last five or more minutes and allow you to point the jet someplace and eject or deadstick to a convenient runway or road.

g] Someone please post the graph of the Hornet static stability margin.

I have the Viper graphs, but YOU show me yours first, O.K.?

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Sorry for the rant, but I am sick and tired of folks claiming all the great things about the Hornet that we had in the Viper prototype and the later operational models years before the uber-Hornet.

The poor soul in the Hornet crash did the best he could with what he had. And another thread might deal with the two-motor jets versus the one-motor ones. That extra motor didn't help him much when it quit, huh?

Gums sends ...

Gums, you don't need any help from me on this one. You got right all the way from my view.

I would still define the Hornet a full FBW jet because its quadruplex digital FCS has full authority to all control surfaces. Mechanical reversion, that is removed from SH, is irrelevant.

Hornet is staticaly stable with good margin. The book with the graphs says "restricted".

Hornet does have an alternative hydraulic and electricity generation cabability. It is called the another F404. It also does have enough battery power for longer than 5-10 mins. It also has an APU to provide some hydraulic power.

This is not about who was the first or who is the best. I am only pointing out that FBW is not that unique to F-16.

F-16 and -18 both fly ways impossible to legacy fighters, still they fly different from each other.

Salute

No problem, Mech.

Our "purist" view of FBW has to do with the fact that there were no mechanical connections of any kind in the Viper. Simple. And same for the shuttle.

BTW, anybody know if the Hornet rudder pedals are hydraulic-mechanical doofers? Viper's pedals moved only a half an inch and were transducers, even for nose-wheel steering.

The extra motor on the Hornet crash episode didn't help much. And it was also true that the Viper motors were different from the Eagle motors due to the single-engine design. I have found that battle damage can be a player on the motors, as you can read from my interview concerning the Dragonfly. OTOH, more weight, higher fuel consumption and so forth.

The Viper EPU provides hydraulics and electrons. If your motor fails, but you have gas left you can fire up the APU and get decent hydraulics. The mod we did for the FLCS power after our "problem" was discovered also used the big, main battery for power, so the EPU was not as important after that.

So it comes down to "purists" as to a pure FBW with no backup versus a "full authority FBW" that also has a mechanical back-up of any kind. If I am not mistaken, I believe that the Airbus also has a few mechanical connections to the servo-tabs on some control surfaces.

respectfully,

Gums sends ...

Gums wrote:

BTW, anybody know if the Hornet rudder pedals are hydraulic-mechanical doofers? Viper's pedals moved only a half an inch and were transducers, even for nose-wheel steering.

Hornet's pedals have long movement like old (hydraulic-)mechanical ones but are only connected to electrical FCS. Brake action in pedals is mechanical connection to brake valves.

I'm glad to agree to disagree with you Gums on the full FBW Wink

AH HA, hmmmmm

So the Hornet has a back-up hydro-mechanical horizontal tail doofer AND actually has a hydro-mechanical brake system? How come the stick moves so much? The Blues don't wear g-suits, as they claim it screws up their control inputs when it inflates and deflates [hence, number six has g-loc and augers last year].

With the side stick that is a hundred percent electric and moves less than an eighth of an inch, no problem. You can also see the "click" when a Bird relaxes pressure on a roll - sucker flat "freezes" at whatever bank angle existed when releasing the stick. Hornet has a slight bobble due to the stick moving against the roll momentum. Check it out next airshow and you'll see it.

Sheesh, only mechanical connections we had to ANYTHING in the "electric jet" were a] throttle lever to the motor, b] ejection seat handle, and c] the emergency blowdown bottle for the nose gear.

Lost nosewheel steering one day due to some wierd electical prob and student studly and I agreed to fire the EPU, as we had also lost brakes [no mechanical connections, see?]. It worked, and we regained the steering. Strange, but true story.

Gums sends ....

Is the 117 not fully FBW?

Gums wrote:

If I am not mistaken, I believe that the Airbus also has a few mechanical connections to the servo-tabs on some control surfaces.

You are entirely correct about the mechanical connections.

I retract my comparison to the Viper.

Embarassed

, OL

vegasdave901 wrote:

Is the 117 not fully FBW?

Believe so. In fact it had the Viper's analog FLCS tweaked for the 117's particular needs, IINM. As for any mechanical backup or reversion? Couldn't tell ya. My clearance didn't go that high. Wink

The Hornet doesn't have full/total FBW, but it definately has full authority FBW. The F-16 techs can adjust their ties, when they mention the weight saving by not incorporating the mech backup system. The F-18 techs could argue that their mech system provides a backup in case of battle damage.

Obi

Not just weight saving, but more responsive maneuvering due to the negative stability margins available with full FBW, lower drag with a lifting tail, more room for fuel, lower cost, and higher reliability without all the mechanical clap-trap.

vegasdave - Yes, the 117 had FBW flight controls without mechanical backups.

Just to clarify the Airbus v. the Viper FCS. Embarassed

The Airbus FBW aircraft have two mechanical connections.

One is through the trim wheel to the stab (typically a jackscrew). Stab is a secondary flight control surface with an elevator attached to it, and the elevator is controlled electrically only by the SSC, no tabs.

The other is to the rudder, probably to a servo tab (Airbus philosophy is that the pilot doesn’t need to know how anything works, just that it does). This reversionary capability is probably a regulatory requirement for any transport category aircraft (single engine or even most twin engine fighter pilots obviously don’t need to worry much about true non-centerline asymmetric thrust).

These capabilities (actually called Mechanical Backup mode) are to be used to keep it right side up & pointy end forward only temporarily with severe hydraulic problems until the RAT is deployed. You’ve got to have electrons (battery is fine if you’ve got the critical hydraulic system) to truly fly it effectively for recovery.

Have tried flying & landing the 330 (the sim of course) in Mechanical Backup with both engines flamed out, no APU & without the RAT. Basically you have only the mechanical trim & mechanical rudder.

You have only slightly more capability than the DC-10 at Sioux City, but it can be done.

For all practical purposes, the functionality and operation of the Airbus side-stick is identical to the Viper.

The one difference is that the Airbus side-stick moves more and has a “Mickey Mouse” artificial feel or spring centering system associated with it. And it has the look of some kind of high end Logitech or Microsoft game controller.

regards , OL

(How do you say Mickey Mouse in French?)

Outlaw,
Don't you remember??? You don't say Mickey Mouse in French! or McDonalds, or anything that deludes their culture. Damn ugly Americans trying to spread their idea's around the world.

Forum: F-16 Procedures

How does the stick work ???