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Elite Joined: Aug 19, 2004 Posts: 1089

Okay... perhaps I misunderstood F16JOAT's question. If he was asking whether or not an F-16 is capable of flight in the most general sense of the word without the use of its rudder, the answer would be yes. That's sort of like asking whether it's capable of flight under any number of emergency conditions. Most aircraft, especially combat aircraft, can generally continue flying after incurring non-catastrophic mechanical failures/malfunctions, battle damage, "acts of God", and so on. If, on the other hand, he was asking whether an F-16 pilot could lock out its rudder and have the fly-by-wire flight control system automatically and sufficiently compensate using all other available control surfaces, the answer would be no. As you stated, the jet must be flown very gently with a locked out rudder to avoid going out of control. Why? Because neither the physical control surfaces or flight control systems were designed to give the aircraft acceptable handling qualities without use of the rudder.

The B-2 was specifically designed to operate without a vertical stabilizer and conventional rudder. Its aerodynamics make it approximately neutrally stable about the yaw axis. The outermost control surfaces (rudder-vators if you will) maintain the B-2's directional stability ONLY with the help of the aircraft's fly-by-wire flight control system. Just like the F-16 needs its fly-by-wire flight control system to maintain pitch stability, so too does the B-2 for yaw stability. The only reason why an F-16 can fly (with great difficulty) without the use of its rudder is due to the fact that it still has a vertical stabilizer. The F-16 is still stable in the yaw axis (at least in non-extreme flight conditions) due to its vertical tail. To my knowledge however (someone speak up if I'm mistaken), the F-16's FLCS isn't wired to use any/all other available flight control surfaces in an attempt to mimic the control forces of the rudder itself. I remember reading on this forum that the F-22 IS capable of compensating for the loss of certain control surfaces by altering its control laws as needed. Then again, the F-22 has, if I'm not mistaken, 4 more control surfaces than the F-16. They are:

1) Independent ailerons (i.e. a pair of flaps and a pair of ailerons on each wing) which is two more than the F-16 which only has "flaperons".
2) Two rudders instead of the F-16's one.
3) Thrust vectoring in the pitch axis which amounts to an additional control surface, albeit not a physical/aerodynamic surface.

Am I missing anything? I guess I sort of am. The F-22 has two engines compared to the F-16's one and can thus use differential/asymmetric thrust to compensate for a loss of one or both rudders. That makes, I suppose, 4.5 extra surfaces, right? The fact that the F-16 doesn't have independent ailerons makes it even less suitable for flight without its rudder. Imagine having to perform a dead-stick landing in that thing under high wind gust conditions with a locked rudder. You might actually be better off finding an ideal spot to eject (both for yourself and to help ensure your aircraft came down in an unpopulated area) than trying to land an F-16 in bad weather without a rudder. Maybe Gums can chime in on this one. I know he landed his F-16 with a failed LEF, but what about a failed rudder? Oh, and one better hope that the rudder is able to lock itself in place at zero deflection or you're in for a wild ride.

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Veteran Joined: Jul 01, 2007 Posts: 336

Nicely stated, R1. I've run the gammut in the sim with locked out control surfaces and I am confident that the jet can be safely recovered in up to 25 knots of crosswind with one surface locked out. Locking out the rudder presents some interesting directional control difficulties on landing but since the jet is landed (usually) in a crab, it isn't as big a factor as landing with a locked out horizontal stab. The main problem is compensated for on the ground by using differential braking at higher speeds which leads to hot brakes and potentially blown tires. But all three of my attempts without rudder in the sim were successful. You are also correct in your assumption of the extra finesse required with the loss of the rudder.

Elite Joined: Dec 16, 2003 Posts: 797 Status: Offline

Salute!

OK, asked and you shall recieve.......

1) The B-2 design came from John Northrop's work of old. His old planes didn't need FBW, nor does the B-2 for benign maneuvers. The B-2 does not share the stability issues that the F-117 has, or that the Viper had/has.

What the FBW does is keep things from getting so bad that the pilot has a chance. They lost the YB-35 or 49 because longitudinal stability was akin to the Viper's. And being a large jet, you could wind up in a situtaion where the control surfaces and pilot skill was not sufficient to keep the thing from flipping end-over-end once the sucker stalled.

2) The "flying wing" designs of Northrop had decent lateral stability without FBW.

B-2 wing has curves and such that use Northrop's vast experience in "tail less" planes.

3) The Viper control surfaces all move independently. This not only helps from a battle damage perspective, but for basic "point the jet" and surfaces move where they have to.

When rolling, the horzontal tail surfaces move in opposite directions to "help" the flaperons.

When landing one flaperon will move further up or down than the other one for roll control.

Sure, Viper doesn't have separate flaps and ailerons, but they sure as hell worked for me.

4) Biggest thing FLCS did for me when I had the LEF failure was to put in max roll deflection and some rudder. Nevertheless, I still had to hold almost full roll away from the folded flap and I also used the rudder trim to help a bit.

On final, nose was way off the rwy heading, but I just flew my a$$ down the centerline until touchdown, with no flare. Planted the thing on the concrete and rode it out.

******************

General rule in the real Viper is don't use manual rudder unless taxiing or rolling out in a crosswind. Let the ARI and basic FLCS control laws do their thing.

later,

I'm no B-2 expert, but I believe that it achieves yaw control by opening the split ailerons, does it not? Where the A-6 and A-10 use split ailerons as speedbrakes, the B-2 (I'm pretty sure) uses them for yaw control as well as speedbrakes. I wouldn't be at all surprised if they're also used for pitch control since they're so far aft of the CG. Somebody correct me if I'm wrong.

Veteran Joined: Mar 24, 2007 Posts: 379 Status: Offline

The reason Jack Northrop's early flying wings did not need FBW was that they had some aerodynamic directional (yaw) stability built in, whereas the B-2 does not. (SixerViper is correct about split aileron yaw control). The XB-35 was driven by four pusher reciprocating engines at the trailing edge. The engine nacelles and the props provided some stabilizing effect similar to a vertical tail. The XB-49 was jet powered and had eight (!!) small vertical tail-like surfaces at the trailing edge (four pointing up and four pointing down). Let's be honest, the early Northrop flying wings were extremely unstable and if FBW had been available, it might have made the airplane useful. Don't forget who Edwards AFB is named after, Capt. Glen Edwards, co-pilot of the XB-49 which disintegrated in flight after control was lost.

Elite Joined: Aug 19, 2004 Posts: 1089

SnakeHandler wrote:

Nicely stated, R1. I've run the gammut in the sim with locked out control surfaces and I am confident that the jet can be safely recovered in up to 25 knots of crosswind with one surface locked out. Locking out the rudder presents some interesting directional control difficulties on landing but since the jet is landed (usually) in a crab, it isn't as big a factor as landing with a locked out horizontal stab. The main problem is compensated for on the ground by using differential braking at higher speeds which leads to hot brakes and potentially blown tires. But all three of my attempts without rudder in the sim were successful. You are also correct in your assumption of the extra finesse required with the loss of the rudder.

Why are you being nice to me? Shocked

Veteran Joined: Jul 01, 2007 Posts: 336

Because you got it right this time. I always give credit where it is due.

Elite Joined: Aug 19, 2004 Posts: 1089

SnakeHandler wrote:

Because you got it right this time. I always give credit where it is due.

That was just a little attempt at humor on my part. Wink

Raptor One

You defenitly got me smiling. LMAO

Guy

Newbie Joined: Apr 11, 2008 Posts: 8 Status: Offline

Again, with so many millions of hours of experience racked up to date by the worldwide F-16 fleet, you can look to several actual events rather than just considering what happens in the sim.

In March 1984, a Block 10 F-16A landed safely at Luke AFB after an inflight rudder ISA lock-out due to a wiring problem.

In March 1989, a Block 10 F-16A landed safely at McConnell AFB after losing the top third of the vertical tail and rudder after a BFM jet wake encounter. Pilot was not even aware of the loss, wingman told him he didn't still have all of his jet.

In October 1990, a Block 25 F-16C on an Eglin AMRAAM test mission lost its rudder and one flaperon tore loose. Landed safely. See photo.

In November 1995, an FMS Block 30 F-16C doing DACT against an F-15 had a failure almost identical to the McConnell jet, with identical results. Pilot not even aware of the loss.

In February 1999, a Truax Block 30 F-16C doing DACT against an F-15 during Sentry Aloha had a failure almost identical to the McConnell jet, with identical results. No handling problems.

In January 2004, a Byrd Block 30 F-16C experienced a jet wash failure almost identical to the McConnell jet. Same results.

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Rudder use in an F-16