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Enthusiast Joined: Jan 10, 2007 Posts: 31 Status: Offline

Hello everybody,
Last monday I had a seminar on my University where I present my work about "Pilot decision support algorithm", in which I present (using one of artificial intelligence methods) an algorithm that help pilot making his decision how much he has to deflect the elevator in the initial state to reach certain final state.
After presentation I got questions related to this: some Ph.D.'s said that if for example the decision was to deflect the elevator about -2 degrees (to make aircraft climb) , the pilot dont know exactly how much he deflect the elevator, they said that he make this by intuition. Is this right???
I have found some topics about elevator deflection indicator, but after what they said I have dilema.

Summing up, my question is, is there any device in military aircraft that say to pilot how much he deflect his elevator in the current time?

Rgards.

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Elite 1K Joined: Aug 19, 2004 Posts: 1092

The Ph.D.'s are pretty much correct. Pilots don't fly aircraft by attempting to move the elevator a certain number of degrees up or down. Pilots use angle of attack and G load readings via cockpit guages, the HUD, etc. to make piloting decisions. Elevator deflection is a means by which a pilot attains a certain angle of attack and/or G load. AI routines would do the same thing in combination with other factors like airspeed, altitude, and so on. Elevator deflection is something measured by fly-by-wire flight control systems to achieve a closed loop feedback system, but it's not something the pilot can use himself to improve flying quality. You've heard people say that the F-16 will be unstable without its fly-by-wire flight control system, right? That's because the pilot can't monitor the elevator position manually and make adjustments fast enough (or accurately enough) to prevent aircraft instability. And even if a pilot could do this, it would take nearly 100% of his concentration just to keep the plane flying level. Forget about trying to do any 9G turns. Elevator deflection IS measured and used to keep some planes flying... but not by the pilot. This is what we have computers for.

Enthusiast Joined: Jan 10, 2007 Posts: 31 Status: Offline

Thanks for your reply.
So you say that if I want the Pilot to deflect the elevator 2 degree down (for example) he would not do this because he dont know hom much he deflect the elevator,right? But can the autopilot do this I mean, can it deflect the elevator -2.5 degrees? (for instance), is there any option of this , or the autopilot dont have the option to deflect elevator at precise position (precise deflect angle?)

Elite 1K Joined: Apr 26, 2004 Posts: 1215 Status: Offline

Most auto pilots in fighters are only altitude and attitude holds. They don't change pitch or roll.

Elevator travel is variable with respect to airspeed and attitude. There fore the actual travel (in degrees) is irrelevant. What is relevant and can be monitored by the pilot and the FCC is AOA and G-Load.

Simply put the pilot uses the TABR indicator in the back of his/her head. "I want to fly over there. I push/pull/bang the stick and great (!) I'm going where I want to. Never have to think about control surface travel."

(TABR=That's About Right)

AS I was writing this, a mishap came to mind. I dealt with the loss of a AirBus where the pilot was aggressively working the rudder to overcome wake turbulence. The rudder was deflected to its max several times before the entire vertical tail came off. Investigation revealed that the technique was encouraged in training and there was no regard to exactly how far the rudder was being displaced.

I referred to this as an example of pilots not really caring about surface travel in degrees and are more concerned with the aircraft's reaction to aforesaid inputs.

Hope this helps...

Unlike PC flight simulators there is not a deflection indicator in real planes. As stated above the amount of motion necessary to achieve a certain shift in attitude or direction, or what the pilot have asked for, differs highly dependent on air speed, altitude, attitude, angel of attach, current G load, gear up or down, air refuel door open, gun firing and possible a couple more variables. It is possible that the software designer does involve degrees in is early principal design programming, but it is more likely a relative motion between zero and max deflection, so you can call it a percentage move. In the Viper, where there is minimal stick movement, indeed the early blocks had no motion at all, but this was later added on pilot requests, it is the amount of pressure that is measured. The pressure is then translated to a request for a specific change in attitude. The flight control system then analyses all the above listed variables and sets the control surface to achieve the necessary change in attitude.

There is a test that is done on the Viper to test these deflections based on various conditions, and then the test procedure states the distance in centimeters deflection from zero that should be measured.

Enthusiast Joined: Jan 10, 2007 Posts: 31 Status: Offline

Head-up displays on the cockpit glass, aircraft alttitude, velocity, angle of attack, g-load. I think that it also displays flight path angle, right?
If yes, I have this question, can FCC predict what flight path angle the aircraft will reach after a certain time if the pilot maintain the same elevator stick position? is there is such posibility?

The HUD as the attitude indication similar to the artificial horizon.

I would say that the flight control system is a Real Time system and don't predict, but rather limits its actions to avoid damage to the airframe or loss of control. The only time there may be prediction involved is when the gun sight is activated, but for that we need someone with radar/fire control expertise to answer.

Others may find that I am wrong here so feel free to correct me.

The F-16 does have trim position indicators, but they don't correlate to a specific number of degrees of travel- they merely show that a certain amount of trim is input, and the flight control computer takes care of the actual degrees of travel based on airspeed and AoA. Thats the way I understood it, anyway. The HUD does have a flight path indicator, which shows where the airplane is actually headed regardless of where the nose is actually pointed. For example, if you have your F-16 on final you can have say 10 degrees nose up but still have the flight path marker "on the numbers" on the runway. Leave things alone and the airplane will hit the ground smack on top of the numbers. Pull the throttle back (but hold 10 deg AoA) and the flight path marker will come down to the threshold of the runway and eventually short of the runway. Leave the throttle at idle and you'll hit the ground right where the flight path indicator is sitting. Push the throttle all the way up and the flight path indicator will move on up the runway, to the horizon, and eventually up to 10 deg above the horizon as the airspeed picks up.

Good info VPRGUY, my Falcon 4.0 landings are much smoother now. What KIAS was saying was:

Quote:

some Ph.D.'s said that if for example the decision was to deflect the elevator about -2 degrees (to make aircraft climb)

Your excellent reply illustrates that thought process simply does not exist.

No pilot I'm aware of thinks "I'm going to have to throw in 15 degrees of elevator to make this approach." Flaps maybe, but not the elevator.

Elite 3K Joined: May 10, 2004 Posts: 3098 Status: Offline

Well, I only have a few hours of dual instruction in Cessnas and a Piper, but I can tell you that it's a lot like driving a car in at least one big way. When you're driving, you don't think, "I need 27.5 degrees of right wheel accompanied by 15 pounds of force on the brake pedal to make this turn."

You actuate the controls until the desired result is achieved Wink

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Quote:

You actuate the controls until the desired result is achieved

Yeah, What he said. Thumb

Elite 3K Joined: May 10, 2004 Posts: 3098 Status: Offline

Just remember - slow, deliberate inputs until large, panicky inputs are required Smile

. Oh yeah, and mount that coordinated turn indicator thingy lower - I can't get my foot up on it very easily when the instructor tells me to "step on the ball" Wink

My instructor would always take up a package of those little donuts to munch on.Well, on the day we go up to practice spin recovery, he tells me to put it in a spin and recover at 180 degrees. No problem, he says lets do it again. this time he sets a donut on the dash and down we go, spinning like hell. "now this time, take a bite outta the donut and recover at 180 degrees" I can't believe this guy, (meanwhile donut is floating around the cockpit) he looks at me and says"Better hurry, terra firma is getting much larger in that windscreen than I'm comfortable with" LMAO

Honest to God, True story I quit flying shortly after my first cross country.

Elite 3K Joined: May 10, 2004 Posts: 3098 Status: Offline

I like his style - make sure you can recover the plane when there's something else nagging at you Wink

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One of these days I'll have the $$$ to go get my ticket Thumb

!

Just be glad you didn't pull the stunt some poor kid did back in the '60s on his first solo cross country - he landed at Groom Lake thinking it was North Las Vegas Laughing

! I wouldn't have believed it myself if it didn't come from someone who was working on the SR-71 out there at the time Smile

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Elevator deflection indicator?