F/A-18 C Force feedback

[AKarhu]

(spring does not know what is G)

Precisely. It doesn't.

[dot]

Thanks, I'm glad we can agree.

[AKarhu]

Well, the discussion is hardly providing any conclusions, but yeah, I figure. :)

 

The thing to understand is this: the spring force on the stick is not altered (except by the stand-by trim motor, when used).

 

It takes that (my guess on the force!) 40-or-so lbs / 20 kgf to pull the stick to the aft stop regardless of the flight conditions. What is altered is the airplane's response to any given flight conditions, requiring you to pull back farther in particular when forcing high alphas.

[dot]

That would be an accurate description of spring joystick, like the one you probably have.

Designers of F -18 are not that silly, stick force increase proportional to G forces in flight.

I have showed you F 18 manual and F 18 pilot report, not sure how else we can progress this discussion if we don't agree on those.

[AKarhu]

Have you gone inside the actual airplane? I've got my own opinion where they are silly or not (they do both).

 

Unless they schedule the trim motor by flight conditions (which would make technically a very silly option, knowing the system), there are no other mechanical means to alter the stick force per displacement. Of course, if you can point that they use the trim motor to schedule the control feedback, then I'm interested.

 

So far, this is all I got to say, simple as that.

[dot]

it helps if you say that this is your opinion, what is frustrating is that you are stating that spring joystick is realistic in a thread asking to implement force feedback.

 

We have internet, reports of actual pilots, and manuals from people who build the aircraft:

 

 

FLIGHT CONTROL SYSTEM DESCRIPTION

The FCS in the F/A-18 airplane employs a digital, full authority, high gain CAS as its

primary flight control system mode. The CAS mode is AOA and air data scheduled with

feedbacks taken from three axis angular rate, two axis linear acceleration, AOA, and air

data sensors. Three cross-axis interconnects enhance the flying qualities of the airplane:

rolling surface to rudder interconnect to provide better roll coordination, rudder pedal to

rolling surfaces interconnect to provide better roll coordination at high angles of attack,

and an aileron to collective stabilator interconnect to compensate for an uncommanded

pitching moment in the power approach configuration with ailerons drooped. A

speedbrake to stabilator interconnect minimizes g transients during speedbrake operation.

A departure warning tone (yaw rate and AOA) is available when the flap switch is in the

AUTO position. The tone initiates at 25 deg/sec yaw rate and increases in beep frequency

up to 45 deglsec. Above 35 deg AOA and below -7 deg AOA, the tone initiates at a

constant frequency and yaw rate warning is no longer available. Above 22 deg AOA,

angle of attack feedback is introduced to generate a proportional nose down command

which provides an effective increase in stick force cues during low speed and high AOA

maneuvering. Inertial decoupling feedback to the stabilator consisting of the product of

roll and yaw rate scheduled with air data is incorporated when the flap switch is in the

AUTO position. This feedback offsets the pitching moment generated by inertial

coupling at high roll rates. Inertia coupling compensation is also used in the yaw axis

using the product of pitch and roll rate to command the rudders to counter yaw inertia

coupling. Additionally, a SRM is provided and is described below

 

*****

The longitudinal and lateral mechanical components of the FCS are comprised of the

following: cockpit control stick, longitudinal and lateral feel springs, longitudinal trim

actuator, linkage and cables between the control stick and stabilator servo actuators, and

an electromechanical ratio changer which adjusts the stick to stabilator gearing while in

the mechanical backup mode. Longitudinal and lateral spring cartridges provide control

stick forces to the pilot. A counter weight is provided in the longitudinal axis to counter

control stick inertial forces encountered during a catapult launch. An eddy current damper

is provided to add an additional lateral stick force increment as a function of lateral stick

rate. The control stick is duplicated in the aft cockpit of the two-place airplane and is

connected to the forward stick via mechanical control linkages. The mechanical linkage

allows the control stick position sensors to sense pilot stick commands from either

cockpit. Longitudinal and lateral control stick movement in either cockpit will move the

control stick in the other cockpit. Linkages and cables connect the pilot's control stick and

stabilators while in the mechanical mode. Design longitudinal and lateral breakout plus

friction and stick force gradients are presented in table L

http://www.dtic.mil/dtic/tr/fulltext/u2/a256522.pdf

 

I can find more if needed.

Edited November 3, 2017 by dot

[AKarhu]

I've given all you need.

[dot]

Thanks I've also learned from this research, for example, the stick forces in X and Y axis are not the same, so in conclusion, no spring joystick can accurately simulate the feel of F18 aircraft.

 

Table I

CONTROL STICK CHARACTERISTICS (from above PDF)

[exray]

Are there any sticks on the market that even have FFB?

 

This.

[dot]

This.

 

MSFF2 on ebay

https://tinyurl.com/yav4gwes

 

ED thread for diy FF stick:

https://forums.eagle.ru/showthread.php?t=172964

 

Magnetic FF stick in development:

 

Also, feel free to email your favorite joystick manufacturer and express your interest in Force Feedback flight stick

[ViFF]

Actually, its starting to make sense to me under the following assumption: "When a spring is compressed or stretched from its resting position, it exerts an opposing force approximately proportional to its change in length"

 

 

Heres how I see it:

 

AoA becomes > 22 degrees

 

AoA Feedback (aka trim motor) kicks in and moves the zero position of the stick forward on the Y axis of the stick.

 

The further AoA > 22 the more the trim motor moves the zero position further forward on the Y axis of the stick, which produces a proportional nose-down command, the force becomes increasingly greater for the pilot to keep the stick at a certain position or the aft stops for that matter (see above law) the more the trim motor gives more down command to the trim system, increased to the max which was what? AoA=48 degrees?

 

Can certainly be done on the MS SW FF2, currently you can find something similar in the helicopters cyclic hydraulic force trim and similarly increased "Return to Center FF" on the extremities in the roll axis of the F-5E.

 

Both by Belsimtek :D

 

I hope they will also implement on the F-18!

 

S!

Edited November 5, 2017 by ViFF

[uri_ba]

BTW I really want to see a 35 pound force FFB stick. Now I'm just sticking to my 22-pound X65F.

 

22?? I have FCC calibrated to less then 20 and it moves the console the stick is bolted to..