RAZ F-15E AFM

[GGTharos]

1 minute ago, Fri13 said:

Does that mean the stick has same force constantly or that the force changes by the G to give a feedback of it?

 

It's something like 4lbs/g approximately.   So if you want to pull say 4g you need to apply 16lbs of force to  the stick.  Obviously at some point (slow enough speed) this breaks down but generally that's how it works.

 

1 minute ago, Fri13 said:

So where example Su-27S provided a AoA limiter, the F-15C doesn't have any other than numerical values on HUD, pilot feel on pants and stick forces?

 

Correct.

 

1 minute ago, Fri13 said:

Why it couldn't be just copied as flight behavior alone with controls is totally different....

 

Yep.  If FM and controls were somehow separate you could 'just' borrow and tweak the FM, but AFAIK they're stuck together so ... 

[Rainmaker]

6 hours ago, GGTharos said:

The F-15ABCD has an electro-hydraulic/mechanical assistive system, called the CAS (Control Augmentation System) which has been tuned to the nines so to speak by NASA and the USAF.   It includes dampers, the ARI, the PTC, the stick is provided with nearly constant-force-per-g feedback and probably a few things I'm forgetting.

 

All limitations in this system are physical; there are no G or AoA limits.

 

IIRC from the E and on it's all a proper FBW though.

 

Edit:  Some resources for you

https://www.f15sim.com/operation/f15_flight_control_system.htm

https://www.f15sim.com/?page_id=16

 

No. A-E all use hydromech with CAS. The jet is not FBW.  Stab travel is 2/3 mech movement and 1/3 CAS assisted. Rudders are 50/50. Ailerons are purely mech. The diff between the A-D and the E is an updated FCC that’s digital 3 channel. More redundancy and CAS isn’t as prone to be kicked offline. Most of the mech system is basically the same and works the same.
 

As for the rest. The mech system has pitch/roll ratio controllers to modify surface movements to give a consistent G for a given stick deflection. Even still, there are certain flight envelopes that doesn’t apply. 

[Rainmaker]

5 hours ago, Fri13 said:

 

Does that mean the stick has same force constantly or that the force changes by the G to give a feedback of it?

 

 

So where example Su-27S provided a AoA limiter, the F-15C doesn't have any other than numerical values on HUD, pilot feel on pants and stick forces?

 

See my post above about the ratio controllers for the first part.  Essentially, the system is supposed to deliver the same G command for a given stick force, no matter the conditions, as long as the jet is capable of doing it. The C in DCS for example, should be a lot easier to fly in terms of being able to pull on the stick and knowing what you are going to get out of it. 
 

CAS can and will null out surface inputs in the are of the flight control system it has control over if it doesnt like what you are trying to do with the stick. To say it has a limiter would be an incorrect statement though. It tries to no let you get into an area that it knows is unstable. What it can’t really do is limit the mech inputs  that the pilot is giving through basic cable/pully inputs. It’s far from what you would think a jet with an AOA limiter would be able to do, like the -16 for instance that can just tell you ‘no’ to any inputs you give it if it doesn’t agree with you. 

Edited May 7, 2021 by Rainmaker

[Rainmaker]

FWIW, the C’s mech system in DCS would translate over to the E just fine, however it’s missing some things like a proper pitch/roll ratio mechanics, rudder limiter system, etc. A lot of the other basic elements of it are done, and done pretty well. 

[TLTeo]

Yeah I'm pretty sure full FBW only became a thing with the last generation Strike Eagles like the SA, QA, and X

[Rainmaker]

30 minutes ago, TLTeo said:

Yeah I'm pretty sure full FBW only became a thing with the last generation Strike Eagles like the SA, QA, and X

The X is for sure. Not sure on the others as I’ve never laid hands on them. 

[Fri13]

2 hours ago, Rainmaker said:

See my post above about the ratio controllers for the first part.  Essentially, the system is supposed to deliver the same G command for a given stick force, no matter the conditions, as long as the jet is capable of doing it. The C in DCS for example, should be a lot easier to fly in terms of being able to pull on the stick and knowing what you are going to get out of it.

 

I don't get that "G command" part how to apply it to DCS. 

 

So as typically we are talking about a gaming devices like joysticks with centering spring and that being its only force. How it should be translated to the simulated stick that has the "same G command for a given stick force"?

 

Like we have now possibly in DCS that joystick deflection from the center is linear to the control surfaces range.

If in 0-100% scale in pitch the 50% is the stick centered, then 75% position is stick half way aft and it would translate that control surfaces are as well half way (75%) from their maximum deflection angle for pitching up, and that gives whatever G you can just get at that flight condition and a force feedback for that G you got?

 

Or so should it be that (regardless we don't have forces in stick) the joystick angle like 75% to pitch up would translate always to example 5 G no matter of the flight condition as the system would turn control surfaces as required to give you that 5G? So you are "commanding G forces" by the joystick deflection angle, and we would be just missing the physical feedback to tell us the required pull force to stick?

 

Quote

The mech system has pitch/roll ratio controllers to modify surface movements to give a consistent G for a given stick deflection. 

 

As the latter I imagine would make flying easier as you would be thinking in G's to pull. "I need to do 7G turn now" and you pull stick to known position and the system gives you that 7G turn on that position. Am I totally lost in that?

 

2 hours ago, Rainmaker said:

CAS can and will null out surface inputs in the are of the flight control system it has control over if it doesnt like what you are trying to do with the stick. To say it has a limiter would be an incorrect statement though. It tries to no let you get into an area that it knows is unstable. What it can’t really do is limit the mech inputs  that the pilot is giving through basic cable/pully inputs. It’s far from what you would think a jet with an AOA limiter would be able to do, like the -16 for instance that can just tell you ‘no’ to any inputs you give it if it doesn’t agree with you. 

 

So the ailerons are fully in pilot control and system can't do anything about it if pilot want to kill self with those but other surfaces has those partial authority to limit the command to help pilot not end to dangerous zone.

[Rainmaker]

26 minutes ago, Fri13 said:

 

I don't get that "G command" part how to apply it to DCS. 

 

So as typically we are talking about a gaming devices like joysticks with centering spring and that being its only force. How it should be translated to the simulated stick that has the "same G command for a given stick force"?

 

Like we have now possibly in DCS that joystick deflection from the center is linear to the control surfaces range.

If in 0-100% scale in pitch the 50% is the stick centered, then 75% position is stick half way aft and it would translate that control surfaces are as well half way (75%) from their maximum deflection angle for pitching up, and that gives whatever G you can just get at that flight condition and a force feedback for that G you got?

 

Or so should it be that (regardless we don't have forces in stick) the joystick angle like 75% to pitch up would translate always to example 5 G no matter of the flight condition as the system would turn control surfaces as required to give you that 5G? So you are "commanding G forces" by the joystick deflection angle, and we would be just missing the physical feedback to tell us the required pull force to stick?

 

 

As the latter I imagine would make flying easier as you would be thinking in G's to pull. "I need to do 7G turn now" and you pull stick to known position and the system gives you that 7G turn on that position. Am I totally lost in that?

 

 

So the ailerons are fully in pilot control and system can't do anything about it if pilot want to kill self with those but other surfaces has those partial authority to limit the command to help pilot not end to dangerous zone.

 

 

The -15 doesn't do anything crazy with springs and stick force.  It has centering springs and that is about it.  There are actuators that reposition the stick from neutral when trim is applied, but it doesn't manipulate force, etc.

 

Ideally, the pitch/roll ration modifies stick to control surface inputs to do just as you say...I want X number of Gs, I supply X amount of force to the stick.  Basically, I move the stick a certain amount, I get a certain amount of G.  It does that by moving the surface less for the same amount of stick movement if you are faster, more if you go slower, etc.  That should stay fairly constant though MOST of the flight regime.  Much easier to max perform the jet without having to guess how much stick force to apply and easing into it as to not blow through the number you want and hearing betty scream at you.

 

In terms of DCS, I don't have the perfect answer on how to blend that into a best fit for the sim world.  We don't get that increased stick force as you move your desktop stick further and further back like you would in a real jet.  At least not in the increase that you could really fly the jet that way.  We'd need bigger springs and stick extensions to really make use of that IMO.  With the force feedback sticks that are out there, I have no idea as I have never used one.  In our case, in my mind, it would have to be simulated in some way though travel amounts.  Right now though, you really have to adjust your inputs based on altitude and speed which the jet's system is really designed to compensate for.

 

Ailerons are not that large, so you are not going to do anything crazy there.  Yes to the rest, in simple terms.

 

 

 

[Fri13]

2 hours ago, Rainmaker said:

 

 

The -15 doesn't do anything crazy with springs and stick force.  It has centering springs and that is about it.  There are actuators that reposition the stick from neutral when trim is applied, but it doesn't manipulate force, etc.

 

Ideally, the pitch/roll ration modifies stick to control surface inputs to do just as you say...I want X number of Gs, I supply X amount of force to the stick.  Basically, I move the stick a certain amount, I get a certain amount of G.  It does that by moving the surface less for the same amount of stick movement if you are faster, more if you go slower, etc.  That should stay fairly constant though MOST of the flight regime.  Much easier to max perform the jet without having to guess how much stick force to apply and easing into it as to not blow through the number you want and hearing betty scream at you.

 

That sounds much easier, and should be possible be set in the gamin devices as joysticks. 

 

2 hours ago, Rainmaker said:

In terms of DCS, I don't have the perfect answer on how to blend that into a best fit for the sim world.  We don't get that increased stick force as you move your desktop stick further and further back like you would in a real jet.  At least not in the increase that you could really fly the jet that way.  We'd need bigger springs and stick extensions to really make use of that IMO

 

Well the force feedback I think could be just overlooked as when most joysticks don't have it, then it is not there. So just adapting the system that joystick deflection in degrees would give correct amount of G's should be doable. For the player it is just easier as there is no force to pull, but then again more difficult as you don't feel forces so you need to look more of the instruments. But in time player would learn to recognize the joystick angles better and it would become easy to pull wanted G without looking HUD. 

 

Question is more that is ED willing to implement that kind system if it isn't there already?

 

2 hours ago, Rainmaker said:

.  With the force feedback sticks that are out there, I have no idea as I have never used one.

 

They have limited force they can really apply. We are talking maybe a 2.5 kg at max I think. There are people who have built own ones, modified existing ones by using stronger motors etc. But it is totally possible to in its force limits to make the increasing force from the center for wanted output value in the game like G-number. So more G's you are pulling then harder the joystick tries to center. 

 

2 hours ago, Rainmaker said:

  In our case, in my mind, it would have to be simulated in some way though travel amounts.  Right now though, you really have to adjust your inputs based on altitude and speed which the jet's system is really designed to compensate for.

 

Okay so there is no such modeling in the DCS for it. What is sad thing. I have always felt that while ED can make very good flight modeling, it is their input/output logic that is lacking severely. That there is missing the "feel" to the plane aerodynamic forces as the joystick input is just read as is, without any control system really sayin anything about it. 

 

2 hours ago, Rainmaker said:

Ailerons are not that large, so you are not going to do anything crazy there.  Yes to the rest, in simple terms.

 

Okay so that is why there has not been any reasons to even add any "safety features" in there but kept as is. 

[GGTharos]

9 hours ago, Rainmaker said:

FWIW, the C’s mech system in DCS would translate over to the E just fine, however it’s missing some things like a proper pitch/roll ratio mechanics, rudder limiter system, etc. A lot of the other basic elements of it are done, and done pretty well. 

 

I misinterpreted what I've read on the F-15E's flight control system then.  Thanks.

3 hours ago, Fri13 said:

 But in time player would learn to recognize the joystick angles better and it would become easy to pull wanted G without looking HUD. 

 

Question is more that is ED willing to implement that kind system if it isn't there already?

 

In DCS it is already deflection = g.

[Rainmaker]

1 hour ago, GGTharos said:

 

 

In DCS it is already deflection = g.

Not when I tested it which wasn’t that many moons ago. 

[Mizzy]

On 8/29/2013 at 1:37 PM, CptSmiley said:

Even if there was such an opportunity, I'd be more comfortable with an in-house solution when the inevitable modification, tweaking, and tuning are required. Also this allows freedom and control over the interfacing amongst systems.

If my memory recalls, the Chinese Asset pack had a J11 (flanker) thingy in it and it was a modified ED Flanker model and FM that ED gave Dekaworks, so it's not out of the range of possibility that ED may well be working with RAZBAM on the F15E. RAZBAM have been with ED a long time and much trust I would imagine. I personally love RAZBAMs work, very professional, I just wish they would do the early Skyhawks they did for MSFS 2004, such a shame they have not, but this is OT so I will shut up now.

[Rainmaker]

On 5/7/2021 at 9:17 AM, Rainmaker said:

Not when I tested it which wasn’t that many moons ago. 

I’ll rebut my own statement on this one. Just did some more testing out of curiosity. Stick pos appears to be properly dictating G. Whether it’s cheated or not, the PTC as far as sustaining G also seems to be working. Does some weird stuff at low airspeeds/high alpha to the stabs graphically, but would have to dive deeper to decipher what going on. 

[GGTharos]

I know, I re-tested it a few days after you mentioned (I was busy building missions before that) - anyway no big deal, I was glad to see it working since it's been tested many moons ago.   And yes, I don't know what it does at the edges.  It's allegedly tuned according to the NASA reports, and I don't recall if they had anything out in public for the force/g implementation.   As for graphics vs function, well, you know how the intake ramps work for example.

The autopilot still likes to lose the plot over extended times.

Edited May 13, 2021 by GGTharos

[Spurts]

On 5/6/2021 at 11:00 PM, Rainmaker said:

The X is for sure. Not sure on the others as I’ve never laid hands on them. 

The EX is just the SA/QA with EPAAWS.  The R&D for the FBW system on the EX was paid for either by Saudi or Qatar.  That is also why it uses F110s instead of F100s.  USAF/Pentagon/Congress didn't want to pay for any new certification testing to save costs so the EX is what Saudi/Qatar paid for other than EPAAWS (pretty sure SA and QA have DEWS, but I could be wrong).

 

BTW, thank you for your first hand knowledge on this subject.

[mytai01]

On 5/6/2021 at 4:00 PM, Rainmaker said:

No. A-E all use hydromech with CAS. The jet is not FBW.  Stab travel is 2/3 mech movement and 1/3 CAS assisted. Rudders are 50/50. Ailerons are purely mech. The diff between the A-D and the E is an updated FCC that’s digital 3 channel. More redundancy and CAS isn’t as prone to be kicked offline. Most of the mech system is basically the same and works the same.
 

As for the rest. The mech system has pitch/roll ratio controllers to modify surface movements to give a consistent G for a given stick deflection. Even still, there are certain flight envelopes that doesn’t apply. 

Last I read, only the F-15EX has true FBW.

[Njinsa]

...which was 'hijacked' straight from F-15QA.

[Coole28]

49 minutes ago, Njinsa said:

...which was 'hijacked' straight from F-15QA.

...which itself was developed from the F-15SA.  Quite a few variants with FBW now.

[Njinsa]

Correct.