FAQ for F-15 AFM Development

[VTJS17_Fire]

Did you miss the fact that the F-15 has two engines, maybe?

Yes, sir! :music_whistling: :doh:

 

Thanks. Yeah, in another test I was at 2400 pph, so if I ad the two indicators it will give me the real data ...

[blkspade]

Something I've mentioned before, yet seems to have been ignored, is the fuel flow from externals with 3 tanks. Fuel seems to get drawn from the center tank nearly all the times along with the wing tanks. I forget if it was the -1 or -34 that indicates that shouldn't be the case unless under particularly high fuel flow requirements. You end up with no point where you could jettison wing tanks and still have a meaningful amount of fuel left in the CL tank.

[cofcorpse]

Can you remember where did you see this? Maybe I missed something, but I don't want to change it without any confirmation.

Thanks!

[blkspade]

Can you remember where did you see this? Maybe I missed something, but I don't want to change it without any confirmation.

Thanks!

 

It was this version of the -1, that would seem to indicate the point I was getting at. Section 1-10. It seems rather strange that with just full internal and center tank you'd have ~17500lbs of fuel, but dropping wing tanks when carrying 3 around this point leaves you at ~14500.

 

Also I've been trying to figure out what mystical fuel type is used in the externals, since the math doesn't add up for quantities the same way the internal does if assuming JP-4.

[Svend_Dellepude]

Am I the only person that has to trim nose up above angels 40? The PTC doesn't seem to be doing anything for me..

[Exorcet]

Am I the only person that has to trim nose up above angels 40? The PTC doesn't seem to be doing anything for me..

I seem to randomly get trimming to ~.8 g or trimming ~1.2 g instead of 1.0. After a while it usually goes back to 1.

[Ktulu2]

Do you have externalk tanks? High, those really affect your AoA, even without thoses, just try flying at like 80k, the plane tends to fall high.

[Svend_Dellepude]

I seem to randomly get trimming to ~.8 g or trimming ~1.2 g instead of 1.0. After a while it usually goes back to 1.

 

always .7 - .8 G for me. maybe i didn't have the patience to wait for PTC.

 

Do you have externalk tanks? High, those really affect your AoA, even without thoses, just try flying at like 80k, the plane tends to fall high.

 

With or without..

[GGTharos]

The PTC moves quite slowly. If you wind it up with a high-g turn, it isn't fast enough to get itself to 1g right away.

 

I seem to randomly get trimming to ~.8 g or trimming ~1.2 g instead of 1.0. After a while it usually goes back to 1.

[SFJackBauer]

4. Control system

1) FFB must be working.

 

Hi. Can you/someone clarify this line?

[Svend_Dellepude]

Well..

For me something happens around 42K. From there and up, level flight is impossible in the region from Mach .85 to 2.3 without constant back pressure, manual trim or use of autopilot.

It's like the PTC reaches a limiter and is unable to compensate anymore.

 

Should it be like this?

 

Config is clean with 50% fuel (unlimited).

[SolUniverse]

How can I map

Wheel Brake Left On/Off:

Wheel Brake Right On/Off:

to my Pedals? When I try to add my left / right pedals the drop down doesnt have any axis to map it

[Mar]

You do that under the axis commands menu, not under systems or aircraft control or wherever the key commands for wheel brakes are under.

[Ergo95FRA]

Hi all ,

 

since 1.2.8 and introduction of new AFM F-15C model, it's impossible to land on the Russian Carrier. Before, even the F-15 is not able to land on a carrier, we can Touch & Go with it. Moreover, it's possible to modif .lua script aircraft file to active tail hook of the F-15 and then, try to land on a carrier, even this plane can not in real life because the gear is not enought strong (like F-14 for example). The hook is normally just for emergency landing on a runway... I know ^^. But, with old model (SFM), we could land on the Amiral Kouznetsov or CVN but now the F-15 fall through the deck and crash in the water .... . That really umbarrassing. Because even the F-86 (new production , and in Beta) could touch the deck. F-15 have now a realistic physics for landing and yet, this is it what crash on the fight deck ( I mean fall through it)

 

So I hope this will be modif and improve in futur. That rest a big challenge and I like it ;-)

 

https://www.youtube.com/watch?v=S5G4uEPSs2k&list=UUdp5JwCwV1BdpqXnTsGsNYQ

 

now with other plane (here F-86 Sabre) https://www.youtube.com/watch?v=_stY0dCGC0k&list=UUdp5JwCwV1BdpqXnTsGsNYQ

Edited August 25, 2014 by Ergo95[FRA]

[nhowell01]

Is anyone else unable to maintain level flight without trimming manually or using the stick with any amount of wind? Currently whenever there is any amount of wind the PTC or whatever system does not seem to be keeping it level for me.

If I am not mistaken, it should be compensating for the wind correct?

In a mission without wind it stays level.

 

Also using Takeoff trim makes the aircraft un-flyable.

Edited August 24, 2014 by nhowell01

[HiJack]

Yes, something has happened to the flight model during summer, I can't put my finger on what but ailerons seems to move in steps, like a small step motor, strange. Cant get a good long refueling anymore :( Initially I thought it was my stick so I greased it up and the stick moves smooth as oil but the stepping is still there :(

[SDsc0rch]

sometimes the flight path marker in the HUD is off to one side, I look back and you can see the rudder has some deflection - can't seem to trim it out....

 

??

[Maverick Su-35S]

CAS should trim for weight imbalance :)

 

The high altitude 'flipping' issue Blaze is describing is probably the rudder issue (pull enough AoA with a little roll, and the plane goes into an auto-roll).

 

Period! And this happens every time you reach above 18 AoA on the HUD indication (although for some reason this indication is always about 10 degrees higher than the real AoA, but whatever...) when you fly above a certain indicated airspeed and altitude. So as Tharos said..., if you have any remnant roll rates before pulling above the said AoA, you'll end up increasing that roll rate and if you dare countering it by aileron only (because as some of you have already learned that the yaw CAS reduces compensation above a certain Mach number) you'll only increase the adverse yaw which will make matters worse. Just get used to flying it as you should and you'll be fine. Learn it's limits and what you should do above those limits.

[Buznee]

Is the F-15 airbrake control supposed to be proportional and adjustable like the a-10c? or is it binary (on-off) like it is currently implemented?

[Ktulu2]

From what I know, (correct me if i'm wrong) its a FC3 feature...like switching weapon.

[Maverick Su-35S]

Hello again! I'd like to address a few questions to somebody here or from anywhere who has enough good knowledge in aerodynamics and/or flight dynamics, because I really don't want to waste time. I know that there's no simulations on a PC that could have reached a 100% accuracy level so far and I'm not asking for that!

 

But I believe that I have the right to ask some questions regarding the F-15C's PFM as long as the DCS's site claims it to be an authentic recreation of the real F-15C's flight behavior, as the statement tells: "Professional Flight Model (PFM), developed in cooperation with F-15 pilots"

 

If there is any F-15C test pilot, active or ex pilot who can help to answer the 2 following questions, I would greatly appreciate. The subject of this post is mostly concentrated on the 2nd question, which is more important:

 

1. What is the highest negative AoA that the F-15C's flight control system allow for the real aircraft? I know that at negative AoA the wings won't benefit of the higher energy vortexes created between the engine inlets and the canopy which help increase both the fuselage's and a good portion of the wing's lift, lateral-directional stability and critical AoA (that apply when flying at positive AoA), because they won't generate at negative angles, so there is a huge constraint in negative alpha due to these factors, but how far this restriction reaches?

 

You do know what a roll due to yaw is, as well as an adverse yaw due to roll (the yaw due to roll is not the subject) when we are at positive alpha (AoA)! For instance, and especially on high sweep wings (like the F-15) with 0 dihedral between the wings, when you have 1G at a constant given AoA and you yaw the aircraft only by rudder input, the leading wing will have a greater lift gradient (what we usually call the lift vs alpha slope) than the lagging wing, which creates a lift asymmetry between both wings, thus the leading wing "rolls around" the lagging one in the same direction of the yaw, but what should normally happen (how would the airplane react) when you have negative alpha (AoA) giving the same conditions, of course at -1G the least? That's right..., you should get an opposite roll due to yaw and vice-versa for yaw due to roll (the plane will yaw in the same direction as the roll).

 

So, for stick forward conditions (where the alpha is enough negative to have the wings produce negative lift) every reaction in yaw and roll is reversed when the corresponding input is solely applied.

 

2. The second question is: Why does the F-15C in the sim tend to react correctly in the first moment when we have the stick held full forward (with 0 side stick or 0 aileron input) having the aircraft settled at a new equilibrium negative AoA, then apply a full boot of rudder (doesn't matter if the yaw CAS is switched off or on) to any side and have it rolling in the opposite side of the yaw (which is correct for negative AoA), just to see it starting to roll in the same side as the yaw as if the AoA became suddenly positive, but the lift continues to be negative? What logic does this have I don't know and if there's any reason why would a real F-15C react this way i'd greatly appreciate the correct answer...!

 

 

Now in order to be more precise in what i'm saying, i've made up a short video where these inputs are illustrated and every reaction by the aircraft can be observed:

 

 

I've only made this video for the F-15's updated flight model investigation purposes, not for criticizing or any other reason than to promote what has already been gratefully achieved and done well...!

 

 

Thank you!:thumbup:

[Maverick Su-35S]

Is the F-15 airbrake control supposed to be proportional and adjustable like the a-10c? or is it binary (on-off) like it is currently implemented?

 

If you don't have an axis available for the air brake at the Axis section of the controls, it only acts as an on-off actuation so far.

[Buznee]

Understood. I guess my real question is how is the real F-15 airbrake controlled and is it proportional? The a-10c is not axis controlled (airbrake switch on the throttle) but is still controllable from fully closed to fully open and anywhere in between.

 

The F-15E seems to have the same basic logic as the A-10C

 

Edited September 18, 2014 by Buznee

[Maverick Su-35S]

Understood. I guess my real question is how is the real F-15 airbrake controlled and is it proportional? The a-10c is not axis controlled (airbrake switch on the throttle) but is still controllable from fully closed to fully open and anywhere in between.

 

Sry, I didn't understand the meaning of proportional in the first place! Judging by the fact that even the F-86F has a full control of the airbrake's deflection using airbrake in/out switches, so does the A-10 and F-16, why can not the F-15C have? But i guess the devs or someone with more knowledge about it could give the answer!

[sobek]

The AFM for the Eagle is not completely done yet.