Flight Model

[C3PO]

Quick question about the flight model: it feels after takeoff that there is quite a bit of movement in pitch, unlike the Viper or the Hornet, making it tricky to fly. Why is this and is it normal? Also, the aircraft needs to be constantly trimmed out, it seems.

[Rudel_chw]

12 minutes ago, C3PO said:

Quick question about the flight model: it feels after takeoff that there is quite a bit of movement in pitch

 

The F-15 its in early access and barely a month since release, the developer is still tuning it, these are fixes that are coming on the next update:

 

 

12 minutes ago, C3PO said:

 … Also, the aircraft needs to be constantly trimmed out, it seems.

The viper and hornet use fly-by-wire flight controls, the F-15E doesn’t and so it has to be trimmed.

[Thx1137]

There is plenty written about pitch already so maybe read those. Yes, it is sensitive in the real jet and can feel weird/oscillate on takeoff if you don't fly it correctly. That said, there will be some *minor* flight model tweaks in the patch so it may change though I think only slightly.

The aircraft isn't FBW like the F18 or F16 so yes, trim changes are made after any airspeed change. You fly it like a normal airplane. 

[Holbeach]

2 hours ago, Thx1137 said:

 

The aircraft isn't FBW like the F18 or F16 so yes, trim changes are made after any airspeed change. You fly it like a normal airplane. 

F-15 has auto trim and does not require manual trim after airspeed, thrust or configuration changes.

[Rudel_chw]

5 minutes ago, Holbeach said:

F-15 has auto trim

cant find any reference to it in the manuals … how do you enable it?

[Holbeach]

2 minutes ago, Rudel_chw said:

cant find any reference to it in the manuals … how do you enable it?

Normal mode is PITCH CAS ON, PITCH RATIO AUTO.

..

[Raven (Elysian Angel)]

Different people use different definitions of "auto trim" it seems, which only creates confusion.
That being said, the only times you need to touch the trim pretty much is after take-off to trim out the "T/O trim", and on landing. Oh, and I personally add 2 notches of UP pitch trim when I'm refuelling from a tanker who's in a turn... But that's it.

[Rudel_chw]

6 minutes ago, Holbeach said:

Normal mode is PITCH CAS ON, PITCH RATIO AUTO.

..

I see, CAS is a three-axis control augmentation  system, not really an autotrim.

[Fromthedeep]

5 minutes ago, Rudel_chw said:

I see, CAS is a three-axis control augmentation  system, not really an autotrim.

Correct, the autotrim is the function of the PTC which is part of the hydromechanical control system.

[Holbeach]

12 minutes ago, Rudel_chw said:

I see, CAS is a three-axis control augmentation  system, not really an autotrim.

Pitch Trim Compensator automatically trims the aircraft, unlike a conventional trimmer, which trims out stick forces.

..

[KlarSnow]

19 minutes ago, Rudel_chw said:

I see, CAS is a three-axis control augmentation  system, not really an autotrim.

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

Read the pitch trim compensator paragraph. Describes it fairly well.

T/O trim (which is enabled by default if you hot start the aircraft currently) will trim the stabs up by default so that rotation and takeoff is easier. It basically changes the neutral position of the pitch trim compensator away from 1G, so after takeoff you have to trim it back to 1G. After that it should be hands off for pitch.

[Rudel_chw]

4 minutes ago, KlarSnow said:

Read the pitch trim compensator paragraph. Describes it fairly well.

found it! It was under "LONGITUDINAL CHARACTERISTICS" …  thank you both, love learning new things

 

[jaylw314]

4 hours ago, KlarSnow said:

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

Read the pitch trim compensator paragraph. Describes it fairly well.

T/O trim (which is enabled by default if you hot start the aircraft currently) will trim the stabs up by default so that rotation and takeoff is easier. It basically changes the neutral position of the pitch trim compensator away from 1G, so after takeoff you have to trim it back to 1G. After that it should be hands off for pitch.

I don't know where that guy is getting his stuff for his project, but holy cow, some of it's pretty cool!

 

Edited July 19, 2023 by jaylw314

[eFirehawk]

5 hours ago, Holbeach said:

Pitch Trim Compensator automatically trims the aircraft, unlike a conventional trimmer, which trims out stick forces.

..

Wait a sec, so you're telling that the F-15E can actually trim itself? Have I been flying it wrong all along? I am away for 3 weeks so can't play DCS to confirm, but in no tutorial I remember anyone talking about the pitch ratio switch. So the condition for auto-trim to be enabled are: All 3 CAS switches to on, PLUS pitch ratio to Auto?

[Rainmaker]

47 minutes ago, jaylw314 said:

I don't know where that guy is getting his stuff for his project, but holy cow, some of it's pretty cool!

 

 

Majority is directly out of Eagle Talk papers. Just transcribed. 

Edited July 19, 2023 by Rainmaker

[PLUTON]

Could you indicate the 3 trim switches (CAS) on the dashboard please?

[jaylw314]

2 hours ago, Rainmaker said:

Majority is directly out of Eagle Talk papers. Just transcribed. 

 

I was talking about some of the hardware he's managed to find, but that too  

[Rudel_chw]

1 hour ago, PLUTON said:

Could you indicate the 3 trim switches (CAS) on the dashboard please?

 

 

 

[KlarSnow]

The CAS switches have nothing to do with the jet automatically trimming in pitch. You should have them on regardless though because they massively improve the handling of the aircraft throughout the envelope and enhance stability and spin/departure resistance. There are zero benefits to having them off in the strike eagle.

The jet auto trimming in pitch is a function of the Pitch Trim Compensator, which is part of the hydromechanical system, completely independent of the CAS.

[badger7966]

I find if you hit the button "take off trim"...two times......and then push plus 4 on your trim button if works just fine...... its a bit jumpy off the ground..... but I aint bitchin....Im sure Razbam will address their already fantastic product.

 

Im still amazed at the quality....and now Razbam have set a new standard.....imo.

[C3PO]

Thank you all for the contributions - and some fascinating new details here.

[Holbeach]

12 hours ago, KlarSnow said:

The CAS switches have nothing to do with the jet automatically trimming in pitch. You should have them on regardless though because they massively improve the handling of the aircraft throughout the envelope and enhance stability and spin/departure resistance. There are zero benefits to having them off in the strike eagle.

The jet auto trimming in pitch is a function of the Pitch Trim Compensator, which is part of the hydromechanical system, completely independent of the CAS.

The CAS and PTC are connected mechanically, electrically, and hydraulically together, within the Pitch/Roll Channel Assembly, to control the hydraulic servos to the flight surfaces.

They are connected to the Pitch Ratio and Roll Ratio switches and all work together, within the PRCA..

 ..

Edited July 20, 2023 by Holbeach

[KlarSnow]

Yes I'm aware they are all connected and influence each other. But if you left the CAS switches off, the PTC would still function normally. Its part of the hydromechanical system and is not reliant on CAS being on to function.

if you have a -1 go look at it. The PTC is covered solely in the hydromechanical section of flight controls, not mentioned at all as being part of the CAS system which is in the AFCS section.

None of this means these systems arent or can't be interconnected or influence each other. But the PTC is specifically not part of the CAS system, its part of the Hydromechanical system, which is always functioning, regardless of what you do with the CAS switches.

Edited July 20, 2023 by KlarSnow

[Holbeach]

@KlarSnow

 

The CAS and PTC are connected with the same hydro pipes to the servos, within the PRCA, but as you say, turn off the CAS and there's barely any noticable difference, auto trim still works perfectly.

It was most noticeable in the T/O run, which was more difficult to rotate, but turning off the CAS, was less dramatic than I expected.

Thanks for the reply.

..

[YoYo]

About FM I think its ok and accurate. The only thing that puzzles me is the fairly quick loss of energy during turns even with the maximum afterburner. Personally, I don't think it should happen so soon.