f4 j/s elevator authority

kdfw · Post by **kdfw** » Wed Jan 16, 2019 2:09 am

Hello,
just updated to the j/s adv version, trying to get a handle on the changes, one issue:

when lightly loaded (half fuel, sidewinders only), takeoff requires some amount of nose up trim or else it will not leave the ground with stick full aft going over 180kts. seems the elevator authority is lacking from what i'm experiencing.

of course i can give it some nose up trim prior to takeoff roll but once airborne and clean up, it just goes vertical without frantic nose down trim to counter this action.

what's going on?

Post by **doodlebug** » Wed Jan 16, 2019 2:35 am

I think that's the nature of the beast in the real world - you also need to switch on your Stability Augmentation System (SAS- Pitch/Roll/Yaw)

kdfw · Post by **kdfw** » Wed Jan 16, 2019 4:08 am

yup, sas is switched on, but that comes into play once airborne.

the fact that it needs large nose up trim just to lift off, then it goes ballistic once gear up (mil thrust) seems a little off...

Post by **Alvaro** » Wed Jan 16, 2019 7:21 am

kdfw wrote: ↑
Wed Jan 16, 2019 2:09 am
Hello,
just updated to the j/s adv version, trying to get a handle on the changes, one issue:

when lightly loaded (half fuel, sidewinders only), takeoff requires some amount of nose up trim or else it will not leave the ground with stick full aft going over 180kts. seems the elevator authority is lacking from what i'm experiencing.

of course i can give it some nose up trim prior to takeoff roll but once airborne and clean up, it just goes vertical without frantic nose down trim to counter this action.

what's going on?

What flaps are you using?. Only HALF flaps are allowed in this aircraft for airfield takeoff. In FULL flaps the hstabs authority is very reduced and hence, rotation and liftoff speeds will exceed the allowable limits. Full flaps are only used for carrier takeoff (only if a/c configuration recommends so - see NATOPS - ) and landing.

Also, you NEVER ever should trim UP a Phantom for take off, only trim down (1 to 3 units). The reason for this is to counter the progressive pitch up with increasing speed caused by its singular pitch flight control system (bellows).

In any case, please, check the NATOPS (F4J/S flight manual) and the ADV User Manual.

kdfw · Post by **kdfw** » Wed Jan 16, 2019 7:47 am

Yes, this is with half flap setting.

Recap:
Half fuel
Sidewinders
Half flap
Mil thrust
Neutral trim
Stick full aft ac does not lift off > 180kts

And yes, nose up trim allows lift off but severe nose up pitch after cleanup.

Post by **Alvaro** » Wed Jan 16, 2019 7:55 am

Does it happen in J and S versions?

What sim version?

kdfw · Post by **kdfw** » Wed Jan 16, 2019 8:00 am

This is p3dv44 on both j and s models. Thanks.

Post by **Alvaro** » Wed Jan 16, 2019 8:09 am

Does anything change if you try a no flaps takeoff?

Also, if you enable "instructor mode" in the ADV menu, what weight and CG does it show when you change your configuration?

Post by **JonathanBleeker** » Wed Jan 16, 2019 8:37 am

One other check, if you slew to altitude instead of taking off, do you have any control at all once at speed?

kdfw · Post by **kdfw** » Thu Jan 17, 2019 3:06 am

ok, let me check these things.

in the mean time, watched related video which explains the behavior of the f4.
https://youtu.be/Y6RcTtGfG3E

Post by **JonathanBleeker** » Thu Jan 17, 2019 12:08 pm

Oh and please verify you are not running EZDock.

Post by **Alvaro** » Thu Jan 17, 2019 8:45 pm

Also, make sure the aircraft.cfg files are NOT edited / overwritten after the ADV pack installation.

Basic F4 aircraft.cfg files CANNOT be used in the ADV version. Just in case...

kdfw · Post by **kdfw** » Sat Jan 19, 2019 7:28 pm

Alvaro wrote: ↑
Wed Jan 16, 2019 8:09 am
Does anything change if you try a no flaps takeoff?

Also, if you enable "instructor mode" in the ADV menu, what weight and CG does it show when you change your configuration?

no flaps seems to make climb event after clean up a little easier, it's the half flap retraction that causes the ac to baloon, which i need to quickly counter by nosedown trim.

JonathanBleeker wrote: ↑
Thu Jan 17, 2019 12:08 pm
Oh and please verify you are not running EZDock.

no ezdock or viewer used.

Alvaro wrote: ↑
Thu Jan 17, 2019 8:45 pm
Re: f4 j/s elevator authorityQuote Alvaro
by Alvaro » Thu Jan 17, 2019 8:45 pm

Also, make sure the aircraft.cfg files are NOT edited / overwritten after the ADV pack installation.

Basic F4 aircraft.cfg files CANNOT be used in the ADV version. Just in case...

i had the classic f4j/s already installed then upgraded to the adv pack (to make f4j/s work in p3dv4.4), it looks like installing the adv pack overwrote many files like the panel folder, so i'm assuming it overwrote the aircraft.cfg as well.

reading the natops and watching the yt vids on the real f4, takeoff speeds are quite high even at light loads. so maybe elevator effectiveness kicking in at higher speeds (>180kts) is reasonable?

another thing that's puzzling is the ballooning with half flap retraction climbing at around 250kts. this can be reduced with some nosedown trim at takeoff but that prevents nose from lifting off at full aft stick. i guess i'll need to play around with the trim values a bit more.

thanks.

p.s. i'm not finding a way to load a fs flight plan and having it followed, hsi modes for tacan tuning i get, but is there a way to load a flight plan and have it followed or at least cdi point to the waypoint?

Post by **JonathanBleeker** » Sun Jan 20, 2019 7:13 am

This aircraft isn't a F-16 or F-15. It has a very high wing loading which translates to a rather high takeoff speed. Loaded with bombs and at MTOW, you aren't likely to be able to rotate and get off the ground below 200 kts. And normally 2 units of nose down trim is required on takeoff to prevent the ballooning, because as you accelerate the trim position will move back to neutral and eventually nose up. It isn't a fixed position.

As for FS flight plans, you can load them, then select the active waypoint from the F-4 menu in the Addons menu. In order to get steering data from the navigation computer, set the nav source switch and knob for the HSI/ADI to NAV COMP, and set the navigation computer mode to BASE instead of TGT. TGT uses the lat/lon entered on the target position indicators, while BASE will use a internally stored lat/lon which in this case will be the selected flight plan point.

kdfw · Post by **kdfw** » Sun Jan 20, 2019 6:15 pm

JonathanBleeker wrote: ↑
Sun Jan 20, 2019 7:13 am

As for FS flight plans, you can load them, then select the active waypoint from the F-4 menu in the Addons menu. In order to get steering data from the navigation computer, set the nav source switch and knob for the HSI/ADI to NAV COMP, and set the navigation computer mode to BASE instead of TGT. TGT uses the lat/lon entered on the target position indicators, while BASE will use a internally stored lat/lon which in this case will be the selected flight plan point.

thanks for this, i couldn't find the nav settings in the manual or in this forum.

one final question, is the pullup light (gpws) supposed to work?