[2.9.9.2406] Confused about design TLADD flight director pull-up command

[Stickler]

According to Lofting & Tossing - Heatblur F-4E Phantom II, in TLADD mode, at timeout of the pull-up timer, the horizontal ADI needle will transition into show [sic] deviation from the intended 3.5 G pitch angle, and then stabilize once 45 degrees nose up pitch is attained.

According to all RL 34-1-1 I have found, the following is true:

In the game, the horizontal needle will initially provide a 3.5G pull-up in 1.5 seconds to 37° pitch (which is approximately 38° pitch, so far so good), but then, instead of stabilizing at 45° (or 38°, or any other angle) command a 6.0 G pull-up until the release timer runs out.

Based on the extract I posted above, it would seem logical that the horizontal bar is removed from view or remains static when pitch angle hits 38°, even though the manual does not explicitly state this (the "maintain pullup acceleration", however, seems to imply that the system would stop rather than increase commanded pullup acceleration at 38°). Neither did I find any mention of the needle stabilizing at 45° IRL, other than several accounts (also of other aircraft of the time) relating that a LADD was performed at 45° of pitch.

A possible reason for 38° instead of 45° being the final commanded pitch angle is that at the expected (high) TLADD release altitudes and (low) speeds, a 38° pitch angle at release might yield a higher bomb range than 45°.

A final pitch of 45° is possible, however, since this should still result in a flight path angle of less (and therefore better for range) than 45° IRL.

Looking at the schematic at the above URL, it is not entirely clear whether a commanded change from 3.5 G to 6.0 G occured during pull-up, however if it did occur, I cannot think of a possible reason.

The depicted aircraft also has a flight path angle of 60° instead of 45° at bomb release. The latter is not entirely implausible since the closer the flight path angle to 90° at release at a given speed, the longer the TOF, which would be of interest to get maximum separation until detonation.

TLDR: Several conflicting sources. Is there a bug in TLADD flight director implementation?

Edited November 3, 2024 by Stickler

[Stickler]

Some additional information:

Observe the attached tracks recorded with a reference aircraft on a standard day, no wind, with four TLADD pull-ups using different AoA and note the pitch and climb angle (pitch minus AoA) at which the horizontal bar starts to move out of view:

#	Timestamp	Pitch	AoA	Climb Angle
1	38.866	34	0.6	33.4
2	32.072	34	0.4	33.6
3	25.285	36.1	2.5	33.6
4	24.952	39.2	5.3	33.9

This indicates that the criterion for the horizontal bar starting to move is neither pitch nor climb angle hitting 38°. The most consistent value seems to be the climb angle, but this is nowhere near 38°.

tladd_1.trk tladd_2.trk tladd_3.trk tladd_4.trk tladd_1.acmi tladd_2.acmi tladd_3.acmi tladd_4.acmi