Takoff trim oddity

[TheSkipjack95]

According to both the navair manual, the FSG manual and the pocket guide, the takeoff trim is supposed to be set at -2° ( that's 2° nose down, for clarity ).

 

However, setting the trim to that ( with corresponding indication on both MPCD page and engine panel on the right side ), results in excessive nose down moment during takeoff, from clean config to moderate load.

 

It needs further testing, but has anyone else encountered that ? I seem to recall it working previously but now it only makes for dangerous takeoffs.

What am I missing ?

[ZeroReady]

I find that trimming down to 2, then going back up one click at a time til it turns to 1 on the display, so one click up from 2, makes me perfectly level on VSTOL with nozzles at 81. I don't even need my hand on my stick, just goes straight up very nicely.

[TheSkipjack95]

Yeah I noticed that too.

 

I mean on regular takeoffs. Line up, trim to -2, flaps to stol, sto stop to 60, slam that throttle forwads and rotate the nozzles at NRAS. Even with early rotation of the nozzles, all I get is increased nose down moment as the speed increases.

 

I suspect I'm doing something wrong with my config, but -2 trim as per the manual just does not work for me.

[ZeroReady]

Maybe a dumb question but are you taking off into the wind?

[ChickenSim]

I would have to double check what the appropriate flight characteristics are supposed to be, but it's important to understand that the takeoff trim setting isn't supposed to be so you can take your hand off the stick or stop flying the airplane.

 

You put it at 2° ND to keep the nose RCS blower closed with neutral stick so that you don't inadvertently kick up debris and FOD your engine. Once you're airborne and out of FOD risk you need to fly the airplane and/or take that trim setting out.

[Ramsay]

Maybe a dumb question but are you taking off into the wind?

It's not a big problem and something you quickly discover if you try to fly the DCS Harrier 'by the book'.

 

The most likely explanation is truncation, as it seems to effect both positive and negative stab changes i.e. -1.0 to -1.9 = -1, -2.0 to -2.9 = -2, etc. and +3.0 to +3.9 = +3, etc. so my trim adjustments differ from the manual by 1° rather than match exactly.