Take off trim question

[Jenson]

Hi there,

 

I read in the manual that the hornet pitch should be trimmed according to the take off weight as follow:

less than 44,000 lbs: 16 degree

45,000 - 48,000 lbs: 17 degree

above 49,000 lbs: 19 degree

 

I have a few questions and wonder if anyone could advise: 

1. Why there isn't 18 degree recommended? 

2. If take-off weight is way below 44,000 lbs, should we adjust it further down to 15 degree or even less? I noted if trim is less than 15 degree, the Master caution will lit, however, when I take off with 35,000 lbs, even if trimmed at 15 degree, the hornet will lift nose up like a rocket after launch. So the real question is, why the take-off trim isn't calculated more precisely based on aircraft weight, especially when take off at a super light weight? 

 

Thanks  

[Bluto74]

I guess the short answer would be because that is what the test pilots determined the best settings for that situation.  Probably not the answer you were looking for but it has all been determined from the weight affecting the CG moment.  You need the nose to pitch up correctly on the shot so 16 gets you correct in the light weight condition.  As you load up the CG moment moves forward so you need more deflection to pitch up.  

 

Also, if you have full burner in coming off the end you will blast off.  Light loads would not have the blower on when getting shot.

 

Edited September 30, 2021 by WaWa74

[Wroblowaty]

Interesting is, why there are gaps between 44000 and 45000 and between 48000 and 49000.  Like when you are at 44600. You are not less then 44000 but not 45000 yet...

[Tholozor]

16° nose-up trim is the minimum trim for catapult launch at half flaps, regardless of total weight, due to how the FCS handles automatic aircraft rotation after launch. Trim settings pre-launch will correspond to a specified reference AoA once weight-off-wheels. The recommended trim settings are in place in order to reduce sink-off-bow after launch and as a backstop safety measure in the event of a single engine failure to maintain control. NATOPS section 8.2.8 covers this is more detail.

Edited September 30, 2021 by Tholozor

[Qiou87]

18 hours ago, Wroblowaty said:

Interesting is, why there are gaps between 44000 and 45000 and between 48000 and 49000.  Like when you are at 44600. You are not less then 44000 but not 45000 yet...

Definitely, if you are between values, default back to 12° (and sink after launch) 

 

I think this is the kind of table that tries to give you a feel for what to do, not a precise instruction (for example, at 44,950lbs someone might prefer to use 17°, someone else will chose 16°...). This is a sim and not real world, I honestly don't check my T/O weight everytime and just do it with a basic rule:

- A/A loadout 17° (meaning AMRAAMS and 1 tank)

- A/G loadout 18°

- heavy A/G loadout (8x AGM-154, or 2000lbs bombs on each pylon) 19°

 

Interesting that the manual doesn't have 18°, this is my most-used setting and it works very reliably when I have a medium-heavy A/G loadout for example...

Edited October 1, 2021 by Qiou87

[Bluto74]

It all works good until you lose a fan on takeoff.  We don't have to worry about that though.

[Bingo41]

I am a little confused about trim. I have been using the weight schedule to setup trim using the HAT switch on my HOTAS.

 

On the left side of the cockpit, behind the throttles, is a "Trim Button." What function does this button have?

 

Bill Clark

[Bluto74]

50 minutes ago, Bingo41 said:

I am a little confused about trim. I have been using the weight schedule to setup trim using the HAT switch on my HOTAS.

 

On the left side of the cockpit, behind the throttles, is a "Trim Button." What function does this button have?

 

Bill Clark

That sets the takeoff trim value of 12 if you are referring to the Hornet.  Which is what you use at the airfields.

 

[Jenson]

So, have you guys experienced the situation when the hornet is super light loaded, the nose will keep pitching up all the way up if you don't touch the stick? 

[pete_auau]

On 10/13/2021 at 1:48 PM, Jenson said:

So, have you guys experienced the situation when the hornet is super light loaded, the nose will keep pitching up all the way up if you don't touch the stick? 

just tried  it  loaded  half  of  fuel added 15  for  trim  and  had  no issues  had  to pull  slightly on the  stick  to raise   the nose  and  then it  kept its  steady  climb

[Foka]

Isn't the a Hornet quiestion, not the carrier question?