horizontal stabilizer position before trim check

Feel free to discuss anything here - as long as it is F-16 related.
  • Author
  • Message
Offline

lippy

Newbie

Newbie

  • Posts: 15
  • Joined: 26 Sep 2007, 09:49
  • Location: Florennes Belgium

Unread post09 Nov 2017, 09:13

Hi everybody,
could anybody tell me why horizontal tail must stay between .250 inch and 2.750 inch down from marking when flight control self test stop, all surfaces at neutral position right before trim check.
Because the only reference is on my crew chief workcards. Nothing in the FI.
You can find other references on horizontal tail rigging ( 1-3/8 ----1-5/8 inches down from marking)
So first, why such a difference between both references? Second, why especially down from marking (safety reasons cause down from marking means a nose up position)? And third does that means other stuff than a wrong rigging when tails are not within limits? Like broken, worning out parts like bearing or tail axle?

Thanks for your answer cause a big "shortcut" from our repair team when I found out tails out of limits was: " Was the self test good?.....yes? so is your aircraft"

And at last did anyone of you ever ground an F16 during a launch because of this?
Offline

indigowarrior9

Enthusiast

Enthusiast

  • Posts: 34
  • Joined: 20 Jan 2017, 21:57

Unread post22 Nov 2017, 20:56

Bare in mind .. i'm not a F16-mechanic of any kind!

So first, why such a difference between both references?

Can this difference in horizontal tail position be explained when one flies with a clean F16 vrs a fully loaded F16?

Second, why especially down from marking (safety reasons cause down from marking means a nose up position)?

Do you have any pictures to show this?

And third does that means other stuff than a wrong rigging when tails are not within limits?

I've no idea on this one..
Offline

Buffalo

Enthusiast

Enthusiast

  • Posts: 42
  • Joined: 12 Jul 2007, 16:32

Unread post26 Nov 2017, 08:03

Same disclosure - I'm not a maintenance troop, and my following supposition may not reflect the reality of why the tail marks are positioned the way they are set...but I'm guessing I'm correct and the position is important.

Our first F-16 fatality was the result of multiple, near instantaneous electrical failures leading to a complete Flight Control System fail. When the FLCS failed, the tail went to the proscribed position which lead to a radical negative g pitch down. The pilot ejected, but was not able to clear the aircraft before impact due to the low altitude/high rate of descent.

The subsequent accident board findings lead to a host of fixes to the electrical system and rerigging the trim of the tail to not cause the high negative g pitch down. It's still an issue at higher speeds, hence the warnings in the Dash 1 to slow down with FLCS issues.

The initial trim position was set to help the F-16 lift / turn better (part of the relaxed static stability concept)...the rerigging of the tail probably shaved a little of that off the performance, but its a better idea. I haven't been in the safety loop for the last 25 years, but have not heard of any subsequent FLCS fails after they engineered in several fixes to the electrical system.

Since the electrical fixes have essentially reduced the probability of a FLCS fail to near zero, you're probably not putting anyone at risk for this issue, but I'd feel better if you aimed this at a LM Aero product support team rather than fishing online from us fossils.
Offline

lippy

Newbie

Newbie

  • Posts: 15
  • Joined: 26 Sep 2007, 09:49
  • Location: Florennes Belgium

Unread post29 Nov 2017, 10:35

Thanks buffalo for your useful feedbacks... even if I still ain't got my answer.

Return to General F-16 forum

Who is online

Users browsing this forum: No registered users and 8 guests