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Will I Ever See The Tailplane Trim?  
User currently offlineAjaaron From United Kingdom, joined Nov 2000, 127 posts, RR: 0
Posted (14 years 5 months 2 weeks 6 days 11 hours ago) and read 3280 times:

If I want to see the stab trim move (i.e. with binoculars as a spotter) when will it occur on say a 747/777/757?

Before pushback?

After hydraulics are on following after engine startup?

On taxy, as the Before t/o checklist is completed?

Thanks, cos I've never seen them move when I'm spotting planes taxying for t/o with binoculars at Heathrow.

However, when I was a passenger on an L10-11, seated at the back on final approach I saw the tailplane move as the pilot trimmed - and boy did it move - fast and pretty substantial movement!

7 replies: All unread, jump to last
User currently offlineDrgreen757 From United States of America, joined Sep 2001, 155 posts, RR: 0
Reply 1, posted (14 years 5 months 2 weeks 6 days 10 hours ago) and read 3249 times:

Most horizontal stab's are already set before you even get on the aircraft, and stay there all the way thru engine start and takeoff. Boeing 757 stab trim is usually set to 4 units of trim. And when it is moved, it will usually be small minute movements that would be hard to see anyway, especially with binoculars.

As for the L-1011, it has an all moving horizontal stab. When the pilots pull and push on the control yoke, the entire Stab moves. The entire surface serves as the elevators, and what would normally be the elevators are trim tabs that can be adjusted up and down.

I hope this helps you out some!


Save the grey ghosts.
User currently offlineL-188 From United States of America, joined Jul 1999, 30410 posts, RR: 57
Reply 2, posted (14 years 5 months 2 weeks 6 days 10 hours ago) and read 3236 times:

I have seen them move plenty of times. Look for it right before and after an aircraft get de-iced.

Some aircraft makers require that the tailplane be set at a certian angle to allow for any fluid to drain from in and not get trapped in components.

If memory serves in the 727-100 it was full Nose Up trim. Correct me if I am wrong.

If you have a freind that has a Super Cub they trim the same way. Just have him jump in the cockpit and crank it through a couple of times.

User currently offlineMinuteman From United States of America, joined Aug 2000, 271 posts, RR: 0
Reply 3, posted (14 years 5 months 2 weeks 6 days 8 hours ago) and read 3225 times:

You're probably not going to see any appreciable movement.

In a typical situation, a horizontal stabilizer is going to trim from around 13 degrees deflected nose up to 2 or 3 degrees nose up alignment with the fuselage (usually, not sure what that works out to in Trim Units). The trimming will occur over the entire climb, so you're talking about a ten degree change in deflection over twenty or thirty minutes.

User currently offlineAJ From Australia, joined Nov 1999, 2406 posts, RR: 24
Reply 4, posted (14 years 5 months 2 weeks 6 days 8 hours ago) and read 3221 times:

On our 747-400s the trim is set on receipt of the loadsheet, so very close to pushback.

User currently offlineMetwrench From United States of America, joined Aug 2001, 750 posts, RR: 2
Reply 5, posted (14 years 5 months 2 weeks 6 days 8 hours ago) and read 3226 times:

The only time you are going to see a lot of horizontal stabilizer trim movement is on the Flight Crew's preflight before the first flight of the day. Or possibly during a Maintenance Check.

High-speed film of an A/C landing will catch it but movement is still subtle during flight.

It's a big suface, doesn't need to move a lot to have a big impact.

User currently offlineTwotterwrench From , joined Dec 1969, posts, RR:
Reply 6, posted (14 years 5 months 2 weeks 6 days 7 hours ago) and read 3212 times:

Stop by the hangar tomorrow. I'll let you move it all yo want...  Smile/happy/getting dizzy

User currently offlineTimz From United States of America, joined Sep 1999, 7228 posts, RR: 7
Reply 7, posted (14 years 5 months 2 weeks 5 days 14 hours ago) and read 3175 times:

As for seeing the tailplane move, dunno. But on the IL-62 the result (the difference between the tailplane's position on arrival at the gate and on departure from the gate) was certainly obvious.

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