Fighting the trim...

EatSleepFly

Well-Known Member
Just curious as to what you all think...

The other day, while trying to pull a fast one on my student (who had given me the controls for a sec. while he was in the process of putting on his hood for instrument work), I secretly ran the trim back a long ways, and kept the yoke muscled forward to maintain our climb-out speed. The idea was to see his reaction to a trim system malfunction and possible resultant unusual attitude after I gave him back the controls (he did fine, and then swore at me, lol
).

Anyways, it didn't occur to me until I was laying in bed that night, but...

Could it possibly do damage to the trim tab, or some other part of the trim system, by holding the aircraft so grossly out of trim for a minute or so? I've never heard anything about it before, but with all the force it took to keep the nose down, it would seem like something could get damaged. Any thoughts?

(This was a Cessna 172 by the way.)
 

Ophir

Well-Known Member
You know, I was looking at the linkages on a Cessna the other day. They run under the floor boards and then back to the controls. It looked to me, and I didn't really get 100% confirmation of this, that the trim controls are intermediate spools that will pull cable in either direction but the affect on the controls still allows the cables to be actuated in a manner that the cable connecting to the controls doesn't have excess pressure on it.

It reminded me of looking at a compound bow. Something like that.


clear as mud huh?
 

Minuteman

“Dongola”
I wondered about this when I was introduced to trim stalls.

The only thing I could dig up was §23.397 Limit control forces and torques, where an elevator control has to withstand at least 200 lbs applied asymmetrically to the yoke or 167 lbs on a stick.

Its probably a gamble between whether my seat goes flying back first or some pulley mount deep in the guts decides to fold over. Don't really have an interest in finding out.
 

pavelump

Well-Known Member
[ QUOTE ]
Just curious as to what you all think...

The other day, while trying to pull a fast one on my student (who had given me the controls for a sec. while he was in the process of putting on his hood for instrument work), I secretly ran the trim back a long ways, and kept the yoke muscled forward to maintain our climb-out speed. The idea was to see his reaction to a trim system malfunction and possible resultant unusual attitude after I gave him back the controls (he did fine, and then swore at me, lol
).

Anyways, it didn't occur to me until I was laying in bed that night, but...

Could it possibly do damage to the trim tab, or some other part of the trim system, by holding the aircraft so grossly out of trim for a minute or so? I've never heard anything about it before, but with all the force it took to keep the nose down, it would seem like something could get damaged. Any thoughts?

(This was a Cessna 172 by the way.)

[/ QUOTE ]

Try this one, if you're feeling brave....


My instructor for my PPL made me do landings with a trim failue. All the way forward, and all the way aft. (well maybe not ALL the way) You want to talk about a tired arm by the end of the traffic pattern? Is it likely to happen for real? Probably not, but at least I have an idea of what it would feel like if it did. I don't imagine you'd want to try this with a student who's having a problem with the flare already!

Come to think of it, it's kinda unsafe. hehe

Dave
 

bluelake

Well-Known Member
it seems to me that in that scenario, your not really working the trim hard (your "setting the trim", but working the ELEVATORS hard to overcome it.

My guess is that the only thing you are working hard is your arm muscles, but I could be wrong.

Related, when I train folks in a Katana (electric trim), we make sure they can fly ANY flight regime with the trim stuck either full forward or aft.
 
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