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Elevator Trim Tabs - thought i'd share this.


shotgun

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Hi everyone,

Thought I'd share to you this topic I just posted at fligthsim.

It's about the elevator trim tabs on most (if not all) FSX default aircraft, animating to the opposite (wrong) direction, EXCEPT for all my Aerosoft planes (Do-27 and Beaver X) which animates the way they shud, correctly.

http://forums.flightsim.com/vbfs/showthread.php?t=161232

Cheers,

Santiago

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And as you see by the answer given there, Santiago, the tab movement is:

Tab up, elevator down = more lift on tail = tail up = nose down

Tab down, elevator up = less lift on tail = tail down = nose up

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Oh, and of course, that means the Beaver and DO27 animations are wrong and the others are right. Animating the trim tab also means you need to counter animate the elevators (even if it is only ever so slightly).

sorry guys...

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And another anecdotal thought to ponder on:

Way back when I was learning my job, we were taught that the trim tab was invented by a pilot. Now as you might know, engineers and pilots have a kind of love-hate relationship. Some folk say "We Engineers" designed flight with the pilots' health in mind - when they move the controls, they exercise their muscles, so we made the planes inherently "unstable". That meant that for a given flight condition, the pilot would have to maintain a steady pull (or push) to maintain the aircraft attitude, thus getting some exercise while sitting down.

Now the pilot, being an inherently lazy individual, just happens to have some brains and so it came about that the trim tab was invented by the pilot to allow relaxed flying...

So they say.

But "Us Engineers" know better. We invented trim tabs to reduce the load on the airframe for a given flight attitude and condition so that the pilots wouldn't cause too much wear on our babies.

However, the "schoolbook" definition that I grew up with was that "The purpose of a trim tab is to reduce aerodynamic forces on airplane and pilot for a given aircraft attitude". Nowadays, of course, you can add fuel efficiency to the equation as a well trimmed plane is less thirsty.

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Thanks a lot Chris!

Like what I mentioned in my reply at flightsim.com, I had no idea until you guys enlighten me up on this :P

I have been flight simming for many years now, but all the while was ignorrant about how trim tabs really operate, until now :D Yes, I do use them all the time, but had no idea they actually operate "inverted" than they way I thought LOL!

All that being said, can I say that the BeaverX trim tab is animating wrongly then? Anyone?

THanks again. I learned something today :)

Santiago

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No, because first you need to know whether the function of the device in the Beaver is actually a trim tab, or a servo tab. A tab is a generic term used to define a variety of devices that, while generally similar in appearance, actually can be completely contradictory in operation.

I have no idea whether the Beaver is fitted with a trim or servo tab, and whether it is there to decrease trim forces, or increase elevator effect. My guess would be the former, in which case the operation in reverse of the trend of the elevator itself would be correct, but this was a 1940's design and there was still an uncertain knowledge of aerodynamics and much of the received wisdom of the Axis powers had tyet to be fully incorporated into Allied thinking. Servo tabs were very common in Thirties light aircraft... so it could just as easily be the latter.

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Just to clear it up........

Yes, the Beaver has a "Trim Tab", and it animates in the wrong direction.

I used to fly one for the US Army...that tells you how old I am.

Jerry

:lol: and I used to mend them for the British Army - even did part of my basic tech training on them. Nearer four decades than three now (just). So much fun to maintain.

You pilots had it better... I have been on "Crank duty" on a Beaver too - of course we had electrics, but the trainees had to do the flywheel wind-up to get the feel...

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Cue the: `You Old Cranker` jokes..?

Perhaps not. :mrgreen:

So the question now is: Could the Beaver be altered for accuracy easily? Probably not, but then the fact that it's only noticed now, it's a minor animation function anyway, and the operating functionality is correct within the sim should we be bothered?

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If I remember rightly, it was noticed quite some while back - even in the FS9 version? Looking at my Beta screens for the X version I see close ups of the tail, so I guess it was looked at then. But as you say, Simon, very few people actually fly their planes from six foot behind :lol:

Old? I'm not old, look at me, I'm still green.

Mould? What do you mean mould?

We still had a half way decent empire when I was a kid.

Mafeking? I am relieved!

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but then the fact that it's only noticed now, it's a minor animation function anyway, and the operating functionality is correct within the sim should we be bothered?

Yes, Simon, i thought so too. As long as the operating functionality is correct, most people (including me) can't be bothered by the wrong animation. I also didn't know which way was "correct" animation-wise, until you guys shed some light :).

Still, it would be nice if they animate correctly ;). It gives ppl like me who don't fly in real life (or works on a plane) a false interpretation of how this thing work :lol:

Santiago

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Chris:

Nice to meet someone who used to crew on the Beaver.

I flew them and the Otter (DHC3) out of Karlsruhe, Germany in the late 60's.

The Beaver is one of the best light airplanes ever built in my opinion. It didn't look it, but it was very light on the controls.

The Otter did the job well, and it looked less boxy, but it flew like a truck.

I started out in army aviation maint before going to flight school.

I care more about how they fly than what is not animated properly.

Jerry

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I agree that the Beaver tab moves opposite of what it should, but I would like to point out that on the Dornier all is correct. On her, the trim moves the elevator and in the right direction. Trim nose down lifts the leading edge.

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