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Author Topic: Spitfire trim tabs position indicator  (Read 4769 times)
Wedge
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« on: February 21, 2011, 11:29:22 PM »

I have question concerning the elevator trim on the Spitfire.



Specifically I would like to better understand the relationship between the elevator tabs position indicator in the cockpit and angular position and range of elevator trim tabs.



If the elevator tabs position indicator in the cockpit is set in the neutral position what would be the angular difference compared to the elevator?

I have noted that the pilot notes recommend setting the elevator trim tabs to 1 division nose down on take-off.

Is the trim tabs setting in an extreme position enough the force the elevators to their maximum defection?

If anyone has any information or experience of either piloting or rigging a Spitfire and could comment or point me at a good source of material on the subject it would be most appreciated.

But any information that anyone has is very welcome.
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Edgar Brooks
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« Reply #1 on: February 28, 2011, 06:38:52 PM »

From what I've read, the trim tabs were simply to allow the pilot to adjust the fore-and-aft trim, to enable him (allegedly) to fly "hands-off," but the trim needed to be continually altered depending on the airspeed.  They certainly wouldn't have exerted enough force to cause full movement of the elevators, otherwise the pilot wouldn't have retained control.  Reading a couple of manuals, for Seafires 15 & 17, on Saturday, both said that, to obtain full nose up, or down, indication, on the dial, should require two full turns of the trim wheel.
Edgar
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JamesF
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« Reply #2 on: April 30, 2011, 11:28:34 AM »

My experience with the SAAF Museum Spitfire MkIX, during 1999/2000, (A while ago, but a Spitfire is something you don't forget in a hurry!), the one notch down setting was basically neutral.  If you look at pics of the Spitfire in flight, the elevators are almost always deflected slightly downwards, a curious characteristic.  Trim tabs work in the oposite sense and will displace or "fly" the controll surface upwards (in an elevators case) if positioned down for example.  Full right nose trim is applied for take off, but this is done by feel, no indicator. The controls of the aircraft are very light and reponsive in flight, and are powerful, the rudder being extreemly so.  I would say the only way to override a full trim application would be to get as slow as possible, (rolling with an elevator trim failure into a turn, is a pretty standard counter measure aswell) but I would'nt like to try it!  I had a go at overriding the full rudder trim after take off one day, to see if I could, should it fail, all that happened is as the speed increased, and I pushed against the trim force, the pedal just came back and pushed my whole body up the seat, despite what I thought was a secure harness.  Quickly wound it off!

You don't really need any nose up trim for take off.  I found I could just see the top of the Spinner and on take off, would raise the tail slightly after starting to roll, placing the spinner on the horizon. Keeping straight was not an issue with all the prop slipstream over the tail, also helped by not using full power (due to it being a vintage aircraft, I only used +6 Lbs boost, half throttle which was plenty!).  All you had to do was hold the spinner on the horison, and at 100 MPH she would smoothly fly off, with basically no pitch input.  Such a lady....

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