Douglas aircraft
 

On the DC3/4/6/7 ( and others) etc there is a large wheel mounted horizontally immediately behind the column separating the two windshields. Could someone tell me what its for, please? Ta.

I'm sure this wheel is the means by which a directional aerial is rotated. Tuning into a known beacon and watching (or listening!) for max signal strength as your aerial is rotated gives you a bearing, and then tuning into a second beacon and plotting the point of intersection gives your position relative to the beacons.
See article.

Rudder trim.

Speedbird 48.

As Speedbird 48 says, for the DC4/6/7, but the DC3 rudder trim is on the central pedestal below the engine control levers, as is the aileron trim.

Douglas wheel
 

Gentlemen

Many thanks for the replies. Two different opinions. I have never known a rudder trim wheel anywhere other than behind or near the throttle box, conveniently to hand when flying. Having just read an excellent book about the DC3 in which great use is made of the manual DF tuning, that seems to be the most likely answer.

Thanks again

Boslandew

A picture is worth a thousand words..

Speedbird48 is correct...it is the rudder trim. I flew as Flight Engineer and then as First Officer on the DC-6 and 7.

Sounds you are describing the ADF or radio compass box which among other knobs has a very small winding handle on some installations and is in the cockpit roof. That is used for manually turning the loop aerial for an aural null.

The large horizontal wheel you describe sounds more like the the manual rudder trim wheel on the DC4. The DC3 does not have that wheel but instead has a winding handle below the throttle quadrant and has a numbered scale. The Lockheed Hudson has similar style trim wheels as the DC3.

Unless the pilot has long hairy ape like arms, the DC3 rudder trim is not easy to operate accurately since the pilot has to lean down to see the handle and numbers and this can lead to distraction when flying on instruments. Worse still the aileron trim wheel is also under the throttle quadrant as is the autopilot engage handle.

Wheel
 

Gentleman, again many thanks.

As DALMD-11 has flown the aircraft then rudder trim sounds like the definitive answer. There's always an answer if you ask the right bloke.

Thanks also for the info on the loop aerial tuning. Now you mention it I can remember such an item in the Beaver used by the AAC in which I flew as a pax in the 60's.

Much obliged

Boslandew