DC-3 Question

[Chris Trott]

At our CAF Wing (http://www.dfwwing.org) we have the R4D-6S, a Harvard, a AT-6, a FG-1D Corsair, a BT-15, and a L-5A. The loudest of the whole fleet is the smallest - the L-5A. It's powered by a 190HP Lycoming and the tips DEFINITELY go supersonic. ANR headsets are a must to fly the plane. We still can't figure out how pilots during WWII could ever spot artillery from them because it would have been impossible to hear themselves think much less the gunnery radio operators on the ground (or ship) hear what they were saying.

[robcap]

To come back to the original question, could it not be a trick to the eye, see our friends forum here:

http://www.calclassic.com/cgi-bin/yabb/ ... 1168285622

Makes sense to me.

Best, Rob

[Prop Jockey]

Hi All,

There's and engine start vid at http://www.douglasdc3.com/ (On the home page) that potentially illustrates Rob's link.

Cheers

Rich

[robbie]

Whoa, don't we get into some technical subjects! I bet this has a few people scatching their heads?.

Chris got it pretty well nailed though.. I believe the intial idea, for this counter rotating setup was to attempt to reduce the adverse torque affect on the A/C, but although it worked very well, it was very exspensive to hold the different parts required for both sides.
Normal props rotate clockwise (veiwed from the rear) and are called (RIGHT HAND TRACKTORS)...hope it spelt tracktors and not trackters?.

Peter will probably agree with me on this, that, the last thing you need on T/Off is a failure of #4 engine! the Visount was a prime example, very hairy trying to correct the gyro torque affect.

The amount of reduction required is calcullated, as Peter said, to prevent prop tip speeds from exceeding mach1. ie the Tyne had a ratio of 14:1 giving a prop speed of around 1,000 rpm at an engine rpm of 15,250.

Hope this makes things easier for the youngsters to understand?.

Robbie

[cstorey]

Peter : you are quite correct that there is an epicyclic reduction gear in these engines. I believe these can be made to counter rotate by the insertion of a further set of planet wheels in the gear train thus reversing the direction , but if I remember correctly from Bill Gunston's wonderful books on engines, manufacturers were often reluctant to do this becuase the gear loading became extreme because the wheels had to become smaller and smaller, and reliability suffered greatly

[Tom Clayton]

I think this whole thing may stem from an error(?) in original FS9 model. The animation is correct with both props rotating the same way, but the visible model has the left prop modeled backwards. I suspect that someone performed some sort of "mirror" operation during the buildup of the plane. When it was being prepared for FSX someone else must have noticed the angle of the blades, watched the animation, and assumed that the model was correct and not the animation.

[Chris Trott]

Normal props rotate clockwise (veiwed from the rear) and are called (RIGHT HAND TRACKTORS)...hope it spelt tracktors and not trackters?.

1) The spelling is "tractor"

2) "Normal" is somewhat subjective. Some British pistons have a "normal" rotation of counter-clockwise (left-hand tractor). Someone told me once why, but for the life of me I can't remember.

[cstorey]

Almost all British piston engines were left hand rotation. This is , in fact, the direction of rotation universally adopted in the automotive world , but most US origin piston aeroplanes used right hand rotation. I do not know what the reason for this was , but I suspect it was because most US installations were arranged with the drive taken off the back of the crankshaft i.e. the engine was installed facing backwards, whereas most European engines had the prop driven off the nose of the crank

[Garry Russell]

The Bristol Hercules was LH but the RR Merlin was RH

I've not looked to see if these are stndard for these manufactures.

Garry

[Adrian Wainer]

Hamilton Standard Hydromatic Prop

http://files.asme.org/ASMEORG/Communiti ... s/5572.pdf

Best and Warm Regards
Adrian Wainer