Single application of helical and spur gears

Multi stage reduction

Shame SB. You only get partial credit - you did not answer how. I hope you (both) do better on the exam.

How about a 1934 ford pickup..( or any stick shift that suits your fancy?... tranny and differential. MR GUY

A lathe has these types of gears in some of them. Helical to drive the chuck and spur gears to run the feeds. Automatic transmissions have a helical gear on the sun gear and spur type gears on the planets and carrier. Different manufactures of gear boxes have this type of setup, whether for speed increase or reduction. Depending on the load. Some spur gears run off the main drive to power accessories.

You will see this often in wind turbine gearboxes. The planetary stages have spur gears because these are easier to assemble plus the low stages are considered not that critical on noise. Also, for planetaries, using helical gears would mean an introduction of increased planet gear tilt which makes these gears critical to edge loading. To counteract that you would have to apply expensive countermeasures like for example flexible planet pins. On the high speed side however (for non planetary high speed stages) noise is more an issue so helical gears are often used to increase the (axial) contact ratio which smooths the running characteristics of these gears, as a bonus it also increases the load carrying capacity of these gears slightly. This however has consequences for the bearings supporting these gears as they have to take a higher axial load so the amount of helix is always balanced out to optimise performance of both bearings and gears.