# Is it possible to add “planets” to the gearbox of a Trent 1000?

The gearbox of a geared turbofan engine has 4 reducing gear small wheels being spun by a larger wheel or gear, simultaneously spinning the shaft that is attached to the fan.

That is 8 points of contact, two for each small wheel/gear meaning 8 the points where friction and subsequent heat would result. I gather the use of 4 small wheels/gears instead of one is for reducing the load on the teeth at each given point.

Would increasing the smaller gear wheels (i.e. the "planets" ) from 4 to 8 or 12 or 16 for a gearbox designed for an engine the size of a Trent 1000 or more render the gear teeth less likely to break or fail?

With some reinforcement on the teeth, would it be possible to make a gearbox for this large engine?

As for the extra heat, cooling and rotating the oil through a cooler or along the length of the aircraft several times over, exposed to the atmosphere at cruising altitude using a high pressure oil pump passing oil through a sealed gear box would take care of cooling.

With the ambient energy loses to heat would this render the engine a lot more fuel efficient and possible?

• how do you increase the points of contact? increasing the number of teeth? but then you have teeth that are way small. then you have to increase the diameter of the gears, and you end up with an gearbox that's way too big. – Federico Jan 19 '18 at 12:57
• The problem with gearbox cooling is not cooling the oil afterwards, but circulating enough oil in an efficient manner to cool the gearbox in the first place. Perhaps this can help you focus your question towards what you really want to ask. – Sanchises Jan 19 '18 at 13:08
• Smaller teeth means it can't hold as much torque, so I think adding teeth will make it more likely to fail. – Ron Beyer Jan 19 '18 at 16:42
• While you mention 4 satellites, the PW1100 has 5 ones. Epicyclic gearing is a crazy technology and efficient gearboxes are difficult to built due to the complex plays to catch in spite of wear if you want all teeth to transfer the load. – mins Jan 20 '18 at 20:37

• “Specifically, the gear ratio is going to get closer to 1” – this is not true. In the limit $N_\mathrm{s} \approx N_\mathrm{r}$, $N_\mathrm{p} \ll N_\mathrm{s}$, the transmission ratio $\frac{\omega_\mathrm{c}}{\omega_\mathrm{s}}$ approaches $\frac12$. I.e., it is possible to have a planetary gearbox with arbitrarily many planet gears, while still getting a useful torque conversion. It just probably doesn't offer as good a tradeoff between power, weight, reliability and efficiency-gain as the 5-planets configuration does. – leftaroundabout Dec 15 '19 at 17:38