View Full Version : towershaft on JT15: RPM constant?

18th Mar 2004, 04:13
Hello Ppruners!

I have an interview coming up and am reviewing systems of the last plane I used to fly. Unfortunately, it has been a while and there are a lot of questions. This is on the Citation V but I assume that this is similar on other types.

I am reviewing the P&W JT15D-5A of the CE-560. Still have questions about the towershaft that drives the accessory section (driving the oil, fuel and hydraulic pump, FCU, and tach generator [N2]) through the high-pressure rotor shaft. After engine start N2 should be 49%. Red line (N2) is 96%. I can’t find the RPM range of N2 right now, but let’s assume the RPM differs by say 10,000 PRM between the lower and upper limit. Does the towershaft RPM differ that much (probably not) or is the towershaft’s speed keep constant? If so how? The FS manual doesn’t say anything it.

7 7 7 7

18th Mar 2004, 12:12
No, the towershaft is physically geared off the HP section shaft, so RPM varies with the engine. All the accessories are set up so that there is adequate output at idle (except the generator for cross starts - hence high idle switch), and various systems control output for higher settings. e.g. oil pressure relief valve on oil pump etc.

Hope this helps, and good luck with the interview.