# Do the compressors and turbine rotate at the same speed?

Since the turbine and the compressors are connected to each other via a common shaft, do they both rotate at the same speed. Because I've read that in some jet engines (single spool engines) they don't rotate at the same speed:

Single spool jet engine. These are those jet engines who have one shaft inside them. The compressors and turbines rotate on a same shaft. The speed of compressors and turbines decreases half way down the compressor stages, that is why they can’t match the local airflow. The various turbines and compressors is forced to rotate at same speed which lead to their inefficiencies.

(quora.com)

Is this true?

• quora.com/…. Refer the 1st answer in this link. – Johnson Nov 3 '19 at 13:50
• Thanks, I added the quote I think you are referring to. If you meant something else, please edit again. – Bianfable Nov 3 '19 at 14:07
• I think your quote is talking about airflow speed rather than the spool speed. That's why more efficient engines have two or three spools, or GTF. – JZYL Nov 3 '19 at 14:28
• Thx for the edit Bianfable! Yes, that was exactly what I was referring to. – Johnson Nov 3 '19 at 15:20

Single spool jet engine. These are those jet engines who have one shaft inside them. The compressors and turbines rotate on a same shaft.

Correct. In a single-spool engine, all of the compressor and turbine stages rotate at the same speed because they're attached rigidly to the shaft.

The speed of compressors and turbines decreases half way down the compressor stages, that is why they can’t match the local airflow.

No, the speed of the compressors and turbines doesn't change. It's the airflow that changes, and causes a mismatch.

• English SE could be of assistance – JZYL Nov 4 '19 at 13:18

Your question answers itself. If they have a single shaft and no gear box, then they rotate at the same speed. If there is a gearbox then that gearbox gives you the speed difference.

• Are there turbine engines with a gear box? I've never heard of one (except for geared turbofans, where the fan has a gearbox, or a turboprop, but never between compressor and turbine). – Bianfable Nov 3 '19 at 12:04