England midfielder Jenas has joined the R's on a permanent deal, which will expire in the summer of 2014.
"The fact that Harry Redknapp was here was a big factor. There's a big challenge ahead of us in staying in league and I want to be part of it," the 29-year-old told Sky Sports News.
"There's no time to waste in this situation, so we need to hit the ground running, starting on Saturday with a win."
Meanwhile, Townsend has signed on a loan basis until the end of the current campaign.