Updated

By Lewis Franck

INDIANAPOLIS (Reuters) - Danica Patrick knew this season would be the toughest of her career but the Indy Car darling hopes to turn things around at Sunday's Indy 500.

In addition to racing for Andretti Autosport she also signed a deal to race in NASCAR's second-tier series part-time for stock car's most popular driver Dale Earnhardt Jr.

She admitted that driving in two different types of cars had proven more difficult than she thought.

"It's definitely the hardest year I've had here at Indy, it's been challenging," said Patrick, the only woman to win an Indy Car race. "Throughout this whole year I've really needed to work on keeping my confidence up, because it's been tough.

"I guess I knew it was going to be (tough) when the decision was made to do both of them.

"I knew it was going to be the hardest year of my career. I didn't know how hard.

"I thought my Indy car stuff would give me confidence for the NASCAR stuff and I would be able to stay happy all the time but, unfortunately, I think it's been a little of the opposite."

After qualifying a disappointing 23rd for Sunday's Indy 500, a frustrated Patrick blasted her team in a trackside interview telling the crowd it was not her fault and for the first time in five years racing at the Brickyard the diminutive 28-year-old heard boos.

"I kind of thought: 'Oh shoot, what did I do?'" she said.

Driving a sleek, open-wheel Indy car versus the heavy, full-bodied stock cars requires different talents and only ex-Formula One driver Juan Pablo Montoya has had any tangible success in both series.

When Patrick arrived at Indianapolis for the first time in 2005 it was a novelty. When she turned in competitive lap times people paid attention.

She qualified fourth and finished fourth in her rookie year while becoming the first woman to lead a lap in the Indy 500.

Covers of magazines and lucrative sponsorship deals followed making her Indy Car's most marketable driver.

"As quickly as they can go 'boo' they can go 'yeah' and cheer for me just like they did any other year, like the first year," said Patrick. "They're here for an emotion and I'm giving them something to be emotional about.

"I hope that Sunday, it's something positive."

(Editing by Peter Rutherford)