A major investor is doubling down on Archer Aviation, but the stock is still down roughly 39% this year.Archer Aviation (ACHR 8.33%) stock is making big gains Tuesday. The company's share price was up 8.2% as of 3:30 p.m. ET, according to data from S&P Global Market Intelligence.Archer Aviation stock is surging following news that Stellantis had made another investment in the company. The new, $55 million investment from Stellantis comes on the heels of Archer's latest successful flight test for its Midnigh ...