Assigning a conventional mortgage to your investment property is common. Based on your down payment, the income from the property should cover the Principal and Interest payments and provide a contingency fund.
Establishing a home equity line of credit on your principle home to pay for the investment property is also a viable option for some. This is a also a safe strategy if you are investment for a short term.
6ix Mortgage Group offers a unique product for seasoned investors. Your contractual payments are interest only, therefore you end up cash flow positive on your property. This is also a good option for short term flips.