Research is something any writer and artist does (or at least needs to do) and that is doesn't eliminate erotic authors. It may be something like reference photos, or porn to discover the "know how" of DP, or something as boring as whether its lay, lie, or laid.
I have just started reading a book entitled The Black Witch, its a horror novel, and a bit outside my norm, but already I can tell the author knows a lot about ships. Whether its was countless hours of researching the differences between stem and stern or what they called old sailors, Michael Rivers is on top of it. I don't know a great deal about ships, so I certainly am not verifying everything he says as true and accurate, but it reads smoothly and he sure could fool me if its not!
The point is that whether or not you are experienced with sex you need to read like you are! If you're not a man discuss with a man how it feels to ejaculate. If you're not a female find out what that moment of pleasure is like for one! If you don't have a husband, wife, or good friend you feel comfortable talking about that amazing moment with then join a forum, there are hundreds of thousands out there, and many of them enjoy talking about sex! You don't necessarily need to experience double penetration to feel the pleasure of something in your pussy and ass at the same time.
Erotica and sex in writing is perhaps one of the most true parts of fiction out on the market today. Not because somewhere at some point a professor banged a cheerleader, but because the act itself is a moment of pure feeling. It has the opportunity to connect a reader to your character in ways that many other pieces won't ever share. If you don't believe me step into the mind of Phedre in Kushiel's Dart by Jacqueline Carey. I was not into pain AT ALL before I "met" Phedre, and when it came to bondage I didn't mind an occassional blind fold, but the idea of having my body completely submitting to another's will...nope. Until I read Kushiel's Dart and saw through her eyes. The world Phedre lived in was so real, so vivid, the sensations she experienced and Ms. Carey wrote about so deliciously connecting that BDSM has moved up my pleasure list.
And it would have been lacking without the research.