Yes, I used a dewalt 13 inch planer to plane a some beams a couple of months ago. This was with wet white pine so the wood was pretty soft. I just took off the bottom plate, put it on the beam, set the speed to slow, turned it on, and it didn't work. It needs weight on it for the blades to make contact with the wood. After some trial and error I found that about 75 lbs did the trick. Does it work well? No, but it did work. It wantted to rock from side to side as it went down the wood. so I needed to balance it by hand it as it cut. I found that by putting the beam on the ground, and lean over to stabilize the beast as it went down the beam I could smooth a side in about 3-4 passes. If the beam is not square to start with it will be out of square when you finnish. Mine were square to start with so things worked ok. Not the best but I was in a pinch and needed a few planed beams the next day, so when ya gotta have it......
good luck