I've recently bought a 29er downhill frame and since I am new to MTB, I was wondering if I can put an other type of fork to this dh frame. Something like an enduro fork with 180mm travel? ! The following fotos are from other buyers that have already installed fork and other components. As you can see all of them have put "normal" forks and not double crown. So I wonder if the frame is a DH or something else... enter image description here
Yes and no.
What really matters for handling of the bike is that the fork you use has the same axle to crown length and the same offset as the fork the bike should have.
The offset is the distance between the front axle and the steering axis
The axle to crown is the length between the center of the hub axle and the crown of the fork.
There's lots of people who've done it with no problems, but it also depends on your frame.
Why you shouldn't do it, is because if you get the wrong replacement fork, it will throw the geometry of the bike off and it won't ride as well as it should.
Unfortunately, this is also a bit of a personal and trial/error thing too. So someone might say "it worked for me no problem" and then you might try it and not like it.
In terms of handling, the head angle might become a little steeper and, in theory, having a lower travel fork might make cornering a little easier but it might also make the bike more unstable at higher speeds. Whether this is noticible in real life, I don't know.