I've been having trouble getting perfect arrow flight out of one of my bows. I pretty easily get it to bareshaft as it's a very forgiving ILF, but then a fletched shaft porpuses. Very frustrating to say the least...I fancy myself an arrow geek...kinda...Today I shot one of my brothers arrows and it flew perfect, though surely not perfectly spined. He mentioned that it maybe had something to do with my bigger fletchings (5" shield cut) vs. his 4 inch parabolics. First I told him he was dumb, but then decided to try it. So i took a pair of scissors and cut the fletchings down closer to the shaft. Same issue. Then I cut an inch and a half off the front end of the fletchings and voila, perfect arrow flight. Is this a thing that people already know? Is this even a thing?

What you're describing is probably quill contact with the riser or shelf.  You got the same bounce when you cut off the feathers, but lost the bounce when you cut back the quill.  This is something that sometimes occurs when transitioning from bare shaft to fletched.  It should always be suspected when you get good bare shaft results and a kick with the fletched arrow.  It really doesn't have anything to do with 5" fletches per se, but may be more likely to happen with longer fletches.  Sometimes can be eliminated by rotating the nock slightly, if it is an adjustable nock.  Sometimes people put lipstick or something on the quills and see where the lipstick rubs on the riser or shelf.

Agree with mcdave, but would add to raise your no k height and see if it doesn't go away.

Appreciate it. I really could never get it to go away raising my knock point which was very frustrating. Normally after I bareshaft I raise my knock point a hair for feather clearance. Didn't work in this case.

Yes Sir when bare-shaft flies but feathers don't,it is pretty certain you are getting contact.
    >>>>-----> Ken

Try raising nock point and see if it goes away.

They said it.  I don't know anything at all about ILF set ups but you might have best results if your bare shaft flies a little nock high. My bales are big enough so that I can shoot a level shot. My arrows might be 2" nock high or more. I definitely have noticed that broad heads will impact low if my nock point has the feather too close to the shelf.
(If you are shooting downward at all towards your target you might not realize that you don't have any nock high in your bare shaft flight)
Tedd

I've shot flu flus, 5.5 in Shields, 5 inch Shields, 4 inch Shield, 4 inch parabolics, and three and a half inch parabolics.

Never had a porpoising issue due to fletch, you're nock point is a tad too low

Terry, I was in the same boat as you until this. In fact, I was on the exact same page as you and was calling my brother dumb for even suggesting it was related to my fletchings.

I moved my knock point all up and down the string and it did not take the porpoising away. I promise it was not knocking point related. Maybe by the time I got it high enough to clear the fletchings it was too high, and porpoised for that reason.

I turned my 5 inch feathers into 4 inch feathers and it was fixed.

I worked on this for 5 days, all common variables were thoroughly tested.   

What bow are you shooting, and what is the exact brace height.?

It's an ilf with a satori riser. I'll get back to you on exact brace. But I took it up almost to 8 inches at one point and didn't fix it. However, thinking about it now, I bet if I would have kept going it would have remedied the issue the same as cutting back the fletchings.

A light dusting with a spray on foot powder will reveal where the contact is. That will help indicate whether it is nocking point,fletching,or whether a nock to feather relation change can help. Glad you got it fixed. >>>----> Ken