vane issue
 

What is better a short or long vane for better accuracy? Then also is it better to have no helical or to have helical for accuracy?

RE: vane issue
 

Well, longer vanes on a helical give the most stabilization because they disrupt the most air. However, there comes a point when you have all that is needed to stabilize your setup. For instance, if you are target shooting, you will probably only need a 2 or 3" vane to correct your arrows. Now, if you are shooting big fixed blade broadheads, you are going to need more.
Helical adds spin to the arrow. Here again, causing more air disruption and stabilizing the arrow. There is a negative to both. That same air disruption that stabilizes the arrow also slows the arrow down. So there comes a point with helical that too much is not doing any good either.
Feathers are even better yet, and they weigh much less than vanes. So at distances up to about 40 yards, you will gain a little speed because of the weight difference. After about 60 yards, your arrow will lose speed more quickly than vanes because of the air disruption that feathers create. (wind resistance).

RE: vane issue
 

Her are the basics of fletchings.

The longer it is the more air it "grabs" and the more stabil it is.

The more helical the fletching has the more spin it gives the arrow. Which the faster the arrow spins the more gyroscopic effect the arrow has and the more stabil it becomes. It is much harder to introduce outside forces to a spinning object than it is an object that is stationary.

The lighter weight the fletching the less the end of the arrow weighs and the better the fletching can control the end of the arrow. The more mass the harder it is for the fletching to correct any flight problems.