Is the fly plaid supposed to be wearable.

[Robinhood]

Is the fly plaid supposed to be wearable as more
than a decoration? If it is, how big should it
be for real use? Exactly how is it worn?

[cavscout]

you would want a piece about 4' or 5' square.

Most plaids that are sold as plaids have a set of pleats sewn into them where they would pass thru the epaulette on the shoulder to provide a nice flat look instead of a wad of cloth . Not to say you could not use some of the this cloth in another way but you wouldn't have a nice flat picnic blanket.

[Caradoc]

Is the fly plaid supposed to be wearable as more
than a decoration? If it is, how big should it
be for real use? Exactly how is it worn?

What more would it be used for? Fly plaids might be usable as a kind of a shawl, but they're generally nowhere near the size of an "evening plaid," or "piper's plaid."

The fly plaid is generally pulled under the epaulet on the left shoulder, and pinned just forward of the shoulder (on the left pectoral) to be left hanging down the left side of the back.

[billmcc]

The fly plaid is just a decoration.

[davedove]

As others have said here, the fly plaid is really just decoration. I'm sure it evolved from some useful article of clothing, but that was long ago.

The only use I can think of for modern use is as a shawl for a lady companion should she get cold.

[Robinhood]

So, if you were to wear it for warmth
or to keep dry in a spring shower, would it
be worn like a poncho, with a hole in the middle?
Would you just drape it around yourself?
Fold it in half first?
Tuck it in?
Would the pin holding it to the shoulder
be a suitable closure?
Would it have loops or pins to hold
it to the wrists or arms?

[Caradoc]

So, if you were to wear it for warmth
or to keep dry in a spring shower, would it
be worn like a poncho, with a hole in the middle?
Would you just drape it around yourself?
Fold it in half first?
Tuck it in?
Would the pin holding it to the shoulder
be a suitable closure?
Would it have loops or pins to hold
it to the wrists or arms?

No. I don't see a fly plaid as useful for anything you've mentioned above.

It's about as "functional" as a cummerbund.

[Iolaus]

So, if you were to wear it for warmth
or to keep dry in a spring shower, would it
be worn like a poncho, with a hole in the middle?
Would you just drape it around yourself?
Fold it in half first?
Tuck it in?
Would the pin holding it to the shoulder
be a suitable closure?
Would it have loops or pins to hold
it to the wrists or arms?

I suppose a full size plaid, i.e. 5' square, could be folded along the diagonal and draped over your shoulders on a cold night, or pulled over your head during a rain, but I've always gotten the impression that it was really just an accent for fancy dress, reminiscent of the great kilt being pinned over the shoulder.

[Kilted KT]

I'm no expert, but it looks to me like the fly plaid is an effort to appear as though one is wearing a great kilt, while ensuring that every pleat stays in place on the kilt and everything looks great.

anyone else have any ideas?

[bubba]

A fly plaid is more representational and decorative than anything. It represents the upper part of the belted plaid from earlier times.