That is what I was wondering.  Just another one of those things that just works even if I don't understand how.

Someone with a slow motion camera feel free to correct me if I am wrong, but I would be surprised to find out that arm contact is occuring before the arrow has already left the string.  Unless you get enough impact to twist the bow in your hand, I can't see that there would be much effect on arrow flight at all.

Brace hieght and don't put a death grip on the handle. Try seven inches or maybe 7 1/4 somewhere in there. If its center cut cant to the right if right handed. Catching your arm should be at a minimum not a regular occurance. This has probably all been said. Just keep at it, it will come together. Forget the recurve while trying to work it out. Have fun shoot straight.

the reason I was asking was because I recently shot a bow that I wanted to buy but it slapped my arm pretty good every time even at the longest recomended brace Height.  If it would work with an armguard I would prolly get it.  I just wanted it to bow fish and shoot bullfrogs with anyway.

Brandon, the type of string material can effect string slap too.  Stretchier strings like the standard B50 dacron are more likely to slap your wrist than a low stretch like fast flight or dyna 97.  Of course, that is only where the string hits as it bottoms out.  Usually it'll hit you right where a watch band would lay on your wrist.  If it hits you up on the forearm close to your elbow, then it's how you're holding the bow and my first post tips would apply.

You know now that you mention that stetchy string thing.  I really thought that bow was actually stretching and going forward and hitting my arm about 3" above my watch.  I don't know much about string material but it was one of the all black and I believe an endless loop.  It was not a flemish twist style string.

How about some of you longbow shooters post some pic's of your grip??? You know what they say about a picture.....

You have not said what type of riser you have on the bow. The riser style has a lot to do with how you shoot (hold) the bow. If straight (Howard Hill style), or locater, or dished, or Recurve style.Recurve style I would think that you would have no issues. I shoot a locater riser and have no issues with string slap. It may be a problem with your release. If the release of the string is not clean it will cause you to slap your arm.

I had trouble with grip and form when switching to the longbow and finally found helpful advice in the few chapters on The Longbow in the second volume of Instictive Shooting, by Fred Asbel.
There's some great written detail about the behavior differences between the longbow and recurve and pics of grip differences.

Basically, the longbow is gripped from the side and pressure from the whole length of the hand is applied. So you grip the longbow firmly, and make it shoot.  Kind of like a mule, you have to force it to work.  
Anyway, when once I adopted these techniques my shooting improved and I too was able to lose the armguard.

I did some more experimenting today with my 41# @ 30" hybrid longbow and it will also shoot a 2213 aluminum arrow with a 210 grain point weight. The arrow weighs around 588 grains. The Longhorn longbow is very quiet upon arrow release too.

Did a little more tinkering and now both my recurve and my longbow shoot the same 32" long, 2018 aluminum arrow fitted with a 150 grain field point. Both shoot where I look. Next step, tuning with broadheads.

Oneshot-Onekill just wanted to bring this back to the top in hopes of the grip pictures. When I switched from curve to LB I hit my arm every shot. I am not sure when or what happened, but I no longer hit my arm.

Hitting your  forearm is not a bad thing! How's your arrow flight. If you look at pics of Howard Hill shootin, he has an arm guard on, even in the summer with his shirt off! I have longbows I shoot and hit my arm. Check and measure the slap mark with the string height, and that will tell how much stretch your gettin after the shot. And it can be a tuning issue, arrow spine and such. In masters of the Barebow vol. 2,a gentleman is shooting a real high brace height on his longbow , try it it might work! There's nothing set in stone. Good shootin, Steve