Trebuhole is what I named my model trebuchet. It has been fired a few times in the past but I was inspired by Bangarang to play with it some more. I had an interesting discussion with James. about the horse being used as a payload, and about the length of the sling ropes.
 Technical Specifications
As shown in the Rough Trebuchet Diagram, there are some measurements that must be considered for trebuchets. Trebuhole has these measurements (in inches):
L5=Varied during trials in order to see if long or short sling rope length is best.
 Dead Horse Analysis
My brother mentioned that since the trebuchet is a siege weapon, it would be beneficial to give disease to the enemy hiding within the castle/town walls. My son then asked if the horse would have AIDS. My brother replied that the horse could have AIDS, but that such a horse would only be beneficial to the attackers if the attackees were necrophiliacs who enjoy interspecies erotica.
 Preliminary Attempt
I decided to use a relatively large toy horse as my payload to attempt to figure out if doing so is feasible.
Unfortunately, the horse was inserted backwards, and the legs caught on the sling and the launch was unsuccessful.
 Subsequent Attempts
I had my kids build a castle out of Legos as a target for the Trebuhole. I then set up a lego horse facing the correct way (legs toward bottom of swing arm). The sling length (L5) here is 11 inches.
I also set up Trebuhole with a longer sling rope length (L5=19 inches) using some blue string.
There was some argument as to whether an elastic string in the sling rope would affect the outcome. So the rope was also replaced by an elastic string. L5 when the elastic was at rest was 11", and L5 when the elastic was fully extended was 16".
At L5=11", the Lego horse was launched 262".
At L5=19", the Lego horse was launched 52".
For the elastic string, the Lego horse was launched 154".
The shorter sling rope length seems to be better for Trebuhole. I believe that the sling falls off of the track or otherwise gets messed up during the launch, hindering the longer string launch distance. However, this may differ for other trebuchets.
After many unsuccessful attempts to have Trebuhole hit the castle with horses and rocks, my kids and I ended up throwing a bunch of rocks at the castle.