Airopult restraint device for large model airplanes. It holds your airplane from going either forward or backward while starting. Works for tail draggers or trike gear. I bought it, but never used it -- as shortly after buying it, I had to get out of flying any airplanes heavier than a few pounds. I've watched these in action and they work great. Includes extension arms.
Go to: http://www.airopult.com for more information.