If I understand correctly the Air knife came first.
Both operate with a DeLaval nozzle to accellerate the air stream to supersonic at the exit. Really, it is rocket science albeit real basic.
Airspade has gone a long way towards making everything custom for the tool from the wand to the valving to the nozzle whereas AirKnife uses a lot of standard off-shelf components.
The only thing I have truly found unique is the patent for the Airspade, It is interesting to note that it appears to be more of a process patent versus a device patent. What is the difference? One protects the device, the other protects the process under which one builds the device.
I'm no patent law attorney so I may have missed something, but I gathered the essence of the AS patent is the methods on how to cnc machine the nozzle in the complex profile they believe to provide the smoothest, less turbulent side flow of the airstream.
Both nozzles accelerate the air to supersonic. Both try to straighten and contain the stream for the first few inches out of the nozzles.
And, both nozzles are fixed-parameter, in that ambient temp, barometric pressure, compressed air temp, flow and pressure may change but the nozzle cannot adapt to those changes. Therefore, you will seldom, if ever, get the perfect air stream from either one on any given day.
In the end I went with the AK for a couple basic reasons. <ul type="square">[*]First, price. AK parts are about half those of the AS. [*]Second, off shelf components. [*]Third, you can still talk to one of the people involve in the initial designing. [/list]
I own/use Air knife. I have used an Air Spade a couple of times. The angled handle and/or nozzle seem like a good idea, but actually using it, I find being right above the tool with the handle and 90 degrees and straight nozzle is less tiring on the arms/easier to control.
Air Spade certainly markets to our industry quite a bit more...
I bought the air knife from Dave a while back and have been very happy with the tool and his available guidance. I'm in the market for a used compressor if anyone has any advice? I would sell and save a lot more trees if I didn't have to rent a compressor. So many trees need root flares exposed! + dig holes for planting.