We Aint Got No Velocity Stacks....
WE DON'T NEEEED NO STINKING VELOCITY STACKS!!!!
As I was flying around one day in my Lazair, minding my own business, my right engine decided it wanted to speed up all by itself. Apparently I was flying too slow for its liking. I was puzzled by this as I prefer my engines to tow the line I lay down. As their Captain I am in charge and rather enjoy my engines following my command. I do not like engines having a mind of their own.
In investigating why this engine was able to determine its own power setting I discovered that under the right conditions, mainly a sideslip or a crosswind, the velocity stacks are able to produce a ram effect which produces an increase in output, or conversely when the conditions are right a venturi effect which reduces power. These effects also seem to lend to some of the "hunting" the rotax's on the Lazair are known for.
I pondered over this situation for some time and thought I could correct this issue and maybe improve on the durability of the engines as they have always been unfiltered in the stock configuration. "To the Batcave" for some tinkering.
I found these really nice bell-mouthed velocity stacks used for a myriad of purposes, and some pretty little compact saucer shaped air filters from Chinatown, made by Chinamen, of ChinaQuality. After modification and sufficient fitting and futzing around the filter system is installed and looks quite good I think.
Flight tests show no degradation to performance, i.e. I get the same RPM as before, the engines run at a more consistent RPM and have less "hunt", and throttle response is unchanged. Overall I feel this is a good and warranted modification, it keeps the bugs out in the air and on the ground, and can only add to the life of the little Rotax. Kits are available
I hate to make promises, particularly ones I am not sure I can keep. While at Oshkosh this year I promised myself I would have the Mark IV ready to unveil for the 2015 show. I am doing my level best to meet this self imposed promise, but there are many factors out of my control. Still I think having a goal is a motivation in, and of itself, and will only help get me off my can and moving forward. Wing construction is still moving ahead. I am fitting the ribs to the spars, I need to build the wing jigs so I can set the washout per the build manual and make the new root ribs.
More Next Time,