View Full Version : Air flow test

lazza - n/a
17-Feb-06, 09:36 AM
I done a little test today just out of curiosity on the air flow coming out of the rear of my duct. What i done was got a length of string and held it in the path of the thrust air from the rear of my duct and what i noticed was the air flow coming from the right hand side of the duct (when viewed from standing behind the duct and looking towards the front of the craft) was a stronger flow than what was coming from the left hand side. Attached is a picture showing the 2 positions that i had the string attached, at point '1' the string was blowing around at about 90 degrees to the duct (ie : horizontal with the ground) whereas at point '2' on the picture it was around 45 - 50 degrees to the duct. (The fan turns anti clockwise when viewed from behind and is 5zl multi wing blades.)

I know its possibly not the most technical test out there but is there a common reason for there to be more air flow from one side of the duct than the other ?

Tip clearance is around 5mm with roughly 1mm variance in places.

The craft it self goes fine and doesn't seem to lift more on one side than the other but i am curious if there is a reason for it.




PS : I got a write up in the local newspaper today so that was cool. My 2 seconds of fame hehe, unfortunately no job offers yet though. http://hovercraft.org.uk/images/icons/smiley_icons/icon_smile.gif

Hovertrekker - n/a
17-Feb-06, 03:35 PM

Most likely due to the lack of flow straighteners and the cork screwing effect of the air due to the rotational direction of the fan. Your observations are not unexpected. Try taping lots of small peices or string around your duct and on your rudders and you'll get a better picture of what the air is doing.

lazza - n/a
17-Feb-06, 06:14 PM
Good idea, i'll give that a go thanks.

Iceman - n/a
19-Feb-06, 10:02 AM
Another method for checking air flow is too use a smoke trace as they do in wind tunnels.

A simple way to acheive this is to mix extra oil (for 2-strokes) or add oil to your fuel to give a smokey exhaust, then with a hoover hose attached to your exhaust pipe you have your own built in smoke trace generator!

Please note, I have not tried this method and I would avoid running at full power but it should give you a good idea of air flow in and around your duct!