Expert: Mark Janus - 3/23/2009

Question
I would like to know if a ducted squirrel cage fan could make suitable propulsion for an experimental aircraft?  Also what the average weight, given a cfm of a squirrel cage vs. a standard propellar would be?  Squirrel cage fans come in a variety of shapes and sizes, could you tell me what an average diameter and length would be for a given horsepower? I'm assumming there is a formula for it.  Any help would be greatly appreciated. Thankyou for your time and consideration. Jesse

Answer
Sorry for the delay in getting back on this question...

I've never seen that done for a ducted propulsor....  I'm not an expert in "fans" which are more of an industrial air movement device...  I do have a few books on the subject and will follow-up with a ball park for you if I can track that down...   in the fan industry, "standard propellors" are referred to as axial flow air movement devices....  a squirrel cage is (I believe) referred to as a cross-flow air movement device....  and then there are radial-flow air movement devices...   the primary difference has to do (as I recall) with the pressure rise that the fan is working against....  radial works best against pressure rise, axial flow works best for cfm, crossflow is kind of a compromise... (again this is from my recollection and I haven't dealt with fans in a bit)....

Hope this helps some, and I will try to track down a formula and/or a ballpark relation for you

Thanx,
mj