> I once built a pusher aircraft. Among the designers and builders, no one
> seemed to care whether the air was being pulled or pushed. The aircraft
> did not know the difference. About the only concern was the center of
> gravity and what the aircraft would do in a spin, since aft c/g and flat
> spins are not conducive to long term good health.
>
> Some early aircraft designers especially liked pusher aircraft because
> there was less chance of shooting your propeller off during battle (before
> they synchronized the guns with the props). The aircraft designers
> figured out that obstructions in front or back of the propeller made
> little difference in the performance of the aircraft.
>
>
> //Aircraft and wind generators are working in open space with little if
> any restriction to air flow, so of course the propeller and its motor
> wouldn't know the difference. In an enclosure, that changes completely,
> unless the enclosure is totally "open" on both sides of the fan, with no
> obstructions to air flow on either side.
>
> //In the electronics industry, we commonly use either or both "pushing"
> and/or "pulling," depending upon available space. When there's lots of
> room for axial blade fans which can move huge volumes of air with low
> noise and little current drain, we use them to push air into a chassis and
> provide suitable exhaust systems which produce the least possible back
> pressure. But when there are space restrictions, sometimes low-profile
> centrifugal blowers are all that fit, physically. High pressure blowers
> don't move as much air volume as large bladed fans do, but they can move
> quite a bit against more back pressure than axial designs, and thus don't
> care much if they are used to "push" or "pull" the air; often, they can do
> either, effectively.
>
> //We use computer modeling for airflow, with a package called Flowtherm,
> available as a module that works with our solid design software,
> Pro-Engineer, from Parametric Technologies Corp. It's powerful, and
> appears quite accurate provided all data (volume, form and location of all
> devices in a chassis as well as power dissipated by all devices) is
> accurate. We occasionally use infrared imaging for real thermal
> evaluation, to verify the Flowtherm results. There are seldom any
> surprises.
>
> //WB2WIK/6
>
>
> I have had a few wind generators at my house and always read that
> obstructions either in front of or in back of the wind generator decrease
> performance. Although I have not done any tests of a muffin fan either
> pushing or sucking and do not claim to be an expert on the subject of
> moving hot air (contrary to my wife's thoughts), my experience tells me
> that either one should work well if the other design factors are followed.
>
>
> I did have a friend, though, who purchased a pellet stove that used a
> sucking blower. The bearings went out in a year because they overheated.
> He called for a replacement blower and was told the company had modified
> the design because of that problem. The new design still used a sucker,
> though, and it has worked for a few years.
>
> 73, Colin K7FM.
>
>
>
>
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>
>
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