ORIGINAL: jfetter
ORIGINAL: stumax
Actually, longer inlets/shorter exhaust is a more efficient way to go for a number of reasons:
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Stu,
Maybe you can reaffirm they are the best choice by helping me out with a static thrust question. We know on an Electra we see 14.25 lbs installed thrust using the stock BVM inlets (granted, they are huge and the inlet-to-FSA ratio is 106%) and the 5612 fan on 12S. When you take the same power plant and put it in the Bandit with the longer inlets (and 96% inlet-to-FSA ratio as calculated by RD), we see only 11.65 lbs. The Efflux also drops from 212 to 191, now is that solely to be blamed on the smaller inlets and lower inlet-to-FSA ratio or do the swept inlets get part of the blame? Likewise do they perform any differently in the air once you start shoving air into them?
Thanks,
Jack
Jack, inlet size is very largely responsible for static thrust, as is the size of the radius on the inlet lip. This is especially true for tractor fans, as they create a region of very low pressure in front of the rotor in the static condition. Consider this region of low pressure acting on the inlets. If the inlets are larger, they have more surface area, and the net force reaction from the low pressure acting on this surface area and higher atmospheric pressure acting behind the inlets, creates a lot of thrust. Usually, the efflux velocity is a better indication of how well the fan is performing, as you can calculate thrust by integrating efflux velocity across the face of the exhaust. In you case, you are seeing a drop in efflux velocity, which will be due to the smaller inlet size and the longer inlets. This will disappear as soon as the aircraft starts moving. Once in flight, the dynamic pressure will be captured at the face of the fan and everything will be sweet. BTW, the Bandit's inlet area is smaller than 96% for the EVF, I would have thought? Can you take a photo from the front with a 6" rule in plane with the inlet?