Quote:
Originally Posted by Marc Bourget
See if you can achieve 5.5" H2O Delta P (top/bottom of baffles) at about 100 mph (100-105) with the exits blocked down.
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Standard day maximum available dynamic pressure is 4.79" H2O at 1000 feet and 87 KTAS (100 MPH true). In rough terms, multiply by 0.8~0.85 for a good upper cowl static pressure rise, 0.6 being more like a GA average (see NASA 3405). So, about 4" delta would be a maximum if the lower cowl volume was at freestream static....which it may not be with the exit blocked. A delta of 5.5" would probably need 110~115 KTAS.
A detail; upper cowl pressure rise
increases as the system exit is reduced, so the delta pressure change with a change of exit area, although significant, may not be as large as one might assume at first glance.