skids and slid for 9.6 metres then rolled due to a drop off in the terrain. has anyone derived a drag factor?
A: We normally don't cover helicopter crashes, however the following may be of assistance/use:
A 1987 research study we did with Calspan includes discussions of drag forces in various soils and can be found at:
- Rollover Potential of Vehicles on Embankments, Sideslopes and other Roadside Features" (6 megs), Deleys, N. J., Parada, L.O, FHWA/RD-86/164, PB87-212783, August 1986
- Executive Summary Report
One of the references in those reports:
- Avery, JP Larson, S "Analysis of Army Fixed-Wing Cargo Restraint Design Criteria" USAAVLABS Technical report 67-3 PB#651219, Jan 1967
- FT = f*FN + v*AS*Xdot
- FT = resultant tangential force, lbs
F = nominal friction coeffcient
FN = normal load, lbs
V = viscous damping term, lb-sec/ft**3 (soil shear strength)
Xdot = velocity ft/sec
AS = total contact area, f**2
(i.e. one would assume that plowing forces associated with 5 MPH and 50 MPH under similar conditions of sinkage, etc would be different)
See the full Calspan report for addition references (Bekker, Schuring, etc) related to motion resistance of soils.