NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Dalton E6B Dead Reckoning Computer
From: Gary LaPook
Date: 2008 Aug 2, 12:44 -0700
From: Gary LaPook
Date: 2008 Aug 2, 12:44 -0700
Also look at the June 14th posts on the topic "3 star fix-canned survival problem" for more information about the use of flight computers gl On Aug 2, 10:12�am, Paul Hirosewrote: > 01 0609 > > Renee Mattie wrote: > > I saw an old Weems and Plath Dalton E6B at Bacon's and snapped it up. > > Imagine my surprise to see that they are still making these things, > > and offering them for sale athttp://www.mypilotstore.com/MyPilotStore/secp/22. > > > On the slide-rule side, the grommet seems to be off-center. �So if I > > set the dial for 60 miles/hour, I'll apparantly go almost 18.1 miles > > in 18 minutes, though almost exactly 9 miles in 9 minutes. > > > Have I got a good one or a bad one? > > A not so good one, I guess. The centering error on mine is barely > detectable, about the width of a line. > > I also have a Jeppesen CR-2 flight computer. It's much more compact than > an E-6B because the effect of wind is calculated by a different > principle. With the side of the device that's pictured at the web site, > you separate wind into headwind and crosswind components. Crosswind and > true airspeed are set on a sine scale (around the outside in the > picture) to obtain wind correction angle. Headwind is mentally > subtracted from true airspeed to obtain groundspeed. > > By contrast, on an E-6B you construct the wind triangle and read > wind correction angle and groundspeed directly. The solution takes > more space, but workload is less. > > Either computer can solve for drift and set in marine navigation. Just > mentally apply a convenient scaling factor of 10, 20, etc. to the values > on the wind and airspeed scales. I solved some of the old Silicon Sea > problems that way. > > For time / speed / distance computations both devices have the same > facilities. As usual with slide rules, the user is responsible for > placing the decimal point, so ship speeds are as easy to handle as > airplane speeds. Or car speeds -- I used my E-6B a few days ago to check > speedometer error. > > When compressibility is significant (say, above .4 Mach) the CR > computers are superior at converting calibrated airspeed to true > airspeed. E-6Bs assume incompressible flow, so they're inaccurate at jet > cruise speeds. But airspeed computation is simpler, and the error means > nothing at typical light plane speeds. > > Deluxe E-6Bs are made of sheet aluminum, while CRs are plastic and can > warp if left in a hot car. > > -- > I block messages that contain attachments or HTML. --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---