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Driftmeter -- interesting use of

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Guest DC3 Pilot

Hi All,Below is a quote from an article entitled "The Navigator" by Sandy Amell (http://home.att.net/~sallyann5/b29/sandy-guest.html). It suggests that, given your altitude AGL, groundspeed can be calculated quickly, only requiring measurement of the time it takes an object to move from the front to the back of the driftmeter window. My question is . . . does anyone know how to do this? And can it be done with the Bitzer driftmeter for the MAAM-SIM DC-3?"Driftmeter. An telescope like instrument pointed straight towards the ground with a built in scale which looked much like a musical staff. This scale could be rotated and the angle of rotation measured. Selecting an object on the ground and rotating the eyepiece so the object moved parallel to the lines would give the angular drift of the plane. Measuring the time for an object to move between two lines at the front and back of the scale could be used to calculate ground speed if the exact altitude above the object were known. The E6B could be used to make this calculation."-- Gary

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>My question is . . . does anyone know how>to do this? And can it be done with the Bitzer driftmeter for>the MAAM-SIM DC-3?Of course, Gary, that's what it does :) Have you not tried it yet?MarkMark "Dark Moment" BeaumontVP Fleet, DC-3 AirwaysTeam Member, MAAM-SIM[a href=http://www.swiremariners.com/cathayhk.html" target="_blank]http://www.paxship.com/maamlogo2.jpg[/a]


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Mark "Dark Moment" Beaumont

VP Fleet, DC-3 Airways

Team Member, MAAM-SIM

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Guest DC3 Pilot

Hi Mark,Yep, I've been using the driftmeter a good bit. No problems at all with its primary function, determining drift.But this fellow is talking about using it to calculate groundspeed, and in a way completely different from that in the instructions provided with the driftmeter.He's saying that, if you know your exact altitude AGL, you can use a stopwatch to time passage of any single object on the ground from the top of the driftmeter to the bottom (just a few seconds), and then calculate your AGL. This is very different from using it to identify an object both on the ground and on your chart(water tower, rail crossing, etc.) and then another object a few miles away, and timing your passage between the two, calculating the distance from your chart. That I've done also without difficulty.I can see how some trig might be neecessary to do what he's talking about, with your altitude AGL being one side of the triangle. But if the only other data you have is the, say 4.3 seconds it takes some smudge on the ground to move from the top to the bottom of the driftmeter, I don't see how groundspeed can be computed. Unless you have a chart showing, for each possible altitude AGL, the distance on the ground between the top and bottom of the driftmeter. With that info, I could do it.Does this help clarify my question?Thanks for any feedback,Best regards,Gary

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Guest kennethg

Yes, I'd agree that ground speed with a driftmeter is a trig problem involving the field of vision of the driftmeter setting the distance over the ground as seen through the driftmeter. I also seem to remember there's a way to do sine functions on an E6B. I still have some of my old pilot training books, I'll start reading to see if I can find that reference.

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Guest DC3 Pilot

Ken,Excellent, thanks. Meanwhile, I'm going to develop data to show the on-ground distance between the top and bottom of the inside of the driftmeter window for altitudes from 500' up to, say, 5,000' (at 500' intervals). The way I'll do this is to find an airport at or very close to MSL (e.g., LAX is only about 100' above MSL as I recall) and then --- using the distance measurements provided on the airport diagram --- fly over it at the various altitudes, use a screen shot, and measure the distance. Once that information is in hand, all I'll need is a stopwatch and a formula to convert feet/sec into nautical miles/hour (knots). So let's come at it from both directions and see if we can't come up with a way to get "instant" ground speed :-).Best,Gary

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Guest DC3 Pilot

Ken,Well, so much for my end of it. The problem is with the top-down view. It isn't scaled for altitude, so it showed exactly the same distance on the driftmeter regardless of altitude. Hope you can come up with a solution to the way the B-29 navigator did it :-).Best,Gary

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Guest kennethg

Hmm, that poses a problem, since the scaling issue is central to the whole trig thing, too. Actually, that may render the whole mathematics issue moot. If the driftmeter's field of veiw doesn't change with altitude, then no matter what altitude you fly at, the space between driftmeter lines will always represent the same distance over the ground. Ergo, there's no trig mathematics to worry about: what the FS2004 driftmeter is doing is simulating a telescope with an automatic zoom feature that keeps the ground at the same apparent size at all times.This reduces the math needed to a simple time-speed-distance equation, which the E6B is really good at. The trick will be to put the numbers on the right scale so we know how to read the E6B. Would you go fly the driftmeter on a no wind day and tell me your airspeed and the time it takes for a landmark to go between whatever marks you want to use on the driftmeter? From that I can figure out how to work the E6B. :7

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I'm a bit confused. Why is the field of view not changing with altitude for you guys? Certainly does for me. Are you using the latest version, by the way? Drift7.zip?MarkMark "Dark Moment" BeaumontVP Fleet, DC-3 AirwaysTeam Member, MAAM-SIM[a href=http://www.swiremariners.com/cathayhk.html" target="_blank]http://www.paxship.com/maamlogo2.jpg[/a]


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Mark "Dark Moment" Beaumont

VP Fleet, DC-3 Airways

Team Member, MAAM-SIM

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Guest DC3 Pilot

Mark and Ken,Mark -- my unzipped driftmeter folder says "drift5," which I assume means version 5. I only downloaded it about a month ago. Maybe I got it from a site without the updated version. Where should I go to get "drift7"?Ken -- just in case, I'll do the calculation you requested and post it here shortly.Best,Gary

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Guest DC3 Pilot

Ken,Okay, here's the data. First, though, I discovered to my amazement that in all the gear I have (amateur radio station, workbench, 3 computers, and heaven knows what else) I don't have a stopwatch :-). What I do have is a great multi-function timer (counts up, counts down, tells time, has five different timers, etc.) but only displays time to the second. No fractions of seconds. Which may be important here.Anyway, I took the DC-3 up, set weather to calm (no wind), in level flight under Sperry autopilot, 6,000 feet altitude, OAT = +1 C. Did 15 measurements, all at 138 KIAS, which calculates to just a whisker over 150 KTAS. That TAS figure was was confirmed by flying directly toward a VOR station and using the co-pilot side groundspeed meter to confirm my E6-B calculation. Every single test came up 6 seconds. Never 5 nor 7. But that only means it could be anywhere from 5.51 to 6.49 seconds :-)Driftmeter measurement points -- to start, I used the top of the meter, directly above the "0" . . . that's the OUTside top edge. To end, I used the INside bottom of the meter. The reason, which becomes obvious if you try it, is that you can't measure accurately something that's coming out of a blocked field of vision. You need to start and end your timing as the object enters the mark. Now if we get version 7, per Mark's suggestion, and the character of the driftmeter isn't telescoped with a fixed image regardless of altitude -- as it is for us now -- then this approach isn't going to work and we have to go back to the article's point that you needed to know altitude AGL. It may turn out to be easier with version 5 :-) :-).Best,Gary

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Drift7.zip is at Avsim, fellas. It's a great improvement in that it is no longer necessary to pull up a different 'view' to use it ... it opens in the panel view. Apart from that, I've just played with the graphics a bit to tidy it up and make the bezel scale more accurate.MarkMark "Dark Moment" BeaumontVP Fleet, DC-3 AirwaysTeam Member, MAAM-SIM[a href=http://www.swiremariners.com/cathayhk.html" target="_blank]http://www.paxship.com/maamlogo2.jpg[/a]


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Mark "Dark Moment" Beaumont

VP Fleet, DC-3 Airways

Team Member, MAAM-SIM

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Guest DC3 Pilot

Mark,Thanks for the heads-up about Drift-7. I downloaded and installed it, modifying my previous panel file per instructions. Worked perfectly first time (though it did take me a minute to find the panel switch :-) :-). The revision adds considerably to the realism of the driftmeter, since now cloud cover comes into play (though by toggling top-down view with the meter up, I can still get the clear view, but that would be cheating :-). I also like the instrument box display. All-in-all, a very nice job of upgrading.Best,Gary

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Guest DC3 Pilot

Mark,A quick question on Drift-7. Which line of code positions the panel icon? I want to move it just a little bit.Thanks,Gary

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In the PANEL.CFG file, gauges/icon gauges usually have four numbers to the right of their panel entry. The first two are the horizontal and vertical positioning (left edge, top edge) of the gauge in pixels, relative to the overall size of of the panel or window bitmap. The second two are the horizontal and vertical size of the gauge/icon. If there is only one number there (i.e. three in all) then the gauge will appear to that size horizontally and will be its default shape vertically.Hope I'm clear here,MarkMark "Dark Moment" BeaumontVP Fleet, DC-3 AirwaysTeam Member, MAAM-SIM[a href=http://www.swiremariners.com/cathayhk.html" target="_blank]http://www.paxship.com/maamlogo2.jpg[/a]


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Mark "Dark Moment" Beaumont

VP Fleet, DC-3 Airways

Team Member, MAAM-SIM

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The depth of knowledge and experience at DC-3 Airways never ceases to astound me. These attachments are drawn up by Alex Saunders, DCA-1325, who has experience of using driftmeters for real in his extensive aviation career. Thanks Alex ... I'm sure you'll find this work of interest and relevant to this thread.http://forums.avsim.net/user_files/146434.jpghttp://forums.avsim.net/user_files/146435.jpgMarkMark "Dark Moment" BeaumontVP Fleet, DC-3 AirwaysTeam Member, MAAM-SIM[a href=http://www.swiremariners.com/cathayhk.html" target="_blank]http://www.paxship.com/maamlogo2.jpg[/a]


_________________________

 

Mark "Dark Moment" Beaumont

VP Fleet, DC-3 Airways

Team Member, MAAM-SIM

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