RE: Meerkat dopplered....177mph  
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RE: Meerkat dopplered....177mph - 2/4/2008 6:51:51 AM   
Mike Connor



Posts: 1380
Joined: 1/10/2002
From: Tulsa, OK, USA
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quote:

ORIGINAL: HighPlains

Ok, a quick example.

Say that the oncoming rpm is measured at 26,000 and the going away is 16,000. So one might think that the actual rpm would be the average of the two or (26,000 + 16,0000)/2 = 21,000. But this is not correct.

The actual rpm by the formula would be 19,810.

Another formula is 2x((R1xR2)/(R1+R2)) with R1 the approach rpm, and R2 the away rpm.

HighPlains, Could you go to post 23 and see if you can get some worthwhile #'s from the charts I posted. I do not know where your numbers are coming from. Thanks, Mike

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(in reply to HighPlains)
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RE: Meerkat dopplered....177mph - 2/4/2008 8:00:32 AM   
HighPlains


 

Posts: 2663
Joined: 3/2/2003
From: Over da rainbow, KS, USA
Status: offline 		I see you edited your last post to add the charts.

I think you can determine the rpm both coming and going from the charts if you place the cursers correctly. Notice that the top of the chart the spacing is rather close, while the bottom is rather far apart. You need to make two measurement, one on the top half, and the other on the bottom half. For accuracy, make the two measurements with the cursers exactly on two lines 5 lines apart. You will have two pairs of numbers. Find the difference of each pair and divide by 5 and multiply by 60 (or just multiply the difference by 12). That should give you the rpm coming and going. Then run the other formula as discussed to find the actual air rpm.

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(in reply to HighPlains)
       Post #: 27

RE: Meerkat dopplered....177mph - 2/4/2008 4:29:03 PM   
Mike Connor



Posts: 1380
Joined: 1/10/2002
From: Tulsa, OK, USA
Status: offline 		I think the light is getting brighter. The attached file shows two blue line at the top. The difference of these two frequiencies are Fcoming. The same thing at the bottom in orange give you Fgoing.

Using these #'s the inflight RPM is.....anyone care to guess?
Just kidding.
I came up with 22459 rpm but I would like HighPlains to confirm what I have done.


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RE: Meerkat dopplered....177mph - 2/4/2008 5:06:56 PM   
HighPlains


 

Posts: 2663
Joined: 3/2/2003
From: Over da rainbow, KS, USA
Status: offline 		Need measurement on the top with numbers. Also need the alignment of the cursers to be exactly on top of the frequency lines for accuracy. Using 5 or more improves accuracy.

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In politics if you want anything said, ask a man. If you want anything done, ask a woman - Margaret Thatcher

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RE: Meerkat dopplered....177mph - 2/4/2008 6:07:53 PM   
Mike Connor



Posts: 1380
Joined: 1/10/2002
From: Tulsa, OK, USA
Status: offline 		The blue lines on top and the orange lines on bottom show where I take the frequency readings. The actual cursor in this pic can be ignored. I make sure the actual cursor line is exact when I extract the number off each location. I understand the average of multiple locations would improve accuracy. The concept is what is important at this moment and I do appreciate your help.

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RE: Meerkat dopplered....177mph - 2/4/2008 7:06:02 PM   
Mike Connor



Posts: 1380
Joined: 1/10/2002
From: Tulsa, OK, USA
Status: offline 		I tried finding the difference in frequency accross 5 lines on top and then divide by 5. After doing the same thing on bottom I came up with similar results for rpm. This is so you know I understood that post.

< Message edited by Mike Connor -- 2/4/2008 7:07:02 PM >

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RE: Meerkat dopplered....177mph - 2/4/2008 7:17:03 PM   
HighPlains


 

Posts: 2663
Joined: 3/2/2003
From: Over da rainbow, KS, USA
Status: offline 		Mike, here is a sketch of the program screen. I am suggesting that you place the cursers as shown both top and bottom for the two pairs of measurements. Each is covering 5 spaces, so in the end you can take the difference between the two frequency measurements and multiply by 12 (divide by 5 and multiply by 60 is the same as multiply by 12) to find the coming and going frequencies. Then use the formula 2 x (Fc x Fg)/(Fc + Fg) to find actual airborne rpm from the tape.

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In politics if you want anything said, ask a man. If you want anything done, ask a woman - Margaret Thatcher

(in reply to Mike Connor)
       Post #: 32

RE: Meerkat dopplered....177mph - 2/4/2008 7:53:12 PM   
Mike Connor



Posts: 1380
Joined: 1/10/2002
From: Tulsa, OK, USA
Status: offline 		HP,
That is what I have done. Thank you for clearing things up for me.

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Mike
http://www.mikesrc.us/

(in reply to HighPlains)
       Post #: 33

RE: Meerkat dopplered....177mph - 2/4/2008 11:29:06 PM   
glowplug50


 

Posts: 154
Joined: 2/28/2006
From: Houston, TX, USA
Status: offline 		Hmmmm

< Message edited by glowplug50 -- 2/4/2008 11:31:12 PM >

(in reply to Flyboy Dave)
       Post #: 34

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