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How far away is your plane?

How to judge this

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John Cole04/02/2009 17:11:24
615 forum posts
24 photos
It's difficult to judge how far away your plane is, even if it's quite close. It's exceptionally hard if it's a long way away. One reason it's hard is because you get no feedback, until it comes down and you have to find it on the ground (or you fly into a tree). Ever found it was a lot further away than you thought? Ever had complaints that your club was flying too close to something, and you all thought you were flying much closer? Here's something I worked out: my Futaba Tx aerial has a button on the top. It's about 1 cm diameter. When my 35 MHz Tx aerial is fully extended, the button is about 1 metre from my eye. So the ratio of button diameter to button eye-distance is about 100:1. So how does this help?

If your plane is flying directly across your field of view and its length looks the same as the button-diameter then it's 100 times further away than its length. So if it's 1.1 metres long and it looks the same "size" as the button then it's 110 metres away. (If it's flying away from you and the wingspan looks the same "size" as the button, it's 100 wingspans away, so if wingspan is 1.8 metres it's 180 metres away. If ANYTHING looks the same size as the button then it's 100 time further away than the thing's size).

If it's flying directly across your field of view and its length looks half the button-diameter then it's 200 times further away than its length; if it's twice as big as the button then it's 50 times further away, and so on.  In this made-up photo, if the plane shown is 1.1 metres long, then the left-hand plane is about 55 metres away, the right-hand one 110 metres and the tiny one above the aerial button is 220 metres away.

The ratio may vary with other makes and models of Tx, so you might like to measure your own.   I'm still thinking about 2.4 GHz!
David Perry04/02/2009 17:15:21
95 forum posts
Thats neat. very neat.
Well observed.
 
D
Owen Hailey07/02/2009 18:46:04
391 forum posts

Hi John

This has all ways been one of the things that has often distroyed a perfactly good and well trimed model, so yaw idear will hopfully save a lot of models flying of the end of the radio signel, and going down big time this has happend to me more than once in the past.
Save that model Owen.   
Former Member07/02/2009 20:14:33
3577 forum posts

[This posting has been removed]

Phil Wood.07/02/2009 23:10:28
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3638 forum posts
27 photos
It'll work with the Hubble telescope providing the aerial tip and the model are viewed through the same lens.
Very good idea for those who have difficulty judging distance John.  You could even advance on this idea and make a clip on aerial  sight that can be adjusted to suit the different way people hold their Tx's.    It's similar to an artist holding up the brush to their subject.
 
Phil.
Eric Bray08/02/2009 00:22:34
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6600 forum posts
2 photos
No, Don't do that, or Tim will assume it is a target!
Phil Wood.08/02/2009 01:36:30
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3638 forum posts
27 photos
Where Timbo's concerned anything is a target.
 
Polyphilla.
Phil Wood.08/02/2009 01:49:29
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3638 forum posts
27 photos
2.4 gig users could use a clip on marker and all they'd have to do is hold the TX at arms length   (or neck strap)  for a second while they check the distance.
 
You could advance on this and market it.
Make a clear screen with a vertical graticule that would show the range according to model length.
 
Phil. 
John Cole08/02/2009 12:13:49
615 forum posts
24 photos

Thanks for the nice comments, folks.  Appreciated. Hope you find the idea useful in practice.  In my case the reason was to do with flying too far away and getting too close to housing.  So it wasn't radio-range, Owen.  My experience is that R-R is further than you can see the model enough to control it.

Tom: I wear single-vision glasses for flying (I find them clearer than Varifocals) but I think I can answer your question.  When flying, you look at the model and focus on it.  When you bring the Tx aerial-buttton up to compare, you still focus on the model, but as the button's a metre away it is also reasonably sharp, especially on a bright day.  Either way, you are looking through the "distance" bit of the bi-focals.

Phil: best of luck in marketing my idea! As I've "published" it, I have no claim on it.

John Cole12/06/2009 17:31:31
615 forum posts
24 photos
When I first posted this, I lamented that it was a shame I had just come up with this idea around the time I switched to 2.4 GHz, and the idea only works of course with  a long Tx aerial.  Well, I've NOW an idea how to estimate model distance if you've moved to 2.4 GHz.  It came to me this morning; I was flying a small (1 metre wingspan) electric with a small high-rev prop.
 
If the model is close to me and I flick from half- to full-throttle, the engine note rises instantly (if your doesn't perhaps you've got soft-start enabled on your ESC; I haven't).
 
I'm flying in a big field with trees about 400 metres away (judged from Google Earth, with the scale switched on).  My rule of thumb is that the model is twice as far away as you think!  So when I'm flying from e.g. left to right in front of the trees, my fear is that I'm about to fly right into them.  Sighs of relief every time I get past!
 
Now the speed of sound in air at 15 degrees C is about 340 metres per second.  So if I'm nearly 400 metres away and snap the throttle open, it should take MORE THAN A SECOND before I hear the change in engine note.  It didn't.  It took less than half a second, so my plane must have been about 150 metres distant, much closer than the trees.
 
If you have a similar distance to measure, work out your predicted delay and then try to learn to estimate it.  Then compare it with the delay you note when you flick open.  Petrolheads are probably better flicking closed (momentarily), because of the potential lag on throttle-open, but I've only tried it with electric.

Edited By John Cole on 12/06/2009 17:39:44

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