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How high?
Topic Started: Jun 30 2018, 11:46 AM (63 Views)
CliffW

http://b3.ifrm.com/30653/168/0/p3028175/Plot.pdfAs you will all probably be aware there is rulemaking going on in the UK and Europe for drones. The BMFA, LMA etc are engaged with the rulemakers trying to ensure minimal effects on model flying. One issue is maximum height above the surface (or point of launch as the CAA currently chooses to interpret it). Models over 7kg have always been restricted to 400ft, and HMG is going to similarly restrict all 'drones'. The BMFA and others are seeking permission for members of model associations to continue to fly sub-7kg aircraft above 400ft.
Anyway, this started me wondering about how high I have been operating my old Mk1 Wot 4 and I decided to by the Hobbyking Altimeter - about £28 including postage.

This claims to record altitude (by measuring change of pressure) up to 8 times a second for up to 8 hours. It just needs an electricity supply of 4 to 6 volts - obtained by plugging into a spare servo slot on the Rx.
It arrived a week or so ago. I have managed to sort out the software and drivers to set it up and download results to my computer, (not entirely straightforward!)

It happens that when I am working, I work in a tower block, so I thought I would test the altimeter by going up and down in the lift with it in my rucksack.

The posted image shows the recorded data.

http://b3.ifrm.com/30653/168/0/p3028175/Plot.pdf

My journeys in the lift were:
Ground floor to floor 1 and back to ground.
Into the lift again to go to floor 20 (with a brief stop at 15 for other occupants)
Then down to 16, then 15, then Ground.
Then up again to floor 4 and a walk down the stairs to floor 3.

I was then able to find the specifications of the building on the internet including the "floor to floor" heights for each level.
So I have been able to compare the altimeter readings with the architect's specification.

Here are the results:

Floor Building Spec Altimeter
1 14.6 ft 21 ft
3 41.5 ft 48 ft
4 54.5 ft 62 ft
15 199.0 ft 197 ft
16 210.0 ft 211 ft
20 261.8 ft 259 ft

As one would expect the accuracy is not so good for small changes from the datum pressure - i.e. the lower floors. But I think the accuracy at the higher levels is astounding, especially for such a cheap device.
Unfortunately, I don't have access to a building with floors that go up to 400ft, but based on these results I think I can be confident that at 400ft this device will be accurate to better than +/- 20ft.

In the coming weeks I will put it in a model and find out how high I actually fly aircraft.

Best wishes

Cliff
Attached to this post:
Attachments: Plot.pdf (109.91 KB)
Edited by CliffW, Jun 30 2018, 11:57 AM.
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Norman Carter
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Some years ago, one of our members, Max Woodhead, had a scale ASH26 glider flying at our field. It had a pop up self launch system and was equipped with a recording variometer. The span was around 4 metres and it soared with grace and efficiency.

We experimented with this to see what height could be achieved and reached around 300 metres before it was difficult to determine it's flight path. Max did a write up for the newsletter which I will search for, it is interesting and shows thermal climbs. We decided that a max height of 250 metres was sensible always steering away from any full size operation.

Maybe Max can add some detail?
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Norman Carter
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There was an article Max did for the newsletter, its in issue 136 from 2011. Will try and get it accessible from here or get our webmaster to include it is the archive of newsletters on the web page.
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Tony Culshaw

Fascinating!
I would never have thought of using a lift to change your height. My solution would probably have been way more complicated.
I’m with you on thinking the higher altitudes will be more accurate as the percentage of error decreases.
Keep us updated please.
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Norman Carter
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Newsletter issue 136 now on the archive available from the Club homepage under the heading "F-flypaper"
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Max Woodhead

Here is a video looking at it the other way, vario was accurate, Braunhilde announcing the height gives zero meters just as the wheel touches down. The 300 meters we did way back was to high for my eyes back then, they are worse now, 100 metres is plenty.


https://www.youtube.com/watch?v=2o8Rc5D-YPk&t=6s

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