Hovering to within 50ft
To further beat a long dead horse:
Actually the laser we used was a battery powered 10 amp gyro stabilized to vertical unit on a tripod so straight up was straight up. It was best to check with a small level on the lens on a cold day as it sometimes froze off level and straight up wasn't - the surveyor would sometimes do his thing and then ask you to climb or descend on the beam to confirm that you were indeed going straight up or down.
If you set up in a swamp and someone walked near the laser you would actualy see the beam start to jiggle and a quick call on the radio to have the person stop moving around was needed.
When the surveyor ( located miles away saw us appear over the hill he would tell us to stop climbing and we would hold postion on the laser Dot in the TV screen and altitute with the altimeter.) Holding altitude once hover was achieved was not a problem - at least the surveyors never complained.
Once the shot was done we would descend - not looking down at the laser of course and pick it all up then move to the next turning point and do it all over again.
Anyhoo - all done a long time ago in a Power project far far away.
Actually the laser we used was a battery powered 10 amp gyro stabilized to vertical unit on a tripod so straight up was straight up. It was best to check with a small level on the lens on a cold day as it sometimes froze off level and straight up wasn't - the surveyor would sometimes do his thing and then ask you to climb or descend on the beam to confirm that you were indeed going straight up or down.
If you set up in a swamp and someone walked near the laser you would actualy see the beam start to jiggle and a quick call on the radio to have the person stop moving around was needed.
When the surveyor ( located miles away saw us appear over the hill he would tell us to stop climbing and we would hold postion on the laser Dot in the TV screen and altitute with the altimeter.) Holding altitude once hover was achieved was not a problem - at least the surveyors never complained.
Once the shot was done we would descend - not looking down at the laser of course and pick it all up then move to the next turning point and do it all over again.
Anyhoo - all done a long time ago in a Power project far far away.
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Bruntingthorpe
Hi Silsoe,
We had plenty of time to experiment try various positions - the thing snagged during backtrack if you remember. I had a still cameraman and a video cameraman both giving me various up, down, forward, back, left right instructions right up to the wire.
we were also out of wind.
My view is that a low time 44 pilot should make a reasonable job of staying within the parameters discussed, especially if the wind is on your nose.
Obviously, a more sophisticated and expensive machine will be preferable.
How much profit do you want to make in completing the task described though?
I have already seen some of the images from Bruntingthorpe. Pin sharp and just awesome.
Jack
We had plenty of time to experiment try various positions - the thing snagged during backtrack if you remember. I had a still cameraman and a video cameraman both giving me various up, down, forward, back, left right instructions right up to the wire.
we were also out of wind.
My view is that a low time 44 pilot should make a reasonable job of staying within the parameters discussed, especially if the wind is on your nose.
Obviously, a more sophisticated and expensive machine will be preferable.
How much profit do you want to make in completing the task described though?
I have already seen some of the images from Bruntingthorpe. Pin sharp and just awesome.
Jack
Thread Starter
fly the cube
My only question though is why do you have such fine tolerances mickjobill? as it seems to me to be some techie saying I want this exact thing when a bit of latitude would not change the angles very much and give pretty much the same picture.
Thanks for the feedback, great stuff!
Reason Im asking is that we need a reliable solution that will work every time.
Ive flown with the best aerial filming pilots in the world and they do not get called upon to fly this kind of profle, it is more difficult than it appears especially for 20 minutes. Some locations would be easier than others in respect to visual clues.
Should we consider two pilots for both saftey (keeping lookout) and performance?
At 2000 ft the box can be bigger. 100x100x100ft. This is probably the practical altitude limit.
So doppler and radar alt are non runners.
I'll follow up the laser system although it may be far from practical to install.
DGPS seems the most practical to install so Ill give that a go first.
The most versatile sytem would enable us to select the cube once we are airborn and over the target, so we can fine tune the position before we commence the actual recording. The position of the cube itself needs to be fine tuned to within 100 ft or so, depending on subject.
Since there is mixed opinion as to how easy it is to fly "the cube", it sounds like it would be a fun compeition to run at a fly in!
Thanks Mathew, Albatross and Nick Helicfii, Buitenzorg for the feedback
Mickjoebill
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The laser can give you altitude to within millimeters. Scientists have used lasers to determine the distance to the moon, and most common rangefinders use lasers these days. This is one the most accurate ways known to determine distance. Determining the altitude isn't the hard part, displaying it so the pilot can maintain it is harder, and the hardest part of all is staying at the correct altitude, and over the correct point. A 4-axis flight director, coupled to a suitable electronic device, should be able to do it easily, but the cost won't be cheap. The US Coast Guard's helicopters can do this from low altitudes, but I don't know about the altitudes required by the OP. I think some sort of laser equipment would be the best way to go, if the funds are available, and it will require a rather large pile of them, I suspect.
Gomer - as has been pointed out to me - what you can do in a SAR helicopter with a 4 axis FD at lowish levels (my rad alt hold works up to 999' in the hover and quite accurately too) won't cut the mustard in terms of accuracy at 1500 to 2000'.
Having said that, my Bar Alt hold will maintain a pretty good height in the hover at 1500' (we use it for FLIR searches) but it does have accelerometers helping to fine tune the barometric information.
Equally the heading hold is good for +/- 2 degrees in the hover - the only problem would be the ground position - back to lasers I guess (or really good trimming)
Having said that, my Bar Alt hold will maintain a pretty good height in the hover at 1500' (we use it for FLIR searches) but it does have accelerometers helping to fine tune the barometric information.
Equally the heading hold is good for +/- 2 degrees in the hover - the only problem would be the ground position - back to lasers I guess (or really good trimming
)
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What a fascinating exchange!
I'd rule out GPS. The last thing you want in an accurate hover like that is to be moving your head (ear canal fluids) or changing your eye focus from 2,000' to 2' to read the screen and back out again. In a two year period of working on trial drops of the parachutes for the NASA Cassini Huygens project I concluded that your head had to be either inside the cockpit or out, but not both. In that particular case we had the luxury of being able to do it at 5kts forward ground speed (not applicable in this case) so my head stayed inside on the GPS during the approach and my observer kept his eyes outside for safety and confirmation.
I'd go with an additional person in the cockpit calling out accurate heights from a rad alt and then concentrate visually on the drift within the remaining two axes by looking ninety degrees out to the right. The double light system suggested would be perfect for fore and aft movement, but I've done it a few times just by lining up a near object and a far object, it works OK. You'd certainly achieve considerably better than 100' accuracy without needing the lights.
For left and right drift you are simply lining up the bottom of your window (or a chino line you've put there) with something on the ground and keeping it at the same position in the window. You'll soon notice if it moves.
The best tip in the exchange above is to settle down. I'd add to that to consciously control your breathing and most important of all....don't move your head under any circumstances. (This proved quite hard on the day a car plummeted past me, having rolled off a cliff-top whilst I was doing a close proximity cliff rescue. The next twenty minutes were largely occupied with looking forward to finding out "what the hell was that flash of red in my peripherals"?!)
JerryG
I'd rule out GPS. The last thing you want in an accurate hover like that is to be moving your head (ear canal fluids) or changing your eye focus from 2,000' to 2' to read the screen and back out again. In a two year period of working on trial drops of the parachutes for the NASA Cassini Huygens project I concluded that your head had to be either inside the cockpit or out, but not both. In that particular case we had the luxury of being able to do it at 5kts forward ground speed (not applicable in this case) so my head stayed inside on the GPS during the approach and my observer kept his eyes outside for safety and confirmation.
I'd go with an additional person in the cockpit calling out accurate heights from a rad alt and then concentrate visually on the drift within the remaining two axes by looking ninety degrees out to the right. The double light system suggested would be perfect for fore and aft movement, but I've done it a few times just by lining up a near object and a far object, it works OK. You'd certainly achieve considerably better than 100' accuracy without needing the lights.
For left and right drift you are simply lining up the bottom of your window (or a chino line you've put there) with something on the ground and keeping it at the same position in the window. You'll soon notice if it moves.
The best tip in the exchange above is to settle down. I'd add to that to consciously control your breathing and most important of all....don't move your head under any circumstances. (This proved quite hard on the day a car plummeted past me, having rolled off a cliff-top whilst I was doing a close proximity cliff rescue. The next twenty minutes were largely occupied with looking forward to finding out "what the hell was that flash of red in my peripherals"?!)
JerryG
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Mickjoebill
Came a bit late to this thread. Suggest you contact Prof Albrecht Grimm at IGI GmbH, Kreutztal, Germany. He is the whizz-kid kid on DGPS aircraft positioning systems and loves new problems.
[email protected] or igi-ccns@t-online
IGI pioneered Differential GPS based survey aircraft positioning systems and x, y and z positioning sub 10' is their forte. I've flown hundreds of hours with his toys and never missed a pic yet.
Good luck
Came a bit late to this thread. Suggest you contact Prof Albrecht Grimm at IGI GmbH, Kreutztal, Germany. He is the whizz-kid kid on DGPS aircraft positioning systems and loves new problems.
[email protected] or igi-ccns@t-online
IGI pioneered Differential GPS based survey aircraft positioning systems and x, y and z positioning sub 10' is their forte. I've flown hundreds of hours with his toys and never missed a pic yet.
Good luck
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"Larger helicopter with doppler autopilot could be considered as last resort but we will be over built up areas so noise is a big issue as is fitting our camera."
Just curious, in this era of Big Brother and one cctv camera to every 14 members of the population, as to WHY you want to hover over built up areas to take photographs with that level of precision.
Cheers,
M
Just curious, in this era of Big Brother and one cctv camera to every 14 members of the population, as to WHY you want to hover over built up areas to take photographs with that level of precision.
Cheers,
M
Thread Starter
"Larger helicopter with doppler autopilot could be considered as last resort but we will be over built up areas so noise is a big issue as is fitting our camera."
Just curious, in this era of Big Brother and one cctv camera to every 14 members of the population, as to WHY you want to hover over built up areas to take photographs with that level of precision.
Just curious, in this era of Big Brother and one cctv camera to every 14 members of the population, as to WHY you want to hover over built up areas to take photographs with that level of precision.
Why do it? There is money in it if we can make it work
We wont be doing council housing estates
Mickjoebill
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1500' long line
problem solved, all you would need then is an experienced driver (a precision long liner) and a bag of sand at the bottom that stays on the ground to keep the line taught. The angle the line is on would give you the lateral drift and the sand the height, you could even put two bags on the bottom spaced 50' apart so one would be off the ground. Do I get a commission.
