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Photoflying under bridges

Flush,

The H doesn't really care about a GPS signal when flown in Angle mode. It's more reliant on the compass and baro altimeter for general stability. Position hold in hover improves when GPS is good, of course. You only really need GPS for RTH and Smart mode. The closer the H is to the bottom of the bridge the greater the probability GPS signal will be blocked by the bridge. GPS does not penetrate steel and concrete worth a ****, and the bridge will have a lot of both. Simply "shadowing" the H from GPS signals by flying low between a bunch of tall buildings can occlude a GPS lock. Being 6 lanes wide the over head satellite view will be severely occluded, with only the satellites on the far horizons being able to providing any signal from the sides of the bridge. Just remember you'll be hand flying the bird in what will essentially be a "stability" mode, and slow the speed slider some to make control more manageable.
Agreed.
But all that steel that goes into building a bridge could have a detrimental impact on the compass. That coupled with the confined space (Photo did say that his inspection would have involved him flying ' as close to the underside as possible') would have made such a flight risky. Then there's the issue about the baro altimeter not being entirely accurate on the H that could possibly cause the aircraft to raise up some feet without any height input from the pilot.
In my book, there's far too many 'ifs and buts' to do with this flight and in my view a honest and properly done risk assessment would render the flight undo-able in any reasonable fashion...Without seeing his client's brief and only going off what Photo has said, I would refuse the job for sure.
 
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Hardly ever. Accidentally activated it and it confused the **** out of me!
Thanx once more for all your relevant input and warnings - I have now told my customer that there will be no flying under the bridge and they fully understood it and the reasons why.
 
You can fly under the bridge - just do not get behind the bridge or get any 'large' obstruction between you and the H. Be sure to maintain operational LOS between the ST16 and the H and you should be fine (oops I found out with a scary recovery). What is the distance between you and the H when under the bridge? The actual question is your depth of field to the bridge understructure and water. When I fly Fpv at 500 yards I still have operational depth of field of a couple feet (thanks to great quality of the H live feed).
 
Most of the comments refer to the effect of the bridge on the H. You also need to consider what's under or the bridge. Is there likely to be pedestrians or vehicles travelling under at the same time. If you do suffer a loss of control, where will the H end up, could you can retrieve it and is it likely to cause damage/harm to anything else?
 
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Also, dont forget that the H will literally try and suck itself to the bridge the closer you get - so don't get caught out.
 
Hi guess someone here has experience of flying under bridges. In a week or so I know I will be asked to perform a surveillance flight under a bridge and as close to the underside as possible. My concern is how "riscy" it is to lose GPS sats (and crash) when under the bridge that is a 6-lane wide mixed steel/concret construction.
Shall I use the DBS/Itelite or std H antenna? Thanx in advance for your respons
If you can fly (you cannot fly till you can control the H without GPS) you will have no problem at all.
 
Flying under a bridge is something I have contemplated, as a company I do work for do bridge inspection work and this could drastically reduce man hours.
You (Photo) say the client requires you to fly as close to the underside as possible. Does this mean they want to inspect the underside? That clearly would require an upwards looking camera, something the H cannot do but is something I would be interested in.
I had thought it was a distinct possibility to fly the H under a bridge with GPS disabled or using the IPS (which I don't have and won't work over water I assume) anyway having just crashed mine into a tree in far easier circumstances then under a bridge I shall decline. Perhaps if I can find a more capable craft one day.
 
I developed for a customer, a y6 that had a camera that could be rotated + or - 90 degrees from horizontal. The camera also extended from the front of the aircraft to have clear up and down vision. These are custom made drones, not something you can find at your friendly best buy!. These flew inside a pipe structure, so no gps.
you just need expensive equipment!
Dick Bottos
 
For serious close in inspection work my choice of aircraft would use Pixhawk, PX4, or X2 flight controllers. For anything more stable and predictable you'd have to go to Lockheed.
 
Also to bear in mind, I think you can get an effect similar to ground effect but backwards if you fly to close to the underside.
 
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That does not happen, but you don’t want to rely on GPS when below a concrete and steel slab.
 
Bit rude.....
What is it that doesn't happen? Inverse ground effect? Why's that then? Negative pressure can't occur above the props? Do tell... I mean surely the whole point of aerodynamics is about changing pressure from one side to another? Are you saying that as the aircraft approaches the underside of the bridge the pressure differential couldn't suck it upwards rapidly to the surface? Me thinks this is even more likely than the effect at ground level since their is greater pressure below and the turbulence of the displacement loops over the top to hold the aircraft down...? But happy to hear your opinion before being dismissed so bluntly....
 
Rather than get into an endless debate over physics, ground effect, aerodynamics, and properties of the atmosphere, compressed and uncompressed, just go fly under a couple bridges and learn what you learn. You can dismiss yourself afterwards. Those that have already done so know what does or doesn’t happen.
 
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Rather than get into an endless debate over physics, ground effect, aerodynamics, and properties of the atmosphere, compressed and uncompressed, just go fly under a couple bridges and learn what you learn. You can dismiss yourself afterwards. Those that have already done so know what does or doesn’t happen.
Agree with you Pat, I have been under sheet metal roofs next to large post and I beams, and it is crazy what can happen. It took all of my concentration just to fly and only quick glances at my screen.

I was unable to get great video. But the challenge was fun!:D I don't recommend this for the fainthearted or new pilots.
 
Agreed. The biggest challenge to flying under or inside a structure is the operator himself. If they are exercising due caution they turned off GPS first and will be hand flying the aircraft. It’s amazing how quickly the aircraft can be over controlled by the operator even in a no wind environment. You’re being smooth, slow, and in small amounts or you get into trouble quickly.
 

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