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Drone Exemptions

Drone Exemptions

Drone Exemptions

(OP)
I’m working on an FAA Exemption for a client to fly commercial drones. A typical FAA requirement is to fly no faster than 100 mph and no higher than 400 feet above ground level. Also, your operational boundary has to be 500 feet away from someone you don’t want to hit. Before I do the math, does anyone know drone aerodynamics to determine if a 55 lb drone going 100 mph at 400 feet altitude will fall within the 500 feet safety zone if power and control quit immediately? This would be a quadcopter type drone, not a glider.

Of interest: a 55 lb drone at 400 feet has 22,000 ft lb of energy, same as a 4 ft x 8 ft x 1inch steel road plate falling from 17 feet. A drone freefalling from 400 feet with no air drag will hit the ground at 110 mph.

Thank you everbody.

RE: Drone Exemptions

Worst case scenario is that the entire drivetrain locks, the rotors break off and you have the quadcopter's body hurtling through the air. Cd is say 0.5 to 1 cross sectional area might be anywhere from front view to plan view (I guess it'll tumble which is a good thing in context).


Cheers

Greg Locock


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RE: Drone Exemptions

(OP)
But will it travel laterally more than 500 feet before it hits earth?

RE: Drone Exemptions

Student posting is not allowed winky smile

It depends on too many specific factors, but the QC would take 5 seconds to fall the ground with no air resistance. 5 seconds * 100 mph = 733 ft. Air resistance downward would be higher than air resistance laterally, so a more realistic calculation would probably still allow the copter to reach 500 ft.

TTFN
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Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
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RE: Drone Exemptions

Oh, I thought "Before I do the math" meant that you were going to the math, not me!

The equation for ballistic trajectory in the presence of drag is not analytically solvable, the easy way is a numerical sim. I'll see if I get time today.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Drone Exemptions

Hi Buggar

I'm with IRstuff on this one, I calculate 4.99 seconds to fall to earth and it would have covered a distance of 739 Ft horizontally before hitting the ground but without considering any air resistance.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: Drone Exemptions

(OP)
Not meant to be a student post. I was wondering if there were established "drone rates of fall". We are writing a subconsultant agreement for drone use and are finding loose legal ends within FAA Exemptions.

RE: Drone Exemptions

I know you've been around the block a couple of times. The bottom line is there is no closed form solution, not even for a normal aircraft. See:
http://andrew.gibiansky.com/blog/physics/quadcopte...
http://andrew.gibiansky.com/downloads/pdf/Quadcopt...
http://www.ijstr.org/final-print/aug2014/Quadcopte...
http://sal.aalto.fi/publications/pdf-files/eluu11_...
http://www.europment.org/library/2014/santorini/by...

TTFN
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Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
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RE: Drone Exemptions

(OP)
O.K., the kid down the street is into drones and he's interested. He has a couple quadcopters and we're going to tie a string to one of them and tie it to a pole hanging out the side of my car, speed down the road, and see how much drag we're getting. We'll have to tie the string as close to the center of gravity as possible and see how it tumbles. Then by measuring the angle of the string, we can compute the drag coefficient at different speeds. That brings up the question, is there an "average" drag coefficient for a tumbling drone? We'll find out.

I tried to talk him into trying a 100 mph free fall from 500 feet up with one of his drones and he came up with the drone on a string out of the car idea instead. This sounds more fun than doing it on a computer. But I'd rather test crash one.

RE: Drone Exemptions

Any weapons range type folks should be familiar with how to estimate this as they have to do it for things they are deliberately dropping from air craft moving at speed. Used to refer to it as 6 DOF "6 degrees of Freedom" models.

I'd probably use a CD value for a sphere of approximately equivalent cross section in the 'lowest drag' orientation.

Don't forget to add a good margin of error.

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RE: Drone Exemptions

He doesn't necessarily need to do a complete freefall, since he's probably got gyros and accels on board for the nav system, and you can use that data to see what it's actually doing. I'd actually be more worried about a tethered test, as I've had lots of time with errant kites, which is what this will look like, and it's very likely that the drone will bounce off the road surface a few times and that'll be that.

TTFN
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Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx

RE: Drone Exemptions

Calculate the trajectory of a 55lb mass with an initial horizontal velocity of 100mph and a vertical height of 400ft. And then draw a 500ft radius around every possible impact point. If there are no people, structures, vehicles, livestock, etc within the area that might be injured by your drone, you'll probably be OK.

However, you probably still need to provide some liability insurance coverage for your activities. And I imagine it would be very difficult (and expensive) to obtain this type of coverage.

RE: Drone Exemptions

In order to limit the maximum range of an unpowered projectile with an initial velocity of 100 mph horizontally at an altitude 400 feet, to 500 feet, a 55 lb drone needs a minimum Cd*area of 2.5 sq ft, according to my whiz bang sim.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Drone Exemptions

(OP)
Greg,

That looks like a good number. Drone Kid and I went to a drone shop to see what was available. The ratio of weight to projected area (and Cd) of all the drones we saw varied so much that we would have to prequalify a specific drone for a specific use. We looked at some 55 pound drones that are allowed by FAA. These things are monsters and you do not want one falling on you from 400 feet.

Your Cd area of 2.5 square feet breaks down approximately to a 1.6 ft. x 1.6 ft. size drone (solid area). We didn't measure the 55 pounders but I estimate that their area is less than that, and they would have to descend in the "projected area" position which isn't likely. Therefore, in all probability, their kill zone is beyond the FAA horizontal limit. There are lawyers that specialize in applying for FAA exemptions. Don't they read these things?

Can you tell me what simulator you used for the drag coefficient?

Thanks.

RE: Drone Exemptions

Is the 500ft requirement considered part of the operational envelope, or is it measured from any potential point of impact, similar to a margin of safety?

RE: Drone Exemptions

(OP)
The 500 feet is the operational limits at 400 feet above ground level and at 100 mph. These are typical FAA mandated limits of operations. My findings are that this is not sufficient to contain a drone suffering loss of power/control as we have determined.

During my research, I found out that drones are being operated by a local utility to inspect their powerlines and facilities. They are operating drones at a nearby substation with 38 houses and an open space park in the "kill zone" of their drones (laterally within 730 feet from drone operations).
I have sent a letter to the FAA and the Utility. This is a politically powerful utility here and if you don't hear from me, I'm probably in a buried electrical vault somewhere.

These Exemptions are public information and are internet-searchable under FAA Section 333 Exemptions. The one for the subject utility is Exemption No. 11238. Most of these Exemptions seem to rely on the blanket 500 ft lateral/400 vertical/100 mph rule. I argue that they should be site-specific. Can't drones be preprogrammed for these variables?

Greg, special thanks for the chart. Your Cd looks like it may fit some of the drones we looked at but when we compared some that had similar weights, their configuration (and Cd) were radically different from each other.

RE: Drone Exemptions

(OP)
Since this is all in the public information realm, here are the coordinates of the substation using the drones. Note the nearby houses. Substa Coord: 32 47 15 N, 117 08 20 W, in Degrees, Minutes, Seconds.

RE: Drone Exemptions

Buggar,
That would appear to be close to Montgomery Field and Miramar airbase . Are you sure you are not within the 5 miles from an airport restriction.
B.E.

You are judged not by what you know, but by what you can do.

RE: Drone Exemptions

Note that there's some over-specification at play; it's unlikely that the quadcopter is actually doing 100 mph in the middle of its inspection, as there is no way the operator could possibly check the video feed fast enough for that speed. Since it is a quadcopter, it can do its work at near zero air speed, which means that if it loses power, it'll pretty much fall straight downward, with perhaps only a little lateral motion due to the lift of the rotors.

TTFN
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Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx

RE: Drone Exemptions

Are these various dimensions and limits being applied and enforced on a worst-possible-case condition prior to being able to operate the device ... or are they only being applied and enforced subsequent to an accident in which it is found that one of the dimensions is being violated?

It's illegal to drive your car on the wrong side of the centerline marking in an area where signs prohibit it. But the auto manufacturers are not required to build a vehicle which is IMPOSSIBLE to drive on the wrong side of the centerline marking.

It appears that you are trying to do the latter, but the actual application may be more similar to the former.

RE: Drone Exemptions

With a CdA of 0.0, ie worst case for drag, you'd need an exclusion zone of 780 feet, and the thing would hit the ground at roughly 150 mph. With CdA=0.23 m^2 it hits at 85 mph. This assumes horizontal elevation at first, which is not worst case, and that the thing is purely ballistic.

These are fascinatingly large numbers.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Drone Exemptions

All of that is why I suspect that there is not a requirement to prove that a violation can never physically happen (as it would be essentially impossible to ever do this), but only either applied "as written", or perhaps after the fact in the event of an incident.

If your operational boundary is required to be 500 feet away then that's how close the operator is allowed to fly ... not 500 feet plus an enormous allowance in the event of some sort of failure. The 500 feet is understood to already contain the allowance for not falling straight down, etc.

If the drone encounters a F5 tornado then it's going to be blown wherever the tornado wants to blow it, no matter what calculations you do!

RE: Drone Exemptions

You say that but...

Back when dropping things off aircraft intentionally our 'safety zones' would be massive by the time all margins of error/safety etc were taken into account.

Most military ranges are a lot bigger than '500 ft' but we'd often still have to be very careful that our foot print was fully in the range.

(Yes we were flying faster and sometimes higher but hopefully you get my point.)

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RE: Drone Exemptions

The question needs to be asked of the regulatory authority if the wording of their requirement is unclear:

Is the 500 foot distance "as written" or does it apply to equipment failure or other such conditions, and if so, what are those conditions.

Over-analysing something isn't a constructive exercise, and applying safety factors on top of something that already has a safety factor built into it will just make it impossible to get through the exercise.

RE: Drone Exemptions

"and applying safety factors on top of something that already has a safety factor built into it will just make it impossible to get through the exercise"

Or not, worked on a project where something in the air stream needed its 1.5 factor on it which was duly done based on aero loads supplied by the customer. The part was pretty beefy but met it's required strength per calculation, FEA & testing.

Only after all this did the customer tell us the loads they'd given us already had the 1.5 in them.

Oh well, that particular piece of conduit is, and for ever will be at least 2.25 times stronger than the max predicted aero load and the safety approval folks were OK with that!

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RE: Drone Exemptions

(OP)
"This assumes horizontal elevation at first, which is not worst case," VERY significant point, Greg! Drone Kid and I watched hours of films of drone crashes and what you say, we frequently saw.

We went back to drone shop and interviewed a few "professional" drone pilots, one an ex-military drone guy. Most important, we learned is that it is easy to pre-program a flight envelope, including air speed, into a drone. The better Geo-fences are accurate to a meter or less with GPS, and tighter tolerances are available with ground based positional stations.

So now my campaign turns to convincing FAA to add flight pre-programming as a primary restriction for drone use at this facility. This should be easy by adding an amendment to the Exemption, which is frequently done to add an additional drone to the Exemption. I sent a letter with copies of Google earth showing the "kill zones" in the local neighborhoods and park. I also have our City Councilmember involved but he's so busy saving the Chargers that he won't be of any help. The electric utility involved no doubt has a contract out on me. I'll keep you posted on this.

RE: Drone Exemptions

Here's what FAR part 91.119 says:

"91.119 Minimum safe altitudes: General.

Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:

(a) Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface.

(b) Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft.

(c) Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure. "

RE: Drone Exemptions

(OP)
I see that the FAA has issued FAA 333 Exemption No. 12602 to Peter Sachs to operate a Tailor Toys powered paper airplane. Is it fair to limit a paper airplane to 100 mph and an altitude of 400 feet?

RE: Drone Exemptions

berkshire - one of these days a plane will hit a drone, but so far I haven't seen a photo of a drone near a forest fire or commercial or private aircraft. Now the DoT/FAA is proposing requiring registration of what seems like every R/C model operator.

Which is strange as there are millions of camera phones in use. There isn't even footage of a place in the sky where the witness says the drone was or a map coordinate or any evidence at all. It's beginning to seem more like the UFO sightings and ball lightning sightings. Scuttlebutt on pilot forums is the FAA is suggesting pilots report anything they are unsure of as drones, just to be safe. Plastic bag in a thermal - it's a drone. Helium balloon - it'd a drone.

Meanwhile private planes continue to claim innocent lives by crashing into homes or into low-altitude, high speed military aircraft.
http://www.nbcnews.com/news/us-news/reports-f-16-m...
and
http://www.cnn.com/2015/10/14/us/lake-worth-florid...
and
https://www.washingtonpost.com/local/crime/plane-c... (from the article "it was the second time that Rosenberg had crashed while landing at the Montgomery County Airpark")

Sorry - it angers me that the FAA and DOT are whining about unconfirmed reports of bad things drone pilots might have done while it's A-OK for a guy with the bucks to buy a twinjet (to replace his crashed twin turboprop) and incinerate a mother and two sons because he didn't really know how to cope and already had one pilot-error crash. http://www.wusa9.com/story/news/investigations/rus... At least Rosenberg won't get any more chances to kill others.

RE: Drone Exemptions

Sorry 3DDave, but you should just resign yourself to the eventuality of licensing. It's the tried-and-true method of gaining some semblance of control over something. Especially, something being embraced by and enabled for the world's growing number of clueless and defiant morons.

It's needed so a set of rules can be verifiably received by each drone user. If you have to pass a test based on the rules and be licensed to operate then said morons can be effectively grounded if found necessary. Otherwise they claim ignorance when caught doing dangerous things.

I see this being done similarly to HAM radio licensing, but due to the plethora of bad examples it may end up being governmentally administered perhaps via DMVs or such.

I don't see drone flying as anything less than driving a car, I want to continue seeing people who are handed driver's licenses being checked in some way for fitness to the task.

If an airliner is brought down by a drone drones will likely be banned for all except licensed pilots. Surely requiring casual drone operators to be licensed before that happens is better for the drone community then the alternative?

Keith Cress
kcress - http://www.flaminsystems.com

RE: Drone Exemptions

At this point, with the registration / licensing ship having sailed, I think legalizing shooting them down if they are over your property or looking into your property or otherwise presenting a risk to you, would be the more effective option ... and more interesting, too ...

RE: Drone Exemptions

I would rather they focus efforts on ensuring the drones are reliable and secure. There's too many stories of 'Heading back to China' failure modes and channel interference causing erratic behavior, neither of which requiring owners to get licenses will affect.**

Crashing a jet liner with a typical hobby drone is unlikely; if it happens it will be an unlicensed operator with a purpose built device doing so intentionally. But since that's an unreliable method, it seems unlikely for any but a nut job to even try; again, not going to have a license.

Instead the US will have a huge, and valuable data repository of identity information, ripe for the hacking in the hands of departments with little information security experience; it will also have a large number of new employees to manage; and it will have a new revenue stream for an ineffective result. Maybe everyone should be fingerprinted and DNA aamples taken as a way to curb other crimes, which is effectively what I just saw the head of the US DoT suggest was the reason for licensing - to make it easier to catch criminals.

Unavoidable - sure, no question. But also a waste of time and resources and a new source of risk to the people forced to participate.

**My favorite was an attempt to fly around a rock tower ~300 foot tall and 100 foot wide. When the drone lost signal it did a return to base - straight line to the take-off coordinates, which was directly through the tower. It could have been programmed to return to last-good-signal point or back-track it's path. The fliers got it back, but it was damaged.

RE: Drone Exemptions

(OP)
In all my recent drone research and watching drone crash videos, I believe the most effective small drone "deterents" are birds of prey - falcons, hawks, etc. Most that I saw were in the wild and the bird was apparently (obviously) threatened. I never saw a video of a drone flying away from an encounter with a bird. Falcons are now used at airports to keep birds out of jet engines. Falconing is an up and coming occupation.

RE: Drone Exemptions

I think it commendable you are offering to help FAA rewrite their 333 exemptions better. No one I ever heard of who applied and received their 333 exemption ever took a lot of notice or exception to that 500' note.

I think you will find that bird attacks account for less than 1% of all quad crashes, so not statistically significant - although they are really really cool to see!


Since laws, regulations, registrations,and penalties only work on those on whom they will work, it means drone regulations will only hinder those of us who fly responsibly; those who don't, still won't, since they have, and always will, ignore them.

"Ignorance of the law is no defense" still applies, so those who fly irresponsibly are not off the hook as it stands now anyway.

So more regulations serve no useful purpose except to extract more money from us who pay taxes and fees. But it is like building 100 new houses in a city: the extra tax income base does not pay for all the additional infrastructure required, so it really doesn't even work. That will be true here also.



www.KilroyWasHere<dot>com

RE: Drone Exemptions

(OP)
FAA responded and said they would take up my "complaint". I followed up with a somewhat terse letter that I was not complaining but merely attempting to assist FAA in enforcement of their Exemption requirements. The beaurocratic dance begins.

I noticed the Exemption had no electrical qualification requirements for drone operators that will be operating around the electrical equipment. I sent a letter to IBEW so they could get their requirements addressed as well.

RE: Drone Exemptions

(OP)
The rest of my post:

I'm challenging the FAA exemption for not complying with the requirements of the situation. I'm a structural engineer and I write contracts all the time for small and large construction projects. We use standard contract forms like those from AIA and CASE and then modify them with an appropriate Special Conditions clause that stipulates details such as I am proposing. Not a big deal in the construction industry. Of course I'm beating a dead horse, but I do enjoy the comments I'm getting from FAA. I enquired about the use of a geofence with drones and they thought I was talking about temporary barricade fencing to keep people away from drone launch sites.

RE: Drone Exemptions

barricade fence - ha!

I recently went to Walmart, asked the computer salesperson where the UPS's were. She insisted I wanted USBs. She eventually said "honey, UPS is who brings our stuff. you want USB." she could work for the FAA!

But Buggar, pray tell, what is a IBEW? some electrical union?

www.KilroyWasHere<dot>com

RE: Drone Exemptions

IBEW "International Brotherhood of Electrical Workers" = electricians union.

Sounds like you are stirring up the doodoo.

I betcha that 500 foot requirement was just pulled out of a hat with no real thought put into it, nor was there ever any real expectation of someone analysing it to death. Probably all of the other numbers are from that same hat.

RE: Drone Exemptions

(OP)
Brian, you are right on all three. You saw my earlier post that these standard "rules" also apply to a powered paper airplane. These "rules" are so absurd for most situations that I can't help myself from challenging them. I am involving my Councilmember also, but he is highly political and very likely to embarrass himself like the FAA is doing. Fortunately, I have the time to play with this right now. I will save up the correspondence and if it looks entertaining enough, I will submit it to our local "radical" newspaper.

RE: Drone Exemptions

The state of Colorado has been doing some testing on interactions between drones and aircraft. I think the biggest take away on this , is that most pilots cannot see a drone , even when they are looking for them.
B.E.

You are judged not by what you know, but by what you can do.

RE: Drone Exemptions

(OP)
I had my meeting with the Regional FAA office. They are essentially going toothless on this and letting the drone user write their own rules. The drone user is SDG&E so their power (electrical and political) is immense. This will likely work well because there are always people chasing lawsuits with SDG&E so they will have to follow stricter flight guidelines than the FAA could ever conceive.

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