BBC 2 tonight 9-30
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FoxhallGH
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The crazy thing is that the BBC would be one of the main employers of PfCO qualified Drone operators, as their world-class and highly respected Wildlife and Drama series are very reliant on Drones.
Late to this thread but I have to agree with the comments about this show being utterly sensationalist.. I think the only good thing they did was talk about how hard and dangerous it would be to try to shoot down a drone.. The rest of it, my god..
- The drone impact onto a wing.. There was no science in that, smash the drone into pieces foam it together and fire it at 200MPH into what they admitted was an old, substandard wing sitting on a workbench.. An airliner coming into land is generating huge amounts of lift over the wing.. A drone that isn't broken into pieces is itself (due to the propellers) an aerofoil of sorts.. When it hits the airflow over the leading edge of the wing, surely it will be swatted away like a fly? Lets hope whomever is about to start doing more testing actually tests in a bloody wind tunnel!
- The FPV flyers, what did they think they were doing flying drones around old aeroplanes? Were they just too excited at the thought of their 15 seconds of fame to realise how bad that could look post Gatwick? Regardless, the commentary by the biggest scaredy cat on earth, Aldo, was ridiculous. Lets not talk about battery life or range or anything..
- The autonomous drone flying through the building at less than 1MPH.. Did he really say it was terrifying? Did his legs stop working? Could he not move out of the way? Even then the damned thing had prop guards on it. Sensationalist nonsense.. Oh and that drone was using LIDAR, a spinning laser range finder, which you can jam with a laser jammer, just like naughty drivers have been doing on our roads for years to jam laser speed guns which are in essence laser range finders that compute the range to a target twice to compute closing distance and therefore speed..
I could go on..
- The drone impact onto a wing.. There was no science in that, smash the drone into pieces foam it together and fire it at 200MPH into what they admitted was an old, substandard wing sitting on a workbench.. An airliner coming into land is generating huge amounts of lift over the wing.. A drone that isn't broken into pieces is itself (due to the propellers) an aerofoil of sorts.. When it hits the airflow over the leading edge of the wing, surely it will be swatted away like a fly? Lets hope whomever is about to start doing more testing actually tests in a bloody wind tunnel!
- The FPV flyers, what did they think they were doing flying drones around old aeroplanes? Were they just too excited at the thought of their 15 seconds of fame to realise how bad that could look post Gatwick? Regardless, the commentary by the biggest scaredy cat on earth, Aldo, was ridiculous. Lets not talk about battery life or range or anything..
- The autonomous drone flying through the building at less than 1MPH.. Did he really say it was terrifying? Did his legs stop working? Could he not move out of the way? Even then the damned thing had prop guards on it. Sensationalist nonsense.. Oh and that drone was using LIDAR, a spinning laser range finder, which you can jam with a laser jammer, just like naughty drivers have been doing on our roads for years to jam laser speed guns which are in essence laser range finders that compute the range to a target twice to compute closing distance and therefore speed..
I could go on..
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Thank goodness that you figured out that propellers are the answer - just use them to pulverize the drone before it can hit the aircraft. As for 1 kg objects in the flow being "swatted away like a fly" - that must be the reason why flies never hit your windshield, and why birds never hit leading edges¡
Oh dear. More complete butchery of basic science.
Don't forget in the UK there's an "us and them" attitude between PfCO holders and normal users.
The PfCOs have spent thousands on training and equipment to allow them to work. They get really annoyed by recreational users (legally or otherwise) taking potential work off them.
I would guess a lot of professional companies would like to see restrictions or even bans on recreational drone flyers - its less competition for their services and footage.
Completely legal. The operators are trained PfCO level, have the required waivers, insurance, risk assessments and supervision.
That said, Gwent did manage to fly their new, shiny sky mantis into a tree during an open day recently.
And here he is.. Maybe read what I wrote? I was talking about the props on the drone.. And speaking of butchering basic science, Is my car a wing generating lift? I hope not, I don't want to take off at high speeds...
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Actually your car is very much like a wing, just not a very efficient one at normal speeds. But what it shares completely with a wing is that the air has to deflect to go around it. The airflow goes primarily over your car. The lift is irrelevant - all that matters are the steamlines. Entrained objects, whether dust, insects or drones will gradually change direction to follow those streamlines, but not nearly fast enough. My example with the flies was to illustrate that when even milligram scale objects can't follow the streamlines over your windshield, what chance does a 1 kg object have of following them over a wing? Anyway - this is a pointless argument - there isn't actually any question about this behavior, which, if you knew anything about fluid dynamics, you would already know. It's how birds, insects and other objects strike leading edges. And if you don't understand why those two are completely equivalent even without a fluid dynamics background then you really shouldn't try to post about physics at all- especially not if you are going to try to argue about it with a physicist.
FoxhallGH
Well-Known Member
Actually - if you watch some Formula 1 racing accident vid's you'll see what happens when a high-speed car doesn't have enough down-force to overcome the Bernoulli effect caused when air has to travel a longer path to get over the top of it than it does to go beneath it ... Your car is very much like a wing generating lift - yes ... It's just not an efficient enough shape capable of travelling fast enough to overcome its weight. When you do get cars able to travel fast enough, you get huge airfoil negative-lift surfaces stuck on them so they do maintain enough pressure on the road surface so they can change direction without losing traction.
All true, but there's a bit of nuance depending on the angle of impact between the object and the airflow over the surface. Flies can absolutely "bounce off" the airflow of a car *provided* that the angle of impact is slight and the air pressure from motion is great enough. Head on, and the fly has no chance; you're getting a gooey mess on your windscreen. In between the two extremes and you have a range where you get things like stunned/dead flies (the ones some birds hunt for on roadsides) and increasingly messy impact splatters.
Applying that to drones and aircraft is going to give similar results, but so far it's a complete unknown as to where the boundaries might lie. There will almost certainly be angles of impact for a given drone on a specific point on the fuselage where there will be almost no damage, but a different angle would be catastrophic. We can make some educated guesses though. A highly fragile radome (usually the nose) is probably going to take severe damage at almost any impact angle, as will being ingested by a turbine, and windscreens have already been shown to be vulnerable to birds, so drones are clearly going to be even more hazardous.
Other than a direct impact with a wing though (the subject of most tests involving drone impacts with aircraft), I think there's a lot more *potential* for the damage to be mitigated by the angle of contact, and that has yet to be quantified. That's also the point at which statistics really starts to come into it. Given the relative velocities, I think it would be most likely that a drone-aircraft collision would be close to head-on for the aircraft, and given the cross sections, much more likely to be with the nose or engines.
Statistically speaking, it seems that overall it's definitely not looking good for the aircraft, but I think the impact tests so far have really only considered the worst possible case in their setups. Start considering real world scenarios with angled impacts, probabilties of impact on different parts of the fuselage, different velocities, and other factors and the numbers *will* fall, but it's currently anyone's guess as to how much they'll fall by.
FoxhallGH
Well-Known Member
At collision speeds between a drone and an airliner, weight is most important for two reasons;
1) Weight gives Mass, and Mass is subject to Inertia. Inertia is what stops the fly suddenly changing direction and skidding happily past your windscreen. The heavier the object (i.e. the more mass it has), then the less ability it has to change direction (or to be technically correct, the more Force it requires to change its direction). Taking inertia into account, you'd be looking at the airflow around a wing deflecting a Mavic sized drone less than a millimetre! (That is a guess as I have no idea how to calculate it, but F = MxA will come into it somewhere).
2) There is a point at which the impact resistance of the aluminium leading edge of the wing, is overcome by the weight/mass of the object. At a certain weight class, a drone will go from being a plastic toy that shatters to pieces leaving a minor scratch on the wing, to being something that punches a hole through the metal sheet. We are now seeing references to 'Joules' in regard to the energy an impacting drone can have on a person or thing. Regulations are now being drafted (in the UK and Europe) that refer to 'Joules' of energy, and restrict flying speeds when the drone is in proximity to people. This is direct application of the old F=MxA (Force = Mass x Acceleration).
One thing that was positive and very interesting for me on the BBC program, was that there were computer modelled impact scenario's shown. Somewhere, somebody has done work that shows the effect of a drone hitting wing and tail leading edges ... I've also found this scary vid showing a comp' simulation of a strike on a turbofan engine ...
There is also this very interesting article:
Drone collisions with aircraft modeled
www.aopa.org
... and the report here:
ASSUREuas - Research Projects - sUAS Airborne Collision Report
www.assureuas.org
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Yeah, the mass and inertia is absolutely going to mean any pressure wave deflection of a drone is minimal, even with the greater air pressures involved with an airliner doing a few hundred knots vs. a car doing typical road speeds. At a very simplistic level F=MA will determine the kinetic energy involved in the impact (potential energy of batteries, etc. being an additional factor), but in terms of the actual damage sustained the angle is still going to play a major part. Then you've got the criticality of various surfaces - a given amount of damage to a control surface or a turbine is going to be a lot more hazardous to an aircraft's safety than some random part of the fuselage that isn't pressurised on the other side or protecting some critical system, for instance.
I was thinking more of the statistics of a scenario where you have a drone and airliner in the same space at the same time. How likely is is that a drone *will* strike a leading wing edge head-on vs. with enough of an offset to cause negligable damage, for instance? Or shatter/penetrate the windscreen? Or a get drawn into a turbine? How much effect (if any) does the airflow being drawn into and through a turbine have on a drone that enters that airflow, for that matter?
Right now, all we have are direct impacts in contrived worse case scenarios, but that's like assuming that every road traffic accident will be a head-on collision, which is clearly not the case. If head-on impacts are only 10% (say) of the likely total, then the probability of a catastrophic impact might fall considerably, although I expect the odds are going to be somewhat higher than that given the most likely vectors involved in any collision. What I'm curious about is how much mitigation more real world scenarios might provide, but mostly a much greater understanding of just how much difference 1kg of drone vs. 1kg of bird makes to an airframe in those more realistic scenarios. Proven bird strikes are considerably more common than even suspected drone strikes, and catastrophic incidents arising from them are still an exceptional circumstance. Targetting zero risk and perfect safety records aside, if - statistically speaking - a drone only adds a tiny fraction to that risk of catastrophic failure vs. a bird then, given there are *far* more birds, is it *really* worth losing so much sleep over?
FoxhallGH
Well-Known Member
You are correct when it comes to the game of 'chance' @zocalo - However, in aircraft safety, the worst-case scenario's are always what's looked at in testing. It's of no use what so ever to look at what happens in a near miss. As long as 'Crazy-Drone-Pilot' keeps posting the YouTube video's showing airliners passing by - then we are going to have to prepare for the worst.
Note that I've added some interesting websites to my post #90 ...
Ultimately in any safety testing you have to assume the worst otherwise you're just living on blind hope alone.
There are also risks you can control, risks you can reduce and risk factors you have no control over. Just because the chance of one thing (ie bird strike) cant be eliminated it doesnt mean you should ignore another potential risk which you have 100% control over and can massively reduce or eliminate (ie drones).
At the end of the day its all about calculated probabilities of failure. You cant eliminate accidents but you seek to make them statistically as close to zero as possible. For example the criteria for the various ETOPS certifications for over-water flight and so on - you need demonstrably small risks of failure and incident etc.
There are also risks you can control, risks you can reduce and risk factors you have no control over. Just because the chance of one thing (ie bird strike) cant be eliminated it doesnt mean you should ignore another potential risk which you have 100% control over and can massively reduce or eliminate (ie drones).
At the end of the day its all about calculated probabilities of failure. You cant eliminate accidents but you seek to make them statistically as close to zero as possible. For example the criteria for the various ETOPS certifications for over-water flight and so on - you need demonstrably small risks of failure and incident etc.
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At collision speeds between a drone and an airliner, weight is most important for two reasons;
1) Weight gives Mass, and Mass is subject to Inertia. Inertia is what stops the fly suddenly changing direction and skidding happily past your windscreen. The heavier the object (i.e. the more mass it has), then the less ability it has to change direction (or to be technically correct, the more Force it requires to change its direction). Taking inertia into account, you'd be looking at the airflow around a wing deflecting a Mavic sized drone less than a millimetre! (That is a guess as I have no idea how to calculate it, but F = MxA will come into it somewhere).
2) There is a point at which the impact resistance of the aluminium leading edge of the wing, is overcome by the weight/mass of the object. At a certain weight class, a drone will go from being a plastic toy that shatters to pieces leaving a minor scratch on the wing, to being something that punches a hole through the metal sheet. We are now seeing references to 'Joules' in regard to the energy an impacting drone can have on a person or thing. Regulations are now being drafted (in the UK and Europe) that refer to 'Joules' of energy, and restrict flying speeds when the drone is in proximity to people. This is direct application of the old F=MxA (Force = Mass x Acceleration).
One thing that was positive and very interesting for me on the BBC program, was that there were computer modelled impact scenario's shown. Somewhere, somebody has done work that shows the effect of a drone hitting wing and tail leading edges ... I've also found this scary vid showing a comp' simulation of a strike on a turbofan engine ...
There is also this very interesting article:
Drone collisions with aircraft modeled
www.aopa.org
... and the report here:
ASSUREuas - Research Projects - sUAS Airborne Collision Report
It's important not to confuse momentum (mv ) with kinetic energy (½mv²). Total momentum is conserved in a collision, and the rate of change of momentum of an object is the instantaneous force exerted on it (Newton's 2nd Law). That result follows trivially from differentiating momentum with respect to time:
d(mv )/dt = m.dv/dt = ma
Kinetic energy (the measurement in Joules that you mention) is only conserved during the special case of an elastic collision, which these are not. The kinetic energy is important because it represents the available energy to do work in the from of deformation and damage - that's primarily where the kinetic energy lost in an inelastic collision goes.
Absolutely. I'm thinking more of the probability of this being a specific issue in the first place in terms of whether pilots really need to be all that concerned about it, viz. "the sky is falling" attitude of the BBC scaremongering, or just accept more of a "sh.t happens" risk of the job viz. bird strikes.
The worst possible case for a bird strike would be a total loss of the aircraft, and that outcome has a probability of X.
The worst possible case for a drone strike would be a total loss of the aircraft, and that outcome has a probability of Y (including allowing for the "clueless, careless, and criminal").
There are FAR more birds than drones, but I don't think a collision with a drone is going to magnify the chances of total loss enough to overcome the probability of a collision in the first place; e.g. "Y" is quite likely less than "X", and perhaps significantly so, so why lose any more sleep over it than you would over a chance of bird strikes? Especially since there is *far* more that can be done, both technically and legally, to mitigate Y compared to X. That's not to say that pilots should disregard the threat of drones altogether, of course, but some solid perspective on how serious the threat actually is compared to something that is currently fairly well understood would definitely be useful for all concerned.
They're concerned about bird strikes. Large sums of money are spent to reduce the risk. They're a proven risk factor that can cause extremely expensive, severe damage ro aircraft.
Drone are similar size, similar weights (denser too) so can easily hold the same if not more risk. So yes they need to be concerned, especially because a lot of the people flying them are idiots.
And even not worst case, even minor bird strikes cause damage that needs repairing or if not, inspections which cause delays and can cost tens of thousands of pounds.
And the exact risk with drones isnt know so they have to err on the side of caution. Drones are also improving in range, endurance and becoming more and more widespread so any risk there is, is increasing.
Loss of airframe? No. Chance of extremely costly, potential safety risks is much more likely. EVERY suspected collision means that aircraft is grounded pending inspection, flights are delayed, a knock on effort and the implications are huge. Thats even assuming there is no damage to repair.
Because there are only so many things you can do to reduce bird strikes, drone use is something you CAN do substantial amounts about to reduce the risk of. If you can act to reduce expensive or potentially catastrophic issues why wouldnt you act?
Until a specific risk factor is known it HAS to be treated as serious and not the other way around. Risk management is everything is dangerous until proven otherwise.
Its clear that drones have potential to damage aircraft to varying degrees in the event of a collision. Its also clear drones are being flown into controlled airspace and in close proximity to manned aircraft. So you have something known to be able to cause damage and knowingly operating in an area where it can collide. So yes its a risk and yes it has to be taken into considering and technological and legal means taken to reduce that risk.
The NATs guy to be fair had the comment spot on about clueless,careless and criminal. The majority dont give a **** about rules and laws (just look at this forum, youtube etc for the questions asked, videos etc). He stole the term from the FAA and used it out of context but for a large chunk of users, he wasnt wrong.
FoxhallGH
Well-Known Member
Thanks for the clarification @sar104 ... I know I'm conveying a very small proportion of the science here. The help is appreciated, as we are now seeing descriptions of a 'Class' of Drone in the latest CAA CAP-1789 as follows:
That's an extract from the "CAP1789 - The EU UAS Regulation Package - Outline" ... We are going to need to get a bit more scientific-minded on this side of the pond!
It's an "or" so this only really matters if we're building our own aircraft from scratch and are trying to squeeze a heavier aircraft into a lower category based on the energy option. I can absolutely see some model aircraft enthusiasts and vendors wanting to do that if it makes the paperwork easier, but it's not going to be something the average drone pilot needs to worry about. COTS drones or other RC aircraft will presumably be categorised for us by the vendor, and I would hope that the same will be applied to off-the-shelf kits. For everything else, I expect online calculators that err on the side of caution will appear soon enough.
Note that the Mavic 2 (any model) weighs slightly more than 900g at takeoff, so unless DJI can pull the "impact energy" trick they're actually going to be in Category 2 (C2), which will probably mean a few extra questions for us on the competency test later this year. Ditto for Phantoms and larger models and their knock-offs/equivalents from other vendors, obviously. C2 also removes the 19m/s max speed limitation of C1, so there's that, and allows for drones upto 4kg, so I doubt too many of us will be troubling the 25kg/C3 band...
AFAICT, each class is a more stringent subset of the one above so if, for example you had a sub-900g drone (C1 on mass) that was capable of exceeding 19m/s then it would instead need to be categorised as C2.
EDIT: If you're interested in the full details and technical requirements of each class, you can find them in this EU document from page 23.
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This doesnt help:-
www.walesonline.co.uk
Taking a drone to an airshow. The restricted airspace had been clearly NOTAMd for weeks ahead.
Drone seized by police on day of Wales Airshow
Drones were 'strictly prohibited' during the Wales Airshow
www.walesonline.co.uk
Taking a drone to an airshow. The restricted airspace had been clearly NOTAMd for weeks ahead.
Some of the explanations that should have come out during the documentary from a rather more contrite Aldo Kane
www.londonlive.co.uk
Ignore after the drone Item (unless it is of interest)
Adventurer Aldo Kane is back with two new shows
From Drones to exploring some of the most remote parts of the planet
www.londonlive.co.uk
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