Breaking News: DJI Demands Withdrawal of Drone Crash Video - DRONELIFE

[BigAl07]

So the study was designed to show that it is not impossible for a drone strike to damage a light aircraft wing. The impact velocity was possible only if the aircraft and the drone were each flying near top speed in precisely opposite directions and the impact was perfectly centered on the leading edge of the wing.

The probability of these conditions occurring in the wild is near zero, and probability is a very important number in assessing the overall danger posed. There is a non-zero possibility that you will be struck on the head by a meteor or a piece of space junk, or a chunk of nasty ice falling from a leaky restroom tank on an airliner. But that doesn't justify a requirement to always wear a hard hat when outdoors, because the probability of a strike is so low.

Seriously?

Just today I had a good friend get impacted by a hawk in his tail of his manned aircraft and luckily it didn't penetrate the skin but it did do some damage in a non-critical area but imagine if it had damaged the elevator directly instead of the horizontal stabilizer.



Now compare the damage a hawk did (who is light, brittle, and much less dense than our sUAS) to a Phantom 4 impacting in the same place on the same aircraft.

Would YOU want to be in the aircraft that strikes one of our drones at speed in a critical area?

 

[BigAl07]

The test was to see what damage would occur if it hit a wing, they were not testing to see what damage would occur if it missed. When they test AC for bird strike damage they fire a bird, often a frozen chicken, at the test object such as the windscreen -- when they do this they do not try to miss.

Birds hit planes every single day so impacts are most definitely possible. Are you suggesting that there is some mechanism the protects planes from drone strikes -- if so I'd be glad to hear about it as this could eliminate the need for any limits on drone flight around planes.


Brian

Hey Brian. I agree with what you're saying except one aspect..

Frozen Chicken - The frozen aspect was found later to be a hoax or at least can't be verified. While I'm not a fan of SNOPES (don't go there) this one has enough "meat" to make it half way believable.
The Chicken Cannon

 

[Raptorman0909]

Hey Brian. I agree with what you're saying except one aspect..

Frozen Chicken - The frozen aspect was found later to be a hoax or at least can't be verified. While I'm not a fan of SNOPES (don't go there) this one has enough "meat" to make it half way believable.
The Chicken Cannon

I'm sure there are those that prefer thawed birds, but frozen is easier to shoot and more predictable as far as velocity is concerned. And yes, they do use frozen birds. That there would be thawed birds as well is hardly surprising even though it's more difficult to fire a thawed bird and not so easy to control speed.

In the article you linked they point out that the USAF uses frozen birds so there is no hoax aspect to it.


Brian

 

[Raptorman0909]

Seriously?

Just today I had a good friend get impacted by a hawk in his tail of his manned aircraft and luckily it didn't penetrate the skin but it did do some damage in a non-critical area but imagine if it had damaged the elevator directly instead of the horizontal stabilizer.

View attachment 105513View attachment 105514View attachment 105515View attachment 105516

Now compare the damage a hawk did (who is light, brittle, and much less dense than our sUAS) to a Phantom 4 impacting in the same place on the same aircraft.

Would YOU want to be in the aircraft that strikes one of our drones at speed in a critical area?

It seems I have to post the same incredulous post about every second month as there is no end to the idiocy from people that think they should be able to whatever they please and think everything they hear to the contrary is fake news. For some people everyday is opposite day!


Brian

 

[sar104]

I'm sure there are those that prefer thawed birds, but frozen is easier to shoot and more predictable as far as velocity is concerned. And yes, they do use frozen birds. That there would be thawed birds as well is hardly surprising even though it's more difficult to fire a thawed bird and not so easy to control speed.

In the article you linked they point out that the USAF uses frozen birds so there is no hoax aspect to it.


Brian

Frozen birds are certainly easier to launch, but unfortunately it's a pointless experiment since the physics of the resulting impact is in an entirely different regime than for a non-frozen bird and the results would be meaningless. Although the mass is the same, the mechanical properties of the frozen carcass that determine the force profile exerted on the target are completely different. The frozen bird is effectively a rigid body until it breaks in an approximately brittle failure mode (depends somewhat on temperature). So while the total impulse is comparable, the yield stress is far higher and the strain to failure much lower than for a thawed bird, by several orders of magnitude, and so the impact forces are correspondingly larger.

I'm not sure what you read, but the USAF has never used frozen birds except, perhaps, by accident, and that was never documented.

 

[Raptorman0909]

Frozen birds are certainly easier to launch, but unfortunately it's a pointless experiment since the physics of the resulting impact is in an entirely different regime than for a non-frozen bird and the results would be meaningless. Although the mass is the same, the mechanical properties of the frozen carcass that determine the force profile exerted on the target are completely different. The frozen bird is effectively a rigid body until it breaks in an approximately brittle failure mode (depends somewhat on temperature). So while the total impulse is comparable, the yield stress is far higher and the strain to failure much lower than for a thawed bird, by several orders of magnitude, and so the impact forces are correspondingly larger.

I'm not sure what you read, but the USAF has never used frozen birds except, perhaps, by accident, and that was never documented.

Not exactly true. At the speeds typically used for these tests it no doubt presents a worst case, but at much higher speeds mass dominates and whether it's hard/frozen or soft/thawed makes almost no difference. Yes, at the speeds they typically use it will make a difference and provide a worst case test.


Brian

 

[With The Birds]

Not exactly true. At the speeds typically used for these tests it no doubt presents a worst case, but at much higher speeds mass dominates and whether it's hard/frozen or soft/thawed makes almost no difference. Yes, at the speeds they typically use it will make a difference and provide a worst case test.


Brian

On your logic the test with the phantom was unnecessary, they need only have looked at data from impacts with similar weight birds.

What your suggesting is like saying there is no difference in leaping off a diving board into a pool with a layer if ice on the surface. It’s not quite that silly but it’s part way there.

 

[sar104]

Not exactly true. At the speeds typically used for these tests it no doubt presents a worst case, but at much higher speeds mass dominates and whether it's hard/frozen or soft/thawed makes almost no difference. Yes, at the speeds they typically use it will make a difference and provide a worst case test.


Brian

That's correct for impacts in the hydrodynamic limit where the impact stresses immediately exceed the material yield stress, but these impact velocities are nowhere near that. This is a completely strength-dominated regime, and so it's not a worst-case test at all - it's a completely useless test.

I'm astounded that you are even trying to argue this. If you know anything at all about material science, terminal ballistics and shock physics then this should be completely obvious.

If you want direct evidence, just watch the video of the Phantom and the surrogate bird. Similar masses but completely different impact dynamics. The gel bird behaves like a liquid, while the Phantom behaves like a rigid, though not solid, body - hence the difference in outcome. If the gel bird had been frozen it would likely have gone straight through and out through the trailing edge.

 

[Raptorman0909]

That's correct for impacts in the hydrodynamic limit where the impact stresses immediately exceed the material yield stress, but these impact velocities are nowhere near that. This is a completely strength-dominated regime, and so it's not a worst-case test at all - it's a completely useless test.

I'm astounded that you are even trying to argue this. If you know anything at all about material science, terminal ballistics and shock physics then this should be completely obvious.

If you want direct evidence, just watch the video of the Phantom and the surrogate bird. Similar masses but completely different impact dynamics. The gel bird behaves like a liquid, while the Phantom behaves like a rigid, though not solid, body - hence the difference in outcome. If the gel bird had been frozen it would likely have gone straight through and out through the trailing edge.

Back in the late 70's we had an F-4 Phantom, yes a Phantom, come back after a training mission where it did a low level run and hit a bird. The plane made it back safely but upon inspection they discovered the plane had hit a Sea Gull. How could they tell it was a Sea Gull you might ask. Well there was a perfect silhouette of the gull wings and body and they could also see the the bird was looking a bit to the right as the birds beak was visible in the hole that was punched through the radome. Parts of the bird made it through 3 bulkheads. The plane was subsonic but going pretty fast, something close to 600mph if I remember correctly.

Yes, the speeds where testing normally occur will reveal a difference between a frozen bird and a thawed one, no question about it, but the idea that a warm breathing bird will have vastly less effect is nonsense. Yep, big difference at 240mph, not so big a difference at 600mph. It should be noted that many of the planes we fly in go that fast or faster, though birds seldom fly high enough to encounter a plane going that fast except for military AC.


Brian.

 

[sar104]

Back in the late 70's we had an F-4 Phantom, yes a Phantom, come back after a training mission where it did a low level run and hit a bird. The plane made it back safely but upon inspection they discovered the plane had hit a Sea Gull. How could they tell it was a Sea Gull you might ask. Well there was a perfect silhouette of the gull wings and body and they could also see the the bird was looking a bit to the right as the birds beak was visible in the hole that was punched through the radome. Parts of the bird made it through 3 bulkheads. The plane was subsonic but going pretty fast, something close to 600mph if I remember correctly.

Yes, the speeds where testing normally occur will reveal a difference between a frozen bird and a thawed one, no question about it, but the idea that a warm breathing bird will have vastly less effect is nonsense. Yep, big difference at 240mph, not so big a difference at 600mph. It should be noted that many of the planes we fly in go that fast or faster, though birds seldom fly high enough to encounter a plane going that fast except for military AC.


Brian.

Those domes are relatively weak - some years ago we studied the effects of various material impacts on them at subsonic and supersonic velocities. The effect you describe is plausible at around Mach 1. But the fact that it penetrated the dome doesn't tell you anything about the relative penetration capability of rigid vs. soft, or give any information on which regime it was in. No one is arguing that unfrozen birds won't penetrate domes at those speeds. If your argument is based on that one observation then this discussion is pointless, and you don't understand the physics at all.

 

[Raptorman0909]

Those domes are relatively weak - some years ago we studied the effects of various material impacts on them at subsonic and supersonic velocities. The effect you describe is plausible at around Mach 1. But the fact that it penetrated the dome doesn't tell you anything about the relative penetration capability of rigid vs. soft, or give any information on which regime it was in. No one is arguing that unfrozen birds won't penetrate domes at those speeds. If your argument is based on that one observation then this discussion is pointless, and you don't understand the physics at all.

First a correction ... the bird went through the radome and two bulheads but nothing made it through the third bulkhead. So, the bird, or parts thereof, went through three surfaces, the radome and two metal bulkheads. Yes, the radome itself is not terribly strong, but it does need to resist the aerodynamic pressure when travelling supersonic so it isn't tissue paper either.

Going back to my very first post on this topic I said, here, let me quote myself... "When they test AC for bird strike damage they fire a bird, often a frozen chicken, at the test object such as the windscreen..." so, the word often means not all the time, it would be better if I'd said occasionally, but were splitting hairs here.

In my next post I referenced the link from Snopes and pointed out that the USAF did in fact use frozen chickens though they appear to have switched to clay. "In the article you linked they point out that the USAF uses frozen birds so there is no hoax aspect to it ..."

And in the last post I referenced an event that happened at my base (Seymour Johnson AFB) to an F-4 Phantom doing a low level penetration run and the Sea Gull it hit at high speed. So, for an entity like the USAF, which does indeed fly fast at low altitude with some frequency they would need to test for higher velocity impact than would be likely for a commercial AC and at these higher speeds the difference between hard and soft is less.

Finally, it should also be pointed out that even commercial AC can encounter birds at high speed including speeds over 600mph as there are instances where birds have been known to fly as high as 37000 feet and those birds tend to be quite large.

Oh, and I do understand Physics pretty well. In summary, as speed increases the difference between hard and soft diminishes, you even admit that, and yet you claim I know not what I'm saying. Your final point focused on the relatively weak radome but ignored the two metal bulkheads -- looks like an unscientific effort at cherry-picking to me.


Brian

 

[sar104]

First a correction ... the bird went through the radome and two bulheads but nothing made it through the third bulkhead. So, the bird, or parts thereof, went through three surfaces, the radome and two metal bulkheads. Yes, the radome itself is not terribly strong, but it does need to resist the aerodynamic pressure when travelling supersonic so it isn't tissue paper either.

Going back to my very first post on this topic I said, here, let me quote myself... "When they test AC for bird strike damage they fire a bird, often a frozen chicken, at the test object such as the windscreen..." so, the word often means not all the time, it would be better if I'd said occasionally, but were splitting hairs here.

In my next post I referenced the link from Snopes and pointed out that the USAF did in fact use frozen chickens though they appear to have switched to clay. "In the article you linked they point out that the USAF uses frozen birds so there is no hoax aspect to it ..."

And in the last post I referenced an event that happened at my base (Seymour Johnson AFB) to an F-4 Phantom doing a low level penetration run and the Sea Gull it hit at high speed. So, for an entity like the USAF, which does indeed fly fast at low altitude with some frequency they would need to test for higher velocity impact than would be likely for a commercial AC and at these higher speeds the difference between hard and soft is less.

Finally, it should also be pointed out that even commercial AC can encounter birds at high speed including speeds over 600mph as there are instances where birds have been known to fly as high as 37000 feet and those birds tend to be quite large.

Oh, and I do understand Physics pretty well. In summary, as speed increases the difference between hard and soft diminishes, you even admit that, and yet you claim I know not what I'm saying. Your final point focused on the relatively weak radome but ignored the two metal bulkheads -- looks like an unscientific effort at cherry-picking to me.


Brian

You are not arguing science - you are arguing anecdotes. Your statement that the difference between hard and soft objects (in lay terms) decreases with impact velocity is true, but the difference is still huge for the velocities in question. I was disputing two claims that you made, first in post #63 - that any research/testing uses frozen birds and second, in post #66, that a frozen bird is of any use even as a worst-case test.

I've not seen any USAF reports, or any other reports at all, on the use of frozen birds. It's all anecdotal. I can tell you that all testing I've seen uses thawed birds or mechanical mocks - surrogates with approximately appropriate mechanical properties at the impact velocities involved, such as the gel bird in the Dayton test. And, as I said, it would make no sense, even as a worst-case test, to use frozen birds because it is much worse than a worst-case test - it's a different physical regime. It's like arguing that a steel projectile would be a worst-case test - it's simply not correct.

The two reasons for convergence of the physics at higher impact velocities are, firstly, strain-rate-dependent strength - (the effect where as you deform a solid faster it's modulus increases due to visco-plastic processes) and, secondly, at much high velocities, hydrodynamic considerations (where the material strength is immediately swamped by the impact stresses and it behaves as a liquid). Chickens don't exhibit much visco-plasticity - they already basically behave like bags of low-density liquid, but we are well below the hydrodynamic regime for frozen chickens because the targets will not support high enough impact stresses. So the frozen chicken impact is in the strength-dominated regime while the thawed chicken impact is mostly hydrodynamic - different mechanisms, not just one is a bit worse than the other.

And, as I said, your example with the F-4 is fascinating, but says nothing about the comparison of a frozen vs. unfrozen bird, because it is only an example of a what an unfrozen bird can do. How on earth do you see that as indicating that a frozen bird would not be far worse? Without knowing the engineering details of the aircraft, if the bird made it through the dome and two bulkheads, I would expect the frozen version to penetrate all the bulkheads and keep going.

This is one of the fields (impact/terminal ballistics, not windshield testing) that I've worked in, published on, and taught, for a long time. The physics involved is not particularly intuitive and until you have studied it somewhat rigorously you are not going to understand it. If you choose to believe your inaccurate picture of this as actual physics then fine - your choice and I can't help you any further.

 

[Raptorman0909]

You are not arguing science - you are arguing anecdotes. Your statement that the difference between hard and soft objects (in lay terms) decreases with impact velocity is true, but the difference is still huge for the velocities in question. I was disputing two claims that you made, first in post #63 - that any research/testing uses frozen birds and second, in post #66, that a frozen bird is of any use even as a worst-case test.

I've not seen any USAF reports, or any other reports at all, on the use of frozen birds. It's all anecdotal. I can tell you that all testing I've seen uses thawed birds or mechanical mocks - surrogates with approximately appropriate mechanical properties at the impact velocities involved, such as the gel bird in the Dayton test. And, as I said, it would make no sense, even as a worst-case test, to use frozen birds because it is much worse than a worst-case test - it's a different physical regime. It's like arguing that a steel projectile would be a worst-case test - it's simply not correct.

The two reasons for convergence of the physics at higher impact velocities are, firstly, strain-rate-dependent strength - (the effect where as you deform a solid faster it's modulus increases due to visco-plastic processes) and, secondly, at much high velocities, hydrodynamic considerations (where the material strength is immediately swamped by the impact stresses and it behaves as a liquid). Chickens don't exhibit much visco-plasticity - they already basically behave like bags of low-density liquid, but we are well below the hydrodynamic regime for frozen chickens because the targets will not support high enough impact stresses. So the frozen chicken impact is in the strength-dominated regime while the thawed chicken impact is mostly hydrodynamic - different mechanisms, not just one is a bit worse than the other.

And, as I said, your example with the F-4 is fascinating, but says nothing about the comparison of a frozen vs. unfrozen bird, because it is only an example of a what an unfrozen bird can do. How on earth do you see that as indicating that a frozen bird would not be far worse? Without knowing the engineering details of the aircraft, if the bird made it through the dome and two bulkheads, I would expect the frozen version to penetrate all the bulkheads and keep going.

This is one of the fields (impact/terminal ballistics, not windshield testing) that I've worked in, published on, and taught, for a long time. The physics involved is not particularly intuitive and until you have studied it somewhat rigorously you are not going to understand it. If you choose to believe your inaccurate picture of this as actual physics then fine - your choice and I can't help you any further.

I'm not arguing that a hard object and a soft object are the same but that as velocity increases the difference decreases -- I've been saying this from the beginning. In your previous post you fixated on the relatively weak radome and completely ignored the two metal bulkheads and I rightly called you out for the unscientific approach taken in that regard. In addition you somewhat reluctantly agree that at higher speeds the difference is less. I didn't attempt to quantify this by implying that at some given speed a frozen chicken and a thawed chicken are the same though at really high speeds the kinetic energy involved dominates and the equation for that doesn't include hardness.

So, in summary we can agree that hard is hard and soft is soft and that at relatively slower speeds the difference in significant but at higher speeds the difference is less significant -- I've not implied anything else. It would have been nice if you hadn't played the cherry-picking game in your prior when fixating on the radome and ignoring the two metal bulkheads. I have no idea why you would have done that other than to be deceptive.

I don't know that there's much more to add to the discussion, the facts about frozen versus thawed appear uncertain with the article in question (Snopes) seeming to answer it both ways -- it can't be both. Short of a technical paper from the USAF that states they've never used frozen birds I guess we'll never know for sure. But, if you have a source that puts the question to bed about frozen birds ever being used I'm all ears.


Brian

 

[sar104]

I'm not arguing that a hard object and a soft object are the same but that as velocity increases the difference decreases -- I've been saying this from the beginning. In your previous post you fixated on the relatively weak radome and completely ignored the two metal bulkheads and I rightly called you out for the unscientific approach taken in that regard. In addition you somewhat reluctantly agree that at higher speeds the difference is less. I didn't attempt to quantify this by implying that at some given speed a frozen chicken and a thawed chicken are the same though at really high speeds the kinetic energy involved dominates and the equation for that doesn't include hardness.

So, in summary we can agree that hard is hard and soft is soft and that at relatively slower speeds the difference in significant but at higher speeds the difference is less significant -- I've not implied anything else. It would have been nice if you hadn't played the cherry-picking game in your prior when fixating on the radome and ignoring the two metal bulkheads. I have no idea why you would have done that other than to be deceptive.

I don't know that there's much more to add to the discussion, the facts about frozen versus thawed appear uncertain with the article in question (Snopes) seeming to answer it both ways -- it can't be both. Short of a technical paper from the USAF that states they've never used frozen birds I guess we'll never know for sure. But, if you have a source that puts the question to bed about frozen birds ever being used I'm all ears.


Brian

That's now two detailed explanations that you have either completely ignored or not understood at all. As I said, I can't help you any further.

 

[alexanderpetrex]

Breaking News: DJI Demands Withdrawal of Drone Crash Video,,,,I know this story was shown early but breaking news Alert just came in saying they want this withdrawn
Ummmmmmm wonder what goes on

I think it just for sake of publicity