Drone damage to airplanes?
- Thread starter JY-tek
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brett8883
Well-Known Member
Nobody is suggesting that a drone collision wouldn’t cause major damage.
However, there are specific requirements of any scientific inquiry that were not satisfied with this particular test. A scientific experiment must be replicable and available for peer review. “A scientific hypothesis or statement is generally not accepted by the academic community unless it has been published in a peer-reviewed journal [Peer Review in Scientific Publications: Benefits, Critiques, & A Survival Guide]. I’m less concerned about it being in a scientific journal as I am having some kind of documentation about the aircraft used and the methodology.
They state this is a Mooney M20 full stop. There have been others who argue that there are variants of the Mooney M20 that can reach 200mph+ which is true but the FAA has only certified ONE aircraft called “Mooney M20” and it has a Do Not Exceed speed of 164 Knots (188.72mph) and max cruising structural speed of 130 Knots (149mph).
FAA explains Do not exceed speed as
“This one is easy – “never exceed” means exactly what it says. It is an absolute limit, and you should never, ever operate as if there were a “buffer” beyond this speed. Such assumptions are likely to result in structural failure.” [https://www.faasafety.gov/files/notices/2015/Nov/V_Speed_Review.pdf]
So if the test was done under conditions that exceed the structural integrity of the aircraft then it should be no surprise that it resulted in structural damage. Maybe they should have shot just the compressed air at it and the same result would have happened? I don’t know ?
If they used a different aircraft then they should have said the correct aircraft that was used or clarified after the issue was brought up publicly by DJI. I’m not aware of any attempts to correct or clarify the type of aircraft used.
If someone intends to refute anything in this post that’s fine but please use references like I did so we can have a scholarly conversation. If you are an expert in these matters then great it won’t be hard for you to find resources backing your argument.
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brett8883
Well-Known Member
I have a technical question and this is that, a question, because I don’t know the answer and should not be taken as a suggestion.
They stated that the used the impact speed of 235mph to simulate a head on collision between a drone going 35mph and a plane going 200mph. To simulate this they shot a drone at a stationary plane wing at 235mph. ?
But in this experiment with the wing bolted to the floor doesn’t that change the impact energy of the system? They have made this a perfectly inelastic collision meaning that the plane and the drone will absorb all of the Kinetic energy into their molecules and both the drone AND the plane come to a complete stop after the test. However, in a real collision the airplane would continue flying in the same direction and would have its momentum reduced by the impact force of the drone minus the kenetic energy absorbed by the structural change of the plane, an elastic collision.
What I mean is that we know if two planes collide in a head on collision at 200 mph the force exerted on the two planes is the same as if each planes hit a brick wall at 200 MPH not 400mph because it is an inelastic collision, both planes come to a complete stop.
So why is it that in a head on collision with a drone and a plane where both the plane and the drone come to a complete stop after the test do we add the speeds together to get to a greater speed then when two planes of the same mass collide? Again might have this wrong but this is where my mythbusters antenna went up
They stated that the used the impact speed of 235mph to simulate a head on collision between a drone going 35mph and a plane going 200mph. To simulate this they shot a drone at a stationary plane wing at 235mph. ?
But in this experiment with the wing bolted to the floor doesn’t that change the impact energy of the system? They have made this a perfectly inelastic collision meaning that the plane and the drone will absorb all of the Kinetic energy into their molecules and both the drone AND the plane come to a complete stop after the test. However, in a real collision the airplane would continue flying in the same direction and would have its momentum reduced by the impact force of the drone minus the kenetic energy absorbed by the structural change of the plane, an elastic collision.
What I mean is that we know if two planes collide in a head on collision at 200 mph the force exerted on the two planes is the same as if each planes hit a brick wall at 200 MPH not 400mph because it is an inelastic collision, both planes come to a complete stop.
So why is it that in a head on collision with a drone and a plane where both the plane and the drone come to a complete stop after the test do we add the speeds together to get to a greater speed then when two planes of the same mass collide? Again might have this wrong but this is where my mythbusters antenna went up
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Do you apply this level of seeming intended scientific rigour in all circumstances or only when you might be seen to have entangled yourself in your own fallacious reasoning?Nobody is suggesting that a drone collision wouldn’t cause major damage.
However, there are specific requirements of any scientific inquiry that were not satisfied with this particular test. A scientific experiment must be replicable and available for peer review. “A scientific hypothesis or statement is generally not accepted by the academic community unless it has been published in a peer-reviewed journal [Peer Review in Scientific Publications: Benefits, Critiques, & A Survival Guide]. I’m less concerned about it being in a scientific journal as I am having some kind of documentation about the aircraft used and the methodology.
They state this is a Mooney M20 full stop. There have been others who argue that there are variants of the Mooney M20 that can reach 200mph+ which is true but the FAA has only certified ONE aircraft called “Mooney M20” and it has a Do Not Exceed speed of 164 Knots (188.72mph) and max cruising structural speed of 130 Knots (149mph). View attachment 74920
FAA explains Do not exceed speed as
“This one is easy – “never exceed” means exactly what it says. It is an absolute limit, and you should never, ever operate as if there were a “buffer” beyond this speed. Such assumptions are likely to result in structural failure.” [https://www.faasafety.gov/files/notices/2015/Nov/V_Speed_Review.pdf]
So if the test was done under conditions that exceed the structural integrity of the aircraft then it should be no surprise that it resulted in structural damage. Maybe they should have shot just the compressed air at it and the same result would have happened? I don’t know ?
If they used a different aircraft then they should have said the correct aircraft that was used or clarified after the issue was brought up publicly by DJI. I’m not aware of any attempts to correct or clarify the type of aircraft used.
If someone intends to refute anything in this post that’s fine but please use references like I did so we can have a scholarly conversation. If you are an expert in these matters then great it won’t be hard for you to find resources backing your argument.
The claim you were making is that “if the University wanted to conduct an actual scientific test they would have conducted the test under realistic circumstances and published the testing methodology. In other words this is fake news”. That is a patent absurdity.
The test is, as had been pointed out by @sar104 able to be performed by any entity with the appropriate equipment and instrumentation and the conditions modified to demonstrate real world expected outcome for any sUAV and airframe.
The take home from the test is that a sUAV will likely pose a greater thread to a full scale aircraft than a bird of similar mass- the consequences are obvious.
brett8883
Well-Known Member
Good points you are right I probably wouldn’t apply the same kind of rigor. I agree that in all likelihood a drone would cause significant damage to an aircraft even at 130 Knots.
But I don’t apologize for being critical. That’s an important part of science. If there is good reason for modifying the parameters of the experiment then fine but you have to explain that.
Now since I wanted to educate myself because I find it interesting and the University doesn’t want to share their research I’ve done some research of my own and found some interesting things.
This website has been helpful Impulse of Force
I found this site that has the math for a collision with a bird and an airplane and yes it appears a rigid body will have a significant effect on impact force do to decreased impact time.
I assume this is also why a head-on collision with the drone moving toward the aircraft makes such a big difference? Because it reduces impact time? According to this calculator which we’ll just use as reference since we don’t have the resources to test it ourselves shows that an aircraft traveling at 200mph hitting a 2lb bird would experience a 2.72 ton force. The same plane traveling at 235 mph hitting the same bird would experience 3.75 ton force a 38% increase in force for only a 17.5% increase in speed.
At the Mooney M20’s listed max cruising speed of 130 Knots +the phantoms cited top speed of 33 Knots=163 knots (187.5mph) the resulting theoretical impact force would 2.39 tons a 57% difference in impact force.
Now I’m no physicist keep in mind but if my math above is correct then it seems a tad bit more then an adjustment. But it does shows just how important the speed of the aircraft makes on the force of the impact.
Critical thinking is the starting position that should be applauded and embraced (particularity compared to fake news allegations). Willingness to attempt accept when we are wrong and increasing our knowledge as a result rather than preferring gut feeling over what we don’t understand must be preferable.
Maybe SAR might come back here and help with the physics of the resultant impact. If memory serves correctly he did go into some detail in an earlier related thread. The fact the wing is stationary for the test had little significance to the frame of references
You need to get your head around frames of reference, because otherwise this is going to remain a complete mystery to you. All non-relativistic velocity frames of reference are completely equivalent. What that means is that it doesn't matter what the velocities of the drone and wing are in the lab frame of reference - all that matters from an impact point of view is their relative velocity. Your "mythbusters" antenna is worthless, and I'm disappointed to learn that you really think that your simplistic understanding of this process is better than that of a team of experienced, qualified, terminal ballistics physicists.
"Elastic" and "inelastic", which refer to the degree to which kinetic energy is conserved in the collision. This is an inelastic collision because the final velocity of the drone and aircraft wing are the same. A fully elastic collision would lead to the drone bouncing off the wing with the opposite relative velocity after the collision. What is always fully conserved is momentum, and you need to look at that rather than kinetic energy. The symmetric case of two similar objects colliding at 200 mph is equivalent to one of those objects colliding with a rigid boundary (aka immovable object) at 200 mph. Note that a brick wall is not remotely an immovable object in that sense. In this case the wing and the drone are approximately stationary in the lab frame of reference after the collision because the aircraft is massive compared to the drone. To translate that to the more likely earth frame of reference, with a stationary drone and a moving aircraft, that's equivalent to observing that the velocity of the aircraft is almost unchanged after the impact with the drone, because the momentum of the drone, which was zero before impact, is still negligible after impact compared to the total momentum of the system. If you were on that aircraft, do you think that you would even notice the deceleration in that impact. The M20 total mass is around 1500 kg. The Phantom is about 1.5 kg. In an inelastic collision between them at 240 mph, the change in velocity of the aircraft will be 0.24 mph.
Nobody is suggesting that a drone collision wouldn’t cause major damage.
However, there are specific requirements of any scientific inquiry that were not satisfied with this particular test. A scientific experiment must be replicable and available for peer review. “A scientific hypothesis or statement is generally not accepted by the academic community unless it has been published in a peer-reviewed journal [Peer Review in Scientific Publications: Benefits, Critiques, & A Survival Guide]. I’m less concerned about it being in a scientific journal as I am having some kind of documentation about the aircraft used and the methodology.
They state this is a Mooney M20 full stop. There have been others who argue that there are variants of the Mooney M20 that can reach 200mph+ which is true but the FAA has only certified ONE aircraft called “Mooney M20” and it has a Do Not Exceed speed of 164 Knots (188.72mph) and max cruising structural speed of 130 Knots (149mph). View attachment 74920
FAA explains Do not exceed speed as
“This one is easy – “never exceed” means exactly what it says. It is an absolute limit, and you should never, ever operate as if there were a “buffer” beyond this speed. Such assumptions are likely to result in structural failure.” [https://www.faasafety.gov/files/notices/2015/Nov/V_Speed_Review.pdf]
So if the test was done under conditions that exceed the structural integrity of the aircraft then it should be no surprise that it resulted in structural damage. Maybe they should have shot just the compressed air at it and the same result would have happened? I don’t know ?
If they used a different aircraft then they should have said the correct aircraft that was used or clarified after the issue was brought up publicly by DJI. I’m not aware of any attempts to correct or clarify the type of aircraft used.
If someone intends to refute anything in this post that’s fine but please use references like I did so we can have a scholarly conversation. If you are an expert in these matters then great it won’t be hard for you to find resources backing your argument.
Where do you get this nonsense from? Even the most cursory search would reveal to you the specifications of multiple variants of the M20, with cruising speeds up to 240 knots. They are all FAA certified.
brett8883
Well-Known Member
So if you did a collision test on a 737 max would you put in your report that you did a collision test on a 737? Is that industry standard??
A Drone for domestic hobby flying will NEVER EVER effects any commercial airplanes. because they are flying deferent levels high. The only danger would happen when an airplane went to lending your head when you enjoy fly your drone in park or a yards. there is an aeroplane want to that park or yards then batter you run away for that aeroplane.
I can see that you are trying to drag this discussion so far down into the weeds that the big picture gets completely lost, but I still don't understand why. You have attempted to discredit this test from almost every perspective imaginable, from motive to funding source to researcher qualifications, with a few attempts to massacre basic physics thrown in. And as each argument gets knocked down you don't even acknowledge it, and instead move straight on to more and more desperate lines of attack. I'm not really interested in this kind of war of attrition.
This was a simple engineering test to illustrate the comparative damage caused by a small drone vs. a bird of similar mass against a GA wing and to demonstrate a testing capability. A normal, reasonable person might have welcomed such a test, especially in view of all the opinions asserted here and elsewhere that drones would cause no more damage than birds, or that drones would just bounce off aircraft structures etc., - i.e. mechanical properties don't matter at these speeds. The impact speed chosen was at the upper end of (but still within) the possible range for the type of aircraft, a standard approach in safety testing if you are not doing a full parametric study to find a damage threshold, for example. It was not an aircraft certification test. It did not need pedigreed airframe components any more than it needed NIST-certified diagnostics.
The result of the test validated the purpose. It demonstrated that the denser, more rigid structure of the drone caused more penetrating structural damage to the airframe's load-bearing components. That it would do that was trivially obvious to anyone with a background in one of these technical fields, but it seemed like it needed demonstrating. DJI didn't like it, of course, because they used a Phantom. And others, such as yourself, took what looks bizarrely like personal offense, creating ever more contrived reasons to dismiss the result, all dressed up as some kind of concern trolling for the purity of scientific method. As much as I feel it is important to refute misinformation here, especially related to science, you have exhausted me on this one, mostly because you don't seem interested in a discussion to arrive at an answer - just in winning a battle.
Dragonfly
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The aircraft wing used was from a small twin seater that has a cruise speed of 13 knots. The drone was fired at the wing at higher velocity speeds than even commercial aircraft fly at into this small low structal leading edge wing that they portrayed as a commercial airliner wing. The data was disproved by many authorities, DJI used the credibility of those authorities to have the video disclaimed.
Disregarding the obvious typo - are you really trying to claim that 240 mph is faster than commercial airliners? It's not even faster than the cruise speed of the higher-end M20 variants. And what do you mean by "the data was disproved"? What data was disproved? And by which "authorities"?
FoxhallGH
Well-Known Member
An added point to make here ... As mentioned in responses to @brett8883 above - the immediate effect of the impact is not changed by 'firing' a high-speed drone at a stationary wing. However, what is missing is that in a real-world scenario, the wing would be continuing to try to fly at 200 mph, and the effects of the airflow on the damaged portion of the wing could be catastrophic! It could lead to the skin of the wing popping rivets and peeling off, and/or a failure of the main-spar. The point I'm trying to make is that the damage and problem is not limited to the time and point of impact! I've had a couple of occasions where I had near-miss issues while training for my Private Pilot License ... Thankfully, both of them were over in seconds and the aircraft was 100% intact afterward and I knew I'd get back OK. I would not wish it on my worst enemy to have them go through an impact situation where afterward, every second, they were wondering if they were going to be able to get back to the ground before something vital fell off their plane!
Thankfully, we don't have real-world video's of actual drone strikes on aircraft, but there are a lot of videos out there showing bird-strike damage, and the consequence of the damage. You don't have to be very imaginative to replace the soft gooey bird with a hard LiPo battery and see that the damage would be the same or worse.
Aviation Safety is about minimising risk. The CAA / FAA etc. can't regulate birds, but they certainly can regulate drone operators.
Earthman
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Have you done any research on this on your own? There are many variations of the aircraft that the wing came from. Just take a moment to look at this post (in this very thread):
Drone damage to airplanes?
I think it’s as much what they don’t show as what they do show. According to the original “blog” Risk in the Sky? : University of Dayton, Ohio by the University the purpose of the test was “to compare a bird strike and a drone strike, using a drone similar in weight to many hobby drones and a...
mavicpilots.com
Also keep in mind this was merely a "Common Representative" aircraft that could be expected to be operating at "Possible Drone Flying Areas" and not just super sonic aircraft that would only be found at insanely high flight levels.
Please provide credible links to support this claim. And I wouldn't include DJI or their lame attempt (And very inaccurate much like your claim above) to discredit it. They have a vested interest in covering up the fact a Phantom could do damage to an airplane.
Tom-Air
Well-Known Member
I know they shoot frozen chicken into the bigger jet engines when testing for damage. It just chops it up and spits it out the back. Smaller planes like Cessna's no doubt would do prop, wing or fuselage damage.
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