6 ms·

I'm not an aviation expert, but it's not implausible to me that the propeller is fragile enough to get bent by a stream of jet fuel traveling at fighter-jet spe

I'm not an aviation expert, but it's not implausible to me that the propeller is fragile enough to get bent by a stream of jet fuel traveling at fighter-jet speeds. On the contrary, a mid-air collision that just bends a couple of propeller blades and not the rest of the drone seems like either incredible flying or incredible luck.

t0mas88 4y ago
Propellers are quite fragile things. If you hit a traffic cone with one on a small trainer aircraft, it's unairworthy immediately and requires an inspection of the propeller and engine.
Symbiote 4y ago
It's not a "fighter jet speed" collision, since the drone is travelling at drone speed. It's the difference, which seems fairly small. The US military said there was a collision, and with this video there seems no reason to doubt them. https://www.eucom.mil/pressrelease/42314/russian-aircraft-collides-into-us-unmanned-system-in-international-waters https://www.eucom.mil/pressrelease/42314/russian-aircraft-co...
guenthert 4y ago
Well, to this non-aviator, the flying as shown is immensely impressive. I mean, a jet approaching a drone heads-on and turning a few yards away? Russian military might not be all that popular on the english speaking internet at this time, but credit were credit is due -- mad respect for that pilot's skill.
- mint2 4y ago
  It’s not head on, the jet is already turned to pull away but the pilot either misjudged distance a bit or intentionally did it. Because they’re pulling away the collision is at a low relative velocity
- chiph 4y ago
  It's not head-on. The MQ-9 is a pusher-prop design (the prop is in the rear), so both aircraft were flying in the same direction. If there had been a direct collision, the impact velocity would have been the difference between them, not addition.
  - guenthert 4y ago
    Ah, right, thanks.
stonogo 4y ago
The idea of fuel bending a propeller blade would to me imply that the drone cannot survivie e.g. rain. This doesn't seem intuitive. However, jets making closer and closer passes while trying to foul the sensors with fuel dumps, culminating in one pass that is so close contact is made, seems more likely. You say "bends a couple of propeller blades and not the rest of the drone" but there's no telling whether contact was made with the drone airframe. We don't get a look at the Russian airframe either (to look for impact marks). The MQ-9 vertical stabilizers are "taller" than the propeller blades. I wonder if the Russian craft struck those, and the propeller was damaged by jet exhaust as the Su-27 pulled away.
- throwaheyy 4y ago
  It’s entirely possible the propeller would be not damaged by rain but would still be damaged by a much larger “glob” of fuel.
chiph 4y ago
Fuel is less dense than water (.8025 g/ml vs. 1.0) and the MQ-9 is designed to fly in all weather conditions. So it's highly unlikely the fuel bent the tip of the prop. Given that just one blade is bent, the contact had to be very fleeting (there wasn't time for the next blade to come around and also strike the Su-27). It's bad luck on the Russian pilot's part to cause something undeniable like this - but this isn't stopping Moscow from making obviously untrue claims. Cold-war story time. In college I had a roommate who was former Navy, and he told me of the time that they pranked the Soviets. Their group of ships had been shadowed by a Soviet "fishing vessel"[0] and they had gotten tired of them stooging around. At the time it was normal for ships to dump their trash overboard [1] in weighted bags. So they prepared a bag by filling it with the 80's best "adult education material" - only with all the good parts cut out and various insults scribbled on the pages. And topped it off with the messiest of slops from the galley. They intentionally did not add the steel weight, and tossed it off the stern. A gleeful crowd gathered to watch as the Soviets swooped in to collect their floating "intelligence haul". Moral of the story - pranking is one thing. Intentionally or accidentally causing a collision? Not cool. [0] Probably one of these: https://en.wikipedia.org/wiki/Primor%27ye-class_surveillance_ship https://en.wikipedia.org/wiki/Primor%27ye-class_surveillance... [1] They now compress and store most waste until they return to port: https://www.youtube.com/watch?v=lpFF6c3C730 https://www.youtube.com/watch?v=lpFF6c3C730
- 2OEH8eoCRo0 4y ago
  My father tells almost the same story of dumping their porno mags in the garbage for the trailing Russkies to retrieve. Mediterranean float, late 80s, USS Inchon I believe. He also spent time in Iceland watching for Spetsnaz.
- reaperducer 4y ago
  Fuel is less dense than water (.8025 g/ml vs. 1.0) and the MQ-9 is designed to fly in all weather conditions. So it's highly unlikely the fuel bent the tip of the prop. Rain does't hurt. Getting nailed in the head with a water balloon hurts. The density of rain and the density of a fuel dump are not equivalent.
- sudosysgen 4y ago
wrp 4y ago
There are some attempts to do the math on whether just the fuel could have done it in the comments to this video (https://www.youtube.com/watch?v=UVzLV-R_-kk https://www.youtube.com/watch?v=UVzLV-R_-kk). Example: The thrust from a propeller blade is typically proportional to the density of the medium it is operating in (plus other factors of course). The density of air at altitude will be somewhat less than 1 kg/m^3. Density of pure liquid kerosene is around 800 kg/m^3, but in this case the kerosene is dispersed as droplets in the air. If we take a hypothetical guess that the air/fuel mixture is around 25% fuel, 75% air, the net density of the mixture will be around 200 kg/m^3. On encountering the fuel mixture of this density, the propeller blade would experience a sudden increase in load by a factor of about 200. A sudden overload of this magnitude would be enough to bend most things. Of course we don't know the actual air/fuel ratio. It could be less or could be more. The velocity of the dumped fuel relative to the drone's airspeed could also be significant. Too many unknowns to be anything like accurate, but appears not impossible for a fuel cloud to bend a propeller blade.
mzs 4y ago
It's not just bent, one blade is even broken in half and what remains is bent the way it would be if it had hit the jet.

t0mas88 4y ago

Propellers are quite fragile things. If you hit a traffic cone with one on a small trainer aircraft, it's unairworthy immediately and requires an inspection of the propeller and engine.

Symbiote 4y ago

It's not a "fighter jet speed" collision, since the drone is travelling at drone speed. It's the difference, which seems fairly small. The US military said there was a collision, and with this video there seems no reason to doubt them. https://www.eucom.mil/pressrelease/42314/russian-aircraft-collides-into-us-unmanned-system-in-international-waters https://www.eucom.mil/pressrelease/42314/russian-aircraft-co...

guenthert 4y ago

Well, to this non-aviator, the flying as shown is immensely impressive. I mean, a jet approaching a drone heads-on and turning a few yards away? Russian military might not be all that popular on the english speaking internet at this time, but credit were credit is due -- mad respect for that pilot's skill.

mint2 4y ago
It’s not head on, the jet is already turned to pull away but the pilot either misjudged distance a bit or intentionally did it. Because they’re pulling away the collision is at a low relative velocity
chiph 4y ago
It's not head-on. The MQ-9 is a pusher-prop design (the prop is in the rear), so both aircraft were flying in the same direction. If there had been a direct collision, the impact velocity would have been the difference between them, not addition.
- guenthert 4y ago
  Ah, right, thanks.

stonogo 4y ago

The idea of fuel bending a propeller blade would to me imply that the drone cannot survivie e.g. rain. This doesn't seem intuitive. However, jets making closer and closer passes while trying to foul the sensors with fuel dumps, culminating in one pass that is so close contact is made, seems more likely. You say "bends a couple of propeller blades and not the rest of the drone" but there's no telling whether contact was made with the drone airframe. We don't get a look at the Russian airframe either (to look for impact marks). The MQ-9 vertical stabilizers are "taller" than the propeller blades. I wonder if the Russian craft struck those, and the propeller was damaged by jet exhaust as the Su-27 pulled away.

throwaheyy 4y ago
It’s entirely possible the propeller would be not damaged by rain but would still be damaged by a much larger “glob” of fuel.

chiph 4y ago

Fuel is less dense than water (.8025 g/ml vs. 1.0) and the MQ-9 is designed to fly in all weather conditions. So it's highly unlikely the fuel bent the tip of the prop. Given that just one blade is bent, the contact had to be very fleeting (there wasn't time for the next blade to come around and also strike the Su-27). It's bad luck on the Russian pilot's part to cause something undeniable like this - but this isn't stopping Moscow from making obviously untrue claims. Cold-war story time. In college I had a roommate who was former Navy, and he told me of the time that they pranked the Soviets. Their group of ships had been shadowed by a Soviet "fishing vessel"[0] and they had gotten tired of them stooging around. At the time it was normal for ships to dump their trash overboard [1] in weighted bags. So they prepared a bag by filling it with the 80's best "adult education material" - only with all the good parts cut out and various insults scribbled on the pages. And topped it off with the messiest of slops from the galley. They intentionally did not add the steel weight, and tossed it off the stern. A gleeful crowd gathered to watch as the Soviets swooped in to collect their floating "intelligence haul". Moral of the story - pranking is one thing. Intentionally or accidentally causing a collision? Not cool. [0] Probably one of these: https://en.wikipedia.org/wiki/Primor%27ye-class_surveillance_ship https://en.wikipedia.org/wiki/Primor%27ye-class_surveillance... [1] They now compress and store most waste until they return to port: https://www.youtube.com/watch?v=lpFF6c3C730 https://www.youtube.com/watch?v=lpFF6c3C730

2OEH8eoCRo0 4y ago
My father tells almost the same story of dumping their porno mags in the garbage for the trailing Russkies to retrieve. Mediterranean float, late 80s, USS Inchon I believe. He also spent time in Iceland watching for Spetsnaz.
reaperducer 4y ago
Fuel is less dense than water (.8025 g/ml vs. 1.0) and the MQ-9 is designed to fly in all weather conditions. So it's highly unlikely the fuel bent the tip of the prop. Rain does't hurt. Getting nailed in the head with a water balloon hurts. The density of rain and the density of a fuel dump are not equivalent.
sudosysgen 4y ago

wrp 4y ago

There are some attempts to do the math on whether just the fuel could have done it in the comments to this video (https://www.youtube.com/watch?v=UVzLV-R_-kk https://www.youtube.com/watch?v=UVzLV-R_-kk). Example: The thrust from a propeller blade is typically proportional to the density of the medium it is operating in (plus other factors of course). The density of air at altitude will be somewhat less than 1 kg/m^3. Density of pure liquid kerosene is around 800 kg/m^3, but in this case the kerosene is dispersed as droplets in the air. If we take a hypothetical guess that the air/fuel mixture is around 25% fuel, 75% air, the net density of the mixture will be around 200 kg/m^3. On encountering the fuel mixture of this density, the propeller blade would experience a sudden increase in load by a factor of about 200. A sudden overload of this magnitude would be enough to bend most things. Of course we don't know the actual air/fuel ratio. It could be less or could be more. The velocity of the dumped fuel relative to the drone's airspeed could also be significant. Too many unknowns to be anything like accurate, but appears not impossible for a fuel cloud to bend a propeller blade.

mzs 4y ago

It's not just bent, one blade is even broken in half and what remains is bent the way it would be if it had hit the jet.