[toss1]

It could be interesting that the 4-6 rotor configuration, range/time of around and hour and 50mi, and the 14,000ft+ performance strongly indicate a fuel-powered device, but that the night vision goggles couldn't see it. It didn't indicate if the NVGs were of the ambient-light-enhancing type or IR type.

This probably tells us that the NVGs were the ambient-light-enhancing type as there would be very little ambient reflective light up there (considering it was last seen flying up into an overcast), and IR NVGs would probably pickup some image from the heat of the rotor motors even on a battery-only device, and any un-stealthed exhaust would glow like a spotlight.

Still, it'd be good to know what device they were using.

I also have to wonder why it flew so close to the police helicopter... and then over the AFB deep into a Class C airspace. Seems too deliberate, trying to get attention, not avoid it.

I've been involved in designing & building gasoline-powered drones, and that range & flight time is very doable. But the performance indicates sophisticated control links and so this is very likely more than just a casual wealthy hobbyist idiot. The NatSec implications are very serious, and at least it appears that they're paying attention to it.

[juancb]

You're overlooking one critical point in your deduction about type of NVGs used. The drone was visible with the naked eye due to a green position light, which should have been enhanced and been visible under through the night vision goggles. The article says the drone was last seen entering IMC at 14,000MSL while the helicopter's ADS-B track shows it reached 12,000MSL which means the helicopter could see the light at least 2,000 feet away, which suggests a bright light that should have been visible through light amplification.

It's more likely that the night vision device was either malfunctioning or pilot error made its use ineffective.

[toss1]

excellent point - I had a nagging thought about that, but just figured the LED had turned off when it started to evade?

But yes, NVD malfunction could be a possibility.

The other possibility is that it was and IR NVG, and the device is very well heat-shielded, which puts it in an entirely different class...

[bombcar]

Would it be possible to have a gas-powered drone that has some amount of time it can run on batteries? I'm thinking similar to the old diesel submarines that would go on battery when they wanted to be stealthy.

[toss1]

Yup, lightweight, high-powered gasoline engine, powering a generator, the output hooks into the regular battery and ESC (Electronic Speed Controller) loop. All the rest of the control is the same

The benefit is the energy density of petrol is ~2500Wh/kg, vs about 250Wh/kg for Li-Ion batteries. This is significantly offset by the weight of the ICE engine & generator, but it is still enough to get very good flight times. It is enough to do using selected off-the-shelf components, but to get really outstanding results, everything needs to be optimized for excellent power-weight ratios.

Two big ones in that space, going back-&-forth and beating each others' records are:

Skyfront: www.skyfront.com https://www.youtube.com/watch?v=KXFoBUR_jqY

Quaternium: https://www.quaternium.com/ https://www.youtube.com/watch?v=cvBjCejUmvY

And yes, at least the units we built had significant batteries in the loop. The main purpose was to be able to land if the ICE engine/generator failed, but also could be used for a less-noisy mode ("quiet mode" is a bit much for most multirotors, as the rotors themselves are quite noisy).

[jonfw]

The least sophisticated way to engineer a drone like this would be to use a consumer grade heavy lift electric drone with an onboard generator and fuel source to charge the batteries

[C19is20]

Gas, gas? Or American Freedom Juice cough?

[matheweis]

Yea, I’ve also built largish drones that could easily get close to these specs - sans endurance and control, and this was years ago.

These days they have off the shelf LTE modems that can stream both video and telemetry, and it sounds like you’re saying endurance is also a solved problem.

This really doesn’t seem like it would take nation state investment.

I’d just like to think any hobbyist capable of getting one of these off the ground would avoid airports and tangling with police helos…

[HideousKojima]

I thought gas didn't really work with quad/hexa/octorotors because gas motors can't cycle up and down as quickly and reliably as electric, and fine-tuned control of rotor speed is essential to how a quadrotor works

EDIT: nope I'm stupid

[spoonjim]

A fuel powered drone uses collective pitch propellers. The blades all spin at fixed RPM but the angle of the blades on each propeller can be adjusted individually with a servo. It actually far outperforms electric motors in maneuverability.

[toss1]

there are a few examples of those, but they are pretty much one-offs. This is mostly because one blade pitch mechanism is messy enough with a helicopter, 4-8 with a multi-rotor is just too many critical moving parts to be effective.

Most of the fuel powered drones will be basically an internal combustion engine powering a generator, which then feeds into the regular battery & ESC circuits (that's the type of machine I was working on).

EDIT: Also important is that much of the yaw control of multirotor drones is done by changing individual rotor speeds to create a net yaw reaction from the acceleration/deceleration of the rotors. With constant-RPM motors, that goes away, along with a lot of yaw control authority.

[postalrat]

It could either be a hybrid with the engine running a generator or use variable pitch props.