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> Presumably bleed air from the jet engine compressor. We don't know that and this is the very first prototype so it could absolutely evolve over time. > Whic

> Presumably bleed air from the jet engine compressor. We don't know that and this is the very first prototype so it could absolutely evolve over time. > Which means this design won't work for piston engine propeller drones In its current, nascent configuration where we are prototyping a new technology using a testbed platform, maybe. Again, this is not a commercial-ready product it's a prototype. > Which is the usual configuration for small non-stealth drones So this prototype doesn't fit on a $10 quad copter so it's... Flawed? > I wonder where in the copyediting process this got left out Prototype. > Because otherwise this design would be bonkers. More or less bonkers than dismissing a completely novel aviation technology before it's even gotten off the ground? More or less bonkers than dismissing a completely novel technology because it doesn't work for your one specific hypothetical use case?

rmccue 3y ago
> So this prototype doesn't fit on a $10 quad copter so it's... Flawed? I didn’t read the original as meaning non-military drones, rather non-stealth military drones. For example, to the OP’s point, the Predator drone is powered by a piston engine - I’m not overly familiar with other military drones, but stands to reason other UAVs use similar tech.
- lupusreal 3y ago
  They're talking about this prototype doing mach 0.7, so it's a safe bet they intend it to have a turbofan. That's much faster than a MQ-1/MQ-9 and also faster than a (turbofan) MQ-20. Dismissing this design because it requires a jet engine just seems bizarre. Like okay, it doesn't work with piston props... so what?
adrian_b 3y ago
> We don't know that and this is the very first prototype so it could absolutely evolve over time. The high-pressure air must come from a compressor, either a separate compressor or the jet engine compressor. Obviously it is much cheaper and much more compact to use bleed air from the jet engine compressor, than to include a second compressor, only for maneuvering. On an aircraft without a turbo-engine adding a compressor would increase the cost and the energy consumption a lot in comparison with the traditional methods of steering the aircraft, so it is not advantageous. However this method without control surfaces should also be usable with turboprop engines, not only with jet engines.
- sebastos 3y ago
  Actually, these active flow control concepts can shape the flow so much that it's possible to create ridiculous L/D, and even create negative drag in certain regimes. So it's possible to be paying for a compressor and have it still come out ahead.
wolverine876 3y ago
Hi - A trick to having great discussions is to be curious and give people the benefit of the doubt. It's also a guideline of HN. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html I also was puzzled by the focus on piston engines and stealth. Just ask why rather then assume something negative; almost always, I find people have a good reason - one that they will never bring up if I attack them. People react: Attack -> Defend; Ask -> Answer. IME, people have a lot of good stuff to say if I give them space, and can sound like idiots of I attack them. 'Why are you focusing on piston engine propeller drones and not, say, passenger airliners or military fighters or all the other flying machines? Do they say that small, non-stealth drones are their goal?'
- LargeTomato 3y ago
  Why do you believe people who flood forums with spam deserve unconditional benefit of the doubt? Do you believe there is ever a level of comment that is so uninformed that the author is not entitled to the benefit of the doubt?
  - wolverine876 3y ago
    If it's truly spam, flag the comment (and downvote it) and move on; there's little of that on HN. I assume you're talking about comments we perceive as low-quality. The obvious solution there is to downvote them, but I think you are talking about responding: Passing judgment is very tenuous business and how I make most of my worst mistakes - then I'm the fool, who is spamming and worse, poisoning the conversation. Much better to be curious and ask. Usually I learn that what I understood as spam was my limitation - I didn't think of another interpretation, or that the author just needed to spell out a good idea a bit more, and now I've learned something. And sometimes the author didn't think of something and they learn something from me, which they wouldn't do if I attacked them. It's also respectful, which is essential, and we have two people with positive interactions, which is also critical in this age. As an example, I personally would say, if I had to judge, that your comments are spamming this discussion, and in multipile ways that explicitly violate HN guidelines. I am giving you the benefit of the doubt, that you are an intelligent person in good faith - which you deserve - and I think we're both rewarded. Seriously, read the HN guidelines (link at bottom of page). They not only explain the ways of HN, they are a good guide to effective social media technique in general. > Do you believe there is ever ... My response is that hyperbolic, extreme hypotheticals lead to arguments and are not useful. Life does not happen at those extremes, nor does the interesting discussion.

rmccue 3y ago

> So this prototype doesn't fit on a $10 quad copter so it's... Flawed? I didn’t read the original as meaning non-military drones, rather non-stealth military drones. For example, to the OP’s point, the Predator drone is powered by a piston engine - I’m not overly familiar with other military drones, but stands to reason other UAVs use similar tech.

lupusreal 3y ago
They're talking about this prototype doing mach 0.7, so it's a safe bet they intend it to have a turbofan. That's much faster than a MQ-1/MQ-9 and also faster than a (turbofan) MQ-20. Dismissing this design because it requires a jet engine just seems bizarre. Like okay, it doesn't work with piston props... so what?

adrian_b 3y ago

> We don't know that and this is the very first prototype so it could absolutely evolve over time. The high-pressure air must come from a compressor, either a separate compressor or the jet engine compressor. Obviously it is much cheaper and much more compact to use bleed air from the jet engine compressor, than to include a second compressor, only for maneuvering. On an aircraft without a turbo-engine adding a compressor would increase the cost and the energy consumption a lot in comparison with the traditional methods of steering the aircraft, so it is not advantageous. However this method without control surfaces should also be usable with turboprop engines, not only with jet engines.

sebastos 3y ago
Actually, these active flow control concepts can shape the flow so much that it's possible to create ridiculous L/D, and even create negative drag in certain regimes. So it's possible to be paying for a compressor and have it still come out ahead.

wolverine876 3y ago

Hi - A trick to having great discussions is to be curious and give people the benefit of the doubt. It's also a guideline of HN. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html I also was puzzled by the focus on piston engines and stealth. Just ask why rather then assume something negative; almost always, I find people have a good reason - one that they will never bring up if I attack them. People react: Attack -> Defend; Ask -> Answer. IME, people have a lot of good stuff to say if I give them space, and can sound like idiots of I attack them. 'Why are you focusing on piston engine propeller drones and not, say, passenger airliners or military fighters or all the other flying machines? Do they say that small, non-stealth drones are their goal?'

LargeTomato 3y ago
Why do you believe people who flood forums with spam deserve unconditional benefit of the doubt? Do you believe there is ever a level of comment that is so uninformed that the author is not entitled to the benefit of the doubt?
- wolverine876 3y ago
  If it's truly spam, flag the comment (and downvote it) and move on; there's little of that on HN. I assume you're talking about comments we perceive as low-quality. The obvious solution there is to downvote them, but I think you are talking about responding: Passing judgment is very tenuous business and how I make most of my worst mistakes - then I'm the fool, who is spamming and worse, poisoning the conversation. Much better to be curious and ask. Usually I learn that what I understood as spam was my limitation - I didn't think of another interpretation, or that the author just needed to spell out a good idea a bit more, and now I've learned something. And sometimes the author didn't think of something and they learn something from me, which they wouldn't do if I attacked them. It's also respectful, which is essential, and we have two people with positive interactions, which is also critical in this age. As an example, I personally would say, if I had to judge, that your comments are spamming this discussion, and in multipile ways that explicitly violate HN guidelines. I am giving you the benefit of the doubt, that you are an intelligent person in good faith - which you deserve - and I think we're both rewarded. Seriously, read the HN guidelines (link at bottom of page). They not only explain the ways of HN, they are a good guide to effective social media technique in general. > Do you believe there is ever ... My response is that hyperbolic, extreme hypotheticals lead to arguments and are not useful. Life does not happen at those extremes, nor does the interesting discussion.