Executive summary appears to be: 36 lbs of thrust with a (dry?) weight of 3.1 lbs and a fuel consumption of about a pound per minute. Sounds shockingly good, so I have to wonder if the compressor is basically an ablative heat shield and this is good for only a few runs.
That said: doing this stunt in what looks like a suburban park strikes me as shockingly irresponsible. This thing can easily kill someone, wreck a vehicle or puncture a roof if control is lost...
Replying at the top here given the conversation down below. Having done RC for many years, been licensed to do it, and having friends that flew helicopters AND jets with a very similar jet turbine in them, I can say with 99.9% confidence that this video was taken at an RC flying field. If this assumption is correct, this has several other assumptions tied to it: a) they are suppose to be there, b) the field is permitted for these types of flights, c) they are certified for these types of flights.
Also, the shot at 4:08 appears to show the runway. The shot at the end where it's landing clearly shows a boundary between longer grass and shorter grass meant for belly landings. We had all of these things at our flying field.
Given the equipment setup, launcher, gauges, fire extinguisher, etc., I'm going with the probability we're dealing with a couple of pros who are capable of conducting this flight in a safe manner at a designated location. You jumping in here making guesses about intent and outcome is a bit shortsighted, and the FUD you are hypothesizing with is simply there to elevate interest in your comment.
Sounds like a great reply. Clearly my worry was misinformed. Thanks; for the first two paragraphs anyway.
Y'know, there was a time on HN where making a supposition like that would be met with... an assumption that it was delivered out of genuine concern and not an attempt at "FUD" to "elevate interest" in the comment. Fuck you, basically.
This whole thread makes me sad. Your post is the most informative and valuable, and it's still just ad hominem flaming nonsense.
I hear you were worried about the setup and safety and I think that's worth considering when you observe things that are new and unfamiliar. I run into it all the time myself: Ebola for example. However, I do think we, as humans, use FUD to project our concerns onto others so they will share the feelings we have. It's an often times necessary habit we must practice in person that doesn't translate well to the Internet. An ad hominem argument is one that attacks a person (or thing) based on a casual connection (or sometimes no connecton/strawman). In a way, make up a story based on the fears is ad hominem because it is only loosely related to the subject matter.
I'm sorry this mad you sad. That was not my intent.
> Sounds shockingly good, so I have to wonder if the compressor is basically an ablative heat shield and this is good for only a few runs.
The compressor isn't the part of the engine which gets really hot here; that would be the turbine. In these kinds of engines the turbine is typically made out of Inconel, which has no problems handling the ~800C exhaust gas temperature seen at maximum thrust. Preventing the EGT from exceeding a specified limit is the main job of the engine computer, so this is not a common failure mode.
The service interval on Jetcat turbines is 25 hours (some manufacturers specify 50-hour intervals, or even longer), for which the significant portion the work involved is a bearing replacement.
While the thrust-to-weight ratio does seem very good, keep in mind that the quoted weight of 3.1 lbs is likely to not include ancillaries (engine computer, battery and mounting hardware). Also, lubrication is provided by oil mixed in with the fuel rather than a closed-loop oiling system.
A thrust-to-weight ratio of 10:1 is impressive, but not out of line with what you'd expect to see from a full-sized turbojet. On the other hand, the thrust-specific fuel consumption for these engines is much worse than a full-sized engine due to the much lower pressure ratio.
> doing this stunt in what looks like a suburban park strikes me as shockingly irresponsible.
It look like an R/C air park, actually. I live near the headquarters for two large hobby companies (Hobbico - makers of RealFlight, mentioned elsewhere, and Horizon Hobbies). One of the two (I don't remember which) built a similar air park specifically to provide a location for flying R/C jets.
>That said: doing this stunt in what looks like a suburban park strikes me as shockingly irresponsible. This thing can easily kill someone, wreck a vehicle or puncture a roof if control is lost...
What makes you think that someone who can:
1: Build this plane
2: Demonstrably fly it very well, with clearly a significant amount of experience in flying RC planes, and probably other high speed RC planes
will overlook all safety precautions and take what is likely the highest powered plane they've flown, where something is comparatively likely to go wrong vs traditional RC planes, and go fly it in their local park with people/houses/etc. around?
Some people with no experience in or awareness of the RC aircraft hobby seem to be terrified of it. It seems particularly common on HN, for some reason.
> I have to wonder if the compressor is basically an ablative heat shield
As an aerospace engineer, this is cringeworthy. How exactly would this compressor function as a heat shield? Is it experiencing hypersonic intake flow as part of an atmospheric reentry vehicle? Makes no sense.
While the misnomer is cringeworthy, I also find it disappointing that you didn't extrapolate that he was wondering if parts of the engine ablate quickly. While the sample size is too small to be conclusive, it suggests that you are prioritizing zinging him over having a discussion.
Could weight be saved in a jet engine by making parts of it ablative? I should think this would play havoc with clearances, so it would only be applicable to parts where the exact dimensions aren't too critical, which I suspect would preclude everything near the compressor and turbine.
Also, ablative heat shielding wouldn't apply to anything not exposed to high heat, so this would only apply to the combustion chamber and everything downstream of that.
EDIT: This makes me curious about the pressures in jet engines. They range from ~pi for early WWII engines (Junkers Jumo 004) to almost 40:1 for modern ones! According to pv=nrt, modern jet engine compressors can get pretty hot, apparently. (Disclaimer, I am not an engineer!)
There appears to be a large aircraft hangar in the middle distance, you see it a couple of times as the camera sweeps across. I don't think you get many of those in suburban parks.
It could be. But if it is, you seem to be arguing that flying a 360 mph missile around in the airspace above an active airport is... safe?
I'm shocked at the nerve I seem to have hit here. I'm not trying to take your model rockets away here, but this is not a harmless device. I think many people here lack an intuition of how fast "360 mph" is or the kind of energies that are involved. This is getting into the speeds seen for muzzel velocities of handguns, and that engine weight a hell of a lot more than a bullet.
Dangers like that require more care than just "it looks safe to me". Where are the people guarding the range and warning off intruders? Where is the posted notification of the testing schedule?
First up, why the hell are you asking here? Ask the people in the video.
Second, you don't know that they don't have permission to do stuff at the airport for say an hour because its posted. Your whole argument amounts to fear uncertainty and danger.
> I'm not trying to take your model rockets away here...
But you'll spout off on an unrelated forum about dangers you don't even know are mitigated? Not to be too blunt, but grow up. These are professional rc modelers. They know the dangers better than you do. You don't design a launch system for a jet turbine rc model without keeping safety in mind.
I spent some time hanging out at an RC club in rural Connecticut that was co-located with a small airport. If you think they just flew their RC machines willy-nilly, you are dead wrong. There was strict coordination with flight control, and real airplanes would take precedence. Traffic was low enough that this worked out well in practice.
And I did in fact witness a jet-powered RC plane being flown there one weekend, which was quite impressive. At no time was a real airplane in danger of some kind of collision.
The point is, RC clubs like this one do think about this stuff, and they do take appropriate precautions.
> This is getting into the speeds seen for muzzel velocities of handguns, and that engine weight a hell of a lot more than a bullet.
No, actually; the average bullet travels at 2,500 feet per second (around 1,700 mph) [1].
Also, the pilot of a member of the Jets of Norway R/C club. These are probably some of the most experienced r/c jet pilots in the world. I'm sure they understand the risks involved better than any of us in this thread.
Handguns are far slower than rifles. .45 ACP usually goes about 1000 f/s.
That jet, flying at half the speed of a .45 caliber bullet, weighs at least one hundred times as much. I think that's the point GP was trying to make.
The kinetic energy goes up by the velocity squared but then any damage done by the impact would be a function of the impulse and the cross sectional area of the impact. I certainly wouldn't like to get hit by this, but it is probably less lethal than those rubber rounds they use in crowd control.
edit - Boxer Rocky Marciano's punch was measured at 1028 joules, which is supposedly a greater kinetic energy than an armour piercing bullet. Direct kinetic energy comparisons are not as useful as you might think.
I think you struck a nerve here because your entire argument is based on an assumption. Do you have any evidence he's endangering other people? Do you know something we don't, like there's a playground passed those trees, or he just pulled up in this public space and launched the jet without permission?
If not, then don't insult someone that appears to be extremely competent with years of experience, and call them irresponsible because you're jumping to conclusions.
People fly 360 mph missiles around in the air above active airports all the time. Even more dangerously, they often sit in the missile while doing it. Something should be done.
edit - this looks like there is the edge of an airfield on the other side of some pylons. If it is near an active airfield, or if there is any controlled airspace in the vicinity, then I would be incredibly surprised if air traffic control was not kept informed as per the existing regulations.
They also look very similar to the engines used by Yves Rossy (aka Jetman) on his wing, although they seem to be a bit bigger and more powerful.
http://www.jetman.com/?page_id=242
> That said: doing this stunt in what looks like a suburban park strikes me as shockingly irresponsible. This thing can easily kill someone, wreck a vehicle or puncture a roof if control is lost...
I'd be more concerned with drunk or texting drivers than a R/C jet engine killing me.
I'm more concerned with drunk or texting drivers than getting eaten by a tiger. Does that mean I shouldn't be worried if someone lets a tiger loose in the park?
That depends. The tiger might get hit by a drunk driver, then eat them when they get out of the car, thus reducing your overall level of personal risk.
You prove exactly the point. People get all up in arms over silly things when there are much bigger concerns in the world.
Someone shows a video of a RC jet flying extremely fast and the assumption is this guy is endangering the public and has no regard for safety of others.
Lets just get congress to waste time implementing laws for both fast flying RC planes and another one to make it illegal for your tiger to eat a person.
On a probability basis, sure, bad driving is much more likely to kill you. That doesn't mean that jet RC flying like that isn't shockingly irresponsible.
You assume this person is shockingly irresponsible. Do you have proof? What's on the other side of those trees?
I assume that one does not simply dive into the RC world with a jet turbine. Instead this individual has probably had a lot of practice with slower planes, does not want to injury anyone, and is not doing this in Central Park NY
Interesting that you think the burden of proof should be on me that flying a couple litres of kerosene around the sky at 370mph is not obviously unsafe.
I have no doubt the pilot is experienced, and that the area in general is clear.
So, the actual argument I made was that just because more people were likely to die from drink driving (probability-wise), it didn't mean flying the RC wasn't shockingly irresponsible.
Note that I didn't agree with the claim that this specific flight was irresponsible, just that the fact that more people might die from drink driving is basically irrelevant.
I carefully noted your original argument. That's why I said that the burden of proof should be on you, if you want to prove that the flying was irresponsible.
The RC jet flying that you see in this video requires an immense amount of knowledge, experience, preparation, and flying skill—far more than to fly a normal electric RC plane or multirotor, or even to drive an automobile. There is nothing I saw in this video that looks remotely irresponsible.
http://www.jetcatusa.com/p160.html
Executive summary appears to be: 36 lbs of thrust with a (dry?) weight of 3.1 lbs and a fuel consumption of about a pound per minute. Sounds shockingly good, so I have to wonder if the compressor is basically an ablative heat shield and this is good for only a few runs.
That said: doing this stunt in what looks like a suburban park strikes me as shockingly irresponsible. This thing can easily kill someone, wreck a vehicle or puncture a roof if control is lost...