# What is necessary for a hypothetical supersonic speed Radio Controlled Jet?

• Noob of the Maths
In summary: You might want to consider using something like an air cannon to launch it into the air.In summary, the project would require a lot of skills and funding, but would be very fast.
Noob of the Maths
TL;DR Summary
What its the necessary elements for a Radio Control Jet?
Hi everyone! :)

While i watched rc jet exhibitions on youtube, i find that the most fast of this RC reached +700 Km/h. When i browse more information about the tourbine, i realized that for a hypothetical supersonic RC the mechanical system of the tourbine must have a complete air compressor and exit tourbine.

Maybe the size of this kind of RC Jet its too difficult to have a complete tourbine with the compressor and afterbuner, but if this could be done...the velocity could be very very fast.

So, yeah, the aerodynamic design must have a lot of attention to resist the G force.

Im very corious about if this its possible to do and achieve the sonic boom.

I am engineering mechanic student, so i don't have much idea about aeronatic principies... but i undertand that building a complete system in a small thing can accomplish many things...

There will be a sonic boom, but nearby it will sound like the crack of a passing high-velocity rifle bullet.

You will need to make it longer and thinner, give it a metal skin, and a sharp pointed nose. It will end up looking a bit like a Lockheed F-104 Starfighter
https://en.wikipedia.org/wiki/Lockheed_F-104_Starfighter

Notice how most model aircraft in the youtube videos behave a bit like butterflies, because the pilot reacts too late, and then by too much. At those speeds you will be unable to control it visually from the ground. You will need to include a MEMS chip with accelerometers and gyroscopes, so it can control it's orientation and angle of attack. It will need an auto-throttle so it does not stall on approach, and GPS tracking so you can find it. Your drone, which is what it is, will require an aircraft position transponder.

Now all you need is a dozen assistants, and some government funding from a military weapons development budget.

sophiecentaur and russ_watters
sophiecentaur, Noob of the Maths and hutchphd
I actually prefer the more elegant term “Erdnagel”.

DaveE and Noob of the Maths
Baluncore said:
r and thinner, give it a metal skin,

Baluncore said:
There will be a sonic boom, but nearby it will sound like the crack of a passing high-velocity rifle bullet.

You will need to make it longer and thinner, give it a metal skin, and a sharp pointed nose. It will end up looking a bit like a Lockheed F-104 Starfighter
https://en.wikipedia.org/wiki/Lockheed_F-104_Starfighter

Notice how most model aircraft in the youtube videos behave a bit like butterflies, because the pilot reacts too late, and then by too much. At those speeds you will be unable to control it visually from the ground. You will need to include a MEMS chip with accelerometers and gyroscopes, so it can control it's orientation and angle of attack. It will need an auto-throttle so it does not stall on approach, and GPS tracking so you can find it. Your drone, which is what it is, will require an aircraft position transponder.

Now all you need is a dozen assistants, and some government funding from a military weapons development budget.
Well that sound like "flight simulator without respawn". Without the assistants and funding luck will be what will be most required. With the F-104 design and considering the amount of fuel... the risks are many, with a great result if it works...

Noob of the Maths said:
... the risks are many, with a great result if it works...
There are too many skills required to take on the entire project alone. Everything can be purchased, with the exception of the one thing essential to taking the next step, the flight control system.

Any large investment in an RC model needs a dynamic autopilot to handle the short term stability flight control. On loss of communications, it should enter an orbit, if it times out, then it should return home by GPS, along the shortest previously used flight path, landing on autopilot or by ballistic parachute.

The quickest way to fly a supersonic RC model would be to develop a general purpose RC avionics package, something that could be parameterised to fly any RC model or drone. Let others sacrifice their aircraft and their physical investment.

Make it open source and available free, so your software would become the essential component in every realistic model that flies more than twice. There would then be a part of you in every one of those future successful models.

Think like Linux. Teach the penguin to fly.

jrmichler, Klystron, boneh3ad and 1 other person
The 'RC' part there means quite lot of problems alone. The plane will be out of visible range and common RC radio range in no time, so you need a reliable fast downlink to transmit telemetry and visual information, and a reliable uplink to transmit control signals. Has to cover a dozen kilometres, at the very least.

Also, the kinetic energy of the thing would be comparable to a cannon projectile. I guess you would have some troubles with the legal part too.

I think this project is definitely not for loners.

Baluncore said:
I actually prefer the more elegant term “Erdnagel”.
Is that German for "lawn dart"?

How do you get a F-104?

Astronuc, Baluncore, DaveC426913 and 1 other person
Is that German for "lawn dart"?
Erdnagel = Earth nail = tent peg.

In the 1940s they could get their propeller planes almost to Mach 1 by putting them into a steep dive. In all cases they were stopped by the planes breaking or becoming unstable as they were not designed for that speed. The British eventually managed to get a Spitfire up to Mach 0.92 before they gave up with the idea.

I'm not knowledgeable about RC aircraft but I suspect your job would be much easier if you didn't try for level flight.

EDIT: I see with some Google that gliders have reached 0.75 mach (not counting things like returning space shuttles and whatever space magic is in the new PRC weapon) so I really don't think the problem is engine power. I can't imagine radio control being an issue in this day and age, so I suspect the problem is regulatory and the small number of civiilians who undersstand supersonic aerodynamics.

The biggest problem is that RC jet turbines don't have a good inlet or nozzle to provide thrust when supersonic. I disagree with many of the above statements - you do not need metal or even composites to make a structure that is able to handle supersonic speeds, and if you restrict yourself to low supersonic speeds, heating isn't much of an issue either. The plane could also be entirely stable, and therefore not require any kind of computerized stability assistance. You would need a telemetry package though, since it'll get out of sight far too fast to just control based on sight from the ground. However, it could be completely controllable with something like an FPV drone rig (basically an onboard camera transmitting back to you so it appears as though you are piloting it from onboard). It would be much safer of course if it had a rudimentary autopilot though that would fly it back to its origin point in case of loss of signal.

The real problem is propulsion. Making an airbreathing jet engine that works supersonically is (for obvious reasons) not a priority for the RC jet manufacturers, so you'd definitely need to make your own supersonic inlet to feed the engine and (possibly) a nozzle modification at the back of the engine too. I know a professor who was looking at making a supersonic drone using RC-derived engines for propulsion a while back (I don't know if that ever amounted to anything though), and he was looking at adding a custom afterburner and variable area nozzle to the engine to achieve the necessary performance, as well as a custom inlet to feed it, and that was for a design speed of mach 1.4.

It probably wouldn't be *that* difficult (technologically - all of these things would be hugely expensive of course) to make an RC aircraft that could do a brief supersonic dash using a supplemental rocket engine, as that takes care of the propulsion, but making one capable of sustained supersonic flight would be a pretty serious undertaking, primarily due to the propulsion requirements.

Benjies and Klystron

That's terrifying just to think about!

PhDeezNutz
Not radar invisible, but I feel you're correct that it probably won't get noticed by the equipment and operators at the local airport.

PhDeezNutz
kalabren said:
Not radar invisible, but I feel you're correct that it probably won't get noticed by the equipment and operators at the local airport.
But would it be noticed by a Secret Service protection team?

PhDeezNutz
anorlunda said:
But would it be noticed by a Secret Service protection team?
I don't know anything about spies.

Military have stuff like this, so you know they're aware of the situation :-)

Benjies
anorlunda said:
But would it be noticed by a Secret Service protection team?
It will be continuously radiating TV pictures back to the operator. Even if it does not show up on the radar, it will be very obvious to any RF energy surveillance system.

PhDeezNutz
Obviously the secret service agents pre-programmed the drone with good photos. There is no need for it to radiate or beam back a video feed.

EDIT: TIL "secret service" isn't spies but the protection for the USA president. Sorry guys! I thought you were talking about agents trying to sabotage the airport.

Sorry if this has been asked already, but isn't there some new FAA standard for drone control and monitoring, in addition to drone/RC flight rules? I understand that bad operators will try to avoid those rules and monitoring, but hopefully for the good guys it provides a reasonable way to fly their crafts...

Here's a good article on the FAA drone rules. It has a link to the actual FAA rules. https://www.eaa.org/eaa/news-and-pu...on-news/news/09-01-2016-drone-rules-in-effect. The oversimplified version is to stay in sight of the drone, less than 400 feet above ground, in contact with ATC, the drone must weigh less than 55 lbs, and the operator needs a license.

The line of sight requirement rules out high speed operation. Note that many handguns have subsonic muzzle velocity.

The FAA is working on rules for drones operating beyond the line of sight: https://www.faa.gov/uas/programs_partnerships/beyond/.

The EAA (Experimental Aircraft Association) has lots of good information on drones. Go to eaa.org, and enter UAS (unmanned aircraft systems) into the search window.

Klystron, DaveE and berkeman
If you really want to build something to break the sound barrier, I'd suggest joining a high power model rocketry club. In the US, Tripoli and NAR are the sanctioning bodies.

Of course, you can fly a lot higher in the black rock desert in Nevada, compared to Maryland, but Mach 2+ is achievable in multiple locations. It is legal if you are certified and you operate under a club altitude waiver.

My builds haven't gone fast enough to burn off paint, yet.

berkeman
jrmichler said:
The oversimplified version is to stay in sight of the drone, less than 400 feet above ground ...
I have a small drone and yes 400 feet is the max altitude rules provide.

cjl said:
you do not need metal or even composites to make a structure that is able to handle supersonic speeds, and if you restrict yourself to low supersonic speeds, heating isn't much of an issue either. The plane could also be entirely stable, and therefore not require any kind of computerized stability assistance. You would need a telemetry package though, since it'll get out of sight far too fast to just control based on sight from the ground. However, it could be completely controllable with something like an FPV drone rig (basically an onboard camera transmitting back to you so it appears as though you are piloting it from onboard).

Point-of-order: I am greatly concerned about the discussion potentially veering into ways to design and engineer what amounts to a remote-controlled missile. A 20 pound object being consciously directed at 1000mph into a target can do a lot of damage.

I see it as no different from discussing how one might make explosives or toxins - i.e.: As long as readers obey the law, there's no harm - and yet - it's still it's arming and informing those who wish to do harm. The PF I know and love frowns on that.

Just my 2c.

PhDeezNutz
DaveC426913 said:
Point-of-order: I am greatly concerned about the discussion potentially veering into ways to design and engineer what amounts to a remote-controlled missile. A 20 pound object being consciously directed at 1000mph into a target can do a lot of damge.
I dunno. The bad actors don't need our help on that. And I don't think what's been covered so far will help incompetent teenagers to design something dangerous on their own. So far the Mentors have discussed this thread some, and it's probably okay to continue for a bit. But it would be good to stick to how to design something that falls within the existing or near-future FAA regulations (and other regulations for other areas in the world).

Klystron
berkeman said:
The bad actors don't need our help on that.
And yet would we not stop a similar discussion about creating explosives or toxins? I think the only difference is that we do not intuitively assume drones are intrinsically weapons of destruction, unlike toxins and explosives. (Remember the cautionary tale of 9/11 - realizing after-the-fact that a mere civilian airplane is intrinsically a WMD).

(Rhetorical. No need to beat this to death. I've stated my concern.)

PhDeezNutz
There's no indication that anyone here, including the OP, has any intention of building this. If they did it likely wouldn't get off the drawing board.

Noob of the Maths said:
Summary:: What its the necessary elements for a Radio Control Jet?

Im very corious about if this its possible to do
That is all, I think. Just a question from an engineering student.

BTW, the answer is yes. If Lockheed can build an F-104 in the early 1960's, this could also be built in 2022. It's just a question of money, knowledge, experience, etc.

DaveE said:
If Lockheed can build an F-104 in the early 1960's, this could also be built in 2022.
That's a cool idea! Gorgeous plane - one of my faves.
I wonder if 21st century technology could make a safe F-104? Just for the cool factor.

DaveC426913 said:
And yet would we not stop a similar discussion about creating explosives or toxins?
berkeman said:
And I don't think what's been covered so far will help incompetent teenagers to design something dangerous on their own.
I think this is the main difference...

DaveC426913 said:
(Rhetorical. No need to beat this to death. I've stated my concern.)
Thanks.

DaveE said:
There's no indication that anyone here, including the OP, has any intention of building this. If they did it likely wouldn't get off the drawing board.
That is not the litmus test that is applied to discussing explosives or toxins. The litmus test is usually could some unknown reader use this information with the intent to cause harm?

PhDeezNutz and DaveE
DaveE said:
What are you waiting for, you can have one tomorrow!
Not a chance man! (talk about lethal weapons!) My wife is not a widow yet and I want to prolong that status.

DaveE
You can probably buy an old Mig-31 from somewhere. They're reliable, still in service, and super fast. Similar role to the F-104 but newer design.

A rifle can launch a missile that exceeds the speed of sound. You will need to make a very small radio control receiver to steer the spinning bullet. There are gyros that will easily fit with the receiver inside a round. The very small control surfaces on the spinning bullet will need to operate at above 1 kHz.

Klystron
Noob of the Maths said:
Summary:: What its the necessary elements for a Radio Control Jet?

Im very corious about if this its possible to do and achieve the sonic boom.
To summarize the thread so far: It is possible, but...

1) You need to design and build an airframe that is controllable over the full speed range
and
2) Is strong enough to withstand the aerodynamic forces
and
3) Low drag at supersonic speeds
and
4) Takeoff and landing speeds low enough to be able to use existing runways
and
5) A semi or fully autonomous control system
and
6) Get permission from the FAA
and
7) Design and build a jet engine capable of supersonic operation
and
8) A suitable telemetry system with pilot interface (think glass cockpit)
and
9) A few things I did not think of yet.

The effort required is years, not weeks or months, for each of the above items. That explains why nobody has done it yet. Also, high speed flight has considerations that are not necessarily obvious. For example, a 2 G turn at 1000 ft/sec will make a circle about 6 miles diameter.

Klystron, russ_watters, Astronuc and 2 others
"...a 2 G turn at 1000 ft/sec will make a circle about 6 miles diameter"

Uh huh, and what is that reduced to at >12g's?

<1 mile

Last edited:
DaveC426913 said:
Point-of-order: I am greatly concerned about the discussion potentially veering into ways to design and engineer what amounts to a remote-controlled missile. A 20 pound object being consciously directed at 1000mph into a target can do a lot of damage.

I see it as no different from discussing how one might make explosives or toxins - i.e.: As long as readers obey the law, there's no harm - and yet - it's still it's arming and informing those who wish to do harm. The PF I know and love frowns on that.

Just my 2c.
Honestly, the way I view it, anyone with the technical ability to make this actually happen won't have that much difficulty figuring out how. This is well beyond just assembling commercially available parts here, even with all the information provided above.

As I said, a significant amount of what I know about it comes from a former professor of mine working with a team of aerospace graduate students and a decent amount of funding, and though I'm confident we came up with a viable concept for a mach 1.4 drone based on commercially available parts, it took a huge amount of time and still involved a lot of custom work to get it (hopefully) functional, and as far as I know, it never actually turned into real flight hardware.

To me, this is very different from something like an explosives discussion, where it genuinely is plausible for someone with little experience to make something that at least is fairly dangerous by themselves without a lot of additional resources. To make a working supersonic UAV, you'd be talking tens of thousands of dollars and hundreds or thousands of hours of design and fabrication work, and that's assuming you know what you're doing.

PhDeezNutz

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