Yep, you heard me right, I'm going to build the world's first supersonic RC plane, almost doubling the world's present RC speed record. Reason why I'm doing this is to get the attention of the aerospace industry so that they might consider me someday.

Yes, I know the technical challenges will be enormous, but that is why I am doing this, to demonstrate what I can do. Plus it will finally be a chance for me to put my degree to use.

Now the biggest challenge will be finding a place for me to actually fly supersonically, not that every flight has to be supersonic. I am aware that when airplanes travel at that speed a sonic boom is usually created. However, since this design will be smaller, so will the sonic boom.

Another concern of mine will be heat, as air friction compresses the air, heating it up. The temperature I estimate I will reach will exceed the maximum of some of the components, so I will need some sort of cooling mechanism, and just fans won't cut it.

Now I know some of you may have alarming concerns, but if you calmly address them with me I will address them. I'm posting this here because I may need advise for the type of parts I need and other recommendations you may have.

Aerospace V logger out.

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Total cost to break the sound barrier twice? Something like $260,000 and counting.

Here is my quick take on it.

First off, I have a hunch that this is either a troll, a kid, or a foreigner, simply based on the loose explanations given. Not only that, but someone possessing an aerospace engineering degree would surely know the challenges of this feat. My biggest concern is the theory behind the EDF!!

Before I go further, I do believe it is possible on a not so extravagant budget, but certainly not $3000.

Let throw my spin on it an break down a few topics.

1) The EDF Idea... It is not possible to use an EDF as any sort of compressor, simply impossible. Therefore, you can cross off the idea of the ability to fly it in subsonic electric flight. Not only that, but without a signifigant choke, or decrease in air speed the fan would explode. The usable inlet speed on a fan like that is below 200mph.

2) Uncharted territory. Aerodynamically speaking, this plane is up against a vast darkness. There simply are not enough studies in transonic wing and foil designs for such a small plane, at such a relatively low wing loading. More than likely you would end up with some sort of diamond shaped foil, in an attempt to avoid compressibility issues and the unavoidable flow seperation. This would result in a very poor handling craft for "daily electric use." and would surely limit it to its specific mission. Not to mention the stall would be horrendous.

3) The engine Idea is simply ludicrous. The only way this might even be close to feasible is with solid rocket engines, most likely 3 H or I class rockets, or fewer (one maybe even 2) J class rockets. Why do I think several I or J class? Burn time... It will take a decent amount of time to get up to speed. Most likely would require 1 I class for the first 80% of acceleration, and the other 2 as a pair to actually push over the hump. Keep in mind, in any sort of fluid dynamics drag increases with the square of velocity.

4) Control. You can forget normal thoughts on control inputs. With a craft at these speeds, it is hard to predict what would happen. I would imagine compressibility could play a HUGE impact on control surfaces, and you would most likely be better off with some type of wingtip control surface (see here, however I would be concerned of an uncontrollable induced yaw) or tailerons/canards. As far as vertical and yaw stability, you would probably be best suited without any sort of rudder, and instead a wedge shaped tail (sounds counter productive, I know, but it will be the most stable at speed.)

4.5) Aerodynamic flutter. To tackle flutter you would have to venture away from traditional RC control and hinges. You would most likely end up with full flying control surfaces. These surfaces would need the rotation point forward of your neutral point, center of gravity forward of the neutral point but aft of the rotation point, and be aerodynamically stable. 

5) Lambda shockwave. When the airflow on top of the wing begins to exceed super sonic (mach 1), the shockwave will create a shift in your center of pressure, and seperation over the 50-60% range of the wing. When this speed is approached your center of lift will venture back to a region somewhere around 50%-60%(+). This raises two problems;

a) You can literally lose ALL control of trailing edge control surfaces (conventional ailerons and elevators)

b) Uncontrollable pitch down. This is why some full scale aircraft actually transfer fuel to change the CoG, to maintain control.

Hint: this is a big factor in the full flying, and wedge or diamond shaped control surfaces I spoke of earlier.

6) This craft would have an EXTREMELY hard time doing this at a low altitude. Your best bet would be simulating the LOHAN mission at an altitude greater than FL 400 (most likely 600+). As you can see here, at this altitude the speed of sound actually decreases. Not only this, but the decreased temperature will help the craft survive the temperature rise due to friction, as well as much thinner air making the feat much more achievable (with less compression concerns.)

7) Design. Although high aspect ratio wings are aerodynamically efficient at subsonic speeds, they are lousy at super sonic, and transonic. Someone earlier referenced a 400mph hotliner (which is false.), however there is a current record of 498mh in a dynamic soaring glider (similar design to a hotliner), however this is soon approaching the limit for high aspect wings, and is flying in a totally different realm of physics than transonic straight flight. If it were up to me I would use some sort of delta, or high taper swept wing ton increase the reynolds numbers over the root chord. It is better to get it as close to the Re's that HAVE been studied at those speeds. As previously mentioned, I would push for full flying stabilators, either in canard or conventional tail fashion. Other than that, it would be as minimalistic as possible, and NOT electric, no reason, no room, simply extra weight... If you want to make it electric, duplicate the airframe with a better choice in foils for low speed flight, and make an electric specific airframe.

8) Construction, this shouldn't be too difficult. Quite frankly at the relatively short time it would be travelling at this speed, and the altitude it would be flying at, I doubt you would need a titanium airframe. Supersonic model rockets are often composite, and if they do have metal it is a small heatshield on the nosecone, or Leading edge of the fins. Carbon should suffice, shoot even aluminum tape on the LE and Nose should be good enough to save the composite. 

9) Control. Manual control is almost definitely out of the question. Your best bet would be an autopilot. As for how well the AP would perform, this is also an unknown. On one side of it, if the airframe is way too twitchy, it could theoretically outperform the IMU's. But at that point the airframe would most likely break apart or be lost anyways. If the airframe is dynamically stable, it should need little to no control input for the short flight, infact you might even be able to simply disable the AP all together for that time. The other question is whether or not the AP could decipher the (what it would see as) absurd GPS readouts, keeping in mind that at 5hz (Ublox 3DR GPS), it would be sampling once every 60 meters (196ft).

These are just the tip of the iceberg when it comes to some of my concerns. 

Sincerely,

Justin.

PS, I wish the LOHAN team luck! I would love to see it break the speed of sound. As previously mentioned I am a bit concerned about the aerodynamic side of things, but who knows, maybe at these sizes, the hurdles I mentioned are less like hurdles, and more like speedbumps.

PSS, to clear the air on some peoples posts, Mach 1 is NOT super sonic. Mach 1 is transonic, where Navier Stokes equations and calculations no longer apply. This is the region where you start to deal with the faster iar on the top of the wing approaches and exceeds the speed of sound, which doesn't necessarily mean the aircraft does. General "supersonic" is right around mach 1.2.

Oh I wish there was a like button!

That Eflite EDF must provide what, 2:1 compression? Should be plenty to ignite!

https://www.youtube.com/watch?v=M_FCQ550770

At 1:10 you can see a perfect example of the onset and result of aerodynamic flutter. If you pay close attention you can clearly see that this is not caused by gyroscopic forces. Follow the flutter as it starts at the TE at the tip of the fins, and it drastically increases until failure.

How are you calculating the drag force?

 Some good points. Just to get a HPR rocket to go supersonic in a level flight would be difficult near sea level. Yes. technically Mach 1 is indeed transonic and goes super sonic about 1.2 near sea level.

 I see what your saying here and it's too technical to describe ALL the factors in a post and not even worth my time to attempt it. But nice effort on your part.

 It would be about like describing all the effort put into an EKF just to cover the ground floor. I've been working on the spaceplane project for 8 years and I've been going to "school" the whole time.

But hey if you really want to do it. You can! It might not look like what you started out with but you can do things like this. I say it's a young fella learning a lot about aerodynamics and aerospace. I say I dare ya! Bring it on! And prove it! If you think you can GREAT just be prepared to face an onslaught head on. And don't quit no matter what.

+1

This is proof that simply having a "degree" in something doesn't mean you actually know anything. But carry on, I'm just here for the entertainment value.

OK, I will bite....

TO LATE !!!!!

These guys have been flying supersonic RC for quite a while.........

GROLLO

enjoy...

Thanks for posting that link, i just lost half an hour of my life i'll never get back reading the comments.  Dear god there are some special people out there!

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