 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
| HomeDiscussion Groups General ModelsRailroadsRocketsRadio Controlled Air ModelsHelicoptersLand ModelsWater ModelsModelGeeks.com Contact UsLink To UsSearch & Site Map |
Model Forum / Radio Controlled / Air Models / February 2004Supersonic R/C
Hi guys, I've given some thought to the subject of high speed R/C, and a recent thread about speed records has prompted me to post. First of all, I know that the following would not be AMA or NAR compliant. I'll keep this to the realm of 'what if'. Hypothetically, I've wondered about what it would take to fly an R/C plane and take it supersonic. For those here that are not familiar with high powered rocketry, it's a subset of the model rocket hobby that involves rockets that can be hundreds of pounds in weight and soar to astonishing heights (to the point of needing waivers from the FAA). To fuel this sport, special large rocket engines are used. These engines have some performance and thrust advantages over the disposable engines you might purchase for a normal model rocket and can be bigger then a coffee can. Starting with one of these engines, say perhaps an 'L' or 'M' size, I imagine that an experienced modeler (with a good aeronautical background) could build a plane with a fiberglass or carbon fiber skin that could be dropped from a carrier plane half a mile uprange from the R/C operator, have its motor ignited, power past mach 1 in controlled, powered flight, then be landed conventionally. If airframe stresses of turning within the control radius ofthe radio (or visibillity of the operator) is a concern, you could have more then one operator spaced across the range. Legal issues aside, can anyone think of any technical reasons this couldn't be done? Best regards, Ben Hallert Take it up on a balloon to 100,000 feet and let gravity do the work for you. > Hi guys, > [quoted text clipped - 30 lines] > > Ben Hallert Ever heard of terminal velocity: Sqrt ((2 * Weight)/(Drag Coefficient * Density * Area). 100,000 feet ain't gonna do it. Mike > Take it up on a balloon to 100,000 feet and let gravity do the work for you. > [quoted text clipped - 34 lines] > > > > Ben Hallert There are turbines available NOW that calculations show will take a model to excess of 500 mph... The problem is maintaining physical control from the ground, and building a model to take the stress.... Such a model will get small to the eye in a hurry, and normal construction methods won't cut it..... But newer more powerful digital servos are available and composite materials are becoming more commonplace... I believe this will be done before long, and I believe the flights will be autonomous when they happen.. Just WHERE it'll happen remains to be seen... It's not likely to be in the States. Bill > > > Hi guys, > > > [quoted text clipped - 8 lines] > plane > > > and take it supersonic. > There are turbines available NOW that calculations show will take a model to > excess of 500 mph... The problem is maintaining physical control from the [quoted text clipped - 10 lines] > > Bill Just a few minor little problems. First, control is only available when the operator can SEE the 'aircraft'. I don't know how you can see a model at over 100,000 feet. Better eyes than mine! The remote systems used by Maynard Hill probably will be of extremely limited value since the distance covered in a very limited period of time is simply huge. Second, the model PROBABLY cannot carry enough fuel to accelerate fast enough to go supersonic if there was a small a turbine capable of providing that much push and I strongly suspect the Feds would be upset if you were building a rocket capable of that feat. Howeve, those are probably just minor technical details. I guess you could talk to the USAF about one of their old F-100's that are being used up as target drones. Be prepared to be disappointed because international treaty requires certian actions taken to 'safe' these airframes. Typically they take a chain saw to the main spar and carry throughs. Oh yes, the third problem has to do with federal law prohibiting supersonic flight over the Contential United States. But that is just another law that can be easily broken if you have deep enough pockets and a senator or two on your 'staff'. LOL! > > > > Hi guys, > > > > [quoted text clipped - 8 lines] > > plane > > > > and take it supersonic. > Just a few minor little problems. First, control is only available when the > operator can SEE the 'aircraft'. I don't know how you can see a model at [quoted text clipped - 18 lines] > can be easily broken if you have deep enough pockets and a senator or two on > your 'staff'. Just a point of info! The high power rocket guys have an event called the drag race. Where they do in fact launch rockets that break the sound barrier. Granted, they're going more or less straight up. But you do hear something of a sonic boom and they do reach between 5000 to 15,000 feet altitude (or more). They also have others, slower, that make it as high as 30,000 plus. And yes, they coordinate with the FAA for these events and get a corridor cleared. Something to see at least once even if you're not into rockets. Chuck > Ever heard of terminal velocity: > > Sqrt ((2 * Weight)/(Drag Coefficient * Density * Area). > > 100,000 feet ain't gonna do it. How quickly the great ones are forgotten. USAF Captain Joe Kittinger broke the sound barrier 40 years ago in free fall from 102,000 feet. http://www.afa.org/magazine/valor/0685valor.asp Thanks, John Don > > Ever heard of terminal velocity: > > [quoted text clipped - 6 lines] > > http://www.afa.org/magazine/valor/0685valor.asp | > Ever heard of terminal velocity: | > | > Sqrt ((2 * Weight)/(Drag Coefficient * Density * Area). | > | > 100,000 feet ain't gonna do it. You'll never actually reach terminal velocity -- you'll just get closer and closer and closer. At first, you'll accelerate at the full 9.8 m/s^2 (or a tiny bit less because you're getting further from the Earth) ... but as you get faster, your acceleration will decrease, until it's almost zero when you get close to terminal velocity. Also, the speed of sound decreases as you get up higher, at least to a point. At 40,000 feet, it's really cold, so the speed of sound may be as low as 660 mph or so (it depends on exactly how cold it is.) So Mach 1 there is a good deal slower than Mach 1 at ground level. In any event, merely giving a formula, and stating `100,000 feet ain't gonna do it' aint gonna do it. If you want to convince anybody of anything, you'll at least need to come up with some reasonable values for those variables and plug them in. If you want to do the math, figure out what the terminal velocity is at 40,000 feet. Are we talking about a body or a plane? In either case, assume it's pointing straight down (minimizing the area.) I'm not sure what value you'll use for the drag coefficient ... Neglecting air resistance, an object falling 60,000 feet (from 100k feet to 40k feet, where the speed of sound is the smallest) from rest wil accelerate to 1339 mph -- well above Mach 1. So, given a small enough cross section, or enough weight -- 100,000 feet IS enough. More than enough, actually. | How quickly the great ones are forgotten. USAF Captain Joe Kittinger | broke the sound barrier 40 years ago in free fall from 102,000 feet. | | http://www.afa.org/magazine/valor/0685valor.asp And there you go, trying to confuse the issue with facts! :)  SignatureDoug McLaren, dougmc@frenzy.com `I didn't believe in reincarnation in any of my other lives. I don't see why I should have to believe in it in this one.' -- Strange de Jim | You'll never actually reach terminal velocity -- you'll just get | closer and closer and closer. At first, you'll accelerate at the full | 9.8 m/s^2 (or a tiny bit less because you're getting further from the | Earth) ... but as you get faster, your acceleration will decrease, | until it's almost zero when you get close to terminal velocity. To follow up on my own post, that's not actually true. Since the terminal velocity will get lower and lower as the pressure gets higher and higher as you fall, you will reach and then exceed terminal velocity, assuming that the terminal velocity of whatever it is you're dropping is less than 1700 mph at sea level and you're dropping from 100,000 ft. (Probably true for just about everything you'd drop.) SignatureDoug McLaren, dougmc@frenzy.com Avoid reality at all costs. >To follow up on my own post, that's not actually true. > [quoted text clipped - 4 lines] >dropping from 100,000 ft. (Probably true for just about everything >you'd drop.) let's see if I got this right, You are going to fall faster than terminal velocity which is defined as the top speed of a falling object?? Actually terminal velocity is the point where drag equals the applied force (gravity) as the drag increases, the speed will decrease, If this was not so, a parachute wouldn't work, and would be just that much more "dead" weight as you penetrate to a denser atmosphere, the drag will increase. I would be willing to bet that you would be hard pressed to come up with a significant number to represent the difference between actual velocity and terminal velocity at any given altitude or density for an object which had been in freefall for a long enough period of time, say in excess of 120 seconds. more information available at: http://www.grc.nasa.gov/WWW/K-12/airplane/termv.html YMMV bob Theoretically, and practically, there would be no difference between actual velocity and terminal velocity for something that has been falling that long. By the very definition of terminal velocity, they would have to be the same for any given instant. The velocity would be constantly decreasing as the object drops into increasingly denser air. At least that's how I understand it. > >To follow up on my own post, that's not actually true. > > [quoted text clipped - 30 lines] > YMMV > bob | You are going to fall faster than terminal velocity which is defined | as the top speed of a falling object?? Yes! :) (Except that the terminal velocity is not the `top speed', as you mention immediately following.) | Actually terminal velocity is the point where drag equals the | applied force (gravity) Yes. | as the drag increases, the speed will decrease, You're assuming that the terminal velocity is a constant. It is not. It varies basied on altitude -- which doesn't really matter when you're only falling 200 feet, but from 100,000 feet -- it matters a lot. The formula given for terminal velocity Sqrt ((2 * Weight)/(Drag Coefficient * Density * Area) includes a density figure. That's the density of the air. Since it's under a sqrt(), dividing the density by four will double the terminal velocity. Some examples -- At 10k feet, the pressure is approximately 0.66 atm, so the terminal velocity would be 23% higher than at sea level. At 50k feet, the pressure is approximately 0.13 atm, so the terminal velocity would be 180% higher than at sea level. At 100k feet, the pressure is approximately 0.016 atm, so the terminal velocity would be 684% higher than that at sea level. | If this was not so, a parachute wouldn't work, and would be just | that much more "dead" weight Fortunately, the pressure at sea level is usually approximately a full atmosphere, so your terminal velocity will be as expected. But if you were skydiving and landing at the peak of Mount Everest (26,000 feet?), you'd land a lot harder than expected (about 70% faster than you would at sea level.) | as you penetrate to a denser atmosphere, the drag will increase. Yes. And the terminal velocity will drop. But what if you're already going faster than the current terminal velocity? You'll slow down, but will never *quite* reach terminal velocity, for two reasons -- 1) the terminval velocity will keep getting smaller as you fall, and 2) you never quite reach terminal velocity anyways -- you just get closer and closer. | I would be willing to bet that you would be hard pressed to come up | with a significant number to represent the difference between actual | velocity and terminal velocity at any given altitude or density for | an object which had been in freefall for a long enough period of | time, say in excess of 120 seconds. The terminal velocity formula has nothing to do with time falling or current velocity -- the only variables are weight, drag, and the force of gravity. To actually calculate the speed at each point as an item was dropped from say 100,000 feet would require knowing the drag coefficient and weight for your item, and require a lot of computation. It's certainly doable, but I'm not going to do it here. But certainly, if somebody were to jump out of a balloon at 100k feet, and open his parachute immediately, he would spend most of his trip down at *above* the current terminal velocity. Besides, this has gotten way off topic :) | more information available at: | http://www.grc.nasa.gov/WWW/K-12/airplane/termv.html And I used http://www.dangermouse.net/gurps/science/pressure.html to estimate the pressure (and therefore the change in the terminal velocity) at a given altitude. (This page was meant for the GURPS game system, but it's theory seems sound. If it's estimate is wrong, then my examples will be wrong, but the general idea won't be affected.) Ob R/C: http://www.austinslopesoaring.com is a new web site that covers pretty much what the name says. If you're in or near Austin, find out where we're flying and join us! :) SignatureDoug McLaren, dougmc@frenzy.com All right team! Let's get out there and rest on our laurels!" actually, YOU are ASSuming that I assumed something I did not. "terminal velocity" is an equilibrium between thrust and drag of a falling object. For all intents and purposes, an object in a stable freefall will reach a velocity so near the equilibrium point that for anyone who doesn't really care what PI to the the 1,000,000,000 decimal place equals is not going to care what the difference between "real" and theoretical "terminal velocity actually is. >You're assuming that the terminal velocity is a constant. It is not. >It varies basied on altitude -- which doesn't really matter when >you're only falling 200 feet, but from 100,000 feet -- it matters a >lot. A human has broken the sound barrier in free fall. Jumped from over 100,000 feet and exceeded Mach 1 before entering the denser atsmophere. > | You'll never actually reach terminal velocity -- you'll just get > | closer and closer and closer. At first, you'll accelerate at the full [quoted text clipped - 10 lines] > dropping from 100,000 ft. (Probably true for just about everything > you'd drop.) > ... Also, the speed of sound decreases as you get up higher, at least to a >point. At 40,000 feet, it's really cold, so the speed of sound may be >as low as 660 mph or so (it depends on exactly how cold it is.) So >Mach 1 there is a good deal slower than Mach 1 at ground level. ... There's a nice java applet on this page that lets you get the predicted temperature at different altitudes: http://www.grc.nasa.gov/WWW/K-12/airplane/atmosi.html It says to expect -69 F at 40,000 feet. This page has a calculator for Mach 1 at 40,000 feet: http://www.grc.nasa.gov/WWW/K-12/airplane/sound.html It suggests that Mach 1 would be 660 mph. Marty Doug McLaren opined >| > Ever heard of terminal velocity: >| > >| > Sqrt ((2 * Weight)/(Drag Coefficient * Density * Area). >| > >| > 100,000 feet ain't gonna do it. >You'll never actually reach terminal velocity -- you'll just get >closer and closer and closer. At first, you'll accelerate at the full >9.8 m/s^2 (or a tiny bit less because you're getting further from the >Earth) ... but as you get faster, your acceleration will decrease, >until it's almost zero when you get close to terminal velocity. >Also, the speed of sound decreases as you get up higher, at least to a >point. At 40,000 feet, it's really cold, so the speed of sound may be >as low as 660 mph or so (it depends on exactly how cold it is.) So >Mach 1 there is a good deal slower than Mach 1 at ground level. >In any event, merely giving a formula, and stating `100,000 feet ain't >gonna do it' aint gonna do it. If you want to convince anybody of >anything, you'll at least need to come up with some reasonable values >for those variables and plug them in. >If you want to do the math, figure out what the terminal velocity is >at 40,000 feet. Are we talking about a body or a plane? In either >case, assume it's pointing straight down (minimizing the area.) I'm >not sure what value you'll use for the drag coefficient ... >Neglecting air resistance, an object falling 60,000 feet (from 100k >feet to 40k feet, where the speed of sound is the smallest) from rest >wil accelerate to 1339 mph -- well above Mach 1. So, given a small >enough cross section, or enough weight -- 100,000 feet IS enough. >More than enough, actually. >| How quickly the great ones are forgotten. USAF Captain Joe Kittinger >| broke the sound barrier 40 years ago in free fall from 102,000 feet. >| >| http://www.afa.org/magazine/valor/0685valor.asp >And there you go, trying to confuse the issue with facts! :) I wrote a program to do free fall jumps by human beings. It took into account both gravity and air density. For a jump from 30,000 meters the statistics are -- the fall from 30000 meters took 256 secs max v = -253.368234 m/sec at 23758.89 meters max a = 3.05881450 m/sec**2 at 19001.98 meters -- Jumping from about 60 miles gives -- the fall from 100000 meters took 343 secs max v = -980.605556 m/sec at 43844.68 meters max a = 30.9256684 m/sec**2 at 27304.72 meters -- Note, the jumper is not in orbit, and the planet is not rotating. -ash Cthulhu for President! Why vote for a lesser evil? I'm pretty sure a model airplane pointing straight down has less drag than a human body does and Joe Kittinger hit 614mph from 102,000. Call me to tell me I'm wrong after the experiment is over. Don > Ever heard of terminal velocity: > [quoted text clipped - 48 lines] > > > > > > Ben Hallert Yes it will..here's a link to Joe Kittinger who jumped from 102,800 feet and MAY have reached Mach1. http://home.att.net/~1.elliott/JOEKITTINGER.HTML Two jumps from a higher altitude are being planned for right now. Brian > Ever heard of terminal velocity: > [quoted text clipped - 63 lines] >>> >>>Ben Hallert >Starting with one of these engines, say perhaps an 'L' or 'M' size, I >imagine that an experienced modeler (with a good aeronautical background) [quoted text clipped - 4 lines] >control radius ofthe radio (or visibillity of the operator) is a concern, >you could have more then one operator spaced across the range. >Legal issues aside, can anyone think of any technical reasons this couldn't >be done? All it would take is time and money. I'm sure a qualified aerodynamicist could work out the thrust-to-weight-and-drag formulas so that you could be sure of reachig your objective. The speed of sound varies with temperature. At 24C (~75F), the speed of sound is 1135 fps. <http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html> You're going to need pretty good bioculars, well-focused, to keep your model in sight from drop through the speed trap. Once the rocket's done burning, I guess things will calm down eventually. Flutter and adequate power to control the surfaces seems to me to be the next major hurdle. You might want to test the model in a supersonic wind tunnel prior to turning the model loose anywhere near humans. Legal and insurance issues aside, you don't want to hurt anyone (I imagine). I'm sure that some people know what it takes to control an RPV at those speeds; whether they can or will tell you what they know is another issue entirely. Let us know how things turn out. Marty > >Starting with one of these engines, say perhaps an 'L' or 'M' size, I > >imagine that an experienced modeler (with a good aeronautical background) [quoted text clipped - 36 lines] > > Marty If it looks like you are actually going to do this, please let us know in advance so I can arrange to be as far away as possible. Thanks. At the speed of sound your model is going to be covering the dirt at roughly 1000 feet per second. Depending on the altitude you choose to attempt this at. But what this means is from your 1/2 mile point of release, you'll have something like 3 seconds (or less) to spot it, orient to it (figure out its attitude) and command it to do...........................? This of course assumes the beast is stable enough on its own to fly straight and level from release to the point you tell it to do something. Otherwise, by the time you figure out what it's doing, and figure out what to do to correct it, and tell it............................................Splat! I suspect it will zip past you so fast, you'll still be looking for it to appear in your field of vision as it disappears behind you. Chuck > Hi guys, > [quoted text clipped - 30 lines] > > Ben Hallert >At the speed of sound your model is going to be covering the dirt at roughly >1000 feet per second. Let's say 1100 fps at a comfy temperature. > ... Depending on the altitude you choose to attempt this >at. But what this means is from your 1/2 mile point of release, you'll have >something like 3 seconds (or less) to spot it, orient to it (figure out its >attitude) and command it to do...........................? 1/2 mile = 2500 feet = 2.27 seconds. Of course, it won't reach top speed instantaneously, so perhaps the flight team will have 5 seconds to spot and fly it on its way toward them and perhaps another 3 before it becomes invisible. Maynard Hill has shown that models can be flown autonomously. Part of the investment in the Fastest RC Plane on Earth will have to be an autopilot and a GPS system. Do what Maynard did: takeoff, turn on the autopilot, watch the flight, recover control, land. (I am NOT in any way criticizing Maynard or his team. Just describing what they did.) Not technically impossible. Not cheap. For those who have the money, it would probably be something to do out on the salt flats. I'd invest in a pretty good bunker myself, just in case, while the kinks were being worked out of the system. Marty > Not technically impossible. Not cheap. > > For those who have the money, it would probably be something > to do out on the salt flats. I'd invest in a pretty good bunker > myself, just in case, while the kinks were being worked out > of the system. If the AMA hasen't banned such attempts, they should. Lest we not have a hobby after the feds take notice. I don't see what all the hoopla is about, chasing records the Air Force beat 40+ years ago with vacuum tube controlled vehicles. >I don't see what all the hoopla is about, chasing records the Air Force >beat 40+ years ago with vacuum tube controlled vehicles. Why does a person climb any mountain that has been climbed before? Why does anyone do anything that even though someone may have doen it before, that anyone has not done it before? Why does anyone ever wish to travel "...just over that hill?" For whatever reason it may be, I am truly thankful for those reasons and the people that climb those hills, mountains, & whatever. HC > >I don't see what all the hoopla is about, chasing records the Air Force > >beat 40+ years ago with vacuum tube controlled vehicles. [quoted text clipped - 5 lines] > > Why does anyone ever wish to travel "...just over that hill?" I would think you would have those answers for us Horace! How many of those "Election" hills have you been up? [ about supersonic R/C planes ] | If the AMA hasen't banned such attempts, they should. It's not up to the AMA. They have no authority to ban such attempts. | Lest we not have a hobby after the feds take notice. I believe that FAA regulations already make such flight illegal, at least except under certain specific conditions (like having official clearance, being in an unpopulated area, etc.) SignatureDoug McLaren, dougmc@frenzy.com Most people will listen to your unreasonable demands, if you'll consider their unacceptable offer. > Hi guys, > [quoted text clipped - 6 lines] > Hypothetically, I've wondered about what it would take to fly an R/C plane > and take it supersonic. sniperzz... it could be done... get a level 2 Tripoli card. Buy a K-500 or 1000 motor ( wont need a L or a M those are wayyyy too big) , build a carrier plane and the "rocket plane". Fly the combo towards you and as it passes overhead fire off the rocket plane... that way it wont pose too much of a problem in nailing your group of ground support. ( mind you that they are all behind the line of motor ignition point. Either the rocket plane will shread in 2 seconds or it will fly for 10 seconds... a final note... put your AMA and Tripoli card near the exhaust of the rocket motor.. if any of the Powers of Might from either group see this flying feat... :) Scot D TRA 539 The key here is Radio "Control". Since supersonic speed will take the model out of sight in a split second, you then have to include the issue of UAV control. The technology is here right now to put supersonic and UAV together to do what you "theoretically" suggest, but from the pure issue of fun, why? I sit here and spin up my imagination, and I still can't see what would be fun about it other than to use it as a "trophy" accomplishment (as in: "Look what I can do!". Sort of like how the character Stuart acts on MAD TV in the U.S.) MJC > Hi guys, > [quoted text clipped - 30 lines] > > Ben Hallert > The key here is Radio "Control". > Since supersonic speed will take the model out of sight in a split >second, you then have to include the issue of UAV control. Maynard Hill set an FIA record using a UAV. It was under human control only at the beginning and the end of the flight. > The technology is here right now to put supersonic and UAV together to >do what you "theoretically" suggest, but from the pure issue of fun, why? ... "De gustibus non disputandum." There's no arguing with taste. The fellow who started this thread only asked whether it was technically possible, not whether it was legal, wise, or entertaining. I think it's technically possible. All you need is time, money, a few moderately clever people, and wide open spaces. The laws of aerodynamics are what they are. The technology exists. I know that I won't invest in the project and I gather that you won't, either. I wouldn't be too surprised if some wealthy people decide to do it or something like it. Folks with money to burn often burn money. :o) Marty Thanks all for your replies! I appreciate your insight and experience. The control issue is indeed a tricky one. I imagine that some of the challenges could be mitigated through use of something like the Co-pilot (which uses IR to keep the craft level based off the horizon). The flutter issue is also significant. I imagine that if there were a situation where metal geared servos were appropriate, this would be it. As to the question of 'why', I imagine that someone who did this would be doing so because of the challenge, but I don't plan on trying it any time soon. As another poster mentioned, it might endanger both hobbies, but the technical challenges are certainly interesting enough to consider. Best regards, Ben Hallert > "De gustibus non disputandum." There's no arguing with taste. > The fellow who started this thread only asked whether it was [quoted text clipped - 3 lines] > a few moderately clever people, and wide open spaces. The laws of > aerodynamics are what they are. The technology exists. It's a lot more than lots of power, autopilots and strong structures. Supersonic flight involves a different set of aerodynamic rules, since the air has no time to respond to an approaching body, and the response of the airplane to control inputs is not so simple. The Concorde was an example of the terrific expense of supersonic flight. I don't think it would be feasible for anyone except someone with an awful lot of money. Dan >> "De gustibus non disputandum." There's no arguing with taste. >> The fellow who started this thread only asked whether it was >> technically possible, not whether it was legal, wise, or entertaining. >> I think it's technically possible. All you need is time, money, >> a few moderately clever people, and wide open spaces. The laws of >> aerodynamics are what they are. The technology exists. > It's a lot more than lots of power, autopilots and strong >structures. Supersonic flight involves a different set of aerodynamic [quoted text clipped - 4 lines] > I don't think it would be feasible for anyone except someone with >an awful lot of money. I think we're in complete agreement: a hard problem, but technically soluble (since it has been solved many times by many aircraft), given enough time and money. I'm not going to put any of my time and money into this project. I'm just answering the narrowly focused question that was asked at the beginning of this thread: could it be done. My amateur guess is "yes." Marty |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2009 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.