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RE: Zero speed landing possible ?
He's mentioned zero forward speed, but does this include a requirement for a zero fall rate?
Most of the "drop" solutions entail letting the aircraft stall, then drop to the ground from differing altitudes... this may not be what he is hoping to achieve, though the latter has not been defined. |
RE: Zero speed landing possible ?
I think that low vertical ground speed is the most important thing, followed by low vertical speed.
Hugo |
RE: Zero speed landing possible ?
Here is a link to a video of an airplane with a dethermalizer. It dethermalizes pretty close to the ground, but you can get the idea.
http://www.rcuniverse.com/magazine/a...article_id=256 I did some test flying of free flights on a really calm day. They were dethermalizing a couple of hundred feet up and I had to take at most three or four steps to catch them. Never experienced it that calm before or since. |
RE: Zero speed landing possible ?
Wow, that really is a zero length landing!
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RE: Zero speed landing possible ?
Somebody has already brought a zero airspeed landing device to market. It is being sold to the lightplane sector as we speak.
Sorry I don't have a link, but I bet there are some. |
RE: Zero speed landing possible ?
ORIGINAL: da Rock Somebody has already brought a zero airspeed landing device to market. It is being sold to the lightplane sector as we speak. Sorry I don't have a link, but I bet there are some. Honest injun |
RE: Zero speed landing possible ?
Yup
And the airplane lands pretty much straight down. |
RE: Zero speed landing possible ?
ORIGINAL: Rocketmagnet Make it as close to the density of air as possible Although the rapid prototype resin is denser than wood, one could make amazingly optimal frameworks (involving loads of little tubes and struts) because manufacturing it wouldn't be a problem. One could use a stress analysis package to optimise the layout of the framework, in the same way the inside of animal bones comprises lots of tiny structures following the force lines. Not as insanely fine as in this picture, but you get the idea. Hugo I built a paper model of a cathedral from stiff paper and although the parts were floppy and paper is kinda heavy, the final stucture was amazing. Paper can be assembled into very strong and lightweight, monocoque structures. In light of the rising expense and diminishing quality of imported balsa, paper and wood glue starts to look increasingly attractive to me as a building method. Imagine an airplane kit you download from the internet in a ZIP file, scale to whatever size you desire, then print out on various thicknesses of paper and cardstock. Simply cut out the pattern, scribe and fold, then glue together following the sequence, finally spray with fuel proof sealer. Even scale features like camo and markings could be printed by the computer printer. There may be a need for a few pieces of plywood in high stress areas like firewall and wing attachment points. Spars might be reinforced with carbon tube or ribbon. Incidently, the cathedral didn't deserve a berth in the van on my last move so I did a little "destructive testing". I intended to crush it under my foot but it just dented on the first try! I was able to stand on top of the building and I weigh 165 pounds! I finally stomped it into a compact pile after jumping up and down on it several times. |
RE: Zero speed landing possible ?
let the plane grow itself? Imagine an airplane kit you download from the internet Hugo |
RE: Zero speed landing possible ?
ORIGINAL: Rocketmagnet Hi all, I would like to build my first RC airplane. However, I much prefer making things that are practically impossible, so, rather than getting a kit I would like to make up my own plane. To make this project as hard as possible, I would like the plane to have the following features: 1. Stereo gimballed cameras at the front, a bit like an owl's head, so I can fly it with a VR headset on. (not too hard) 2. The ability to make a zero speed landing. (hard) 3. Some feet and legs, so it can absorb the impact of the landing, or possibly land on a perch. (hardish) It's number 2 that I would like some advice about. Does anyone have any experience making a plane which can do a very low speed or zero speed landing? Doing some research, I think the plane will need the following: 1. Wings which can reshape themselves considerably to be able to provide maximum lift at the low landing speed (slats and flaps) 2. Wing load, gyroscope, wind and ground speed, angle of attack and acceleration and ground distance sensors. 3. Computer control for the landing. There are two ways I can imagine landing at zero speed. The way some birds do it is to fly below the landing point (a perch), then fly up towards it, reaching an almost zero speed apex just at the landing point, then grabbing it with their feet, and using them to come to a complete stop. This sounds physically possible, but requires some way to accurately sense the perch, which would need either an electronic perch, or a good realtime vision system onboard. The other way is to land on the ground, but I can't imagine how it could be possible to come to a stop in the air, without needing to fly below the ground, and without flapping the wings. I would prefer the land the second way. Can any aerodynamics experts suggest whether or not they think this is physically feasable? I am not interested to hear from people telling me that this will be a difficult/impossible project. I know, that's why I'm interested in it. Many thanks in advance for any replies. Hugo Just for your consideration, there are several known ways to move an object away from the ground: -Difference of densities (like hot air or helium balloons) -Ballistic (like stones, bullets and rockets) -Magnetic repulsion (like fast trains) -Change of velocity or acceleration of the air by a surface (like airplanes, kites, autogyros and helicopters). You have mentioned the last one is of your interest, as well as exploring new approaches. As you know, proper surfaces moving in the air create a reaction force named lift, by changing the velocity (or direction) of the air. That change in velocity is the famous acceleration of the formula F=m*a. These surfaces have kinetic energy while moving, as well as potential energy when located high above the ground. That energy can be transferred from one type to another by reducing velocity (decelerating) while gaining height, which the bird does for "perching", as the roller-skater does at the top of the track. Exactly the same is done by 3D models, which transfer the lift force from the fixed wing moving in the air to the steadly rotating wing called propeller or air screw, while reducing the velocity of the CG gradually to zero. A more violent reduction of that velocity is called crash, in which the kinetic energy is used to put the model parts apart. Violent stop by brakes or counter rockets is possible, but it has been proved not practical for human transportation or heavy machines; however, sudden stop in midair can be done with light models with Variable Pitch Propellers or 4D. Next, I refer you to several links that may help your imagination and skills putting together the machine that you want. See Advanced Video Tutorials (Lunar landing) at http://www.wild-wings.co.uk/ http://www.youtube.com/results?searc...deo_avg_rating http://www.youtube.com/watch?v=XD1tX...eature=related http://www.youtube.com/watch?v=kIuS4...eature=related If you prefer achieveing something different from 3D or 4D, just think of combining the flying of your fixed wing machine with differential of densities, ballistic (as mentioned above), drag (like parachutes), or transformation of kinetic energy to potential (like the deceleration by cable-hydraulic device of the war carriers, shock absorbers of the cars, parachute at landing, etc). Consider; however, that weight will always be the enemy of any flying creation. Best regards! |
RE: Zero speed landing possible ?
So, how would you go about designing a wing which produces the maximum lift at very low velocity? I assume that it basically needs to have the highest possible angle of attack. And therefore it needs to be heavily cambered to prevent stalling? Is there a maximum possible AOA? 45 degrees? Is there, could there be such as thing as an optimum wing for maximum lift (if you don't care how much drag it produces).
Hugo |
RE: Zero speed landing possible ?
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You want a wing that has a lot of under camber.
That is why I had mentioned using stacked aileron type of design. ( see drawing) When you go from normal flight to slow speed you bring the portion of the wing that is shaped like a flap, that will increase the camber of the wing creating lots of lift and drag. You could also actuate the aileron as a flaperon adding even more camber and lift. At this point you would have to use some sort of reaction type of thrust to control the roll axis because I doubt that the ailerons would have much effect on a highly cambered wing. You may also want to pick up a book such as Andy Lennon's on model aircraft design, there is a lot of good info in there. Edit to add: The idea of a variable camber wing is one which I have been thinking about for some time now. While there are a lot of issues involved with such an idea it has this as a draw for me. When you increase the camber it will increase the lift, it will also increase the drag so when you apply it it will act much like hitting the brakes are far as airspeed goes. The down side is that you will also change the pitching moment as well, so your tail surfaces and controls will have to be able to compensate for this. Another down side will be the added weight for the structure, hardware and controls needed to make it work. As far as tail surfaces a flying horizontal stab rather than the traditional stab and elevator may also be needed as well as fairly large surfaces to allow for shifts in the apparent COG. One of the hardest thing to overcome is going to be the loss of control effectiveness as airspeed decreases... As well as a myriad of other things that I can not think of at the moment. |
RE: Zero speed landing possible ?
Very well put, Iron Eagle!
Actually, there have been competition model sailplanes that have used variable camber airfoils with flexible skin. There is much research and experimentation regarding this for war airplanes. The idea is to mimic the wing of the birds, which can adapt to a broad range of air velocities and conditions, keeping a high efficiency. A wing of fixed shape can only be efficient and good for a narrow range. The limits to create such a wing are the weight, as you mentioned, as well as the complexity of controls and mechanisms and the availability of flexible and strong materials. You are correct about the maximum angle of attack and camber, Hugo. Coefficient of lift is directly proportional to the AOA, since more mass of air is deflected and higher is the pressure differential between top and bottom surfaces. In order to keep the same velocity, more engine's muscle is needed, to overcome the increased drag (associated to lift more than to velocity). There is a physical limit to that, although: The bottom surface of the moving airfoil always compresses the air, for which there is no limit. However, the top surface always expands the air above it, more and more with the increment of the AOA. Around 20 degrees or little more (for cambered efficient airfoils), the molecules of air loose their bond or attachment to the top surface. Beyond that point, the air stops contouring docilely around the airfoil, allowing it to modify its velocity and pressure, and offering physical support or lift for the airfoil. Beyond that point, irreversibly the air detaches from the upper surface, initiating great turbulence, which causes loss of the low pressure above the surface, as well as much friction and waste of energy. Then, the airfoil stalls, and the lift is gone. |
RE: Zero speed landing possible ?
ORIGINAL: lnewqban Then, the airfoil stalls, and the lift is gone. Most assume the lift is gone because of the usual action of the airplane, but it most certainly isn't. |
RE: Zero speed landing possible ?
I totally agree, Da Rock.
I should have written that the lifting force is drastically diminished. The forces pushing up do not disappear completely, since the bottom surface keeps compressing and deflecting some mass of air downwards. I believe that can be observed when the dethermalizer of a model opens, making the wing stall, slow down and becoming part of a parachute. It is also evident during high speed stalls, when the airfoil looses the grip on the mass of air, but still pushes it through. Since the turbulence and the chaotic flow that is created right after the stall point is reached consume more energy than the flow below the stall point, a pronounced decrement of the velocity of the airflow and airfoil follows, which makes the stall irreversible if the AOA is not reduced. Usually, recovery from stall takes dropping of the nose first, and then, incrementing the velocity of the airfoil. More about stalls can be found at: http://en.wikipedia.org/wiki/Stall_(flight) I would also add that the intensity of the stall varies with each airfoil and the profile of the wing. While for regular airplanes a soft or gradual stall is desirable, the more intense the better it is for aerobatic machines. Thank you for your observation. |
RE: Zero speed landing possible ?
I once did a zero speed landing with a Genesis. Granted, I was landing into a 20 knot headwind... :D It's kinda funny watching a pattern ship hover horizontally down to the runway... got a pair of 10's on the landing for my effort, too!
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RE: Zero speed landing possible ?
Of course you could always keep the "wing" moving but this has been dismissed as a "hovering device"...
Too bad though... that effectively rules out fans such as in the Mollier Aerocar, VTOL craft, etc. |
RE: Zero speed landing possible ?
Autogyros have done zero speed landings from day one.
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RE: Zero speed landing possible ?
Exactly... and it's not "cheating" the wing just keeps moving in a circle... :D
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RE: Zero speed landing possible ?
Birds have millions of years of R&D to get were they are. Humming birds are at the extreme end of a "zero speed landing" and ducks are not quite as close.
Perhaps the most valuable advance for the humming bird is the "computer" needed to control all the variables (camber, thrust, AOA...). Birds use a combination of variable airfoil and vectored thrust to land on a perch. Although airspeed can be lost while climbing to the perch, they always use the variable airfoil and vectored thrust to finish the job. I don't remember the names, but I have seen planes that use a ducted fan or even a motor (usually electric ) that can rotate to provide a more vertical or even rearward thrust. Those techniques are less complicated (lighter) than, but similar to the basic principals used on a Harrier. You may even consider a combination of seperate motors for horizontal and vertical lift. If you want to land like a bird, watch how they do it. They may not talk, but actions speak louder than words. |
RE: Zero speed landing possible ?
ORIGINAL: opjose Of course you could always keep the "wing" moving but this has been dismissed as a "hovering device"... Too bad though... that effectively rules out fans such as in the Mollier Aerocar, VTOL craft, etc. I almost put money down on the Moller Aerobot in the mid 80's. At that time he had estimated a year to two til the first production kits would be ready. Here we are in 08' and it is still little more than a concept. That shows just how complicated the whole issue is as far as manned transport. However, when dealing it as a modeler we have not got the same threat to the passengers in the vehicle. It is so sad that he has not gotten it into production yet as I think it would be a boon to GA. As I mentioned in a prior post there is a computer base system that could be used in a model that was called a stamp back in the 80's and 90's, it may have been surpassed by a newer or smaller computer system that could be installed in a model but I do not know for sure if that is a fact. I have been out of robotics and electronics for some time now and do not know what is the "latest and greatest" thing out. I would have to think that given the micro- tech that I have seen in phone and alike that something that would aid in the control of a model aircraft is out there. Still trying to get an aircraft/robot to perch is a daunting task. I think that it can only be done with vectored thrust as well as a reaction control system to take over when aerodynamic controls are no longer effective. Back in the old days I worked with the platforms and control systems that made such things possible but they were well out of the price range that could be used in any hobby. But like anything else as the tech. becomes older there are cheaper and smaller devices that will work I just am not up on it (guess it is about time to get a subscription to "nuts and volts" again). DA, I have a fellow club member who brings out a new auto gyro every few weeks to the field. It is a kick to watch him put them through their paces! He has a new "gyro plane" he just built that is wild, with a smaller rotor and a small wing it has an amazing flight envelope... |
RE: Zero speed landing possible ?
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Here's my feeble contribution. This is the second one over about a 6 yr. period unchanged from the first one. Funny it was mentioned at the beginning of the thread about the way birds approach on their landings in a horizontal direction, then swooping up to slow down just before landing. I found that was the best, most stable method for landing this thing. Absolurely no wind blowing, Coming toward myself at about half throttle, nose slightly high, maybe 10 degree angle doing about 15 to 20 mph. about a ft. off the ground. When it's about 10 ft. away gradually pull back stick while adding throttle. It will end up stopping about 4 ft. off the ground. Slowly back off the throttle and it will settle down slowly. One thing about the flat plate wings is, they don't have a very abrupt stall speed. This also has a very rearward CG. When you go into a hover at altitude with enough power on, the wing stalls then it wants to tilt the nose straight up. It will sit there hands off with the tail sitting still and the nose describing about a 6 in. circle. With a little stick finagling, you can get the nose to stop. Flying surfaces are almost twice the size as scale. Hope this helps a bit for what your in for:D
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RE: Zero speed landing possible ?
a computer base system that could be used in a model that was called a stamp back in the 80's and 90's Flypaper, that's a sweet plane! In how much distance could you go from 20mph to stop? Hugo |
RE: Zero speed landing possible ?
I usually come in from the side, and when it's level with me, start pulling up. It ends up about 6 ft in front of me pointing straght up. On a calm day, it always takes off vertically. This is a fun plane that gets flown regularly, even on windy days. For instance, with the rudders top and bottom and going along at full throttle, about 35 mph, full rudder and a bit of elev. and it will do a 180 degree turn in almost its own length. Flies on its side, knife edge flight just as happy as upright. The little castor wheel on the corners are fully functional with springs and are necessary as most landing are not always soft.:)
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RE: Zero speed landing possible ?
If someone has said this, please indulge me. I got half way through this thread and my eyes started to cross. It seems to me that when a bird's wings start flapping he is not so much flying as vectoring thrust, ala Harrier, geese, humming birds, the Bell X-14,the Osprey, the Klingon Bird of Prey. By definition to arrive at zero velocity deliberately, by "flying" on a wing is a contradiction in terms. You cannot be and not be at the same time and in the same sense. Rocketmagnet's second requisite offends logic.
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