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Some ideas about RC planes
January 22, 2006 on 6:49 pm | In Technology | 4 CommentsI’ve always been a big fan of aviation, and always wanted to learn to fly RC planes, and even build a few of my own, but living in Iraq during the embargo years didn’t help much in fulfilling this dream.
Anyways, I’ve been reading and following RC groups around the net for quite some time, and though I still haven’t flown an RC plane, I think I’ve learn quite a lot from reading all the forums around the net.
One of the topics that are often discussed is long endurance RC planes, especially within the UAV (unmanned aerial vehicles) communities and how to achieve this. Most of the discussion usually revolves around using composite materials in building the air frame, or how to improve fuel consumption and engine efficiency, and sometimes (very rare) someone thinks about hybrid RC planes but without having any clear idea on how to do this.
So, here are some of the ideas that I’ve had across the years:
First, I want to talk about hybrids. When thinking about a hybrid, most people tend to use the same analogy for cars, which is using the gas powered engine to charge a set of batteries that are later used to power an electric motor that in turn drives the car. This usually works in cars because cars don’t usually utilize the power provided by these engines to its full extent, and spend a considerable amount of time idling in traffic jams. This analogy falls apart with airplanes since they are bound by physics laws and have to keep moving above a particular minimum speed. So, what kind of hybrid solution can be used?
Well, my idea is about using solar cells to provide electric power. I think it has already been proven that its possible to fly a glider using solar power alone, at least during day, and have a gas powered engine kick in only when the plane requires extra thrust, say during climb. Even if those solar cells don’t provide enough power to drive a propeller, they can still be used to provide power to run the flight electronics and servos, and even drive a relatively high power video (and/or telemetry) link for many hours.
Integrating solar power in an RC plane, even with not so efficient cells, doesn’t add a lot of weight. There are many (extremely) light weight, and flexible solar cells being sold around the net for very reasonable prices, that will not add much weight to the RC plane. If you consider the weight saving from requiring having less battery packs on board, there is a good chance that there won’t be any increase in weight at all. You would still need to have some battery packs on board to provide for backup and insure stable operation, but no big packs would have to be carried on board.
Next in line, there is engine efficiency. There has been a lot of talk about how 4-stroke engines are more fuel efficient, and how fuel injection, electronic ignition, and using smaller carburetors can dramatically reduce fuel consumption, so there’s not much to talk about here.
One, simplistic, way to increase flight time is to simply carry more fuel. The way I am thinking about achieving this is by designing a wet-wing, aka using the wing structure as a fuel tank. While this is no new idea in real planes (even small Cessna planes use wet-wings), I still have to see someone implement this in an RC plane. Some of the advantages of using a wet-wing design include increased available space in the plane haul, relatively lighter and possibly smaller haul design since the weight of the fuel will be carried inside the wings. Other benefits include less strain on the area where the body of the plane attaches to the wings, since the body will be considerably lighter.
The major hurdle, and the reason I think no one has done this on an RC plane, is that it’s not really easy to seal the wing structure against leaks while still maintaining the flexibility and light weight of the (dry) wing. Another reason is that in building such a wing, you need to thoroughly consider the materials that will be used in the construction of the wings, since the fuel can be corrosive against many materials.
Considering the huge advances in composite materials, and how they are being increasingly used in the construction of RC planes, such as carbon fiber, epoxy, Kevlar, and Teflon, I believe its has become more feasible to build such a wing. It will still require a considerable amount of engineering work in making casts for the custom wing molds, but I believe it’s doable.
Another idea that I’ve been thinking about, though I don’t know if it works or not, is using part of the thrust generated by the propeller as a sort of a super charger (or turbo charger if you want), to increase the amount of air that is going to the engine, and hence increase the total power generated by the engine. Of course we are talking about internal combustion engines here. In a very simplistic way, this can be achieved by using an adapter to increase the area of the carburetor air intake, hence catching more of the air flow generated by the propeller. Again, I don’t know if this will provide any significant increase in power, or if it will provide any increase at all, but I think it’s not that hard to experiment with to find out.
Of course, one could integrate ideas and build a wet-wing and have the top surface of the wing covered with solar cells. It will be quite a feat to do that, but I think the outcome, if properly engineered, would be quite remarkable.
I guess that’s about it for this post. I have a lot of other ideas for UAVs, dealing with automatic route planning, maintaining constant low ground altitude (while avoiding crashing), terrain following, and laser guidance, but I think that I would be getting myself in a good amount of troubles by discussing those topics anywhere online, especially if such topics are raised by an Iraqi guy. I already get enough hostile comments from many people around the net just because of where I come from. I guess there are a lot of ignorant people out there who truly believe that ignorance is indeed a bliss, but what can you do about that?
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How about a miniture blimp?
Put solar panels for power, a cell phone for gps and control. Probably will stay up in the air much longer than RC planes. With proper knowledge of jet stream and local weather it could probably go hundreds of miles ie. like weather ballons.
One can even devise a miniture helium tank to replensh the slow leak of the blimp.
Of course you’ll pay a lot of money for roaming charges.
jonglee1977
Comment by jonglee1977 — 30 January 2006 #
Nice to see you here jonglee1977. Did you get my last email about the mirror?
I did some reading about that, mostly studying the feasability of a high altitude (not so) mini blimp that carries some 5-6lb of payload plus all the power, control electrronics, and communication equipment. I was more thinking of integrating a satellite phone to relay telemetry and recieve commands through SMS, which would reduce operational costs considerably. However, there are a number of hurdles to overcome. First, you need to carry enough batteries to power the blimp during the night. Second, the extreme low temperatures encountered at such altitudes. Third, the relatively uncontrollable, and unpredictable weather conditions at high altitudes. At over 60,000ft, you will encounter quite high wind speeds, which could stress the blimp. Finally, while it has already been done, though not for long periods of weeks, the use of such a vehicles are rather limited. You might want to google jp aerospace, or take a look at this guy, who is working on a mk2 of that project.
On the other hand, a long endurance UAV does have a wide variety of uses, from the military, to survelliance, and even as a relatively safe and low cost test platform for new technoligies (no humans on board, so there are no lifes at steak of something goes wrong). One of the problems with long endurance UAVs is supplying enough electrical power for the electronics. Sure its possible to use an alternator connected to the main engine, but that adds a considerable amount of weight, and draws a considerable amount of power from the relatively small engine that runs the UAV. By using solar panels, the need for an alternator would be eliminated, at least during day missions. Another use for the solar panels could be to supply power to run an auxilliary electric engine, which would enable the UAV to travel faster, or reduce the load on the main engine, by reducing or even eliminating the need for the main engine to produce thrust and just run at idle to produce power for the flight electronics.
Those were just some of my thoughts on how to approach the problem of designing a long endurance UAV. As I said in the original post, I have another bunch of ideas regarding ground control, navigation, (real) automatic landings and takoffs (rather than some form of controlled crash landing), laser guidance (for droppable payloads), among other things.
Comment by IraqiGeek — 30 January 2006 #
Yes I checked out the mirror, you can also download additional stuff from the wincegcc forum on yahoo if you want to add them to your mirror.
As to your ideas, well those aren’t the things an average person with some basic electronic knowledge can build. You might as well try to be NASA. I can build a car sized blimp, heck they probably sell it on Ebay. A ballon requires no power to stay up in the air, so night is not really a problem. I think the old derigibles were able to make trans atlantic flights with an 8 gallons of gas and a small 50hp engine.
In contrast, a RC plane will stay in the air for 10-20 minutes with a gas or glow engine.
The glider attached to a weather ballon was cool. I think the germans attached a biplane to their derigibles. This is probably something you can build. Although it sounds like your interest lies with planes rather than ballons.
Well it was nice banter,
Jonglee1977
Comment by jonglee1977 — 30 January 2006 #
Jonglee1977,
Nothing that I have mentioned can be regarded as NASA level technology. Most of it has already been done in the RC community, only on separate projects, and never combined in a single effort. If you google around, you will find a good number of RC builders who have managed to build UAVs that can fly for 2000-3000km, without using any hi-tech methods. Sure they did some mods to the engines and communicaions, but those were nothing that the experienced RC builder couldn’t do. I have also found a couple of people who were talking about building wet-wing designs, tough never found any reults.
Its getting a lot easier, and cheaper, to use compisite materials such as carbon fiber and epoxy to build RC planes. Get a descent CNC router (you can build one for under $1000 if you have some tools and good knowledge about CNCs, again google around to see how many DIY CNC projects have been done) and you could pretty much make any shape or size art you want, with virtually any material you can get access to.
As for control software, there are many RC autopilot projects, some are open source, others are commercial, but still, available to the average RC builder. Check out sourceforge to see how many people are working on that. Also take a look at the Paparazzi autopilot project which has some very nifty features. Look at gumstix who sell some powerful and increadibly small xscale based computers running Linux. A 400MHz Xscale can do give a reasonable amount of processing power, considering that you don’t have a GUI overwheliming it, and that its running Linux, which runs a lot faster and provides a lot more flexibility than WinCE does. The rest is all software that can be done with a couple of descent programmers, not rocket scientists. There is very little, to no electronics design invilved.
All of the Satellite phones I have worked with in the past provide a serial interface, which operates using standard AT commands, the same goes for a good deal of mobile phones. If you dont like to use phones at all, google around to see how many types and models of wireless modems are available. Some use AT commands, others provide a seamless wireless serial interface that is redicolously easy to interface and use. As far as electronics are concerned, there is a goodchance that the biggest prblem you will face is finding or making an efficient antenna for your wireless modem that is small and light enough to fit on board the UAV.
Comment by IraqiGeek — 31 January 2006 #