AlphaSheeppig

The presentation went surprisingly well. The two presentations before me were really bad, so any nervousness I had been feeling vanished. The questions were tricky, but I was prepared for them... They were the generic sort though - along the line of asking me to elaborate on how I validated my simulations, the guy that kept asking obvious questions (to test whether I understood what I was saying, I guess), and then the one who asked me to speculate on where results from some other unrelated case would fit into my data - ironically, it was the exact same thing my advisor asked me when I first started getting results. Thanks to everyone who gave advice. All of it helped. To anyone who stumbles across this at a later time looking for advice, the best advice I can possibly give after having been through it once is to have in depth knowledge what you are talking about.

Lol... You mean everything then? It's a LOT of work, but a good place to start is to go to a local college and university and ask what textbooks they prescribe first years in whichever fields you're looking at learning, and then work through those books. In my personal experience, math is the hardest to understand, so I'd guess it's easier to start with, say, physics, and then as you require this or that mathematical technique, go learn that technique. I find that math is often easier to learn when you see it's applications right from the start so you don't get overwhelmed by the abstractedness (if that's even a word) of it all.

Yes, it can be done practically... Get yourself a cheap R/C plane from a hobby store, get a wireless security camera with decent picture quality and a good range that can transmit to your laptop, and then use duct tape to tape it onto the plane, and then be prepared for a lot of crashes until you get the hang of flying it. To control it with your iPhone is a different story, since as far as I know, the iPhone isn't capable of transmitting radio waves you need to control a typical R/C aircraft (usually 27 MHz or 2.4 GHz, depending on what type of plane you use). There's a video tutorial on how to make one here.

The F-117 is really in a class of it's own. They say bats fly into it at night because their echolocation can't pick them up... It's not really any curved surface that is a problem, but rather concave surfaces, since these tend to reflect the radar waves straight back. In general, with modern stealth aircraft (now I'm talking along the lines of the F-35 and F-22), the approach is more to eliminate the concave surfaces (such as where the wings meet the fuselage) by blending these with a flat surface, or by making it a sharp corner. These have the disadvantage that at some critical angle they reflect the radar waves straight back, but if the angle is even slightly off, then the radar is deflected enough to be invisible, if it is detected, it would be pretty small, and would maybe be mistaken for a flock of birds or something. I guess it could possibly be the same with the rotor blades... If the rotor blades were made of a composite material such as carbon fibre (which is very likely) then they are semi-transparent to radar to start with...

In terms of radar invisibility, the blades need not be the classic airfoil shape. They can be angular or diamond shaped, which ruins their aerodynamics, but deflects the radar. You just put on a bigger rotor and more powerful engine, and it makes up for the reduced lift from the rotors. Look at the F-117, which is shaped such that it reflects radar, no matter which direction it comes from. There is no reason why you couldn't apply the same principles to a helicopter. The pics I've seen seem to show some sort of sharp corner on a surface of what seems to be a rotor blade. A big no-no in subsonic aerodynamics, because it reduces the lift and increases the drag drastically, but it would greatly reduce the radar cross section of the rotor blades. The tail rotor, which is much more clearly shown in pics, seems to be masked, and has stumpy blades with a very short chord - basically taking a minimalist approach. The helicopter must be a real bitch to control, but I guess that wasn't really one of the designers' priorities...

For the silence, have you considered the ridiculously loud whoosh whoosh whoosh of the blades spinning through the air at close to the speed of sound (for any decent thrust), and then maybe some humming from some transformers to power the magnets and then the engine or generator used to make the electricity - batteries are out of the question for any reasonably sized craft because they just weigh far too much. Apart from the magnets, the propulsion system you are proposing is known as a ducted fan. They are indeed more efficient than open rotors, and produce more thrust, and produce less noise... The main reason helicopters rotor blades are open is because ducted fans are just far too heavy. The number one rule when designing anything that can fly is to keep it as light as possible.

Yup, the answer is 8. How far did you get with trying to work it out? Consider that the left hand side, being made up of sin and cos, will oscillate between some maximum and minimum values...

Thanks for the advice, everyone. I guess it depends on the audience and how attached they are to the old ideas. I hope there are no tricky questions, because I don't think quickly on my feet. I'll let you all know how it goes. The conference is in July though. An abstract and a six page paper, in fact, which has been reviewed, and got the comment "there should be some confidence in your results"... which I'm hoping is true. There's always that nagging feeling that my advisor just accepts my findings because he trusts my calculations, and that the paper was accepted based on his name as a co-author.

I've given a small number of presentations before, and they've all gone pretty well. The catch is that they have all been to my class mates, a whole lot of parents at my valediction when I graduated, and the board that currently funds my research... i.e. the sort of people who aren't really interested in details, and are easily impressed with pretty graphs and flashy videos. So I know the basics, i.e. keep it simple, lots of pictures and little writing to keep attention, speak loudly and clearly, and practice and all that. The tricky bit is that my school has quite kindly agreed to fly me half way around the world in July to give a presentation at the most important conference in my field. My research has revealed a fundamental flaw in the currently accepted theories which proves the underlying assumptions completely wrong. I have absolutely no idea what alternative theory to suggest, only suggestions as to what new variables the theory would have to include. My research advisor is confident with my results, and the paper for the conference proceedings has made it through both stages of peer review with mostly positive comments, but I still can't help being very nervous about the whole thing. And the audience will be experts who will actually listen and understand what I'm saying and be able to pick out mistakes... My question is, does anyone have any tips for making the whole thing go smoothly? Basically, what's the best way to present my research without everyone saying "This kid's an idiot."

By not fall down, I mean if it was balancing on the end of a vertical pole... Not that it would float in mid air. Sorry, I didn't really make that clear....

It's a good idea to pick a prof who has a huge reputation, i.e. someone that reviews for several established journals in your field. Also, when you first speak to him, don't be embarrassed to ask him outright about funding. Access to a big grant is a good focus. In terms of how long it takes, most people I know who have or who are currently working towards Ph.Ds say the most important factors that determine how long it takes depend on your field, but include factors like how long it takes for your test equipment to be built; waiting for simulations to run; waiting for funding to continue research; your prof asking you to focus on something you hadn't even considered; and most importantly, the amount of work you do unrelated to your research for your school. Most people who take 7 or 8 years at my school take that long because they keep being asked to do lecturing jobs on the side. But, if you can secure a good grant and a solid income, does it really matter if it takes a year or two extra? When I took over my office, the previous student left up a sign on the door with Newton's 3 Laws of Graduation: "A student in procrastination tends to stay in procrastination unless an external force is applied." age of a Ph.D candidate = Flexibility of prof / motivation of student, or a = F/m... or, F = m a "For every action towards graduation, there is an equal but opposite distraction."

It wouldn't be antigravity as such, because it wouldn't actually move up. It would be more a sort of balance... It would resist rotation. It could be used to keep an object upright on a moving vehicle, I guess. It would need to be very well built because any slight unbalance in its symmetry would lead to fairly high forces if it were to spin very fast. This is probably the problem your mechanical engineer ran in to.

A PhD student in the same corridor as me has made a (mostly reliable) lightweight bulletproof vest from a similar principle...

The problem is the momentum in the turnaround (if you assume the velocity stays the same) goes from +p to -p which is a total of p - (-p) = 2p, which needs to be given to the mass by some device (eg. a semi circular wall...) and that momentum is also transferred to the vehicle which cancels out all the momentum you gain from accelerating the mass and preparing it for the acceleration. The momentum of the vehicle will go between p and -p and the vehicle will move backwards and forward on the spot (and possible rotate, depending on how the turnaround is done...)

I can't speak for the original poster but having lived in Southern Africa all my life, I can speak from experience. Most likely semi-desert grassland with small hills. (350 to 500 mm of rainfall a year) I'd guess 2 lights and maybe a heater and stove. Maybe an average of 500W concentrated over a 5 or 6 hour period in the evening. General electricity to live off... Rivers around most of the country are very scarce... "Rivers" are spaced an average about 10 to 20 km apart (which is a very well educated guess) and do not flow very fast (in fact, a lot of them are stagnant except for when it rains), and are on average about 2 m wide and 1 m deep in the 3 month rainy season, and about 1 m wide and 0.3 m deep for the rest of the year. I'd have to drive 100 km to get to a river that exceeds those dimensions. Most of the water is polluted and carries a very high risk for diseases like cholera, bilharzia, etc, but people ignore this and live off it anyway. Most subsistence farming takes place near these streams. Water for irrigation is usually raised using buckets.

I think he means like some sort of antigravity that would make things fly instead of fall.

It depends what country you're in, but in general electronic or mechanical engineers are always needed. Although, if he really wants to get a well-paying job easily, he should get whichever engineering degree he wants and then go work for a bank or a management consultancy firm. Although, to be perfectly honest, I learned the hard way that that's a really bad way to choose a career path. Here in South Africa where I live, the easiest engineering degree to get a job with is one in extractive metallurgy (there are about 3 times as many job openings as there are people looking for jobs), so that's the one I picked when I finished high school. I found it really boring, and dropped out after two years, and decided to just do what I was interested in. I did aerospace engineering, even though everyone told me there was no job market in the country. Not even one aerospace engineer from my graduating class is unemployed at the moment (although half of them are working in mechanical engineering jobs, and a couple in business). Anyway, it's way easier to be successful at something if it's what you're interested in.