k1234

Thanks for the explanation - I had never thought of having a twin-IC hybrid. One question - do engines last well on full power, or is it just a matter of tuning and designing them so that they can run on full power indefinitely?

Hybrid as in 'electric'? I'm fascinated, as I anticipated it would be a decade before this sort of technology made sense for light aircraft. Can you tell use more?

I saw this debated a few years back, and someone posted the regulations regarding position lights. They were quite stringent regarding brightness, beam direction and colour. It would be easy enough for someone who knows basic electronics to make lights, but you might need specialist equipment or knowledge to verify that they met the regulatory requirements. Another issue that came up is that the average current draw might be lower for flashing LEDs, but the peak current draw is actually much larger for LEDs than Xenon strobes unless you do some clever stuff. A traditional strobe light works by charging up a large capacitor to hundreds of volts, which then discharges near instantaneously. An LED flasher, like for a bicycle, typically just switches the LEDs on full power for a short duration. This means that you are drawing high power for a short period of time, rather than low power all the time. As the previous poster said, strobes are more difficult than steady lights. I think heating was also an issue. It's a fallacy that LEDs don't make waste-heat. They do, and for some of the new high power types, getting rid of it can be a major consideration. Unless there is a get-out clause for homebuilt aircraft, which I haven't heard of, I don't think it's as simple as it might first appear.

Sorry, I just read over the thread again and I don't know where I got that from.

You say you're a student. Are you seriously entertaining designing a motor, or is this part of some class exercise to find out what sort of motor you should build if you were building one for real? If the former, then I'm personally with Mark 100% of the way. If the latter, then I think people might be more willing to offer help if you simply came out and said so. Presumably you have access to an academic library - go look up market-research techniques. You probably can get some valid qualitative information out of asking questions on the internet - but there are good and bad ways of going about it. I don't know much about it myself, but I used to live with someone who studied these things. I learned to appreciate that it's not all nonsense. Lastly, even a non-engineer such as myself can see that half the innovations proposed on this forum would kill someone if they were taken to completion. In serious fields like engineering or medicine, we need straight talkers like Marc. Learn to welcome negative feedback and take it with good grace, even if you don't agree with it.

One thing would be to ask whether you should scale the weight by volume or by surface area. Surface area should be squared, and volume cubed (to see why this should be so, imagine a 1cm cube, and a 2cm cube. The first will have an area of 6cm^2 and a volume of 1cm^3. The second will have an area of 24cm^2 and 8cm^3). Some components of the aircraft will scale with volume - such as the foam cores - but others will scale with the surface area. This is likely to be the case for fiberglass because you won't generally be able to reduce the thickness of (e.g.) 3 ply by 10%, and the same will probably be true for foam sheets and plywood used to make bulkheads. Likewise, the instruments and some other components (seatbelts) etc. will probably weigh the same as for the full-size aircraft. What this means for you is that although you are reducing the volume by 25% you are only reducing the area by 18% and you may end up weighing considerably more than your calculations would suggest. You might be able to ameliorate this with different materials - thinner fiberglass etc.

My understanding is that the Junqua Ibis uses flaps to get a stall speed of 52 knots. I think the canard elevator acts as a flap too. I haven't seen plans, so I don't know precisely how this works or whether the flaps are large enough to make a substantial difference.

This is a problem in the UK - it's almost impossible to get non A4/series paper sizes. I solved the problem for the printed text by simply shrinking to fit A4 (this is simple on Linux with the pdf2ps and psresize commands). I will print the templates onto A3 if/when I need them - wasteful but there aren't that many. I reckoned the paper was 'legal' but I cant confirm this. The good thing about printing pdfs is that they don't normally rescale unless you ask them to. They just chop bits off of the edges. But I second the question about rescaling issues - is there any good way to check the metal templates for size?

Would the micro bond to the unsealed foam be stronger than the bond to hotwired foam? There might be another reason aside from weight.

Well, guess who bought that particular CD? Mr Tait was a pleasure to do business with.

It isn't the same situation at all - if a single engine quits, your decision is made for you. If you have a twin you need to decide for yourself what to do. And it's very difficult to decide to crash. If you decide to continue under power, a conventional twin leaves you with problems such as asymmetric thrust and yaw. You can easily get yourself into situations such as flipping inverted whilst still above the stall speed. As a general subsonic rule, narrow wings (high-aspect ratio) produce lift more efficiently than delta wings, so a traditional long-ez canard will almost certainly be more efficient than one with a delta-canard like the one you showed. That much is basic aerodynamics. But designing a new canard is the sort of thing I wouldn't personally mess with unless I had a degree in the subject - and I don't and I gather you don't. Look at the history of the GU / Roncz canards and how long it took to get it right. I've nothing against innovation (quite the opposite - we're all reading this forum because we're willing to accept the unconventional), but I've learned through experience that true innovation is very hard and takes a long time. As a scientist, whenever I start a new experiment, something I never considered emerges to make my life complicated. Whenever I program a computer, bugs appear when the program is asked to do something I didn't consider. Both these spheres of life are relatively safe, but you seem to have decided to risk your life with a design that is really very different from anything that has gone before. Twin engines. A delta canard. A larger wing. Other innovations that you're keeping secret. You say you believe in progressive 'baby steps', but this certainly doesn't seem to be the approach you're taking. Are you working alone? If I were you, at the very least I would pay a qualified competent person to check over my design. There's currently a thread just as long as this one about the design of blended winglets. The changes you're proposing really aren't trivial. Seeing as we like to be radical, my 2c would be that within 15 years, electric - or at least hybrid - aircraft will become quite feasible. My radio controlled helicopter uses batteries that give 4 horsepower / kg in a tiny motor that weighs a few hundred grams and is over 80% efficient. So 25kg of batteries and 25kg of motor and electronics could very feasibly give you the same power output as a 125kg Lycoming 0-235, albeit only for a few minutes. I figure that an electric Long-EZ might save 100kg over an O-235 engine, so you could carry a quarter-ton of batteries instead of the usual fuel load. With today's technology that would give you a flight time of an hour or so. But if some of the rumours I've heard about Lithium-air batteries are true, then we might reasonably expect this to increase by a factor of up to 10 over the coming years. This would put an electric and a IC long-ez nearly on a par in terms of range, except I'd wager the electric aircraft will remain more expensive for some time. What does this have to do with twins? Electric motors are so much smaller and lighter than IC engines that it would be far easier to integrate them into a wing or strake. They also require far less cooling, which would be good for aerodynamics. But the real experience from radio-control modelling is that it's now far simpler to build twin/multi-engined aircraft than it ever was with the internal-combustion variety. With a hybrid approach you could carry 25kg of today's batteries at a cost of about $3000. If your main engine failed, you might get half an hour at 80 knots before they ran flat. You could have five 4-kg motors spread along the wing, each producing 25hp flat out. Loss of any single motor would be a relative non-event. Loss of 2 or more motors would only be significant if they were on the same wing. Lose the generator... And unless you are over the Pacific you will very probably have time to find a suitable airport and set up a good approach. I admit I'm being more than a little speculative here, but at the same time I don't think that this is pure fantasy. In your position I would be significantly worried that by the time I'd got my complex new design worked out and built, it would be nearly obsolete because buying a few electric motors off the shelf was so clearly the right way to go.

I read the cheese-eating comment as humour. There's a current thread on this very topic on the yahoo canard group for anyone who can stomach some genuine jingoistic prejudice. I'm with Marc all the way on that one.

Some more non-building noobie comments... It's something I've wondered, and like the previous poster I figured that there are things I clearly don't understand well enough that I would modify them unless it was well established that it was safe to do so. Having said that, I believe the Berkut has a lengthened fuselage, not to mention a bigger engine to counterbalance it. Also, I probably weigh 30kg less than some builders. I see a lot about people building longer noses in order to move the battery forwards... Perhaps I could afford to build a slightly longer fuselage with more room for the passenger, even if many other people couldn't? (I'm seconding the question).

I do pre- my pushbike before I ride it. Brakes and tyres. And I have sometimes found problems. I once found a problem with my hang-glider that would almost certainly have resulted in loss of control. Your choice.

Thank you. And likewise.