Discussion in 'Instruments / Avionics / Electrical System' started by spduffee, Feb 28, 2015.
What's the fun in that...?
I pretty much agree with this, though I'd only do it if the engine had mags (e.g., wasn't reliant on DC power to keep running).
What we *should* do, in this case, is set up the plane like a consumer appliance. Rather than putting the battery under the cowling, seat, or whatever, make a pull-out drawer that lets you switch batteries in moments. Over-center clamps on the terminals, so you can disconnect one battery, pull it out, and drop in another in just moments. Or get home, pull the battery, and drop it in the charger so it's ready next time.
Personally, I'd have two batteries... have one on the charger, and just swap when ready. Carry the spare along if you're on a trip.
Love to do this with something like a LiPo pack, but you'd have to have discharge protection on the airplane to ensure you don't draw the battery down too far.
Could be me, but I don't consider building a generator fun, it's like a science project for a middle schooler. If you really want to build one, it would be very simple. Basically you need a DC motor. To get an idea look here for some simple wind generators, but bigger to handle charging a 12v battery. You would probably need something about the size of a heat/AC blower motor or electric engine cooling fan motor. You'll need a prop or fan to drive it the desired RPM at the desired airspeed and a regulator. The question to me is why? You'll probably have 50% or more than the cost of buying one invested and probably not be as neat or efficient.
Bicycle generators are biased towards 6v, they produce AC, and about 6watts.
If I were going to do this.. it would be a with a r/c motor, a rectifier bridge, and a vreg of some sort... But.. I wouldn't do it.
what's stopping you from driving off the engine?
1. Some engines don't have a provision for a generator or alternator. Hence you have to work out brackets, belts, deal with vibration, etc.
2. Aircraft without engine-driven electrical systems get a break as far as requirements to carry expensive equipment. For instance, if you don't have an engine-driven generator or alternator, you are not required to carry a transponder *or* ADS-B within the 30 nm Class B veil.
You might as well ask, "Why build a homebuilt airplane when you can just buy one?"
That's a key factor, I think...with a homebuilt, you can try weird stuff just out of curiosity. I might try a wind generator at some point, just for fun.
A few years back, I noticed an electronic compass that included an altimeter as well as both a local and remote thermometer. Gave it a try in the Fly Baby, just to see if it might work out as kind of a half-EFIS with a carb heat sensor. Didn't really pan out. The compass only gave 22.5 degree resolution, and transmitting on the radio messed it up. The altimeter worked fine, but there was no "static port" and hence the reading varied with throttle/speed (as the cockpit pressure slightly changed).
I love it when I get a concise, accurate reply. Thank you Ron.
So... in that situation.. I'd be mounting the generator directly behind the prop, so it's directly in the propwash. since that's an area of nasty air anyway, hopefully it's performance hit will be smaller. And you could potentially sneak it up so it's hidden and not adding frontal area.
Now I want to experiment.
(Large wind-generator-powered light bulb comes on)
Hey, what ABOUT going full-chat consumer grade: Use "C" or "D" Cells!
According to Wikipedia, rechargable NiMH D batteries can produce up to 12 amp-hours, and non-rechargeable alkaline up to 18. Twelve NiMH cells will give 15 volts, and six-cell holders are readily available (or use three 4-cells). Put a big diode in line and you'll have 13.5v available at your electrical bus. The RC guys have a bunch of nice connectors, too.
They won't handle the current draw of a starter, but you'd probably be able to operate a small comm radio all weekend. And if it starts getting weak while away from home, you go to 7-11 and buy a set of replacements.
D cell NiMh's should be able to start an airplane. I don't know how well they'd like it..
Tenergy D Ni-MH 10000MAh Rechargeable Batteries - 4 Count
That's a 1.2v nominal, 10amp hour cell.
That site says the cells are ok up to a 16 amp discharge. Which is probably the continuous rating, 1.6c isn't exactly a lot. I'd expect that cell to be able to happily spit out 5-10c for at least a minute without any real complaints.
Each cell is 6oz each, and you'd need 10 for a decent pack. So that's 60oz, throw in some support structure and you're really looking at 70oz all up. .... suddenly I wonder why people stick with the nasty little lead acids.
A lot of the glider contingent is switching to LiFePO4, which would be a much better choice than NiMH, in my opinion. LiFePO4 batteries are pretty light for their capacity, and provide relatively constant voltage as the battery is discharged. I will probably soon be purchasing one to replace my current sealed lead-acid battery.
NiMH batteries require a special charger to be charged safely, and I have heard of a couple of inflight fires caused by (factory-installed) NiMH glider battery installations. Not something I want in my airplane...
Figuring a way to jettison a LiPo battery pack might be prudent...
Lead acid batteries cause fires too. NiMh is a "pretty darned tolerant" cell technology. If there were fires, there's something else afoot. A "sane method" for charging nimh, is just voltage limiting. They can tolerate that without any kind of timer or current limiting.
Oh, and they don't catch fire if punctured, like LiPo will. LiFePo is the "really durable cousin" of LiPo. Both are "better" than NiMh for wh/kg, but they don't beat NiMh for price, or durability.
A Lithium Iron Phosphate battery is not the same as a LiPo battery. The chemistry is different, and the former is safer.
It is good to see all of the great alternatives to using and making a wind-driven generator; however, the question was not 'should I build one?' but rather 'how can I build one'? Doesn't anyone have any suggestions on how to piece this part to that, wired to that over there, et voila, based on the model of the Swedish guy? I still can't find any directly applicable videos or how-to's. The Swede had 30 hours of successful flying with his, so it must be a good design.
I wonder if you could incorporate a wind turbine of sorts into the the airfoils somehow. Would it be better on the leading edge, trailing edge or somewhere in between? Or is that just a bad idea?
I think the reason nobody has given specifics is that it will depend on the exact motor you choose to convert. If I recall, that R/C starter (I have one around somewhere) has a threaded shaft with a nut holding the drive cup on, so it should be fairly simple to bolt a propeller to it... you can use a model airplane prop or what it looks like he did, a simple bent aluminum prop. Similarly, the mounting depends on both the motor as well as the aircraft structure you'd be mounting it to.
There are a number of ways to regulate the output. If you have no battery, the simplest might be to use the Key West regulator commonly used on 2-stroke engines; unlike most other regulators it doesn't require a battery in the circuit. If you do want a battery in the circuit, just about any solid state regulator should work, from the ones sold by Rotax to cheaper but probably identical ones from snowmobiles or motorcycles.
I'd suggest testing it by holding it out the window on the highway before installing it onto your plane.
I built an electric motor in middle school and rebuilt more alternators and generators than I could begin to count. It's really kind of boring, but building a plane is another story. I see building a plane as the ultimate challenge. I've built balsa models and they can be a challenge, so I can hardly wait until the day I can build one.
Spud there are tons of howtos and videos on making a wind generator on the internet. Start with youtube and watch for something you like.
A Piper Cub flier of my acquaintance surprised me one day with a story of a certain well-known wind genny disintegrating in flight. It sent a blade up into the belly of the Cub and narrowly missed gelding my storyteller and the subsequent vibration was so bad that the instruments were unreadable and a forced landing was required. He then further surprised me by telling me that another generator, taken from a small tractor was substituted and driven by the radiator fran from a Peugeot car. I had to block my ears...
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