A challenge to you all

Discussion in 'The light stuff area' started by stan40353, Sep 11, 2011.

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  1. Jun 6, 2012 #401

    Head in the clouds

    Head in the clouds

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    So there is life after death, though its a bit slow... hopefully I'm over the worst.

    I wasn't thinking very straight, although I don't think your wing skin construction could benefit a Pt103, excellent though it appears for an experimental. However it certainly could be ideal for fuselage construction for an ultralight self launcing glider perhaps. Or the strongback fuselage of course.

    Once I was in bed I realised that someone mentioned you had a redrive and of course that makes all the difference. But I thought the big block (990cc) B&S was 33hp. Is it 50hp?

    Well that's a nice weight/size to design around but it appears we've got to look at least up to 6'3" and 230lbs. And that's a big ask of an aircraft that has to weigh about the same... and definitely means a tractor configuration so that the pilot can sit on the CG because it seems we have to cater to weights from 130lb to 230lb so that means that correct ballasting for pilot weight differences would be critical if the pilot was not on the CG.

    And then there's also the height to consider, which would be from 5'4" perhaps to 6'4" which is a difference of at least 6-7" in eye/head level when seated.

    Groundbreaking - OK, it's very difficult to do anything at all that is new in aircraft but a novel and quick folding method would fit that description, so would the use of some new technology which might become more efficient or less expensive in the future - electric perhaps, as would hydrogen peroxide if a cheap supply and safe storage were to become available.

    Not being well I didn't go into even slight specifics of the new battery technology that is being developed. Sure lithium is the lightest metal and those batteries have a certain power storage density, which is very good at present but, as I understand it, can be improved with more advanced cathode development.

    Also, as I understand it, lithium batteries use a lithium anode and a lithium solution for the electrolyte. This new technology revolves around using an alloy of light metals which is heavier than lithium but the use of a different electrolyte means these batteries would have a much higher power density (apparently) than lithium batteries, making the batteries lighter and smaller overall. Since the developers are still in the process of filing their patent applications I don't know much more but I think it is unreasonable to suppose that electric power storage possibilities have already peaked. Clearly you have little faith in the ingenuity of mankind.

    The Antares would be just one example showing that a self launching ultralight glider is feasible but I don't think the whole concept need be limited to 'the lightest floaters'. By using electric power under Pt 103 we have the very significant advantage of not having to count the battery weight in the empty weight so we have that bit extra to use in the structure. We could, just for example, consider variable geometry wings, the obvious one being the use of Rutan's 3 point fowler flap arrangement, which could bring the stall speed into the allowable Pt103 envelope, and be very beneficial during climb, but also provide a quite reasonable soaring and cross-country performance when cleaned up. Something along those lines would be truly groundbreaking because it would attract many flyers from the soaring fraternity, making it feasible for someone to develop a business around producing them. And you would be well aware that once a market reaches a certain mass then it becomes viable to develop the molds and methods to make a quality product more cheaply.

    I can understand your scepticism about the electric power thing in general but I think you're weighing in at the extreme end of the scale. The eLazair and others have already shown that you are significantly out in your estimate of 5-10 minutes flight time. Bear in mind that 16 of the batteries that I discussed before, as fitted to my current project only weigh the same as 5 gallons of gasoline and the tank. So that's 288Ah at 14.4V. The following links take you to the suppliers of these 18hp electric motors and some videos of well conducted tests that folks have carried out. One shows the motor linked to light gearbox for psru, when he holds the pinion that is the power-on, no output state of the motor, about 8A I think. The last link provides very useful actual measurements, and keep in mind he's using a total of 16Ah of batteries, the batteries I just quoted are 18x as much power as that. I won't offer my interpretation because I think it's an excellent option for more discussion on this subject.

    As far as getting a gasoline powered airframe shaped up I thing Auto's sketch is great and a good start and we all understandably have different ideas of what we'd like so I'm thinking that we might all use basic parameters to sketch up our own configurations. I am thinking that I might model the Sky-Ray and describe why I construct and position each major component as I do, and that will allow others to follow the general procedure but form their own configuration. Given the constraints of weight and powerplant they may all end up fairly similar but the benefit will be that all can understand why the more outlandish ideas can't work.

    That will have to wait though, while I catch up on work.

    I will be very interested to hear what everyone thinks about the likely endurance of the electric power with the 288Ah pack, allowing for time to climb to say 1000' at full power and then the rest at cruise - just for starters...

    Here are the links -

    HobbyKing R/C Hobby Store : Turnigy CA120-70 Brushless Outrunner (100cc eq)
    Turnigy CA120-70 power benchmark report - YouTube
    Turnigy ca120-70 on dirtbike gearbox - YouTube
    Electric
     
  2. Jun 6, 2012 #402

    delta

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  3. Jun 6, 2012 #403

    rtfm

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    Hi again,
    No worries mate. The Valley Engineering Big Twin is a Generac 990cc. They have done some internal rework, and the new engine now produces 50hp. The extra work costs an additional $700 USD over their "normal" Big Twin, which already had some internal work done on it to produce 40hp @ 3600 rpm (32 hp continuous). Even at 50hp, a 1-litre engine isn't exactly overworking...

    And the 120lbs weight includes 20 amp alternator, starter, oil cooler, oil filter AND prop. I don't know how much the redrive weighs, but from looking at it, it might be in the region of 12-15lbs. I can weigh the prop, of course, but a 6-ft wooden prop weight is pretty standard. I'd guess 5 lbs. So that puts the engine itself (so we can compare apples with apples) at about 120 - 15 - 5 = 100lbs. 2lbs/hp That's right on the money, isn't it? And it's a four stroke...

    And a nice thing about the VE Big Twin is that the engine itself is designed to run at 3200 rpm all day in pretty harsh conditions and with minimal TLC. And that's *before* the forged pistons and other high-spec internal goodies which can only improve reliability at the same engine RPM. In an aircraft with plenty of cooling available, and with lots of TLC, I can see the engine outlasting the airframe...

    Regards,
    Duncan
     
    Last edited: Jun 6, 2012
  4. Jun 6, 2012 #404

    Sir Joab

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  5. Jun 6, 2012 #405

    StarJar

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    Guys, I just want to step in and report on a few things I've been researching. (I was assigned brakes, wheels and rudderpedals, but I'm not reporting on those yet.)
    I brought up the idea of using vertical shaft B&S engines since they cost so much less.
    I started a thread on using bevel gears (from marine outboards) but that concept isn't so rosy anymore, because just the set of bevel gears cost about $400, even before you start putting together a case for them.
    So then I started looking at converting a vertical shaft to be used horizontaly by re-mounting it.. Well first let me say that last week I found a store (on the net) that was selling verticle shaft B&S engines for about $600 (28hp). They also sold the horizontals for $1700(for comparison). I tried to find that website again but couldn't. But I did find some other verticals for less than $800(28hp).
    But the thing is, the vertical shafts are not an inferior engine. It's just that they sell so many more of them, because most everything is designed for them now. I went in some forums to find this out.
    Secondly, these size engines all have pressure oil systems. Autoaddict mentioned it before, that he thought all you have to do is modify the oil pickup tube. Maybe also plumb an extra oil resevoir onto the engine. Then make a mount to acommodate the engine which will now be on the front of the engine. That doesn't seem too bad, to me.
    I know we're looking at a million possibilities of engines right now. I just want to throw this one on the stack, and hopefully someone who knows more than me about these, can tell us if there's any big difficulty in doing this.
    There is not a whole lot on the internet about it except, kids trying it with smaller engines (with slinger oil systems) for go-karts. However, Autoaddict mentioned that there is a yahoo group for small aircraft engines that has pictures of some for aircraft. I applied to join the group a couple days ago, but havn't got in yet.
     
    Last edited: Jun 6, 2012
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  6. Jun 6, 2012 #406

    litespeed

    litespeed

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    There can be little doubt about the abilities of the big twin to push enough air for lively performance- but will it weigh to much?

    From 254lbs at 120lbs for the drive package that leaves 134lbs for all the airframe, wing, tank etc.

    Is 134lbs a reasonable amount?

    Or would be stuck with too little airframe and wing?

    The other concern would be the price-$5500 is a lot for this type of engine.

    I will refer back to the Simononi which whilst only having 220lbs of thrust versus 240lbs, it is a considerable 75lbs heavier.

    Yes it has the bigger prop and a bit more thrust but the weight penalty is great. And price is high-plus for those having to ship long distances- that extra weight could be very costly.

    I will keep looking.
     
  7. Jun 6, 2012 #407

    litespeed

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    Verner Motor, Czech Republic | ultralight | aircraft | LSA

    The Verner JCV 360 is a real contender at the $5000 odd price range.

    Its is 4 stroke, twin cyclinder, water cooled and has a 1:2.76 redrive built into the design.

    The power is 36hp and wet weight installed with water in radiator is a mere 30kg / 66lb.

    So for a 54lb weight saving, similar price.

    This package allows for a 190lbs approx for the airframe- much easier to build to.

    For a similar sum you can go for a water cooled Simononi Victor 1 which is 44hp and weighs the same as the JCV.

    My point been for the same price as the Big Twin - many better and far lighter alternatives are available in air or watercooled and two or fourstroke.

    Remember the big problem is price and the Big Twin is no cheaper and in fact more than the abovementioned engines.

    In thrust we trust
     
  8. Jun 6, 2012 #408

    Lead Brick

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    I'm not sure how you came up with these numbers. Forgive me, I couldn't find the exact battery you are talking about here. But I think you are missing something in your calculations. The motor above is rated between 30-70 volts. That means that you shouldn't try to run it below 30 volts or above 70 volts. The power rating quoted on the Hobby King web page says 20+ horsepower, which is a motor in the 15 kw range. This number is almost always given at the max number of volts, i.e. 70 volts. If each of the batteries is 14.1 volts, you would need to put 5 in series to get the 70 volts to use all the power this motor needs to make the 15 kw of power. This cuts your Ah to about one-third of the 288 ah you've stated, or 96 Ah at 70 volts, as you would need to combine 3 groups (of 5 cells in series) in parallel. Ninety-six Ah is still quite respectable however.

    It's unfortunate that Hobby King doesn't list the max amperage of this motor. They only say you should have an electronic speed controller rated at 250 amps. Let's for arguments sake say that the motor does pull 250 amps. And lets say a plane designed with this motor, with gear reduction drive (because at 70 volts it will be turning 10,500 rpm), can climb at 500 ft/min. To get to 1000 feet you'd need to run the motor at full power for two minutes, that's 8.33 amp hours of the battery. Let's say you cruise at 50% throttle, that would eat up around 125 amp/hour. As you can see, after the initial climb out you, could put around for about 40 minutes. And that doesn't leave you with much to do a go around if you blow a landing.

    But cruise speed will most probably not require 50% amp flow; and the motor probably doesn't pull 250 amps at full power, so this might be very acceptable. The only real killer to the deal is finding a way to charge the battery quickly. Most circuits in the States are rated below 40 amps. You would need to charge from at least 4-5 different circuits to charge the batteries quickly (around 2 hours), lest you trip the breakers.

    This whole discussion on electric has really got me thinking along those lines for myself, but maybe not for this plane though. I'm thinking more along the lines of a motor glider. This is where an electric ultralight would really shine...so many advantages in that arena.
     
  9. Jun 6, 2012 #409

    addicted2climbing

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    While I dont think that Electric power would work well for this project due to budget constraints, I did have an idea I wanted to try for an electric powerplant on a motorglider. Since Electric motors like to spin at a rate where their efficiency is the highest, I wanted to use a gearbox to keep the motor spining where it should be for efficiency sake. But to controll the speed of the prop I wanted the ability to shift gears sort to speak as on a bicycle. I am also interested in electric personal vehicles and had been researching a CVT drive for a bike I had in mind. However, I always thought that a CVT would work well coupled to an electric motor as a gearbox for a propellor. I ended up buying a Nuvnci Developers kit which is a CVT hub gearbox that uses no gears. It relys on friction drive internaly on Ball bearings that contact at different tangent points thus changing the reduction. The kit came with a moter driven actuator to control the shifting and it all can be programmed to set different shift points based on load of the motor. As the throttle is advanced it could keep track of the load and maintain a constant thrust and possible amp draw. Then in the air, the motor would have less work to do as the CVT would be doing most of the work. So in a sense it would almost be like a constant speed prop on an ultralight... That is if it works...

    http://fallbrooktechnologies.com/docs/DevKit_Datasheet.pdf

    The one I have is set up for bikes so it has a max input/output speed of 1000rpm, but they make other versions up to 10K input/output. However mine could be used as a midway point with the motor geared to the CVT so it will never se emore then 1K and then the output geared to the prop at 3:1 for max 3000rpm or so..

    Does this sound plausable?

    Marc
     
  10. Jun 6, 2012 #410

    Hot Wings

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    Does this sound plausable?I

    It does, and is why this solution keeps popping up. But it isn't a good idea. A search of the archives here might turn up a recent thread related to this for more detail.

    Basically the problem is that fixed pitch props work best at the design point for which they are designed. Engines and motors also perform best at their design points. The idea of a CVT to match road speed with the best RPM for the engine is great if we are talking ground bound vehicles that can apply the power to the ground for propulsion at near 100%. Auto manufactures have gone to great lengths to make their engines efficient over a broad rpm range so they will work with conventional transmissions with discrete ratios. CVT's are really a better option but the market just hasn't accepted them - yet.

    Aircraft still use engines, and now motors, that have a single point at which they get good efficiency, but unlike a car they have to transfer the energy to the environment for propulsion via a propeller. The propeller has it's own set of parameters that define it's efficiency and unfortunately they don't have the near 100% transfer efficiency over a large range of RPM that the tire/road surface interface does, especially if it's a fixed pitch prop.

    So, the problem isn't so much matching the engine speed to the prop as it is matching the prop configuration to the airspeed. This is why the generally used solution is a constant speed prop that changes it's pitch allowing the engine, or motor, to work at it's design point.

    It's a bit more complicated than that but I hope my quick explanation gets the basic idea across.
     
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  11. Jun 6, 2012 #411

    Himat

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    Not to me.
    Instead of adding a gearbox the solution would be to design the motor to have an rpm range that match the wanted propellor speed. Check out electric model helicopters, as far as I know all less one have the motor driving the rotor by some sort of gearing. The odd one out have the motor rpm designed to match the main rotor speed.
     
  12. Jun 7, 2012 #412

    Autodidact

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    Here's the high aspect ratio, direct drive idea, it could be pop-riveted aluminum tube or wood and blue foam. Wood and foam might be better since it damps vibrations better than metal. This drawing wasn't as much fun as the other one, I had to work harder at it, and I don't think it looks as good as the other one - forgive me for not even trying to draw the propeller :) ! Anyway, that's all I can come up with (I know, it looks like a KR-1!):

    m-glider.jpg
     
  13. Jun 7, 2012 #413

    addicted2climbing

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    Wow that is a nice drawing. did you do it by hand or on a computer program? Kind of has an ASK14 look to it... Is the original poster interested in a motorglider? I know I am..

    If you leave the center section you have it could accomodate short or long wings depending on what builders want.. Fusleage would need to be optimized to work for either and not end up too short coupled in the motorglider format. Engine would need a recoil or electric start unless you want to do the dive and restart ala Fornier RF4 which seems a bit scary..

    Or another option is the crossing spars used in Sailplanes and then the fusleage does not need the mid section. Choose your wings and go fly... Or wing extensions like on 15/17 meterships...

    The windrose had what they called 6 day wings, but it had some serious bad handling and a few spun in. Maybe something more benign with relatively low aspect ratio wing by sailplane standards would work.
     
  14. Jun 7, 2012 #414

    Autodidact

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    Actually, it's not reeeeeaaally meant to be a motorglider at all. It's just supposed to be a clean monoplane optimised for a low power engine with a small propeller. The mono-gear is just part of trying to make it clean (and light) without going to great lengths to sculpt a really low drag airframe. I guess it could have that option, though.

    It's a pencil drawing; they get dirty so I've taken to rubbing them with my finger to try and get a shaded look.
     
  15. Jun 7, 2012 #415

    StarJar

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    Seems like motorglider UL's are starting to gain popularity. I would think, like an 18% thick wing, would help, without too much downside. One could even be made with thinner wings and struts, probably.
    I guess we are straying to the edge of the thread. We need our feerless leader back.
    My favorite things so far are;
    fuselage /engine platform
    gas springs on landing gear
    B&S vertical engine, remounted horizontally, oil system modified
    fabric covered
     
    Last edited: Jun 7, 2012
  16. Jun 7, 2012 #416

    Dana

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    One thought I just had about vertical shaft engines (at least all those I've worked with) is that the cooling air blows down, i.e. towards the PTO end. That might work on a pusher but is bad for a tractor. I also don't think reworking the oil system would be that easy; it might raise the price to near that of a horizontal engine.

    -Dana

    What do you do when you see an endangered animal eating an endangered plant?
     
  17. Jun 7, 2012 #417

    deskpilot

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    I LIKE it. Turn up at any fly-in and you'll be the center of attraction. I think the spinner will be slightly larger in reality but who cares. Great pencil drawing mate......almost a lost art form. Pity you didn't include the wing tip wheels/legs/ what-ever?
     
  18. Jun 7, 2012 #418

    StarJar

    StarJar

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    The way I see it, all you have to do is weld a tube, and provide a holding area/cooler for the oil at the new bottom. They all have oil pumps.
    The propeller would be the new fan, maybe with some new tin. And also rotate the carbs 90 degrees.
    They have thrust bearings, and strong radial bearings.
    I will find out if this 'for sure', when I get into the small engine yahoo group, which I'm still waiting for.
    $700 to $1700 is a big price gap.

    Dana; your signature line there, is hilarious
     
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  19. Jun 7, 2012 #419

    Autodidact

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    Thanks!

    Actually, those are attached at the break between the center section and the outer panels, and I've shown them here in the retracted position! :D
     
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  20. Jun 7, 2012 #420

    Hot Wings

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    I will find out if this 'for sure', when I get into the small engine yahoo group, which I'm still waiting for.

    Several builders there have done this conversion. One guy has done several. It's a pretty easy conversion and from the pics posted if you have any small engine experience a couple of hours is all it should take for the internal modifications.

    There was some speculation that the conversion might leave the rockers with inadequate oil, but if there have actually been problems I missed the reports. It could also be that no one has much time on one of these converted units.

    A couple pics of a Briggs conversion from the site:

    BRIGGS-7.jpg BRIGGS-3.jpg BRIGGS-6.jpg
     
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