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Thread: Poorman Aero

  1. #1
    Senior Contributor Versus's Avatar
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    Poorman Aero

    Here I go, the aircraft building from start to finish- the poor man style. This will be a lengthy thread, for two reasons. First one is that it is a summer here and it is a vacation season, so materials might be a problem if the shop folks are on holiday. Yesterday I went to buy balsa and glue and I found doors closed, but without notices, so I will check tomorrow again. Second reason would be the actual knowledge, since I am learning aerodynamics and fluid dynamic on my own, as well as other things that tag along in standard aircraft building, like static and dynamic in constructions (the part that deals with physical things, like making wing strong and light, but also elastic so that it can withstand forces and moments during all phases of flight), fabrication, materials etc. The idea is to mix theory and practice in order to get solid knowledge about this matter trough trial and error method. In order to make it interesting, I will try to describe this process with great deal of humor but also in a way like I am some sort of serious company, so all phases will be covered, regardless if they are actually important or not for the project.

    So without further due, lets start.

    Aircraft are very complex machines and it is very important to set the foundation right when attempting to make one. But before continuing, I have to make a small digression.

    During my college days, we had drafting classes which created a sort of trauma for me, due to following reasons. First of all, any technical drawing, absolutely depends on coordinate system, meaning that in order to get translations and projections right, the coordinate system must be at 0, at all times. You can do it with rulers and compass, but the best way to set the coordinate system is to actually buy a drafting board, that has fixed sliding rulers. Like this one : http://southeasttrumpet.com/wp-conte...ting-board.jpg. However, at those times (the age before CAD) these drafting boards were too expensive for me, so my drafting was very painful, since I had to manually draw the coordinate system and than proceed with actual drafting, constantly checking if the lines are parallel. It is needles to say that I spent a lot more time and paper, doing the draft like that and lost a lots of nerves, getting the drawing right. Actually I lost so many nerves that the drafting board became my life nightmare. However, doing those drawings, I've noticed one thing. In case that the coordinate system is set up wrong, if x,y and z are not under 90 degrees (zeroed in), that small error, that is barley noticeable with naked eye, has the tendency to progress trough the drawing and as it progresses it multiplies, leading to the completely messed up result after hours and hours of drawing. Back than, in 1995 I gave it a name : the systemic error. While sobbing over messed up drawing,at late hours, my favorite masochistic exercise was to trace it trough every translation, rotation and projection and each time I've punished myself like that, the cause was always the same, the badly drawn coordinate system, the 90 degrees nightmare. As a mean of compensation, I used thicker lines, so at the end I've managed to pass exams, using my glasses as an excuse for thicker lines. So my technical drawings were accurate but they were never as elegant as ones drawn by wealthier students with drafting boards. Later on, this zero trauma, played the crucial role in shaping up my views at the world and I've found out that, it exists outside the pens and paper world. It exists in real life and it causes the same problems.

    So in order to avoid it in this project, initial foundations must be set right.

    Aircraft is a product and that product exists because the need for it exists. So an aircraft comes into the physical existence in order to fulfill the needs that created it. Those needs are its reason for existence and they are its purpose.

    So what is the purpose of this particular aircraft? Well, since I am learning new things the purpose of this aircraft is to be a trainer and since this is not a copy, yet it is a original design, it is an experimental aircraft.

    According to this, it follows that the type of this aircraft is a trainer and that its class is experimental.

    So as a trainer and as experimental aircraft, produced by a man with very limited funds and knowledge, its design needs to stress safety that translates to its structural integrity meaning that it has to be durable and easily maintained. Also, since its primary role is to train aka it is used for practice of knowledge, it has to be easily adjustable and upgradable. This means that its construction will be modular. Since the airfield is far away, this aircraft must be hand launched which means that it will be small. When boiled down to actual requirements this means that, structure wise it has to full fill the following characteristics :

    1. Low cost
    2. Durability
    3. Ease of maintenance
    4. Modular design
    5. Small dimensions


    In terms of flight characteristics, if the design succeeds, it is a sail plane, with no control so pretty much all it has to do is to fly stable in one direction and land (preferably in one piece). So the flight requirements would be :

    1. Stability in flight.


    I've sketched up the initial idea ( this is a very general and rough sketch, dimensions are irrelevant at this stage but they will become more important later on).

    See you soon...
    Last edited by Versus; 03 Jul 13, at 21:34.

  2. #2
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    Is this going to RC?

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    Senior Contributor Doktor's Avatar
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    Was wondering the same. Looks too tiny on the frontal drawing.
    No such thing as a good tax - Churchill

    To make mistakes is human. To blame someone else for your mistake, is strategic.

  4. #4
    Senior Contributor Versus's Avatar
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    For the first phase, it will be a pure glider (sailplane) without control. When it passes that phase, control will be added in a gradual fashion, so second phase will be a controlled sailplane and if it passes that, the engine will be added in the third phase. So in a way this project will be an evolution from a free flight to powered flight.

    I don't have any experience with building an aircraft or flying one, so adding everything at the start would be an overkill and it will drive the cost up.

    Yep Doc, it is small but not tiny. Wingspan is around 30 cm and the length is around 25 cm, but it will grow as the experience and knowledge grows.

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    My favourite hobby is crashing RC planes and helicopters. I have about 10 wrecks in my spare room and 2 planes and 1 helicopter awaiting crashing.

    For scratch building you can't go past hobbyking for all the bits and pieces - so cheap. If you get yourself a good transmitter it can do all your models - you just need to
    buy a new receiver for each new model. I have a futaba 6ch and 6ch recievers cost about 5 bucks. Plus you can transplant good parts from wrecks to bring the price
    down on your next model.

    My dad vomits every time I tell him the price of my latest crash. When he was flying it cost thousands. Now you can do it for under 100. Crashing back in his day brought
    about tears - not it's laughter.

    Good Luck!

  6. #6
    Senior Contributor Doktor's Avatar
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    Long live the Chinese...

    for $20 i can airborne and land crash about anything
    No such thing as a good tax - Churchill

    To make mistakes is human. To blame someone else for your mistake, is strategic.

  7. #7
    Contributor chanjyj's Avatar
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    What? $20? Send me the link!

  8. #8
    Senior Contributor Doktor's Avatar
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    Next time me and the kid go on a rampage, I will look for a producer's webpage (If I don't forget )
    No such thing as a good tax - Churchill

    To make mistakes is human. To blame someone else for your mistake, is strategic.

  9. #9
    Senior Contributor Versus's Avatar
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    We have here hobby king, turnigy, robbe, futaba and couple of others too, most of the stuff is between 30 and 40 euros, that would be 50 to 70 US dollars while servos vary from 5 to 45 US Dollars. But again, prices are ok but my paycheck sucks, but also I am learning with this thing, so that is why I have to be so picky with this project.

  10. #10
    Contributor chanjyj's Avatar
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    Quote Originally Posted by Doktor View Post
    Next time me and the kid go on a rampage, I will look for a producer's webpage (If I don't forget )
    Yeah. $20 for anything that can fly without being blown apart by a gust of wind would be amazing.

  11. #11
    Senior Contributor Versus's Avatar
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    Further analysis of the design and its application, brings about the question of aspect ratio for the wings. Low aspect ratio in this case would be better choice than the high aspect ratio, because the low aspect ratio wings are more structurally safe although they produce significant induced drag when compared with the high aspect ratio wings. On the other hand high aspect ratio wings give lower induced drag but have more of parasitic drag. In order to reduce the induced drag, winglets will be placed at the tips of the wings and with little luck and skill they will be blended with the wing.
    For the fuselage, the initial idea was to drill a hole in which counter weight could be placed, in order to balance the airplane. However, since parameters that determine the weight and overall performance are still unknown, the question of CG needs to be tackled differently. Since the "fuselage" is simply one straight piece of wood, the new idea for the solution of the CG problem is to shape that piece of wood so that it can have sliding guides, on to which the ballast could be suspended and moved. Once the balance is achieved the ballast will be fixed. This will make the building of the fuselage a bit more complex and it also might add the weight but with this system, balancing should be easier and faster.

    Also I have a couple of good news, I've managed to find balsa and also an affordable laser cutter.
    Last edited by Versus; 05 Jul 13, at 18:03.

  12. #12
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    Quote Originally Posted by Versus View Post
    Further analysis of the design and its application, brings about the question of aspect ratio for the wings. Low aspect ratio in this case would be better choice than the high aspect ratio, because the low aspect ratio wings are more structurally safe although they produce significant induced drag when compared with the high aspect ratio wings. On the other hand high aspect ratio wings give lower induced drag but have more of parasitic drag. In order to reduce the induced drag, winglets will be placed at the tips of the wings and with little luck and skill they will be blended with the wing.
    For the fuselage, the initial idea was to drill a hole in which counter weight could be placed, in order to balance the airplane. However, since parameters that determine the weight and overall performance are still unknown, the question of CG needs to be tackled differently. Since the "fuselage" is simply one straight piece of wood, the new idea for the solution of the CG problem is to shape that piece of wood so that it can have sliding guides, on to which the ballast could be suspended and moved. Once the balance is achieved the ballast will be fixed. This will make the building of the fuselage a bit more complex and it also might add the weight but with this system, balancing should be easier and faster.

    Also I have a couple of good news, I've managed to find balsa and also an affordable laser cutter.
    Laser cutter?!?!? I thought you were doing it on the cheap!

    With my crash victims I try and make the CG 1/3 the length of the wing from the leading edge. Seems to work alright.

    I assume your doing balsa frame with heat shrink covering?

  13. #13
    Senior Contributor Versus's Avatar
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    Quote Originally Posted by Gun Boat View Post
    Laser cutter?!?!? I thought you were doing it on the cheap!

    With my crash victims I try and make the CG 1/3 the length of the wing from the leading edge. Seems to work alright.

    I assume your doing balsa frame with heat shrink covering?
    The one I've found, that shop charges 30 euros per hour for cutting so this will be the greatest cost in the project at this stage. I would do it manually but due to the size of the aircraft, I don't have the tools that can do it at that scale (they are too bulky and more suitable for the bigger things). As for CG, it usually sits there but since I don't know exactly how heavy and how big this design will be, this option should provide good results. For the fuselage and the cg adjustment, that is a problem, the airplane is small so weight is the biggest problem. The only solution I can think of at this stage, is to use tube for the fuselage and than go trough it with the ballast.

    Anyhow at the end, this is the scale I am looking for for the final rc model. http://www.youtube.com/watch?v=k0uPXqpvymg
    Last edited by Versus; 06 Jul 13, at 14:04.

  14. #14
    Senior Contributor Versus's Avatar
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    Materials have been bought, balsa and some sort of compressed foam that can be sanded and hot glued, so pretty much the stuff for the airframe is there. New problem accrued however and that is the machine for foam cutting. CNC set up would be ideal, but my thin paycheck can't allow that so I have to deal with this. Preliminary design of the machine has been conjured in my mind and the materials for its construction are there, so during the next week the construction will began.

  15. #15
    Senior Contributor Doktor's Avatar
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    Let the games begin, says I.
    No such thing as a good tax - Churchill

    To make mistakes is human. To blame someone else for your mistake, is strategic.

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