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  1. #1

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    Question How to launch a small bipe?

    I've built myself a Zaunkönig from Fiberplanes (http://www.fiberplanes.de/cnc.htm) but so far the longest flight has been five meters, so i would like to ask for some advice.

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    The way I see it there are several obstacles to a successful launch:
    1. I'm not a good pilot. Actually I'm quite far from being a good pilot. My screen name isn't a coincidence (and no, SBS isn't an abbreviation for my name, it's short for S-t Behind the Sticks). OK, I'm a little bit better at flying gliders than motorplanes, but that didn't help at all when I've tried to launch the Zaunkönig.
    2. I have very little experience of motor planes, and even less of i/c-planes. This is my first pure 1/2A-plane (I've had an electric before).
    3. When launching my (electric) gliders I hold them under the belly, approximately at the CoG and 'throw' them like a javelin (well, actually they more or less flies out of my hand and doesn't need much throw). But when trying to hold the Zaunkönig the lower wing gets in the way so I can't get a good grip.
    4. If I grip behind the wing and throw the plane it seems I can't get a clean throw. Due to the short length and span she seems to be quite a bit 'wobbly' at first, and so far the wobbles have resulted in a some sweet 'ground-kisses'. Nothing serious, just a broken firewall once, and a couple of broken props.


    So, what do you suggest I do? I was thinking of a discus-launch by holding the lower wing but I haven't dared (yet)? I also thought of glueing a hand-grip under the belly, but figured it would be to ugly (but that wouldn't stop me if it's considered the best way to go). Or is there a better way?

    I appreciate all your hints, tips and advices.

    /Stefan

  2. #2
    combatpigg's Avatar
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    Stephan..this plane will fly very easily if...

    1. The wing loading is low enough
    2. The power / thrust is strong enough
    3. The model has the correct balance
    4. The model has the correct amount of control surface travel
    5. The model is assembled geometrically "true" and the controls have no slop or defects.

    I have a few biplanes in the size range in your picture. They hand launch very easily with just a slight push away from me. They all weigh about 14 ounces or less.
    Any combination of factors that I listed can add up to failure, especially if the .049 engine isn't producing about as much thrust as what the model weighs.
    WHO GUNNA FEED MAW KEEEIDS..???

  3. #3

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    Low wing planes are harder to hand launch than high wing which you've figured out. I grew up throwing all my planes and still throw a lot of them so I've got it down pretty well.

    If at all possible it's best to have someone else either hold the transmitter or throw the plane. Two hands works best for something like your bipe. One hand behind the wing (lightly) and one just gently under the nose holding the plane level while you take about a 4-step run to launch.

    If you're by yourself then you hold behind the wing and before you let go you grip with only two fingers so the plane can rotate while you're still holding it. When it rotates to the position you want it to fly out of your hand you release. Depending on the power you want anywhere from 10 degrees down to 10 degrees up. Most guys who don't know how to hand launch want to throw their planes 45 degrees up where it stalls and goes back into the ground.

    Also, go to your hard and pick up a stick with your throwing hand and hold your transmitter in the other hand. Practice throwing the stick and getting your hands on the transmitter sticks without bumping them. That will save you a lot of frightening moments after launches.
    Work is what I do for the love of it. A job is how I pay for it.
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  4. #4
    Pond Skipper's Avatar
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    Here you go this will make it easy as it can be and help avoid some under belly damage



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  5. #5

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    Quote Originally Posted by combatpigg View Post
    Stephan..this plane will fly very easily if...

    1. The wing loading is low enough
    2. The power / thrust is strong enough
    3. The model has the correct balance
    4. The model has the correct amount of control surface travel
    5. The model is assembled geometrically "true" and the controls have no slop or defects.

    I have a few biplanes in the size range in your picture. They hand launch very easily with just a slight push away from me. They all weigh about 14 ounces or less.
    Any combination of factors that I listed can add up to failure, especially if the .049 engine isn't producing about as much thrust as what the model weighs.
    Thank you for your fast reply.

    My all up weight (except fuel) is 330 gram (11.6 oz). The engine is a Surestart with the choke 'throttle' and I measured it to 16400 rpm with the 5x3 (?) yellow Cox safety prop. Do you think that is enough power-to-weight ratio?

    I have balanced it once, but I will do it one more time just to make sure.

    I haven't measured the deflection of the control surfaces - I just made it as big as I could. IIRC I have at least +/- 30 degrees.

    Aah, the geometry. Finally a question I have a crystal clear answer to. The slop in the linkage is almost negligible. There are some slop in the servos (yup, I used the cheapest I could find...) but not very much. I would say the wings have some, very small, deviations from the ruler when I hold it against the wing, but I need to hold them against a light to be able so see the error. As for the fuselage it is built using my patent pending Chiquita jig.....


    All in all, I know it isn't a perfect build, but I hadn't expected it to fly just a couple of meters. The impression I get (but, given my small experience, it might be wrong), is I need to get the plane up to speed before the rudders have any effect. But hitherto I've hit the ground before I've had the chance to accelerate enough.





    @CafeenMan:
    It's a good advice you give, practising to put the hand on the sticks in a hurry. As for me, I think I'm above avarage in that aspect because I like to fly with a transmitter glove during the winter and sometimes it gets a bit hairy to get the hand back in there when launching in gusty winds....

    Last time I had a friend launching the plane for me, but I will try your method next time I launch myself. Thanks.



    @Pond Skipper
    Thank you for the picture. Clear plastic sounds heavy. I dont mind the looks of the plane as long as it is functional. Do you think balsa is to soft/weak?


    /Stefan

  6. #6

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    With small planes I like to give them a couple of test glides to test the controllability, balance and throws. I look for a soft level or slightly sloping landing zone about 100 feet long oriented with the wind. Long grass or soft snow is ideal. I run a few steps and give the plane a firm push straight ahead into the wind and then fly it till it lands. Don't throw it up or down, just push it straight ahead firmly. If it tracks straight ahead without stalling or diving and with little or no transmitter input required, I consider it ready for a power on test flight. If I have to get on the sticks immediately to prevent a crash then something is wrong. I make adjustments and test again. Power on test flights are made with about 2 or 3 minutes of fuel onboard.

    On another point 30 degrees of throw is probably WAY too much on any flight control surface except maybe the rudder. I have planes that are very sporty with 10 degrees of throw or less. If your plane is properly built and balanced you shouldn't need more that 15 degrees to 20 degrees of throw.

    The picture that you have posted makes the propeller look much larger than 5 inches, it looks like 9 inches or so. A 5 x 3 prop is great for a faster plane but I find slower draggy planes fly better on a 6 x 3 or even a 6 x 2. APC makes a 5.7 x 3 which is very nice for high drag planes I think it would be ideal for your biplane. I have a 2 meter glider that climbs with authority using a Cox Medallion and an APC 6 x 2.
    Last edited by 049flyer; 04-18-2014 at 05:46 PM.
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  7. #7
    combatpigg's Avatar
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    Stefan....
    Try reducing your control movements.
    All you should need is 10 degrees for the elevator and even less than that for the ailerons.
    Everything else sounds OK, but you do not have a large amount of power at your disposal.
    If the CG is on the verge of being too sensitive, if the power is marginal, if the controls are set too be too twitchy...then this combination of conditions will make trying to fly beyond 15 feet difficult.
    What can sometimes happen is the engine is set for almost max rpm on the ground because it has disappointing output. Then the hand launch is a strong throw that causes the fuel in the fuel line to starve the engine momentarily and at the most critical time the power drops below a usable level.
    Under 12 ozs is an excellent weight for that size of plane..! give the model a level push away from you at eye level. This is all it takes if all the other conditions are met. Allow the plane to gradually swoop down as it gains speed and it will be flying on it's own right at the 15 foot mark, ready to start it's climb to freedom.
    Measure all of your trim settings on a flat table with the model set perfectly level. Measure the same distance off the surface of the table to all parts of the horizontal stab / elevator, center of leading edge of wing and center of trailing edge. If the model is perfectly trimmed it will not need much assistance to fly. Make sure that you do not have any left thrust on the engine..a small amount of right thrust is better if you have made a mistake....but perfectly straight forward thrust angle is what I aim for with a model like this.
    To check thrust angle, remove the prop and bolt the model / engine to a perfectly flat plate and allow the model to rest on it's nose.
    Now take a carpenter's square and use your eyes to judge how squarely the model stands while looking at it from every possible direction. You can also take "key" measurements at this time off the table to each wing tip.
    I use 1/8" round bamboo sticks for the wing struts on planes this size and push them through tight fitting holes in the wings...but do not glue them until I get the model all checked out with these careful measurements, then I use thin CA glue to lock the struts to the wings and trim the extra bamboo away with a razor saw.
    WHO GUNNA FEED MAW KEEEIDS..???

  8. #8
    Pond Skipper's Avatar
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    Locally we use thin lexan for rc plane windshields, comes in many thicknesses for your plane 4g worth would do. 1mm thick.

  9. #9
    MJD's Avatar
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    Already been said, but I just read this - control throws 30 degrees? Egads, it's a half-A! Save that for later. Get it flying smoothly on low throws - if it won't do that it sure isn't ready to fly with 3D throws. Small bipes have low moments of inertia and they will do terrible things to you on slow launches with jumpy controls (guess how I know). And don't be afraid to keep the CG forward at first.

    Got a hill with long grass?
    Sorry I'm late dear, I had to help my uncle Jack off his horse.

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