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Thread: Factors affecting ability to successfully hand launch

  1. #1
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    Factors affecting ability to successfully hand launch

    Hi folks,

    Relative newbie here. Have my Z3 put together and have made a few flights with her. The first flights were done before I put any fpv gear on the plane. I was able to successfully hand launch it for each flight with the following setup and conditions:

    2x 3S batteries (4200+5100mah), Castle 75A ESC, Eflite Power25 1250kv, 10x5e prop
    In all my successful early flights (perhaps 5 or 6) I generally had noticeable amount of wind.
    (maiden flight video showing a successful hand launch)

    Fast forward to this weekend.... the antenna that I had been waiting on arrived and I added fpv gear to the Z3. Things added include:
    • 400mw 1.3Vtx
    • 1.3 Skew Planar antenna
    • Ritewing Mobius toughbox
    • flight camera
    • 808#16 camera
    • associated cables
    • and a couple of air scoops made out of 1/2 of a plastic spoon for airflow.


    So...having added the gear a flying buddy came over and I decided it was time to try to make a short range fpv flight with her. Trouble is I never got her into the air. I'm still inexperienced enough not to be certain of what the troubles really were. But... it seemed to me that she would just roll over and nose into the ground no matter what I did. I'm guessing I just wasn't getting enough speed and airflow over the control surfaces to have any control and get her into the air. At the field I just assumed it was the extra weight that made the difference. However, in hindsight I realize I had several factors I think might have been working to make it harder this time. Those include...


    • extra weight of the fpv gear
    • was a calm day, lack of headwind that I had on prior successful attempts
    • Also, I put in a single 3S 8000mah battery this time.


    With regard to the last point... am I right in assuming that I might have gotten slightly less rpm/thrust by putting a single 3S battery in the plane? What I'm guessing/thinking is that the single battery might drop voltage a bit lower when opened up to full throttle than the pair of batteries did. I have no clue if this could be significant or not...just an idea....wondering what you guys might suggest? Also... would I be correct in assuming that it would be noticeably easier to hand launch into a decent headwind than it would be on a calm day?

    As a result of the failed launches I needed to inject a bit of CA glue into key spots on the nose to get some of the strength back (I nosed her in multiple times trying). Nothing awful happened, just a little battle weary now on the nose section. But, this had me looking carefully at ecalc for my battery/prop options. From what I can see, with my 3S setup and my 10x5 prop ecalc suggests I'd have ~68oz of thrust. By simple switching to a 4S setup with the same prop it suggest that I'd goto 111oz of static thrust and the max current would still be below (slightly) my ESC's continuous current rating.

    So.... I ran out and grabbed the only 4S battery my local hobby store had... a 4000S Eflite battery. Haven't tried to fly with it yet, but hopefully it will make a big difference and I can get back to hand launching. Having said that, this little episode has me looking at bungee launcher options for the first time. I *REALLY* don't want to be carrying around any more kit than I need to though. Not sure where I'll go with it. Perhaps a bungee launcher that is basically just a stake and a bungee cord without a launch-rail-frame setup? I've seen a video where someone seemed to use this type of setup (might have been AtariJoe?). Looked like it worked for him... not sure how it would go for this newbie though...

    anyway... thanks for listening... and most importantly thanks for any words of wisdom you guys can share that might help.
    Last edited by Flyswamper; 28th September 2014 at 08:15 PM.

  2. #2
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    A headwind can make a very significant difference. Ever seen that "how to launch a ZII" vid by rockyFlyer? On his first launch he tosses his ZII unpowered like a baseball into a huge headwind and it climbs about 20 feet before he powers it. Having that unrealistic expectation made my first launch attempts rather comical to observe. Here's a link to the vid if you haven't seen it. www.youtube.com/watch?v=1U2LaAnzQQU

    The next thing that comes to mind is CoG. I'm sure you did your due diligence but in the interest of covering all the bases did you check your CoG after installing your FPV gear, and about where is your CoG now?

    Of course as your calculations showed going from 3S to 4S should also make launches easier. Another thing that helps (and I know this sounds super obvious too) is to really put some force into your toss.

    Nothing wrong with a bungee or a catapult, but when you mentioned tying a bungee to a stake it conjured up a frightening visual. Be sure to secure that stake!

  3. #3
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    It all comes down to having enough static thrust. If you have 80% or more of your plane's weight in thrust, you should be able to get it airborne without too many problems.

    Also, rather than a bungee, try a trebuchet. This pulls the plane more gently and gives it plenty of altitude on release.

    -Alex
    If it is broken, fix it. if it isn't broken, I'll soon fix that.

    [url]videoaerialsystems.com[/url] - Performance video piloting

  4. #4
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    3s is too little V for that low of KV, 4s is what you need, 3s is nominal at best if not loaded full of fpv gear, if you going 3s you will need around 1450 kv

  5. #5
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    Factors:
    Wing loading
    arm strength
    headwind
    power available
    technique
    Flying through the cash.

  6. #6
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    4S, 4S, and only 4S on the Z3. Had a great flight today on 1250kv on 4s with 10x5e. Jumped out of my hand and into the air.

    On 3s this thing dove to the ground and bent up the nose...

  7. #7
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    Thanks fellas... I've got a 4S battery for it now, but I think I'll wait for a bit of headwind (which shouldn't take too long!) before I give her another toss. In hindsight, I guess I didn't realize just how much assist I was probably getting from the wind at launch time. Thanks for the suggestions and feedback.... It all helps!

    I had initially planned to go 4S with this plane, I just hadn't bought a 4S battery yet. So... I went out and gave it a try with 3S. The relatively easy/successful launches I had with just 3S I guess gave me a false impression about how easy it would be to keep doing it that way with my current motor/prop. (which I bought planning on 4S...).
    Last edited by Flyswamper; 29th September 2014 at 08:33 AM.

  8. #8
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    Show me your trebuchet I will show you mine!
    Quote Originally Posted by IBCrazy View Post
    It all comes down to having enough static thrust. If you have 80% or more of your plane's weight in thrust, you should be able to get it airborne without too many problems.

    Also, rather than a bungee, try a trebuchet. This pulls the plane more gently and gives it plenty of altitude on release.

    -Alex

  9. #9
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    Factors affecting ability to successfully hand launch

    The most intriguing bungee thing I've seen so far is this.....

    http://www.mygeekshow.com/watchmygee..._Launcher.html

    Curious what others say


    oh...and the one with the smallest trebuchet wins.
    Last edited by Flyswamper; 29th September 2014 at 07:46 PM.

  10. #10
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    Quote Originally Posted by IBCrazy View Post

    Also, rather than a bungee, try a trebuchet. This pulls the plane more gently and gives it plenty of altitude on release.

    -Alex
    Sorry Alex, but LOL at this advice. A trebuchet, really??? No way someone is going to build one of those easily, much less launch a wing from it

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