RCadvisor.com blog
Strange Flight Characteristics Suggestions?
  • Hi Carlos!


    Im really enjoying your revamped website, and i am enjoying your Book Model Airplane design made easy.


    I have a question about some funny flight characteristics that one of my planes is exhibiting and i was hoping you could help me understand what is happening and why it is happening.


    The plane in question is a 55inch F3A style Foamy called a Rainbow or Firenza


    http://www.rcgroups.com/forums/showpost.php?p=21325781&postcount=822


    The problem is it seems to snap out of a loop right at the top and i dont know why?


    If i fly straight and level at full throtle and pull up into a fairly tight loop when it gets to the top it snaps out.


    If i dive to build airspeed and then try the same loop it still snaps out at the top.


    However if i try to do a much larger more gentle loop it continues round just fine.


    Can you help me understand what is happening and perhaps suggest a solution?


     


    many thanks


    Ben


     

  • Does it always snap roll in the same direction? Could there be a warp on
    the wing? What is the throttle setting at the top of the loop?

    It sounds to me like the model is tip stalling at the top of the loop. Looking at the pictures, it has a healthy amount of taper.

    Carlos
  • Hi Carlos
    When you had talked about moving weight to the tail and such can that be done one the sim. maybe it will help with your answer.
  • Hi Carlos


    Yes it always snaps in the same direction.


    I have checked teh wing and it doesnt look warped to me.


    Is there a certain method for checking?


    I Think i am holding full throttle at the top of the loop, but i may be easing off to 50% as a force of habbit from my heli days!


    I will try again this weekend and see what happens.


    I am also trying a new Prop i am going from a 12x6 to a 13x6.


    Will report back on Saturday!!


     


    Thanks


     


    Ben

  • Here is something to check: do a lateral balance of the model. In other words, see if both wings weigh the same.

    I don't think I have any special tricks for checking for warps and the alignment of a model.

    Carlos

  • Shawnee said:

    Hi Carlos
    When you had talked about moving weight to the tail and such can that be done one the sim. maybe it will help with your answer.



    Yeah, running some numbers might help.
  • Hi Carlos<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />


    Just thought I’d give you an update.


    I checked for wing warping and as far as i could tell both wings were perfect.


    I checked for lateral balance and there was a very slight imbalance but not very much and it was to the left side of the plane when the plane snaps out of a loop to the right.


     After 2 more flights yesterday I came to the conclusion that it is basically my flying style compared to what the plane was designed to do. I think I was just trying to fly the plane far too aggressively for what it was designed for. It is a pattern plane and I was trying to do more Hot Dog, Fast tight manoeuvres with it and it didn’t like it.


    If I tried to do a fast tight banked turn like a pylon racer it would also violently snap out of it on the opposite direction to the turn.


    If I flew big graceful manoeuvres it flew well.


    The wing was designed with quite a large taper and I had a pretty heavy power system in it so i was right at the limits of what the recommended flying weight was. it was just about 2.5Kg all up.


    Most people who fly this plane fly on smaller power systems and lower wing loadings.


    So will all those things taken into consideration I decided it was not the plane for my flying style.


    Unfortunately at the same time I was making all these realisations, I caught myself out and it snapped out of a tight turn and hit the ground hard completely destroying the plane.


    The frustrating thing is at the same time I was making these realisations I had decided to sell the plane just moments before it hit the ground!


    Oh well at least I have space in my Hanger for another plane now!


    I just need to find something I can use the same power system on.


    Cheers


    Ben


     


     

  • Argh!!! I am real sorry to hear about the crash. If it is a pattern plane, then it must have had a relatively thick wing airfoil. It is hard to tell from the pictures.

    It sounds like you were experiencing accelerated stalls. It does not matter in which direction the airplane is pointing - it can stall at any time.

    That was an important lesson that you learned. For wild 3D flying, wing loading is key. I have resumed working on my Kilo3D design, and keeping the weight down is a primary design goal.

    Carlos
  • I think you may be have been experiencing high speed stalls due to too much elevator deflection.  You're probably right that that plane was just not designed for quick pitch changes.  If that's what was happening, the way to solve it is to reduce elevator throw.  Another possibility is that the plane was nose heavy.  If so, it would require some up elevator trim to fly level at mid throttle.  I'm not sure why, but it is my understanding that planes trimmed this way have more of a tendency for high speed stalls with full up elevator.  Maybe it's because you need that much more up deflection to make a pitch change than you would have if the plane was balanced more to the rear.  

    I learned the same lesson from a wise member of our club: "As soon as you're bored or frustrated with a plane, you MUST sell it.  If you don't, you'll surely crash it".  A few days after he said that, I destroyed a carefully built foamy trying to wring some excitement out of it that just wasn't there.

    Anyway, too much elevator deflection for any airframe with snap the plane at any speed, especially when ailerons are deflected.  This, by the way, is the cause of the dreaded "downwind turn stall" myth.  Ah, but that's a story for another post.  
  • That's a good saying. It also explains a lot of my crashes in simulators.

    Carlos
  • Thanks for the comments guys


     


    Yes the airfoil of the plane was pretty thick. I should have measured it before i threw everything out, It would have been interesting to know whatthe percentage thicknes was.


    There was nothing of the airframe worth saving.


    Now i have a 60 size 6s power system spare


    Any suggestion on what i could put it in?


     


    That is a very good saying, i will bare that in mind for future!


     


    I too am finalising my 1kg Biplane that i rebuilt from Depron and its turning out Great.


    Cheers


     


    Ben

Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

In this Discussion