Page 2 of 2 FirstFirst 12
Results 41 to 48 of 48

Thread: Move the wing for better CG?

  1. #41
    www.SkupTech.com mike mcs repair's Avatar
    Join Date
    Aug 2004
    Location
    chugiak AK
    Posts
    8,920
    Post Thanks / Like

  2. #42
    Southern Aero's Avatar
    Join Date
    Jan 2008
    Location
    kcco/1ga2
    Posts
    104
    Post Thanks / Like
    Quote Originally Posted by stewartb View Post
    Movable (forward extending) leading edges? Hell, dream big.
    Been dreaming big for years! Hope to have one flying in the next few months on my stretch. Building a short and a long wing version, short will probly fly first
    ......... it doesn't cost any more to go first class! you just can't stay as long.
    Likes mike mcs repair, stewartb liked this post

  3. #43
    PerryB's Avatar
    Join Date
    Aug 2007
    Location
    Northern Calif.
    Posts
    1,440
    Post Thanks / Like
    I have a simpler solution. Just sell the Cub and the house and get a helicopter. And then get a second job to cover the maintenance costs.
    After Monday and Tuesday, even the calendar says WTF !

  4. #44
    Little_Cub's Avatar
    Join Date
    Feb 2011
    Location
    Palmer, Alaska
    Posts
    264
    Post Thanks / Like
    Quote Originally Posted by stewartb View Post
    Isn't part of the reason for extending the SQ-12 and Rev 2 to re-gain elevator and trim authority to take advantage of the high lift/high AOA wing mods? Why is extending the tail aft a bad thing? It provides a good benefit-weight ratio. Judging by the SQ-12 videos and the pirep gross loads it carried it was well balanced. The Rev 3 wing may escalate things to another level, too. Interesting stuff.
    I believe the new SQ is trimmed however adding to the arm (tail) or adding weight makes the control forces heavier.. haven’t spoken with Wayne.. still dreaming! In a perfect world it seems best (for everyday fun machine) to simply balance what works and limit the mass. Your right though.. wing candy adds another dimention to chase.

    I know how these dreams usually end.. ‘pop’!

    Enjoying the process however




    Sent from my iPhone using Tapatalk

  5. #45

    Join Date
    Jun 2007
    Location
    New Zealand
    Posts
    480
    Post Thanks / Like
    Quote Originally Posted by Little_Cub View Post
    The further you go the better.. until its too far however we normally fly in front of a Cub, with a big engine it's not balanced
    even before flaps add to the equation.

    Anyone know the math or what the result of moving the wing will bring? If we are moving the whole fuselage
    back relative the forward moving center of lift it doesn't seem like it would take much to get to the sweet spot again.
    Yes the wings movement will add to the forward CG but would think its a limited effect with a short arm.

    What if the center of lift approaches the CG point? Normally the center of lift remains behind the CG.. what is that result
    as it gets closer?

    I know there are some engineers on board

    Please PM if you don't like to broadcast.
    fknapp_at_alarmspro (dot) com

    Thank you!
    Frank,

    Here's my spin on it.

    With a conventional plane the centre of gravity (C of G) is in front of the centre of lift (C of L) and a downforce is maintained with the tailplane to keep the plane in equilibrium. See attached pic.

    You need to maintain a margin between C of L and C of G. Once the two coincide you no longer need down force on the tail and the aircraft becomes unstable. Even if the margin is too small the aircraft may become difficult to control. The RV-6 is a good example of the latter, they are easy to get into an aft C of G situation and a friend of mine told me that when he was doing the flight testing for his, he was pushing forward on the stick and the nose was still coming up. This is exasperated with low wing aeroplanes due to the geometric relationship between the wing and the C of G as the angle of attack increases. The opposite extreme that we can all relate to is flying an empty C206 where they fly like dogs and you can need power in the flare.

    Putting the flaps down actually helps. Cubs pitch nose up with flap which is the same as having a more aft C of G isn't it? This is to do with the centre of lift moving forward once the flaps go down. (Yeah, I know, lots of new drag above the drag line too.) The C of L also moves forward as the angle of attack increases, so as you slow up they become less stable and the lower stick force isn't just to do with less airflow over the surfaces.

    There are a couple of other factors in play here too. One is pitching moment and the other is downwash. I have a compilation of articles written by Barnaby Wainfan (sp?) that might've been in kit planes magazine and he explains pitching moment at least. His stuff is really easy to read, if you want to do something like this, I recommend you find a copy.

    I did a test flying programme for a Murphy Rebel and with the flaps down, there was not sufficient elevator authority available to flare it. Stalling it one time it even bunted, indicating the tailplane and elevators gave up flying. The flaps cover about half the span and are quite large chord and go right up to the fuselage and I put the elevator authority issue down to the probably significant downwash coming off the wing. As I understand it from reading, the Bearhawk has a gap between the wing and the flap to maintain some proper airflow over the tailplane when the flaps are down. Cub guys might not be doing the right thing closing up the gap between the flap and the fuse………...

    The thing that would put me off the most in moving the wing forward on a Cub type build, is that you will be no longer seated in line with the leading edge of the wing, significantly affecting visibility in the turn. It will be like a 152. Try and find some air to air pictures of the Rans S-7 and you will see the Captain is seated even further forward than a Cub with fantastic visibility.

    Just this week I had a disagreement with a colleague who claimed the USA35B airfoil was just a Clark Y in drag (pun intended) and I disagreed saying the USA35B coefficient of lift (Cl) is much better than a Clark Y. At home he laid the data for various airfoils over each other and had to eat crow about the USA35B. But one of the airfoils he put on the graph was a Liebeck airfoil that he is keen on. It has a much better Cl than the USA35B and more importantly has a much lesser pitching moment which means your elevators would be more effective, which is really partly what you are after. More than one way of skinning the cat!

    I am an amateur aerodynamicist, so I offer my apologies in advance if I have not got some things quite right or my explanations are difficult to follow.

    Cheers,
    Andrew.
    Attached Images Attached Images
    Thanks Little_Cub, PerryB thanked for this post

  6. #46

    Join Date
    Mar 2016
    Location
    Vermont USA
    Posts
    358
    Post Thanks / Like
    Frank,
    So, now that the event has been run, what did you build?
    I do not even know if you had the new plane there. I see 33 combined this year, very nice.
    Presuming you did have the new plane, how far did you move the wing to achieve the balance in the new plane?

  7. #47
    Little_Cub's Avatar
    Join Date
    Feb 2011
    Location
    Palmer, Alaska
    Posts
    264
    Post Thanks / Like
    Quote Originally Posted by CharlieN View Post
    Frank,
    So, now that the event has been run, what did you build?
    I do not even know if you had the new plane there. I see 33 combined this year, very nice.
    Presuming you did have the new plane, how far did you move the wing to achieve the balance in the new plane?
    We were flying Lil Cub.. same as last year. We are still teasing all the possible changes.. that seems to be
    almost more fun than flyin' it you get it done then you always consider 'the next'!

    With the new flaps Lil Cub is doing about everything we can ask.. it balances very well with almost no stick pressure.
    For the next one we want to attain 100+ and have low end, it will be more of a daily traveler.

  8. #48

    Join Date
    Mar 2016
    Location
    Vermont USA
    Posts
    358
    Post Thanks / Like
    Nice, I was suspecting there was not enough time to engineer and build the new plane in time.

Similar Threads

  1. Move airplane wing from New Orleans West?
    By trkling in forum Cafe Supercub
    Replies: 0
    Last Post: 03-05-2011, 09:44 AM
  2. My new J3 (and move pics)
    By ATCT in forum Cafe Supercub
    Replies: 11
    Last Post: 05-21-2008, 01:31 PM
  3. alaska move
    By jr.hammack in forum Experimental Cubs
    Replies: 4
    Last Post: 04-22-2005, 11:45 AM

Tags for this Thread

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •