Register

If this is your first visit, please click the Sign Up now button to begin the process of creating your account so you can begin posting on our forums! The Sign Up process will only take up about a minute of two of your time.

Page 1 of 2 12 LastLast
Results 1 to 25 of 33

  1. #1

    Join Date
    Aug 2005
    Location
    New York, NY
    Posts
    681
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    symmetrical wing question..

    Hi all,

    I was debating with my friend that an aerobatic plane with a symmetrical aerofoil 0 degree wing & tail incidence the airplane will fly.. but his point is you need an up elevator to keep the plane in the air.... please give your views on this.

    Thanks,
    High
    I will say it only once Yak 54 the best aerobatic plane ever made.

  2. #2
    Lnewqban's Avatar
    Join Date
    Apr 2007
    Location
    South Florida
    Posts
    4,034
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    All the wing with symmetrical airfoil needs to fly is some speed and some angle of attack (respect to the incoming air).

    To keep the wing stable and at that AOA, the stab is needed.

    Symmetrical airfoils don't produce lift at zero degrees of AOA.
    Lnewqban - "God will not look you over for medals, degrees or diplomas, but for scars. He has achieved success who has worked well, laughed often, and loved much." - Elbert Hubbard

  3. #3
    Moderator BMatthews's Avatar
    Join Date
    Oct 2002
    Location
    Chilliwack, BC, CANADA
    Posts
    11,991
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    With a 0-0 setup it will fly but with some amount of up trim needed.  As the CG is shifted back more towards the model's nuetral point the amount of up trim will become less and less.   When the CG is at the neutral point then the amount of trim will be zero and the model will be neutrally stable.  At that point it will be truly a 0-0 flying model.  BUT.. it would be flying with a positive angle of attack as noted by Lnewqban.

    Note that neutrally stable does not mean UNstable.  The model will fly just fine.  But it will need constant attention from the pilot to correct for any disturbances caused by turbulence.

    Now when you add some up trim it could correctly be said that the model is no longer truly 0-0.  And that would be right.   So in a way you're both right.  It just depends on the CG location.  And to some extent where on the model the wing is located.  A high wing model will produce a high drag center and that acts like positive incidence as well when it comes to the model self stabilizing.  Similarly a low wing with big "grass" wheels can have so much low centered drag that it needs to have some positive incidence in the wing to achieve an effectively 0-0 setup.
    Witty saying to be plagarized shortly.....

  4. #4

    Join Date
    Aug 2005
    Location
    New York, NY
    Posts
    681
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    Remember the ultra hots by Dan Santich this plane i think this plane had the 0-0 incidence.
    I will say it only once Yak 54 the best aerobatic plane ever made.

  5. #5
    Moderator BMatthews's Avatar
    Join Date
    Oct 2002
    Location
    Chilliwack, BC, CANADA
    Posts
    11,991
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    Yes, and on top of that one the normal setup for all of the hot 3D fun fly flat foamies is an honest 0-0-0 setup as well.  But again, if the CG is located forward from the neutral point by very much some up trim will have to be used.   It may not be much but it would be there to allow the model to fly hands off in level flight at a moderate cruise speed.  And up trim is merely an alternative to built in postive and negative incidence angles.  Or as the terms are used these days in modeling some decalage angle or longitudinal dihedral.  This is why 0-0-0 setups built into the model are only seen on models where the owner is expected to trim the CG location back enough that it is very close to the neutral point and the amount of angular difference between wing and stabilizier needed will be so small that. it is most easily provided by a click or two of up trim or a turn or two of the elevator clevis.
    Witty saying to be plagarized shortly.....

  6. #6

    Join Date
    Jan 2007
    Location
    Taylorsville, KY
    Posts
    2,229
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    I set up my CL planes 0-0-0 and push the c.g. back until twitchy then bump fwd a 'smidge'. Not technical speak but works. Varying the wing AOA is what causes ascent and descent. I don't fly 3-d or aerobatic RC but the principal is similar.

  7. #7

    Join Date
    Aug 2010
    Location
    Montgomery, TX
    Posts
    260
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    I use "twitchy", "bump", and "smidge" all the time in my technical speak.  Of course, I also use the TLAR method of design.  Let's go flying!

  8. #8
    Moderator BMatthews's Avatar
    Join Date
    Oct 2002
    Location
    Chilliwack, BC, CANADA
    Posts
    11,991
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    Arup, on a control line model you'll automatically and unconciously select the amount of up elevator needed to fly level in any event  So your model will not truly be flying at an actual 0-0-0.  It'll be 0-0-x due to the slight up trim needed to hold level flight.  Only during the vertical parts of squares and wingovers will it truly be 0-0-0 when the model is pointed straight up or down.
    Witty saying to be plagarized shortly.....

  9. #9
    thailazer's Avatar
    Join Date
    Mar 2008
    Location
    Ampur Mae TaengChiang Mai, THAILAND
    Posts
    1,163
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    BMatt & Lnewqban..... Good posts! Here's an additional question: My Tiger 2 with fully sym wing flys fast just great with little trim. When I start doing landings (i.e. flying slower) I normally dial in 4 clicks of up trim. Is this because the horizontal stab is less effective at lower air speeds, or simply that I have to increase the angle of attack to fly slower?
    Tiger Flyer #49

  10. #10

    Join Date
    Nov 2005
    Location
    Auckland, NEW ZEALAND
    Posts
    1,925
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    Yep, lift is proportional to angle and airspeed, you can go slower, and higher angle, until you reach the stall angle, then you go faster, but down, unless the bottom edge of the air is a bit close.
    Evan, WB #12.

  11. #11
    rmh's Avatar
    Join Date
    Dec 2001
    Location
    , UT
    Posts
    12,605
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    forthose who actually fly models : I have a UMX300 (a tiny one ounce 6channel radio electric model)
    This model has flat foam wing with huge ailerons. I programmed the tx (DX8) to provide
    A- flaps for landing /take off (flaps are actually the ailerons)
    B flaps coupled with elevators (upflap with down el /down flap with up el.)
    Now I can watch the SPEED differences required to stay aloft when the wing is either FLAT/ Symmetrical or cambered.
    There is a huge difference in speed and lift.-with only a few degrees of camber
    However changing power, creates instant climb or descent. These silly little models show instantly the differences in wing configuration - power requirements etc. and all in a 30x50 ft room!
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Ge96275.jpg 
Views:	5 
Size:	20.5 KB 
ID:	1561712  
    Libby is still watching you

  12. #12

    Join Date
    Jan 2007
    Location
    Taylorsville, KY
    Posts
    2,229
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    ORIGINAL: BMatthews

    Arup, on a control line model you'll automatically and unconciously select the amount of up elevator needed to fly level in any eventΒ* So your model will not truly be flying at an actual 0-0-0.Β* It'll be 0-0-x due to the slight up trim needed to hold level flight.Β* Only during the vertical parts of squares and wingovers will it truly be 0-0-0 when the model is pointed straight up or down.
    Thanks for clarifying the point I was trying to make. Changing the elevator causes a change of stab-elevator combo incidence as a system which then changes AOA of wing.

  13. #13
    Lnewqban's Avatar
    Join Date
    Apr 2007
    Location
    South Florida
    Posts
    4,034
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    ORIGINAL: thailazer

    BMatt & Lnewqban..... Good posts! Here's an additional question: My Tiger 2 with fully sym wing flys fast just great with little trim. When I start doing landings (i.e. flying slower) I normally dial in 4 clicks of up trim. Is this because the horizontal stab is less effective at lower air speeds, or simply that I have to increase the angle of attack to fly slower?
    Yes, the tail is forcing the wing to adopt a higher AOA, so the coefficient of lift increases for reduced airflow and lift force remains about the same to sustain horizontal flight.

    When you dial in 4 clicks of up trim, you are modifying the camber and the AOA of the stab-elevator surface.
    By doing that, you are increasing the down lift of the tail, even for the reduced speed.
    The down lift pitches the nose of the plane up enough to increase the AOA of the wing as much as the reduced speed demands.

    Remember that lift is proportional to AOA and to the square of the air velocity:

    http://en.wikipedia.org/wiki/Lift_coefficient
    Lnewqban - "God will not look you over for medals, degrees or diplomas, but for scars. He has achieved success who has worked well, laughed often, and loved much." - Elbert Hubbard

  14. #14
    rmh's Avatar
    Join Date
    Dec 2001
    Location
    , UT
    Posts
    12,605
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    lift is porportional to the square of the air velocity? Could you clear that up?
    Libby is still watching you

  15. #15

    Join Date
    Dec 2006
    Location
    DENHAM SPRINGS , LA
    Posts
    537
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback
    CKAero.net Team YS, Futaba, cool power, Central hobbies, Hyde Mounts, contra, xtreme composites

  16. #16
    Lnewqban's Avatar
    Join Date
    Apr 2007
    Location
    South Florida
    Posts
    4,034
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    Grammatically incorrect?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	He97153.jpg 
Views:	6 
Size:	53.2 KB 
ID:	1561918   Click image for larger version. 

Name:	Wr54904.jpg 
Views:	11 
Size:	118.9 KB 
ID:	1561919  
    Lnewqban - "God will not look you over for medals, degrees or diplomas, but for scars. He has achieved success who has worked well, laughed often, and loved much." - Elbert Hubbard

  17. #17
    rmh's Avatar
    Join Date
    Dec 2001
    Location
    , UT
    Posts
    12,605
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    A little
    Libby is still watching you

  18. #18
    MTK's Avatar
    Join Date
    May 2004
    Location
    Whippany, NJ
    Posts
    4,738
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..


    ORIGINAL: ARUP

    I set up my CL planes 0-0-0 and push the c.g. back until twitchy then bump fwd a 'smidge'. Not technical speak but works. Varying the wing AOA is what causes ascent and descent. I don't fly 3-d or aerobatic RC but the principal is similar.
    On your CL model, if your prop is turning to the outside of the circle and your thrust angle is truly 0, you would need rudder offset to keep the lines from going slack. Your wing, stab and engine/motor might be zero, but the model still needs to fly in constant slip
    Regards,
    MattK
    (Rcmaster199@aol.com)

  19. #19
    thailazer's Avatar
    Join Date
    Mar 2008
    Location
    Ampur Mae TaengChiang Mai, THAILAND
    Posts
    1,163
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    CL models always want to go outbound due to centripetal forces. I never had any rudder offset on my models years ago and doubt you would ever need any.

    But back to the original thread. Good stuff here. Anyone want to post a good curve of parasitic (form) drag and induced drag versus AOA? Always good to know how one gets "behind the power curve".
    Tiger Flyer #49

  20. #20
    rmh's Avatar
    Join Date
    Dec 2001
    Location
    , UT
    Posts
    12,605
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    There are a jillion web sites which address that stuff ad infinitum
    How about practical demonstrations of the question - as it affects models?
    When we flew Stunt - in the 1950/60's we always included a little rudder -in case something went wrong (power loss) and the lines lost tension
    The "bucket on a string" physics usually did the job .
    Libby is still watching you

  21. #21
    Ben Lanterman's Avatar
    Join Date
    Oct 2002
    Location
    St. Charles, MO
    Posts
    1,406
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    Well - I have always thought it is better to try to raise the level of understanding when it comes to models and aerodynamics than to lower the level. The forum is called "Aerodynamics" after all. I have a badly bent heart (7 bypass total, valves, etc. ) and when I have a question about heart health I don't want an answer like - well it just beats you know!

    It is OK to give a good answer and then if necessary move the level of science up or down until understanding is arrived at.

    "lift is porportional to the square of the air velocity"

    The example given in the figures several answers above is terrific in it's simplicity. It is only a little bit of math. It won't hurt. The lift equation is

    L = .5 * Cl * r * V^2 * A

    L = total wing lift
    Cl = wing lift coefficient
    r = air density
    V = air velocity
    A = wing area

    So write it as

    L is proportional to V^2 or....

    the lift of a wing is proportional to the square of the air velocity (relative to the wing).

    When you go twice as fast you get four times the lift out of the wing.

    Ben
    Ben Lanterman

    http://public.fotki.com/benlanterman/
    http://webpages.charter.net/benlanterman/Index.html
    http://www.photo.net/photodb/folder?folder_id=208093

  22. #22
    Lnewqban's Avatar
    Join Date
    Apr 2007
    Location
    South Florida
    Posts
    4,034
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    ORIGINAL: thailazer

    Anyone want to post a good curve of parasitic (form) drag and induced drag versus AOA? Always good to know how one gets ''behind the power curve''.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Qo38769.jpg 
Views:	4 
Size:	114.2 KB 
ID:	1562293   Click image for larger version. 

Name:	Hc91867.jpg 
Views:	5 
Size:	79.4 KB 
ID:	1562294   Click image for larger version. 

Name:	In28363.jpg 
Views:	4 
Size:	34.3 KB 
ID:	1562295   Click image for larger version. 

Name:	Hb80920.jpg 
Views:	4 
Size:	36.7 KB 
ID:	1562296  
    Lnewqban - "God will not look you over for medals, degrees or diplomas, but for scars. He has achieved success who has worked well, laughed often, and loved much." - Elbert Hubbard

  23. #23
    rmh's Avatar
    Join Date
    Dec 2001
    Location
    , UT
    Posts
    12,605
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    ORIGINAL: Ben Lanterman

    Well - I have always thought it is better to try to raise the level of understanding when it comes to models and aerodynamics than to lower the level. The forum is called ''Aerodynamics'' after all. I have a badly bent heart (7 bypass total, valves, etc. ) and when I have a question about heart health I don't want an answer like - well it just beats you know!

    It is OK to give a good answer and then if necessary move the level of science up or down until understanding is arrived at.

    ''lift is porportional to the square of the air velocity''

    The example given in the figures several answers above is terrific in it's simplicity. It is only a little bit of math. It won't hurt. The lift equation is

    L = .5 * Cl * r * V^2 * A

    L = total wing lift
    Cl = wing lift coefficient
    r = air density
    V = air velocity
    A = wing area

    So write it as

    L is proportional to V^2 or....

    the lift of a wing is proportional to the square of the air velocity (relative to the wing).

    When you go twice as fast you get four times the lift out of the wing.

    Ben
    OK - double the speed - the lift goes up four times. Simple and concise.
    Sorry if my approach to aeronautics is based in application for the novice modeller.
    I personally thought the info here was to be constructive/ easily understandable to a model builder flyer .
    I personally see no advantage in presenting math to layman. most flyer I know don't speak math.
    With one notable exception who is world renown in physics. (Prof Robert Beck Clark) and he NEVER explains flight using tech terms -especially to neophytes
    Having past experience in presenting technical stuff to juries - -I got broken of that approach long ago.
    For the modeller - the fact that a little speed increase OR decrease -creates a BIG change in lift -is worth knowing
    Realistically we fly in a fairly small, low speed range - but the rule ,of course is still valid.
    So basically control the speed -other than wingloading it is the largest factor in providing lift.
    Unless the AOA is a larger part of the physics -which are involved in flight.
    Libby is still watching you

  24. #24
    Ben Lanterman's Avatar
    Join Date
    Oct 2002
    Location
    St. Charles, MO
    Posts
    1,406
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    I have never assumed the novice builder is without math or physics skills - only about aerodynamics in particular. I belong to a club that is filled with engineers and tech guys who have no trouble with the math or physics. I always ssume that is the case until the questioner says they can't understand what you are saying. I would think guys at a keyboard have elementary math skills.

    This isn't presenting things to a jury (I would hate to be on a jury and felt that I was being talked down to) - it's simply talking aerodynamics. It's a lot more fun when you really understand the details about what is going on. Questions like this one using symmetrical airfoils, factors in real airfoil design (not just drawing curves), etc., are fun and just not that hard to understand. The thing is that aerodynamics isn't magic or wild guessing. It is based in science which most of the guys that post here have had some of.

    Why not present it that way? We have disagreed on this before - I can't stand your approach. I just realized why I stopped answering questions months ago.

    Ben
    Ben Lanterman

    http://public.fotki.com/benlanterman/
    http://webpages.charter.net/benlanterman/Index.html
    http://www.photo.net/photodb/folder?folder_id=208093

  25. #25
    rmh's Avatar
    Join Date
    Dec 2001
    Location
    , UT
    Posts
    12,605
    Gallery
    My Gallery
    Models
    My Models
    Ratings
    My Feedback

    RE: symmetrical wing question..

    ORIGINAL: Ben Lanterman

    I have never assumed the novice builder is without math or physics skills - only about aerodynamics in particular. I belong to a club that is filled with engineers and tech guys who have no trouble with the math or physics. I always ssume that is the case until the questioner says they can't understand what you are saying. I would think guys at a keyboard have elementary math skills.

    This isn't presenting things to a jury (I would hate to be on a jury and felt that I was being talked down to) - it's simply talking aerodynamics. It's a lot more fun when you really understand the details about what is going on. Questions like this one using symmetrical airfoils, factors in real airfoil design (not just drawing curves), etc., are fun and just not that hard to understand. The thing is that aerodynamics isn't magic or wild guessing. It is based in science which most of the guys that post here have had some of.

    Why not present it that way? We have disagreed on this before - I can't stand your approach. I just realized why I stopped answering questions months ago.

    Ben
    You don't have to like my approach-however -based on conducting seminars to model groups and running /conducting mechanical training schools for machinery technicians and preparing and giving testimony to juries - A tech approach tends to "loose the audience". We never talked down to these groups or a jury - that is a sure fire recipe for alienation. We talked to them in conversational English. And notwithstanding your opinion, all the information required can be passed on in this manner.

    You are fortunate in having a tech savvy club. My observations are that this is not a typical scenario amongt most modelers.
    They are of good intelligence but by and large they are not into tech speak.
    Tech speak is great for those who prefer it and it is a excellent method used by professional groups to rapidly exchange precise data -
    Libby is still watching you


Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
All times are GMT -6. The time now is 01:49 PM.

SEO by vBSEO 3.6.1 ©2011, Crawlability, Inc.