Herri Posted January 16, 2017 Share Posted January 16, 2017 Please tell me; If a wing has a straight (level) upper but a slightly tapered lower part, does this count as dihedral. (Seen from the front, lower thicker at the root tapering up to the tip) I thought not but I would like to hear from someone who really knows. Thanks Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted January 16, 2017 Share Posted January 16, 2017 I can't claim to be that someone but I would look at it as a tapered wing with a tiny amount of dihedral - so small that it would only have a marginal aerodynamic effect anyway - why the question? Quote Link to comment Share on other sites More sharing options...
Peter Jenkins Posted January 16, 2017 Share Posted January 16, 2017 In my opinion, yes it would have some dihedral effect but it would depend on the span and the difference in thickness that's being discussed. If it were the top surface that sloped downwards then that would be anhedral (which tends to reduce stability) but the same issue on span and thickness difference applies. Quote Link to comment Share on other sites More sharing options...
Herri Posted January 16, 2017 Author Share Posted January 16, 2017 A friend of mine is building a glider tug. I asked if he wasnt going to build in a small amount of dihedral and he said it already had dihedral. For me, it was a straight wing but according to him the tapered lower section counts as dihedral. I find that hard to believe. Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted January 16, 2017 Share Posted January 16, 2017 Weight is paramount in aircraft, therefore less structure is needed towards the tip, and weight saving made, where flying surfaces hold surfaces together. A spin off of any alteration in wing thickness or sweep back is that stalling should not occur along the whole wing at one moment. If for example, if the thin tip reached its stall speed, this should not be true of the thick wing root at that time. So their are benefits of tapering a wing, that that the whole wing should not stall at the same time, but dihedral produces more self righting in relation to the horizon. All this detail is overly simplified by the way. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted January 16, 2017 Share Posted January 16, 2017 Mmm, well I suppose it depends on the degree of taper. But from an aerodynamic point of view, even with the maximum taper likely to be possible, the effect would be very marginal. Yes, technically it is dihedral. No, is of very little practical value as such would be my view! BEB Quote Link to comment Share on other sites More sharing options...
Peter Jenkins Posted January 16, 2017 Share Posted January 16, 2017 Dennis, the last thing you want is for the tip section to stall first. The correct sequence, for a nicely behaved stall is for the wing root to stall first, then the tailplane and then the wingtips. Having the wing tip stall first, which is a problem with a highly tapered wing such as on the Mew Gull, gives a vicious wing drop as you get to the stall. I've seen one Mew Gull bite the dust on an approach that got a tad too slow. Washout is what is normally used to ensure that tips stall after the wing root. Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted January 16, 2017 Share Posted January 16, 2017 I was quite amazed that a small indoor Piper Cub I have built has almost no dihedral, yet is stable (not amazingly stable I grant you) but it turns well on just rudder. I get the feeling the pendulum effect of having a high wing has more to do with the stability in this instance. Cheers Danny Quote Link to comment Share on other sites More sharing options...
Herri Posted January 16, 2017 Author Share Posted January 16, 2017 Oh well, looks like I was wrong. I thought the whole wing had to have a "V" to be dihedral. Thanks for the comments guys. Herri Quote Link to comment Share on other sites More sharing options...
Jonathan M Posted January 16, 2017 Share Posted January 16, 2017 Posted by Danny Fenton on 16/01/2017 19:37:40: I was quite amazed that a small indoor Piper Cub I have built has almost no dihedral, yet is stable (not amazingly stable I grant you) but it turns well on just rudder. I get the feeling the pendulum effect of having a high wing has more to do with the stability in this instance. Cheers Danny The same is reported in indoor scale of certain WW1 types, even including the Fokker Triplane... serindipitily avoiding the loss of scale points. Edited By Jonathan M on 16/01/2017 20:01:20 Edited By Jonathan M on 16/01/2017 20:01:43 Quote Link to comment Share on other sites More sharing options...
Jonathan M Posted January 16, 2017 Share Posted January 16, 2017 Posted by Herri on 16/01/2017 19:19:18: A friend of mine is building a glider tug... I assume its a model glider tug Quote Link to comment Share on other sites More sharing options...
Herri Posted January 16, 2017 Author Share Posted January 16, 2017 Posted by Jonathan M on 16/01/2017 20:00:24: Posted by Herri on 16/01/2017 19:19:18: A friend of mine is building a glider tug... I assume its a model glider tug You assumed correct. Quote Link to comment Share on other sites More sharing options...
Mannyroad Posted January 16, 2017 Share Posted January 16, 2017 I always thought that it was the upper surfaces that needed to be V'd to count as dihedral, as co-planar upper surfaces wouldn't provide the self-righting that dihedral does. Just felt like keeping it going. ha! My Simon Delaney designed 'Sportstar' (see avitar) has co-planar top surfaces and tapering undersides. I can't say there is any noticeable dihedral effect. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted January 16, 2017 Share Posted January 16, 2017 Dihedral is defined as the angle between two geometric planes so in the example the top surface has no dihedral but the bottom surface does. As BEB points out in that example there would be also be marginal dihedral between the mean aerodynamic planes of the wing as well. Quote Link to comment Share on other sites More sharing options...
John Davies 4 Posted February 3, 2017 Share Posted February 3, 2017 I`m certain that I can remember in the back of my mind , I was building a model with a foam wing , and in the instructions it said to join the wings inverted as the lower surface was tapered upwards towards the tip and the wing was flat on top from tip to tip ! and that`s what gave it it`s dihederal . Trouble is I can`t remember which model it was, but something tells me it might have been a Gangster 63. I still have the wing from it up in the loft, i`ll take a look at it next time I go up there . Could be wrong though, it seems like half a century ago............ well a quarter anyway lol. Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted February 4, 2017 Share Posted February 4, 2017 If you've ever built a Chris Foss Phase 6 that's exactly how the instructions ask you to glue the 2 foam wing panels together - inverted on a flat board - to achieve the correct dihedral. Quote Link to comment Share on other sites More sharing options...
Keith Lomax Posted February 6, 2017 Share Posted February 6, 2017 Isn't the lift on the wing perpendicular to the leading edge? If that is the case then whether or not a wing has dihedral depends on the angle between the two leading edges, so the information given at the start of this post is not sufficient to decide. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted February 6, 2017 Share Posted February 6, 2017 Probably relates more to the chord line and distribution of lift but assuming a taper provided by the same section being reduced, the leading edges will have a dihedral angle between them. Whether it will provide any noticeable effect is a different point! While on the subject of unknown information, we also don't know if there's any wing sweep - sweep back will provide roll stability and vice versa...to the point where anhedral may be required to counteract excessive stability on a swept wing - or considerable dihedral being needed as per the example of the Schleicher ASK13 glider which had sweep forward to provide better access and visibility for the instructor in the rear seat. Quote Link to comment Share on other sites More sharing options...
Herri Posted February 6, 2017 Author Share Posted February 6, 2017 The wing in question has no sweep back, the leading and trailing edges are parallel. It is a two piece wing, each part being approx 1,25 m. The difference in thickness between the root and tip is only about 10mm. The top of the wing is flat. The question arose as the builder was inserting a wing tube. I asked "what about a bit of dihedral" and was told "it has dihedral" Hence my question on this forum. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted February 6, 2017 Share Posted February 6, 2017 Herri If you are asking purely as a technical point then it does geometrically have dihedral but whether this has an aerodynamic dihedral effect is open to question. Surely it is the effect of a given dihedral angle that is more important than the detail of its definition. Quote Link to comment Share on other sites More sharing options...
Dave Bran Posted February 6, 2017 Share Posted February 6, 2017 And then there's the matter that a high aspect ratio wing will gain dihedral by flexure as its unlikely to be so rigid as to avoid it. Quote Link to comment Share on other sites More sharing options...
Piers Bowlan Posted February 7, 2017 Share Posted February 7, 2017 You obviously felt Herri, that the model in question didn't have enough dihedral, but enough dihedral for what? For aesthetics a bit of dihedral looks better, particularly with a high wing model as the wings tend to look a bit 'droopy' without. But beauty is in the eyes of the beholder! Aerodynamically speaking for a high wing aircraft even if the wing is 'flat' it will have a certain amount of aerodynamic dihedral and conversely a 'flat winged' low wing aircraft will have some aerodynamic anhedral. Your friend's aircraft with a tapered wing and a flat upper surface has some geometric dihedral which will enhance lateral stability. Is it enough? Enough for what? For an aerobatic aircraft too much stability is generally not a good thing, which is why military fighters are not particularly stable as it does not fit well with agility. For a trainer lateral stability is a desirable, particularly for a rudder/elevator model without ailerons (essential). As has been said earlier, wing sweep also improves lateral stability. Also, high wing aircraft possess some pendular stability by virtue of most of their mass being centred below the centre of lift. Can you have too much lateral stability? Yes, it manifests itself as dutch roll, often experienced on swept wing aircraft unless a suitable fix is employed (anhedral and/or a yaw damper). Just my 2p worth. Edited By Piers Bowlan on 07/02/2017 08:28:20 Quote Link to comment Share on other sites More sharing options...
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