Tim Cheal Posted April 7, 2014 Share Posted April 7, 2014 Thnaks Stevo Colin, Is the wing bolted on? It may be that next time it is level and the problem has gone away (perhaps a wire trapped underneath for example)! Tim Quote Link to comment Share on other sites More sharing options...
Stevo Posted April 7, 2014 Share Posted April 7, 2014 Bolted on??? Hey, sore point guys. Converted my Flair Cub to a bolt on wing. Wing Dowels in the L.E. Dowels never got glued in properly. Wing departed company on the Maiden. Eeek. Fortunately this particular type is held on with Bands And, as the say, Thnaks Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted April 7, 2014 Author Share Posted April 7, 2014 Hi Tim, No, the wing is held on the old fashioned way. This being the case I guess it's quite possible for the wing to go on in a slightly different position each time or even incorrectly. I will have to look into this. Quote Link to comment Share on other sites More sharing options...
Tim Cheal Posted April 7, 2014 Share Posted April 7, 2014 Sorry Colin, I didnt answer your question. Its the dihedral that causes roll with yaw (as does sweepback, but there shouldnt be much of that on a Cub!). It actually effectively changes the angle of attack but its easier to think of this as pushing the wing sideways (at 90 deg to normal flight) through the air, one wing will have airflow hitting it on the bottom, but the other side has airflow hitting it on the top (you will need to imagine the first half of the wing is not in the way). The one half will want to rise, and this is dihedral stabilising the model. Hope that helps. Tim Quote Link to comment Share on other sites More sharing options...
Tim Cheal Posted April 7, 2014 Share Posted April 7, 2014 Colin, indeed. With that in mind are you sure it was in the middle, and not offset to one side? Sorry about the wing departure Stevo!. Tim Quote Link to comment Share on other sites More sharing options...
Stevo Posted April 7, 2014 Share Posted April 7, 2014 And here's the result:- Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted April 7, 2014 Author Share Posted April 7, 2014 So Tim, The opposite to how I was visualising it, but the same mechanism? On take off then, this would mean the left wing is low (assuming incorrect positioning), but as the Cub unsticks the left wing rises to equalise the dihedral and therefore induces roll to the right I until stability is achieved in level flight? Am I visualising it correctly, or am I showing my ignorance here? I'm willing to learn 'cause although I have a reasonable knowledge of aerodynamics, I'd be the first to admit its become rusty and has glaring holes. Quote Link to comment Share on other sites More sharing options...
Former Member Posted April 7, 2014 Share Posted April 7, 2014 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted April 7, 2014 Share Posted April 7, 2014 I suspect this yaw/roll stability theory may be a bit of a red herring - if there was that much of an effect the model would return to level flight rapidly and automatically. As Tom says, don't be in too much of a hurry to pull the model off the ground. Where do you stand to take off? My preference (and one thing I've been very pleased to see has become the norm at my club) is to stand in the pilot box for take-off from the beginning of training, removing the danger and inconvenience of people and buddy leads wandering about on the runway. The flying benefit is being able to judge the model's attitude during the take off run and early climb out much more accurately, avoiding the situation I described in an earlier post and seemingly endorsed by Tom's post. Some people will contend that they are unable to judge yaw from this position but they mostly seem to be able to cope while landing, so I believe this is another red herring. Edited By Martin Harris on 07/04/2014 19:30:59 Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted April 7, 2014 Author Share Posted April 7, 2014 OK guys, this is all very helpful and sage advice. However, as mentioned at the very beginning of this post, these were my very first flights with R/C - ever! So far I have not undertaken a take off nor landed this plane. As a full size pilot my instructor did not yank my Cub off the ground, he didnt even use full throttle; I'm quite sure he knows what he is doing. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted April 7, 2014 Share Posted April 7, 2014 As he flies a Pitts Special he is obviously no stranger to tailwheel operation and torque/slipstream/P factor effects so what was his diagnosis? Is this tendency going to be a real problem for you in his opinion? Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted April 7, 2014 Author Share Posted April 7, 2014 You've got me there, Martin. I must confess that I didn't get around to asking him this, as I was still on a high from actually flying something I'd built with my own hands. If this happens at my next opportunity I'll ask him. He didn't say it would be a problem for me, but looking at it I'm thinking myself that it might be. I'm wondering if, when it comes my turn to attempt a take off, whether my reactions will be fast enough. Flying a Cub in RF7, if the throttle is set right, it simply rises off the ground and only slight input from the elevator sees it climbing. This is what I expect my Cub to do, but currently it doesn't. However, in flight it's actually easier to fly for real than in the Sim! Quote Link to comment Share on other sites More sharing options...
Tim Cheal Posted April 7, 2014 Share Posted April 7, 2014 Hi Colin>> Sorry I got dragged away earlier. Imagine the wing sitting above the cub with the left wing forward of the perpendicular to the fuselage>> And the wing has dihedral. As the aircraft accelerates along the line of the undercarriage track (straight ahead for the fuselage) then the aircraft will tend to roll right). As your instructor experienced. This is equally true of the undercarriage is fitted at an angle to the fuselage (and of course the wing). As the weight comes off the fuselage the aircraft is no longer constrained to track along the line of the undercarriage track, and so ‘weathercocks’ to present a more balanced wing profile (in fact the fuselage is now crabbing). Hence the roll stops once airborne. This all may be complete rubbish, but something to consider. Tim Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted April 7, 2014 Share Posted April 7, 2014 I've assumed you have ailerons - in which case there should be very little dihedral (1 degree on the full size IIRC) - or is this a rudder only version which would need significant dihedral? Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted April 7, 2014 Share Posted April 7, 2014 Just one out of left field here (as we do seem to be struggling a bit on this one!) The wing is held on by bands - are we absolutely sure there is no chance of the wing leading edge lifting as the model accelerates up to flying speed? I, like others I'm sure, have seen this happen on more than one occasion. A bit of a long shot I know - but worth just checking? BEB Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted April 7, 2014 Share Posted April 7, 2014 Decent call BEB - Colin, if you can lift the leading edge even a little bit with quite reasonable force then you need more bands/tension. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted April 7, 2014 Share Posted April 7, 2014 Some models just have quirks Colin, if you know it do's it, your ready for it. Also without me knocking your pilot, maybe he holds a bit of rudder in to steer, and being a cub its a little slow to react to correction. All the Cubs I have had the rudder is quite powerful Edited By john stones 1 on 07/04/2014 23:59:21 Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted April 7, 2014 Share Posted April 7, 2014 Another problem of course that Cubs tend to suffer from is their relatively narrow undercarriage track - so once they start a swing it can be difficult to correct it. But having said that of course, the swing is much more likely to be to the left rather than right - unless of course the pilot pre-loads right rudder? BEB Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted April 8, 2014 Author Share Posted April 8, 2014 Wow guys, Been sitting down watch a film and all your replies came in. Sorry about that. OK, first, the rubber bands. There are 8 of them, so I don't believe the wing is lifting. Second. My pilot did mention that perhaps my Cub needed more rudder throw and it does fly with a very small amount of right rudder trim. Lastly, now that you mention it BEB, he did mention that the Cub's narrow track might be a contributory factor. I had forgotten that! Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted April 8, 2014 Author Share Posted April 8, 2014 Checked some of the suggestions on the fusalarge today. The fusalarge is level on its undercarriage, which is tracking correctly and there is no binding on any of the wheels. The tail wheel is fine and is not bent or out of line. The tailplane was found to be 1/16" high on the left, which I've corrected ( and hopefully it'll stay that way). Possibly a very slight twist was induced at the covering stage. Whether this contributed to the symptoms and whether or not it has alleviated them I won't know until I can once again get down to the patch. Watch this space! Quote Link to comment Share on other sites More sharing options...
Stevo Posted April 8, 2014 Share Posted April 8, 2014 Hmmm... I don't think 1/16" will make too much odds in the grand scheme of things... This space is being watched, believe me... by about everyone who posts on here!! Interesting to see what the wings have to say... Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted April 8, 2014 Author Share Posted April 8, 2014 I'd be inclined to agree with you, but I'm checking everything. I plan to go through the list of suggestions; it's a process of elimination. As soon as I can get down to the patch again and get the assistance of an instructor, I'll be checking the alinement of everything most carefully. If it does turn out to be the wings then maybe I'll bite the bullet and have a go at making another set! We'll see. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted April 8, 2014 Share Posted April 8, 2014 If you have ailerons I wouldn't bother making a new set of wings - just use them to trim for level flight - but there again you said it's fine in flight anyway. If you built the model yourself, did you take care to shape the leading edges correctly? It wouldn't be the first time that a beginner had left the leading edges squared off which can make the low speed handling very suspect. Thinking back (not all that far, actually) I did have a nasty wing drop on take off with a foam Cub a couple of months back which I would have to admit to being due to mishandling a last second take-over on the buddy lead and climbing away from the ground too quickly...luckily it didn't end in tears! Edited By Martin Harris on 08/04/2014 17:04:46 Quote Link to comment Share on other sites More sharing options...
Colin Anderson Posted April 8, 2014 Author Share Posted April 8, 2014 Hi Martin, Yes, I did build the wings myself. Although I'm new to R/C I'm not new to building; although prior to this Cub it was a long time ago. The leading edges do have the correct and same profile. My wing does have ailerons and as you say I can use them to adjust the trim. However, (and this is where my knowledge is rusty) don't control surfaces have a greater effect as speed increases? If so trimming the ailerons for level flight might induce roll on take off? Please enlighten me on this. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted April 8, 2014 Share Posted April 8, 2014 Never really thought about it in any detail (but BEB will probably know) but the out of trim forces would also increase so probably largely self correcting and has proved that way with a friend's extremely badly warped wing). However, experience in a full size glider with a warped wing (corrected by trim tabs) did show an increasing stick load at extreme speed when I tested it beyond its normal (but within allowed) speed range but I don't recall whether it involved any actual stick displacement. Quote Link to comment Share on other sites More sharing options...
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