John Botomley Posted April 5 Share Posted April 5 I've built and flown a tandem wing design from September 1981 RCM&E - Bert Streigler's Delanne D200. From the get go it has exhibited odd handling characteristics. Specifically: Squirrely take off runs - leading to a removal of the rear wing tip skids and replacement with a steerable tail wheel Any attempt to loop results in it rolling out to the right. Inverted flight - rolls out to the left Slightly barrelly rolls are OK but slow........................... The control system is ailerons on the front wing and elevators on the rear wing with a conventional fin and rudder Options being considered are an elevon control system and or a 6 axis gyro Thoughts, hints, experience........................ Photos show model in original format Many thanks John B Quote Link to comment Share on other sites More sharing options...
J D 8 Posted April 5 Share Posted April 5 Take it you have checked all control surfaces movements are equal in the directions they move. Just looking at your pic from the front, pretty sure it is straight on/square. I can see a greater gap between the fore wing and the rear wing on the port side than on the starboard side. Given that the two wings are closer fore and aft than most tandem wing types this could result in a greater effect on one side with a condition that is called Biplane interference being unequal and result in the rolls you have. I know its not a biplane but due to the closeness of the wings to each other it is likely possible. The squirrely take off, as design it has a short moment arm [ length of fuselage] and as you removed the tip fins this will result in less directional stability. An increase in the center fin area may well help. However given all that wing x 2 area in front and below it there may well be a lot of aerodynamic blanking of the fin during initial take off run. Working rudders on tip fins would be an answer but possibly more faff than the worth of it. Basic 3 axis gyro may be helpful but not something I am familiar with. Quote Link to comment Share on other sites More sharing options...
Martin Dance 1 Posted April 5 Share Posted April 5 I think it's welcome to the wonderful world of the tandem wing! What you are experiencing is fairly typical of the type and explains why it was never popular in full size aviation. Look up 'Flying flea'. Apart from JD8's observations I would also check the foreplane and lower plane incidences, it could be that in practice one of the planes is flying close to its critical angle of attack, so that any change in pitch brings that plane even closer to the stall or of course further away from the stall. Modifying the aircraft so that you can change its incidence might help, otherwise enjoy its quirky personality! Quote Link to comment Share on other sites More sharing options...
Piers Bowlan Posted April 5 Share Posted April 5 Are you using differential aileron John. I just wondered if adverse yaw might be causing issues with rolls. Perhaps a larger fin area might help too? Quote Link to comment Share on other sites More sharing options...
Peter Jenkins Posted April 6 Share Posted April 6 On 05/04/2024 at 09:16, John Botomley said: Any attempt to loop results in it rolling out to the right. Many thanks John B Hi John Do you fly "thumbs" of finger and thumb? I have found that many who fly "thumbs" tend to roll right when they pull up into a loop. It's the geometry of the thumb. I first noticed that when I was practising for my B and found that if I turned my wrist inwards so that the thumb could now just pull straight back then the roll to the right disappeared. I have since moved to mounting my Tx on a tray and re-taught myself to fly fingers and thumb - that's an even better way to avoid cross control inputs. Quote Link to comment Share on other sites More sharing options...
John Botomley Posted April 9 Author Share Posted April 9 Thank you for your thoughts and ideas. Incidences have been checked - OK. The photos are somewhat distorting the alignment. The lower part of the tip fins is all that has been removed, so that the steerable tail wheel can touch the ground!. Noted re the aileron differential, and yes a three axis stabiliser is being actively considered. According to the full-size design work by Maurice Delanne - the vertical gap between the front and rear wings is critical to his design principles and Bert Streigler's write up on the D200 confirms this. I already fly with a tray. Attached is the original article and view of the plan FYI Sept 1981 RCM&E Delanne plan article Page 1.pdf Sept 1981 RCM&E Delanne plan article Page 2.pdf Sept 1981 RCM&E Delanne plan article Page 3.pdf Quote Link to comment Share on other sites More sharing options...
Alan Gorham_ Posted April 9 Share Posted April 9 (edited) Have you balanced the aircraft laterally? There's a honking great silencer hanging off the right side which may well account for the screwing out of erect loops to the right and inverted loops to the left. Edited April 9 by Alan Gorham_ Quote Link to comment Share on other sites More sharing options...
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