Michealvalentinsmith
Well-Known Member
On a past thread here there has been some discussion of the practicality of using a plank platform for a footlaunched gilder - and speculation of the best design and past relative failures.
Problems of small static margin and CG range have been brought up, the most suitable airfoil, the possible use of differential ailerons, the effect on stability on weight shift control for pitch etc were discussed.
Here is a wing that brought all the concepts together and seems to have worked. The article is in French and as a JPEG file I cannot copy and paste to a translator program , but can understand enough to glean some numbers and facts.
What is apparent is that the design was able to use ailerons - not spoilerons as is typical - and did not need additional tip rudders or drag devices to counter adverse yaw, most likely due to aileron differential allowed due to minimal pitch effect over the short CG to aileron lever in a plank.
It appears to have used a MH 78 foil section, and weighed only 58 kg. The LD (finesse?) was 16 -only a little better than the best flexwing HGs and not comparable with modern rigid wings with similar spans at 19:1, but certainly competitive regarding weight, with many wings approaching and exceeding 70kg.
It begs the question whether such a design could be made competitive with an LD in the 18:1 range with modification - perhaps a small thresher tail etc.
Problems of small static margin and CG range have been brought up, the most suitable airfoil, the possible use of differential ailerons, the effect on stability on weight shift control for pitch etc were discussed.
Here is a wing that brought all the concepts together and seems to have worked. The article is in French and as a JPEG file I cannot copy and paste to a translator program , but can understand enough to glean some numbers and facts.
What is apparent is that the design was able to use ailerons - not spoilerons as is typical - and did not need additional tip rudders or drag devices to counter adverse yaw, most likely due to aileron differential allowed due to minimal pitch effect over the short CG to aileron lever in a plank.
It appears to have used a MH 78 foil section, and weighed only 58 kg. The LD (finesse?) was 16 -only a little better than the best flexwing HGs and not comparable with modern rigid wings with similar spans at 19:1, but certainly competitive regarding weight, with many wings approaching and exceeding 70kg.
It begs the question whether such a design could be made competitive with an LD in the 18:1 range with modification - perhaps a small thresher tail etc.
