Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by REVAN, Jun 1, 2017.
Topspeed100, Holden, Aircar, + ???
Too many already on that list.
Any luck gaining access to the document? I suspect it will focus on drag characteristics, but we might get lucky and there could be some wind tunnel data comparing yaw moments for a sheared tipped vs a square tipped wing. With a straight trailing edge, the sheared tip is not quite the design I'm envisioning, but it is part way there, and could show some evidence to contribute toward risk reduction for the concept.
Great question ! I don't know . Neither does anyone else posting on this thread. If you watch the video closely you will see that at the .013 mark the airplane has just taken off and he virtually stops in midair and turns the plane 45 degrees and then brings it back. Wings are level the whole time. Watch very closely for the lack of forward movement at this juncture, yet he can virtually turn the airplane at will. Also notice the direction of flight which I must assume is into the wind.
Next move to the 1:10 mark and notice that he again performs a directional change with either no banking or minimal banking. Because of the slow speeds the exhibition is being demonstrated at, I feel that banking would lose some of the lift and then require added speed. Thats my opinion, not an engineering treatise.
Move to the 1:24 mark and you will see a banked turn and you can judge for yourself the area it took to complete the turn.
Move to the 1:44 mark and you will see that he swoops down to set up for the next maneuver and then rises to scrub speed. He makes another effortless flat turn. I judge that about 3 to 4 wing lengths were needed. The wing is 32 ft. The factory video below appears to have done even smaller turns.
https://www.youtube.com/watch?v=x8eg-A8GT7U (note: Check out the factory video points below for some even better looks at skidding and turning a Storch)
Now there is no way to know exactly how big a radius each turn occupied, but you can see that both were extremely small. One could argue that they were approximately the same, but in no way can anyone definitively say the flat turn required more space than the banked higher speed turn. IMHO
Now move to the real point as I percieve it. In the Storch factory video, the pilot is shown fliting about only feet above the ground in a field. At several points he makes skidding turns with the wings flat. The turns are executed so quickly that barely the length of the airplane is traveled before the skid is completed. In the general discussion of a skidding turn, I think everyone pictures a full 180 degree skidding turn. The use of a full skidding turn (in a Slepcev) would have a limited use. Something like the box canyon discussion perhaps. Now realize that to perform a banked turn you will need a little time to enter the bank and reset your speed accordingly because you are definitely going to make a major change in lift and drag. All of this takes time which may be of the essence and cause a not necessarily larger radius, but a closer proximity to the impediment directly in front of you.
The Storch on the other hand does not require an increase in speed but can turn immediately with wings level (if need be) and reverse course. It is also capable of banking its wings and turning, but it will need the same actions of increasing speed somewhat and losing a little time, again placing the pilot closer to the impediment. So, being able to immediately effect a small radius turn with no hesitation seems a better choice. The question is whether there is now a danger to the pilot because of skidding. Well which danger does the pilot wish to face, closing quickly on the canyon face ahead, or a possible skid. If the airplane is stable in a skid, the pilot can then choose the option he is most comfortable with.
Now lets consider one last caveat. As mentioned before, when landing, the application of skids just above ground level allows immediate directional changes in smaller amounts without dropping a wing. I furnished a video showing an experienced backwoods pilot attempting to make a landing which required a slight change of direction at about 15 feet above ground level just before touchdown. When he tried to make the last second adjustment his wing dropped and he almost crashed the lower wing. From what was demonstrated in the factory Storch video, a simple momentary skid would have been easily done with the wings level.
Now there is video proof of everything that the Storch is capable of. There are no physical dimensional measurements available. Again I say I don't have any accurate measurements and neither does anyone else. You just have to watch the videos and form your own opinion as to whats true and whats hyperbole.
2:11 Coming right at you and skidding How large was that turn ?
5:09 Close up of Flat turn
5:42 last second course change with no wing drop
6:37 low skid How short was that turn ?
Update: As I predicted, the two professional pilot/authors with thousands of hours (one has 16,000) have now been sumarily dismissed as credible references. They have a different opinion and back it up by training other pilots, but expectedly they know nothing either.
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The cause of ventral fins I presume.
As I see it, high yaw inertia is at its best a double edged sword. Yes, it does take some more aerodynamic force to establish the spin. But once the forces to spin are initiated it does take more aerodynamic force to stop the airplane from spinning. On a high inertia airframe counter spin control input may be needed even before the spin is established , whereas on a low inertia airframe centring the controls may be sufficient.
At the extreme low inertia end, look at light aerobatic radio control models. These models can be commanded to tumble, but the moment the controls surfaces are centred they fly straight.
Yeah, there is several double edged swords beside inertia. That's why spin resistant design is difficult. As far as I know no spin resistant airplane (certified) has also qualified for intentional spins. (Columbia, Cirrus and probably ICON are spin resistant)
The dynamics of sport R/C models are hard to get much data from. They are so light they don't really react like full size. Most of the trainers just won't spin at all unless the CG is way back.
Not to mention that they also tend to be overpowered for their size. Hammer the throttle and they can muscle their way out of bad positions.
There's no way to put a measurement to the radius from looking at the video, but the 'S' turns starting at 1:28 may have a tighter turn radius. The turn rate looks higher in the banked turn and the flight speeds appear similar.
Anyway, it would be appropriate if you'd take this flat turn stuff to a separate thread dedicated to flat turns. This subject has little if anything to do with this thread's topic. This thread is not about STOL airplanes or bush-flying techniques. It's about spin resistant control concepts. There are planes that can spin at 20 knots and planes that can spin at 100 knots. It's not about the speed, it's about stability and control authority when the wing is stalled.
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