I guess Auster were onto something when they fitted these to my plane.
alioth wrote:
I guess Auster were onto something when they fitted these to my plane.
The dude in your video is onto something, in particular as he puts the split flap design into the perspective of the airplane (Darkaero 1) they´ve designed and it´s primary purpose of archiving minimum drag (interference) at high speeds.
As with most aerodynamic devices on airplanes there´s always compromises and in the case of split flap device the cost is take off and landing roll and distance performance. Probably the right choice for an American oriented 2 seater aircraft with speed as a selling point.
I guess Moran-Saulnier was onto something, from a short field performance point, when they designed the Rallye with what´s referred to as “highest complexity” slotted Fowler Flaps type devices on the Rallyes back in 50s ;-) I want to remark that the system, with the added complexity, in all honesty does come with added costs from time to time when a roller needs to be replaced – but it sure is a joy to watch the beauty of engineering and aerodynamics taking advantage of natures forces. In the case of this type of lift device – the cost is added weight and interference drag and therefore cruise speed/range performance.
There is no way of predicting how well that flap actually will work on that particular wing with that particular foil. Two trailing edges is not something a standard CFD software will handle regarding lift and drag on a wing. Based on experience from other aircraft, it will probably work OK. But, you could also end up in weird problems with vibrations etc due to those two trailing edges. Only one way to find out 
LeSving wrote:
There is no way of predicting how well that flap actually will work on that particular wing with that particular foil. Two trailing edges is not something a standard CFD software will handle regarding lift and drag on a wing. Based on experience from other aircraft, it will probably work OK. But, you could also end up in weird problems with vibrations etc due to those two trailing edges. Only one way to find out
Yes, you´re of course absolutely right, in that the actual wing flap design and its impact on aerodynamic Lift (in the corner of CLmax in particular) will certainly be dependent on the wing design and other design parameter’s, and surely the design boys are simply pointing out the general characteristic advantages and disadvantages of the various flaps designs. The Flap system integration and its impact on the actual aircraft behavior and handling characteristics is not much addressed in the video and the split Flap system may well (or not) produce flow separation, which could be computer simulated with the right technology or by simple flight testing. Either way, I don´t think they can go really badly wrong with the system on that aircraft design, but time will tell.
Very nice video! Interestingly, Diamonds went for split flaps for DA42 and plain flaps for the DA40 although I would think they’ll keep the same approach. They went the same route for optimization for sure, but with other constraints. E.g the airspeed is different and so the final drag impact.
Yeager wrote:
or by simple flight testing
They will flight test for sure either way. They have hired a pro test pilot for that job. They have lots of odd experimental solution, like that split rudder also. They also have an experimental engine (not a trusted Lycoming). The aircraft is built around one particular experimental engine, which is a very bold move, technically and commercially when thinking of selling kits in the future. There is no easy way to fit a Lycoming anymore, it’s too heavy and too big (CG would be way off for instance). The only other option would be a Rotax 915/916, but much less HP.
I have kept an eye on them for a couple of years now. Really cool guys, implementing new solutions wherever they can, and they are good at it. They aren’t making life easy for themselves though. They are doing lots of stuff simply to see if they can get away with because it offers some advantages in terms of construction, weight and aerodynamics. Split flaps is obviously a lighter and simpler solutions that fits well with using carbon fiber as material, because it’s possible to make a thin and stiff sheet without any additional supporting structure. Perhaps the perfect solution for a light, simple and aerodynamic clean flaps, but only when using carbon fiber ?
Split flaps is nothing new or particularly odd though. The Sonex line of aircraft have an odd type flap system. It’s hinged on the underside of the wing only, thus producing a gap when set. Still perfectly smooth when up. I don’t know if it even has a name, kind of an open split flap.
LeSving wrote:
The Sonex line of aircraft have an odd type flap system. It’s hinged on the underside of the wing only, thus producing a gap when set. Still perfectly smooth when up. I don’t know if it even has a name, kind of an open split flap.
Having the flaps hinge on the bottom of the wing, quite often anchored on the bottom of the wing spar, and having an open slot when extended, is a feature many aircraft have, nothing really odd, and still called plain flaps. A good example here, FF to 3:58
Leaving that gap open as opposed to having it closed by the curved upper flap skin or some other means will create some earlier flow separation at the rear gap line. The question being is it beneficial or detrimental to have an additional turbulent flow created on the top of the flaps? Does it affect the CL, by how much? Does it add to total flap drag, by how much?
Dan wrote:
is a feature many aircraft have
Ha, I didn’t know. But probably should expected, as the Monett family is very francofile Any other than the Jodel?
I have wondered how they came up with that solution. But looking at the Sonex wing (as well as the Jodel), it’s not exactly lift constrained when taking the weight into consideration. Producing drag is probably more important than producing more (excessive) lift, and this is the simpler way of doing it ?
The Pipistrel Alphatrainer is weird in that sense. It has these long and slender flaperon along the entire span. Obviously the will produce lots of lift and very little drag. This is something some people have a hard time getting used to. The L/D at full flaps is still in the order of 15:1 or something. The best way is to sideslip it like a flap-less Cub for shorter strips (which is not something the average C-172 pilot do all that often). They do however have an option for airbrakes as the last “notch” of flaps, but it requires replacement of the entire wing if you didn’t think about it when purchasing from the factory Then it will land like a normal airplane. I think the LSA versions have airbrakes as standard.
