The biggest myth about split flaps 

This is SO true. Gets my goat everytime.

Agreed! So much better to say, "Hey we did the math comparing each of these under the same conditions, on the same equipment, and this is the result."

Hah!

@@timcross2510 Seems like a simple and reliable design to me.

It also eliminates any chance of control surface flutter.

Oh thank God they were able to clear up your confusion.

Turbulence (ride quality) was your biggest worry?

@@36thstreethero no, efficiencies of their flap design was my worry. I incorrectly assumed this type would create more turbulence and thus drag.

Modern airliners have another variation of Fowler flaps with multiple elements and slots for the most part. Useing the B-52 is an example of a simple Fowler flap as drawn vs todays flaps.

Also, the P-38 is another glaring omission.

Modern airliners are using mostly slotted or double slotted fowler flaps.

I agree. You just don’t see videos of people designing aircraft and telling you why. Usually you have to infer

More enjoyable experience flying imho. I always love the manual flaps in the piper over the Cessna electric flaps as I continue to learn to fly.

Better ergonomics too. No need to stare at the flap indicator.

@@ammerudgrenda If you learn how the flap handle moves with relation to the detent, and how the airplane feels with different flap settings+airpseed+power settings, you don't have to stare at the indicator.

air is Stationary wind tunnel testing is NOT conclusive.

smart to make the failure mode symmetric. let em know. this is the kind of stuff that next time will appear in an air crash investigation. they should fix it now.

@@daviddavids2884 You got things mixed up. Stationary air does not exist, which is the reason why wind tunnel testing does not conclusively simulate flying, but it's still usefull.

The linkage is not a very elaborate design. Complicated sure, and fancy too, but not elaborate. Maybe somebody is running out of time.

They do increase drag but they increase lift allowing the aircraft to fly at slower speeds without stalling, improving take off and landing performance

@@kickedinthecalfbyacow7549 Yes, all flaps increase drag and lift. My point was that the split flaps on the Spit and Hurri seem to be more speedbrakes than lift devices due to the deflection angle.

Flap position 1 is 10 degrees deflection. It is the only flap position that extends the flaps trailing edge outside of the basic wing planform. At full 40 degrees, the flaps are definitely not projecting past the trailing edge. A true fowler translated the leading edge of the flap rearward to the trailing edge of the basic wing. Which is about 300% farther aft than a Cessna. All slotted-flaps must translate aft to open the slot. As the slot gap has to remain about the same for each deflection angle, it cannot simply open more and more with angular deflection. It has to open the slot rapidly to its defined point before deflecting. The proper technical term for Cessna flaps is "Slotted Flaps with Fowler Action".

@@jj4791 You are just making stuff up. The definition of Fowler flap is that the flap moves rearward as well as downward. There is no requirement that it move to the trailing edge of the wing. Slotted flaps rotate, but don’t translate. Fowler flaps translate and rotate. Cessna 182 flaps are Fowler flaps. End of story.

@@LTVoyager It looks like Cessna has used Fowler flaps (with rearward translation, although not much) since the 170B of 1952... and the same design continued through the 172 and 182.

I would assume so, I would say their numbers are underrated "gentleman's agreement" numbers, should be friggin fast.

I agree. The Cessna 172 flaps move down and back which increases the wing chord. Which is a Fowler flap. However, The 172 manual that I have refers to the flaps as the single-slot type.

Congratulations on your build completion and flight. That’s quite an accomplishment!

Nope. Just a slotted flap, which DOES move back and down, just not nearly as far. A Fowler flap is characterized by being RETRACTABLE in operation. Meaning a large section of it slides UNDER the top surface of the wing. To see one in operation just look out the window over or just behind the wing of any airliner during landing. Fowler flaps are usually accompanied by rather large fairings extending aft of the trailing edge to hold the complex tracking, linkage, and actuators that operate them.

In order for a slot to open, the flap has to move aft. A fowler flap has the leading edge of the flap nearly reaching the trailing edge of the basic wing. It also translates aft a significant distance, without deflecting any noticeable amount. Where position 1 flaps is just an increase in wing area Cessnas definitely deflect downward as much or more than they translate aft. Which at most might be 4-6" rearward. And the flaps trailing edge still remains within the basic wing planform as viewed from above, when fully deflected.

The Cessna 150 and 152 had Fowler flaps. The 150 will drop down to 40 degrees and is like a barn door

Split flaps just need to be released and fall down via gravity, now the UP and REMAIN up/sealed with less drag is the actual problem. So springs etc are often employed here.

@@w8stral The flap seems very light, will gravity be much help in this case?

@@w8stralgravity will overcome the airflow? Ever try to open the door of a Cessna in flight or your car door while driving down the highway? I’m not so sure that would work.

Bottom rear half of airfoils have downward suction. I do not believe they went with a reflex airfoil so there should be downward suction. Now will they FULLY deploy? Nope. But flaps 10 or flaps 15? Yup. Spitfire flaps for instance fully deployed to Flaps ~20 with zero input from pilot other than: deploy. Where Cessna door is a compression zone. Same Cessna door on rear half of fuselage is a SUCTION zone and would auto open partially(one reason P51 was faster than Spitfire for instance. It dumped its higher pressure heat into a suction zone decreasing fuselage drag and decreasing drag of the radiator(p47) partially did this as well(though by default rather than on purpose). Cheers @@rnordquest

All this time I thought the purpose of wings was to provide lift, but there's actually a region of downward suction, amazing lol. And I thought that the purpose of extending flaps was to gain lift by deflecting more air, which should give an equal and opposite force on the actuating linkages, boy was I a dummy lol.

I’ve seen plenty of discussion about that online. We were taught they were “slotted Fowler flaps”, I think the manual only refers to them as slotted flaps. A quick google says the wing are increase is only just over 4%. I guess it’s one of those topics to throw into a group of pilots then sit back and watch the arguments lol

Yes, @@electricalmayhem, it is a short-travel design in those Cessnas.

That was one of my thoughts - a 30cm deflection of the flap handle has to extend a relatively large chunk of wing into high speed wind. Gonna be tricky for sure to balance the forces with any possible spring assist.

@@frollard I'm not talking so much about the simple flap lever to flap angle ratio, but the way they've clocked the positions of each end of the linkage relative to each other. There are ways to set it so that you start with more leverage over the flap and end with less (control lever initially moves faster than surface, then slows down to match its speed) which is what they've done, or you can set their relative positions so that you start with less leverage (when you don't need it at low flap deflection) and gain leverage as you move it further (moving arm faster than flap).

Are you sure? I’ve ever been up close and personal with a single DC-3- and it didn’t have flaps. Looking at photos of planes on the web, and I don’t see any indications of flaps- but, admittedly, all those photos are from the top, so for a split flap, wouldn’t see anything!

@@dphuntsman Plenty of photos of the DC3 flaps extended on the web. Unusual in they extended under the fuselage as well as the wing.

Airliners need far more effective flaps with substantial chord extension and effective wing area increase to create viable configurations for takeoff and landing from a wing optimized for their cruise speed. The speed range of anything with a piston engine - even the DarkAero - is much narrower so less effective flaps are viable.

They presumably want more mechanical advantage. In that design, the driving torque tube would rotate very little.

Split flaps work via gravity, so it is usually either DOWN or UP. Force in question is just the weight of the flaps, so not much. Now getting them UP and sealed can require more force as aerodynamically suction is pulling them down on the trailing edge often. Can splitflaps do detents? Sure. Will DA do so? Who knows. Will they know exact forces? Not a chance, unless they did aero work. These guys do not have access to a wind tunnel and seem to do their aero work in CAD to get lower airfoil pressures(if they have done so). Now they should have a pressure polar of their airfoil if they look hard enough, but it would not surprise me if they do not have this either. This is often not published except as examples using say Clark Y airfoil for 12% thick@Re~1,000,000 They could actually use Clark-Y pressure polar as ~close enough though and it would not surprise me if this is EXACTLY what they have done obtaining forces + a large safety fudge factor. If much larger fighter sized aircraft can do it with just average pilots and MUCH larger flaps, and no mechanical advantage augmentation, It boggles the mind how this tiny aircraft would have flap stick forces worth mentioning. But then again, I have seen engineers completely botch simple into complex moronacy so... =)

Thanks!!

Thank you! All the modeling work has been an endeavor of its own. Not certain on the total number of hours put into that effort but it’s on the order of 1000’s.

@@DarkAeroInc. Hi from across the pond. I graduated 51 years ago in Aero Eng and Design. My final year project was Foam Stabilised Compression Panels. I used used 20 gauge Al skins and a 1 inch polyurethane core . I wrote to De Havilland for advice and they supplied the adhesive free !! Subsequently I proved mathematically that the Southwell Plot could be used to predict the failing load , in compression, for this “weak in shear” structure. My tests indicated that this could be the case , but at a review in front of the whole course, I was rubbished by a lecturer , that my results were a coincidence and the Southwell Plot only applied to structures in compression which were weak in bending. This humiliation triggered me big time, and after a struggle I proved mathematically that I was correct. So…..how have you tested that your design is structurally sound. And….your design looks really “hot”. How do you propose to conduct stall and spinning trials ? Are you going to fit an anti spin chute during these trials, just in case !! You would be wise to do so. Do you intend to fit leading edge “triangles” inboard , to ensure you get tail buffet stall warning ? Great video by the way. Such a clean design will produce a very flat glide angle I imagine. If you have a flap linkage failure say, will you investigate during flight testing , the use of sideslip to increase your descent rate ?

Fowler flaps are often on Ultralight aircrafts In Europe. For instance in Italy they make the ultrafast two seat aircraft called Risen with fowler flaps.. Please note, with 100hp Rotax they guarantee the top speed at sea level 320km/h (173knots) and with turbocharged Rotax 915 -142hp they guarantee maximum cruising speed at 16 thousands feet 450km/h !!! (243 knots ) !!! Will Dark Aero be able to achieve the same velocity with much stronger engine ??? Risen has got the ultimate aerodinamics IMHO. Extreemly efficient and it is all carbon fiber too. What I like about Risen compare to Dark Aero, that Risen is not using any metal(aluminum) honeycomb, but rather materials which can never ever rust.... On the other hand what I like about Dark Aero is the gear(looks strong) and the 2 baggage compartments.

They have a split rudder so there is a little bit braking in the air, and you can control how much you want

Yes, the split rudder is intended to be used as a speed brake,@@minorlion1327. If drag is needed, it has the advantage of causing minimal pitch change... unlike the split flaps.