The biggest myth about split flaps

[@xpeterson]

I love the ball park numbers you guys use. So many places shy away and just say “it depends on multiple variables” which I imagine is true but gives no perspective for reference or insight to the bigger picture.

[@ashlionell]

This is SO true. Gets my goat everytime.

[@AM-hf9kk]

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."

[@brianb-p6586]

It's interesting that the B-52 and B-29 are listed as examples for the Fowler flap, given that it normal practice for modern airliners that are much more familiar to viewers

[@beverlychmelik5504]

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.

[@kittycatpilot]

Also, the P-38 is another glaring omission.

[@Matt_10203]

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

[@8literbeater]

Most Cessna singles have slotted Fowler flaps. --- 140A 150 152 170B 172 175 180 182 185 205 206 207 210 --- to name a few

[@RobertCraft-re5sf]

it's obvious that you guys are making this aircraft as simple and reliable as possible while also maximizing its speed and performance. Such an awesome plane.

[@timcross2510]

Hah!

[@RobertCraft-re5sf]

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

[@Grarder]

I love your videos! So cool as both a systems engineer and an aero nerd to see the decisions being made and why. And the engineering explanations are just fantastic. Can't wait to see this thing in the air!

[@MichaelSkinner-e9j]

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

[@gwzipper1]

You've got four potential failure points at the rod ends at either end of the two pushrods travelling aft from the main torques tube where, if you were to lose any of them, you'd risk ending up with a differential flap deployment - a catastrophic condition. One tube traversing from flap to flap with a single input pushrod would solve this. Same geometry in a side-on view, single centerline pushrod in a top-down view. Not sure if there is some other system taking the space that would otherwise prevent the cross tube at the flap hinge position, but I'd strongly recommend against the actuation configuration shown here. Split flap concept though - I like your choices here!

[@PetesGuide]

Within the first 20 seconds you cleared up my biggest worry about split flaps-the turbulence-without saying one word about it. Awesome storytelling and lead-in guys!

[@billcarrier9622]

It also eliminates any chance of control surface flutter.

[@meazy451]

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

[@36thstreethero]

Turbulence (ride quality) was your biggest worry?

[@PetesGuide]

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

[@Thomipangang]

Thanks for adding in the extra clips from within the cabin! Have a merry Christmas and a happy new year guys! Hope to see this beauty flying next year!

[@CanardBoulevard]

As a pilot I much prefer manually actuated flaps. Have you done some design analysis on the mechanical advantage of your flap lever? It looks a little short compared to other aircraft of similar size I have flown with manual flaps.

[@w8stral]

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.

[@jessechen4971]

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

[@rnordquest]

@@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.

[@w8stral]

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

[@iforce2d]

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.

[@williamwilliam728]

Soon this newborn will be taking its first flight. What a journey this is. Awesome engineering from you boys and good luck with the test flight. Merry Christmas and a Happy new Year!

[@jorgentoll314]

Interesting video! I guess it also comes down to deflection angles. Since you mentioned the Spitfire and Hurricane using split flaps, they had just two settings, either up or down and the flap deflected almost 90°. It seems to me that such large split flap deflections are more akin to speed brakes than lift devices.

[@kickedinthecalfbyacow7549]

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

[@jorgentoll314]

@@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.

[@78779]

When will you fly? It seems like progress has been very slow of late. Can’t wait to see your fantastic aircraft airborne.

[@mirekslechta7161]

Fowler flaps: we have them guite often on ultralight airplanes in Europe, for instance Risen. In Italy they make the ultrafast two seat aircraft called Risen. 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.

[@getinthespace7715]

I like that the design is optimized for being efficient at speed. no gaps, and as simple as possible.

[@slehar]

The Cessna flap is slotted when half way out, but Fowler fully extended. The slotted / Fowler flap is like a new biplane wing, tilted to catch the airflow deflected by the “upper wing” and deflecting it some more.

[@tedsmith6137]

Interesting and informative explanations. You might consider getting rid of any background 'music' or soundtrack. It is really distracting, serving only to make it a little harder to concentrate on, and understand, the narration.

[@blakechinn5792]

Really happy you guys are staying simple with manual bar for flaps. Easier build, less failure points over time, simple.

[@jeffpogue6962]

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.

[@ammerudgrenda]

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

[@reubenmorris487]

@@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.

[@Jazz3006]

Is there a concern about the force required on that short handle to activate the flaps? Just looking at it has me a little concerned if there is an attempt to open the flaps at any relevant speed. (Even at a 50kt airspeed, there would be a pretty high torque because of the surface area of the flap.) It seems to me that this is also why most older aircraft I have seen with manual flaps have relatively long handles.

[@LTVoyager]

My Cessna 182 had Fowler flaps. They moved rearward significantly before descending downward.

[@TheJustinJ]

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".

[@LTVoyager]

@@TheJustinJ 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.

[@brianb-p6586]

@@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.

[@SuperYellowsubmarin]

Another exemple of a fast light aircraft using split flaps is the JMB VL3. Also, some flaps are more easily mixed as flaperons to inmprove low speed handling, which is the important limiting factor besides stall speed and stall characteristic. Looking forward to first flight !

[@mirekslechta7161]

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.

[@jasonhill1729]

The flaps have been installed for several years at this point AND almost all of your most recent videos have consisted of simple reviews of existing systems... what have you guys been doing these past few months??? What's the reason for the stalled progress? Is there some major design issue that's keeping you from flight testing? C'mon, show some real progress or tell us what's wrong!

[@pergeltzer1020]

When do you expect first flight

[@martinluton6513]

Great video, you fixed my misconception that split flaps are more draggy than plain flaps. I hate to be ‘that guy’ but the actuation linkage builds in the opportunity for a linkage failure to give asymmetric flap deployment. If you are able to put the torque tube on the hinge line of the flaps then you could have a single linkage from the flap handle to the torque tube rather than two, meaning that if any articulated joint in the system failed you would be left with a symmetrical failure rather than an asymmetrical one. Please keep the videos coming, you’re doing incredible work.

[@daviddavids2884]

air is Stationary wind tunnel testing is NOT conclusive.

[@snorttroll4379]

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.

[@Berend-ov8of]

@@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.

[@Berend-ov8of]

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

[@Patshes]

Get that thing flying!!!🆒😎👍!

[@985aviator]

I thought most Cessnas have Fowler flaps not slotted flaps? Can’t wait to see this bird fly! I just finished my RV-6A a couple of months ago. First flight was an incredible experience! However the first flight of a new clean sheet design has to be the pinnacle of home building. Congratulations on your success so far!

[@usaerospace6707]

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.

[@tomcoryell]

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

[@christopherpardell4418]

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.

[@TheJustinJ]

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.

[@Dilbert-o5k]

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

[@foesfly3047]

There is so much educational value in your videos ♠️

[@doccls]

One of the advantages of the split flap is that the separation bubble stably extends the pressure recovery aft of the airfoil trailing edge into the freestream, allowing the upper surface pressure to stay below static as opposed to having to recover to near stagnation. We (NASA) used this aspect to design a wing for a glider for Mars exploration; it was to be folded up in an entry capsule, then released to fall away and unfold. The flowfield conditions presented during pullout were challenging - transonic Mach and low Reynolds number. We found that a split-flap design maintained the high CL capability needed to achieve the pullout maneuver even under these conditions. Of course, the relatively high drag was also advantageous, as it would slow the glider and give more time for the pullout to occur.

[@billyk4711]

The most common Cessnas, like the 172 series use Fowler flaps, not slotted flaps. However, the Piper Cherokee series has slotted flaps.

[@johnfitzpatrick2469]

Merry Christmas Riley, River and Keegan from Sydney Australia. Thank you for your time and commitment to education. Each time I receive a Dark arrow video, I think... Holy sh#t and then: great it's learning time. Love the British spitfire flap info and "possible to manufacture split flaps"- in aluminium with ribs for strength. Merry Christmas and peace of the lord be with you. 🌏🇭🇲🌲

[@CafeenMan]

You guys have put so much work and love and energy into this aircraft. I wish stuff like this didn't end up in bankruptcy most of the time.

[@GWAYGWAY1]

I have always thought of most Cessnas having Fowler flaps as they extend as well as droop.

[@electricalmayhem]

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

[@brianb-p6586]

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

[@mdellertson]

Yawn… every video is theoretical. No demonstration of the actuality of the theory.

[@daemn42]

With a little change in geometry you could have gotten more leverage at the handle over the flap as it approaches full deployment rather than less. As it is, you have most leverage when it's not needed, and least when it would be nice to have. We do this on big heavy RC sailplanes to avoid breaking the servos when the flaps are fully deployed just in case we don't get them up before touchdown. For you it'll just be a matter of the flaps feeling really heavy at full deployment.

[@frollard]

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.

[@daemn42]

@@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).

[@mitseraffej5812]

Another aspect of the marvel that Concord was is that it had no lift augmentation devices at all, neither leading or trailing edge. Low speed flight was achievable because of the double delta wing, same as the Space Shuttle.

[@MurraydeLues]

DC3 had split flaps as well. Very informative video.

[@dphuntsman]

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!

[@MurraydeLues]

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

[@paulking7019]

Krueger flaps. They increase camber too, like all other flaps. They just do it at the leading edge. This is not to be confused with things like Slats and Slots that do not increase camber. There can also be a hybrid Slat/Krueger flap. More types are probably out there that are only found on certain aircraft for unique circumstances or situations like flaperons. Ailerons that also function as flaps.

[@kiereluurs1243]

Please leave out the pointless and annoying 'music'.

[@cfdfirefighter]

Been following for a long time….y’all ever gonna fly this thing?

[@deani2431]

I much prefer manual flaps as I like to do short approaches, and deploy when I am sure I made the field, and electric is just too slow.

[@Johnny-Too-Bad]

It's been a long time but the finish line is in sight.

[@OlegTsilinchuk]

Guys, did you consider placing the torque tube coaxial to the flap pivot? In this case it seem to have more reliable mechanics. At least now if one of the links fail there would be differential lift created, which could be very dangerous obviously

[@brianb-p6586]

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

[@rangefreewords]

I noticed the projected rated speed of the aircraft will be around 230knots, will you need static whicks with this composite flap aircraft for less noise, interference in your electronics and in comms?

[@Tjkrusinski]

The CAD work is super impressive. Can you estimate how many hours you've spent building the assembly of the whole plan in on shape?

[@DarkAeroInc]

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.

[@californiadreamin8423]

@@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 ?

[@waywardscythe3358]

I'm excited for flight testing, and I'll be interested to hear how the flap deployment feels in flight.

[@chrissugg968]

I like the mechanism attached to the flap itself especially. The geometry of it means that you're increasing the force you can apply to the flap as it extends further out into the airflow (and so would be harder to move manually).

[@OlegTsilinchuk]

Guys, did you consider placing the torque tube coaxial to the flap pivot? In this case it seem to have more reliable mechanics. At least now if one of the links fail there would be differential lift created, which could be very dangerous obviously

[@dermick]

Was thinking something similar - I like the way the RV does it - you can have asymmetric flap deployment if you have a pretty serious hardware failure on an RV, but there is very little hardware in the solution, and you can inspect the critical bits during preflight.

[@humanspirit3432]

You can save few kilograms by replacing torque tubes and shafts with simple cable drive (like on engine-less gliders)

[@TheBumpking]

Actually, the plane already use a mix of push-pull rods, torque tubes and cables (for the rudder). And it seems to be one of the most common configuration for light aircraft. Cables are lighter but have several drawbacks : - inferior rigidity of the controles - cable tension monitoring - pulley derailment - maintenance - ... But yes, i'm pretty sure that for flaps control, using cables make sens.

[@blancolirio]

Simplest fowler flap design Ive seen is on the Aviat Husky, which came from the Callair. Split flaps on the early C-310s.

[@mirekslechta7161]

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.

[@leeoldershaw956]

Fly the airplane !

[@SoloRenegade]

Cessnas use Fowler and split flaps

[@asherdiamantberg5862]

Please do a total fancial Cost analysis

[@sukocoimam4519]

How about stall speed for each flap design in same wing and AoA? Is there any different. And what DA1 project design landing speed and runway requirement?

[@billstrahan4791]

I'm curious if you'd taken a look at assymetric flap deployment versus aileron authority. If any of the linkages were to fail in the flap system, is there sufficient aileron authority to counter the roll until the other flap can be retracted? I don't think it's a likely failure mode but with you attention to detail I'm just wondering if you've examined it.

[@w8stral]

One does this in VERY high speed aircraft where flutter is the biggest problem, or sometimes in sailplanes where once again, flutter is the biggest problem. In low speed aircraft this is not a problem. In civilian aircraft with their wings full of fuel, once again, flutter is a big problem and due to $$$ of such aircraft, they can afford to have multiple roll capabilities. In their case, they LOCK OUT aileron movement except at LARGE stick deflections and they still allow down aileron, it is not just UP aileron. Of course swept back wings helps here as well so... This is essentially impossible to do on a mechanical only simple aircraft design. Even the commercial boys have a SMALL flap behind the engines providing roll controll and the main flaps DO NOT move for roll control.

[@billstrahan4791]

@@w8stralNot sure what flutter has to do with any of this. Nor was I suggesting using the flaps for roll control. I was asking that, if in the event of a linkage failure resulting in an asymmetric flap deployment, was aileron authority sufficient to maintain control.

[@waywardscythe3358]

I'm guessing that wouldn't be a high priority design consideration. I know from my flight training on a C172 to expect that an asymmetrical full flap deployment would too severe to fight with aileron control at all. I doubt many other pilots received training quite as terrifying as mine was but it should be pretty well ingrained that the pilot should undo the last flap adjustment if that failure happens.

[@w8stral]

I thought that was obvious so answered you in a different way. Ok, here goes, basic algebra time and WHY flaps are NOT considered primary flight control and why aircraft can LOSE a flap and still land with flaps down. Aileron CL max is? ~2.5 or so(tip stall territory and you die anyways so... not cool), but when problems occur is possible. Percentage of wing ==? Looks roughly 30% Flap Cl goes to max of? 2.3 percentage of wing = ~60%. Wing CLmx ~0.8-->1. Lets call it 0.9. Lever arm length to CG Moment Flap = 2.3-0.9 = 1.4* center of flap lift @30% or ~0.42. Moment aileron = 2.5-0.9 = 1.6* center of aileron lift @75% = 1.2 1.2 Aileron >> 0.42 Flap Losing a flap or one flap stuck down is ANNOYING, no question, and you will have to LAND faster to compensate for loss of lift, but it is not a death inducing event like losing an Aileron. If you lose an aileron: Bail out because if you are in the aircraft when it crashes--> You are dead 100% of time, if you bail you have a 0.00001% chance of living but slightly possible if over water, or fly with a parachute. @@billstrahan4791

[@w8stral]

Yup, decreasing the half flaps deployed that are down will decrease your landing speed as one has less downward lift from ailerons on opposite side. @@waywardscythe3358

[@deansiracusa3966]

I’d always thought that split flaps just created more drag versus lift when extended. Thanks so much for this detailed explanation!

[@trumanhw]

I know by "deflection" you mean that the flap is angled downwards ... However, I wish people addressed how it manipulates the airflow: It must also deflect air as a lift source & can't just be pressure differentials.

[@RePeteAndMe]

4:00 "right at the hing line" Sure, but a double joint... hmmm, I'll have to make sketches, but smoothing a wing feels doable, so doable that a split flap feels bargain basement. But if flaps are used a tiny percentage of flight time, yeah, maybe. LOL How many folks have searched the same possibilities? So the odds are low and I'm probably going to explore anyway

[@russellwilson5246]

cool..hey i have a question in the form of an assumption..i asume you do not need to aerodynamically or weight balance split flaps?

[@mirekslechta7161]

Fowler flaps: we have them guite often on ultralight airplanes in Europe, for instance Risen(from Italy) , or Stream(from Czech Republic). In Italy they make the ultrafast two seat aircraft called Risen. 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(crossed Atlantic from Africa to South Anerica using 200l tank only) 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.

[@gufo_tave]

Damn, when I opened the video I read: "The biggest myth about SPIT flaps"... intending the Spitfire's ones. Incidentally, that plane used split flaps...

[@JoeKyser]

Take a shot everytime they say flap. Yeeehawwwww

[@thomashong7016]

How much force to deploy landing flaps?

[@raphaelpanier9712]

Hi, thank you for this informative video ! Considering you experience with carbon fiber, I would like to submit an inquiry. I am building a folding bikes with carbon fiber tubes and steel lugs. The torsional stiffness of the Roll Wrapped tube is disapointing. I your opinion, how much better would a Pull Winded or Braided tube would perform in torsion compared to a Roll Wrapped ? Regards

[@markplain2555]

Would I be able to speak with you guys? . . . I have an HP-18 glider. This is a flaps only glider (there is no spoiler). The flaps are operated with a crank handle, meaning you have to turn a crank that has a gear reduction system that moves a series of connecting roads and moves the flaps. I frikken hate it and am looking for an alternative (I have not flown the glider yet). . . I wanted to do something similar to you guys, remove the crank handle and make a manual lever. But I was told, "DON'T DO THAT !!!" . On landing, I will crank my flaps to 40% to commence landing and then crank them some more - all the way out to 90degress as needed to reduce airspeed and altitude. The thing is that I was told that the amount of force required on the lever is something in the order of 60 to 80lbs and my level was intend to be about 18inches.... oh and my glider is flying at 50knots or 57MpH. . . Your manual lever looks like it is a mere 6 inches in size. Do you not think you will need some serious arm strength? . . Can you make a video discussing why you chose to manual and not electric. What is your anticipated landing speed? What are your anticipated loads? when landing how many degrees of flaps will you put out? . Thanks.

[@chrisruf7590]

The crank is not so much for mechanical advantage as to purposefully slow the transition from one setting to another. If you can suddenly dump flaps from 50 degrees to zero on final you will suddenly drop 15 to 50 feet, as the wing has to speed up to reobtain equilibrium. This would often cause a crash. This is why the rear spoiler flap combination used on the Mosquito and Ventus is no longer used on modern designs even though it allows very steep approaches.

[@markplain2555]

@@chrisruf7590 Thanks for the response Chris. I had no idea that dumping 50 degree flaps would result in such a drop in height. That is VERY good to know. However, the crank system still has a 2:1 gear system where 2 turns of the crank has a 1 turn of a gear that moves the flaps. I have heard 2 complaints of this system: 1. you struggle to to keep up with cranking the flaps to get the right flap setting as you approach landing. 2. you have to often turn your head and check the flap setting at a time your head should be looking out the window. . But the alternative (I was told) is a big stick handle like (I think) the I-26 glider. This has way too much load on your left hand while your right hand is holding the control stick and making light movements. So the thought process is "the crank system" is the best choice. I personally believe I should figure a way to install spoilers on my HP-18 (that would be a mega project - maybe too big a project for me). . I'm also thinking of keeping my crank system, but installing an LCD indicator that tells me how much flap I have out and I don't have to turn my head to look at the setting - at least get rid of one of the 'issues' of the crank system. . But now looking at the video shown here - they have a very small mechanical handle for their flap system. Is that wise?

[@brianb-p6586]

@chrisruf7590 the gliders that I flew (basic old Schweizer 2-33) had linked air brakes and spoilers controlled by a sliding handle that could be deployed very quickly. As the primary method of descent angle control rapid response was desirable, and because it was not a flap system it did not cause a pitch change. If the crank handle of the another design is deliberately slow, that is presumably to avoid rapid pitch changes, rather than avoiding sudden altitude loss.

[@chrisruf7590]

@@brianb-p6586 do you mean linked flaps and spoilers?

[@brianb-p6586]

@chrisruf7590 no - that's a reasonable guess, but the 2-33 doesn't need flaps. The Wikipedia article describes them as "top and bottom balanced divebrakes", but the components on the upper surface of the wing are front-hinged mid-chord panels that are typically called spoilers. The components on the lower surface of the wing are similar (including mid-chord position) except that they are hinged on the rear edge. I assume that airflow tends to force the lower parts open and the upper part closed; the net result is that they are relatively balanced, so they are reasonably easy to move and to hold at any position without a latch.

[@Averey486]

Hi I am very interested in your project DarkAero I just love how affordable it is and the range of the aircraft would you say this is a good beginner friendly aircraft I just can’t wait for the plane to be ready for its first journey through the skies and into everybody harts finally. Will the plane ever get a rocket propelled parachute system. Or BRS Aerospace: Whole Aircraft Rescovery Parachute Systems or does it already have one

[@jackoneil3933]

Thank you for the excellent synopsis on Flap types. Might you know if split-flap designs might be inherently different at high extension angles to Fowler design as far as L/D? I was reciently chatting online with other pilots about the how the early model Cessna 310s had a pronounced loss of lift (not stall) on landing if throttles were reduce below zero thrust, and the Beech Barons like the B55 model with Fowler flaps much less. Both were similar wing-area, airfoils and weights.

[@86jam184]

100% did not believe you about the drag. Thanks for posting the naca papers! So freaking cool! Ok, so now we believe the data. But how do we explain why?

[@arturoeugster7228]

gurney flaps, have you forgotten?, those small ones at 90° Very effective, used on a sail plane by Dick Schreder on HP-8

[@flashcar60]

In applications such as gliders, where drag minimization is most critical, the plain flap can be reflexed, thereby reducing the drag at the best glide speed.

[@daviddilley538]

Great discussion and Explanation…always thought split flaps were a simpler but cruder solution…and they’re not!

[@DrDeFord]

Stick with manually actuated flaps! Being able to quickly change your coefficient of lift is great for slow flight/maneuverability/canyon flying!

[@AndyMatrix]

Guys how about a DeltaHawk DHK180 installed on this beauty? 5000NM range :)

[@ronliebermann]

About twenty years ago, a pilot who had modified the elevator on his plane got killed when the plane over-steered. His sudden climb caused him to experience eight G’s. Flap design, and all control surface design, isn’t the simple principles shown in this video. All aircraft air-flow dynamics are finalized in the wind tunnel. Not on paper. Results occur in the real world.

[@petersmythe6462]

I think the thing with split flap drag is probably somewhat deflection-dependent. At maximum deflection the plain flap may well be acting almost like an airbrake, completely stalled. Clearly this should be more drag than the split flap. But what about at moderate deflection? That is, for the use case where the goal is improving L/D rather than improving lift alone?

[@hotliner2872]

"The flap allows us to have a smaller wing"... not really true. For a given wing size you would just need to land faster (less of a concern for an aircraft designed for hard surfaces). My hunch is the airspeed changes 10kts or so with flaps, not night and day. It would be perfectly reasonable to have a 'speed' or 'race' version of this plane without flaps (to save a little weight, & add a wee bit of strength/stiffness, and reduce parasitic drag a wee bit... but in a race plane a wee bit can matter). It could even be programmed or set up for spoilerons to lower landing speed ((where the ails rise to some fixed angle as the neurtral point to act as an air brake, tho this is no help on takeoff). Just a nit, you guys rock.

[@tztz1949]

German sailplanes have this all solved with flaperons. In the 70s. Easy with the internal mixers solvable/efficient/effective

[@gideonfourie8722]

Excellent video. I don't quite get to the "biggest myth" part, - I suppose it's the high drag assumption - but I love the factual nature of the presentation.

[@peterhenman2662]

Juan Brown just mentioned on his latest video about the Lockheed at Chino that split flaps create drag and no lift. At least that's what I remember him saying.

[@therealaim-9xmissile]

Working on getting my ppl and I dream to one day get a experimental kit aircraft and I’m definitely keeping my eyes on you guys! A zenith is cool but I’m honestly a low wing type of guy and I love the design, look, and performance of this aircraft. Keep it up guys 😎

[@benjaminschaefer6757]

Capital work, gents.

[@Dremekeks]

Interesting! Another composite plane that has a split flap is the TL-Sport Sting!

[@malcolmwhite6588]

That’s not the biggest myth about split flaps - well outside the aviation industry it’s not the biggest myth about them anyway!😂🎉😮

[@yellowrose0910]

Great flap discussion. Just a minor nit: "The split flap comes out on top of the split flap when it comes to drag for a particular lift". The graph shows you mean the split flap has a better (ie lower) drag/lift ratio, so it's "on top" in performance, ie desired. However, the statement, especially if the graph were not there, could also imply the opposite: that the split flap has a higher drag/lift ratio (numerically "on top" of the simple flap) and thus is less desirable than the simple flap.

[@katungyejohnson3333]

Good idea but making this system entirely manual could make flying tedious. Perhaps using cables and automating it to work in synchrony with relevant systems such as brakes, lift, or landing would make flying much easier and possibly the manual part can act as redundant system.

[@flymachine]

I disagree somewhat, what you’re not giving enough focus is how critical specific flap design is for specific types in specific applications - for a swept wing that cruises at transonic speeds then has to slow right down with high wing loading and given AoA profiles you simply can not beat the slotted fowler type fundamentally, split flaps have limited benefit in a higher wing loading and in adverse conditions I am dubious - it’s one thing to do the math for basic application but wing loading, cross wind, AoA, operating speeds etc. all need to be factored to truly understand the pros vs cons. I do agree that if simplicity is prioritised on your specific design the split flap is basically viable. I admire the work you guys are doing but this is so far a variation of established norms, I have not seen anything stand out revolutionary but I hope you will achieve revolutionary in the final performance, perhaps the story of how she came about and the effort itself is the true hero. Happy landings I’ll be watching!

[@SydneyEV]

Junkers style flap, same as Fowler flap without the retraction hardware penalty.

[@appa609]

Stay safe and be careful. Far too many aviation projects go under when the owner-designer-pilot dies during flight testing.

[@MortenMF14]

Just curious, is the cockpit designed for taller pilots? (talking 190 cm+ (6"4)?

[@Max_Janszen]

Man, if there was another model that could be offered with a clean stall of 54kts and max cruise of 250kts, you'd have the sport pilot market on it too with the rule changes coming

[@SpiralDiving]

Yes flaps increase lift and drag but split flaps produce relatively more drag. You use flaps to lose energy - the change in stall speed may be useful and this is seen more in Fowler flaps. in the cessna 172s i've flown they were fowler flaps but maybe that wasn't the case in older ones?

[@andym.s.5231]

Gonna be honest this makes sense for angles up to ~45 degrees of downward deflection but the Spitfire was straight 90. I have no clue how those functioned at all like flaps (above altitudes where ground effect wouldn't help). To me they look like lift-killing airbrakes.

[@MarcinP2]

For fighter aircraft a lot of designs had maneuvering flap position so the split flap would be at low deflection and cause drag. Hurricane and Spitfire only had two flap positions - extended and up and predictably used split flap.

[@SimanSlivar]

Kinda surprised you didn't go with an aeromomentum engine. Though I guess it is water cooled but it would have been lighter and much more efficient.

[@gendaminoru3195]

too simplistic in discussion of split flaps - not gonna poke holes in your story here, but you know better. You only have one graph of one airfoil section and thickness. I'm also reminded of the rationale you have for using split surfaces.

[@M5guitar1]

I was expecting your fingers to get smashed becuase of the way you are were leaning on the trailing edge and waving your fingers about. Ouch!

[@jerrywatt6813]

,any decades ago I worked a lockheed with early composite materials and some I suspect are not open source as yet but I'm glad they are in wide use today so widely I always thought them quite amazing in testing !😊

[@aelas65]

What if split flap hinge is shifted forward leaving some gap ahead of flap, would it provide some extra benefit of slotted flap with high energy air pass through and very little extra complication ? Thx

[@mosca3289]

This is a fantastic learning opportunity for all of us.

[@AnthonyTaylor]

If you try to apply flaps during landing, how much force is required to deploy compared to if the plane was stationary

[@Fatherof12]

Nothing wrong with split flaps - or manual actuation, but it seems pretty clear from the arrangement of the cockpit and the landing gear that there just isn’t enough room for an electric jack screw that links both sides without some serious kung fu on the linkages