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."

[@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.

[@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.

[@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

[@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!

[@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.

[@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!

[@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.

[@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.

[@getinthespace7715]

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

[@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!

[@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.

[@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.

[@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.

[@seanyounk1]

You guys are my favorite KZbin Channel. I think you are doing a wonderful job here of building a fan base to help launch the DarkAero 1. I have no doubt you guys will be very successful in time.

[@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 !

[@LTVoyager]

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

[@Triple_J.1]

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]

@@Triple_J.1 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.

[@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.

[@foesfly3047]

There is so much educational value in your videos ♠️

[@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.

[@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.

[@Triple_J.1]

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

[@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. 🌏🇭🇲🌲

[@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.

[@shahramkhesareh8068]

I have seen almost all of your videos and they make me glad and amazed,as making an aircraft needs to know several fields of science and knowledge's and you have all of them together. Your job tells me that you were good students and are very qualified engineers now. Congratulate.

[@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).

[@jimboagogo]

Fowler and split flaps have one disadvantage which is the inability to use negative deflection in cruise. You have a good, simple and reliable design, well done!

[@mosca3289]

This is a fantastic learning opportunity for all of us.

[@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?

[@genexplore]

One thing that's great about aero is that butt math and intuitions conceal the actual complexity of what's involved (leading to myths and misconceptions). I'm impressed at your guys' ability to condense these really complicated subjects down to something digestible and understandable.

[@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.

[@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

[@matthewrank109]

this channel is top notch. what you all have built is so impressive

[@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 !😊

[@R760-E2]

Riley's presentation was great. Although I don't usually get much fired up about the new composite airplanes, I wish you guys well on this venture (certainly no pun intended!) I hope that handling qualities are as important as performance to you guys.

[@kwaaaa]

Love the shared decision making process and explanation on the "why" about this channel.

[@pergeltzer1020]

When do you expect first flight

[@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

[@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.

[@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).

[@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.

[@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?

[@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.

[@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 😎

[@oyeog77]

I wonder how it’ll feel to pull that manual flap handle in flight. Really hope I can try it some day 1:30

[@12345fowler]

One of my biggest surprise when transitionning to the PA-28 Archer was my intstructor asking me to do a flaps up circuit and landing. He asked me at what speed I would fly the circuit and landing and I was all bent to say for sure faster than the regular speeds used traditionally. That's when he told me just fly the same speed as normal no need to fly faster just the attitude will be more nose up and power setting would be different. The "flaps enable slower speed" is really only true for the stall speed (a few knots of difference as per POH) but as you would never fly that slow anywhere in normal flight that wouldn't do any difference.

[@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.

[@EricTheBlue2010]

Could you link the video your sampling the airfoil smoke demos? I've seen these stills before but can't find the source video.

[@desertpoj]

Hi. One thing you mentioned was sealing. The gliding community have always been ahead in this area and use Mylar sealing and turbulating tapes. I have an 18 metre flapped Schempp-Hirth Ventus and it is sealed and turbulated within an inch of its life. A gliding buddy of mine has an RV in which he set various records in, including the elapsed time London-Cape Town-London record for a 200 hp aircraft. That is beautifully taped; everywhere! Have you considered what tapes you will use? I’ve attached a link to the first glider supplier I found. I live in the U.K. and have no connection with the company, but their site has a great selection for you to browse. Just a thought. My mate’s RV is impressively fast with a stock engine. But there’s not a gap an air molecule could squeeze through! I notice that the ailerons don’t yet seem to be sealed.

[@cypher1o1]

Is there eventually going to be a flap indicator for the split flap similar to the spitfire since you cant see the flap position from the cockpit? Incase of malfunctions l.

[@deansiracusa3966]

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

[@gregswank4912]

How much force does it take to engage the flaps at the appropriate flight speed? The angle of deflection on the flaps seemed to be similar to the deflection angle of the lever, which doesn't appear to give it much mechanical advantage.

[@Relou4e]

There is a great version of the legendary Libelle glider with those flaps. With the additional airbrakes it had a maximum descent angle of 1:4, strong ground effect and strong deceleration it was great to land on very short strips. I loved it!

[@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.

[@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

[@IainMcClatchie]

If the split flap has both less drag (both in cruise and deflected) and more lift... what's the advantage of the plain flap? It doesn't seem simpler. What is the area of the flap, and what is the expected torque and force that you have to apply to the flap handle?

[@brianb-p6586]

They explained the structural advantage of the plain flap for conventional built-up aluminum construction in the video.

[@christopherpardell4418]

Shouldn’t that torque tube run the full width of the flap with at the very least a crank arm at the far end if not in the middle as well?

[@flyer5769]

A question if I may! On the split flaps. Technically you have two cord lines when the flaps are lowered? How is that affecting the flight characteristics.

[@RubyRhod]

There are a lot of wanna-be engineers out here on youtube, but you guys seem to really know your stuff. You showed the pros and cons and your choice makes completly sense to me. It would have been nice to hear an opinion why the big 2 choose fowler flaps for their big birds (I'm just a regular mechanical engineer for farm equipement; this topic is really interesting, but I have no idea what to make of all the possible choices). again: great video! loved it!

[@brianb-p6586]

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.

[@AnthonyTaylor]

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

[@Patshes]

Get that thing flying!!!🆒😎👍!

[@davidchow9528]

Looks like the individual cranks for the flaps are at the root of the wings. What about locating them at the center of the flaps so there would be less twist force on the flaps (and their hinges) and also have half as much of a longitudinal chord in the flap which may help with flutter from such a long span.

[@spdcrzy]

The flaps are stupid lightweight. Probably five pounds, at most. The heaviest parts of the flap mechanism are all internal to the fuselage, so leverage is still as high as possible while minimizing the moment of inertia in the wings themselves.

[@davidchow9528]

@@spdcrzy I'm not worried about the weight of the flaps. The aerodynamic force on the flaps is much greater than the weight of the flaps.

[@spdcrzy]

@@davidchow9528 that's the question though - will it be, really? Even if it's five hundred newtons per flap, I doubt it would be an issue. And I don't think anybody has ever done a full carbon fiber flap with carbon fiber IN the linkage - it will likely be more than stiff enough to prevent torquing in any way.

[@davidchow9528]

@@spdcrzythe concern is not just the force but also flutter. the carbon fiber for sure is stiff enough but what about the hinges and bond points. the greater the chord the higher the likelihood of flutter especially at lower speeds. to me attaching the crank mid cord makes the most sense. But what do I know I didn't do any analysis. Just bringing up an idea for the dark arrow team.

[@ArneChristianRosenfeldt]

Where is the space for a crank in the wing?

[@waywardscythe3358]

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

[@thomashong7016]

How much force to deploy landing flaps?

[@aleshkovalev]

Is there any ratchet mechanism to hold cockpit handle in place?

[@ThomasTheTankEngine22]

Let's go! I've been refreshing your page everyday for the past week 😂.

[@appa609]

The Fowler Flap is mostly a plain flap that lengthens the chord. Is the CLmax of 3.0 calculated with respect to the original wing area or the actual area of the flap-down wing?

[@mytech6779]

I see most of what you are getting at, It depends on the intended type of field used by the aircraft. If you will always be at runways with nice clearways then you may only care about getting maximum lift to reduce touchdown speeds and reduce stress on tires and gear, drag can be modest. If you plan on locations with steep final approaches to shorter runways, then energy management is more of a concern than minimum touchdown speed and adjusting drag is more important than lift. A generally versatile behavior is for a small deflection to add some lift with minimal change in L/D (Maybe even a slight improvement over the clean wing.). Then as flap angle increases a rapid increase in drag relative to lift. (Gliders take it to the extreme of adding spoilers to the top of the wing.) This doesn't require ideal flap behavior of course, as long as the flap design is "good enough" then the cruise and manufacturing concerns, that were mentioned in the video, become major factors.

[@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.

[@spdcrzy]

What other aircraft exist in this particular design envelope that you've chosen? I can't think of any other single-engine aircraft, experimental or production, that fits in a two-car garage, has retractable landing gear, a full carbon fiber (NOT fiberglass) airframe, and THIS much range at high speed. Am I also correct in assuming that even though the flap control link is at the root of the wing, the stiffness of both the linkage and the flaps themselves ensures that any potential fatiguing or failing due to torque from the loading forces is a non-issue?

[@billyk4711]

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

[@MortenMF14]

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

[@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.

[@N34RT]

It would be greatly helpful if you would specify the maximum split flap deflection for CL max.

[@heartsky]

Always excited to see more DarkAero progress!

[@derykian6029]

Is there anything going on in the mechanism to reduce the deployment force through, say, mechanical advantage?

[@PatrickJWenzel]

Aerodynamics tells me with the hinge point fixed at the front of the flap, when the flaps come down the trailing edge will effectively come forward thereby decreasing the mean chord. CoP will come forward (relative to CoG) reducing the relative moment arm and inducing a pitch-down tendency requiring nose up trim. That will be interesting to see confirmed during flight testing.

[@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?

[@trespire]

Love the simple and elegant design. Design simplification is an art form.

[@78779]

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

[@brianb-p6586]

This is good, and explains DarkAero's reasoning well. For a extensive overview of flaps, Wikipedia has a good article under "Flap (aeronautics)".

[@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

[@crawford323]

What was the L/C combination with Fowler and Kruger?

[@brianb-p6586]

What is Cₗmax for your test wing without flap deployment?

[@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 ?

[@brettharman8921]

great video, do you have an idea of the forces that the mechanism to lower and lifting the split flaps are experiencing?

[@The_Juan_Percent]

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

[@bakerrv]

Interesting that you would look at the reduced drag in a split flap verses the plain flap as a goal, when one of the goals with flaps, I thought was to increase lift and drag? Cheers!

[@watashiandroid8314]

I guess a lower drag to lift flap would be better for takeoff purposes.

[@electricalmayhem]

@@watashiandroid8314most light aircraft can take off less distance then landing. And in a slippery plane like this one you want to be able to increase drag for landing and easier approach, for example in gliders using airbrakes.

[@watashiandroid8314]

@@electricalmayhem of the 6 light aircraft I have flown enough to be familiar with, maybe one could take off in a shorter distance than it could land. Brakes tend to be far more powerful than the engine in a light aircraft, and from what I recall, most light aircraft can land in a shorter distance than they can take off in. The 6 aircraft I've flown enough to talk about: Cessna 150M, 152, 172M, Aeronca Champ (O-200), Bellanca Citabria (O-235), Super Decathlon. The one aircraft which I think can take off in less distance than land is the Super Decathlon.

[@electricalmayhem]

@@watashiandroid8314 Hmm you are right for GA aircraft, looks like I've been spoiled with microlight/Sports aircraft which are fibreglass with Rotax 912's giving a good power to weight ratio! (WT9 Dynamic, Rans, Vans etc) Been a while since I flew a cessna.

[@snorttroll4379]

just have a separate air brake that is big and deploys on touch down@@electricalmayhem

[@RandyMcNeil2]

with as slippery as you are making the Dark Arrow, how in the world are you going to slow it down for landing? I see the split rudder, but what else?

[@billcarrier9622]

I've been wondering if you have a schedule to complete all outstanding air-frame tasks and get into flight testing.

[@johnmolli214]

With the single flap actuation lever at the inboard end of the flap, it sure looks like there will be a huge torsional load on the flap itself and very high forces on the single actuation arm and its related linkage. I would love to know what you have computed these loads to be.

[@rickestabrook4987]

Great explanation guys,. Could you please reply with the anticipated load (lbs) at the flap handle during the clicks of extension? Thanks!!

[@w8stral]

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... =)

[@rickestabrook4987]

Thanks!!

[@Dremekeks]

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

[@John-hi5lp]

How do you do prefight control check if split flap is under the wing? Is the movement visible to the pilot?

[@nigelwilliams7920]

Do what they did on Migs: add a small arm on the leading edge of the flap which pushes a curved pin up thru a hole in the top of the wing when the flap is dropped. Position it where it can be seen from the cockpit, i.e. at the outer edges of the flaps. That way a quick over the shoulder glance each side will confirm flap position. The pin has a tiny cap which finishes it flush with the wing surface when the flap is closed. Put a red LED on it for night flying.

[@AC-jk8wq]

Nice update gents! Does the center of lift move back when the split flaps are deployed? (A Mooney characteristic) If no…. No trim change required with deployment. If yes…. Trimming while deploying flaps at the same time and rate, is nice… Safety opportunity…. Nothing worse than flaps accidentally retracting. Fast uncommanded retractions can be extra hazardous, as the stall speed may exceed the current airspeed without warning! (Hand slips off the handle, position lock not engaged) Split deployment… is there a way that the flaps can accidentally deploy or not retract on one side and not the other? A few minutes during the transition training should cover how best to use the flaps, trim, and what to avoid during slow flight. 😃

[@ascherlafayette8572]

Sees like high drag flaps would be desireable on an airframe this light and streamlined, it's always good to be able to get down when you want to

[@minorlion1327]

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

[@brianb-p6586]

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.

[@kizzjd9578]

What do you call the flaps on a commercial passenger airliner where the whole flap moves like 1m backwards and down?

[@daviddavids2884]

7:02

[@kizzjd9578]

@@daviddavids2884 so which one

[@TheBumpking]

Basically, these are (multi-)slotted fowler flaps, a combinaison of slotted flaps and fower flaps (the two types of flaps see on the left of the board).

[@Dilbert-o5k]

​@@TheBumpkingright of the board?

[@TheBumpking]

@@Dilbert-o5k yes right, my bad

[@confusingdot]

I really know nothing, but I have a question about how difficult or more efficient a design would be that curved the flap rather than created a pivot point. My layman side of me thinks that the design wouldn't be too difficult to create.

[@DarkAeroInc]

We have experimented with a “compliant” type hinge where the skin bends rather than using actual hinges. It can be made to work but it makes service difficult/impossible because the control surface is an integral part of the fixed wing structure. We tabled that hinge design but the next iteration would be a compliant hinge that can detach for service.

[@confusingdot]

@@DarkAeroIncThat sounds really cool to be able to see. I could see the compliant mechanism needing more complicated or heavier materials.

[@brianb-p6586]

@@confusingdot the compliant system would be really interesting, but in addition to material issues it could also require higher actuation force.

[@confusingdot]

@@brianb-p6586 Thanks. i can see it being a lot more force needed for the whole part to be compliant. I wonder if only a small compliant mechanism could be added just for the gap in their current design that would help smooth the transition.

[@rudyberkvens-be]

So best L/D is the criterium to choose for it. But typically you want more drag during landing so you need an additional system to achieve this?

[@daviddavids2884]

no, more drag is not wanted. lift always comes with a drag 'penalty'. thus, flaps ALWAYS make 'extra' DRAG, along with extra lift. and, during landing, correct throttle management - for the extra drag - becomes a very big deal.

[@brianb-p6586]

The DarkAero has a split rudder design that works as a speed brake (adding drag) if both rudder pedals are pushed at the same time.

[@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.

[@ronboe6325]

Thinking out loud here: Wondering a good case could be made to paint the inside of the flaps to protect the skin from UV. Thinking there may be - over time, enough exposure to compromise the structure.

[@DarkAeroInc]

Great question! The exterior skin of the flaps is currently coated with an experimental UV resistant clearcoat we are evaluating. The interior skin could be painted or coated as well for added longevity. The paint configuration we have on the prototype is more for testing so it doesn’t represent what we envision for long term operations.