Why we designed our own retractable landing gear 

I’m looking forward to seeing the plane in the sky! Who is waiting for the plane presentation on Oshkosh?

Understanding the aero forces is critical. There will be a max airspeed where gear 'freefall' doesn't happen. That'll be part of your ODM. I, like others commenting, also believe the gas strut is not overly sound in terms of reliability. I also concur with a previous comment re unlocking, this needs to be a very robust and simple mechanism. No doubt this is designed with failure modes understood, and likelihood of combined failures etc. but the gas strut sees all the same temp. changes, is exposed, and sees cycles with the gear every time, regardless of when its needed in an emergency. Its preferable to have freefall / emerg. unlock systems designed to not see all that. I am not a fan of the open exposed 'half gear'. I don't think it would take much from tyre and runway detritus or other debris to maybe give that a problem in normal retract or extend, but especially emerg. extend where its only the gas strut and gear mass doing the work. Go look at how dirty a used aeroplane undercarriage bay can be. Be very clear and do many many assessments of the effects of aero loads on retract and extend. I have commented before on this here. Airloads will catch up any backlash, and then the system will catch up, then the airloads catch up, ad nauseam. Wears things out quickly. Gear cycles are greatly affected by this even at low air speeds. What are the target times for up and down cycles? These should be derived from airspeed increase / decrease rates on take off / landing. Again, another set of limits that go into an ODM. I am very impressed by the effort and detail of this design, but do also think that some more failure and wear studies / tests are appropriate particularly with the gear. Good luck and keep working hard! (and feel free to contact me any time (42 years in aircraft design, manuf. and maint. of 330kts, +6-3g aeroplanes). I'd enjoy a good discussion, and would love to help you make sure this becomes the best home build light aeroplane.

The transparency that you guys operate with in this design phase definitely helps engender trust for both your designs and brand. It's great to see you operate like this

Very interesting video. Knowing from experience that gear failures are one of the most common failures you get on complex aircraft, failure mode planning and analysis is always of interest to me. With that in mind...gear switch failures are common. What is the failure mode (i.e. the weak link) should an up or down limit switch fail, and the actuator continues to run - does it stop against a physical limit? Does the clutch let go? What causes the drag links to overextend? I don't see a spring in there anywhere. Also, what actuates the up/down lock mechanism, and what is the override to unlock the gear should that mechanism fail in flight? I always found it fascinating when studying gear systems, that the design is typically "the ability to retract is optional, but the system will move heaven and earth to extend the gear." In that in any given failure mode, the default is to end up with the gear down and locked. Witness hydraulic systems which utilize continuous pressure to keep the gear retracted - loss in pressure for any reason causes the gear to free fall. Things like a mechanical uplock (obviously required in your design due to the actuator) make me nervous unless I know there is something I can do that will absolutely release that lock in the event of some kind of damage and/or failure. With that in mind - is there a blow-down or other emergency extension method if there is a mechanical failure of the actuator gearbox? I'd hate to have a gear up landing because of a sheared/jammed pinion tooth.

Gas springs have a very high failure rate. Is there a higher quality gas spring type you are using for emergency gear lock?

The force being applied on the pinion teeth must be pretty large.

Great work guys to reduce passive weight and make your own solution. However gas struts as a redundant mechanism concern me. You also have no way of checking the gas strut condition after it has been installed, it will always look the same in checks same but how do you know if the preload is still there?

The gas spring idea is good because it will help the motor push the gear down against drag while you are coming in for a landing, and the air will help compress the gas spring working with the motor on the way up after taking off. However gas springs are notorious for leaking, and without feeling it by hand with the plane held off the ground I see no way to check the spring force of it to make sure it's still working. If it were to leak and fail, it would cause the electric motor to have to endure much higher load during normal use, potentially causing that to fail as well. I would want a filling port on it or a strain gage on the mounting bracket or some way to verify they are working as part of the pre-flight

Why did you not use the mechanical advantage of driving the locking strut to move the gear rather than the main arm?

Why not do a simple pneumatic actuation system? Replace the gas strut with a double acting cylinder and make the up lock pneumatically actuated. A 14 gram CO2 bottle with a piercing valve would be your emergency blow down. Engine driven or 12v mini compressor, mechanical valve, and some indicator lights would be all you need.

Looking forward to that nose gear dop test!

Your composites course was a 10! Please do a follow-on course on machining and mold-making. You guys are the best, thank you

Soo...how are you going to ensure that the gas strut seals haven't blown out? I mean, practically, how are you going to pre-flight verify that they'll work? You could replace them at annual or find a rebuildable/rechargeable alternative I suppose.

Very exciting, guys. I wonder if you guys ever went over to Boeing Surplus in Kent near South Center Mall area? It's not there anymore but back in the day you could buy sheets of titanium and nose cones from B-52s and rows of old passenger plane seats from 707s and even older Boeing builds. The 10x10' bin of used drill bits sold by the pound was also great and I still have some of em which were used like twice before the tolerances were shaved down and all are made of cobalt or titanium which i think i got for like 10 bucks for a couple pounds of em! I have a Rand-McNally world map they had in war rooms from WWII and a metal desk that weighs like 2 tons! Its no longer there but you could have likely sourced half those parts right in bins there what an amazing resource that place was

It looks like you have several spur gear reductions in a row. Can you say why you didn't go with a simpler high-reduction-ratio system like a compound cycloidal? These are usually more compact, and are used in industrial robots which require very high torque from very compact gearboxes. That said, I think most RC servos have spur gear reductions as well, and don't use compound cycloidals. Is it a tolerance problem?

So when is the fixed gear version being made? Gas strut for the emergency gear extension? Those things barely work when cold soaked.

I have a boat with a power bimini roof using a very similar actuator. I needed to wire a special fuse that pops and resets the actuators.

Thanks for the update. The aircraft is developing nicely.

Really, all of the most beautiful and sleek and simple aspects of a small plane all into one on this. And lightweight carbon fiber. Two seater. Nice space for cargo. Great engine. Tricycle landing gear. This plane is so awesome.

That landing gear has been a beast for you guy’s. It’s inspiring to see you take on these challenges with such positive innovative persistence. Looking forward to seeing your continued progress!

Thanks for the update, guys. That's really smart and elegant solution! Excellent work, gentlemen.

I love that they are using a neo550 and versa planetary, it's kind of weird to see it in this application.

Thanks for the update. Appreciate the in-depth explanations.

That gearbox looks amazing 🤩 cheers guys! I love this project !!!

Details, details, details. Keep pushing! You're getting closer to first flight!

Another awesome solution to a complex problem. You guys really rock!

I’ve been waiting for this vid!

How do you know if a gas strut for emergency extension goes bad and leaks out all the pressure? How about operation in cold weather?

I'm intrigued that the landing gear retract towards the tail. Given the limited space there really isn't another way, but for emergency gear release, in most planes the gear retract forward so that when they are dropped with gravity they are assisted by drag rather than prevented or the drag resisting the gear dropping. But I like the simple solution

Great review guys! Good to see the progress.

Why did you settle on a compound spur-pass design over a coaxial geartrain like a planetary or harmonic drive? The large exposed spur gear on the main pivot shaft seems risky from a lubrication/contamination perspective. Also, what engineering and environmental factors do you design to on a mechanism like this for an experimental aircraft? I've worked on and designed several mechanisms compliant with NASA STD-5017, curious if there are any equivalent FAA requirements or guidelines you use for things like friction factors, torque margins, or fault tolerance.

Great content guys! And I cannot wait to see your beautiful aircraft up in the sky!!

Excellent presentation style, and really interesting problem solving. Keep up the good work boys!

How much does CG move back when the gears retract?

Extension under failure mode: what about a clock spring type solution around the gear pivot point? Does that place too much stress on the motors? Or too much weight?

Well done ..thank you for sharing

More amazing work guys!

Excellent stuff bro

I look everyday for your videos. Awesome

Would driving the drag link instead of the strut reduce the force required from the actuator? This build series is one of the best on RU-vid. I can’t get enough your detailed explanations. Great work!

Awesome project!! You guys are doing this right!! Make haste slowly!!

The landing gear system is nearly the same movement as a garage door. I would use a garage door spring to deploy the landing gear when unpowered and help fight aero drag. I think both side of the landing gear could be mechanicly linked and have one actuator, there is no point having one side work but not the other in case of failure. Suspension doesn't look like it has much travel.

Very nice work!

Good work lads. Keep it up

I love how much detail you're willing to show. Impressive design, love to see it!

this is such an awesome plane. i want one.

I don’t know how significant this will be but my concern with the retracting configuration is that there will be an aft movement in the centre of gravity when the gear is retracted and a forward movement when the gear is lowered. How much movement will there be, and to what extent will this affect longitudinal static stability, pitch control, and stick forces during take off and landing. I assume that during gear up flight you will want the CoG close to the CoP in order to have light stick forces. I would also be interested to hear more about FAA involvement and certification.

The projects just keeps getting more interesting. Can't wait for the first flight, but a lot of it depends on the performance of the landing gear. Hopefully, the drop tests, taxing, and post flight reveal that you came up a with a good design. I can imagine a few tweaks here and there, but great job regardless.

As I've mentioned before. I've been a aerospace manufacturing engineer for 30 years ( no you tube arm chair warrior here) and I'm just always so impressed with your work, logic and innovations. Pro all the way. You guys work the same way I do, and let me tell ya, its rare. Would love to meet you guys one day. Keep up the fantastic work guys.

You could run a mechanical hand crank line from the cockpit to the landing gear locking arm to get it to lock out incase of electrical failure. The gas strut is going to add to the stress of the actuator by a fair margin.

Looks great guys! Question on the back up gas spring: it’s fully passive as is, would it not be better to have a pneumatic cyl that you can hand pump from the cockpit? Pilots like to be in control. 😂

Great job 👍🏻

Trying to understand why the rear landing gear was engineered to over travel so far passed the natural 90 degrees from horizontal? I worry those shocks may weaken over time and not have the necessary force to push forward to lock the arm in the event of the gear motor failure.

Great design....but, if I may suggest an alternative idea for the Emergency system; The use of the "Emergency compressed gas piston" is going to add a lot of stress on the gear motor, especially when it gets towards the end of the "gear up" cycle for 2 reasons; 1 maximum amount of compression thusly increased pressure 2 loss of aerodynamic advantage. At the beginning of the up cycle w/ all of that aerodynamic force, it's easy for the motor to move gear (even when the piston pushing the gear) but at the top of cycle, you lose the aerodynamic pressure and you're fighting the gas compression- putting a lot of stress on the motor & gear teeth. Not saying the motor can't deal with the forces, just saying the intentionally lightweight components are going to be working in a "max effort" configuration. AN ALTERNATIVE solution might be to pull the gear in an emergency. We understand that the disengaged clutch and the release of the mechanical up lock will allow gear free fall; all we need to do is extend gear pass the point of aerodynamic resistance, right? This is where Emer Proc is crucial; free fall of gear requires speed reduction to X before attempting. At this reduced speed (thus reduced force) the gear could be "pulled" forward by cable or worm gear from the cockpit by manual crank or electric motor. The gas compressed strut is an elegant solution but I fear the added stress on the gear motor and gears might result in a long-term maintenance issue. I love watching your videos, wish I was there! How rewarding it must be to design novel answers for a true 21st Century Aircraft. PS my comment is the result of a 32 year flying career including Army Black Hawks, Turbo props, Regional Jets and retiring (at 55) off the 767, so my approach definitely comes from a pilot's mentality more than an engineers. 🍻

Thats really cool. Just wondering if you could use load sensing on the motors incase your end of travel switch failed the motor would sense over current and stop driving?

Instead of limit switches you should do a Hall Effect sensor on the actuator and use the teeth of the landing gear to determine position. It’d let you show % open and it’d cut to one sensor rather than 2 switches. Less likely to wear over time too.

Amazing. You guys are so smart! Have you considered the fact that the gas struts might fail too? Maybe use two, one on each side for redundancy. (older cars with gas strut assisted hood opening mechanisms commonly fail, this is why I ask)

It’s interesting - it seems like a super high angle of attach for the gear, especially in a flare. Any comment regarding this? Thanks as always guys!

Excellent!

Great video! I do have a question: the gear on the landing leg seems quite exposed, will there be some kind of cover? I can imagine that this could get quite dirty (especially on grass fields). Anything in between the landing-leg gear and the gearbox pinion gear (e.g. small stone, other hard debris stuck in grease) would not only disable the electrical retract/extend but potentially also the emergency extend.

Very cool project, the landing gear design is pretty neat. Would it be an option to incorporate a turboprob engine like a Turbotec TP-R90 in the future? Those modern regenerative turbines are roughly as efficient as piston engines.

All u need is a hand crank and cable for emergency attached a cable and pully to the pivot points and have a hand crank somwhere in the cockpit to use similar to the cessna 310r

If you use a hybrid servo motor, it comes with an encoder does it not, so you just have to program the number revolutions you need the servo to make for the travel required for gear down and gear up. Would this method have reduce weight? I do not think limit switch are that heavy?

good work. to what extent are the cog wheels in the gear box hardened? Did you also consider a worm screw?

IMO hope you're using brushless motors. Brushes in my electric chainsaw have failed twice. What if something on one gear fails?

G,day Riley, River and Keagen from Sydney Australia. The Dark arrow is looking areospace category. Landing gear extend Emergency extension to the down and locked position, (automotive gas struts) they wear out if forced over their design capacity. Example Rear station wagon door. Q1. Will the strut motor and gears place pulling force on the gas strut? 💡😎

Carrying that plane around like it's nothing and hauling around in a uhaul truck hahaha. Crazy how light it is. Love seeing the progression of this project

Nice design 👌

Hi, thanks for the Video! One Question: Do the drag struts have any kind of travel limitation in down locked position? Cause since the gear is actuated through the main strut, the the drag strut may fall out of allignment when the gearbox developes some play from wear. Im sure you already thought of that, but i didnt find the answer in the video!

Will preflight cleaning of the strut gear sector be required? It looks like contamination could be an issue. ?

I wonder if those gas struts will still output the same force required to lock the gear out through the varying temperature ranges it'll see during regular use

Can you set up to use main gear as a speed brake into a partial extension to come down fast? I would still love to see turbocharging for high density altitudes and high altitude cruise.

Cool ideas here but the complexity of the gear design in both manufacturing and operation would be my concern. Not sure about the carbon leg or gas strut in very cold temps. How does electrical/ mechanical failure of the motors, clutches affect emergency lowering? Seems like the suspension shock/strut is quite heavy. Titanium spring leg would probably be lighter and certainly more reliable plus zero maintenance and likely cheaper to produce. Recommend you do the gear drop tests at -40 to see how the carbon reacts. There are also known long term effects on CF strength from moisture, temperature and impact exposure within the matrix.

Please make sure the gas spring fill is accessible with sufficient clearance for regular pressure checks using a shock inflation pressure gauge

What are the odds of the gas spring to be weared out in an emergency event. Should Not be better to user just a regular string?. This should be solved by regular maintenance and be replacement scheduled?

Excellent as always guys, but I’m not quite liking that gas spring idea. I don’t know enough about the entire gear system, but I have built things using gas springs and I know the failure rate of them. Tell more about this spring. Thanks

Wooow is amizing 😮

Stepper motor would be nice to set limits and travel speeds. Like slowing it down when it gets close to travel limit or as it’s latching. Then have limit switches also as a back up.

Great video. You guys seem to be making great progress. May I ask what make of Hydraulic power pack you were looking at initially?

Only thing with gas spring is it's much less effective when it's cold. Why not use something with a reservoir like a high end nitrogen shock? Works for off-road applications. (It's probably a dumb idea, I know. But maybe it's partially not?)

Interesting solution but until now I haven't seen any landing gear drop and reserve energy tests. How this gear will absorb landing impacts? How the gears will reacts to impacts loads? Have you guys calculated and tested the ground loads according to FAR23?

Great video. Can you show some more details on sequencing logic and explain how the landing gear locks are released?

Very cool.

Will there be some rubber boot or housing to prevent the gear from kicking up a pebble into those gears? Great video as always

One question mark the gas strut for emergency extend. They do make custom gas struts for aircraft but it would be expensive. Mfgs don't list prices, only available by quote. Consumer grade struts (pickup tonneau cover) have no quantifiable engineering specs, service life/cycles, etc.

Did you guys buy hull of somewhere cus i swear we have that hull at my university where they are electrifying it

I love your project!!! I have a question why don't you eliminate the bolted bracket that keep the telescopic suspension and embed it on the landing gear frame itself as you will avoid 3 big bolts an a machined part?

At 2.11, why is the lower shock mount not in the same plane as the trailing arm, that bushing does not look like it would allow enough flex for the amount of travel, seems as there will be binding. Anyway awesome stuff, good day

hm. How do you lift the gear from down lock position if it is locked? someone/something should push on a "knee" between drag links, that [knee] also seem to be able going up and down, that makes drag links to be not really a good stabilizer at a rough landing with a strong kick from the front. Actually I would rather use something retracting on that knee instead of a gearbox, because the box has too big lever at the end.

How does this effect the change in CG while landing and taking off?

Very similar to an rc retract with a small motor driving the ststem via pinion and gear. On rhose systems i believe its timed to operate a certain number of seconds to complete a cycle.

If battery and electric engine technology gets lightweight enough would you consider trying to convert this aircraft or make a version of it that uses those systems?

Forgetng amount of space for a second, would having gear pivot forward when retracting make a huge difference in ensuring it can be extended safely no matter way (since you then have both gravity and airflow working to lower gear) or is that a fairly minor thing when considerimg all aspects? From a emergency deployment point of you, wouldn't it be simpler to have a rope/handle in cockpit that you could pull to 1- clutch the motor 2-bring landing gear down to lock ? (or a wheel you turn in cockpit to pull the rope in with enough torque).

I admire your tenacity and patience in designing and building Dark Aero 1. For those of us not blessed with patience - just hurry up!

The CG shift when the gear retracts is concerning to me. Still, a very cool design all the way around. Well done.

Very Forward thinking. I can't help but wonder about the Gear box integrity over time. Given air loads on cycling. Good Luck on the project.

Hey, would you ever make a sale on the courses?

You can also not install the gas spring and the pilot use load factor to push the gear into the lock position.

Great video , thank you, I say limit switches are prone to failure in addition to the hardware overhead, I would recommend to actually add some sensitive current sensors (its already required) to the DC motor to monitor when it reached its limits, I understand that the aerodynamics force resistance might make it a little bit more difficult to decide on when we reached limits, but I am positive it is very doable.

yeah!