More on ducted propeller systems

By popular request, a video that explains the strange effect which helped scuttle several military flying craft of the 1950s and 1960s.
The Hiller Flying Platform was a great idea but one of the factors which contributed to its failure was the fact that the self-stabilizing effect of the duct lip made it simply too stable and thus, too slow.
Whether this effect played any part in the failure of the Avrocar or the SoloTrek is up for debate.
Hope you enjoyed the video.

[@FidoFerrari]

"I'm so bad at drawing, I can't even draw the curtains on a cold night".

[@fredpinczuk7352]

My grade 9 draft teacher (yes, before CAD, we had draft classes) worked on the Avro project. And one small correction, the craft used three jet turbines, not one. He actually showed original blue prints of the prototype.

[@minkorrh]

Too cool. A Canadian low point that was, F you Diefendumbass. We presently have another PM just like that idiot.

[@bobert4him]

I'm a hovercraft (ground effect vehicle) enthusiast. I've always been mystified as to why the flying platform never succeeded. Thank you for this explanation. Please know that ducted fans are extremely popular among hovercraft designers as horizontal thrust fans. They provide a framework for protective screening that prevents fingers or large objects from contacting the propeller blades as well as the superior performance.

[@KuraIthys]

Still doesn't explain why a multi-engine design never arose. Rather than trying to redirect the thrust of the lifting fan, why aren't there additional fans mounted at a 90 degree angle solely to produce forward motion? Seems a rather self-evident solution if rotating the engines proves to be a problem...

[@rosebarnes9625]

@@KuraIthys you are still going to have the unbalance to deal with. The first gyrocopters had the same problem.... would accelerate down the runway until takeoff, then lift up and immediately tip over to upside down because of the difference in lift caused by the difference in air speed between the side of the rotor that was advancing and the side that was retreating. Helicopters solved the problem by changing the pitch of the rotor as it went around using a "swash plate", gyrocopters solved it much simpler by simply allowing the rotor blade to "teeter" back and forth so the advancing blade rises as it moves forward then descends as it retreats on the other side of the craft.

[@DJDevine]

I love the way you communicate information, you give us the facts and examples with a little tongue and cheek fluidly. Always gives me a smile... Cheers

[@ColinRichardson]

Perfect. I wanted to make a floating sign that didn't move very fast... Sounds like the self stabling is exactly what I need.

[@therealgaragegirls]

Love your presentations and your personality. You make such complicated subjects so easy to understand.

[@cobracar1]

Thanks for your videos. I appreciate your effort in making them. They are well planned and thought out for easy understanding.

[@mickthebass6086]

Brilliant.!! Thanks for sharing Bruce, It was so interesting, educational and humorous. I look forward to your findings using the ducts on a quadcopter. Keep up the good work..

[@analog56x]

Thank you for sharing your knowledge Bruce!

[@ficosk8]

Super awesome! Thank you and Best regards from Bavaria!

[@jp-um2fr]

I have just gone back to electronics as a hobby after a 51 year break. I was rather shocked to find that any mention of fans for cooling is almost taboo. I like fans. Heat governs the life of an electronic component. However the fans that are used for PC's, power supples and servers etc. are ducted but have large tip clearances, any thing up to 3mm on a 60mm dia fan. It would cost no more to make this gap 1mm. Maybe they should watch your viseos. Thanks for confirming what I had already guessed, it's just logic. I'm subscribing - great channel

[@ChiliConCarnage]

Love your videos Bruce. Thanks for explaining things in such an easy to understand way.

[@sunshine7453]

Great job of explaining a complex system in a simple manner. Your graphics are good! Thanks!

[@farmertony4504]

This is the 4th video of yours I've watched. I LOVE finding great new teachers with YEARS of content just waiting for me :)

[@Stratobrick]

I really appreciate your knowledge and the clear way you share it.

[@HiTechDiver]

Excellent video and explanation.

[@cvetoslavgergov305]

Thank you so much for those videos and for the time and effort put into them.

[@bgauweiler]

Bruce, Did you ever record a video of the thrust stand performance of a ducted vs. unducted propeller?

[@ferrarikingdom]

if you are still interested there is a German bloke that did exactly this

[@davemwangi05]

@@ferrarikingdom who is he ? Links? IT seems this man did not do it.

[@ferrarikingdom]

@@davemwangi05 kzbin.info/www/bejne/noG4h6WIps2sg80

[@Ritefita]

this guy tried, but didn't get it yet kzbin.info/www/bejne/h5TGg5Wpj7uaZ7s

[@tommee10533]

A good explaiination how ducts work. Thanks for posting!!

[@TheRCAddict]

Great video Bruce :) Whiteboard videos are awesome and 100X better than school and more informative!

[@sebastianmort7694]

Absolutely fascinating...Thank you again.

[@ducpao]

Thanks for the very helpful explanation!

[@dinax51]

Nicely explained, thanks Bruce.

[@GimbalGuy]

Very, very informative video. Thanks for the great work!!!

[@harryguy76]

Have you done the test of ducted prop thrust vs non ducted prop thrust...very interested in the results.

[@HighFlight2k2]

Very interesting. Thank you Bruce.

[@RC.Aviators]

very informative and easily explained. keep up the good work bruce... just love your videos...

[@garthfpvtv]

Thanks for taking the time to do this Bruce. Really interesting.

[@qntt2002]

Rally interesting and inspiring. Thank you! More of the same please!

[@sganzerlag]

Thanks for the video! It was very instructional and entertaining.

[@jamesthomson1017]

This is awesome yet simple information. Thanks

[@KraussEMUS1]

Very important information! Thank you!

[@fuyingbro]

Excellent explanation of these effects on movement on ducted systems. Well done sir.

[@mertlale6952]

Thank you very much for this video. This video will be very useful for our model satellite team. If we manage to do it it is basically free stability and thrust.

[@DrDiff952]

Thanks Bruce. I am so curious to see how your ducts work out. Especially on a miniquad

[@DJignyte]

Great stuff, cheers for your work!

[@allant9432]

Very interesting bruce,i cant wait to see your video of them in use,i do enjoy your channel

[@PyroChimp75]

great info thanks Bruce!

[@ShotgunAFlyboy]

I'd love to see a sort of "drone trailer" that used one of these ducts and is simply a pull-behind for a quad that provides a huge battery bank.

[@DavidDeLuge]

Another very informative video, Bruce.

[@GG7clips]

I guess it shows I'm not the youngest to admit I like your whiteboard videos the most. Thanks for the explanation, Bruce.

[@willardb123]

The Bell X22, if I recall correctly, resembled a quad with a tail attached to it. Had 4 tilting ducted fans and operated much like the V22 Osprey does today. It was intended to have V/STOL capability but it was much too finicky. It's a shame only two were ever built though, was a beautiful aircraft.

[@gilessteve]

Thanks for posting this interesting video.

[@meljones7066]

Thanks a lot for that Bruce, very interesting.

[@rscofieldfly]

Very interesting video Bruce! I think there might be a similar, although less dramatic effect on bare propellers. Not sure what it is, but if you think of the rotating blades as a disc, the rear blades have air being pushed out towards the blade tip whereas the leading edge of the disc gets air angled in towards the root.

[@Irigoyen4]

Thanks for clearing that up! :)

[@tramsgar]

Thanks a lot, Bruce!

[@Optamizm]

Thanks for that, Bruce!

[@MichaelSHartman]

Thanks for the explanation.

[@pauls5745]

so much budget spending experimenting with this, but they did recoup some r&d when it was directly applied to VTOL craft. thank you for explaining in excellent detail (without math!) how the deign functioned and why it was a fail :)

[@apocraphontripp4728]

Thank you so much for the video. I think Mr Tesla figured this out. Let me get back to you on how to make it work.

[@crackedemerald4930]

5:44 "it was too stable" holy Zephyr

[@GiovanniEsposito5]

Great explanation! Plain and simple aerodynamic lesson that explain why elicopters are and will be much better all round flying crafts that multirotors or any ducted fan configurations...

[@OliFPV]

Awesome explation 👌 thxxx mutch 🍀 and lovely greetings from Germany 😘

[@GBLynden]

Excellent video my friend!

[@DodgeDitchburn]

Nice bit of info and also history stuff =D Cheers Bruce!

[@Grearson]

Very, very interesting. Looking forward to see testing results of thoses ducts on a Miniquad =)

[@dronesovergeorgia2065]

Another great video. I can se this used on larger slow flying video quads.

[@web3developers]

very helpful! thanks so much!

[@chrisaranega7661]

someone need to do a video compilation on all he times you say "brilliant" in your vids! haha loving the vids mate. very informative

[@garycragg1]

Very interesting video. Thanks Bruce keep them coming. ps how did you crack the left lens in your glasses?

[@andybrice2711]

Perhaps the 1960s was a great time to be in aviation. But I'd argue the current era is just as exciting with far more advanced rapid prototyping and simulation tools now available to every hobbyist.

[@pekkert]

Great video..

[@theretrogamer5843]

Great video thank you!

[@gcardinal]

Amazing video!

[@4legdfishman]

Great video! Very educational and easy to understand. Question. What are the effects of a double rotor stack with each rotor turning in opposite directions? With the duct and with out. Thanks!

[@tailspins1]

great job

[@myMotoring]

I think they could have used variable geometry lip to manipulate amount of lift generated on any part of the lip and directing the thrust in that fashion

[@dlwatib]

Like in the previous video, invoking the Bernoulli effect only confuses the issue because it's the vehicle that's moving, not the air. The forward edge of the duct is traveling at the exact same speed as the trailing edge. Since there is no air speed differential between the two surfaces, there can be no Bernoulli effect. But there is a difference in the Coanda effect between the two surfaces. As you point out, it's increased on the leading edge and diminished on the trailing edge. In effect, the trailing edge was stalling because of the steep angle of attack. It was designed to attack in an upward direction, not in a forward direction, so unsurprisingly, it fails to perform well going forward. They could probably make it work by adding a small airfoil above the shroud directing air downward into the trailing half of the duct. An airfoil at that position could be adjusted to have the correct angle of attack and compensate for the loss of the Coanda effect. Of course, with the pilot exposed they don't have many opportunities to reduce drag by creating a slipperier vehicle envelope so the speed is always going to be relatively limited. But they should be able to get it to go as fast as a motorcycle.

[@rokoksekerat88]

Its a very kind of you sir, thanks :)

[@EitriBrokkr]

I wonder what would happen if you could vary sections of the lips, profile

[@crackedemerald4930]

that's a basically how a helicopter works

[@EitriBrokkr]

I was thinking of a bunch interconnected metal flaps like the nozzle of a jet engine, but independently controlled

[@raphaelsilvas2025]

actually I was thinking that maybe have a sort of mesh that slide modified the shape of that round bevel at the rim

[@RealCheesyBread]

It would have been interesting if they had implemented a way to modify parts of the lip. So if the platform was tilting in one direction, then somehow the lop on the opposite side could be changed.

[@Richardicus881]

I thought of this too, although in reverse (make the angle/curve of the lip in the direction you are going change to reduce lift on that side). I think that either way the net result is a loss of lift upon changing the shape, creating a need for larger motors. But I sure hope someone is gonna build a drone based on this idea to find out!

[@eggaweb]

That's what I was about to say :D

[@meateaw]

I've been thinking about that; but, ultimately I think you would end up reducing your total lift too much. The only solution I can really think of is to change to a different source of lift. So maybe a ducted fan on top of a plane. So you transition to an entirely horizontal flight and use a different lifting surface to maintain altitude.

[@GordieGii]

A quad with ducted props should be immune to the effect, as I explained above.

[@GordieGii]

+Peter Avram Like a helicopter? How about a twin prop, one at the front and one at the back. This would be immune to the effect (as I've explained above) front to back but self stabilizing side to side.

[@miguelh.m.m.6911]

You're awesome. Even better than the Discovery chanel. Hope there will be a second video about the antennas.

[@user-tc9uy3fk9o]

Bruce, thanks a lot for your video. It contributed greatly to my understanding of DF Dinamicd. Could you please comment on whether projects on variable coanda lip DF have been completed or are in place?

[@gunner678]

Fascinating!

[@recommit]

Great informative video, thank you Bruce. I was thinking about a successful use of fast, horizontal travel using vertically ducted fans, Hovercraft! Using lateral thrust to propel, they have proven that they can still provide sufficient vertical lift even when enduring horizontal wind forces, I only wonder how much lift they can provide when used in aircraft in the same instance, when a pressure enhancing skirt is not applicable. Will it still provide vertical lift, or will lateral air forces kill lift? If it does however provide lift, then the Martin system may use lateral propulsion?

[@oscarzt1652]

very interesting. a bit of science and history!

[@WIE110]

Nice explanation!

[@budpuppy5657]

Sounds absolutely perfect for a hovercraft

[@BobDiaz123]

It will be interesting to see the operation of Blade's Inductrix Quad. They are positioning it as a beginner's quad. It scheduled to come out in the USA in less than 3 weeks.

[@stevenq4859]

great video

[@protovision2010]

Great vid Bruce, and bonus points for mentioning the AVRO flying car! Recommend watching the entertaining made-for-tv CBC movie 'The Arrow' with Dan Ackroyd

[@Crlarl]

In Winnipeg, we have an Avrocar on display. It is really cool.

[@legacyfound]

Nice presentation Bruce, Thanks heaps! One question though; Did you or anyone ever ty stettin in openable sloths on the duct itself to spoil the effect in the intended direction of travel ?

[@davidriley7659]

It sounds like ducts would be best for stable camera quads used in filming. Also, i wonder if one of these could be used with a vertical propeller for movement, kind of like a PPC

[@Optamizm]

***** This is what I was thinking...

[@sickvic3909]

***** Probably not, airflow is still across duct in one direction tilted or not.

[@owenkilleen]

***** Bruce, do you have an email? I'm going to buy my first quadcopter parts from online, I'd like to run my budget and the list by you. Owen

[@davidriley7659]

owenkilleen I'm not bruce, nor do i care

[@owenkilleen]

***** you tube won't let me post a comment straight in my own comment field. David

[@aronkay5274]

Hey RCModels huge fan! great Vid! Just wondering whats the point of those knobs in the middle of propellars?!

[@SerafinTirado471]

Wow, make a Elec version of that navy duct fan platform using a whole lot of lipo with one big brushless motor. Great for fire dept, Search and rescue, Police, hunters, or recreation. Some time you just need that small jump and leap that ladders or crane can not reach and helicopter are just to big to get into. Like, Two Thumbs up.

[@jurijstorozuk6170]

Good video, thank you.

[@TheTractorsman]

Thank you Professor Bruce, that was very helpful and explains a lot, there is a 4x ducted fan quad on youtube somewhere, i will look and post link if i find it. Cheers,;-)

[@Javiercav]

really nice video, i hope in the future you will make more technical/historical videos of some other topics

[@zachcarrizales5038]

Can you talk about differences between thrust stand tests and dynamic thrust tests (testing angle of incidence and efficiency) when air is moving past it in operating conditions for quadcopters? People judge a lot on static thrusts stands but certain props dont show the same comparable thrust while flying on a quad. Love your stuff

[@danielhowsare778]

Really interested to see how it will perform in practical tests

[@havelockvetinari9395]

Great explanation Bruce. Would the Hiller flying platform or a quad be better if you coupled it with a pusher prop?

[@goriverman]

Thank you for explaining that. As a young boy I bought a flying model called the flying platform

[@chrisb3420]

Super interesting. I wonder if they could have used some sort of air-distruptor fins coordinated with flight attitude to reduce the lift of the lower area thereby allowing it to stay tilted...

[@Elecifun]

Great video. Does the Parrot AR Drone count ?

[@steamboatmodel]

Another good video, but the one of the problems with the Are Car was it would not hover higher than two feet above the ground.

[@MittDinTube]

Very interesting as usual Bruce :) But what if you want the upside of ducted fan, that is reduced turbulence and safety but skip the lip and have a straight edge? You would get less lift then with a lip but you would have less effect of this coanda effect problem you are describing?

[@LesPiecesDuPuzzle]

Hi. Thank you for this very interesting video. It makes me think about turbofans wich are, in my point of view, a mix between a jet engine and a ducted propeler as 80% of the air taken from the intake is not going in the compression chamber but merely propulsed thru an outlet vain and the edge of the turbofan have a shape for generating some coanda effect.

[@mantisengineerteam7300]

Great video :)