HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Sep 19, 2013, 08:04 AM
Registered User
EddieWeeks's Avatar
Baton Rouge, LA, USA
Joined Dec 2001
949 Posts
Discussion
Why are VTOL so complicated

NASA and many others continue to make very complex VTOL

This is all you need... A tri-copter

X8 Hover VTOL (0 min 45 sec)
EddieWeeks is offline Find More Posts by EddieWeeks
Reply With Quote
Sign up now
to remove ads between posts
Old Sep 19, 2013, 08:05 AM
Registered User
Joined Oct 2004
2,759 Posts
How do you handle a failure while in an hover? full size planes have to take that into account as well.
Brandano is offline Find More Posts by Brandano
Reply With Quote
Old Sep 19, 2013, 11:02 AM
Registered User
Ran D. St. Clair's Avatar
United States, CA, Sunnyvale
Joined Dec 2006
817 Posts
That's not really a VTOL. OK, so it is literally capable of a vertical take off and landing, so it is literally a VTOL, but when we say VTOL we usually mean that it is capable of forward flight as well. Perhaps what you have there is capable of forward flight, but it just isn't shown in the video. It looks like you may be able to tilt the forward motors, or at least you have provisions to be able to do so.

Your point is somewhat valid though. VTOL on a model scale has become relatively easy. It can be done in many ways using off the shelf components, and the method you propose is entirely viable. It has been done many times. Let's see you do a clean outbound and inbound transition before you call it easy though.

As for full scale, we are also on the cusp of getting there. The enabling technologies are improving rapidly. Many of the issues come down to practical economics. Most missions can be accomplished more cheaply and efficiently without the need of VTOL capability.

A small helicopter is a man carying VTOL and the technology has been around for years, but a host of economic, infrastructure, and legal reasons prevent them from becoming a daily commuter vehicle. Those reasons are slowly dissipating thanks to technology that has little to do with the aircraft itself. Fully autonomous flight control, "Highway in the Sky" type traffic control systems, full scale electric and hybrid power systems, and greatly improved batteries are all enabling technologies that will allow full scale VTOL aircraft to span the gap from possible to practical, but we are still 30 to 50 years away from hailing an airl taxi on your smart phone.

Yes, there are safety concerns as well, but I think those problems are entirely solvable, partly by making the critical components incredibly reliable, and partly by simple redundancy. Various sensors and smart technology will almost always detect problems before they become life threatening, so the combination of all these things will make them very safe.

Perhaps the last and most important requirement for full adoption will be infrastructure. Driving to the airport to fly a personal VTOL makes no sense. Millions of continuous flow runways integrated into the roadways, will eventually allow seamless transition from ground to air transport. In the shorter term, thousands of hellipads will spring up wherever they are needed.

All of this implies that the practical VTOL is not only an aircraft, but is also a car. If you can't get from doorstep to doorstep quickly then what's the point?

Don't expect to fly these vehicles, and you will probably never own one, even if you live long enough to see their wide adoption. They will be fully autonomous and you will be a paying passenger. Initially there will be much concern about flying in something without a pilot, but by 50 years from now driverless cars will be the norm. At some point, driving your own car will be illegal except in special circumstances. A human driver will be considered far too unsafe. Once people get used to that, a pilotless aircraft will be no different.

Air taxis will be too expensive for most people. They will primarily be used by business executives and government officials, or for special occasions, similar to a limo. Only the very rich will have one in their garage.
Ran D. St. Clair is online now Find More Posts by Ran D. St. Clair
Last edited by Ran D. St. Clair; Sep 19, 2013 at 11:12 AM.
Reply With Quote
Old Sep 19, 2013, 12:49 PM
Registered User
Joined Feb 2013
33 Posts
Interesting design. I wish I could build something like that, but I have no idea how I would rotate the motors for forward flight.
NathanCurl is offline Find More Posts by NathanCurl
Reply With Quote
Old Sep 19, 2013, 01:35 PM
Registered User
RCvertt's Avatar
Joined Aug 2007
4,096 Posts
Quote:
Originally Posted by EddieWeeks View Post
...This is all you need... A tri-copter
The wing area and CG isn't in the best place on a tri with swept back wings. The cg is further aft on that sort of flying wing which makes you extend the rear motor back further than I visually like. Also a lot of wing area back there for one motor to combat for pitch. Depends on the mission though. For a quick jump up and down it works good enough.
RCvertt is offline Find More Posts by RCvertt
RCG Plus Member
Latest blog entry: Chupacabra sighting !!!
Reply With Quote
Old Sep 20, 2013, 02:59 PM
Registered User
Ran D. St. Clair's Avatar
United States, CA, Sunnyvale
Joined Dec 2006
817 Posts
After more careful review of the video, I see you do have full tilt capability on all 3 motors. That is all the more impressive on the rear motor which also tilts for yaw. It appears you have all the hardware necessary to make clean transitions. It's also a fairly clean setup, so it should have decent performance when flying on the wing as well. The one problem you will have, and this is not meant as a criticism, is that the low pitch, fixed pitch, props will not allow it to fly especially fast or efficiently on the wing. You may be able to extend your flight duration significantly if you can shut off the two forward motors when in forward flight.

Nice job!
Ran D. St. Clair is online now Find More Posts by Ran D. St. Clair
Reply With Quote
Old Sep 20, 2013, 04:25 PM
Registered User
Joined Oct 2004
2,759 Posts
I wonder if the YAK52 style of constant speed propeller could be adapted to VTOL's.
Here is a picture:

If the speed of the prop increases, the centrifugal force applied to the weight at the blade root causes the blade pitch to increase, while a spring fight this force to keep the pitch low at low torque. The blades are mechanically geared together to ensure they are symmetric. I can see a problem if the prop blades were ever to stall, though. I presume that the range of pitch change is mechanically limited as well
Brandano is offline Find More Posts by Brandano
Reply With Quote
Old Sep 20, 2013, 08:59 PM
Registered User
RCvertt's Avatar
Joined Aug 2007
4,096 Posts
Some ESC's have a governor mode that attempts to keep a constant head speed. Some say it helps with a quadcopter but most people seam to fly without it. Not sure how it helps on a fixed pitch prop.
RCvertt is offline Find More Posts by RCvertt
RCG Plus Member
Latest blog entry: Chupacabra sighting !!!
Reply With Quote
Old Sep 21, 2013, 12:25 AM
Registered User
EddieWeeks's Avatar
Baton Rouge, LA, USA
Joined Dec 2001
949 Posts
Quote:
Originally Posted by Ran D. St. Clair View Post
After more careful review of the video, I see you do have full tilt capability on all 3 motors. That is all the more impressive on the rear motor which also tilts for yaw. It appears you have all the hardware necessary to make clean transitions. It's also a fairly clean setup, so it should have decent performance when flying on the wing as well. The one problem you will have, and this is not meant as a criticism, is that the low pitch, fixed pitch, props will not allow it to fly especially fast or efficiently on the wing. You may be able to extend your flight duration significantly if you can shut off the two forward motors when in forward flight.
Nice job!
Thanks Ran... Your a wise man... This planes job is aerial photography...
As of now I used a tail sitter flying wing with a 15mp camera to take aerial pics.
My biz has grown and I am flying 2-5 times a week... This new plane only needs to
take off vertically and land vertically... each time only in hove for 5-10 sec...

Your right about the props.... but the flight plan for photos is up to 400 feet as fast as possible...
Shut the motors off... take some pics during the glide, then back up.... no high speed or
penetration. So the low pitch props should be fine..

My solid state 8 ch switch does not work.... Will not be able to test transition any time soon..POS... http://www.bpesolutions.com/rcequip.html#anchor426732

Test flight today at low power glide then hover was unremarkable... (good thing... LOL)

Eddie Weeks
EddieWeeks is offline Find More Posts by EddieWeeks
Reply With Quote
Old Sep 21, 2013, 12:30 AM
Registered User
EddieWeeks's Avatar
Baton Rouge, LA, USA
Joined Dec 2001
949 Posts
Quote:
Originally Posted by RCvertt View Post
Some ESC's have a governor mode that attempts to keep a constant head speed. Some say it helps with a quadcopter but most people seam to fly without it. Not sure how it helps on a fixed pitch prop.
I did that years ago with 100cc gas engine and VPP... it works well.. but somewhat heavy
EddieWeeks is offline Find More Posts by EddieWeeks
Reply With Quote
Old Sep 21, 2013, 01:55 AM
Registered User
EddieWeeks's Avatar
Baton Rouge, LA, USA
Joined Dec 2001
949 Posts
Quote:
Originally Posted by RCvertt View Post
The wing area and CG isn't in the best place on a tri with swept back wings. The cg is further aft on that sort of flying wing which makes you extend the rear motor back further than I visually like. Also a lot of wing area back there for one motor to combat for pitch. Depends on the mission though. For a quick jump up and down it works good enough.
I don't understand this post....For forward flight the CG is right where it needs to be... In hover the three motors are right were they need to be... So... whats the problem ?

My experience with multicopters indicate .. you can have different motors, non matching props, different length arms.... It just does not matter... the multicopters fly fine no mater what..

The only issue I see is the prop wash from the front motors causing a pitching moment while the motors are at 45 deg...

Eddie
EddieWeeks is offline Find More Posts by EddieWeeks
Reply With Quote
Old Sep 21, 2013, 11:00 AM
Registered User
Joined Oct 2004
2,759 Posts
In the device I posted the constant speed is the result of the variable pitch, rather than being set by a governor. The theory is that the prop will chase the optimum pitch to make use of all available torque, and keep a better efficiency through a large speed range. I don't know how well this would work on a system where torque changes are quick and frequent, like in a multicopter.
Brandano is offline Find More Posts by Brandano
Reply With Quote
Old Sep 21, 2013, 02:09 PM
Registered User
RCvertt's Avatar
Joined Aug 2007
4,096 Posts
Quote:
Originally Posted by EddieWeeks View Post
...My experience with multicopters indicate .. you can have different motors, non matching props, different length arms.... It just does not matter... the multicopters fly fine no mater what..

The only issue I see is the prop wash from the front motors causing a pitching moment while the motors are at 45 deg...
Multirotors have gotten more stable than the old AeroQuad I used three years ago so it may be worth trying again. I recall the CG of the two aircraft not lining up so it caused some hover stability issues back then.

The unwanted pitch at 45 degrees can be handled with corrective power from the back motor.
RCvertt is offline Find More Posts by RCvertt
RCG Plus Member
Last edited by RCvertt; Sep 21, 2013 at 02:16 PM.
Reply With Quote
Old Sep 21, 2013, 02:15 PM
Registered User
RCvertt's Avatar
Joined Aug 2007
4,096 Posts
Quote:
Originally Posted by Brandano View Post
In the device I posted the constant speed is the result of the variable pitch, rather than being set by a governor...
If the system needs weighted prop tips and other added mechanical complexity, it might be D.O.A. At least until we get some high powered zero point batteries. Sounds like it's worth testing though.
RCvertt is offline Find More Posts by RCvertt
RCG Plus Member
Last edited by RCvertt; Sep 21, 2013 at 02:46 PM.
Reply With Quote
Old Sep 22, 2013, 04:08 PM
Registered User
Ran D. St. Clair's Avatar
United States, CA, Sunnyvale
Joined Dec 2006
817 Posts
Quote:
Originally Posted by EddieWeeks View Post
My solid state 8 ch switch does not work.... Will not be able to test transition any time soon..POS... http://www.bpesolutions.com/rcequip.html#anchor426732Eddie Weeks
You should look into the OpenAero2 code for the KK2 controller being discussed in a nearby thread. It might just solve your transition problems very nicely.
Ran D. St. Clair is online now Find More Posts by Ran D. St. Clair
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Help! Why are DLGs so expensive and where can I get a Beginner DLG benjamin presten Hand Launch 114 Mar 18, 2013 08:39 PM
Discussion Why are people so quick to buy in to the divisiveness? Kcal Life, The Universe, and Politics 41 Mar 06, 2013 08:38 PM
Discussion Why are there so many functioning VTOLs now? NighthawkF-117 VTOLs 10 Jan 14, 2011 01:14 PM
Discussion Why do things have to get so complicated? AustinTatious Life, The Universe, and Politics 33 Jun 08, 2009 05:05 AM
Which Fuel - Why's this always so complicated?? seagull2200 Fuel Plane Talk 11 Nov 23, 2005 02:41 AM