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Old Feb 19, 2013, 01:45 PM
Looking for the perfect heli
Morton, IL
Joined Jan 2005
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Fantastic.
As I begin considering a parts list for the initial build, do you guys know of a source for ducted props, or will something need to be fabricated? I have a radio already (DX6i) but will need literally everything else. Any and all suggestions greatly welcome. I do prefer as much gyro assistance as possible.
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Old Feb 19, 2013, 02:49 PM
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leadfeather's Avatar
Joined May 2006
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Quote:
Originally Posted by Michael_Blue View Post
Fantastic.
As I begin considering a parts list for the initial build, do you guys know of a source for ducted props, or will something need to be fabricated? I have a radio already (DX6i) but will need literally everything else. Any and all suggestions greatly welcome. I do prefer as much gyro assistance as possible.
For most of the electronics (motor, esc, battery , prop, fcb) , look at the quadcopter builds. Lots of recommendations there; just pick the size you want to go with.

You can buy counter rotating props in many sizes. You'll probably have to make your own foam rings for the ducts.

I recommend using epp for the fuselage. Much tougher than other foams.

For stabilization, the KK board is probably the simplest to use. However the Wii based boards require a lot of computer work to get going, but offer many options and choices. The information for the Wii and KK is in the multicopter electronics forum.
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Old Feb 19, 2013, 03:21 PM
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Buy the props with a finer pitch and a greater diameter than what you need for the duct, and trim the tips so that they are as flush to the duct as possible
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Old Feb 19, 2013, 03:46 PM
Looking for the perfect heli
Morton, IL
Joined Jan 2005
119 Posts
Will do.

I'll be researching different duct ring designs and their purposes if anyone has input there. Found a couple suppliers for EPP, looking at the KK2.0 board (looks incredible, nice and cheap, too), and will definitely be trimming-down the props.

I will need available channels for the tilt function, and any changes that need to made to the mix while in that position would have to be assigned to a "mode" switch, hopefully the KK2.0 can achieve this.
There may be one more channel needed for retracting gear and/or folding ducts (more on this later).

If anyone has experience in programming anything like this and would like to partner up when I get to that point, I'm definitely open to collaboration.

I'm very encouraged by and thankful for the incredibly helpful and friendly responses!

Thanks!
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Old Feb 19, 2013, 10:04 PM
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Just so you have been fairly warned... Ducted props are a huge pain in the (body part of your choice). In theory they can double the lift, but in practice you will be lucky to get enough extra lift to make up for the weight they add. They are also very delicate and are constantly getting chewed up by the prop. They don't protect the prop, they just get pushed into the prop. For maximum efficiency you want a minimum prop tip gap, but unless you have exceptional engineering and building skills you had better have at least 1/4" clearance. Do yourself a huge favor. Get your design working without the ducts and add them later if you are still inclined. By the way, the X-22 was never very fast. Those big ducts have a huge amount of wetted area and make for tons of drag. Also, when vertical, those ducts present a huge amount of sail area. Your ability to penetrate even a modest wind when in hover mode will be severely limited. Dump the ducts and use a slightly larger props and you will gain benefits in every direction. Mostly you will improve your chances of getting airborne, having some fun, and learning some things before your money and dedication run out.
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Old Feb 19, 2013, 10:32 PM
Looking for the perfect heli
Morton, IL
Joined Jan 2005
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I consider myself fairly warned.
Actually, I really appreciate the insight. While I don't intend to use ducting as deep as on the X22 and hope that shallow ducting has fewer of the negative aspects you mentioned, I am fairly committed to the safety aspect and added efficiency (however small) gained by the design. I do understand that if anything bumps them there is a real chance of them getting pushed into the prop, and this is a concern on the smaller scale model but an issue of great importance on the larger (and full) scale prototypes, moving forward. At this point the intent is to attempt to make them from a strong enough material to greatly limit the possibility. In RC scale, machined billet aluminum may be enough. Larger scales would require something more like a carbon composite or possibly titanium (if the cost isn't too prohibitive). Regardless, it is an excellent point.
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Old Feb 20, 2013, 01:25 AM
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Austria
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Quote:
Originally Posted by Michael_Blue View Post
I consider myself fairly warned.
Actually, I really appreciate the insight. While I don't intend to use ducting as deep as on the X22 and hope that shallow ducting has fewer of the negative aspects you mentioned, I am fairly committed to the safety aspect and added efficiency (however small) gained by the design. I do understand that if anything bumps them there is a real chance of them getting pushed into the prop, and this is a concern on the smaller scale model but an issue of great importance on the larger (and full) scale prototypes, moving forward. At this point the intent is to attempt to make them from a strong enough material to greatly limit the possibility. In RC scale, machined billet aluminum may be enough. Larger scales would require something more like a carbon composite or possibly titanium (if the cost isn't too prohibitive). Regardless, it is an excellent point.
Hi Michael,

Have a look here: http://www.rcgroups.com/forums/showp...14&postcount=3

However, I agree with Ran D.s above statement!

Rgds Michael
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Old Feb 20, 2013, 07:54 AM
Looking for the perfect heli
Morton, IL
Joined Jan 2005
119 Posts
Wow, thanks!
So you had these 3D printed? Pretty cool! If I had that tech available, I'd be all over it. Unfortunately, I'll likely have to CAD something up and have it machined, regardless of material. How far have you gotten on these, and are you still working on it?
Funny, as soon as you guys were talking about variable geometry nacelles, I was wondering about something like an air-bladder. Looks like that's pretty similar to the patent you found. It would be a pain to implement, but fun to think about.
Thanks!
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Old Feb 20, 2013, 10:56 AM
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here's the way I'd go about it: build a ring out of plywood or laminating several layers of pretty stiff balsa wood with epoxy, with the same diameter as the ducted prop and with spokes supporting a central motor mount. Then attach to this ring blocks of stiff foam to cover the distance between the motor mount and the prop disk. Laminate another few layers of balsa to match the prop disk, then more foam for the bellmouth and for the rear portion of the duct. Rough it up to shape manually, then spin the entire thing around the motor mount and carefully sand it to shape, possibly using some dies to check the shape as I go. The end result should be light enough and capable of surviving a few bumps Probably with some refinement is even possible to hollow out most of the foam while the shape is built up.
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Old Feb 20, 2013, 11:09 AM
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United States, CA, Carlsbad
Joined May 2011
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Quote:
Originally Posted by Ran D. St. Clair View Post
Just so you have been fairly warned... Ducted props are a huge pain in the (body part of your choice). In theory they can double the lift, but in practice you will be lucky to get enough extra lift to make up for the weight they add. They are also very delicate and are constantly getting chewed up by the prop. They don't protect the prop, they just get pushed into the prop. For maximum efficiency you want a minimum prop tip gap, but unless you have exceptional engineering and building skills you had better have at least 1/4" clearance. Do yourself a huge favor. Get your design working without the ducts and add them later if you are still inclined. By the way, the X-22 was never very fast. Those big ducts have a huge amount of wetted area and make for tons of drag. Also, when vertical, those ducts present a huge amount of sail area. Your ability to penetrate even a modest wind when in hover mode will be severely limited. Dump the ducts and use a slightly larger props and you will gain benefits in every direction. Mostly you will improve your chances of getting airborne, having some fun, and learning some things before your money and dedication run out.
I agree with this as well. One misconception as well is that efficiency is what gives you longer flight times. A less efficient aircraft with better disk loading can have longer flight times than a more efficient aircraft with worse disk loading.
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Old Feb 21, 2013, 05:01 PM
Looking for the perfect heli
Morton, IL
Joined Jan 2005
119 Posts
Good to know. Any idea on how that scales up? Is there a way to measure or design for this property? Thanks!

Just for more info, as there are a ton of VTOL designs out there...This isn't going to be a plane converted to VTOL or a heli converted to FF flight. The design is completely a hybrid VTOL craft from the beginning. The props/fans will be mounted high and slightly outboard of the body for stability, but will tilt from different points, staggering them when in "fast hover", etc.
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Old Feb 21, 2013, 05:28 PM
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Being high or low makes no difference at all to stability. The plane will be unstable no matter what you do, you can at best dampen the tendency to depart with gyros. On some setups hawing the nacelle tilt point some distance from the CG helps with control effectiveness, but it never increases stability. In this setup you shouldn't be too concerned with the vertical position of the CG, but keeping the rotors/fans high will help minimizing ground interferences, and will protect them somewhat when close to the ground.
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Old Feb 22, 2013, 08:35 AM
Looking for the perfect heli
Morton, IL
Joined Jan 2005
119 Posts
Interesting, that's new to me. I'd like to learn a bit more about it.
As I look around at other designs, I see some that look like they should be pretty unstable, or easy to destabilize with a sudden gust or weight transfer. Some have just 2 fans, I saw a design that had 1 fan, directly in the middle bottom of a small craft. I can't imagine how to keep that upright.



At least it will protect the fans some, being mounted up higher.
Thanks!
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Old Feb 22, 2013, 10:19 AM
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A vtol plane does not hang by the prop hub. It sits on a column of air that tilts with it. Unless you have a system like a fully articulated helicopter rotor or some form of active electronic correction there is no way to make a vtol plane stable. Ok, there are ways, but all seriously limit the flight envelope, like having a large lateral area higher up than the CG so that any sideways movement will tend to straighten the plane.
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Old Feb 22, 2013, 12:16 PM
Looking for the perfect heli
Morton, IL
Joined Jan 2005
119 Posts
OK, good to know, thanks!
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