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Old Mar 05, 2012, 11:48 AM
Watt Waster
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Joined Oct 2010
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Gift Cards and ... Ducted Propeller

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Originally Posted by ExperimentalAir View Post
... put out little business card holders full of gift cards, usually just in front of the register, near the entrance, or at the hostess stand. ... Once you know what to look you will surely find them and the place will be happy to have the repeat customer As for the ducted propeller, it's a neat idea. I believe the physics of that arrangement are a little complicated, like the tip-to-duct clearance being important. It would be cool to try though.
Wal-mart and other chains have gift cards at all the registers and it doesn't seem to matter how much $ you put on them (wife tells me the lower limit is $5). Around Xmas time, and other holidays, to include birthdays, they expect people to get them for cash gift giving since they fit easily into an envelop. I don't mail them since anyone how gets their hands on it would have free cash to spend. What I do instead is get two or more every time I go to the store and put $5-20 on them. If I have four or five when I visit the gas pumps at Sam's, I can use up a few and have them for the next RC project. If I go to a register in the store and notice a few in the trash can, I ask for them. Since my wife works at a store with gift cards, she brings me home the spent ones from customers. I bet I have near 200 already and she normally brings home a few more every other day. I use them like a puddy knife, motor mount (doubled), control horns, and all sorts of things. Very useful and so cheap I can mix epoxy and just toss the mixer I cut from one of the cards.

As to ducted, or inducted propellers concepts, it is difficult to get an efficient thrust from just about any set up you can imagine. If you are making a cartoon style flyer with an exaggerated fuselage of a jet design, and can keep the ready-to-fly weight in the feather weight category, a high rpm (kV) motor and small propeller might product enough thrust. Most folks find it best to put the propeller just outside the tube in the rear as a pusher, but the best propeller is often too long to fit inside, or near the tube/fuselage. Sparks and others has been experimenting with ducted and inducted propeller cartoon jets, with mixed results. The fans are the better way to go, but outside the objectives of the experiments. Oddly enough, when using a 3 or 4 bladed propeller, they often didn't do as well producing more thrust than a 2 bladed propeller as an inducted configuration.
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Last edited by Tsavah; Mar 05, 2012 at 11:52 AM. Reason: spelling ...
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Old Mar 06, 2012, 10:12 AM
Ed @ Experimental Airlines
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United States, AZ, Phoenix
Joined Sep 2011
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Cygnus uav

Here is the most radical design so far for me, using all the foamboard techniques described here. The Cygnus is a twin-fuselage, twin-motor pusher canard designed to carry a detachable payload pod under the canard that will allow good unobstructed view forward, back, and sideways for cameras and instruments. She still needs a couple of tweaks and much better landing gear, but it does fly, and looks weird as hoped!

CYGNUS Foamboard UAV (9 min 14 sec)
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Old Mar 06, 2012, 10:34 AM
Smashes Things
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Montpelier, VA
Joined Feb 2005
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Nice Cygnus Ed. Why not put the rudders up on the canard? It would look like a plane flying backwards!
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Old Mar 06, 2012, 12:01 PM
Watt Waster
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Joined Oct 2010
1,833 Posts
Wide Cord vs Thin

It does appear you prefer a thin cord wing over a wide. The thin cord wing seems to give a "glider" look, where as a wide cord wing might look stubby. I suspect the long wing is easier to determine various factors since most gliders use the same design, but are there any disadvantages to a wing that is not as long, but is wider? Off hand I cannot think of any real disadvantages to using a wider corded wing that is not as long.
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Old Mar 06, 2012, 01:25 PM
Out the Window
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United States, FL, Alachua
Joined Jul 2004
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Quote:
Originally Posted by Tsavah View Post
It does appear you prefer a thin cord wing over a wide. The thin cord wing seems to give a "glider" look, where as a wide cord wing might look stubby. I suspect the long wing is easier to determine various factors since most gliders use the same design, but are there any disadvantages to a wing that is not as long, but is wider? Off hand I cannot think of any real disadvantages to using a wider corded wing that is not as long.
He is probably using a 9" cord because of the size of the dollar tree foam. I really like the looks of the Axon, it is a interesting design and flys well. I was wondering about putting a wing with a wider cord and wider ailerons on it. I have been trying to build a airplane that will roll well and was thinking that a shorter wing would roll eaiser/quicker.

I built a Russ40 Trainer airplane that is a great design, but I could not get mine to roll....it would do everything else. Russ could make his roll well, but he is probably a better flyer than I am....well not probably...he is! Anyway I designed a wing with the same sq. inches but shorter and a wider cord/ailerons. I also took out the polyheadral. It did roll better, but was less stable. Everything makes a difference in how an airplane flys, I just need to know more about these differences. I have the greatest success when I build to plans, but am always wondering "what if"!

It would be interesting to hear what Ed has to say on the subject.

Ray
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Old Mar 06, 2012, 08:39 PM
NKK for short...
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United States, IN, Mitchell
Joined Oct 2010
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Quote:
Originally Posted by Tsavah View Post
It does appear you prefer a thin cord wing over a wide. The thin cord wing seems to give a "glider" look, where as a wide cord wing might look stubby. I suspect the long wing is easier to determine various factors since most gliders use the same design, but are there any disadvantages to a wing that is not as long, but is wider? Off hand I cannot think of any real disadvantages to using a wider corded wing that is not as long.
The deeper (wider, as you put it) the chord is, the more drag the wing creates, which shortens the glide path among other things. It also takes more power to get the same speed.

So for maximum efficiency you want a bigger wing span with a thinner chord.
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Old Mar 07, 2012, 07:14 AM
Ed @ Experimental Airlines
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Joined Sep 2011
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It's a complicated subject, but yes I do generally prefer a relatively higher aspect ratio (shorter chord) wings for lift efficiency. A longer span wing imparting a smaller downward velocity change (lift) on a larger volume of air creates less induced drag than a short wing imparting a large downward velocity change on a small volume of air. This is all highly dependent on individual design needs.

But like Ray said, another very important underlying reason has a lot to do with the materials I like to use. Using the integral control surface technique and 20" wide Readi-Board, the maximum practical total chord for a 30" wing section is 10" = (8" upper surface + 8" upper surface + 2" for camber and leading edge radius + 2" control surface).

I use almost exclusively two main wing designs:

#1
5" airfoil +1 1/2" control surface = 6 1/2" total chord
two thickness formers inside wing
13% wing thickness ratio
half-length spar usually OK
structurally sound, good efficiency and stall characteristics
provides enough scrap material from one foamboard piece to make formers
aspect ratio 10:1 for a two-section wing (medium a.r.), 5:1 for single section (low a.r.)

#2
7" airfoil + 2" control surface = 9" total chord
three thickness formers inside wing
11% wing thickness ratio
truly needs a strong full-length spar for multiple sections
great heavy lifting, OK stall characteristics
need more foamboard for formers
aspect ratio 6.7:1 for a two-wing section (low a.r.), 10:1 for three-section)

Now, I ain't no engineer, and a lot of this is subjective experience being an RC builder and flyer, and private pilot. A lot of it comes down to my personal confidence in knowing if I use such and such a chord and number of formers I'll get a wing like this or that each time.

BUT there are a lot of very smart and creative guys out there and I sincerely hope they will take liberties with the technique and try all sorts of other wing shapes, aspect ratios, thicknesses, and other improvements. Hopefully we can keep it fun and exciting enough to keep scratchbuilding alive even when you can buy a RTF plane for $20.
Ed
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Last edited by ExperimentalAir; Mar 07, 2012 at 09:19 AM.
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Old Mar 07, 2012, 07:22 AM
Ed @ Experimental Airlines
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United States, AZ, Phoenix
Joined Sep 2011
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Time to celebrate - after 70,000 views, I got my first "thumbs down" on YouTube, from somebody in Qatar. How random is that?!

Still raking in the 3.3% female viewership though! Ladies just love the foamboard. Or maybe that's just the standard error rate for guys mistakenly registering as girls.
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Old Mar 07, 2012, 11:28 AM
Long Range FPV'er
Joined Feb 2009
573 Posts
Polyhedral in Armin wing... How?

Ed,

Do you know of a technique to put Polyhedral/Dihedral in the Armin wing??


Thanks
Michael
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Last edited by Mykro; Mar 07, 2012 at 11:34 AM.
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Old Mar 07, 2012, 11:45 AM
Ichy to Build and Fly.
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United States, FL, Davie
Joined Feb 2011
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Ed,

Thank you for excellent ideas and costs unbelievable to make.

Here is my "Boxer" as my 6 year old calls it .. and it is one of the most amazing planes to fly ...

Thanks
- Mosaic
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Old Mar 07, 2012, 01:51 PM
Space Coast USA
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Quote:
Originally Posted by Mykro View Post
Ed,

Do you know of a technique to put Polyhedral/Dihedral in the Armin wing??


Thanks
Michael
While waiting for Ed, let me make a suggestion.

Make the main wing and cut it in where you want the dihedral or make a separate dihedral section. Sand or cut the proper dihedral angle into the mating edges and do one of two things.
#1 - Glue a piece of foam over the cutoff portion to close the wing opening. Do the same on the other side. Then trim to match the airfoil and glue them together. Or, cutout plywood dihedral spars to fit on each side of the main spar and insert into each wing piece. This will provide the correct dihedral and strengthen the joint. Epoxy all together.

To provide additional strength if needed, cover about 1" on each side with newspaper and attach with 50/50 water-elmers glue.
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Old Mar 07, 2012, 03:32 PM
addicted to the sound ehhhhhhh
Joined Dec 2011
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I love this thread! Just purchased 6$ of foam board at dollar tree some new razors and 20$ worth of colored tape. Where can i find scrap angle aluminum?
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Old Mar 07, 2012, 06:55 PM
Space Coast USA
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Space Coast
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Quote:
Originally Posted by englanito View Post
I love this thread! Just purchased 6$ of foam board at dollar tree some new razors and 20$ worth of colored tape. Where can i find scrap angle aluminum?
License plates.
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Old Mar 07, 2012, 08:53 PM
Smashes Things
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Montpelier, VA
Joined Feb 2005
2,400 Posts
Higher Drag Wings vs. Higher Efficiency

I appreciate Ex Air's comments about his choice in wing. And I have 7 inch chord 60 inch wing that I am flying and having a really fun time with it.

But, the area that I fly in is about 300 x 1000 feet, and then tall trees and houses on the sides. And today the wind is gusting 0-18 mph. In this environment I have a difficult time with a high efficiency wing.

Please give me feedback on this and tell me if it makes sense.

Here is what I am feeling. With the high efficiency wing it wants to make longer lines, and when the wind is gusty and I have a light plane like these I sometimes have some very difficult turns when the wind dies and I am suddenly stalling in a turn and have to throttle up to avoid the dive and I end up flying fairly high up and fast to avoid the problems.

But if I had a higher drag wing with the same lift I would be giving it more throttle at a slower airspeed. Then when the wind direction changes, the plane will respond much more quickly by itself (it has a higher prop push happening) and I won't experience the same tip stalls due to variable winds.

Said another way, the plane will more easily keep a constant airspeed when the prop thrust is higher because when the airspeed drops it will accelerate more quickly and when the airspeed is higher the drag will slow it down.

So, I am thinking about going to, not only a higher chord and less span, but perhaps a biplane config to increase drag while maintaining lift.

Does that make sense to anyone but me?
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Last edited by RCTyp; Mar 07, 2012 at 08:57 PM. Reason: lift instead of life
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Old Mar 08, 2012, 12:14 AM
addicted to the sound ehhhhhhh
Joined Dec 2011
138 Posts
I probably missed it but what size cord wing did you use for your noob tube?
5" , 6" or 7"
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