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Old Jun 24, 2007, 12:28 AM
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Montag DP's Avatar
United States, GA, Atlanta
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Build Log
"Zenith" EDF - V1 & V2 (page 11)

Hi all,

I started a thread in my blog about a month ago with some ideas to design and build a plane this summer. The plane will be a sort of mini hotliner, but powered by a ducted fan jet above the wing. Here's the link to the blog:

http://www.rcgroups.com/forums/showthread.php?t=686822

Initially, I planned to just design it on paper and cut out the parts by hand. I once tried to scratch-build a plane when I was just starting out (I must have been about 14 at the time), but I had under-performing equipment that I had robbed from my Hobbico Aero Cruiser (which was heavy and underpowered), and I didn't put much prep time into the design. Instead I basically just started cutting wood and came up with something. Needless to say, it didn't work out so well.

After putting some thought into the design and having some exchanges with RCG members who have done scratchbuilds, I found a couple of really good free programs online which will make it possible to design this in CAD and have it laser cut. Bill Stevens of StevensAero offers a laser cutting service, so I will most likely buy the wood from him and also have it cut at his shop.

Link to TurboCAD LE download: click here

EDIT 7/25/2007: It looks like the website that I got this program from is down. I don't know if it's possible to download the trial anywhere else.

EDIT 12/28/2007: The website with the download is back up at http://www.freecad.com/dcd/CAD_Progr...s/index-4.html

For the airfoils, I am using Profili V2. It's not exactly free--the designer asks for a $13.75 registration fee in order to get full functionality--but it is well worth the cost. It has a huge database of preprocessed airfoil polars, most of which you can find here, can compute Reynold's numbers, pressure distributions, preprocess new polars, and compare polars using a variety of criteria. You can also add all sorts of features to your wing ribs automatically, like cutouts for spars and longerons and lightening holes. However, the thing that appealed to me most was the ability to export airfoils as .DXF files, which can be used by CAD software.

Link to Profili V2 download: click here

Anyway, after several years of building planes and helicopters from kits, I decided I would really like to do this one myself. I believe the thing that piqued my interested in EDF hotliners was Erik v. Schaik's thread on the Simprop Liftoff: link. Most of my recent airplanes to this point have been aerobatic planes, and I would like to do something fast for a change.

My plane will be a pod-and-boom type glider, with a thin wing and no dihedral. The plan is to use the Wemotec Microfan mounted on top of the wing, Razor 300 motor, a TP 1320 3S pack, and three servos (2 aileron, 1 elevator). I may add rudder functionality, but for now I will keep it simple and light.

Below are some sketches. I don't have the original one saved anymore, but it was basically the same as the first one below but with the wing farther forward. After doing some preliminary CG estimates, I decided to move the wing back further, and thus the second sketch was created (which is the first below). Finally, I decided to simplify the wing shape and increase the chord a little, represented in the second sketch below.

40" wingspan
28.5" length
5 5/8" chord

Dan
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Last edited by Montag DP; Feb 27, 2008 at 10:47 AM. Reason: Title change
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Old Jun 24, 2007, 12:36 AM
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Fountain Valley, California
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Very cool Dan.
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Old Jun 24, 2007, 12:51 AM
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Montag DP's Avatar
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Thanks, Will.

The next step was to layout some of the design on paper using drafting methods, to get an idea of how the fuselage side will look with the wing and formers located.

I did that just last week. A scanned version of it is attached below. It was done in pencil, but I had to go over it with pen in order for the scanner to see anything. That was done pretty hastily about 2 minutes ago, so the lines aren't all that straight anymore.

I went over the major details in pen. What you don't see are some of the more minor details and also dimensions thrown all over it to help me draw it in CAD.

Tomorrow, I will start highlighting the design process. I have some of the drawings done already, and I will attach screenshots of them. When I am done with the project I will consider distributing the plans as freeware or maybe even selling them if the plane works well. That's a long way away, though.

Oh yeah, anyone have any brilliant names for this thing? Feel free to post them.

Dan
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Old Jun 24, 2007, 05:17 PM
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United States, GA, Atlanta
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Side View

I have actually started drawing up some of the parts, like the fuselage sides, one of the formers, and one of the ribs. If you check my blog you'll see some of those pictures.

However, I think it will be beneficial to have a top and side view of the entire thing, and maybe some of the details highlighted. This way it will be much easier to extract dimensions and draw individual parts in the future.

Today I spent a couple of hours turning my fuselage side and airfoil into a full side view. Tomorrow I will work on the top view. Mounting details for the ducted fan jet will come once I get it (I still need to order the Microfan).

Here are some details of the side view. It's a lot cleaner than the hurried sketch shown above.
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Old Jun 24, 2007, 05:27 PM
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One thing I'd like to say: since I've never designed a plane before, if any of you out there with experience want to jump in and give suggestions, feel free.

Dan
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Old Jun 24, 2007, 07:32 PM
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Midvale, Utah, USA
Joined Mar 2005
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It looks like a great design, but I dont think you would be able to qualify it as a hotliner..... That big ducted fan will slow it down too much. Basically what a hotliner is, is a strong, slippery, sailplane, with a powerful motor that is used ONLY to get it to altitude. At height, the motor is turned off, the folding blades fold, and you DIVE for speed.... with a slippery low drag plane, gravity will give you more speed than any prop/EDF could ever give under power. You will just have too much drag with the EDF up there slowing you down to do what hotliners do....
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Old Jun 24, 2007, 08:26 PM
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Quote:
Originally Posted by dacaur
It looks like a great design, but I dont think you would be able to qualify it as a hotliner..... That big ducted fan will slow it down too much. Basically what a hotliner is, is a strong, slippery, sailplane, with a powerful motor that is used ONLY to get it to altitude. At height, the motor is turned off, the folding blades fold, and you DIVE for speed.... with a slippery low drag plane, gravity will give you more speed than any prop/EDF could ever give under power. You will just have too much drag with the EDF up there slowing you down to do what hotliners do....

You're right, it's not exactly a hotliner. But it would be, more or less, if I went with a direct drive motor and folding prop on the front. I wanted a hotliner-type design, but I also really wanted to use a ducted fan jet motor, so call it what you want.
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Old Jun 25, 2007, 03:45 PM
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foamie dude's Avatar
costa mexico
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looks great so far. do you have plans made for the wing yet?
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Old Jun 25, 2007, 06:36 PM
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Quote:
Originally Posted by Montag DP
One thing I'd like to say: since I've never designed a plane before, if any of you out there with experience want to jump in and give suggestions, feel free.

Dan
my only suggestion would be to drop the fan unit in preference of a prop system... the prop can get you flying as fast with more thrust and less drag when you just want to glide around.
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Old Jun 25, 2007, 11:42 PM
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Montag DP's Avatar
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Quote:
Originally Posted by theKM
my only suggestion would be to drop the fan unit in preference of a prop system... the prop can get you flying as fast with more thrust and less drag when you just want to glide around.
That's true, but everyone and his uncle has a hotliner with a folding prop. Besides, where's the design challenge in bolting a motor to the back of a firewall?

In all honesty, it's not out of the question. I just like the ducted fan jet for the cool factor.

More to come tomorrow, hopefully.
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Old Jun 26, 2007, 06:30 PM
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A little sneak peak at the top...foamie dude, you might be interested.
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Old Jun 26, 2007, 11:22 PM
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What do you guys think about those longerons on the back half of the wing? I'm debating whether or not to keep them. They might be overkill, but then the main spar is pretty close to the leading edge, and I don't want the back half twisting when I cover it...maybe I'll just reduce their width. Decisions, decisions.

Update: One minor change, they are at least getting cut off at the outer rib, instead of extending all the way to the tip.
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Old Jun 27, 2007, 12:14 AM
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The torsional strength of most open construction wings isn't enough to prevent warps from covering... the best you can do is just cover it as straight as you can, and then fix coverings by twisting and reheating with the heat gun/iron.

Most torsional strength comes from D-box like structures.
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Old Jun 27, 2007, 10:35 AM
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Montag DP's Avatar
United States, GA, Atlanta
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Quote:
Originally Posted by theKM
The torsional strength of most open construction wings isn't enough to prevent warps from covering... the best you can do is just cover it as straight as you can, and then fix coverings by twisting and reheating with the heat gun/iron.

Most torsional strength comes from D-box like structures.
You're right, I guess I shouldn't have said I don't want it twisting, but that I want to minimize twisting and maximize strength in that area. The ribs are very thin, especially in the back, so I think I will leave the longerons in place.

One issue is that since the ribs are so thin in the back, it may be hard to fit the longerons in the slots without breaking them. For that reason, I'll make a replacement set of ribs when I get them cut.
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Old Jun 27, 2007, 11:47 AM
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I saw this comment "Unfortunately the zoom increments in TurboCAD are fairly large, so I can't give a good image of the entire wing" and "TurboCAD"... There's a button in the top menu bar that looks like a square with two arrows in it pointing left and right, this will zoom the drawing to fit the window, so essentially the max viewable zoom. The other way to get drawings out to graphics is to save as JPG, where you can set the resolution of the drawing from screen size all the way up to quite insane.

I reckon that TurboCAD is simply awesome for 2D drafting (that's what the Twinkle plans were drawn in).
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