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Old Aug 15, 2006, 11:48 PM
Roll Tide!
Joined Oct 2005
325 Posts
Question
Guru specs

Dear friends,

Since I am a newbie and since I know nothing of aerodynamics or aircraft design, I thought I'd ask the gurus in this forum to be so kind as to provide specs for a plane I would love to build and then fly to my heart's content. Your suggestions will be appreciated very, very much.

Airplane characteristics: A very simple and very light stick design, like the gws j3 stick. Meant only for calm conditions or indoor flight. Will use gws gear typically found in small sticks like the gws j3 stick or lite stick (ips A motor, pico servos, etc.)

I own and fly a slow stick and a j3 stick and I love them. However, I would like to fly something that is extremely slow--an airplane that I could walk along with--or almost. It should have a long glide, power off. It will not be used for aerobatics, only for lazy floating around.

To keep it simple for myself, the wing and stabs will be rectangular structures made out of balsa and covered with craft tissue or solite. For the wing, I will make ribs, similar to the inner ribs of my gws slow stick.

So, here are the questions (Please use inches as unit). What would you suggest as measurements for:

1 Stick (fuse) length (no greater than 36")

2. Wing span and chord

3. Horizontal stabilizer span and chord. (Also elevator width).

4. Vertical stabilizer height and width. (Also rudder width).

I'll use .047 or .055 wire for the main gear and .032 or .047 wire for the skid, depending on the size of the airplane.

One last note, I've built a couple of airplanes using the slow stick and j3 sticks as general guidelines, but they just don't fly slow enough. If I can make this dream come true, I'm going to name it the Snail Stick.

Thanks again for any help and/or suggestions you may have.

Warm regards,
amigo
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Old Aug 16, 2006, 03:31 AM
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Staffs, UK
Joined Nov 2003
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If you want it to fly VERY slowly on that power train it basically wants to be lighter than your existing planes. If you can work out how to build a slowstick size model with the weight at least 30% lower then you'll have more or less what you want. It will require very careful selection of building materials.

BTW planes that fly very slowly under power are generally high lift/high drag and do not glide well.

Steve
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Old Aug 16, 2006, 05:12 AM
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East Anglia, UK
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In addition to the above..all that is required is to get a bigger plane than you have already for the same weight..needless to say this gets flimsy and unsuitable for all but the lightest breeze.

In general you tend to use things like carbon fibre, depron and ultra lite covering materials like solite with the bare minimum of structure to lay them over.

If you take your IPS setup and put it on something about 50" wingspan, and keep the weight down to less than 9oz, you will get what you want.

However, achieveing that, is very, very hard.
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Old Aug 16, 2006, 10:27 AM
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Punta Gorda, FL
Joined Apr 2002
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You can do it with lots of $!

Build it with tiny (0.03" tail and 0.04" wing, 4 grams) carbon rods and fuselage tube (8 gram). Weight 0.5 oz.
http://www.goodwindskites.com/merch/...lidroundcarbon
Build it with aramid (Kevlar) thread with rigged flying and landing "wires".
http://www.cstsales.com/aramid-ss2.html
Cover it with light mylar film (0.0005").
http://www.modelresearchlabs.com/pricelist.htm

Use two small servos. 0.25 oz.
http://www.slowfly.com/store/view.ch...view=%23913506
LiPo 2 cell 250Mah battery 0.5 oz.
http://www.hobby-lobby.com/etec.htm
Brushless motor and prop 0.75 oz.
http://www.astroflight.com/e/env/sto...oducts:af-799c


Total weight less than 2 oz.

Fuselage length 30"
Wing span 45"
Avg. wing chord 7"
Wing loading under 1 oz. per square foot (area)
Stab area ~60 square inches
Rudder ~30 square inches.

At a coefficient lift of 0.6, it will fly at an airspeed of 6 MPH (fast jogging speed)
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Last edited by Ollie; Aug 16, 2006 at 10:34 AM.
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Old Aug 16, 2006, 01:32 PM
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Thats good Ollie. I couldn't get MUCH below 8mph..!!!
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Old Aug 16, 2006, 04:35 PM
Roll Tide!
Joined Oct 2005
325 Posts
Guys, thanks so much for your prompt replies and wealth of information! You have saved me many hours of research and this information will help me come up with a workable plan.

Would you recommend a lot of camber for the wing or more or less the same as in the j3 stick wing?

Thanks again,

You guys are great!

amigo
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Old Aug 16, 2006, 05:44 PM
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Theoretically heavily undercambered wings stall a bit slower,..but possibly a bit more viciously. Ollie?

A lot of indoor planes have saggy covering that balloons up to get the right shape..
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Old Aug 16, 2006, 07:49 PM
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Use two pieces of 0.04" Dia. and 48" long carbon rods. Over lap the ends 1/2" and wrap them with thread and CA. That makes one loop 94" circumference for the wing outline. Make the outline into an ellipse by ~ 9"root chord x ~45"span wing outline. Hold the ellipse outline with rib-like threads in tension from LE to TE. Run a thread from tip to tip and tension it to bend in the "dihedral" with a curve. The tip to tip thread is enough tension to raise the tips about 2" compared to the root. The mylar film attaches to the carbon rods of the outline. The film has a saddle shape. By stretching film from LE to TE with enough tension. The airfoil arc depends the film tension so the camber is about 3 to 4 percent. It takes some craftmanship to make a neat covering job.
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Old Aug 17, 2006, 12:03 AM
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Joined Oct 2002
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You need more camber than most wings but it is still a case of there being a "best" and that limit is likely around the 6 to 7% camber value. For very low speeds a simple circular arc is as good as any shape. You basically want it to look like a free flight indoor model but with roughly a 45 inch wing span. Using super thin but low stretch line as wing bracing just like on rubber powered indoor models will allow you to build the model that much lighter by allowing the use of smaller "spars" on the leading and trailing edges. The lines take the flight loads that way and the spars just need to withstand compressive loads for the major part.

So what you're actually after is a slightly larger version of that funny looking indoor RC model that looked like it had mickey mouse ears for the tail sections. Which is pretty much what Ollie is describing above.
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Old Aug 17, 2006, 05:38 AM
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The one that is called in German 'Housefly' or somesuch?


I keep meaning to do an outdoor 'dragonfly': Ollie has just showed me how
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Old Aug 17, 2006, 08:06 AM
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I leave out the Rec. weight of about 0.25 oz. Sorry.

For a design, there three budgets. (1)Weight - lift budget. (2)Thrust - drag budget. (3)Cost - effort budget.

A design can fly it slower with a bigger model.
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Old Aug 17, 2006, 11:00 AM
Roll Tide!
Joined Oct 2005
325 Posts
Thanks again, friends. Your are all very kind to take the time to write me with such detailed information, including building techniques. I don't take your generosity for granted.

I am going to study all of this information and decide on a course of action. Be aware that I'm only a rookie and not a first-rate, experienced modeller, but I've got to try it. I'm obsessed with the idea of a dreamy, dragonfly-like floating machine. Maybe rcgroups should institute a psychological help thread so we can figure out what makes us try stuff like this!

Best regards to all,
amigo
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Old Aug 17, 2006, 01:16 PM
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amigo,
I enjoy design with a purpose. I thank, you for your purpose.

Please name it Super Slow Dragonfly.

Span 54"
Average 8.5" wing chord
Wing area 459 square inches (3.2 square feet)
Fuselage 48" length
Stab area 90 square inches
Rudder area 45 square inches

The fuselage is made from a 0.08" Dia. carbon rod. Stiffen the fuselage with rigging aramid threads like spar rigging shrouds. Weight 5 grams. Cost $2.85.

The wing outline of carbon rods are two pieces 0.04" Dia., 36" length and two 0.03 Dia., 36" length. Weight 10 grams. Cost $10.

Tail is from carbon 3 pieces of 0.03 Dia. 36" length. Weight 4 grams. Cost $7.50.

Mylar 0.0005" thickness silver film. Weight neg. Cost $12.

High Performance contact adhesive 3M #1357. Weight neg. Cost $10.

Kevlar thread .010 dia x 1000 ft 22 lb test. Weight 2 grams. Cost $10.00.

Firefly coreless motor, 4 to 1 planetary gear box, prop and coreless speed control. Weight 16 grams. Cost $70. Thrust 86 grams (3 oz. of thrust)

Three cell LiPo 250Mah battery. Weight 22.5 grams (0.72 oz). Cost $24.90.

Two Blue Arrow Servos. Weight 7.2 grams. Cost $34.

Berg 4 Receiver and special Crystals . Weight 11 grams. Cost $48.

Total weight (78 grams) 2.75 oz.

With an airfoil camber of 6% and a coefficient of lift at 0.8, the air speed is 5 MPH.
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Old Aug 17, 2006, 01:55 PM
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Quote:
Originally Posted by vintage1
The one that is called in German 'Housefly' or somesuch?


I keep meaning to do an outdoor 'dragonfly': Ollie has just showed me how
Here is the link:

http://www.braunmod.de/eprodukte.htm

Jürgen
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Old Aug 18, 2006, 05:31 AM
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That is a housefly.

THIS is a dragonfly
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