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Old Mar 20, 2008, 11:02 PM
Bernoulli+Newton=Lift
magic612's Avatar
Somewhere south of Chicago, IL
Joined Jan 2006
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Build Log
"Lazy Boy" FFF 2 meter electric sailplane - plans, pics, video

This thought had occurred to me a while back; why were there no FFF sailplane designs floating around here? A week or so ago, I noticed that there was a build log for one of Tony65x55's excellent designs, a FFF glider (the Blu Sail), with a hook or motor option. If I'm not mistaken, he designed 60" and 72" versions of that plane.

So here's where my design varies:

78.5" wingspan (full 2 meters)
KFm1 airfoil (Tony's was a KFm3)
Motor-only option (I don't have anyone to tow one up for me!)
Standard R/E tail, instead of a "V" tail
More "room" for batteries, radio, motor

I don't want to knock what Tony did; he's got a great design! This is just another option to have out there, that's a little different, and a little more simplistic in design and construction.

I normally prefer Depron foam, but I wanted to design this sailplane so that it would be as accessible to as many people as possible, so I used FFF. It utilizes a single, 40" CF spar. Though technically a polyhedral design, the center 48" is flat and uses a KFm1 airfoil, making the wing a quick, simple build. Only the outer wing sections are angled up - quick to cut, fold (for the KFm1 foil) and glue on. Though sailplanes typically benefit from a small fuselage, I did make this one somewhat larger to afford additional space for less than ideal components. And I did not round any corners; it is a simple rectangular shape the whole length.

There is no landing gear; it's just a belly-lander. A folding prop would be ideal, but because the fuselage has a fairly significant radius from the wing to the nose, I successfully used a standard 10" APC prop, and with a little flared landing, haven't broken a prop yet (going on 5 flights so far, and hard winter ground). The wing simply sets into KFm1 cut channels in the fuselage, with rubber bands to hold it in place. Controls are R/E/T.

Again and again, where possible, I went for simplicity of construction and form. It may not be the prettiest sailplane out there, but it's a simple, quick build, and hopefully will provide others with many hours of gliding enjoyment.

Specifications as I have it set up:

Wingspan: 78.5"
Length: 52"
AUW: 18 ounces
Motor: Ultrafly FRIO E/10/09 (almost any "bell" type outrunner producing 100W or more should be sufficient)
Battery: 11.1V, 1250 mAh LiPo
Servos: GWS Naro x 2
Wing area: 580 square inches
Wing loading: 4.5 ounces per square foot

Tony has the video linked below in post #6.

UPDATE: Managed to get a better version of the video uploaded to YouTube; posted here:

Lazy Boy video #2 (1 min 5 sec)
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Old Mar 20, 2008, 11:14 PM
Bernoulli+Newton=Lift
magic612's Avatar
Somewhere south of Chicago, IL
Joined Jan 2006
1,952 Posts
Center wing section is made from a piece of FFF 8" from the fold, and a step that is 3.25" from the fold the other direction. Apply spray adhesive to step and fold onto main wing section. Tape or glue CF spar to section at the back of the "step" as in the picture.

Voila! More than half of the wing, done!
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Old Mar 20, 2008, 11:20 PM
Bernoulli+Newton=Lift
magic612's Avatar
Somewhere south of Chicago, IL
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Fuselage goes together fairly quickly, but care must be taken to make sure it is done squarely and symmetrically. I started by gluing the formers to the bottom of the fuselage, ensuring each was centered. Then, before gluing the fuse sides on, I glued 1/16" thick plywood braces to the each side, to give greater strength to the fuselage, and to hold the wing down more securely.

Then, being as careful as possible to glue the sides on symmetrically, I attached the two sides of the fuselage to the bottom/formers subsection, checking for squareness as I went.
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Old Mar 20, 2008, 11:23 PM
Bernoulli+Newton=Lift
magic612's Avatar
Somewhere south of Chicago, IL
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Moving back to the wing, I made the outer wing sections. I followed the pattern that I made for the outer wing sections, carefully cutting the tapered main wing chord and also the step. I used the natural fold of the FFF as the leading edge. Picture 1 show one completed section, and one uncompleted. Second picture shows a cross-section view of the KFm1 airfoil.

When attaching the outer wings to the main section, angle them up 15 degrees on each side. Easiest way to do this is to measure 4 inches up from the tip of the outer wing section - that'll net you the proper angle.

OPTIONAL: I did include on the plans some plywood braces with the 15 degrees built into them. These are designed to fit right on the "step" of the KFm1 airfoil, and have a slight radius behind them for strength and to help protect the bottom of the wing. I did not add these to my plane, because I felt confident in my glue / tape job on the wing joints, but if desired, please feel free to utilize these pieces.

If you use this option, you'll want to carefully slice the "step" on the main wing to meet the step on the outer wing tip. I designed the "step" of the outer wing to be angled slightly in to account for this brace, but slicing the main wings step is unnecessary if the brace is not used.
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Old Mar 20, 2008, 11:30 PM
Bernoulli+Newton=Lift
magic612's Avatar
Somewhere south of Chicago, IL
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Next up was installing the radio gear. I glued servo rails between the plywood braces, and screwed them in place, knowing that there would be significant forces on these servos. The pushrods are a full 36" in length, so that the servos can be as far forward in the sailplane as possible. Rods are just .047" piano wire, and it is simply pushed through the foam formers, with carefully shaped "V" exit holes at the end of the fuse for the pushrods to reach the control surfaces.

The motor mount is a 1.5" square piece of 1/8" thick plywood, glued to the former #1 AND fuselage pieces. A small section of the canopy cover was cut to form the top so that the motor mount was attached to all four fuselage sides. Motor is angled down about 5 degrees - no offset to the side. I didn't figure a cowl was necessary, and the motor will stay cooler that way being out in the open, and likely being used a full throttle to gain altitude fast.
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Old Mar 20, 2008, 11:37 PM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Magic, she's gorgeous! She looks like she flies pretty nicely too but I had to URL

Lazy Boy electric sailplane (1 min 1 sec)


to get the video.

Congratulations on a great design!

Tony
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Old Mar 20, 2008, 11:38 PM
Bernoulli+Newton=Lift
magic612's Avatar
Somewhere south of Chicago, IL
Joined Jan 2006
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I applied packing tape to the outer wing joints, for strength. Tape on the belly for landings. Battery hatch was cut for the front of the fuselage. And CG is right about where the step is on the bottom of the wing. Wing attached using 4 strong rubber bands.

That's it! Pretty easy, I think. And with a strong enough motor, it'll gain nice altitude quickly. Unfortunately, the wind was blowing pretty hard today, and it was also pretty cold, so not exactly weather for chasing thermals. But I'm looking forward to some lazy summer days of gliding this plane around.

Hope you do too! Please share your designs if you do.
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Old Mar 20, 2008, 11:42 PM
Bernoulli+Newton=Lift
magic612's Avatar
Somewhere south of Chicago, IL
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Hey Tony, thanks for posting the video for me! I appreciate the kind words, too! Your Blu-Sail design inspired me to finally design this sailplane, PLUS all the KFm airfoil research you've done helped this come together. All in all, much appreciated.
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Old Mar 20, 2008, 11:45 PM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
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Very cool, nice work

Tony
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Old Mar 21, 2008, 05:10 PM
Bernoulli+Newton=Lift
magic612's Avatar
Somewhere south of Chicago, IL
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Quote:
Originally Posted by Tony65x55
Very cool, nice work

Tony
Thank you again, kind sir!
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Old Mar 24, 2008, 09:06 PM
OOPS! I meant to do that!
kevin estes's Avatar
St.louis,Mo.
Joined Nov 2007
44 Posts
Nice work !Great pics.You make it look so simple.
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Old Mar 24, 2008, 09:37 PM
Bernoulli+Newton=Lift
magic612's Avatar
Somewhere south of Chicago, IL
Joined Jan 2006
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Kevin,

Thanks! It's really not that hard, either. All the lines are clean - really no difficult radii to cut. Straight and simple, and almost all the curves are very large radii (like on the fuselage, except for the tail-end underneath). There's not much to it to build it - and that was my intent: To make it simple!

Besides, for what FFF costs, it's not much $ to build one - I think I used a total of four sheets of foam, and that was to make it easier to build the outer wing sections. Still had quite a bit left over from those four. As long as the motor is powerful enough, it's super easy to fly too. I've flown it in 5-10 mph winds several times already, and didn't have any trouble.
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Old Jul 23, 2008, 09:33 PM
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Daytona Beach, Florida
Joined Nov 2006
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materials

Hi all!! I have been building RC and FF planes for many years, but am new to foam. I have really wanted to make a foam glider and this is a perfect craft. I pretty much understand most of the plans etc., but am curious as to the dimensions of the CF spar. Also, what is the thickness of the foam? Is it the same for all components? I have found most of the places to get the materials, and specifically the FFF. Is it 6MM? Thanks for any help...Les
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Old Aug 08, 2008, 08:25 AM
King Nimrod
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Aiken, SC
Joined Aug 2008
28 Posts
Fantastic! This stuff has come a long way from when I was sticking balsa together. I am more than impressed - stunned is more like it.
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Old Aug 09, 2008, 07:26 PM
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Joined Dec 2006
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Seems like the last couple of sheets in the 10 sheet plans are not showing the tail section like they should. I would like to build this model but would like to make it like you did originally. Am I missing something?
Also, what size is the spar that you used in the wing? HELP!!!! Carl
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