Big Blu 96 - 96" KFm9 Winged Glider - RC Groups
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Jul 12, 2011, 04:26 PM
jackerbes's Avatar
Build Log

Big Blu 96 - 96" KFm9 Winged Glider

I got a maiden flight with Big Blu 96 today and she flew very nicely. I don't think I could be happier with this build.

Big Blu 96 - 96" KFm9 Winged Glider Maiden Flight (5 min 18 sec)

The specs for the maiden flight are:

AUW: 1460 grams = 51.5 oz.
Wing Loadingt: 9.4 oz./sq. ft. or 28.5 grams/dm2

For the record, this plane is based on the works of Tony65x55, Foamenater, and all the others who give of themselves so freely on these forums in the interest of the hobby.

The inspiration to have another and larger glide, and the basic design of the fuselage for this one, arises from Foamenater's Blu Sail II glider thread. The plan for that was scaled up to 61" in length provided the basic for the fuselage.

The wing is much like the Blu Sail II but is a later KFm9 (four steps) variant. It is based on Tony65x55's 96" KFm3 glider wing plan that was published in the Blu Baby thread almost four years back.

I took some liberties with the wing to give it a straight leading edge and also turn it into a three piece (three 32" sections) disjoint-able wing to allow for easy transport. And Big Blu 96 has a removable tail also to help with transport.

And my thanks to Tony65x55, Maguro, Rolland Benson, and all the others from the Blu Sail II thread for their help and inspiration, that is what helped me discover gliders.

14 July - Photos added...

29 July - Images with wing parts and plans added...

Last edited by jackerbes; Feb 14, 2012 at 10:46 PM.
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Jul 12, 2011, 05:12 PM
RCDUD3's Avatar
Beautiful Jack, just beautiful!
Jul 12, 2011, 06:03 PM
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Dickeroo's Avatar

Terrific maiden flight

You've got the knack, Jack. Excellent work. She flies beautifully. Congratulations.

Jul 14, 2011, 08:50 PM
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How did you make the wings so the panels would attach and stay in position in flight?
Jul 14, 2011, 11:26 PM
jackerbes's Avatar
Originally Posted by Rolland Benson

How did you make the wings so the panels would attach and stay in position in flight?
I used two fibreglass tubes (.260 O.D. x .187 I.D.) as spars and joiners, and the joining was done with .187 fiberglass rods. The rods are have about 2.5" of engagement in the tubes.

I got some photos of that today and will put them up soon, you may seem them the next time you come on. And I'll follow up with all the details on where to get the tubes and rods too.

The tubes and rods added about $15 to the cost of this build, making it the most outrageously expensive foamie I've ever built. But I have no regrets at all...

Last edited by jackerbes; Jul 14, 2011 at 11:43 PM.
Jul 14, 2011, 11:59 PM
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Big Blu 96 - Removeable tail details...

The tail assembly is made from single layer pieces of FFF, leading edges are stiffened with 1/8" dowels, vertical stabilizer is hot glue welded to the horizontal stabilizer.

I was not sure that the tail feathers on this would be big enough, too big, or work well. Plus when I started looking at their size, I made them easily removed from the fuselage.

I have to loosen the set screws on the Micro EZ connectors on the elevator and rudder horns and remove some rubber bands and the tail is off.

There is one 1/4" dowel peg to located the tail positively, a typical wing hold down dowel through the fuselage below the leading edge of the hstab, and another peg sticking the end of the full length fiberglass tube that is the backbone of the foam fuselage.

The rubber bands are hooked to the peg in the end of the fuselage, come up through holes in the hstab, cross the hstab along each side of the Vstab, and then go down to the hold down dowel.

Jul 15, 2011, 12:13 AM
jackerbes's Avatar

Sailplane Calc - The Spreadsheet That Made Big Blu Fly Well!

I used the Sailplane Calc spreadsheet to work out the details on this as I made some rough drawings for building it (sorry, no plans yet...). I scaled up the BS II fuselage, used Tony65x55's 96" wing plan, made some minor modifications to both of those as I worked.

I guessed at the wing location and once I had the wing built and the fuselage build in progress, I played with a motor and battery to decide the battery location.

When it was nearly complete and after frequent consultations with Sailplane Calc, it was decided that I needed to have a balance point 4.52" back from the leading edge and would fly it with the CG set to 3.69" back from the leading edge. That CG was going to have a 10% static margin to produce the slightly nose heavy condition needed for a good maiden flight and also essential to a glider having some penetration.

The two attached images are the results I got from Sailplane Calc. Lots or numbers, probably of no interest to most, but I love them! They are what made this a plane that flew well on the first try.

Edit 23 July 2011: Adding links for spreadsheets used...

The Sailplane Calc spreadsheet can be downloaded at either of the following links:

Updated link for that spreadsheet:

And this copy of the RC Soaring Digest has a tutorial for using it (page 37 or so and on):

Last edited by jackerbes; Jul 29, 2017 at 09:21 AM.
Jul 15, 2011, 10:22 AM
Registered User
Clever idea for attaching the rear tail group. That would made this airplane easy to transport in most any car along with you three piece wing.
Jul 15, 2011, 10:31 AM
jackerbes's Avatar
You're right, and that is what I had in mind.

I can fit that 61" fuselage in my Dodge Dakota (with a jump seat) with the tail on if I am the only one in the truck and can let the nose hang out the rear sliding window. Tail off, it can share the cab (tail or nose up on the dash) with a passenger or two.

The tail goes on in a very consistent and repeatable manner. I'll mark the pushrods at the Micro EZ connectors and that will get them close enough to the same place every time.

Jul 18, 2011, 06:31 PM
Onward through the fog.
Cybernaught's Avatar
Nice work Jack,

It takes me back to my two meter days. Though they were high start not motorized. There's just something about a glider over head moving slowly and gracefully that just makes you feel good. A great stress reliever.

Jul 18, 2011, 07:46 PM
jackerbes's Avatar
It is a wonderful thing...

Another 2-7/16" and it would have been in the fabled 2.5m class. And I could have done that easily enough.

The flex in the wing is spooky, I have not done any intentional stress testing yet but I think there is an easy 18 to 24 inches of up flex at the wing tips. By the calculations the plane only has about half of the Effective Dihedral Angle that a polyhedral glider should have to have good Spiral Stability. But it has good sprial stability anyway as it happens. And a think that is, at least in part, due to the fact that it grows it's own dihedral under power. Reminds of watching B-52's taking off, the "BUFF' had something like 15 feet of lift at the wing tips with all the slack out.

That has a 15 x 12 folder on it and it only takes a few hundred RPM to float it out of my hand. I'm getting a very nice climb at about 3,500 RPM on that prop and that works out to about 200 Watts and speed of about 35-40 MPH or so.

Got a loose/moving servos issue sorted out today and am looking forward to some air time tomorrow...

Last edited by jackerbes; Jul 27, 2011 at 08:18 PM.
Jul 18, 2011, 08:12 PM
jackerbes's Avatar
I wonder if this means that I'll have to keep building bigger and bigger planes to keep the "jones" satisfied?

I did a big lazy loop with it the other day just to see what the wing would look like. It was at low throttle and I backed off as it got near the top, also eased it around through the bottom of the loop and it handled it fine. I just had to know...

As it went over the top it was very stable, I think this is going to be a great inverted flyer too. A inverted flat spin induced by full forward and full right stick is a good "dethermalizer mode" on the Blu Sail II, looks like it might work for this one too.

We've been having hot weather, in the 80's and 90's I want to go thermal hunting tomorrow...

Last edited by jackerbes; Jul 29, 2011 at 02:38 PM.
Jul 22, 2011, 01:40 PM
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Jul 22, 2011, 03:49 PM
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Wing Spar Tubes and Spar Joining Rods

For me, the key to build on this wing was figuring out a material to use for the spars and joiner tubes. Once I got those figured out the build proceeded quickly and easily.

An internet search produced many hits for CF, fiberglass, PVC, and other tubular materials that might be used. Among those was the Goodwinds LLC Company. Among their recreational and hobby products, they sell a lot of materials used by kite builders.

I found an attractive material for the wing spar tubes on their Fiberglass Tubing page

That tubing is described as a fiberglass tube that is a filament wound epoxy tubing (FWET) tubing that is strong, durable and relatively stiff, yet somewhat flexible. It was said to be able to withstand higher winds than carbon tubing without fracturing because of it's inherent flexibility.

I called and asked about it and was told that it would have more and better strength for flexing, absorbing the flex, and then recovering, than would similar (and much more expensive) CF tubings. So I decided on this tube:

Product # - 007210
Description - FL-260
Length - 32.5"
O.D. - .260"
I.D. - .187"
Weight(grams) - 27 grams (10 grams per foot of length)
Unit Price - $2.59

On the Goodwinds page for Solid Fibreglass rods I found a rod that was sized right to fit in the tubes as joiners. That is this rod:

Product # - 007026 (or 007026B for black)
Description - .187 solid fiberglass (white or black)
Length - 48"
O.D. - .187" (3/16")
Weight(grams) - 40.7 grams (10.2 grams per foot of length)
Unit Price - $1.39

To build the wing would take four of the tubes and one piece of the rod. The tubes will be cut to the needed lengths and that could be done with a Dremel tool or some other common cutting tools.

I ordered enough tubing and rods for two builds, the shipping cost was reasonable enough ($8.00) and it cost a little less than $30 (with shipping) for enough material to build two wings ($15.00 per wing).

The guys at Goodwinds are easy going bunch, I told them that they could cut the 48" rod in half or to the length of the 32-1/2" tubes if it would make the shipping any more reasonable for me or easier for them.

The cost of the spars is a little stunning when you compare it to the $9.00 cost ($1.50 per sheet) of the six sheets of FFF needed for the rest of the material in the wing. But I swallowed the pain and proceeded with the project. This wing is going to cost more than $3 per foot by the time I get it finished!

When the tubes were received I cut two of the tubes to exactly 32" long for the center panel. Then four 15-1/2" long tubes were cut from two more of the 32-1/2" tubes for the spars in the outer panels.

The spar tubes are a little less than half of the length on the outer panel as it is not practical to have a full length spar on a wing with a joint in it to create the dihedral for the polyhedral tips. The polyhedral tips were 16" long so the spars were cut to 15-1/2" in length for the outer wing panels.

Four pieces of the white .187" rod were cut, 6-3/4" in length, to make the four joiner rods.

I had plenty of extra .187" rod, I also cut four 2" long rods to be used as temporary alignment pins for when I was building the wing panels. The ends on all the rods were rounded a little with gentle sanding with 150 grit sandpaper. Sand with strokes towards the tips, going back the other way runs the risk of strand being raised from the rods.

The rods were a slightly too snug fit in the tubes by a small amount (about .002" or so). I took a #12 drill (0.1890" or 4.8mm in diameter, easily found at Home Depot or Lowes) and drilled the ends of tubes to a depth of about 3-1/2" (the length of the drill). That made the rods an easy sliding fit in the tubes with no looseness or play. Run the drill bit in and out slowly going a little deeper on each entry. Run the drill motor at a few hundred RPM, pull it clear several times to clear the debris before getting to the full depth of the drill's length. This removes very little material, any reside can be blown out of the tubes (don't suck!).

That's it, the spar tubes and joiner are ready to be installed!

The build instructions on the wing will follow shortly...

Last edited by jackerbes; Jul 23, 2011 at 09:35 AM.
Jul 22, 2011, 04:45 PM
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Big Blu 96 - Wing Build - Part 1 of 5

Big Blu 96 - Wing Build - Part 1 of 5

I've numbered the photos 01 up and the numbered steps also refer to an image with a name that starts with that number. This How-To is not (for me) extremely detailed it assumes you may have some experience in building with FFF.

This is a KFm9 wing, it will have three steps and they will be located at 28%, 50%, and 75% of the root chord and be parallel to the leading edge all the way across the wing.

Three pairs (a total of six sheets) of still joined FFF with the skin on the outside are needed for this build. There will be a fair amount of scrap left over, the joined edge at the fold will form the leading edge of the wing. And that makes for a beautiful leading edge too!

01 - Two 24" x 48" sheets of FFF still joined with the factory folded edge. The folded edge is to the left, the skin side is on the outside. If your two sheets are folded the wrong way, they cannot normally be reversed without breaking the skin. If the skin breaks, put a strip of clear package sealing tape on the outside of the folded edge so that it overlaps about evenly on both sides. I use the square tube and measure back from that to make marks, then draw the cutting lines with a 48" sheet rock cutting square.

02 - The sheet was turned, one sheet hangs down from the table, and the first line is cut. The width here is the full 9" chord width and that will form the bottom of the wing panel, and the skin will be left on the outside of the wing.

Keep a sharp clean tip on the snap off tip utility knife, lean the knife back as far as possible when cutting (to avoid snags and "ball ups") and make cuts against a straight edge keeping the knife vertical. I make one light cut to cut the skin, then two or three more light cuts until the knife contacts the cutting mat.

03 - The other FFF sheet is now top side up, the cutting line for the 28% step is drawn 2-1/2" back from the leading edge and then the cut made. As seen there, the square is laying on top of the two sheets folded to draw the cutting line. To make the 28% step cut you want to put the top layer flat on the mat and cut only the top layer, not both layers.

04 - Wing panel with the 28% strip sticking up, joined by the folded edge.

05 - The panel is 48" long now, it will be cut to 32". First I make a clean up cut on the end to get a smooth square edge. The yellow square and the PVC tube are used to get the parts square for the cut and the cut has been made in this photo. Repeat the layout 32" apart on the other end, make the cut, and the 32" center panel is cut.

06 - Working with the 48" long piece of scrap that was cut off in step 03 to leave the 28% step, cut three 1-1/2" wide full width filler strips.

Then cut the remaining piece of foam so that the ends are square to the cleanest undamaged long side and then cut it to 32" (or a little more) in length. Then cut six more strips as follows:

Three - 2-5/8" x 32" - 28% step support and 50% step strip

Three - 4-1/4" x 32" - 50% step support and 75% step strip.

To be on the safest side, you can cut these a little longer than 32" to leave material for clean up cuts on the ends and to match the length to the panel widths as they are installed.

Those six strips are not seen in the photo, if you cannot get all of them out the the two remaining pieces you have now, you can cut them later out of the scrap pieces you'll get when you make the two outer wing panels.

07 - Remove the skin only from the the 1-1/2" wide filler strips (not! from the wider strips!). Pick the end of the skin up and pull it up and away at a slight angle (too steep and it tears at the pinholes). Holding the end of the skin and running a finger along under the plastic will work too.

08 - One of the filler strips is cut to 32" long. The 28% step is folded down flat on the center panel and a line drawn to mark it's location. Then make a dashed line or several marks all the way across 1/2" or so in front of the 28% step line. Those marks will be used to align the filler strip beneath the 28% strip and 1/2" in front of the 28% step line.

09 - Working on a piece of baking parchment (36" or so long) put PU glue on the back of the filler strip (I always hide the side with markings). I use only Gorilla Quick PU, the small plant spritzer has water in it, I have some flexible plastic spreaders handy and the big plastic lid is a place to lay things with glue on them. And I wear one or two disposable gloves.

Run three thin beads of PU on the filler strip (only on the side that will be down) in a wide evenly spaced "S" and spread it evenly with the spreader. You want it to be just visible as a shine on the surface, no more than that or you'll have a real mess on your hands. Make sure to get 100% coverage on the edges and ends. Full contact gluing is the goal here.

10 - Spritz the area where the filler strip will lay all the way across. You can't use too much water but a light even coat is what works best. Lay the filler strip down aligned with the marks (not! the 28% line). I don't want to glue the 28% strip to the filler yet so I lay another clean (no glue on it) piece of baking parchment on top of the filler, fold the step down flat, check the alignment again, lay a flat piece of 1 x 6 on top of the step and weight it all down. Peek in on the ends and make sure the filler strip has not shifted and is even with the wing panel on the ends.

To be continued...

Last edited by jackerbes; Jul 29, 2011 at 02:33 PM.

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