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Old May 02, 2009, 03:08 PM
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Build Log
Blu-Guppy a 96" KFM3 Sailplane

I've been wanting to build a 96" KFM3 sailplane for a while now. Tony65x55 designed a 96" KFM3 wing over a year ago in response to a request. I took this design and made a few modifications for the Blu-Guppy. You can find a long list of Tony's designs here. The fuselage planform, and the box structure were borrowed from Ultralajt's Guppy2. The Guppy is a T tail, but blue foam does provide sufficient strength for a T tail, so I opted for a standard tail configuration.

This build log details my attempt to make a blue foam soaring machine that looks good and flies well. Based on previous models I've made, I know that a KFM3 wing can thermal reasonably well. Now we will find out if I can make foam wings and a fuselage that can handle the stress when scaled up to 8 feet. The finished wings look up to the challenge, but the nose of the fuse is really thin, and has to handle a motor swinging an 11" prop. Hmmm.

Roger

EDIT: Photos of my original hand drawn plans have been replaced with computer drawn ones.

Full sized plans for the Blu_Guppy can be found on post #71, tiled plans can be found on post # 78, and plans sized for Kinkos (36'x48") can be found on post # 119.

Dick Kline himself designed a new logo for the Blu-Guppy. You can find it in post #212.
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Last edited by maguro; May 24, 2010 at 08:57 AM.
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Old May 02, 2009, 03:15 PM
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The fuse was cut from four pieces of 1/2" blue foam and two pieces of FFF.
The pieces were tack glued and sanded.
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Old May 02, 2009, 03:41 PM
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The wings use a CF arrow shaft, balsa, plywood, and spruce to make the spar.

I drilled the 1/4" spruce spar and glued a piece of steel wire to it. The spruce with the wire was then glued to the cf arrow with epoxy thickened with micro balloons. Once the epoxy set the 1/4" ply joiner was epoxied to the spar, and the unit clamped together. The 1/4x1/2 balsa and spruce spars and the ply joiner were epoxied and clamped together. Finally the entire unit was glued together with polyurethane glue, and clamped.
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Old May 02, 2009, 04:41 PM
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Blu-Guppy a 96" KFM3 Sailplane

The wing is cut as one piece plus the KFM strips. I added a stripe of reinforced tape to the front at the leading edge, and then folded the top over. The spar was glued to the inner panel of the wing with pu glue, the top folded over and the assembly was weighted down with containers of lead shot. When finished the outboard panel was glued in the same way. Finally I cut off the excess pu glue, and added the KF strips.

The photos below show the right wing being assembeled, the finished left wing, and both panels end to end. Now if I can only find a wing joiner.
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Last edited by maguro; May 02, 2009 at 06:04 PM.
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Old May 02, 2009, 04:52 PM
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I'm sorry about the lack of consistency in the size of the photos. I'll try to do better.

Roger
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Old May 02, 2009, 05:53 PM
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After I sanded the outside of the fuselage, I split it open and hollowed it out with a Dremel tool. I built a plywood cage to support the sides of the fuse, the carbon arrow, and the servos. The idea came from Ultralajt's Guppy2. I routed out as much plywood as I could to lighten the cage. I cut a plywood disc to mount the motor and fitted it in the nose. Once the new motor arrives from HobbyKing.com, I will be able to cut the mounting and cooling holes in the ply disc, and finish the assembly of the fuse.

The fuselage is far too thin as is. It is obvious that I have to strengthen it. I plan to epoxy kevlar cloth to the inside, and fibreglass the outside with urethane. That should give the needed strength.

Since I can't finish the fuse, I did the tail feathers. The fin and rudder are just fff with bamboo skewers added to the rear of the fin and the bottom of the rudder for stiffness. The horizontal stab is reinforced by two rows of bamboo skewers. The my skewers are not long enough to span the entire stab, so I joined them with a bit of brass tube. Piano wire was bent and glued in the elevator.

This is about as far as I can go for now. I need the motor before I can finish the fuse, and a wing rod that will fit inside the cf arrow before I can finish the wing.

Roger
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Old May 02, 2009, 07:00 PM
Geaux Saints
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Looking great.

Kevlar inside and fiberglass outside on the fuselage. Almost bullet proof.

Good build log also.
I'll be following the progress.
Mike
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Old May 02, 2009, 11:21 PM
skumgummi dave
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maguro:

This is a superb effort! I eagerly await the completion of your project.

Regards;

Dave-
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Old May 02, 2009, 11:58 PM
If it flies, I will crash it
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Nice work Roger.

It is interesting, allot of the methods you are using are similar to what I used on my ill fated Magnum 2 meter design. The main difference I see in your model is that it is much sleeker and should be much lighter then mine was. I choose to use a v-tail to avoid problems with damaging the H-Stab on landings. Do you plan on a skid of some sort?

I will be watching this one. I still have the innards from my model and I may try to rebuild it again. Hope to get some tips here.

Thanks Roger.

Rob...
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Old May 03, 2009, 08:06 AM
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Rob,

I do plan on adding a fin to the rear to protect the stab and the rudder which extends below the tail boom. Here is a sketch of the rear of the plane. Sorry it was drawn over my original plans, so thee are a lot of lines.

Roger
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Old May 03, 2009, 10:53 AM
If it flies, I will crash it
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Thanks Roger,
I think I was confused before. It looks like your H-Stab is mounted on the top of the boom. I was under the impression it was on the bottom. That was the way I designed mine since it made it easily removable for transportation but I changed my plans because of the vulnerability issue.

You have a cool looking design. I can't wait to see how it turns out.

Rob...
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Old May 04, 2009, 11:17 AM
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I took a micrometer to my arrow shaft. The inside is 6mm +/- a few thousandths. The one place I found that carries 6 mm solid rods in the US, is out of stock. Does anyone know a good place to get them?

Roger
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Old May 04, 2009, 11:37 AM
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Quote:
Originally Posted by maguro
I took a micrometer to my arrow shaft. The inside is 6mm +/- a few thousandths. The one place I found that carries 6 mm solid rods in the US, is out of stock. Does anyone know a good place to get them?

Roger
www.rcfoam.com

Ron
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Old May 04, 2009, 12:41 PM
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Thanks Ron. Unfortunately they are the ones that are out of stock.

Roger
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Old May 05, 2009, 08:44 AM
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I added the front wing hold downs last night. I'll add the rear hold downs toady and post some photos. The front hold downs are taller than I planned, so some creative work with foam will be necessary to make the fuse look right.

Balancing the wings showed that the right wing is about 1/2 oz (15g) heavier than the left. I'll have to correct the problem or the plane will have a constant right turn tendency. I'll wait till after i decorate the wings, because that will most likely change the balance a little.

My new motor left Hong Kong on May 1. That means at least another week before it arrives.

Roger
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