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Feb 05, 2017, 01:58 AM
F3Foamie Pilot
Thread OP
Build Log

LEG Fat Albert, Take 2

I've decided to pick up where I left off on the FA build.

After sorting through my build pictures it became apparent that waiting till I complete the project and then posting the build would be a major pain in the a**.

I have made good progress at this point and it will take some effort to organize my notes/pictures.

The highlight/focus of this build will be the removable radio. Making the servos removable has proven to be quite a challenge and work, but in a fun way.

I selected the KST DS125MG servo for several reasons, they look cool, have 83 oz torque @ 4.8 v and most importantly, will make the mounting work very well.

The biggest challenge was being able to route the servo leads through the wing. I decided to use 7/16" brass tubing. I practiced the whole install on a scrap EPP wing panel that I had. I wanted to make sure that I could successfully bore a hole through the wing panel with out screwing it up.

I used the dremel to cut notches/teeth on the tube, then rotated it in the EPP to bore the hole.

Also I decided to make a 6" joiner out of 15/32" for the 2-7/16" tubes so the tubes would act as an additional spar. Used JB weld to attach tubes.
Last edited by Slopemaster; Feb 05, 2017 at 02:27 AM.
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Feb 05, 2017, 02:21 AM
F3Foamie Pilot
Thread OP

Servo Mounts

I purchased the inner wood rings from Aloft Hobbies with the servos. They fit perfectly.

I fabricated the outer rings from 1/8" light ply. The reason I did this was to prevent the servo opening from deforming during the tape/covering process.

The main mount that the servo goes into to is glued in the wing cut out. The outer ring is inlayed and glued in the wing too.

The top inner ring will act as a hole filler and will attach with the servo screws when the servo is installed.

I fiberglassed all of the wood parts to add strength.
Feb 05, 2017, 03:27 AM
F3Foamie Pilot
Thread OP

Servo Lead Tube

As stated, I used 7/16" K&S brass tubes for the servo leads. This was the smallest I could use and still be able to fit the female end of the servo extension,

The tubes are 12" long and they are extended 13" into the wing. So I used a 15/32" x 6" tube as a joiner.

I decided to establish the servo cutouts first before the holes for tubing.

I had to be careful when boring the hole in the wing. I used several straight edges to try and maintain proper alignment.

After making the tube hole in the left panel, I couldn't decide how I would be able to make a perfectly matched hole in the right wing panel.

I knew that if the tubes didn't line up perfectly, then I would not be able to maintain alignment of the wing halves

What I ended up doing, which worked very well, was reverse the tube so the cutting end was facing the right wing panel. Then I placed both wing panels in the wing beds and proceeded to bore the hole in the right panel.

Before I joined the brass tubes I had to custom cut the opening where the servos are to allow the leads to go in.

Two issues were when I glued the tubes together I had to maintain 2" separation of the 7/16" tubes. I used an automatic center punch to slightly dimple the 15/32" tube toward each end. This way it kept the 7/16" tubes from going in to far when I glued it together.

Used JB Weld to join the tubes. I applied the JB to the outside of the servo tubes, this way the excess was on the outside which was easy to wipe off. If you apply the epoxy to the inside of the 15/32" joiner tube then it would get inside the tubes.

Another problem was to maintain the proper alignment where the cutouts are. I solved this by cutting a small reference align mark on the tubes with the dremel.

The total weight of tubes and servo mounts is just over 3 oz. Location is approximately 2.625" aft of CG. I will have to add additional nose weight but that's OK, I want a heavy build.

I used 30 minute epoxy to glue tube in LH panel by applying a thin layer to tube. I would have liked to use Goop but the tube fits very snug in the wing panel so I needed a lower viscosity glue.

Used Goop for main servo mount and outer closeout ring.

Next step will be to glue wing halves together, Probably use 30 epoxy again for tube and wing joint.
Last edited by Slopemaster; Feb 05, 2017 at 04:11 AM.
Feb 05, 2017, 10:08 AM
Registered User
acclivity's Avatar

That is some seriously cool work. Nice job.
Feb 05, 2017, 01:43 PM
U down with EPP? Ya u know me!
Aerogance's Avatar
Looking good! Clever idea with the servo mount.
Feb 05, 2017, 01:56 PM
gas tires and oil
prplgoat's Avatar
those frames look cool!
it's way easier to route servo wires by removing the connector and running it through like a plastic straw...
Feb 06, 2017, 12:20 AM
F3Foamie Pilot
Thread OP
Thanks for the positive feedback.

It's been an interesting project. I have to admit, it's quite a bit of work for removable servo's but I like doing these kind of things.

Next up will be gluing the wing halves together, then install the spars.

I will be replacing the supplied spar tubes with 5mm solid carbon spars that I purchased from Aloft Hobbies.

I had to visit several local hardware stores to find spar joiners that fit properly, but I was successful in my search and have already joined the spars. Will post pictures later.

The battery/receiver will be installed the the body. This should be very similar to my P-80 build.

I'm anticipating quite a bit of fixed ballast in the nose due to the servo tubes and glassing the elevons and vertical fin.

I will be able to fine tune the CG by adding additional lead (if needed) in the battery compartment, same as the P-80.
Feb 06, 2017, 11:37 AM
Impatience is a virtue
MCH27t's Avatar
Cool build. Given the tumbling plank landings I tend to make, I'd be a bit concerned about bending/kinking the brass tubes. Once they're bent, the wing is likely done.
Feb 06, 2017, 01:51 PM
altitude adjustment
thumbhead's Avatar
I like the idea of easily replaceable servos. Not sure I understand the function of the brass tube.

Feb 06, 2017, 02:39 PM
F3Foamie Pilot
Thread OP
Originally Posted by thumbhead
I like the idea of easily replaceable servos. Not sure I understand the function of the brass tube.

The brass tube is for the servo leads/extensions.
Feb 06, 2017, 10:23 PM
F3Foamie Pilot
Thread OP
Wing halves are glued together.

Next up, spars.
Feb 07, 2017, 11:03 PM
F3Foamie Pilot
Thread OP
Top aft spar is glued in. I used Goop. I am supporting the wing cores in the beds.

Jack did a wonderful job of ensuring that the cores and beds line up perfectly. Makes it a lot easier to build a straight wing.

I decided to extend the top aft spar to the servo mounts. The bottom aft spar will be the stock length for existing spar slot.

When I cut the 3 meter long x 5 mm carbon to the spar slot length, the remaining piece fit perfectly between the servo mounts, so it made sense to use the whole piece rather than cut 6" off as scrap. I just had to extend the spar slots on each end about 3".

I have not decided whether to use Gorilla white glue to fill in top of spar slot or spackle.

All spars will be 5 mm solid rather than the supplied tubes.

I did a flex test earlier by supporting equal length of solid verse the hollow, then hung a weight from the center.

The solid spars definitely flex less than the tube spars.
Last edited by Slopemaster; Oct 02, 2018 at 11:46 PM.
Feb 08, 2017, 12:10 AM
Registered User
acclivity's Avatar
Originally Posted by Slopemaster
Jack did a wonderful job of ensuring that the cores and beds line up perfectly. Makes it a lot easier to build a straight wing.
I think that is of major importance. I know some other kit makers say build it on a flat table... never works out very well. Building in beds ensures things are correct, imho.

Keep up the good work.
Feb 08, 2017, 11:31 PM
F3Foamie Pilot
Thread OP
Top main spar is in, used goop.

I had to shop around at the local hardware store to find new spar joiners that would fit the 5mm solid spars properly. They fit the new spars very tightly.

New joiners are hardened steel pins aka, roll pins. The slot in them was nice, it allowed the excess JB Weld to escape.

They are a lot heavier and thicker than the kit supplied aluminum joiners.

Overall the new spars/joiners add 2 oz total, compared to the supplied spars/joiners.
Last edited by Slopemaster; Oct 02, 2018 at 11:46 PM.
Feb 09, 2017, 11:44 PM
F3Foamie Pilot
Thread OP
Top and bottom spars are in.

Wing weighs 15.5 oz. so far.
Last edited by Slopemaster; Oct 02, 2018 at 11:46 PM.

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