rebuilding a brushed foamy Parkzone Decathlon to a 400 size brushless motor

[Frank v B]

Why not another conversion:

A Parkzone Decathlon with a brushed motor and proprietary radio (servos have 5 wires!!) system landed on my lap.  It has hung up in somebody's workshop for years and was never flown.  It appears to have 15 years of dust and nicotine on it.

steps:
- remove the old geared power system and radio.  No transmitter supplied with it.
- remove the nicotine.  Queue the Windex and shop towels.
- supply and install a 400 size brushless motor with 15 amp esc.
- install micro servos and move the stuff around to achieve a good balance point. (25%-28% of chord). 

My experience with Decathlons runs deep and scary.  The solution is to have the CG waayyy forward.  If not, two things happen:

i) the plane will wallow side to side like a tail-heavy Cub which eventually leads to a death roll; and,
ii) because the thrust line is far below the drag of the wing, throttling up fast will send the nose skyward, doubling the effect of the first problem.  Will add down thrust to tame it.

Pre-build stats:

Total weight without flight battery: 15.5 oz.

The new motor has at least twice the power output so the weight savings are not as critical as the Valencia's 39%.

Frank

ps: Andy, notice the little black wire coming out of the tail in photo 89.

[bweaver]

@Frank v B

re: "A Parkzone Decathlon with a brushed motor and proprietary radio (servos have 5 wires!!) system landed on my lap." 

I thought there were rules about that kind of thing happening.  I sure hope you were OK.

Regarding your starting another new project:  I am going to start calling you the 'Marathon Man'...

(You're putting our build and repair activities to shame.) 

[Frank v B]

Oh, Bruce.  What can I say?

Onwards.

- Cleaned the plane.  It now shines and the white paper towels are orange with nicotine.  Gross.
- gutted the motor and radio

Motor installation
- picked an Axi 2212/20 from my pile of motors.  Chose it because it was heavier.  A 125 watt motor (12 amp, 3S).
- stuck a piece of balsa in the cowl where the prop shaft is and marked the edge of the cowl.  Then pulled it out and marked the back plate of the motor's "X" mount to determine the thickness of the plywood and balsa motor mount.  Cut a piece of plywood and two pieces of balsa to make up the proper thickness.
- photo shows the motor measuring stick, the plywood motor mount and the two balsa spacers.

Off to dinner.


Frank

[msatin]

Another interesting project Frank.
And I can't even get the wings back on my Slow Poke. LOL

[Frank v B]

Mark,

re: "And I can't even get the wings back on my Slow Poke."

Don't worry.  It's in keeping with the model.  You didn't buy a "Fast-Poke"


Frank

[Frank v B]

Keep going....,

Photo 93 - one stab half had failed.  Sewed a carbon rod onto the bottom to stiffen it.  The foam was too thin to poke it inside.  Yes, dental floss.  The needle is still attached on the left side of the picture.  A drop of glue on both sides of both sewn portions and then cut off the excess.
Photo 95 - new servos inside.  The blue servo was missing the right mounting lug so a washer was used to catch the lip of the broken lug.
Photo 96 - motor in place.  It comes out of the cowl correctly.  Screwed into the old plastic firewall.
Photo 97 - I was not kidding about cleaning off the nicotine first.

Frank

[Frank v B]

Today I completed the following:

- installed the receiver, hooked up the servos and pushrods
- tested the servos and centered them, powered up the motor to make sure it was spinning the correct way... it wasn't.
- installed the cowl and the prop.  Used an APC 7x6 prop so it will be tamer.  The old prop was an 8x4.
- trimmed some stuff and cleaned it up


FINISHED!!

Total weight- exactly 16 oz.  before the batteries.  (Will use 3S)
It gained 1/2 an ounce because I used the heavier AXI motor to make it nose heavy.
Power will at least be doubled so a great trade-off.

Frank

[davidk]

That's one pretty plane.  Nicely done.

[Frank v B]

Maidened it yesterday at Fraidenfest. 

Summary:  It flew great!!!  Nicely overpowered with about double the power going through it. (140 watts) with a 1300 mah 3 S battery.  It handled the gusty conditions just fine.

When I landed and took it home found a few problems:

1) the bottom rudder hinge near the control horn was cracked and was flopping around.  Surprisingly it worked.
2) the elevator had nearly split in half near the center.
3) one of the two strut supports on one side was broken off so it was flapping in the breeze.

The Fix:
Photo 95- shows the missing section where the rudder is supposed to hinge at the fuse, shows the split in the elevator (shows white).
Photo 96- two strips of 1/32" plywood and a strip of CA hinge material.
Photo 98- my selection of clamps.  Found the green ones today at Dollarama (10 small, 8 large) for $1.25. They are sold as plant clamps and come in a mesh bag.  The neat thing is they have lighter springs than the standard ones.  The standard red ones have a lot more force and the yellow ones even more.  The problem is they crush the foam.  The green ones are waayyyy better for foam!
Photo 99- the plywood makes a foam sandwich with the CA hinge material trapped inside (5 minute epoxy).  The green clamp is holding the foam skid together while the glue is drying.  The skid had opened up.  Note that the plywood strips are longer than the rudder.  The forward edge of the plywood is in line with the hinge line above the elevator.  Once the glue is dry I will fill the gap with balsa and trim the trailing edge of the plywood at the back end of the rudder.  The new horn will be screwed in on top of the plywood.
Photo 00- the broken strut.. the right one in the photo.  I have drilled a 1/16" hole in the remaining stud.  Attached the strut with dental floss, 4 wraps, a square knot and two half hitches (use any damn knot you wish! )
Photo 01- placed drop of carpenters glue (yellow) on the knot to secure it.  It will flex enough.

Frank

[Frank v B]

Had a mishap with the second flight and it cartwheeled.  The motor mount broke.  The balsa sheared along the grain like it was supposed to.  The cowl split into two pieces.

Glued the parts back together and held the pieces together with clamps until the glue dried.  Lined the inside with 5 minute epoxy and then added strips of carbon veil on the inside.  Once in place, covered it with strips of waxed paper and pressed down on it to adhere everything.

Sanded the outside of cowl to get the gloss off it and attached it to a stick. Sent it to the paint shop ....outside my front door.... and sprayed it.
Cadez would be proud.

Photos before painting.

Frank

[Andy Hoffer]

Did you have to sew the antenna wire back on?!!   

Andy