Graupner Electro UHU build

[Frank v B]

Have not built anything yet this year.  

Came across this kit in my shop while hunting for a part for Rob Dickenson's project.  Of course, the only way I could find the part was to clean up my shop!  Time to get it dirty again.... and just to drive Piker nuts that I have started another project.

The kit fell into my hands at last year's Kitchener's swap meet.  I was looking at it because it was the plane that revolutionized electric flight.  It was the first electric airplane that performed.  He wanted me to buy it.  I said "I don't need another airplane" he said "I'm not taking it home.  How about $20.00".  I love helping people solve their problems.

Plastic fuselage, built-up wings, designed for a Speed 600 electric motor, 75" wingspan

Have to reverse engineer this one: 
- Build the plane and weigh it,
- select the motor and battery combination to balance/power the plane

The kit was complete except for the wing joiner rod (piano wire).  It has the dihedral angle bent into it.  Kinda important.  Will probably build it in one piece.

One wing half was completed in the kit.  The first photo is a stock photo of the ARF kit.  The photo of the second wing half on the board was an hour into my build last night.

Frank

[Frank v B]

First problem:  the plastic fuse appears to have become brittle over about 20 years.  A small crack developed in the fuse in the middle of the canopy opening.

Solution: pasted two strips of carbon on the inside with 5 minute epoxy and covered it with plastic to allow me to press it into place.

This fuse will probably disintegrate into a million pieces at the end of a vertical landing (planting). I may have to contact Bruce to teach me how to fly to avoid this problem.

Frank

[Frank v B]

- Leading edge sheeted and wing joiner stuff* done.
- first coat of paint on the fuse.  A light coat to see if the paint reacts with the plastic.  The yellow that shows up on the rear end of the fuse is called "sunshine".

One day closer to spring!

Frank

* a catch-all technical term.

[Frank v B]

Shaping the wingtips, or..... how to make down bedding for your pet gerbil.

A razor saw and a razor plane make quick work of it.

[Frank v B]

OOPS, forgot the golden rule of painting any white surface with bright red paint.... you must start with a grey primer.  Didn't do it so the white will keep showing through.  Just completed  3 thin coats of spray paint.  The white will show through even after 10 coats.

I hereby invoke the modellers rule to maintain sanity.  "Don't worry about a mistake if you can't see it at 50 feet!"

Done.  I feel a lot better now.  Sorry, Cadez.  I failed Painting 101.

Frank

[Frank v B]

joining the wings

- made a piano wire dihedral brace
- glued the wire and the root ribs with 15 minute epoxy and pinned it to the building board.
- calculated that 7 degree to each wingtip makes a total of 7 3/4" when one wing is flat on the board.  Slipped a balsa brace under the tip to hold it up.
- included a piece of carbon veil over the joint and covered it with waxed paper.

Once the glue on the dihedral joint has dried, I will fibreglass the centre section.

[Frank v B]

Basic covering done.  Will add trim stripes to the wing and coloured wingtips.

Next is servo installation so I can weigh everything and decide on the power package.

[piker]

Wow!  That was fast!  Lookin' good!

[Frank v B]

Now for the math:

fuse and canopy 12.5 oz
wing 10.6 oz.
battery (1300 mah) 3.5
Total weight less power system 26.6 oz.

Call it 2 lbs (32 oz.).  Proper motor would be about 150-175 watts (75-85 watts per pound).

The EFlite chart shows the BL 450 produces a max of 175 watts.  Go to my motor drawer and see what I can conjure up.

Note that the old brushed motor and nicad power system was about 180 watts but the plane was about a pound heavier.  This gives it about a 30% increase in watts per pound.  As well, the BL motor is about 85% efficient versus about 50% for the brushed motor.  This should give a large performance boost versus the brushed system.  Now the detail-oriented mathematical members will weigh in with the correct numbers.



Frank

[Frank v B]

Installing the E-Flite 450.
   
This motor has an X-mount so the old nose piece had to be cut open and a new firewall built and installed.

1) Cut the nose of the plane with a Dremel drill with a 1/8" drill bit.  Opened up and smoothed with a sanding drum.
2) make the firewall- made from 3/32 balsa to get the contour right.  Then copied onto 1/16" plywood to make 2 copies.  The balsa was sandwiched between the 2 plywood firewalls.
3) Attached the motor with 1 screw so I could center the motor by twisting it.
4) cut a horseshoe-shaped balsa spacer (3/32" balsa).  Used to evenly space the spinner and the front of the fuse while the glue dries.  When the glue is applied and the fuse is held vertically, the firewall actually floats in the fuse.  Once the glue sets, it is back filled with glue and fibreglass.
5) glued a piece of fibreglass to the firewall/fuse to tack it in place.  Covered it with plastic so it dries smoothly.

Let it cure over dinner.  Then permanently install the firewall.

Frank

[Frank v B]

Final steps of the motor installation

- permanently glued in the firewall.  The white at the edge of the plywood is 5 minute epoxy with micro balloons.  On the back, I used strips of fibreglass.
- drilled vent holes around the perimeter of the firewall.  The large hole in the middle is for the back end collet that holds the shaft.  The elongated hole at the top is for the motor wires.
- installed the motor.
- found a 10x6 folding prop in my collection.
- cut out the spinner cone so it would fit over the metal center of the folding prop.
- side view of the finished nose.

Frank

[bweaver]

That prop looks like it has been previously planted. 

Otherwise the plane is looking real good.  Surprisingly.   

[Frank v B]

Bruce,

Yep.  Now that you mention it, it was on the front of my Siren (GP warmliner).  Stopped using it because it was too big for the motor and burned it out.  I had a second identical motor so history will not be repeating.  The planting is actually a belly landing in slop. 

Gliders don't have wheels. 
Ground has mud.
Now plane and prop have mud.

Frank

ps, now turn over and burn the other side.

[Frank v B]

Attaching the wing.  It requires symmetry for proper flight or symmetrical misalignment if you are Bruce.  Here is how I did it.

1) drilled 2 holes in the fuse at the leading edge of the wing.
2) inserted a small sharpened dowel in the port (left) hole so it did not protrude.  Applied a dot of black* paint onto the tip of this dowel.
3) held the wing on the fuse and pushed the dowel into the wing.
4) drilled out the spot on the wing and glued in a longer sharpened dowel.
5) installed the wing on the plane with the left wing dowel in place.  Measured the wing from the back of the wingtip to the tail so the distance was equal.
6) with a pencil, marked the centreline of the fuse (centre seam) on the wing and drilled a hole.  Tapped it for a 10-24 nylon wing bolt
7) inserted the short dowel in the starboard (right) hole, added a drop of black paint, installed the wing and pushed the dowel backwards to mark the wing.
8 drilled the right hole into the wing at the dot and glued in the wing dowel. Andy, if this photo looks out of focus, you need to drink another glass of wine.
9) before the glue dried I installed the wing and wing bolt so it would dry in the correct orientation.

The photos tell the story.

The photos
i) the wing attachment parts (L) nylon bolt  (C) short dowel with the black paint (R) long permanent leading edge dowel.
ii) fuse wing attachment with the short dowel with the black paint.
iii) the black dot the paint left on the leading edge of the wing.
iv) the nylon bolt in the fuse (drilled and tapped), the two leading edge dowels in the wing.

Frank

* yes Bruce, for you the colour could be red, blue or even pink.

[Frank v B]

Just installed the tail feathers, aligned everything, connected the servos to the tail feathers with piano wire.

Next steps ESC, RX and a test fire..... then done!

Frank