Building the Guillow's DC-3 (35.5" span, now 38") with RC /BL motor conversion

[Frank v B]

Simon,

Thanks

re: your question "..have you calculated the new area vs the original? Is it 15% bigger?" 

No, I have not calculated it.  That would require math.   The only logic I used was to add chord to dampen pitch and to add span to dampen roll.  The rest is TLAR  ("That looks about right").

I don't know if it is 15%.  It is "just enough".     It still needs to be scale and not look awkward.  I can only judge that when I can pin it to the tail end of the fuse and look at it from all sides. That's why I have not sanded it yet.  I have built in significant options that can be adjusted with sandpaper.

The personal guideline I use is that when two options present themselves, I lean to the corrective one.  Err to right thrust, err to down thrust, err to wash-out.  On small planes (less than 36" span) add to span, add to wing area nearer the tips, err to larger rudder with greater throws, err to more power, smaller prop (reduce torque on take-off), nose heavy, more elevator area, less elevator throw, more aileron throw, lighter than usual landing gear wire (to absorb a bounced landing)....... and most importantly, reduce overall weight.
Each adjustment may be small but the totality of these decisions have a huge effect..... in my opinion.... but then, what do I know?

Frank

[Frank v B]

Stabilizer finished for now.  All the ribs are in place and the new outline pencilled in.  Note the pencil notch in the front because it has to go past the front of the stabilizer saddle of the fuse.

Frank

[Frank v B]

The fin/rudder

It is made up of shaped ribs that are almost 1/2" thick at the high point (scale cross-section).  Everything is butt-glued with few continuous pieces to take the loads. The leading edge of the rudder also has the corners cut off.  It may be scale but it weakens the structure.  Also it does not pass the 50/50 rule*.  Here is the final design:

Larger area for both the fin and rudder.- did this by using wider wood and moving the leading edge forward and the top higher.
The thinner stabilizer (3/16" thick versus designed 1/2" thick) meant the bottom of the fin rudder has to go down further.

After the glue dries I will sand the fin contour to fit the curve on the top of the fuse.



Frank

* 50/50 rule of details on model planes: if you cannot see it from a distance of 50 feet and 50 km/hr, don't waste your time on it.

[Frank v B]

Fin/rudder

To answer Simon's question on whether the fin/rudder was 15% larger I have forwarded this photo to Andy.
He has volunteered to calculate it..... probably to 6.. if not 10 decimal places.

Frank

[Frank v B]

Starting the wing.

Changes:
1) Per Michael's suggestion: move the motor nacelles outward.  The motor needs 5x5 props on 3S so I need a little extra space.  Am achieving this by increasing the flat wing center section from 8" wide to 9" wide.
2) add more wing area in 3 ways  i) A wider trailing edge (see photo) ii) about an inch more span for each outboard wing section, iii) reducing the taper by making the wing tip a little wider.

Photo 3284- shows the extensions glued onto the two main spars.  The doubler is just angled for the photo but it will reinforce the joint.  Also notice how the left-most rib is 1/2" further out versus the plans (grey area).

Photo 3285- shows the spar extensions glued in place but it has to be trimmed before the rib can be installed.

Letting it cure overnight.

Frank

[Andy Hoffer]

Fin/rudder

To answer Simon's question on whether the fin/rudder was 15% larger I have forwarded this photo to Andy.
He has volunteered to calculate it..... probably to 6.. if not 10 decimal places.

Frank

Good job @Frank v B !  Your expanded version, using the Shoelace Algorithm for Calculation of Polygon Areas (https://myengineeringworld.net/2014/06/shoelace-polygon-area-excel.html), is 20% greater than the original.

Oops, sorry!  I meant 20.1154204699% !! 

It has plenty of margin for (your) errors!

Andy

[Frank v B]

Andy,

Thank you for your computational skills.  It is more than I thought and "more than enough"

Frank

[Frank v B]

Port wing- outboard end

The left wing has been built and drying.  Had to be creative to add some area.
1) Note the root rib is to the right of the drawing by about 1/2"
2) the back end of the trailing edge is about 3/8" back of the plans
3) the tip is about 1/4" further outboard
4) add this to the 1" longer center section

That should add up to about 15.1248635235 % larger than scale....and "just enough"

Frank

[Andy Hoffer]

Port wing- outboard end

The left wing has been built and drying.  Had to be creative to add some area.
1) Note the root rib is to the right of the drawing by about 1/2"
2) the back end of the trailing edge is about 3/8" back of the plans
3) the tip is about 1/4" further outboard
4) add this to the 1" longer center section

That should add up to about 15.1248635235 % larger than scale....and "just enough"

Frank

@Frank v B is definitely a quick study!   

Andy

[Frank v B]

The other wing half.

To make it easier to make all mistakes/adjustments symmetrically I left the first half on the board (bottom) while I built the second half (top).  I made an asymmetrical mistake on the B-25.  Not this time.

Had to match the increased span, increase chord and the adjustment to the aileron size.

Letting it dry before adding the leading edge and the small spars (stringers).

Frank

[Frank v B]

Oops

While I was processing the photo (reducing size and adding blurr for Andy) I noticed that the trailing edge at the aileron ran on an angle.  At the root end you could see the line on the plans and the trailing edge ran over top of the leading edge of the aileron by about 1/4".  Went back to the building table straightened it out.

Executive summary- this guy learns from his own posts.

F.

[Andy Hoffer]

Yup.  If @frank hadn't been distracted by the expletives encoded in the pile of pins in the top right corner of photo #3291 this never would have happened!  Pity!

Andy

[Frank v B]

Andy, keep deciphering.

The motor nacelle.

Put together the starboard (right) nacelle.  The two changes : i) I added a bit of right thrust- approx. 2 degrees.  ii) added a ring of 1/32 plywood at the motor mount between the 2 balsa rings.  The clamps are holding the two balsa rings with the plywood ring in between.  These clamps are terrific.  Dollarama $1.25 for 10 small ones and 6 larger ones.  In the gardening section in a string bag.  I just cut the little nubs off the clamp faces so they do not puncture the balsa wood.

Will be finishing this nacelle completely until it is fitted, including the wing attachment method.  Then build the second nacelle exactly the same way.

F.

[Andy Hoffer]

OMG.  This is amazing.  I can clearly see and read everything from corner to corner in Photo #3292. We should declare this National F³* Day.  I must be hallucinating. 

Andy


(*Fully Focused Frank)

[Frank v B]

Next Problem Challenge:

This was designed as a static model.  The wing saddle is a center rib (keel).  Then extruded plastic fillets are glued on to create the contoured wing saddle.  Three problems: 1) no strength 2) no way to give my grubby paws access to the radio/servos in the fuse. The formers are in the way, and 3) no wing attachment stuff to make the wing removable.


The photo shows the cut out center rib/keel and portions of the formers.

The little hamster in the hamster wheel in my head is going to be working overtime to figure this one out.    Time for a coffee break. 

F.