Sr. Falcon EDF Power - Kit Bashing

[GuyOReilly]

Winter project identified.
I had 2 - 70 mm EDFs laying around.
With 2 kg of thrust each, that should be plenty for a 6-7 pounds airplane.
Bunch of stuff to figure out prior to starting the build.
That will be fun!!   
 

[GuyOReilly]

Quick calculation and the weight would be likely around 8 lbs. due to battery and 2 EDFs. 
QUESTIONS:
1- Should it be powered by 2 batteries or one?  The ESC are rated 70 AMPS and for 4-6 cells.
2- The nose wheel and steering is in the way of the planned battery tray. How about a tail wheel instead?
3- I need to test the engine/ESC/battery combination prior to mounting.  Any suggestions on test stand?
4- Wings are rubber bands mounted, how about changing to bolt-on for more rigidity?
Thank you.

 

[Frank v B]

Guy,

This is the original kit from the '60's or early '70's.  It is still all balsa (incl. balsa and ply doublers).  The main indication is the rubber band wing fastening.  The later revised kit's changes were lite-ply fuse sides but wing bolts.
re: EDF related questions- I know nothing.
re: nose wheel. Twin EDF tail dragger is radical.  If form follows function then that explains why there are few or no tail dragger jets.
re: nose wheel servo- If you are going twin EDF, where are you putting them?  If on the wing, finish the nose and put the servo ahead of the firewall holding the nose gear. Consider putting the nose wheel bearing plate ahead of the firewall as well.  This way the belcrank can be as far away from the planned battery hatch.

My two cents.

Frank

[GuyOReilly]

Thank you @Frank v B these are useful suggestions.
I will use the nose wheel and place the servo forward.
The EDFs are located ahead of the leading edge and probably will be mounted below the wing.
One possibility is to make the wing with 2 outer sections leaving the main center section mounted with the EDFs (but detachable for inspection) with wing bolts.  That would make transport easier and field prep faster.
I have the design of the "reactors" from Aerofred and in the process of modifying them to fit and to have access for maintenance.
More to follow.

[GuyOReilly]

I found thios design on THINGIVERSE:
https://www.thingiverse.com/thing:1218072

There is only one image and I cannot determine its size based on the information available.
@ppalumbo or another member familiar with #D printing could let me know if the inside could accommodate a 70 mm fan.
3D printing might be better than ply and balsa construction. 
Thank you.

[GuyOReilly]

Tested the EDFs this morning. Using 3C only at this time... 

https://www.youtube.com/watch?v=Z8t-yrk2vWw

Looks like the wing mounting could work with simple attachment for power to the EDFs and another "Y" connector for the connection to the receiver.

[GuyOReilly]

Test fitting fuselage parts prior to any gluing.
I made certain there was a right and left sides... this time... 
The quality of the parts is great and the die cutting (crushing?) is better than some other kits I have had the pleasure of building.
Beginners, please abstain from building this as a first project; instructions on the plans are sparse and confusing.
The fuselage will be built first as this will reduce the parts count in the box and that is the amount of space available at this time (basement needs a big clean).
Nose gear will be attached to the firewall prior to installation.  Following @Frank v B suggestion a separate servo for the nose gear will be place at the front of the firewall to allow room for the batteries.

[GuyOReilly]

Fuselage completed, almost.
Rudder and Fin done.
Much sanding remains to be done.

Next elevator: the main spar was flimsy balsa that snapped and is being replaced by a scrap piece of rigid 1/4 by 1/2, laminated  with 1/16 for a 5/16 total thickness.  This will be fine sanded to fit the slotted stabilizer ribs.  Pictures to follow when assembly starts.

PS: I dropped a small set screw for the servo pushrod connector and it vanished in the ether. Trying to locate a replacement...  HAAARRGGG          
 

[GuyOReilly]

Nose wheel set-up working.
https://www.youtube.com/watch?v=9q9cag7cQuQ

[GuyOReilly]

Elevator completed, except for shaping and sanding the tips.
Wing started, just trial fitting parts.
The front and rear wing spars are 1/4 think with a 1/16 spruce cap.  They are STURDY!
Aileron servos are the fat Hitec HS-125MG. The low profile of these servos will allow mounting flush with the wing bottom surface.
I bought the last supply of Kleet hinges (3 packs of 3) from John's Hobby shop. I was informed that they are ordering more...
As a final note, I think that I determined how the EDFs will be mounted to the wings (to be described in a future post).
 
Photo #97 - dry fit of parts.
Photo #98 - a spacer (not glued) used for the center section.
Photo #00 - Center section sheeted.
Photo #01 - Dry fitting of parts for the right wing.

[GuyOReilly]

Proposed aileron servo set-up.
Advantages:
1- uses existing aileron bellcrank plywood support with matching slots in the ribs.
2- servos can be fixed/screwed onto the platform, photo 06.
3- covering can be applied to the plywood.
4- minimal additional drag caused by the protruding servo, photo #07.

Disadvantages:
1- adding a former to support the covering fore and aft of the plywood, photos 08 and 09.
2- servo located near the fuselage (risk of aileron twisting?!?) but that is where the plans call for the aileron control to exit.
3- need to drill holes for servo extension (holes will also be needed to the ESC and battrery cables), photo 07, 08 and o09 clearly show the slots through which the spars pass.

[GuyOReilly]

One wing done, much sanding to follow; the glue for the other wing is drying.
The motor mounts have been cut and dry fitted and will be installed after the wings are joined/epoxied.
Holes for wiring will be cut in the ribs subsequent to the installation of the motor mounts to help ensure alignment.

[GuyOReilly]

I could not resist putting it together.
That was needed to determine C/G and up/down thrust line.
TLAR... so far...

[Frank v B]

Per your usual practice, the next post will be the test run on the floor of your shop.  Should be interesting.
What did your research show about thrust line angle of the motors since they are under the wing.  Are they 0/0 or some down thrust to avoid 737 Max 8 issues?
I have sent you a note about some checklist items/questions.

Frank

[Michael]

Looks amazing!

Based on my experience with kit-bashed twins, I would leave the trust line at 0/0 with the flat bottom of the wing.

It looks like it will be a smooth flyer, likely needing a fraction of throttle to fly.

Very nice!