Building the Guillows B-25 (26.5" span, now 31") with RC and brushless motors.

[Frank v B]

Fuselage stringers installed and fill-in sheeting.

The fuse is quite strong even at this early stage.

Andy, the box of code letters (pins) has been shaken.


F.

[Andy Hoffer]

Fuselage stringers installed and fill-in sheeting.

The fuse is quite strong even at this early stage.

Andy, the box of code letters (pins) has been shaken.

F.

Hmm...  @Frank v B, this looks like a really juicy message from Cynthia!!   

Something about your van, the basement and the garage.  I can't imagine what that would be about.....

Andy

[Frank v B]

The wing:
BTW I found the ribs.  They were hiding in plain sight.  They didn't look like regular ribs because you have to cut out all the notches for the spars.

The main decisions:
1) Ditch the polyhedral.  It was a minor gull wing.  Am making it straight with dihedral at the fuse.... for simplicity and strength.
2) Increase the wingspan Am adding 1.5" to each half.  The total span will be just less than 30".
3) Increase the chord. Starting at the root rib with the same chord but tapering less towards the tip. This adds more wing area at the tips for stability and reduces the twitchiness of small models.
4) Plug-in wing halves.  The wing halves will plug into the fuse with carbon rods.
5) Ditch the scale ailerons: Will cut them out from the trailing edge stock and make them go to the motor nacelle. Note: the original TE was two glued pieces of 3/32 balsa.  Replaced it with proper trailing edge stock.


The method: build one wing half in its entirety, including motor installation, then make the second wing half exactly the same way with all the same errors.... mirror image of course
Guiding Principle: as long as all mistakes are symmetrical, the plane will fly.

The purple pen is at the new wingtip.  The plans show the old wing in grey.

F.

[Andy Hoffer]

Good construction log @Frank v B !  The thought process is inspirational!

Andy

[Frank v B]

Andy,

Re: "The thought process is inspirational!"

Do you realize this sounds like a compliment.  Are you OK?

Ribs glued in place.  The ribs outboard of the motor were spaced farther apart.  Only the trailing edges were trimmed.  The reason for not touching the leading edges is so the spar slots would still line up.

Frank

[Andy Hoffer]

Andy,

Re: "The thought process is inspirational!"

Do you realize this sounds like a compliment.  Are you OK?

Ribs glued in place.  The ribs outboard of the motor were spaced farther apart.  Only the trailing edges were trimmed.  The reason for not touching the leading edges is so the spar slots would still line up.

Frank

Yikes!  This is serious. Must be COVID.  I better get to Emerg right away!  Nice knowing you @Frank v B !!

Andy

[Frank v B]

Andy,

re: "I better get to Emerg right away!  Nice knowing you"

Go to Emerg at Sunnybrook.  One of my long-time customers is a psychiatrist there.  In fact, he is a geriatric specialist....always looking for a challenge.

Frank

[Frank v B]

Stringers added to the top of the ribs.

Note the trailing edge near the wingtip is lifted off the board by a piece of 3/32 balsa to add wash-out.

Frank

explanation- "wash-out" (trailing edge is higher than the leading edge, sometimes called "twist") is added so the wingtips will stall last.  Generalization: if lift is lost at a 12 degree angle of attack at the root, the tips will have a 14 degree stall.  You will lose lift but the tips will still be flying.  It gives you time to save the plane.  If the tips have "wash-in" (trailing edge lower than leading edge), the plane will flip on its back at the moment a stall sets in.  No way to save the plane.

[GuyOReilly]

@Frank v B, with all due respect, here is an explanation about the structural angle of incidence difference between the root.  Both the root and tip will still stall at approximately 16 degrees angle of attack from the airflow.  This of course depends on the airfoil selected/used.

Washout is commonly achieved by designing the wing with a slight twist, reducing the angle of incidence from root to tip, and therefore causing a lower angle of attack at the tips than at the roots. This feature is sometimes referred to as structural washout, to distinguish it from aerodynamic washout.
Source, Wikipedia, the source of all knowledge  : https://en.wikipedia.org/wiki/Washout_(aeronautics) 

[Frank v B]

Guy,... same thing....  Tomato, tomatto.  I looked at it as angle of attack, the article looked at it as wing incidence. One looks forward, the other looks backwards.



Added the three bottom stringers (spars?).  Photo 120

Oops, mistake.  Realized I installed the tip rib backwards because the slots did not line up (photo 121, love the out-of-focus element).  No problem with a little bit of sandpaper.  Problem solved.

Frank

[GuyOReilly]

Guy,... same thing....  Tomato, tomatto.  I looked at it as angle of attack, the article looked at it as wing incidence. One looks forward, the other looks backwards.
Added the three bottom stringers (spars?).  Photo 120
Oops, mistake.  Realized I installed the tip rib backwards because the slots did not line up (photo 121, love the out-of-focus element).  No problem with a little bit of sandpaper.  Problem solved.
Frank

SAME THING?!? Absolutely not the same thing...  The angle of incidence and the angle of attack are DIFFERENT THINGS!!!   Please advise if I should bring my From The Group Up or Flight Training Manual or other publications on the topic of aeronautics.  Bernoulli must be rolling in his grave.
I will let @Andy Hoffer to comment on the out-of-focus picture.

[Frank v B]

Back to building*:

Finished the port wing and rough sanded it.  Will round the leading edge after the motor is installed so the gluing surface is larger.
The root rib is at the root rib of the plans to show you the extra wingspan.

Motor stuff is next.

F.


* Guy, re: Bernoulli.  The only turning in the grave he will be doing is when he says "Not that Frank guy again".  I did a presentation to Ryerson Aeronautics about 7-8 years ago with the title "Bernoulli has left the building".  They invited me/us back 6 months later to do it again.  We will settle this over a beer...post Covid.

[Andy Hoffer]

Back to building*:

Finished the port wing and rough sanded it.  Will round the leading edge after the motor is installed so the gluing surface is larger.
The root rib is at the root rib of the plans to show you the extra wingspan.

Motor stuff is next.

F.


* Guy, re: Bernoulli.  The only turning in the grave he will be doing is when he says "Not that Frank guy again".  I did a presentation to Ryerson Aeronautics about 7-8 years ago with the title "Bernoulli has left the building".  They invited me/us back 6 months later to do it again.  We will settle this over a beer...post Covid.

I will definitely have my vicennial beer for this one.  I think it would be huge fun for @GuyOReilly and I to do a ground school presentation to @Frank v B !!  We will bring the latest editions of both "From the Ground Up" and the "Flight Training Manual".   I think we should be able to get this done with a two-day session at the field. 

Andy

[Frank v B]

Motor position.

Photo 123- the motor on top of the plan to determine the size of the stand-off.
Photo 124- the plastic nacelles held in place.
Photo 125- the front view of the motor location.

Decision:

The easiest way to handle the motor location is to

1) glue a balsa fake firewall to the leading edge of the wing
2) build a balsa box with the proper stand-off to bring the prop out of the cowl.
3) screw the motor in place so it is absolutely in the middle of the cowl
4) remove the motor and glue a 1/32 plywood firewall to the front of the box so it will hold the screws, re-install the motor.

F.

[Frank v B]

Installed one firewall.  I had to roughly shape the leading edge because of the contour of the plastic.
Found a piece of trailing edge stock to handle the sweep of the leading edge.  Glued it and clamped it in place.

F.