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Author Topic: Frank's re-build of a Knox Hawkshaw's design/build  (Read 381 times)

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Offline Frank v B

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Frank's re-build of a Knox Hawkshaw's design/build
« on: April 14, 2019, 10:04:17 am »
It's raining.... no flying.... gotta build something.

Fred Messacar begged* me to help him get rid of some of Knox Hawkshaw's** airplanes.  Found homes for the big quarter scale lawn-mower ones (Rudie N. of Beeton) and I took some of the smaller ones.

This plane was Knox's own design and more my style.  It looks like a mid-air fusion between a SuperSportster and a Spitfire... with an open canopy requiring a pilot and a scarf.  54" span, .40 size

The plane is a little heavy which I like.  The airplane will groove instead of flit.  Notice the custom machined Oleos.  They are fixed.

Main challenges:
- this is a one-piece plane.  It must be become a plane with a bolt-on wing.  No room for a one-piece plane.
- It really needs to have the covering peeled to the bone.  It is in awful shape.
- it has these funny holes in the nose with some kind of tubing coming out of the firewall.  These must be filled and contoured.  See photo 66.  Notice this photo shows rain drops on the fuse (had to bring it in from the garage).  Also, notice how the wheel in the foreground is out of focus to drive Andy nuts. ;)

Steps:
- peel all the covering
- separate the wing
- re-shape the nose.  It realllllyyyy needs a spun aluminum spinner.
- install a compact big-a$$ motor.  Always overpower an airplane. 8)
- re-cover the plane.

Will work on it on rainy weekends.   May it not be finished until December. ;D

Frank


* this word used for my own protection.  Fred and my wife talk. ;D

** see post about Knox http://temac.ca/smf/index.php/topic,6492.0.html
« Last Edit: April 14, 2019, 11:44:21 am by Frank v B »


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Offline Frank v B

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Re: Frank's re-build of a Knox Hawkshaw's design/build
« Reply #1 on: April 14, 2019, 11:49:24 am »
I was wrong on two fronts:
1) the landing gear are machined spring Oleos.  Very neat but not removable.
2) rougher than I thought.... a lot rougher.  Sections had three layers of covering (first layer was Koverall fabric and up to two layers of Monokote in areas.  All but 4 of the 30 wing ribs have been repaired, sistered, re-glued, etc.  Spars have been spliced and the leading edge has been spliced.

Frank
« Last Edit: April 14, 2019, 12:37:11 pm by Frank v B »
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Offline Frank v B

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Re: Frank's re-build of a Knox Hawkshaw's design/build
« Reply #2 on: April 14, 2019, 12:34:47 pm »
How rough was it?

Just cut the wing off with my Dremel Multi-Max plunge cutter.  Wow.  It may be easier to start over with the wing.

This will get done before Xmas if it rains 40 days and 40 nights. ;)  By then I will have my sailboat finished since I will be limited to two models on the Ark. 8)

Frank
« Last Edit: April 14, 2019, 12:38:30 pm by Frank v B »
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Offline Frank v B

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Re: Frank's re-build of a Knox Hawkshaw's design/build
« Reply #3 on: April 14, 2019, 01:52:36 pm »
Two more decisions made:
1) am keeping the wing.  There are two neat Knoxisms I want to preserve i) the oleo LG ii) the slotted hinged aileron that exposes a rounded edge on the upper portion as it is deflected downward.  The hinge line is about 3/8" inside the aileron to achieve this.
2) Change from belcrank ailerons to individual servos in the wing. For you newcomers to the hobby.  When this plane was built in the '90's, a standard Futaba servo was $28.00, a 12" extension was $10... (each! 2 needed) and a "Y" harness was $15. A total of $70 (incl the old 7% GST) That is about $150.00 in today's dollars.  Belcranks allowed ailerons to be operated with one servo.  Now servos are so cheap it is a no brainer.
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Offline piker

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Re: Frank's re-build of a Knox Hawkshaw's design/build
« Reply #4 on: April 15, 2019, 01:56:38 pm »
Just catching up here after being away from the internet for a few days.

That's a cool restoration, Frank!!  I'll be following along as usual.

Offline Frank v B

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Re: Frank's re-build of a Knox Hawkshaw's design/build
« Reply #5 on: April 16, 2019, 10:59:57 pm »
Ripped out the wing center section at the leading edge of the fuselage area and the trailing edge area.  This wood was totally fuel soaked.

Have decided to completely sheet the top of the wing with 1/16" balsa.  This will smooth out the rough ribs while adding strength to the wing.

Will cut back the bottom of the ribs and add 1/16" cap strips.  Again to strengthen the ribs and smooth out the curves.

The top sheeting will add some thickness to the wing but the wing is relatively thin to begin with.  Invoking the 50/50 rule 8)

Frank
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Offline Frank v B

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Re: Frank's re-build of a Knox Hawkshaw's design/build
« Reply #6 on: April 18, 2019, 10:51:18 pm »
Filled the wing centre section with solid balsa at the leading edge (for wing dowels) and trailing edge (for nylon bolt hold- downs).

Put cap stops on the bottom of all ribs.  Cut back the ribs to be capped by about 1/16" and added 3/32 cap strips. This made the rib's curve smooth and allows me to sand it smooth since the cap strip sits proud of the leading edge sheeting ("D" tube).

Cap strips really strengthened the ribs.  They were a mixed bag of 1/16, 3/32 and 1/8".   30 of them had been repaired at least once.  Several had 3 repairs.

Sorry there are no photos.  My computer doth protest!  It won't post photos.  Must be Andy's revenge. ;D

Will bring the wing to Wednesday's Build class.


Frank



Frank
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Re: Frank's re-build of a Knox Hawkshaw's design/build
« Reply #7 on: April 19, 2019, 08:55:08 am »
RE: "Sorry there are no photos.  My computer doth protest!  It won't post photos."


Offline Frank v B

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Re: Frank's re-build of a Knox Hawkshaw's design/build
« Reply #8 on: April 19, 2019, 09:06:45 pm »
Bruce,  Computer still says "No".... burp.

Two decisions:

1) glued the aileron servos into the wing.  Hitec 82MG's.  They stick a little out of the bottom but the 50:50* rule applies.
2) Changed the top ribs to cap strips versus sheeting the whole wing.  The bottom cap strips were so strong and easy to sand that I capped the top of the ribs as well.  Just finished 34 ribs.  Finished this before the Maple Leafs could score in tonight's game. 8)

Frank

*50:50 rule- if you can't see it at 50' and 50 km/hr don't worry about it.
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Offline Frank v B

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Re: Frank's re-build of a Knox Hawkshaw's design/build
« Reply #9 on: April 20, 2019, 10:23:34 am »
Found the photos.  rebooted the computer and 25 photos showed up on the desktop.  The long lost ones.

How rough was this plane......??

- one wingtip   770
- the other wingtip  767
- covering on top of covering 769
- wing center section  771
- aileron torque rods and previous rib repairs 768

Frank
« Last Edit: April 20, 2019, 10:25:58 am by Frank v B »
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Offline Frank v B

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Re: Frank's re-build of a Knox Hawkshaw's design/build
« Reply #10 on: April 20, 2019, 10:30:29 am »
Rebuild photos:

- filling in the center section after separating the wing.  Photo 776
- wing with the bottom of the ribs cap stripped.  Photo 781  Note the aileron servo wire has been fed through.  The yellow on the leading edges are previous balsa repairs.  This photo is taken from the center section looking at the starboard wingtip.

I wish I could say that photo 781 was deliberately bad to send Andy into a tizzy.  It was just poor photography, lack of knowledge and lack of caring about photography.   ;) :D.

Frank

« Last Edit: April 20, 2019, 10:56:37 am by Frank v B »
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Offline Frank v B

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Re: Frank's re-build of a Knox Hawkshaw's design/build
« Reply #11 on: April 20, 2019, 10:46:04 am »
Installing the motor:

- cut back the original motor mount (wood) with a Dremel cut-off wheel and sanding drum.
- made a template of the firewall out of scrap balsa (3/32) so all the nooks and crannies are cut out.  It needed to be 1/2" higher.
- drew the firewall onto 1/4" plywood and cut it out with a bandsaw.

The motor is a no-name 35mm approx. Power 32 size.  Will put 4 cells in it.

Funny.  When I cut through the basswood motor mount with the Dremel cut-off wheel, it got hot enough to make the oil in the wood bubble out.  Slime!

Done deal.

Frank
« Last Edit: April 20, 2019, 11:02:15 am by Frank v B »
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Offline Frank v B

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Re: Frank's re-build of a Knox Hawkshaw's design/build
« Reply #12 on: April 21, 2019, 11:12:24 am »
Installing the motor 2:

- attached the motor to the firewall with cap screws and T nuts.
- the firewall/motor combo just fits with a little pushing, shoving and twisting.

The first photo shows the pieces required to install  the motor:
- the motor/firewall assembly
- the spinner back plate
- a 3/32" balsa spacer so the prop nut can push against the backplate since the threading does not go deep enough.
- a 1/16" balsa spacer that is going to slip between the nose ring of the fuse and the backplate of the spinner.
- the prop nut and washer.

Approach:
- the firewall floats in the fuselage so it can find the proper alignment (zero/zero trust angle).  Note the 3 blobs of epoxy on the firewall in photo 117
- five minute epoxy will tack the firewall in place with the fuse held vertically (nose up).  See photo 115 with the fuse suspended from the ceiling. For all you sailors, that is a proper Clove Hitch used to attached the thing to the screw in the ceiling.  Note the balsa spacer between the nose of the fuse and the spinner back plate.
- when cured, permanently attach the firewall with epoxy and fibreglass.

Don't worry.  It works.

Frank
« Last Edit: April 21, 2019, 03:03:51 pm by Frank v B »
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Re: Frank's re-build of a Knox Hawkshaw's design/build
« Reply #13 on: April 21, 2019, 06:55:30 pm »
I could say something, but I won't.  :D

Offline Andy Hoffer

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Re: Frank's re-build of a Knox Hawkshaw's design/build
« Reply #14 on: April 21, 2019, 10:30:41 pm »
I am truly enjoying these chapter's of @Frank v B 's Rebuild to be Rekilled Encyclopedia.

A testament to his wondrous capacity for self-inflicted torture.

Andy 8)