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FF2017 Int. Racers: Crosby CR-4

HilldaFlyer

Well-known member
#21
I glued the top fuselage panel to the horizontal panel and cut off the back end in order to fit the tail.


I didn't realize how long this 1/4 scale would be. Shown here with the tape holding the panels together while the Gorilla Glue cures.
 

HilldaFlyer

Well-known member
#22
1/6th scale Crosby CR-4

At this time in the build the rules announcing 1/6 scale was made. Nothing lost... rescaled the plans and adjusted the design a bit. Instead of having a "+" profile with formers, the 1/6th scale will have a box fuselage with rounding top and bottom panels. The prototype will be made with Ross foam. The plans are designed to be very approachable to people with intermediate FT build techniques. Here are the plans I just finished.



Let the prototype build begin... (again).
 

FAI-F1D

Free Flight Indoorist
#24
Wow! There's some nifty stuff here. I've actually see a couple ideas for how to approach my Sk-4 build.

What are you using to bond the fiberglass?
 

HilldaFlyer

Well-known member
#25
Looking good! Really like the internal control rods for elevator and rudder - very clean and simple.
Well, the 1/4th scale is big enough hide just about everything... I'm going to try that on the 1/6th scale, but if it doesn't fit, I'll have external control rods... We'll see.
 

HilldaFlyer

Well-known member
#28
What flavor of the Kwik Kick do you use/prefer?
Edit: Ok, now that I look at it some more there is only one type/flavor. Kwik Kick is both the name for the resin and the hardener, right?
Yup - one flavor of kwik kick... I did, however, purchase all the other mixtures to test the flexibility ( I guess people in the epoxy field call it modulus). I think the more flexible resin will perform better, or not break so easily... we'll see.
 

HilldaFlyer

Well-known member
#29
Looking good! Really like the internal control rods for elevator and rudder - very clean and simple.
Thanks- clean yes. One thing that I'm concerned about with this configuration is weight in the tail. The music wire used is pretty hefty to alleviate twist. I first tried using extruded carbon fiber, but because it is linearally extruded, all the fibers are unidirectional so twisting will separate the strands. I'm hoping the motor way out in front will compensate for the tail weight. With the small wings on these racers... got to keep the weight down.
 

HilldaFlyer

Well-known member
#30
1/6th scale Fuselage

This week I got the prototype of the fuselage assembled.

These are the fuselage panels, the bottom panel will fit internally about half way from the top and bottom panels. I have yet to design the bottom panel... I first want to see how the wing fits before I make the pattern.


Here it is with the nose and turtle deck formers in place and the middle fuselage former (you can barely see it about half way up the nose cone at the height of the tape. The cockpit is located at the double tape between the short and tall formers.

At this point all I want to say is yuck! Not yuck to the plane but working with foam board makes blocky looking aircraft. I've measured several times and the width is to scale, but it still looks too wide. I wanted this to be rounded a sleek like the real thing. Blocky and square is the really easy way to build, but if I wanted to make the fuselage more "rounded" I would make it more of an octagon shape. I may do that because I'm just not happy with the blocky look.

The tail is too fragile for the forces that will be put on it, so I doubled up the thickness.


 

PsyBorg

Wake up! Time to fly!
#31
Is there no way to do the "Roll the foam on a table edge" trick to get the more round fuselage and do all round internal rings as the framework? I think maybe if you make the sides that are now vertical a little longer you could probably get a near perfect roll all the way around where you wouldn't have to use former's for the turtle deck are as that would all be part of the frame.

I don't know much about design or build techniques but seeing rounded engine cowls come out nice in some build videos using that trick makes me think it can be transferred over to fuselages with a little practice and maybe some modification on methods. I am probably wrong tho as most my ideas seem to get shot on the launch pad :p
 

nerdnic

nerdnic.com
Mentor
#32
This week I got the prototype of the fuselage assembled.

These are the fuselage panels, the bottom panel will fit internally about half way from the top and bottom panels. I have yet to design the bottom panel... I first want to see how the wing fits before I make the pattern.


Here it is with the nose and turtle deck formers in place and the middle fuselage former (you can barely see it about half way up the nose cone at the height of the tape. The cockpit is located at the double tape between the short and tall formers.

At this point all I want to say is yuck! Not yuck to the plane but working with foam board makes blocky looking aircraft. I've measured several times and the width is to scale, but it still looks too wide. I wanted this to be rounded a sleek like the real thing. Blocky and square is the really easy way to build, but if I wanted to make the fuselage more "rounded" I would make it more of an octagon shape. I may do that because I'm just not happy with the blocky look.

The tail is too fragile for the forces that will be put on it, so I doubled up the thickness.


Getting nice lines with foam can be tricky, it might take you a few versions to get the look you want!
 

HilldaFlyer

Well-known member
#33
Is there no way to do the "Roll the foam on a table edge" trick to get the more round fuselage and do all round internal rings as the framework? I think maybe if you make the sides that are now vertical a little longer you could probably get a near perfect roll all the way around where you wouldn't have to use former's for the turtle deck are as that would all be part of the frame.

I don't know much about design or build techniques but seeing rounded engine cowls come out nice in some build videos using that trick makes me think it can be transferred over to fuselages with a little practice and maybe some modification on methods. I am probably wrong tho as most my ideas seem to get shot on the launch pad :p
Thanks for the ideas... and sure - I've played with rolling the foam and it works well, but it seems that it never meets up with the abutting side just right. The other trick that you pointed to is how to get the framework inside so it all fits nice. I've redesigned and I'm going to try a octagon shape and see where that takes me.
 

HilldaFlyer

Well-known member
#37
Work is coming along. Been too busy to post progress... but progress is three steps forward two steps back.
I've been spending a good deal amount of time working on the 1/4 scale Crosby. I built a wing for the 1/4 scale and it was too thin for the retracts, so I redesigned and now the top panel is too short with all that curve. The wings for the 1/6 scale are done, but the three fuselages I built I am not happy with the shape, so I'm starting over.

I've purchased 5 possible motors and bench tested each with several props so I don't over-prop the motor ESC. Details coming soon.




Cockpit on top fuselage 1/4 scale


Added formers to the bottom of the fuselage. The fuselage will be skinned with fiberglass.
 

HilldaFlyer

Well-known member
#38
I've spent the last few weeks working on getting retracts into the 1/4 scale Crosby. The first wings I designed to be thinner that scale will not accommodate the landing gear, so I redesigned the wings back to the scale thickness, or pretty near.


The trailing edge was beveled to 4 cm from the edge and about 2 cm from the tip.


At first I tried to make a flat mounting plywood and angle the landing gear within it. This was quite difficult to repeat, however, I think this would be the easiest to attach.


Here is the 3rd or 4th attempt using triangles to elevate the front of the landing gear mounting plate.



Another angle.


Inside


Outside

Here is the gear extended.




Working on the gear cover - here is prototype #1 that has a sliding door to cover the hole.




 

HilldaFlyer

Well-known member
#39
Crosby CR-4 1/6th scale

continued from post 30 -
If you're having a hard time following this post... you're not alone. I started building the 1/4 scale model first and then when the final rules were posted, I started again on the 1/6th scale. So here is the advancements for the 1/6th scale model.

I commented above that I didn't like the square boxy looking fuselage. So, I've redesigned the fuselage to used formers that will be covered in fiberglass. I haven't started building the fuselage, but will over the Thanksgiving break.

I have, however, built the main wing and the tail. The main wing ended up with a twist in it so it will have to be redone in order to fly, but I learned a lot from putting it together.

Here is another prototype of the fuselage with an octagon shape... again, I didn't like the way it turned out, so it is scrap.


Gluing the central former.

Attaching the other side.

Didn’t like the way it turned out either… scrap it!


 

HilldaFlyer

Well-known member
#40
Crosby CR-4 1/6th scale

Started work on the wings…



Fiberglassed the outside surface.

Used tape and a sanding block to taper the trailing edges.



Made some spars, 2 mm carbon fiber rod with 3.14 oz fiberglass shear webbing.



Cut attached the foam spars/spacers to both wings.



Glued the wing halves together and the real spar to the foam spar.



Cut out the flaps.



Attached flap servo.



Attached flaps to the wing with polyester tape hinges. The blue masking tape is holding the hinges in place until the epoxy cures.



Added control horns.



Attached aileron servos.



Cut away part of the upper wing surface that impacted the flap function. This part of the wing will be underneath the fuselage, so the cut away will not show.



Glued top wing surface to the bottom.



Finished the tail.



Covered the tail surfaces with 0.73 oz fiberglass.

Time to get back to the fuselage...