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#1 SRWitt Nov 30, 2012 03:34 PM

Digitizng an old plan
 
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Hello all,

My first post in this sub forum. I've been browsing all sorts of plans lately looking for something to build as my first R/C airplane trainer. My base I'm starting from is the 1959 22" J3 Cub plan by Gerald Zeigenfuse, modified by Dave Robelen. I'm currently working on digitizing the plan in Draftsight by Dassault Systems.

A bit about me, I have a degree in mechanical design/drafting, and have found draftsight to be an awesome and free 2d drafting software, a good knockoff of Autocad. If you know Autocad, Draftsight is a breeze to pickup, without having to shell out dough for a legal version of software. I am an exprienced R/C Heli pilot, not quite 3d flying, but I can do some basic aerobatics.

Anyways just starting this post to share my work with everyone, today I've been working on modifying the wing plan, correcting some issues I've noted with the hand drawn version, hopefully I will be able to get a revisioned version of this plan cleaned up and easily scaled in .dxf format for ease of scaling and symetrical building. My plan is to scale the plan 150% for a 33" span, I'm not quite sure what I'm going to settle on for a power system, I've got a selection of lipos from my R/C Cars and helicopters, from 800mah 3s-2200mah 3s, and a 2200 2s.

I'm thinking a 10gram motor will do the trick, but not quite sure, more time and more research, I will settle on the power system once I get an idea of the AUW of the build once I get to that point.

Anyways onto todays work so far, I've traced the wing ribs, and plotted my root/center section ribs to have a built in 5* dihedral. At 33" span this gives me just under 3/4 of an inch at the tips. The plan is to build the plane as a full 4ch plane, possibly 5 after I learn the ins/outs of flying planes vs helis.

#2 RCROBBY Nov 30, 2012 03:56 PM

If you are going to get it laser cut, I would add tabs/notches to interlock everything since you have it in CAD. this makes for a stronger and faster building model.

#3 SRWitt Nov 30, 2012 04:02 PM

Quote:

Originally Posted by RCROBBY (Post 23406109)
If you are going to get it laser cut, I would add tabs/notches to interlock everything since you have it in CAD. this makes for a stronger and faster building model.

No laser cutting as of yet. You do bring up a good point though, although my degree is drafting/design, I've worked more on the fabrication side of things. I've been working as a CNC programmer/operator since graduating from school. I've worked with 3 axis routers and 3 axis VMC's. I may notch the LE/TE for the ribs, as it looks like this was the original designers intent, I'll look into notching the fuse formers/sides as well.

Another side project I've got going on is working on designing a 3 axis router for my hobby projects, planning a 3ft by 2ft working area. With the possibility of adding a low powered laser for laser marking wood and cutting foam(albeit very slowly).

#4 SRWitt Nov 30, 2012 05:37 PM

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An hour later, have the wing mostly layed out, just have to add spars, dihedral braces in the center section, finalize the wing tip supports and add gusseting. Rib spacing is 1.5" and 1/16" thick, not sure if I will stick with 1/16 thickness when scaled up or go with 3/32-1/8.

As far as spar sizing, I'm thinking a single 1/8X1/16 on the bottom, and 2 1/16 x 1/16 on the top (in the scaled up wing).

#5 Roto Rob Nov 30, 2012 06:29 PM

I had a micro Telemaster kit with a 10 gram CD type motor. It is close in size with a 35 inch span. It had plenty of power for loops, etc. Used most any small 3 cell lipo I had, from 500 mah to 900 mah.

#6 SRWitt Nov 30, 2012 07:34 PM

Quote:

Originally Posted by Roto Rob (Post 23407364)
I had a micro Telemaster kit with a 10 gram CD type motor. It is close in size with a 35 inch span. It had plenty of power for loops, etc. Used most any small 3 cell lipo I had, from 500 mah to 900 mah.

Funny you mention the Telemaster, I have the prints for the Telemaster 400. Still thinking of building it as well, and I just might, the Cub is helping me keep up on drafting techniques, trying not to get to rusty while being layed off.

#7 SRWitt Nov 30, 2012 09:19 PM

1 Attachment(s)
Another hour of work or so, I've got the wing tip braces drawn, still need to build cross members for the center wing section to build in the dihedral, and draw up a jig to align the wing root ribs at the matching angle when assembling the outer wing panels. No spars have been added as these are per the original plan.

I got the fuse sides traced, there is approximately 2.3* incedence per the original plan between the wing and horizontal stab. As drawn the stab slot is horizontal, with the LE of the wing being slightly higher than the TE. How will this affect an RC version? Its easy enough for me to change.

As is, I changed the front of the fuse to put the firewall former perpendicular to the stab, it is angled slightly forward at the top on the original plan. I'm not sure if thats do to the processes used to digitize and create the PDF of the plan that I am working from in the CAD software. The change in angle is very slight, could have been built in down thrust for the F/F version.

*Correction from the first post, I have 2.5* of angle on the center section ribs and wing root ribs, combined for 5* dihedral, which on the 22" wing gives approx .9" height at the bottom of the wing tip, and 1.34" on the 33" wing.

#8 SRWitt Dec 03, 2012 03:14 AM

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Got alot of work done tonight. A couple more parts to draw and I will be ready to do a trial build at the originals 22" span. All of the formers are drawn/modified. I've modified the formers and fuselage sides so they are notched together, all formers except for F2 and F7 notch in at the top and bottom of the fuse sides, F2 and F7 notch at just the bottom.

The only parts I have left to draw are the dihedral formers for the wing center section and wing panel root ribs, and parts to form the cowl forward of F1. Just to tired to continue tonight. I'm going to the Hobby shop tomorrow to pick up the wood I need that I dont presently have so I can start building something this week. :D

#9 RCROBBY Dec 03, 2012 07:59 AM

Quote:

Originally Posted by SRWitt (Post 23406171)
No laser cutting as of yet. You do bring up a good point though, although my degree is drafting/design, I've worked more on the fabrication side of things. I've been working as a CNC programmer/operator since graduating from school. I've worked with 3 axis routers and 3 axis VMC's. I may notch the LE/TE for the ribs, as it looks like this was the original designers intent, I'll look into notching the fuse formers/sides as well.

Another side project I've got going on is working on designing a 3 axis router for my hobby projects, planning a 3ft by 2ft working area. With the possibility of adding a low powered laser for laser marking wood and cutting foam(albeit very slowly).

We seem to be birds of the same feathers, My degree is in CAD/CAM as well with CNC as a minor. My day job however is on the designer side of things though. I do CAD in the day and CAM/CNC in the evening, lol. I built my own router 27x42 cutting area but decided to purchase a laser as I wanted a larger cutting area.(36x48)

Looks like you are making good progress with the plans/parts.

#10 Steve85 Dec 03, 2012 12:43 PM

1 Attachment(s)
Quote:

Originally Posted by SRWitt (Post 23406939)
As far as spar sizing, I'm thinking a single 1/8X1/16 on the bottom, and 2 1/16 x 1/16 on the top (in the scaled up wing).

SRWitt,

I doubt your spar will be stiff enough for your scaled-up design. The LE and TE don't actually add much strength or stiffness, so perhaps you should consider a built-up spar that combines stiffness, torsional rigidity and light weight. At your size model, I'd go for two medium-hard 3/32" square balsa spars about 30% of the wing chord behind the leading edge, one top and one bottom. Once they're installed, glue some 1/32" balsa sheet joining the front faces of the two spars between each rib. These "shear webs" will increase the stiffness of your wing by several times.

If you like, you can add one or two 1/16" square sub-spars to the top of the wing ahead of and behind the main spar to help prevent the covering from sagging, but they won't contribute much extra strength.

Steve

#11 SRWitt Dec 04, 2012 03:59 PM

1 Attachment(s)
Progress today. I've got most of the parts layed out(for 22" original design), and ready to start building. All I have to finish now is the cowl section. Anyways heres the parts layout(minus cowl pieces) in PDF. Once I get a mock up built, I will start working on a scaled up version. The parts are layed out as they are in the PDF so I could pick each section in my cad software and print 1:1 on 8.5x11 sheets from the .dxf file. I haven't tried poster/tile printing the PDF but it doesn't look to be as friendly requiring six sheets to print vs the 3 I can print from the CAD software.

#12 segraves Dec 05, 2012 06:35 AM

Quote:

Originally Posted by SRWitt (Post 23440994)
... I haven't tried poster/tile printing the PDF but it doesn't look to be as friendly requiring six sheets to print vs the 3 I can print from the CAD software.

Poster/Tile printing to 8-1/2x11 in Landscape mode should require only 3 sheets.

Cheers,
Bill Segraves

#13 SRWitt Dec 05, 2012 04:25 PM

Quote:

Originally Posted by segraves (Post 23445943)
Poster/Tile printing to 8-1/2x11 in Landscape mode should require only 3 sheets.

Cheers,
Bill Segraves

It makes no difference, I tried switching between the two, Adobe still wants to use 6 sheets.

#14 BJ64 Dec 06, 2012 06:34 AM

I've asked this in another thread (slow response), so I hope you don't mind me asking it again in here.

I'm new to CAD/CAM & CNC, but I'm looking for some simple and cost-effective software that will allow me to input some accurate cross-sections, arrange them as per the offset's (spacings) on the plan, and then CNC hotwire the fuselage foam sections from there (to end up with a plug to mold from).

I've had a look at DevFus and DevFus Foam etc. - but they seem to go the other way. i.e. input a 3-view and create the cross-sections from that. As well as the 'virtualized' 3D fuze sections.

I need to find something that will accept my cross-sections + known spacings and produce to a 3D solid and cut from there.

The 'long hand' way to do it, of course, is to cut all the cross-sections in something like 3mm ply, cut the foam to the required spacing, and manually hotwire around each 'sandwich section'. But that's a lot of scroll-sawing, smooth-filing etc. of ply, then arranging that lot to build up a set of foam sections. If I could do away with the woodwork, and just use a CNC hotwire to produce the foam sections, it should end up saving me a heap of work.

Any info would be greatly appreciated.

BJ:)

#15 SRWitt Dec 06, 2012 11:35 AM

Quote:

Originally Posted by BJ64 (Post 23455207)
I've asked this in another thread (slow response), so I hope you don't mind me asking it again in here.

I'm new to CAD/CAM & CNC, but I'm looking for some simple and cost-effective software that will allow me to input some accurate cross-sections, arrange them as per the offset's (spacings) on the plan, and then CNC hotwire the fuselage foam sections from there (to end up with a plug to mold from).

I've had a look at DevFus and DevFus Foam etc. - but they seem to go the other way. i.e. input a 3-view and create the cross-sections from that. As well as the 'virtualized' 3D fuze sections.

I need to find something that will accept my cross-sections + known spacings and produce to a 3D solid and cut from there.

The 'long hand' way to do it, of course, is to cut all the cross-sections in something like 3mm ply, cut the foam to the required spacing, and manually hotwire around each 'sandwich section'. But that's a lot of scroll-sawing, smooth-filing etc. of ply, then arranging that lot to build up a set of foam sections. If I could do away with the woodwork, and just use a CNC hotwire to produce the foam sections, it should end up saving me a heap of work.

Any info would be greatly appreciated.

BJ:)


Sorry can't help ya out with this one. I know next to nothing about cnc hotwires.


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