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Old Jan 01, 2011, 11:28 PM
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Scratch built BE1900-video added

Hello, Im looking for some help and idea to building a light strong aircraft. Ive got a scaled up set of the 3 view shown here. It will be 60in ws, brushless, and planning about 45 to 55oz. Im planning to start the wings and ive drawn some ideas for the ribs. Once I get the design down I can place my parts order. I have some questions though. Thanks for any help, Ive never done a build thread but ill post anything if anyone is interested.

1. I was planning 3/32 ribs set at 2.5in over 60in. Is this to much or not enough? 1/16 ribs?

2. the wing will be 1.2in thick at the fuse and .5in at the tip. How would I build a double taper? Would it be easier to only taper the bottom or top?

3. Would the wing be stronger/heavier fully sheeted or center sheeted and cap stripped out towards the wing tip.

4. could a balsa spar be used instead of basswood?

Im planning flaps, although they will probably be just a built up plain flap.
the two wing halves framed and joined via ply joiner. Any thoughts or ideas id be happy to hear. Ive built many kits but nothing from scratch and nothing scale. I might try retracts in this too if I have the room or weight. thanks
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Old Jan 06, 2011, 08:02 AM
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Boston, MA subburb
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Quote:
Originally Posted by olds455 View Post
Hello, Im looking for some help and idea to building a light strong aircraft. Ive got a scaled up set of the 3 view shown here. It will be 60in ws, brushless, and planning about 45 to 55oz. Im planning to start the wings and ive drawn some ideas for the ribs. Once I get the design down I can place my parts order. I have some questions though. Thanks for any help, Ive never done a build thread but ill post anything if anyone is interested.

1. I was planning 3/32 ribs set at 2.5in over 60in. Is this to much or not enough? 1/16 ribs?

2. the wing will be 1.2in thick at the fuse and .5in at the tip. How would I build a double taper? Would it be easier to only taper the bottom or top?

3. Would the wing be stronger/heavier fully sheeted or center sheeted and cap stripped out towards the wing tip.

4. could a balsa spar be used instead of basswood?
snip . .
thanks
I built a 54 inch wing for a 48 oz aircraft. The wing style was D-tube construction with build-up ailerons and cap strips over the ribs. Total weight was 9 oz with two 20 in-oz servos (Futaba S3114s) in the wing.
1. I used 1/16th inch balsa (on 3 inch centers) for ribs and cap strips. My next build will use 2 3/4 inches between ribs only because that dimension gives me evenly spaced ribs over the wing span.
2. I recommend less of a rib thickness taper toward the wing tip in order to prevent tip stalls. On my next tapered wing, I plan to use a 12% thick rib at the wing root and 14% thick rib at the tip. See http://www.rcgroups.com/forums/showthread.php?t=468596 for more of an explanation. As far as the taper direction, you could build the wing upside down, using tabs on top of ribs to keep them level, with the top spar flat on your building board which would produce a slight added dihedral. One person said the wing looked better with a flat top spar.
3 /4. I use a D-Tube construction with an I-beam spar. The spars were 1/4 inch x 1/16 inch spruce separated by vertically-grained, C-grade balsa. Only the center portion to the 2nd rib is fully sheeted to help with compression forces. The wing is very rigid and very resistant to twist.

If you were to epoxy carbon fiber strips on a balsa spar, it would be strong enough but you would need a different set of materials, methods and skills. It may also be more flexible and not support free movement of ailerons. See http://www.charlesriverrc.org/articl...spar_build.pdf for one construction method. Another is to just epoxy carbon-fiber strips on thinner balsa spars as in http://www.rcgroups.com/forums/showp...3&postcount=81 and separate the spars with webbing.

Alan
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Old Jan 06, 2011, 11:55 AM
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Ware, herts. U.K.
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I can see how you'd need to keep the weight down on that one!

I can save you at least 50% on material for the wing alone - probably more.
The trouble with using the complete aerofoil for rib sections is that you land up having to waste a lot of balsa by cutting out lightening holes. The solution is not to put the holes there in the first place. The only time you need the whole aerofoil is for the cutting out template. What I do is lay the template on the sheet and cut only the top line, then move the template down about 3/8"-1/2" and cut the top of the next. That way you waste next to nothing. You are probably going to spar web most of the wing anyway so just use that to join top to bottom.
Cut out and join all the soft 1/16th sheet you need for the upper surface, glue on the spars (tapered to the tip to save more weight) then cut and fit the top sections of wing ribs. You then have a complete wing top to build the rest of the wing onto.

This works like a dream on constant chord wings, but can easily be adapted to wings like you are going to be building. In that situation I would 'slide' the template round a bit on the sheet when cutting out the smaller rib parts near to the tips. This works fine at our scales unless you are really picky about faithfully reproducing the wing section at the tips.

I'll post you a picture of my latest wing done this way... It's 82" span and the spars are Cyparis - as strong as Spruce with far less risk of splitting and as light as hard grade balsa.
To give a better impression of size the top sheet is three complete 36"x4" x1/16" soft balsa sheets glued together. I have included a photo of the first wing structure complete so you can see how much air and how little balsa.
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Old Jan 06, 2011, 01:54 PM
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Ware, herts. U.K.
Joined Sep 2008
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As a further reply to your questions...

1. 3/32 is fine for the wing root but 1/16 would be my suggested for outboard of the engines. But SOFT balsa in both situations. Rib spacing 3" as Al Offt says - again using soft sheet. Could go to 3.5" outboard of engines.

2. Further to my earlier post build wing top section upside down on the baord to start. You will then have a straight upper surface tapered in plan. You could then just add the underside by eye. I would set up a couple of rib undersides and lay the bottom spar in, cutting intermediate rib sections to suit. That way you set wing thickness at key points and interpolate, sanding out any slight irregularities.

3. Definitely sheet the top surface for strength and visual reasons. Being the more curved surface the balsa is used to best effect there to withstand compression forces in flight. I would only sheet the underside from LE to forward spar to make up the rigid D-box that will stop the wing twisting.
Never centre sheet! Always put all structural materials at the wing's outer surface.

4. Yes a balsa spar can be used, but you would have to use a larger spar in order to get the same strength so the weight comes back. Having said that we all still build far too much strength into our models so it may well be that balsa of the same size as basswood would in practice be found to be adequate.
You will of course be paying as much attention to building the fuselage as lightly as the wings...

Personally, particularly as you are thinking of installing retracts I would build the model in four sections.
Section 1. The heart of the model - wing centre section out to the far side of the engine nacelles with all the nose forward of the main spar permanently fixed. This will allow the use of a single retract servo (SuperTek S138GH suggested for slowness - or programmable digital Hyperion Atlas) to be used to operate all three wheels. All the radio gear will have easy access positioned in the centre section.
Section 2. Tail and fuselage aft of main spar. Two servos will be positioned upside down in this and pull-pull connected to tail surfaces for lightness. A D9 connector can be used so that these are automatically connected the moment the tail end is plugged into position. I use a 20swg wire loop and pin fixing system for all my models so weight is negligible and it is more than strong enough.
Section 3 and 4. Plug in wings outboard of nacelles.

The model in my atavar was done this way. Span is 112" due to be published soon in RC Model World.
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Old Jan 07, 2011, 03:23 PM
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Thanks you Al and 4wings. Ive got the parts on the way. Ive made the inner and wing tip templates and have my table ready to get started. Im planing ti use 1/16 throughout for ribs and sheeting. Either 1/16 or 3/32 for webbs and im not decided on spar material. Im planning on the "d" tube as ive built plenty of these before. the ribs are now going to be about 1.35 thick at the root and .75 at the tip. Im going to look at spacing the ribs out some. I may or may not try to lighten the ribs any. I want to get the parts together and weigh the parts, then make a choice from there. Im still working on how to join the wings to the fuse. Ive always used the two dowel and rear bolt method.
I was planning to box the fuse with 1/4by1/4 balsa with formers top and bottom with stringers. Or build former halves with stringers, possibly sheeted.

I was planning on air retracts for the ease but the wing needs framed up first.

Eyes4wings, could you elaborate on "never center sheet". are you refering to the center of the wing top and bottom? That wing technique is very interesting.

Ive seen alot of the webbing set up to form the "i beam" in the center of the spar. ive always put it on the trailing edge of the spar.

Is either way better?

Thank you guys for the help
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Old Jan 07, 2011, 04:32 PM
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eye4wings's Avatar
Ware, herts. U.K.
Joined Sep 2008
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I assumed that when you said centre sheet you were referring to the method sometimes used for the tail of fabric covered aircraft. If you have a strong covering for these surfaces, silk, nylon, Solartex, Diatex etc., (and probably bracing wires or struts) fine, but the sheet is then of very little help to the strength, mostly replacing any inner wire cross bracing in the full size.
That is a technique you would not use for your mainplanes... but if you've built plenty, you would know that anyway.

If by centre sheet you meant spar bracing, then I misunderstood and apologise.

The purpose of the customary vertically grained sheeting joining the top and bottom spars is to convert two rather whippy (and wimpy) beams into one deep and very strong one. With spar webbing the bottom spar in flight supplies (together with any underside sheet skin) the wing's tensile strength and the upper one is in compression. The member in tension will remain straight and effective unsupported but the compression one will tend to bend out of line and fail. The spar webbing (1/16" would be fine) stops this happening. If there is really strong compression (when pushing the I beam to its limit) the top spar member could still twist and break the glue bond with the web, so at high stress points I will sometimes partially web the other side of the spar members to stop this happening. For normal situations this is not vital because the glue bonding the top spar to the ribs will also work to resist the twisting tendency.
I am not aware of anything that would normally dictate whether it is better to web the front or rear edges of the spars. Quite probably other factors like wheel well sizes or accessibility of control runs will make the decision clearer.
Personally I do not like the central webbing that some us. I would always prefer to stress a glue joint in shear than in pure tension. The central position loses the small extra adhesion to the top skin and requires a thicker sheet web to get a similar glued area.

On your fuselage construction I suggest that 1/4" square is overkill and that if you build the sides to start with using 1/16" soft sheet formed to a quarter circle section a single strip top and bottom of 3/32"x1/4" would be enough. You would then be able to set up the fuselage sides over the wing centre section rather like two separate I beams - although more 'C' shaped actually - which will allow full access to get the fixings placed before you add the top and bottom quarter-circle shaped formers and sheet over them to complete the mostly cylindrical fuselage. This is the lightest structure that I have found using balsa.
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Old Jan 07, 2011, 04:57 PM
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Thanks Ill get some pics and update when i get started.
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Old Jan 08, 2011, 08:57 AM
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ref: Ive seen alot of the webbing set up to form the "i beam" in the center of the spar. ive always put it on the trailing edge of the spar

I attach webbing to the center of the spars because my experience has shown that glue joints are weakest in sheer (sideways motion). If you attach the webbing to the outside of the spar and the wing gets stressed up/down, the glue joint on the outside of the web would separate earlier than between the spars. You might want to convince yourself by gluing two sets of two 1/4 inch square pieces together in a "X" and then try pulling one set apart perpendicular to the joint while twisting the other set apart.

In addition, I wrap the spars/webbing combination with unwaxed dental floss secured by CA glue to minimize separation in high stress areas: center joint (or jointer box) of wing panels and/or the outer joint of a polyhedral wing.

Alan
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Old Jan 08, 2011, 09:13 AM
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I've been investigating retracts for a 48 inch WS plane and decided on mechanicals with one servo similar to that shown in post 4 of http://www.rcgroups.com/forums/showthread.php?t=383680

I don't know what is involved with pneumatic retracts but from what I have seen in pictures, they seem very complicated and consume a lot of space for a 60 inch wingspan plane. Also, If you do make a three-piece wing (joints outside of the engine nacelles), the single servo, mechanical retract could work.

Another alternative for mechanical retracts is to use one servo per retract as shown in the picture at http://www.rcgroups.com/forums/showp...70&postcount=9

Alan
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Old Jan 08, 2011, 09:36 PM
IWC
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This company use to have a really nice 3-D drawing of a 1900 on their website. I believe the drawing illustrated the balsa framework. He was considering a kit at one time.
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Old Jan 11, 2011, 09:03 PM
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I got another response from parkscale. It's still put on the back burner. I picke up a set of jet pro air retracts that should work out well. My balsa arrived but due to changes in the wing I'm now going to use a different le and I have to make each rib separately. I did build the horizontal stab and elevators today. They weigh .7 ounce. Pics to follow.
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Old Jan 12, 2011, 10:08 AM
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Originally Posted by olds455 View Post
I got another response from parkscale. It's still put on the back burner. I picke up a set of jet pro air retracts that should work out well. My balsa arrived but due to changes in the wing I'm now going to use a different le and I have to make each rib separately. I did build the horizontal stab and elevators today. They weigh .7 ounce. Pics to follow.
Look forward to the pictures. Hope your winter has been mild.

Our family visited Anchorage on bus tour from Anchorage to Valdez, Fairbanks, Denali, Seward and back to Anchorage in July of 2009 (the year of 80+ degrees). One of the best trips we have taken. Really liked the open space/park in the center of Anchorage.

We'll getting another Noreaster today - 12 inches so far with 18 inches projected. The street has been plowed but I'm working from home part of the day and will dig out around dinner time.

Good luck with your build,
Alan
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Old Jan 12, 2011, 05:50 PM
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Based on the three view, at 60" span I get 367 square inches wing area. Not much wing for a scale plane this size. Keep it light!

eye4wings, I like your two piece wing rib idea. Is it practical for such a thin wing? Savings?
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Old Jan 12, 2011, 06:49 PM
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Well here are the pics. the parts look better in hand. theyve only been rough sanded and need final shaping and finish sanding. The le on the stab is 1/8x1/4, ribs are 1/16, te 1/4x1/4 and 1/16 sheeting. On the elevators, the le are 1/8x1/4 doulbled where hinges go, 1/16 rib and 1/16 sheeting. I didnt get any width measurments at work to day for the vertical stab and rudder. On another note, my friend got my ribs designed in profilli(?) and ill have them tomorrow to transfer and cut.

Eye4wings, could you elaborate or show a pic of your fuse technique you refered to?

Ive only used air retracts so thats what im planning to use. they should be here in a couple days.

At 58in i get 334 of wing area and at 55oz the wing loading comes to 23.8. My dash-8 is about 33, its quick but manageable. well see how this one goes. I figured if the wing is 12oz, the fuse 12oz, the tail 4oz, and the retracts 4oz comes to 32oz. this leaves 23oz for motoers,esc, bat ect. To just frame the wing, the components weigh 5.5oz so there's some room. We'll see.

Winter has been decent, we had a warm spell with temps to 40+ then a snap to -10f. its been about 10 to 25 the last couple weeks. Not to bad.

One question to all? The elevator is on two angles. How is a decent way to hook them together for parallel movment?

Thanks
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Old Jan 15, 2011, 04:42 PM
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ive been busy lately with the 1900. Ribs were transfered and cut during down time at work. Then some free time yesterday and this morning i was able to complete these. They weigh 3oz as they sit. The control surfaces need built and alot of planning comes next. How to operate those surfaces, where to mount them, the retracts, rib doublers for retract mounts, wing brace for joining, sheeting, wing tips, ect.

I was planning one servo for flaps and one for the ailerons. flaps hooked via torque rods. the outer flaps connected to the inner flaps somehow.

If anyone has any tip or ideas on how to build nacelles, operate the four flaps, operate the two elevator halves, build the fuse ect, i would appreciate any info recieved. Thanks
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