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Old Jan 14, 2013, 01:44 AM
White Hat and Proud
cncworkbench's Avatar
Australia, VIC, Melbourne
Joined Nov 2009
58 Posts
Hi Scott,

A credit to you, great documentation and build thread...

Looking forward to view the thread as the construction unfolds.....

Andy
www.rcplans.com.au
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Old Jan 14, 2013, 10:26 AM
Just plane Mad
paramtn's Avatar
utah
Joined Dec 2002
407 Posts
Build

Scott

Wow you are a master. This will be a work of art when finished. I can not wait to see it fly. Should be great for aerotow events. This type of building does not happen much these days so it is always rewarding to see your projects. I'll be watching as you go. Let me know if you need anything soldiered or any other parts we can make here in the shop. If you need an extra set of hands in your shop I would be happy to help. Good luck.

Ted
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Old Jan 14, 2013, 11:47 AM
Pledged to Always Chase Wind
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USA, UT, Salt Lake City
Joined Oct 2004
1,631 Posts
excellent pictures and build log.

Subscribed!
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Old Jan 14, 2013, 07:03 PM
Registered User
Utah, USA
Joined Jun 2007
616 Posts
Rudder servo and bellcrank

For rudder pull-pull I always use a remote bellcrank so that the servo output shaft doesn’t have tension put on it from the pull-pull wires. I am using a Nelson BB bellcrank, but those are no longer available. You can also make bellcranks out of the Hitec heavy duty servo arms. The distance between the pull lines is 1˝”. Both the bellcrank and rudder horn have to be the same. Glue the tray in place when satisfied with the setup. The left longeron is still taken off to ease the in and out of the equipment trays.
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Old Jan 15, 2013, 07:09 AM
quickee
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United States, UT, Sandy
Joined Jul 2005
665 Posts
Scott
Looks great-can't wate to see it in the air.Nice pictures.
-Ron-
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Old Jan 15, 2013, 10:15 AM
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Canada, ON, Toronto
Joined Jan 2004
808 Posts
Scott, I would put a bigger arm on your servo for two reasons, first to give you the straight run to the bellcrank, and secondly to increase your rudder throw. You're losing throw with a smaller radius servo arm going to the outer hole on the bellcrank. The 645 can certainly deliver enough torque for that change.

Best fix would be to move your pull-pull wires to the outer holes and the pushrod to the inner holes on the bellcrank, but as you said, the bellcrank and rudder horn distances have to be equal. Is the rudder horn cast in concrete yet?

DS
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Old Jan 15, 2013, 10:24 AM
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Utah, USA
Joined Jun 2007
616 Posts
Seadog,
I actually did a drawing of the pull-pull setup. Using the complete throw of the servo, and measuring the movement of the bellcrank at the pull locations, as well as measuring the corresponding rudder movement, I will just about bang the rudder against the elevator in each direction.
My main concern was to use the full servo movement to maximize the precision and torque available.
The rudder horn is not cast in stone, but is the same setup as used on the Charlesworth plans and with the Flair Ka8.

Scott
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Old Jan 15, 2013, 10:31 AM
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Canada, ON, Toronto
Joined Jan 2004
808 Posts
Sounds like you've got it covered. I figured you would!

Dave Smith
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Old Jan 15, 2013, 05:29 PM
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Utah, USA
Joined Jun 2007
616 Posts
Battery tray, modified

The battery tray mount was supposedly modified to a lower position in the nose (see CAD drawing) but that apparently didn’t make it to the cutting files I received. As I will be using 2 LiFe packs and switches, plus an electronic switch and voltage regulator, I decided to modify the tray to allow me to slide the packs out of the plane for charging and maintenance.

Lots of ways to do a sliding tray; look at the photos to see how I did it. The sliding base is 1/16" ply. It is tapered to maximize the space. Cocking the tray so it is under both rails makes it easer to get in. After pulling it out about 1/3 of the way it is free. The 1/8 ply stop on the end has 2 purposes: to grab on for pulling out, and to keep the tray from getting stuck like a Morse taper! Glue the tray/rail assembly in place when satisfied with the fit.

With all 3 equipment trays glued in place, you might as well glue the left longeron in place also.
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Old Jan 16, 2013, 11:48 AM
yyz
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USA, CA, Paso Robles
Joined Dec 2004
2,405 Posts
Scott,

Serious skills! Looks great.

I'm curious about the use of Titebond vs CA. I haven't built an all-wood glider in a number of years but wondered about your experience w/ Titebond's ability to penetrate into the joint vs CA.

Mike
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Old Jan 16, 2013, 12:09 PM
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Utah, USA
Joined Jun 2007
616 Posts
Planning for lead

There is no fat pilot flying this sailplane, so you WILL need weight up front to balance correctly. The farther forward lead is put, the less is needed. From my limited experience and reading of other build logs, somewhere between 20-25 ounces of lead in the nose will be needed to balance. I would think that this model will weigh around 8.5 lbs. ready to fly; my Flair Ka8 weighed 9.5 lbs., and this is a lighter design. That would be a wing loading of only 13 oz./sq.ft.; pretty light. Might need ballast to fly better.

I sealed off the top of F2 and filled the space with type lead and enough epoxy to hold everything in position; it weighs about 17 oz., which is a start. If using a lead shot and epoxy mix, then either put it in a zip lock bag and fit in place, or pour it in after most of the planks are in place. For further weight control, the nose block can be made of balsa to hardwood, and hollowed for lead if needed. It won't be glued on until just before finishing. There is also space for lead around the aerotow release, the next bay back, and even on the front of the battery tray.
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Old Jan 16, 2013, 12:20 PM
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Utah, USA
Joined Jun 2007
616 Posts
Stab hold down

I doubled the thickness of the stab hold down nut plate with 1/8" birch ply, also making it a little longer to spread out the stresses. If there will be a servo in the stab, then I recommend drilling the bolt hole about ˝" forward from the marked location to give more servo space. I put in a T-nut for a steel bolt. Your choice on small diameter steel or larger diameter nylon; there are arguments for each approach.
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Old Jan 16, 2013, 12:32 PM
Registered User
Utah, USA
Joined Jun 2007
616 Posts
CA vs. aliphatic/Titebond

Mike,
My experience with CA is that sometimes it wicks too well, especially with liteply, not leaving enough in the joint to hold well. Wood glues, of which the aliphatics are some of the best, leave a joint stronger than the wood itself (try ripping one apart and it will split the wood before the glue joint) and have some gap-filling properties. Titebond also is not as brittle as CA's, which in flying any model airplane can be a plus. Yes, it takes longer to wait for the glue to dry.
Can you build this whole model with CA, thin and thick? Sure. I just think it will be more expensive and won't be as solid. Not sure how well it will hold the planking.
I have the time; I am willing to wait.

Scott
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Old Jan 16, 2013, 08:00 PM
yyz
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USA, CA, Paso Robles
Joined Dec 2004
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Thanks Scott. Great answer and makes complete sense.
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Old Jan 17, 2013, 04:24 PM
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Utah, USA
Joined Jun 2007
616 Posts
Cutting the nose planking

Lightly sand the formers and canopy frames to take off the sharp edges and blend the surfaces.
Using 1/8" sheets, cut 18 planks for both the top and bottom nose using the supplied templates. The templates say 9 planks, but 18 is correct. The planks are cut at a 5° angle on each side, AWAY from the template. There are several ways to do this:
1. Modify a Master Airscrew Balsa Stripper to cut at an angle (see photo)
2. Cut a hard block of wood at an angle and attach a blade to it
3. Freehand the cut at an angle

I also thought about some sort of sanding or routing fixture. In the end I used #3, a freehand cut; I used the angled block as a check. If/when the planks need to be fit more precisely I will use the angled block, with sandpaper attached, to "touch up."

Keep the template aligned with the balsa grain while cutting, which will mean flopping the template end-for-end for the next plank.
I used the hardest 1/8" balsa I had (15-18#) for most of the planks as the curve is not that bad, and I need weight anyway. Lighter weight wood will be easier to clamp, tape or pin in position; your choice. I did cut about 8 medium planks (8-9#) for the top part of the nose where it transitions into the canopy frame. When the bend got difficult, I put the front 1/3 to ˝ of the plank in boiling water for ˝ hour, clamped in place, then glued and reclamped after it dried and had conformed better to the curve. As with any planking or sheeting, try to match the hardness/stiffness on each side to keep the stress on the fuselage equal.
By the way, the lower planks can be cut shorter if you are into conserving balsa, as they only go back to F9 instead of F12.
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