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Sinbad Jr. 30 inch Glider (Read 744 times)
Reply #30 - Jun 21st, 2017 at 3:46pm

Brad   Offline
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Portland, Oregon area

Posts: 272
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The good news is that I loosely assembled the entire plane and roughly placed the radio components into position and the balance was just about perfectly located!!  I'm sure I'll have room to move components enough once the plane is completed to adjust for any changes.

Bad news.  Weight  Angry  I'll definitely weigh this again taking more time to make sure it's correct, but the entire plane with radio gear (less receiver) showed 72 grams.  I am pretty sure the airframe is around 55 grams (plus/minus) that leaves 17 grams for the motor/prop/battery and radio gear.  It's more of a plane than a motorized glider.
 

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Reply #29 - Jun 20th, 2017 at 2:49pm

Brad   Offline
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Portland, Oregon area

Posts: 272
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Staubkorb:  that's 28 grams for the wing and motor!!  I think half of that weight is the motor, mount and prop.  I'm guessing the final plane will top 50 grams.  I think I have weaponized the Sinbad Jr. !!!

I will be covering with Esaki tissue for the most part.  I'm not sure what the checkered tissue is?  Here is a photo of the tissue we've selected to use.

pb_guy: thanks for the clarification.  Creating an I-Beam from the spars is what I had been aware of.
 

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Reply #28 - Jun 20th, 2017 at 1:07pm

pb_guy   Offline
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So I'm just a kid at heart.
Youbou, BC, Vancouver Island

Posts: 657
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The shear webbing does 2 things (3 if you consider adding weight a function). It absorbs diagonal/transverse stresses between ribs, and it remakes your spars to an "I-beam" by tying the top and bottom spars into a single piece - which increases their strength to weight ratio.
ian
 
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Reply #27 - Jun 20th, 2017 at 12:54pm

staubkorb   Offline
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Stick & Tissue
Germany

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Is that 28 grams total airframe weight?  If so, that's not bad for that model.  What will you be covering it with?
 

WWWoFF
Wonderful Wacky World of Free Flight
(with a bit of rc thrown in for giggles)

Comparing Spammers to a pile of organic waste is an insult to the organic waste!
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Reply #26 - Jun 19th, 2017 at 9:58pm

Sky9pilot   Offline
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Looks great.  The compression will be the flight loads put on the wing. 

The battery and ESC will helpful in setting CG.  Hope you'll have enough room to move that around in the fuselage. 

A paper tube cowling made from copy paper and white glue wouldn't add much weight but cover some of the mount and wires from the back of the motor.  Just remember to add some holes to allow air to flow to cool the motor. 

You might want to figure a scoop on the fuselage and exhaust also to cool the ESC and Battery as well.
Tom
 

If God is your Co-pilot...switch seats...
Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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Reply #25 - Jun 19th, 2017 at 1:32pm

Brad   Offline
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Portland, Oregon area

Posts: 272
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The wings are now officially joined.  I will add additional shear webbing out to the second rib from center.  I still have to decide on how I will mount the wing:  rubber bands as per the plan or with small, light nylon screws into blind nuts (or similar) with a front peg in hole method.

I also mounted the motor/prop setup.  28 grams.  Hmm.  That seems heavy but I have no frame of reference on a 30 inch span wing.  I will be covering both sides of the power pod sides with light 1/16th balsa for added rigidity. 

The removable canopy/nose piece is looking better and I have a plan for keeping it aligned and in place.  My servo tray is 1/64th ply laminated to 1/16th light balsa.

I built the power pod before buying the motor -  Undecided - and it does sit quite a bit further forward than I had anticipated.  It's not bad, but I'm sure that the battery will need to be under the wing, toward the rear to offset the weight.  I will also need to make 'removable access panels' on the fuselage sides for access to the radio system.

On the shear webbing:  I had heard that the strength of the wing is primarily from the top and bottom spars and that the shear webbing adds considerable strength mostly by adding strength to the spar under compression only.  Keeping it from collapsing into the tension loaded spar.
 

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Reply #24 - Jun 17th, 2017 at 2:30pm

Sky9pilot   Offline
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Kelso, WA 98626 USA

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I yield to Drela!!!
 

If God is your Co-pilot...switch seats...
Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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Reply #23 - Jun 17th, 2017 at 12:05pm

pb_guy   Offline
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So I'm just a kid at heart.
Youbou, BC, Vancouver Island

Posts: 657
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The direction of Shear webbing doesn't really matter that much. Preferably, however you run the grain, it should be consistent. Because the engineering loads run diagonally, and since wood is stronger in tension or compression along the grain, you would ideally use 2 layers glued at (for example) 45° angles, or whatever works for your setup from the top of one rib to the bottom of the next.
from: https://www.rcgroups.com/forums/showthread.php?2660216-X-RES-2M-sailplane/page4#...
Quote:
"Contrary to popular belief, the grain orientation does not affect the wood's ability to withstand a shear load, which is in effect compression along one diagonal, with equal tension along the other diagonal. The little load diagrams in Figure 3 are the same for the two grain orientations, except for a 90 degree rotation."

ian
 
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Reply #22 - Jun 16th, 2017 at 4:47pm

Sky9pilot   Offline
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Kelso, WA 98626 USA

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Brad, might I suggest some vertical sheer webbing between the upper and lower spars from the center to the second ribs out on each side.  Adds a considerable amount of strength for very little added weight.  1/16" sheet with the grain running vertical fitting snug to each spar.
Tom
 

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If God is your Co-pilot...switch seats...
Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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Reply #21 - Jun 16th, 2017 at 4:23pm

Brad   Offline
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Portland, Oregon area

Posts: 272
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I have the removable canopy/nose coming together nicely.  I little bit of work on the belt sander should have it shaped up quickly.

I also have worked out a bamboo center strengthening spar.  It passes between the two spars and extends past the center to the next rib.  It also passes through the power pod base.
 

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Reply #20 - Jun 14th, 2017 at 5:49pm

Sky9pilot   Offline
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Kelso, WA 98626 USA

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Your power pod looks great. The wires just taped to the outside of the pedestal will work fine.

Yes the down and right thrust is to keep the model from balooning up on full throttle and the right offset is to counter the prop torque.  If you look at the set up on full size aircraft there is this same type of setup.  Especially of the big radial engines.

The stick and wire push rods is a great idea.  If you're going with the pull/pull setup you need to use strong thread that is not going to stretch and sag with the weather! 

This is coming together very nicely!
Tom
 

If God is your Co-pilot...switch seats...
Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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Reply #19 - Jun 14th, 2017 at 4:53pm

Brad   Offline
Senior Member
Portland, Oregon area

Posts: 272
****
 

Here are some shots of the power pod progress.  I'll have to drill out a hole in the firewall for the wires to pass through.  I'm not sure how fancy I'm going to get with trying to conceal the wires going down the side of the pod and into the wing.  The pod currently weights less than 2 grams (my scale only measure in full grams   Sad) and reads 1 gram and I don't want to add too much extra weight.

Also a shot of the standard micro servo I have as an option.

Once I get the front deck built, I'll temporarily piece everything together and work on the electronics placement to achieve proper balance.

Brad
 

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Reply #18 - Jun 13th, 2017 at 5:28pm

Brad   Offline
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Portland, Oregon area

Posts: 272
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Tom:

What is the purpose of the down and right thrust?  To compensate for torque?

I might go old school on the pushrods:  balsa strips with wire ends attached with wrapped/glued thread.  I haven't seen any really small flex cable in sheath.  I've also seen some really nice looking pull/pull set ups using thread.
 
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Reply #17 - Jun 13th, 2017 at 4:12pm

Sky9pilot   Offline
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Kelso, WA 98626 USA

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WoW...things just keep getting smaller and smaller!  I'd try to keep the majority of the rc gear at or just in front of the CG and use the battery to adjust the CG by moving fore and aft as needed.  I use foam or some other way to make sure the battery couldn't move once CG is established.  I think pushrods are the way to go for the servos link to the flying surfaces at the tail.  The thinnest, lightest wire with proper bushings to secure along the length  to keep out flexing of the wire.  I look forward to seeing this come together.  The power pod reminds me of several gliders I had with power pods.  This will work nicely.  You may still want to build in some down and right thrust in mounting the  motor. 
Tom
 

If God is your Co-pilot...switch seats...
Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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Reply #16 - Jun 13th, 2017 at 3:31pm

Brad   Offline
Senior Member
Portland, Oregon area

Posts: 272
****
 
Here are some shots showing the radio gear I have for the Sinbad Jr.  I have two slightly larger servos versions as well, but each is about a gram heavier.  The only thing not shown is the ESC (electronic speed control), but it's very small.

The photos also shows my progress on the power pod and the motor I got.  I'm going to build the pod directly into  the wing when I join the two halves.   I'll make a second wing if I want to fly without the power pod.

I'm also making the entire top/front of the fuselage removable for radio access.

I need to get out my soldering iron and shrink tubing and figure out how to hook all this up.  I ended up buying about 3 adaptor cables that I need to cannibalize to be able to connect the ESC and the battery (to the receiver and the charger).  I guess I missed the fine print that read "some user assembly required"!!!
 

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