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Old Jan 26, 2016, 09:05 AM
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Quote:
Originally Posted by vincent123 View Post
Now, I defined the carbon rods as infinite stiff, is about fair compared to the wood spars.

Now I see that the spar-webbing construction is most stressed, perhaps I should think about reinforcing this connection.. ?

The ribs are surprisingly less important in this approach!
Vincent:
What stress levels do the colors equate to?

It's common in FEA to be distracted by the red color ... which simply depicts the highest stress (but not necessarily a failure-inducing stress).

Also, the stress level in the shear web is exactly as one would expect ... low at the neutral axis, and high at the spar caps. You may want to glue pre-cured unidirectional CF to the spar caps. Alternatively you may want to change the spar geometry ... wider at the root and narrower at the tip.

It shouldn't be much of a surprise that the ribs don't carry much load. The spars carry the load.

Be careful with your FEA ... it's very easy to get distracted by the toolset, and then get sucked into "overanalysis paralysis." At some point you'll need to move forward with the build. (also known as "shoot the engineer and build the airplne")

-Dave
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Old Jan 26, 2016, 01:18 PM
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Hi Dave,

The colors are just colors, I could not select wood as material.
I was interested how rib1 and rib2 behave, as they need to translate the spar forces to the carbon former fuselage connectors.

Evantually, I kept my original design: first 2 ribs thick to translate the forces, and classic spar webbing design.
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Old Feb 07, 2016, 06:56 AM
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Webbing

Webbing ... boring job .... nevertheless ... has to be done !
Wing is pretty stiff, torsional stiffness will end up fine after sheeting.

Test mounted the wing .. so far so good.
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Old Feb 07, 2016, 12:41 PM
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Wow Vincent that looks so sharp, and built like a battleship to boot.
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Old Feb 07, 2016, 01:19 PM
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Hi there, thanks !

Building is progressing slow nowadays ...
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Old Feb 07, 2016, 11:39 PM
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Beautiful workmanship. I'm getting nervous jitters thinking about the maiden. Take your time. The suspense is wonderful.
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Old Feb 08, 2016, 01:31 AM
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To be honest, I'm dying on the airfield during a maiden !
Heart pounding like hell in my throat, sweaty hands ....

And this one, with the EDF drawing high currents, i'm planning to take off, and land after a short flight, being afraid my battery depletes before being able to settle for a nice landing approach.

Trying not to think about it, yet .. ;-)
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Old Feb 08, 2016, 04:12 AM
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Stunning. Beautiful lines.
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Old Feb 09, 2016, 05:55 AM
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It s gonna be huge wing surface...
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Old Feb 09, 2016, 08:31 AM
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Huge wing is good with high wing loading and clean, swept lines!
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Old Feb 09, 2016, 12:16 PM
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I chose a relative small wingspan and as a result pretty large root and tip, so that the drag at speed would be lower aswell as the landing speed.
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Old Yesterday, 03:18 PM
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How do you work out the placement of the components in relation to cg. That's one thing iv always struggled with when scratch building.
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Old Today, 12:34 PM
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Quote:
Originally Posted by Artful Owl View Post
How do you work out the placement of the components in relation to cg. That's one thing iv always struggled with when scratch building.
Good question.
For all the components of the airframe, including reciever, servos, spars, webbing, sheeting, formers, planking and so on, I calculate the individual contributions to the CG location.

For the past designs, my estimate was pretty good (FZ2, FZ3, Zdelta): meaning i never needed to correct the CG with lead, but only by shifting the battery.

The battery is my only degree of freedom in a finished scratchbuild. I allow myself a +20mm and +20mm degree of error. meaning the battery compartment allows me to shift the battery with 20mm forward or backwards.

The relative contribution of a component is calculated as:
mass x lever
The lever is the distance of the component's center of mass to the desired CG of the airframe. Make the lever distance for components in front of the CG ariframe positive, and the rear of the CG negative.

The sum of all these contributions needs to be zero
mass1xlever1 + mass2xlever2 + ....=0

In office excel, you can then play with these distances while you are designing.

Hope my explantion was good enough?


Vincent
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Old Today, 01:14 PM
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It probably beats my method of taping all the power components on a stick after the wing is finished, rubber-banding the stick to the wing, and moving the stick back and forth until it all balances.

My fuselages are close to being sticks anyway, nothing like your sleek beauty.
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