Scratch-Built & Purpose-Built Electric 34% SU-26 - RC Groups
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Dec 14, 2016, 05:03 PM
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Aeroplayin's Avatar
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Scratch-Built & Purpose-Built Electric 34% SU-26


After two years of conception, design changes, calculations and testing, maiden day finally arrived yesterday.

This thread will be intended to document the journey -- from discussing the new design elements that I wanted to move from concept and formulas to actual in-flight performance, to basic concepts about powering giant scale planes with electric systems. One of my first discussions will be about why I decided on a purpose-built electric RC plane, and the material selection and design process that went into it -- specifically the new wing configuration that I ended up with, why it was chosen, what I expected from it, and how it actually functions in the air.

It's a little early to tell exactly what the complete flight/performance envelop will look like as we begin to push the plane harder and harder over the next few weeks, but for now, I could not be happier with the combination of responsiveness and stability I've seen so far. I don't want to start backwards, but I always felt that an RCG thread needs plenty of pics and videos, so I'll start with pics and jump around the time line to keep it interesting -- I hope.
Last edited by Aeroplayin; Jan 04, 2017 at 07:14 PM.
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Dec 14, 2016, 05:15 PM
Now I'm a "Low Flyer"
high flyer Rich's Avatar
Congratulations Jim! That's a huge undertaking! Looking forward to seeing the details on the power set up, AUW and flight time.
Dec 14, 2016, 05:22 PM
I fly, therefore, I crash!!!
SteveT.'s Avatar
Very nice Jim!! I like Sukhois

SteveT.
Latest blog entry: My hangar...
Dec 14, 2016, 05:24 PM
3D? I only got two thumbs!
Congrats on getting it in the air! I notice several interesting things in the photos, but I'll wait to see your additional posts.
Dec 14, 2016, 05:44 PM
"BIG" Vyper Addicted
Chris SW's Avatar
Subscribed. Good looking plane and i am really looking forward to hearing about the concept.

Never designed or built anything so large so i am a little in awe.
Dec 14, 2016, 05:44 PM
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Sideslip's Avatar
Jim,
Looks very interesting, and I'm sure you're enjoying the project. I will be reading right along with everyone else, an excited to see some video, down the road.

Curious about the angular vents forward of the horizontal sab. I'm sure you'll explain those as well.

Subscribed,

Bert
Dec 14, 2016, 05:50 PM
I fly, therefore, I crash!!!
SteveT.'s Avatar
I would be willing to bet they are air exhaust vents...

SteveT.
Latest blog entry: My hangar...
Dec 14, 2016, 05:52 PM
If it has wings it will fly...
ckleanth's Avatar
Congratulations mate..
Dec 14, 2016, 06:57 PM
Registered User
Sideslip's Avatar
Quote:
Originally Posted by SteveT.
I would be willing to bet they are air exhaust vents...

SteveT.
Oh, without a doubt. Just curious as to his thought on why there and why that shape. Did you rule out any structural deficiencies first. What might happen when Tom pulls 9 Gs in that 1K poptop?

Just curious,
Bert
Dec 14, 2016, 07:12 PM
Registered User
Aeroplayin's Avatar
Thanks, guys. And please feel free to ask questions because it will help me remember some of the things worth talking about.

A little over two years ago, I borrowed design software and downloaded a few free 3D viewers, and started designing something without a clear image of what the profile would look like. I was basically piecing concepts together. I was not worried about the 10% rule, and if the plane ended up looking like nothing I had ever seen before, so be it. As long as I was able to either incorporate or test certain things that were unexplained in my mind, and learn something from it, the project would be worth it.

This is what I knew I wanted the plane to be and do:
  • The wingspan would be something right around 100"
  • The cowl width would be something right around 11.5"
  • The fuse would be between 9 and 10 inches at the wing tube so that I could have room to easily manage electric power and control components
  • It would have sheeted foam wings, stabs, and turtledeck for strength and rigidity at a lighter overall weight
  • It would have a wing thickness that would give me what I considered to be an acceptable glide ratio and lift coefficient
  • I was also looking for a decent drag coefficient since this plane would NOT be built primarily for speed but I would want to control the down line speed too
  • It would have different laminar at the wing root than at the tip and be relative to thickness, which is not uncommon
  • It would have a shallow sweep on the leading edge, and a deeper sweep on the trailing edge for personal preferences
  • The 1/4 cord sweep would be a slightly forward sweep, more like the Edge wing, and less neutral than the Extra wing
  • The spar thickness sweep would also be slightly forward as well, and combined with the thickness, would potentially eliminate the need for SFGs
  • The wing area would be big enough to keep the wing loading under 32 oz/sq ft, and a wing cube loading between 8.5 and 8.8 oz/cu ft, which of course depends on the final all-up weight with a moderate main battery pack capacity
  • The horizontal stab would be big too, and about 25 to 26 percent of the main wing area
  • The main wing would probably be based on the NACA 6 series symmetrical, so a 63-015A or 63-014A or something in-between would be the choice
  • The overall weight would be low enough to offer an acceptable power loading with available RC motors that can turn a prop that makes sense for the airplane's wingspan -- 25 inches, minimum.

So with this incomplete checklist, I started drawing.
Last edited by Aeroplayin; Apr 02, 2017 at 08:42 PM.
Dec 14, 2016, 07:15 PM
Registered User
Aeroplayin's Avatar
Quote:
Originally Posted by SteveT.
I would be willing to bet they are air exhaust vents...

SteveT.
Yes, they are air vents. I was going for a shark vent look s but they somehow got reversed in the design file, but I'll probably correct that for the next plane. Considering how cool everything is running right now, I may open a few on each side at a time. What do you think about them -- if they were leaning forward of course?
Dec 14, 2016, 07:28 PM
Registered User
Aeroplayin's Avatar
Considering the checklist, the first plane I though about was a Davis Acro Pro I because of the exaggerated wings and stab surfaces. I though about extending the moment, cutting larger tapered ailerons, changing the flat stabs to an airfoil, and eliminating the flying wires. But after doing all that, the plane may have end up just looking like an Extra 260 or Laser Z.
Dec 14, 2016, 07:31 PM
I fly, therefore, I crash!!!
SteveT.'s Avatar
I think they look great either way!!

SteveT.
Latest blog entry: My hangar...
Dec 14, 2016, 08:00 PM
Registered User
Aeroplayin's Avatar
Thanks Steve.... I like them too.

Anyway, this tool was the key to getting this whole thing off the ground. Once I was able to find someone whp could digitally cut a wing design accurately, and also CNC the plywood parts, there was no reason not to do it.
Dec 14, 2016, 08:53 PM
3D? I only got two thumbs!
The cooling slots certainly do look neat. I think angled the other way might give it a more agressive look. I've always wondered how the airflow coming out the typical vent on the bottom affects aerodynamics (blowing air out the bottom adds lift behind the cg?), and your approach would seem to dump air out both sides symmetrically for neutral effect. But it is dumping the air right in front of the H stab, I wonder what effect that has? I could imagine anything from a nice extra boost of airflow especially in harrier, to somehow messing up the airflow.

That is a neat machine for making the wings. I'm guessing that's an abrasive wire under tension pulled back and forth? Or is it a hot wire? (The cut surface I see doesn't look like the glassy skin I get with a small hot wire, but then again that's not the kind of foam I've usually cut.)


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