Nodd's Plank

[Nodd]

I'm interesting in doing some slope-soaring however our closest spot, on the Hudson River, has a tree-line that you have to get above before you reach the lift. We usually fly electric Easy-Gliders, stuff like that there, as you need something powered to get into the lift. That's fun-n-all but I wanted something a little more sporty than an Easy-Glider. So I've design this goofy little EDF powered plank to fool around with.

The following will document the build, subscribe if you'd like to follow along.

The design is centered around this little 55mm HobbyKing electric ducted fan...



The EDF will be buried in the rear of the fuselage with large intakes both above & below the wing...



I'm planning to build with wing from the following materials using a symmetric KF stepped airfoil...



I'm going with a four servo wing so I can get crazy mixing some airbrakes & other nuttiness...



Well that's the plan for now. This should be a cool little project, doesn't have to be perfect, fun is the main goal. As with all my builds, I welcome comments & advice...

[CHELLIE]

Subscribed Nice wing design, on the wing tips, i would take out the angle, and have them 90 degrees to the wing, reason being, that will help to make the wing track like if on Rails, Take care, Chellie

BTW, I get to do the Maiden Flight LOL

[JetPlaneFlyer]

Cool looking plank!.. If it were me I'd probably do the spar some other way though, the carbon strip near the centre of the wing and laid flat isn't going to add much bending stiffness to the wing.

I like the tip fins as they are

[Bill G]

Originally Posted by JetPlaneFlyer

Cool looking plank!.. If it were me I'd probably do the spar some other way though, the carbon strip neat the centre of the wing and laid flat isn't going to add much bending stiffness to the wing.

I like the tip fins as they are

I thought that also, but given the 2x10mm carbon fiber spar spec it should be adequately rigid for a model of this size, especially when combined with the laminate. I have a section of 2x10 Midwest CF spar, and it is amazingly stiff, even at length. The "neutral axis" analogy is sometimes overemphasized, where in practice a structure can still be quite strong and practical, given the requirements and constraints of the model. Using a rod would require accurate channeling of the foam, adding to the complexity of the design.

[JetPlaneFlyer]

Yeah, probably a fair point, the huge size of the spar will to some extent compensate for it's structurally poor position and orientation... But it would be 10 x more rigid if you split it into two 5mm x 2mm strips and glued them verticality butted up on the back face of the KF step

[gramps2161]

Nodd if you do the carbon fiber do it in a I frame use 3/32 lite ply for the up right between the carbon on top and bottom makes for a very strong spar, but light.

As always I will be following along on this neat build.

[riverrat]

Subscribed

[crash_out]

Neat, simple design. Be careful, they are very touchy about CG. I've built a couple of planks, and none surpassed CG testing...

I'm not trying to be a jerk, honestly. Really, don't take it that way.

But why are you putting elevons and ailerons on it? To get a higher roll rate than pitch control? Just curious...

[Yakfishingfool]

nice

[CHELLIE]

Originally Posted by JetPlaneFlyer

Cool looking plank!.. If it were me I'd probably do the spar some other way though, the carbon strip neat the centre of the wing and laid flat isn't going to add much bending stiffness to the wing.

I like the tip fins as they are

+1 Maybe a CF Tube on the edge of the wing and then over lap it with the 5mm foam board, Just My 2 cents worth.

[Nodd]

Awesome feedback, thanks folks.

As suggested I may play with the vertical fin design some more although I understand one of the odd quirks with the KFm-4 airfoil is that it can apparently be flown with no vertical stabs at all. Somehow its natively yaw stable *shrug*. Not sure I believe that but I've heard it mentioned a few times. This bird will have fins though.

I have to agree, my spar design could be improved. As soon as I ordered the CF I realized I should probably have gone with a vertically oriented spar & not horizontal. So here's what we're gonna do...



The new CF spars should arrive in a couple of days (RCFoam.com rules!). I'm thinking just the one spar instead of two maybe all I need. I'll make that call once the wing is together & I can gauge its rigidity.

A few folks, not surprisingly, are wondering why I'm not just using full span elevons. The reason for that is I maybe flying this in confined spaces with small landing areas. I'll need air-brakes to slow her down. If you attempt to use elevons as flaps you end up pile-driving into the ground. With a four servo wing however you can use the outboard ailerons to counter the downward pitching from the inboard "flaps". Basically mix in crow braking...



I expect it'll take some fine tuning to get the deflection angles right but from what I've seen, this is the way to stop a plank.

Okay well this is sounding good. I hope to begin construction soon. Stay tuned.

[mclarkson]

Looks beautiful, as always.

Do you do any calculations / simulations with regard to weight / balance / CG / etc. during the design phase?

(I just built a KFm4 plank, myself, but I won't sully your thread with it. )

[dgjessing]

I've done a wing like your second design - it's very, very strong.

[rusty case]

Nice looking design. It's almost a Reaper.

[gramps2161]

Nodd I missed the fact that your using cloropast for the wing that stuff is pretty strong. Your new wing layout with the spar should be good.

[Nodd]

Once again, thanks for the encouragement.

Originally Posted by mclarkson

...Do you do any calculations / simulations with regard to weight / balance / CG / etc. during the design phase?..

I looked into software that'll do that, stuff like SolidWorks & other engineering CAD tools. Unfortunately I don't have $7000 to drop on such software, so I use the next best thing... "that looks about right". I also do mockups during the build to see where things are headed & make changes if necessary. If anyone knows of affordable CAD software that'll calculate mass distribution, CG etc I'd be very interested in hearing about it.

Originally Posted by dgjessing

I've done a wing like your second design - it's very, very strong.

Good to know. Yeah I figured the spar wasn't all that important for a model of this size so I just went with big chunk of CF & shoved it up under the foam-board without too much thought. I think that would have been fine but what the heck, lets do this properly. No doubt the new vertical spars will be rock-solid & then some.

[Bill G]

Originally Posted by Nodd

Once again, thanks for the encouragement.



I looked into software that'll do that, stuff like SolidWorks & other engineering CAD tools. Unfortunately I don't have $7000 to drop on such software, so I use the next best thing... "that looks about right". I also do mockups during the build to see where things are headed & make changes if necessary. If anyone knows of affordable CAD software that'll calculate mass distribution, CG etc I'd be very interested in hearing about it.



Good to know. Yeah I figured the spar wasn't all that important for a model of this size so I just went with big chunk of CF & shoved it up under the foam-board without too much thought. I think that would have been fine but what the heck, lets do this properly. No doubt the new vertical spars will be rock-solid & then some.

I couldn't see much practicality for software mass calcs either. After enough builds of varied subjects, you can narrow down CG setting to a small shift in the battery, easily determined before the build is completed, while you still have flexibility but are far enough along to nail it down. The good ol' stick with simulated weights, fans, motors, batts etc taped on can work amazingly well. As you were saying, a program like Solid Works or the Pro-E that I used to work with will do mass calcs, but would require more effort than most would care to invest, as you would have to accurately model all of the components/materials and their weights/mass densities.

The only build where I made a major revision (still wasn't a problem and worked out even better) from the initial planned component location, was when I went off of a smaller version of the model I had built that was built using different construction methods and materials. If I had just used "off top of head" instinct given how I was planning to build the subject, then I would have realized how things would pan out.

[JetPlaneFlyer]

Originally Posted by Nodd

.... I understand one of the odd quirks with the KFm-4 airfoil is that it can apparently be flown with no vertical stabs at all. Somehow its natively yaw stable *shrug*. Not sure I believe that but I've heard it mentioned a few times.

Yeah, some KF fans make some wild claims for the airfoil. Sadly most of them are nonsense and I'm sure the 'yaw stable' one is a good case in point. Sure, some may fly without vertical stabs, but no better than a normal airfoil would have on the same layout.

You did the right thing putting vertical stabs on

Steve

[Nodd]

Yeah I really can't comment on the pros & cons of the KF airfoil. This'll be my first.

Design in progress
Based upon feedback here on the forums I've made a few tweaks to the design. First is more vertical fin area...



It was also suggested that I also move the duct intake forward a tad...



So here's the latest & greatest...



Thanks again for the input.

[Turner]

You should use that color scheme for the final finish. It looks great.

[Nodd]

hehe, that's just the CAD colors to help visualize the various parts. Sometimes it comes up with some pretty nice schemes. Unfortunately I already ordered the tape for the wings & yeap, it ain't those colors. I think she'll still look pretty slick though. You'll have to wait-n-see to find out what I have in mind *evil grin*

[Turner]

I figured it was the CAD but I still like it. Very distinctive in it's own right but also highlights the unique features of your design.

[mclarkson]

I'm sure you've said at some point, but what software do you use?

[soarrich]

Nodd
If you stand 9G servos up they mount really well in 3 thickness' of foamboard.
I made a 60" wing using foamboard without a spar without problems, I built the KFm-4 airfoil a little differently though:
http://www.wattflyer.com/forums/showthread.php?t=68902

[soarrich]

I'm seeing a lot of FOD with that bottom air-intake.