KFM Airfoils

[Darryl Adams]

I have been a non maker for months due to my parents illnesses and work preasure, but now the work preasure has ceased :-(

I was looking at KFm wings using foamcore, as an interesting experiment that is not tool intensive and would allow me to learn to fly model aircraft in the hope of eventually learning to fly drones.

Has anyone used the KFm in a delta wing, and is there any shapes I should avoid? I was looking at a KFm3 setup with a square section to mount the motor and electronics. Ideally I want to just use one piece of foamcore as I hould have everything else I need.

Also, would a KFm airfoil work with coreflute?

Thanks and regards

[Iain Chalmers]

On 15 May 2018 at 17:07, Darryl Adams <vora...@gmail.com> wrote:

I have been a non maker for months due to my parents illnesses and work preasure, but now the work preasure has ceased :-(

I was looking at KFm wings using foamcore, as an interesting experiment that is not tool intensive and would allow me to learn to fly model aircraft in the hope of eventually learning to fly drones.

Has anyone used the KFm in a delta wing, and is there any shapes I should avoid? I was looking at a KFm3 setup with a square section to mount the motor and electronics. Ideally I want to just use one piece of foamcore as I hould have everything else I need.

In my experience, delta wings with KFm construction are a pain - they are hard to not end up very tip-stall-y. They fly OK at speed in a straight-ish line, but slow speeds and sharp turns (like, for example, trying to land them with any accuracy in a small-ish space) are awful - they'll tip stall without warning and spin into the ground. It's surprising, because delta wings generally tend to just "mush along" at high angle of attack, at least if you've got enpugh motor power left to drag it along like that, but all mine would without any warning and at seemingly random speed/turnrates, turn into sycamore-seed style out-of-control spinning things. I strongly suggest avoiding sharply tapered wings without carefully designed/built foils and washout - which you pretty much cannot got with KFm designs.

Less tapered planforms work "better than you'd expect given the rudimentary aerodynamics of the wing". Plank wings, lightly tapered wings (no less than 75% or maybe 60% narrower at the tips compared to the root) and not too radically swept back tapered winds all worked out way better than I expected them to. Nothing like as "floaty" as the balsa and composite thermal gliders or slope soarers I flew ~20 years ago, but perfectly functional with modern (well, 3-4 year ago) inexpensive electric/LiPo model plane gear.

If you're leaning towards deltas for the two-control-surface simplicity aspect, go for a swept tapered design instead - Google for pictures of a design called a "Zagi", I found anything even _vaguely_ that shape, so long as you didn't make the tips too narrow, would fly just fine. Having said that, back then I was playing around with ArduPilot - back when it was actually run on Arduinos - and the software made it much easier to build standard "3 axis rudder/elevator/aileron" designs because of the assumptions baked into the software and control algorithms. 

Also, would a KFm airfoil work with coreflute?

As the saying goes "With sufficient thrust, pugs fly just fine. That doesn't make it a good idea..."  :-)

It's _super_ easy to radically overpower electric model planes these days, people fly _literal_ pizza boxes for the YouTube lulz/hits... I personally dislike the brute force approach to making things fly - ymmv.

One other suggestion, if the objective is "eventually learning to fly drones" means "learning to fly autonomous aircraft of fixed wing design" rather than "playing around with RC models", you might get closer to your objective way faster by buying something like a Bixler from HobbyKing - at least that way you'll be starting with a known-good aerodynamic package, so you can rule out questions like "did I design this right?" when it crashes, knowing that the airframe is a known quantity and it's your piloting skills that need attention... The "learn one thing at a time" approach... There were a few R&D-ers flying Bixlers a few years back.

If your "eventually learning to fly drones" objective means "eventually learning to fly quadcopters" - get a simulator and fly a hundred or two hours of directed practice (which means "plan a route then attempt to fly it, including take off and landing plans, and rate yourself by how close to the plan you flew", as compared to "use the flight sim as a video game, where you just react to what's happening with no particular plan for what your doing or what skills you're trying to acquire or evaluate".)

cheers,

Big

Thanks and regards

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[Kris]

To add to Big's comments, I built a couple of coreflute planes under Tim's direction and they flew really well. Having figured I had mastered the art as it were I bought a bixler and promptly thoroughly ruined it... Twice.

The simulator was actually pretty handy when I got it running with my TX. It taught me the muscle memory for the controller but not really how to fly. Though it is instructive for learning how to flip direction control in your head when the plane is heading toward you as oppose to away.

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From: Iain Chalmers <big...@mightymedia.com.au>
Sent: 15 May 2018 17:40:36 GMT+10:00
To: sydney-h...@googlegroups.com
Subject: Re: [RnD] KFM Airfoils

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Sent from my Breville Talkie Toaster with K-9 Mail. Please excuse my brevity.