CHALLENGES OF THE SWAPPABLE FT DELTA

First, let's be clear:  I love Flite Test.  I love their education mission, their personalities, and their passion to bring RC flight into reach of us wannabe fliers who aren’t made of money.

But their FT Delta, the third in the original Swappable Series, is a harsh schoolmaster.  If it had been my first plane, there wouldn't have been a second.  Heck, if it had been my third plane, I would have thrown in the towel.  (Fortunately, I was pretty rough on planes in the early days, so sometimes I flew a new FT Flyer every week.)

This isn't a criticism.  I'm offering one man's experience to new Delta fliers so you can be successful faster than I was.

Some have enjoyed glowing success with the Delta and even posted YouTube videos of beautiful first flights, like this young man at FliteReview.

I suspect a bunch of others didn't do so well.  I didn't.

It took me months to get the Delta off the ground.  So, if you bit off more of the Delta than you could chew, or if you're considering it as your next plane, read on.  

The Delta looks cool with its swept wing and fighter-jet twin tail!  But it introduces a pile of new aircraft features all at once.  Elevons, elevon mixing and trimming, delta wing, Kline-Fogleman (KF) step airfoil, and a challenging center-of-gravity (CG).  It also introduces the first time most of us launch without a rudder.  Plus, oddly enough, there's no tail-dragger skeg, another first.

STRIKE ONE

My first Delta was a stock speed-build kit from Flite Test.  After watching Josh Bixler's efforless takeoff in his Delta review video, I thought I knew what to expect.

I was wrong.  I could hardly get the plane off the ground.  The plane would ground loop violently or else get off the ground a foot or two and immediately yaw left into a nose plant.  Pretty much like this guy at We Crash Stuff.

The transmitter stick moved the elevons just fine, but didn’t affect the Delta’s behavior.  Granted, elevons are inherently ineffective until you're airborne.  It was frustrating.  Most YouTube pilots just revert to hand launching, and maybe that's the answer.  But I'm stubborn.  If it could be ground launched, I wanted to find out how.

The lack of tail-dragger skeg and the rearward CG meant the elevons and battery were dragging the ground.  That wasn’t pretty, either.

DIVIDE AND CONQUER

Since I wasn’t successful – nor having much fun – with the Delta, I decided to break the problem into smaller pieces to solve.  I built and flew an FT Flyer with a KF-step airfoil and ailerons to see what kind of lift and stall characteristics I should expect from a KF.  That plane introduced me to a poor CG (my own fault entirely), how to recognize it, and how to wrestle it back to the ground in one piece. 

I built and flew a Nutball with elevons to learn about those and how to trim them.  The Nutball taught me that elevons without a rudder leave me at the mercy of any disturbance – wind, thrust angle, or imperfections of the landing gear or runway – to cause ground loops during takeoff.

TRY, TRY AGAIN

Armed with that experience, I built another Delta, but this time with dual rudders and a tail-dragger skeg to protect the butt end of the plane and rear-slung battery.  Here's the template:  Delta revised rudder template.

The rudder servo is mounted fore and above the elevon servos.  The foam board mezzanine combined with the rudder control horns mounted well above the elevon horns prevents the control rods from interfering.  Plus, the clearance allows screwdriver adjustments of the elevon pushrod stoppers.

[Photo by Patrick Baldwin]

The tail-dragger skegs lift the power pod off the ground about an inch.  That's enough to keep the battery and the elevons off the ground.

They're angled inboard to give the vertical stabilizers their catchy outboard slant, but not so much as to jam the power pod.  (Yes, I name each of my batteries.  Meet battery "I".)

I glue a piece of gift card to the outboard side of the skegs for strength.  The "V" notch in the leading edge gives clearance and support for the BBQ skewer that anchors the rear of the power pod to the wing.

The gift card extends upward about an inch and a half on the vertical stabilizers to reinforce their attachment to the wing, too. 

Even so, sometimes it took me 30 minutes and a dozen tries to get the plane off the ground.  But I eventually succeeded.

TAMING THE BRONCHO

Once aloft, I found the Delta to be twitchy and random, even prone to uncommanded 360-degree rolls on occasion.  I flew it, but it wasn't much fun.  It was like riding a rodeo broncho!  Trimming was a joke as the Delta wasn't the same plane from one moment to the next.  It was like something was throwing in random elevon movements. 

Come to find out, that's exactly what was happening.  The culprit was play in the control linkages.  The control rod was loose in the control horn hole, and it didn't take much elevon flutter to throw that Delta around the sky like a wild thing.  Its high speed magnifies the effect of even the smallest elevon wiggle.

I tamed it by taking up the slack in the control horn hole.  A few inches of dental floss tape wrapped around the Z-bend wire filled the space and calmed the broncho.

Give yourself every advantage when trying the Delta.  Add the shown rudders and tail-dragger skegs.  You can still go "commando" and ignore the rudders, if you like.  But they're there if you need them.  It still may be challenging to get off the ground, but you’ll have a fighting chance.  Also, firm up the control linkages to remove the rodeo-like behavior I experienced.

Or you may want to break up the problem like I did to learn the features of the Delta piece at a time.  The FT Flyer and Nutball are good testbeds to experiment, first.

Either way, you may just save yourself some frustration, some discouragement, and some unkind words spoken in anger.  If so, you'll be miles ahead of me.

-- Mike