High Speed Electric and the Pipe Dream
 

Well, plans keep getting bigger.....

This fall, near the end of flying season, I was given a Byron Originals Pipe Dream kit, a giant scale "trainer" of late '80's vintage. Zenoah G38, an older but serviceable Futaba radio (7u, computer, 1 model) and most of the things I needed to complete it. I rounded out the parts needed, built the plane and did some of my usual edits to the original plans. Little things like full span flaperons, and best of all, a bomb drop arrangement I designed and built for it. I built 2 linkages for the drop mechanism, one that allows 2 bombs to be carried and dropped separately, and another that releases both hardpoints at once, for carrying bigger things.

I completed her the day before the first snow struck. Since then we've averaged more than a storm a week, it seems. All set up, engine roughly tuned (to be fine tuned on THE DAY), computer computing, everything tweaked. Frustrating.

Maiden is still weeks away (snow. cold. wind. rain.). And yet the Pipe Dream has found another purpose, not entirely unimagined.

A friend of mine designed and built a high speed electric plane, should be pushing into the 100mph+ range. It's quite small, about 1.5# with a svelt 30" wingspan. Minimal drag means no wheels, so it's to be hand launched. And there's the rub. It's stall speed is better than 25mph, so that'll be tricky.

We've rigged up the Pipe Dream and it's bomb drop mechanism to work as our launch system. 500' will give alot more time to get the 'lecky all trimmed out before the ground rises up to smite it.

I added a tail fin bracket to constrain the plane's yaw tendencies, and adapted a high-tech shoe-lace to the bomb release. Used the Y linkage I'd built previously to achieve simultaneous release of both shoelaces. I set the electric to about -2 degrees incidence to aid in the release. Plan is take off, climb to altitude, slow to just above stall, and release the lecky for high speed passes galore!

Whaddya'all think? Is this gonna work? CG is good, the 'lecky moves it back about 1/4", and I've set it so it's at a safe forward position under all conditions. We'll maiden the PD first, then maiden the 'lecky via the pipe dream. I'll have the flycamone watching the lecky for it's maiden, should get some cool drop footage.

Hope you enjoy the pics!

RE: High Speed Electric and the Pipe Dream
 

The problem here is that the airfoils on the electric aircraft will be generating all sorts of aerodynamic forces. Since the airplanes are secured together tightly this will affect how your airplane flies. That means positioning is crucial. This is a much different situation than a glider on tow. I would personally work out weights and moments on paper before trying to send this thing up. That way you can calculate exactly where AND at what angle the airplane should be mounted at. It's more complicated than simply hanging the airplane at the center of gravity. Is your disconnect system 100% foolproof? A partial disconnect will send both models plummeting to their demise.

How did you calculate the 25 mph stall speed?

RE: High Speed Electric and the Pipe Dream
 

I don't think I'd be too worried about the forces that that little plane will exert. We have an archaic trainer style plane rigged up with a glider launch on top of the wing at our club. I've only seen it used once at last years air show. The glider wing was considerably bigger than the 'tow' plane and though awkward looking it didn't seem to fly that unusually at all..... I do agree with the release mechanism being foolproof though...that could get nasty.

RE: High Speed Electric and the Pipe Dream
 

Cool. I've never done it, but on paper it seems like quite a challenge. I am glad to know it's not so bad in practice.

RE: High Speed Electric and the Pipe Dream
 

I’m not sure about any problems that you will have but that looks awesome!!!!:D

RE: High Speed Electric and the Pipe Dream
 

Thanks, guys!

Yeah, I/we considered that the carried plane will have an aerodynamic effect on the Pipe Dream, but there are pretty good margins working for us. The PD has a huge fin and rudder, so yaw stability should be fine. The carried plane does add side area, but as the CG's coincide, if each plane is stable, the combo should be OK, I think. Also, the 'lecky's wing area is about 80% of the PD's stab area, so as long as it doesn't move in carry, the trim changes should be constant and manageable.

The release mech. should be pretty foolproof. If it were to hang half released, you're right, nightmare. It is pretty simple, though, and we kept things clean to try to minimize the potential for fouling. It's simply 2 strings ending in wire loops that engage a pin type bolt. When the hardpoint pin is pulled back, the string ends will release, that part is pretty foolproof. The pins retract completely, nothing left to bind on, and the servo is plenty beefy for the job, 51 in. oz.

When the strings release, the "popsicle stick" they go over under the wee plane falls away (new one needed each drop), and so does the little plane. The only problem I can see would be the strings winding up about one another, and snagging the tail of the carried plane. That would be bad. I'll try to clean stuff up so that snagging isn't too likely...

We'll release at as low as practical a flying speed, well out over our field, and with several hundred feet under us. That way if it all goes wrong, I can ditch the combo safely in the tall grass. But I'm pretty confident that it won't come to that. We'll do a few more test drops as the time grows near anyway, to check for quirks looking to sink us. It worked flawlessly in the basement a half dozen times, but the airspeed is admittedly pretty low there. Proof'll be in the pudding.

I did see a senior telemaster (our club trainer) attempt a 2m glider-on-top carry the first time I visited our field 3 years ago. It's a fairly common practice, and their release system was similar in concept to mine, though less robust. Unfortunately, that one didn't go so well. The glider wasn't securely enough mounted, and it "rolled" on the carriage, until it's wingtip contacted the telemaster's wintip. The rig was about 25' off the ground on take off at the time. This spoiled the lift on that wing, and with the low airspeed, the combo hauled itself another 20 or so feet up, wallowing half or less in control... The telemaster pilot released the glider as the beast reached it's apogee, and the telemaster proceeded to stall in, buring it's motor in the runway. Perfect 1 point landing, lol. The glider was fine. Telemaster flew again the next summer. Not auspicious, but it was pretty cool to see.

Hopefully this rig does a little better.

J

Oh, the stall speed was estimated using motorcalc or a similar electric aircraft design tool, based purely on the basic wing geometry and loading. This type of tool has provided us with believeable numbers for other aircraft the two of us operate. That stall speed was for the electric only, and I only mentioned it as it is the primary reason why we're attempting this. Hand launching a 30" plane at that speed would be a bit challenging without a fair breeze blowing. So long as this works, the aerial drop gives alot more time to get'er on the wing, as it were!

RE: High Speed Electric and the Pipe Dream
 

KOOL i like that idea
cant see any probs with it
good luck