Schleicher KA-7

[Nodd]

I originally wrote this review for RCAerotowing in 2013 however the website ate the article shortly thereafter due to "reasons". Anyway here's another copy, this time with updated edits denoted in red...

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High Ridge Soaring – Schleicher KA-7 Sailplane
Review by Chris Evans - April 2013



Our friends at Troy Built Models EDIT: did offer a selection of giant scale sailplanes including this beautiful KA-7. The two piece, four meter, wing is built up plywood/balsa, partially sheeted & covered with film. That’s mounted to a cavernous fiber-glass fuselage with a rather substantial steel wing rod. A removable horizontal stabilizer is bolted up to the rear. Controls are elevator, aileron & rudder with the option to install spoilers & an aerotow release. Judging by the size of the huge wing spoilers are somewhat of a must-have. She’s a real floater.

EDIT: Well actually I wouldn't go as far as to say she's a “floater” but she will thermal quite nicely in moderate lift. Not so much in light air.

What You Get
As a child I associated the size of something’s box with how much fun it would be. This box would have sent my fun-scale off the charts, it’s HUGE! Nestled neatly inside lurked a sleeping beauty. Once you unpack the big parts you’ll also find an assortment of goodies including a molded canopy, a nose-skid, the wing rod & a sizeable bag-o-hardware.



Components Included in the Kit

• Major airframe parts: wing panels, fuselage, tail pieces, canopy, nose skid, wing-rod
• Wheel & mounting hardware
• Various hardware kits, including a pull-pull system for the rudder, servo hatches, control-horns, push-rods, linkages, hinges & other knickknacks

Needed to Complete
The following is a list of additional items we used to complete the model:

• Servos – Four Hitec HS-645MG servos (ailerons, rudder, tow-release), two Hitec HS-635HN servos (dual elevators)
• Radio – Spektrum DX7i 2.4-GHz Tx
• Receiver – Spektrum AR7010 7ch Rx
• Castle 10a BEC
• Rx Power – 3S 2200 mAh LiPo
• Hobby-Lobby Aerotow Release
• Two 300mm MPI Servoless Spoilers
• Miscellaneous – Servo extensions, glue, epoxy, thread-locking compound
• Several pounds of lead-shot for nose weight
• One metal push-rod for the tow-release

Assembly
At first I thought the instruction manual was missing but soon discovered it’s available instead as a PDF at troybuiltmodels.com. The KA-7’s manual is mostly clear & to the point line drawings. These are numbered so you can proceed step-by-step but oddly begin at step 45. After proceeding through step 50 we then jump back to 40 & only then do we arrive at step one. After some head-scratching I decided to ignore the numbering system & begin the build by installing the tow-release (step 44).



It’s a little unnerving drilling a big honkin’ hole in the nose of such a pretty fuselage. I took care to begin small & work my way up to the final sized hole. You don’t want to go straight for a big drill-bit, that’ll chew things up for sure & nobody likes a chewed up nose. With the release epoxied in place I dropped in a Hitec & married the two with a standard push-rod. The cockpit area features pre-cut locations for the servos. They were a perfect fit, an indicator of well thought out design & good tolerance quality. An encouraging start I thought.

Well it was encouraging until I heard reports of a potential issue with the wheel mount on these planes, specifically the area of lite-ply where the wheel hardware bolts up to.



Well as you’ve probably guessed, the plywood structure surrounding the wheel mount looks like Swiss-cheese, lightning holes everywhere. Maybe that saves an ounce or tow but drop an 18 lb glider on that & something’s going to give. My buddy Tommy did just that landing his HRS ASK-21, which has identical construction. Apparently the wheel just telescoped up into the fuselage... CRUNCH! So, yeah I took some time to reinforce that area with solid (non-Swiss cheese) plywood. Basically I added a flat plate over the existing wheel mount then atop that added an extra bulkhead, fiber-glassed here & there. Fingers crossed that’ll hold together during those not so greased landings.

EDIT: Four years later, the gear is still holding together solid even after quite a few heavy landings.



The elevator is an interesting design. Although it’s one piece, it employs two servos, one on each side. Looking at the size of the control surface I’m not sure why this is necessary. I’d figure a single servo should be sufficient but I suppose this dual setup provides an extra measure of strength & added precision. Well it would have if I could get the two servos to play nice with each other. Multiple servos on a single control surface are nothing new but they were for me. Long story short… as I was using analogue servos on a Y-harness, I had issues getting them to move in perfect unison. I ended up ditching the Y-harness & ran each on its own channel, then used the radio to fine-tune the endpoints & trim. They still buzz & fuss a little but they work. I’ll probably invest in digital servos instead, install a programmable mixer or better yet, just remove the connecting structure between the two elevator halves & be done with the buzzing. So I have a few options there.

EDIT: I ended up cutting the elevator in the middle so that each surface is independent. Problem solved plus this gives me a level of redundancy if something goes wrong with the elevator.



If you’ve done pull-pull rudders before, this’ll be business as usual. All the hardware is provided including wire & some very nice connectors. Guide tubes are already installed. All you need do is drill exit holes at the rear of the fuselage then install two short “plastical tubes”, as the manual calls them. These keep the wire from chafing. Another Hitec goes up front & drops snugly into the pre-cut hole. After some tensioning I had the rudder operational with minimal fuss. The hardware is top-notch & made these steps quite enjoyable.



The ailerons are hooked up in a fairly standard manner using hatches to mount the servos. The provided carbon-fiber push-rods, ball joint connectors & fiber control horns were all really nice. Unfortunately I managed to lose some of the bits in my workshop clutter. I’m sure they’ll turn up someday & be used on another project but for now, good old metal rods & a Z-bend will do just fine. Props though to the manufacturer for supplying such complete & quality hardware.

[Nodd]

The rest of the electronics; the receiver, battery, BEC, etc. aren’t mentioned much in the manual. There’s room enough in this fuselage to play a game of baseball so I guess they figured you’d stick that stuff in wherever. Due to the lightning holes everywhere in the radio-tray, I opted to bolt in a simple plate to mount my electronics too. I also made up a battery tray complete with hook-n-loop strap.



The canopy is a project in its self. Probably the most challenging part is trimming the clear part to size. There’s a subtle ridge molded into the plastic as a guide but one slip of the knife & you’ll be cursing from here to Sunday. My nerves in tatters I resorted to using the Dremel tool instead & sanded/melted the excess to the line. That worked quite well. While effective, the canopy latch system is somewhat primitive. The rear is held in place with a couple of tabs that index slots in the fuselage. These you need to locate & cut yourself which proved to be quite a challenge. The front of the canopy is held down with a high-tech rubber band/hook arrangement. This all works fine but there’s likely a better way.

EDIT: I hate this canopy. Its difficult to open/close at the field. The way the rear indexes the two tabs & how it fits under the wing is a pain. And the rubber-band system that holds down the front, while effective, is also a pain to use. Spend some time & install a proper canopy latch, magnets or something.



To attach the wing you’re tasked with drilling several holes. One set for a carbon-fiber anti-rotation pin. Another for a retaining bolt that secures the wings against the fuselage. A plywood template is provided to aid in aligning these holes precisely. Hopefully they’ve addressed this issue by the time you read this but my template apparently was meant for some other sailplane, it totally didn’t fit. I was able to fabricate something that did fit, wasn’t a big deal. Thankfully the main wing-rod system is already setup. The steel rod is quite substantial but looking at the structure surrounding the tube, I’m thinking 100 mph outside loops might not be a good idea. I’m not sure I’d consider this an aerobatic airframe. Then again perhaps I’m just being over cautious having recently pulled the wings off not one but two sailplanes. I’ll leave that call up to you. Me, I’m going to stick to lazy thermal hunting with this bird.



The spoiler bays are already cut, you just need to remove the covering. They’re setup for use with servoless spoilers. A set of MPI 300mm e-spoilers from Esprite Models was a perfect fit. Not having to deal with servos & fiddly linkages was a real treat. I think electric spoilers are here to stay; they just make too much sense. There’s been some debate about their reliability Vs traditional setups however they’re so easy to swap out, plus the quality can only continue to improve, I think they’re the way to go. Well at least for this airframe that is.

EDIT: I got a lot flack about my use of e-spoilers. Stories of them burning out prematurely, of them being unreliable & so on. Well that's not been my experience at all. I have e-spoilers in three sailplanes & not one has ever given me an issue, even after years of use.

On the underside of the wing I added some black Ultracote. As I’ll be thermalling her, visibility at altitude is important. A dark shape against a bright sky is much easier to see Vs the stock white. Yeah maybe black undersides aren’t all that scale but then again neither is piloting her standing 2000 ft below on the ground.

The nose skid & wheel went on without any issues. And with that it was time to balance her. Now there’s a bit of a story here but I’ll get to that in a bit. After suspending her at the recommended CG I added 2 lbs of epoxy soaked lead-shot to the nose. I used a cardboard roll to protect the tow-release from the mess.



The radio setup was fairly standard; 30% expo, 60% dual rates, 25% differential. The only mixing was some aileron to rudder using the tow-release switch to disable that during tow. Oddly the manual suggests 30mm throws for all control surfaces. That didn’t sit right with me, seemed like a whole lot for the elevator & almost nothing for the rudder. I decided to go with what I thought was good instead.



So there she was all complete & ready to fly. She’s an impressive looking bird for sure.

[Nodd]

In the Air

This is not the sort of airframe you can simply take down the local ball-field & fling into the air. As with most of my giant scale sailplanes, I do the bulk of my flying at aerotow events where I have access to equally giant tow planes. For the KA-7’s maiden flight I travelled to Lancaster PA where there was a three day aerotow hosted by the Lancaster Area Susquehanna Soaring club. Some of the best RC scale soaring pilots on the East coast attended, including my buddy Len. He graciously agreed to fly the maiden & o-boy was I glad he did…



Before I get into what happened next, let’s rewind to when I installed 2 lbs of lead in the nose to balance her. The PDF manual clearly suggests a CG location of 100mm back from the wing’s leading edge. On the diagram this looks about right, sitting at approximately 25 percent of the chord. What the manufacturer seems to have failed to take into account is the KA-7’s aggressively forward swept wing. This I’d soon learn greatly affects the CG geometry.



So after performing the usual maiden flight routine; range check, control surface check, battery check, insurance check, it was time to get her airborne. The 1/3 scale Pilatus Porter tow plane began its rollout & in maybe 50 feet we were both off the ground. “Huston, we have a problem!” exclaimed my test pilot. Well actually he said a few colorful metaphors followed by “… just take me straight up!” During the assent the KA-7 was exhibiting some very disturbing flight characteristics, pitching wildly. After reaching around 1000 feet the release was popped & she was flying on her own. She immediately entered two distinct flight modes; one pointing straight at the ground & the other pointing straight up. There was no flying level to be had, classic symptoms of a grossly tail heavy airframe. One of the other pilots announced, “we’ve got a situation here!” I heard my poor test pilot mutter in a somewhat daunted voice, “how on Earth am I gonna get this down?”



Well she started to come down alright but thanks to some smart piloting, by staying on tow, we had some time to figure this out. First thing was to dump in full down trim. That slowed the wild oscillations a tad but not enough to save the day. Next Len held almost full down elevator. Things improved slightly but this wasn’t looking good. With tens of thousands of dollars worth of RC sailplanes parked along the edge of the field & people already running for cover our attentions turned to where we could crash her safely. Then in a last ditch effort to save her, Len extended the spoilers & by some miraculous aerodynamic fluke the KA-7 stabilized. She touched down, perhaps a tad roughly but she was on the ground intact! “Len you’re my hero!” I almost hugged him.



Returning to the flight line the KA-7 was soon surrounded by no small amount of pilots all with opinions on where the CG should reside. Then out came the laptop & tape measure & after some number crunching it was determined the correct CG should be somewhere right around the LE, not 100mm behind it! She was, in Len’s words, “screamin’ tail heavy.” Oops! That’ll be the last time I trust the instruction manual for the CG. You live, you learn.

I borrowed an additional 3 lbs of lead from the other pilots, dropped that in the nose & set her back in line for a tow. EDIT: I later removed about a pound of that. Once again Len took the rains & wow what a difference. She inched gracefully off the grass & took a stable position slightly above the tug. Upon release Len fiddled with the trim some, then handed the transmitter over & said, “here you go”. Almost giddy with excitement I took control & spent the next 15 minutes sporting a sizeable grin. Serene, graceful, placid, tranquil are terms that came to mind. What a beautiful sailplane.



With ample dihedral the KA-7 will roll back to level & self-stabilize. Pitch is rock solid; she maintains a slow stately pace with no need to ride the elevator. Hands off, she’ll fly herself. Turns are clean & although I’ve yet to really crank her over, we didn’t notice any tendencies to tighten up & spiral in. It is necessary to hold the turn somewhat or she’ll level off but that’s sort of a good thing.

Although I wasn’t intending to thermal during this test flight, the KA-7 was maintaining altitude nicely. After 15 minutes it was my choice, not the sailplane’s to come down. She’s a bit of a floater for sure. I tested the spoilers while still way up there. Looking like there was no need to mix in any elevator, I was confident I could land her. “Want me to land her?” asked Len. “I think I got this thanks”, I replied nervously. A few minutes later I bellowed out, “in the pattern! landing!” Crossing over into the field I fed in full spoilers & like an old helium balloon she gently descended. Len, still at my side, reminded me to “work the spoilers”. So moments before touch-down I began to retract them. She kissed the grass ever so softly, rolled for a few feet then gently set her left wingtip down. I shook Len’s hand & with an even grander grin, went off to retrieve her.

Preventing Hangar Rash and Arriving at the Airfield in Style



The KA-7 features a two part wing which leaves you with two, six & a half foot wing-panels to deal with. The fuselage is even bigger & quite bulbous. Thankfully the horizontal stabilizer unbolts which helps a lot. You’re probably not likely to fit this behemoth in a sub-compact car, although if the back seat folds down you may be in business.

EDIT: Actually one time I did manage to fit this into a sub-compact but it wasn't happy in there.

I’d recommend using wing-bags to minimize dings. You’ll probably want something for the h-stab & perhaps the rudder too. The canopy is quite delicate, especially the rear part. I’ve already snapped off a small piece. Ideally you should transport that attached to the fuselage, covered with a blanket.

Some sort of stand for the fuselage might help too. Unlike other RC models most sailplanes fuselages won’t sit upright unaided. Once at the field though, get the wings on & you don’t really need a stand.

In Conclusion
For the price you get a lot of sailplane. She’s big, beautiful & when setup correctly, a joy to fly. I’d consider this an excellent introductory airframe for giant-scale soaring. Her big four meter span combined with classic vintage lines should look at home at any scale aerotow or slope event. The dramatic forward swept wings & sharp looking graphics add to her appeal. Defiantly not at all out of place sitting next to expensive European airframes & monster scale composite ships, the HRS KA-7 fits right in.

This is not a glass slipper, neither is it a high performance ship. However what she may lack in sleekness, she more than makes up for in style. Although I wouldn’t consider this an aerobatic bird, I’m betting she’ll perform low G loops & rolls without too much bother. Just bear in mind that’s a built up wooden wing, not a steel I-beam. Take it easy on her! She’s also not likely to be super efficient at thermal duration or in light air at the slope. But that’s not really what she’s about. For casual scale flying, lazing around in a thermal or cruising the slope, I think she’s perfect.

Although the manual has some shortcomings & the wheel area could use reinforcing, I wouldn’t consider this a difficult build. While she’s considered an ARF, expect to spend a week or two putting her together. Much of the assembly was quite enjoyable so time well spent. This also allows you to get to know her & makes it all the more special when she finally takes to the air.




I’ll be taking her along to a bunch of events this Summer. She’s a sweet easy-going sailplane, should be a lot of fun.

Maiden Flight Video

EDIT: I'm still flying this glider four seasons later. T-HEVY has become a common sight at most of the major East Coast USA aerotow events. I've likely had hundreds & hundreds of tows with her, lost count long ago. Despite a few shortcomings, I have to say this has been a great experience.

[Nodd]

Initial Control Setup
Elevator: 1” (25 mm)
Rudder: 1 3/16” (30 mm)
Aileron: 3/4" (20 mm)
Expo: 30%
Differential: 25%

Specifications:
Aircraft Type: Giant-scale sailplane
Pilot Skill: Intermediate
Wing Span: 157” (3998 mm)
Length: 80” (2032 mm)
Wing Area: 11.2 sq.ft (104 sq.dm)
Weight: 20 lbs (9.4 kg) EDIT: mine is 18 lbs
Wing Loading: 28.6 oz/sq ft (87 g/sq.dm)
Cubic Loading: 8.4 oz/cubic.ft
Controls: Aileron, elevator, rudder, spoilers, tow-release
Construction: Fiber-glass fuselage, built-up balsa and plywood wing & tail, 16mm steel wing-rod
Radio Channels: 3 minimum - 7 used
Transmitter: Spektrum DX7i 2.4-GHz Tx
Receiver: Spektrum AR7010 7ch Rx powered by a 2200 mAh LiPo
Servos: Four Hitec HS-645MG servos (ailerons, rudder, tow-release), two Hitec HS-635HN servos (dual elevators)
Spoilers: MPI 300 mm servoless
Tow Release: Hobby Lobby
Instruction Manual: PDF available at troybuiltmodels.com

References:
Castle Creations, Inc.
540 North Rogers Road,
Olathe, Kansas 66062
Phone: 913-390-6939
Web Site: castlecreations.com

Esprit Models
1240 Clearmont St. NE
Unit #12
Palm Bay, FL 32905
Phone: 321-729-4287
Web Site: espritmodel.com

Hitec RCD
12115 Paine St.
Poway, CA 92064
Phone: 858-748-6948
Web Site: hitecrcd.com

Hobby-Lobby
5614 Franklin Pike Circle,
Brentwood, TN 37027
Phone: 866-512-1444
Web Site: hobby-lobby.com

Spektrum – Horizon Hobby, Inc
4105 Fieldstone Road
Champaign, IL 61822
Phone: (217) 352-1913
Web Site: spektrumrc.com

Troy Built Models
1650 Honore Ave.,
Sarasota, FL 34232
Phone: 941-342-8685
Web Site: troybuiltmodels.com

[jgallacher]

Excellent article Nodd.

[hello82]

whew! yeah great article with some exciting video to get the heart pumping! glad it all worked out! Hope to see her live soon.

Matt

[lenb]

Nice Job resurrecting the article Chris, thank you.


len

[Gliderboyglasgow]

do you still have a copy of the instructions as I have just bought the model but did not get any instructions with it

[ARUP]

Great score!

[Nodd]

I just had a good rummage around my workshop for the KA-7 manual. Sorry but I'm not sure what I must have done with that. If I recall the build was fairly straightforward. If you have any specific questions, feel free to ask.