The Emerald

Kit Review, February 1999.

I bought my Emerald directly from Tim Renaud in December of 1997. Former WC Skip Miller is producing the kit now, and has made a few changes to the construction, though I don't know what the changes are. Skip can be reached at WoodLogic.

As you can see, the wings are red, and the fiberglass/kevlar body is unpainted, except for the white nosecone. The kit was built completely stock with the following additions:

1. Root ribs added - The molded wings have no root ribs and I was afraid of crunching the wing roots on poor landings or handling them.
2. Ballast tube - a brass ballast tube was run in the body with the center at the CG. A lead filled brass tube fits inside to increase the weight by up to 21 ounces.
3. Crush Brace - a 1/2" square balsa brace was added inside the fuselage at the wing fairing leading edge
4. Skeg and Nose hook - Tim McCann's nice super skeg and nose tooth were added for saving shins. Highly recommended.

Total construction time was about 30 hours, including figuring out placement of the radio and building two sets of stabs. Why did I build two sets? The first set used the stock plan and came out at 48 grams with joiners. The second set had some engineering applied, vertical shear webs were added to the spar, a CF reinforcement strip was put in the TE and the joiner tubes were shortened. These changes saved 7 grams out of the tail, they are stiffer in lateral flex and 20g (3/4 ounce) can be taken out of the nose. Your choice. (Ed: previously reported weights were double the actual, I have a beam balance 2X multiplier which was not accounted for in the reported numbers.)

The fuselage is a nice smooth layup with a 1" kevlar tape strip. Nose cone fit is perfect, needing only a wrap of masking tape at the nose for friction, and a slight trim at the rear joint. I filled the void in the nosecone tip with microballoons and epoxy. Carbon pushrods are provided, top notch. Overall the fuse is almost fat, not like the ultra skinny bodies on some planes like the Eagle so radio installation is easy.

R&R fabricated my model, all the mold work was fine. The hinges are installed, mylar wipers on the ailerons, and plastic knuckle pieces on the flaps. The ailerons use a skin hinge on the top, it is springy and requires a good servo. Minor complaint, the leading edge needed some touchup and filling to be shaped properly. I used a bead of microballoon/epoxy for the low spots. I don't like flaps that go all the way to the wing root, butting up to the fuselage wing fairing since it always leaves a gap. This can't be aerodynamic.

Trim:

The towhook position listed in the instruction sheets was pointed out to be incorrect. The position shown on the plan is supposed to be correct. The CG shown on the plan is way off. I am happy with the CG at 5.2" back from the LE. The first flights were at the recommended CG location, and boy was the thing flying fast. Camber for thermalling had no effect unless large amounts of up trim was added. With the CG far back, the plane slows down a lot more. Gee, now the plane stalls when camber is added, so some down elevator compensation is needed.

Speed setting (reflex) at ~1/16" up for ailerons and flaps has no visible effect on flying speed, but I add it since it can't hurt.

Landing required lots of down elevator (95% on my Stylus) most of it in the first 30 degrees on flap motion. Get the idea that a good computer radio is needed?

Launching

The plane launches as well as any plane I've seen. My towhook started out right on the CG and the rotation to climb was immediate, with just a blip of down to stop the stall. Then I tried launching with a draggy retriever on the winch and the popoffs started. Moving the towhook forward has cured that, but with some loss in altitude. Oh well. Launches are simple, step on the pedal, and throw it straight. The club Real Balls(tm) winch can't bend the wings.

Flying

The plane was my primary ship in all the local contests of 1998. With the launch setup working, and any sense of lift, the glider did what it was supposed to do. Spot landings require a fair amount of speed (get outta the way!) to keep the roll response up, but it is still slow enough to handcatch without flaps. I've put a good 60 hours of thermal flying time on this ship, and it is easy to fly. On a practice day, it has made ten seven minute tasks in a row, and I don't consider that to be abnormal. It has made an 11 minute task, all of the time under launch height, when nobody else in the round made over 5 minutes. For a contest pilot, this plane will not be the limitation if the wind is less than 10 mph and there is SOME lift somewhere.

Update August 15, 1999.

It's the annual Thermal Master contest for the Yurchevich plaque. Cloud cover is near 100% with threatening showers. We're using the newly acquired Rahm winch, it's a mega launch contest to make 5 minutes in dead air. The plane makes the times with about 30 feet to spare. Some lift is coming through now and it's now time to make three 10 minute flights. The plane out-hangs the Psychos to make 2 of the tens under launch height, and then everything shuts down for the day as it starts to rain, only a 5:44. The huge launches and good minimum sink (with camber on) performance rule the day.

Update Sept 20, 1999

The club is having the annual two day contest and conditions are relatively tough. At least there is lift to be found, but nobody is specking out. Thirteen flights over 2 days with launch on rotation, and no throwaways means consistently making the most of the air your given. The Emerald is chosen except for two flights where the wind is up over 10 mph, and it buries the competition on the first day. I blow one landing, otherwise it's within a few percent of the round winner every time.

The most significant event was a flight downwind past the point of no return. A Psycho is in rapidly moving lift two minutes ahead of me in a 7 minute task. Out over the swamp and the Diamond chases the lift through 200 feet of sink, with a Merlin in pursuit. The Psycho has to bail, and the Diamond makes the lift band and hangs/drifts for 5 minutes, getting back to the spot with nothing to spare.

Specs

122" span, SD7037 airfoil.

Mine weighs in at 73 ounces without ballast. Attention to detail and meticulous building practices could shave 1 to 2 ounces off the final weight, not much chance to save weight with the wings/fuse/radio/hardware fixed. The ballast tube added 2 ounces, so shoot for 69 ounces.

Radio : Hitec throughout, Supreme receiver, HS 205 elevator, HS 80 rudder, HS 205MG flaps, HS 80MG ailerons, 1100 4AA nicads. Aileron servos are light duty and may require changing to a more robust servo.

Overall

I like the kit quality, and wing strength. Cost is very reasonable for a molded plane. Good floater type, landed out a few times when the wind was up by overestimating the penetration. Personally I like planes with more penetration, and will give up something on the minimum sink performance. The Bird of Prey is 8 ounces lighter and can stay up better in marginal lift, but has far less range. Youze payz the cash and takez dem choiz.

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