Supra Instructions

by

Larry Jolly

Portions published in "Quiet Flyer"

The Supra from Vladimir's Models The Next Step Just mention the name Dr. Mark Drela, in association with the design of a new sailplane, and you will immediately recognize that the design is cutting edge and capable of impressive performance. Mark's method of total airframe design and engineered structure is proving to be the winning solution for lightweight, slippery sailplane design. Combine Mark's engineering skills, and Vladimir Gavrilko's manufacturing capabilities, and you have the new Molded Supra, distributed in the U.S. by Barry Kennedy, of Kennedy Composites. I was very luck to have been in contact with Barry while Vladimir was getting ready for production of the Supra. This constant hounding paid off as Supra #1 showed up on my doorstep.

This review is based on that airplane and may differ slightly from the final version that Barry offers for sale. I asked Mark to describe the Supra design philosophy and I 'll turn it over to him now: The Supra combines a large number of design features, which have been developed and proven on previous gliders. * The low wing loading is combined with "fast" airfoils, which vary considerably across the span to account for the decreasing Reynolds numbers towards the tips. The center AG40d airfoil is very similar to the popular MH32. The tip AG43d airfoil is nearly the same as modern DLG airfoils. *

The planform has a fairly strong taper, enabled by a slight amount of washout. The washout suppresses tip stall, but doesn't noticeably impair high-speed performance. The strong taper has two main benefits: - It is structurally favorable, and allows a large aspect ratio for a modest spar weight. - The light narrow tips give low yaw and roll inertia, improving handling and thermal signaling. *

The generous dihedral, which is almost universally used in DLGs, was adopted for the Supra for the same reason: It improves thermal ling characteristics and reduces the pilot's workload, especially when the glider is far away. * The unswept planform has very small torsional loads in the high-camber launch configuration. This greatly reduces the amount of washout twist during launch, and gives a good span wise load distribution and good launch performance regardless of wing bend. *

The wing pylon mount was pioneered on Tom Kiesling's very successful Mantis TD gliders, and has also proven to work well on my Supergee DLG. It was adopted for the Supra for the following reasons: - It keeps the messy fuselage flow off the wing at all times. - It allows laminar flow on the fuselage nearly all the way to the towhook position. - It protects the flaps somewhat during landing. * The tail unit is a close adaptation of the Bubble Dancer's tail, and gives low weight together with mechanical simplicity.

Mark Drela (printed by permission and received by e-mail from the author) The Supra specification as reviewed: Wing Span 134" Length 67" Wing Area 1052 sq/in. Profiles AG 40 transitioning to AG43 Wing Loading 8.2- 9.0 oz/sq.ft. Flying Weight 64 oz. Dry Control Airtronics Stylus Transmitter Airtronics 927777 FM Receiver 6-Airtronics 94761Z Digital Servos Cermark 4HR-AAU 1650 ma NiMH Battery Pack Distributor Kennedy Composites 1935 Highvalley Trail Grand Prairie, Texas 75052 Phone 972-602-3144 Website www.kennedycomposites.com You can find a very nice three-view drawing at: http://www.kennedycomposites.com/images/supra/supra_3view.pdf

From The Sport Tube Barry ships the Supra in a SportTube to minimize the chance of damage and maximize the chance that you will get what you paid for. Inside the tube I found a three piece molded wing, Kevlar graphite molded fuselage pod, graphite tailboom, molded fin-rudder, and stab. The accessory kit comes with all necessary hardware, including three sets of joiners; 0 degree, 2.5 degree, and 5 degree dihedral, pushrods, ballast tube, and a Hoopes Design "Wiring Harness" is an available option. The wing molding is a work of art with all surfaces skin hinged and no leading edge mismatch or overlaps. Assembly The Supra follows standard techniques for assembly that will be familiar for those experienced with a molded sailplane build. Always check that your work area is clear of objects that might leave blemishes or dents in the flying surfaces while you are installing servos and pushrods. The pod and the tail boom are manufactured as separate components and must be joined by the builder.

I recommend that you first cut the access ports for the servos, receiver, and battery pack. Then place a piece of masking tape under the wing outside the pylon mount. Mark a line 3.6" and 3.8" from the leading edge. Mount the wing and using a 90-degree triangle, transfer the 3.8" mark to the bottom of the fuselage, and grind the access hole for the tow hook so that the towhook centers it's travel at the 3.8" mark. Now bond the towhook in place with a mixture of epoxy and Cabosil. Make it thick enough so that the mixture stays put and doesn't migrate throughout the fuselage. While the tow hook is setting up, move on to the tailboom. Trial fit the stab mount and fin assembly to the boom. Mark the areas where the stab mount and fin rings will contact the boom. Remove the stab mount and fin, and then scuff the mounting area to ensure a good epoxy bond. After you have scuffed the area give it a good rub down with denatured alcohol to remove any release agent.

To assemble, set the boom up on a surface that will give clearance for the fin-rudder to hang downward. I used the groove in my band saw table with a weight over the boom to secure it from any movement. Don't forget to place the stab mount on the boom, but don't glue it in place yet. Slide the fin assembly part way on the boom and apply a thin coat of thickened epoxy. Let the fin hang down and clean any excess epoxy from the boom with denatured alcohol. After the epoxy has cured you can secure the stab on its mount and adjust it so that it is square to the fin. When you are happy with the alignment, epoxy the stab mount to the boom. Check it often during the cure process to make sure the stab hasn't rolled around the boom. In my pictures you will see that I glued the Teflon pushrod housing directly to the outside of the tailboom. This is standard practice for most models that utilize these pushrods.

When I build my next Supra I will use internal pushrods, which will require bonding the tubes to balsa spars and then supporting them with foam rings inside the boom. I only mention this because if you choose the internal pushrods you must proceed with that installation prior to joining the boom to the pod. My tailboom fit the pod pretty well so that I only had to scuff the pod, and the inside of the boom, mount the center panel, and bond the tailboom in place securing it with a wrap of tape over the joint. If yours is loose, the best way to proceed is to set up a center line on a table or plate and use blocks under the wing and stab to ensure that everything goes together straight and stays that way while the epoxy cures. After the boom is secure, either finish the pushrod installation internally, or mount them on the outside. You will find that if you try to secure the tubes directly to the sides of the pod, matching the curves, you may induce a lot of drag to the system. I minimized the drag by using balsa stand off supports inside the pod so that the housings had a fairly straight run. Whatever you do, make sure that the pushrod installation is tight and smooth, as this will greatly affect airplane performance.

Make a spacer for the rudder control horn so that the attachment point is .3" off the rudder. This will make sure there is no rudder pushrod bind at maximum deflection. The rest of the model goes together very easily. Prior to mounting the wing servos, work the flaps and ailerons by hand until they loosen up, and show equal travel. Mine were fairly stiff and had to be worked to get the maximum down flap travel. I used Airtronics new 94761 digital servos throughout and found them up to the task. The wing is pretty thin at the aileron pocket, so I removed the aft lugs, and tucked the aileron servo up against the spar. I used the 2nd hole on the short side of the star arm that Airtronics provides for both ailerons and flaps. Before you mount the aileron servo you will find that the lead is just long enough to protrude from the tip root of the wing. If you take a piece of monofilament line, about 2" in length, and heat shrink it to the servo cable; it will help keep it from retracting into the wing tip.

When you are sure that the radio is programmed and the servo arm is in the right place, 5 minute epoxy the servo to the upper skin. After it is secure, go back and Goop or Zappa Dappa Goo, the servo to the bottom wing skin as well. This really stiffens up the aileron servo installation and will reduce the chance of aileron buzz when you are showing off how fast your Supra will come home. Install the flap servos and check both aileron and flap linkages for slop. I found that the control horns had slightly oversized holes for the clevis pins. A little shot of thick CA fixed them up and everything was tight. If you use the Hoopes Connector that Barry is stocking for the Supra you will find that it works well, and speeds assembly. I felt that the leads going forward to the receiver could have been a little shorter but it was easy to stow the excess inside the pod.

Finish up the radio installation in the pod. Check that everything fits, as the pod is pretty snug. I like to exit the antenna as soon as practical and then tape it to the bottom of the boom, letting the last 2 inches hang vertically away from the graphite boom. Balance the model at the 3.6" mark and set the stab so that it is parallel to the boom. Go to Kennedy's site for the entire servo throws in various flight modes, as the radio settings are real close.

FLYING THE SUPRA OK here it is; WOW! I honestly didn't think a new design could be so much better than current standards. This model is a dream to fly; "User Friendly" fits it so appropriately. The Supra climbs like a model that weighs much less, and covers ground like a model that weighs much more. With its sleek low drag design, the model has rapid acceleration, making it quick on the tow, and seamless when changing from crawl to cruise. If you use the 5-degree joiners, the model is docile, almost to the point of feeling slow in roll. Changing to the 2.5 degree joiner's increases roll rates, but your workload will increase slightly. In all modes, the Supra is tolerant to elevator abuse, and will not bite. This model is going to become very popular because it offers so much soaring potential and is so easy to fly. Low time pilots will find this a natural model to utilize in order to get into competition thermal soaring. With the low weight and generous flaps, landings are very controlled and accurate. I believe that this is one of those models that will leave its mark as a vanguard, the first of a new breed that will forever change what is expected in a competition sailplane design. As outfitted, the model has flown very well for me. The Airtronics 94761 servos remained tight and control the Supra well. Thanks Mark, Vladimir, and Barry - this is one sweet sailplane.