Building JD AEROTECH CHRYSALIS

[joker2]

Building subject from kit. I have already modified wing structure to include carbon fiber tape laminate spar and carbon fiber tube for leading edge. Looking for discussion of spoiler installation options

[Wazmo]

Have you seen the Ask J & D entry on Chrysalis spoilers (http://www.djaerotech.com/dj_askjd/dj_questions/chrys_servospoiler.html)?

[joker2]

Have you seen the Ask J & D entry on Chrysalis spoilers (http://www.djaerotech.com/dj_askjd/dj_questions/chrys_servospoiler.html)? That's the way Joe and Don have it on the drawings except with a different wire lead. I'd rather not glue the servos in place and I'd like to have access without cutting through the covering. I weight the wing assembly this morning minus servos and covering and I'm at 315 grams. JR 285s will add about 16 gram so with covering I should be between 340 and 350. I Fly a Riser2M kit built with spoiler whose wing is 345.

[joker2]

Just got some Hi-Tech 45 which are only .375 thick. The fit in the wing with room for a 1/16 balsa plate mount the can be screwed into runners along ribs from bottom side of wing making a removal spoiler servo pack. The servos come aboard at 8 grams plus wire and mount.

[joker2]

Carbon fiber tubing used as leading edge

[kwmtrubrit]

This is how I did my spoilers on my Riser 100. A ply plate is screwed on the bottom of each wing and the spoiler is attached to that. I used goop to hold the spoiler, but a servo mounting bracket would work just as well.

Keith

[joker2]

I have taken Keith's suggestion and build servo boxes that mount from the bottom of the wing. The boxes are made from 1/32 boxwood sheet with a 1/8 X 1/8 balsa frame bonded to the sheet with thin CA. After bonding I sanded frame thickness down to about 1/16 which made for a stiff plate. With the plate temporarily mounted I glue 1/2 lengths of the 1/8 X 1/8 balse strip to the ribs and main spar. Tack glued with meduim CA/ removed/ servo box/ glued with thin CA. Final mount of box in wing uses 2 X 1/4 brass wood screws. Using the 1/32 basswood plate gave me enough room to use JR DS 285 servos which were my first choice

[joker2]

With the servos mounted, I've chose to program them individually using a multiplex connector so the the throws and reversing of the servos can be individually addressed. The servo mount was the last major stumbling block in the construction. The main wing is complete in the three piece configuration and the emmpanage parts are also done. I chose to use the lightening hole design provided by Joe and Don but I used 3/4 oz fiberglass cloth to reinforce the leading edge of the horizontal and vertical stabilizers. I've also used carbon fiber reinforcement in the main spar box. The servo boxes only added 5 grams to the wing mass.

[sailfree]

Joe,

Looks great. Can't wait to see it fly. :)

Larry

[joker2]

The vertical stabilizer/rudder assemble and horizontal stabilizer/elevator assembly were spot glued together and sanded to a symmetric airfoil using the methods described in the assemble of a bubble dancer on the web. I probably didn't achieve a perfect HT-21 airfoil but I"m sure I reduced the drag. The leading edges were covered with .75 oz. fiberglass pressure bonded using a home made press shown. .007" carbon fiber tape has been added to improve rigidity which was also pressure bonded. The press is constructed from 1/2" plywood and uses window sill foam to load the contour. The press is lined with cling wrap as a release agent. All parts are assembled with either 30 minute epoxy or finishing epoxy. The carbon fiber tape stiffeners were applied with 30 minute epoxy. The stiffeners are intended to reduce the chance of flutter under winch launch. The parts will be assembled with ultra-coat continuous hinges which also combats the on set of flutter.

[Don Stackhouse]

The vertical stabilizer/rudder assemble and horizontal stabilizer/elevator assembly were spot glued together and sanded to a symmetric airfoil using the methods described in the assemble of a bubble dancer on the web. I probably didn't achieve a perfect HT-21 airfoil but I"m sure I reduced the drag.

It certainly won't hurt, but won't be a significant difference from just rounding the leading edge and tapering the trailing edge. Tail drag is a pretty small percentage of the total drag. Sure does make itl ook nice, though.

On an all-flying tail surface the airfoil shape is more critical, to avoid aerodynamic hysteresis issues. This is less of a problem on a two-element tail surface (such as a fin+rudder or a stab+elevator) which is one of the reasons (among others) we used that approach on this design.

The leading edges were covered with .75 oz. fiberglass pressure bonded using a home made press shown.

Nice work! A vacuum bag would also work, if you had the necessary equipment. However, the press does a nice job if done right. We used screw presses for years to apply the balsa skins on the old wood-wing versions of the Monarchs. Each press was tall enough to handle a dozen panels at a time. I still have the presses out in the barn. We switched to vacuum bagging when we went to glass skins on the Monarch D series and the Wizard.

.007" carbon fiber tape has been added to improve rigidity which was also pressure bonded.

Unfortunately those stiffeners add weight in the wrong place and do not add the stiffness in a way that will help. The net result actually makes flutter more likely, not less.

First of all, the stiffness that matters is torsional stiffness The rib-like carbon strips add chordwise bending stiffness, which is not the same thing at all. In addition, they add weight, which makes flutter more likely, and they do it in a way that keeps the C/G of the surface aft, which also makes flutter more likely.

For an individual flying surface, to eliminate the forces that drive flutter, you need to keep the local C/G of the surface and the torsional axis (or "shear center") of the structure at the same point as the aerodynamic center (typically at 25% of the chord aft of the leading edge).

For something like a control surface, you need to keep the surface's shear center and C/G at the hinge line, or as close to it as possible. Adding a +/-45 degree cloth strip (glass like you used is fine, Kevlar cloth is better, and carbon cloth is best, but also the most expensive and hardest to find in light enough weights) wrapped around the leading edge of the control surface does help, since it adds torsional stiffness while still keeping the weight forward, near the hinge line. Adding chordwise strips has almost no effect on the torsional stiffness, and adds a lot of weight way aft of the hinge line. The exception to that is if the reinforcement aling the leading edge is so stiff that the stiffness of the wood in the control surface is negligible in comparison.

However, the biggest factor on control surfaces in the vast majority of cases is the stiffness of the hinges and control linkages. There have been some reports of control surface flutter on the Chrysalis, and in virtually all cases it has been traced back to control linkage stiffness problems. Adding weight to the control surfaces only makes this problem worse, by providing the tail surfaces with more mass with which to shake the linkages.

Once balance and stiffness has been dealt with on the control surfaces, you still have the stiffness and balance issues for the entire tail panel to deal with. Any weight you added to the control surface means that much more you need at the tail panel's leading edge to get the C/G of the entire assembly far enough forward. The same is true of added stiffness. And of course the weight you added to the tail panels now means more mass that the tail boom has to keep under control. This is definitely one of those problems that can snowball on you, each added fix creating a new and larger problem in the next link in the chain.

Keeping the linkages and hinges stiff should take care of the rudder and elevator. The place that could benefit most from added stiffness in the structure would be the stab and fin, not the rudder and elevator. A spanwise strip top and bottom alonlg the hinge line, and another diagonal set running from the root leading edge to the tip at the hinge line is probably the best place to reinforce things. Split that 1/2" wide carbon into 1/4" wide strips, that should be plenty.

However, the biggest issue is keeping the control linkages as stiff as possible.

The press is constructed from 1/2" plywood and uses window sill foam to load the contour.

Clever idea! With enough pressure, lightweight beaded styrofoam would also work.

The tricky part with a press on an airfoiled shape is getting enough pressure on the sloped part of the leading edge. That's where a vacuum bag has an easier time meeting the requirements.

The press is lined with cling wrap as a release agent. All parts are assembled with either 30 minute epoxy or finishing epoxy. The carbon fiber tape stiffeners were applied with 30 minute epoxy. The stiffeners are intended to reduce the chance of flutter under winch launch.

Ist priority: control linkage stiffness. 2nd priority: bending and torsional stiffness of the stabs and fin, without adding much mass and inertia to achieve it.

The parts will be assembled with ultra-coat continuous hinges which also combats the on set of flutter.

True, although a good tape hinge, such as 3-M BLenderm also works very well.

Don Stackhouse at DJ Aerotech

[joker2]

Don: I started with 89 grams of wood in the kit for the surfaces. By the time I finished cutting the lightening hole I was down to 39 grams. The wood seems weak in the cross grain direction so I opted to press bond 1/2 X .007" carbon fiber which added 5 grams after I had alcohol wiped and cured the assemble. I built a general hinging tool for monocote type hinges so there is no leakage. The parts are mounted in the tool and a sharp 45 degree angle are sanded in the rudder and elevator. The tool helps align the parts prior to sanding to create a sharp straight interface for the hinge. I assembled the parts using 1 3/8" strip of ultracote light which greatly simplifies the hinging process making a clean flexible hinge. I have started covering using ultracote. My color scheme was chosen from a color wheel for contrast and visibility. Verticle Stab. + rudder is 19 grams covered and hinged. Horizontal stab. + elevator is 40 grams covered and hinged. Total emppenage is 59 grams vs. the original 89 grams. The stiffners added only 5 grams to the package. I told the guys that if it doesn't fly it's my fault because I have modified the assembly of the kit. I fly with guys with big power winches and expensive planes and I've had the opportunity to look at their construction after they have crashed. I feel good about what I've done to date. The kit is very good quality. I just like to build. Its getting close.

[sailfree]

Joe,

We're flying at Harold 1100 Sat. See you there. Sailplane is looking great.

Larry