LilAn Resurrection

[ChuckA]

Two years ago, I began construction of a new version of my 2001 RES sailplane, the LilAn. I posted a thread here showing how I built it without laser cut ribs or plans. http://www.rcgroups.com/forums/showthread.php?t=699593 I liked the LilAn’s flying qualities better than the flying qualities of my Ava so the Ava was relegated to my backup RES.

On Saturday, September 13, 2008 I was flying in the Coffee Airfoilers contest when my LilAn had an unfortunate encounter with gusty crosswinds from Hurricane Ike. We were launching to the south and the sun glare made it difficult to see the model in the zoom. I started the zoom a little late and the LilAn did an abrupt tumble just as it pulled up and two pieces flew off the model. When it stopped tumbling, the LilAn was in a flat inverted spin. The stabs were missing and I assumed that the stabs had fluttered off but my timer said that the stab had snagged the retrieval line. Someone yelled “Extend the flaps!” but that’s hard to do with an RES model.

The model stabilized in a flat inverted spin and I could do nothing but watch it slowly spin down. The rate of descent was slow enough that a club member had time to grab his camera and get three pictures as the lilan neared the ground. I have been crashing models for 70 years but this is the first time I got a picture of the crash. The pictures show the end of it’s 177th flight

My timer retrieved the two pieces that flew off the model and they turned out to be the right stab and the right wing tip. The left stab was still attached to the model by the covering material and the photos show that it was folded down against the fin in the spin. I gathered up all parts and carried them home for post crash analysis. Long ago, I learned to carry ALL parts home for salvage because many crashed models have been salvageable if all the pieces were recovered.

Examination of the broken parts revealed that only the center wing panel and the stabs were totally destroyed. The inboard two inches of both stabs were still attached to the fuselage. The right stab had sheared off just outboard of the joiner wires and a brown mark on the leading edge showed where the retriever line had hit the stab just outboard of the second rib. The left stab had failed in a downward direction just outboard of the second rib and was attached to the stab root only by the bottom Monokote. Other parts suffered only minor damage and could be easily repaired so all parts were placed in storage for rebuilding next winter. The fuselage was broken between the wing bolts but was otherwise undamaged and held together only by the pushrods and antenna tube so the fuselage parts were glued together to prevent further damage before putting the remains in storage.

The first step was to jig up the fuselage on the workbench and align the parts. The fuselage was glued together with thin CA and 5 minute epoxy. This made the fuselage strong enough to grind the paint off the break and reinforce it with a one inch wide glass tape and laminating resin. After the epoxy had cured overnight, the area around the break was sanded to bare fiberglass and a 4 inch wide strip of 6 oz glass laminated over the damaged area. Once the epoxy had cured, the fuselage was hung on the wall until the winter building season.

It is now the winter building season and this thread will cover the rebuild.

[Robglover]

Cool! Nice photos, it will be good to see her back this spring.

[ChuckA]

As I watched the LilAn spin down, I did not expect to have enough to salvage. The model impacted the ground almost level inverted and contacted the ground on the nose and right wing tip. The center wing panel was obviously destroyed but the fuselage could be repaired and outer wing panels appeared to have little damage. The center wing panel spar failed under axial load at the right edge of the bolt beam. I stripped the failed spar from the remains and examined it for other damage but found none. The right outboard panel trailing edge was broken just outboard of the root rib but no other damage could be found. I am impresses with Mark Drela’s spar design and plan to continue using it in my RES sailplanes.

The fiberglass fuselage repair done the day after the crash was sufficient and only sanding, filling, and priming was required to get it ready for painting. The washing the dirt off the top of the nose cone and a little epoxy in the crack was all that was needed to get it ready for painting.

Repair of the outer wing panels only required cutting off the fragments of the tip panels and repair the right panel trailing edge. I clamped the trailing edge to a straight edge and laminate some 2 oz glass cloth over the crack. A little sanding and filling with vinyl spaking compound and the repair was ready for covering.

[Tim K]

If it was coming down so slowly, why didn't you catch it? ;)

[jtlsf5]

If it was coming down so slowly, why didn't you catch it? ;)

Chuck isn't quite as mobile as some of us younger guys.
JT

[ChuckA]

If it was coming down so slowly, why didn't you catch it? ;)

Slow is a relative term. I wouldn't have attempted to catch a 4 pound model moving fast enough to break the main spar even if i could have managed to sprint 300 feet to the crash site before it reached the ground. :)

[Tim K]

edit

[sleep4]

I was there. It made a pretty loud whump when it hit the ground. I was impressed also by the mostly surviving main spar while all else around it crumpled. Hats off to Chuck for the repair thread. I'm not so sure I could have undertaken the task. But then Chuck's been at this for a long time.

[ChuckA]

The right tip broke off in flight and only suffered minor damage to the root rib and top leading edge sheeting. The left tip suffered more damage when the model hit the ground and I considered building a new tip. When I stripped the covering from the left tip, the bottom sheeting was splintered, and trailing edge was broken. Removing the bottom leading edge revealed a couple of broken ribs but the damage wasn’t that bad so I decided to repair it. The broken ribs were spliced with short balsa doublers before installing new bottom sheeting. Titebond was used to glue the bottom sheeting in place and clothes pins used to clamp the sheeting to the ribs. New root ribs were built the old fashioned way. The root rib pattern was glued to a sheet of 1/16 inch balsa with rubber cement and cut out with an Xacto knife. Two more ribs were cut using the first as a pattern. The new root ribs were glued in place and new top sheeting of both tips were spliced in. The repaired tips were glued to the outboard panels to complete the outboard wing structural repair. A little sanding and filling of the tip joint was all that was needed to get the outer wing panels ready to cover. Now all that was left was to build a new center wing panel and stabs.

[ChuckA]

A friend liked the way the LilAn flew and wanted to build one so he made a DXF tile for laser cutting a set of LilAn ribs. I can stack cut a set of ribs for a center panel in less than 30 minutes but, since he was doing all the hard work, I decided to use laser cut ribs for a new center wing panel.

This is the third LilAn center wing panel to be build so a few improvements were made in the construction sequence. Normally, I build the wing and strap it to the fuselage to check out the alignment before drilling the bolt holes. I wanted to fit the wing to an existing fuselage so I started by building the bolt beam and drilling the bolt holes to match the fuselage, Since we were going to laser cut ribs, we could have cut nose and tail ribs for all except the end ribs. Cutting the ribs full length leaves more options about spar constructions so we elected to cut full length ribs and cut them to length as required by the spar dimensions. The rib and spar locations are drawn on the bottom sheeting with a ball point pin using a triangle or square and 48 inch long straight edge. Bottom sheeting and the trailing edges are laid out on a grid. I use a magnetic building board but anything with a grid can be used. The bolt beam and spar is glued to the bottom sheeting with filled epoxy and allowed to cure before starting to install the ribs.

Laser cut ribs are more accurate so I was able to do away with shimming the leading edge of the bottom sheeting. The end ribs are installed intact but the other ribs must be cut into nose and tail ribs. Place the nose of the rib against the spar and mark the location of the leading edge. Then cut the nose rib free being careful to make the cut perpendicular to the bottom of the rib. A Miter Cut Precision Cutting Tool makes it easy to cut the ribs square to the bottom of the rib. The nose rib is glued to the spar with epoxy and to the bottom sheeting with thin CA. Be careful to glue the rib to the bottom sheeting only where the rib touches the sheeting. The aft rib is cut by placing the trailing edge of the rib against the rear of the spar and marking the rib at the bottom of the trailing edge rib slot. Cut off the spar section the rib with the Miter Cut and glue to the spar with epoxy. The rib is glued to the bottom sheeting and the trailing edge with CA.

When all ribs have been installed and the epoxy cured, shift the wing to the edge of the work bench and clamp the bottom sheeting to the ribs to glue with CA. The end ribs were installed with the outboard panels plugged in to assure that they are at the proper angle before gluing in place with CA. The rest of the wing construction is the same as in http://www.rcgroups.com/forums/showthread.php?t=699593

[ChuckA]

Since the original thread glossed over the spoiler installation, I will go into my spoiler installation in a little more detail. Before starting wing construction, stack the ribs and drill holes for the spoiler string guide tube or for the spoiler servo wires if using spoiler servos in the wing. I have used both over the years but prefer to use pull strings if possible. The only reason I would use servos in the LilAn wing would be if I had to remove the center wing from the fuselage for transportation. Connecting servo plugs is easier than fishing the spoiler strings through the fuselage to the spoiler servo. The LilAn was designed to fit in my van without removing the center wing panel so I use pull strings to actuate the spoilers. Installation of the polyethylene guide tube is easier if the end of the tube is molded to shape. The jig is just a ½ inch dowel and two screws mounted on a scrap of pine. Warm the tube with a Monokote gun and let it cool.

The rear frame of the spoiler well is 1/8 by ¼ balsa centered on the rear of the spoiler and is raised slightly above the rib at the back edge. The rear edge of the frame is sanded down to the airfoil contour and the forward portion is then sanded down until the trailing edge of the spoiler is flush with the wing upper surface.

I became frustrated with balsa spoilers warping as the model aged and began building spoilers from foam and fiberglass. Little actual working time is required to fabricate the spoilers but construction is spread out over several days because of the epoxy cure time. The spoilers are built from 6 oz glass and blue foam scraps left over from other projects and are laid up on a glass plate. Construction of the spoilers may be the subject of a separate thread if I get around to writing it.

The spoiler horns are cut from nylon sheet and glued in the spoiler using a simple jig to be sure that the horns on both spoilers are identical. This is important if using a single servo to actuate both spoilers or if using a y-chord to actuate both spoilers with a single radio channel and two wing servos.

The spoilers are held closed by short magnets cut from rectangular magnets I found in the hardware section at Lowe’s epoxied to the spoilers. Old Xacto blades make good latch plates for the spoiler magnets and I usually have several (if I haven’t emptied the trash lately). Rigging of the spoilers are covered in http://www.rcgroups.com/forums/showthread.php?t=699593

[ChuckA]

A new set of stabs has been built and resurrection is completed except for painting and covering. Since I have nothing new to add about painting or covering, this is the end. I have been in no hurry to finish the rebuild because I had another LilAn almost ready for covering before the crash. The new model was finished before starting the rebuild so now I will have a backup LilAn ready for next year and can sell my Ava.

I hope some of you have found this thread useful and will give a little more thought about rebuilding a wreck before carrying it to the dumpster.

[Mark Miller]

Chuck,

Nice to see you are keeping the Vette safe and sound under a cover.

Mark Miller

[ChuckA]

Today, I flew the LilAn for the first time since I crashed it last September. It has been ready to fly since early January but bad weather on the days I could fly has prevented an earlier flight. The LilAn required no trim changes since the last flight which means that the new center wing panel aligns well with the original outboard panels. Now I have two LilAns ready for the flying season.

[Wylie Shaw]

Chuck Whoooo RAH!!!!! excellent you just can't keep LiLan down, great job....
glad to see that she is back in her element...


Wylie E. Coyote..... :D :D :D

[Captain Canardly]

Way to GO Chuck!
I'm having a bit of new life in between my 65 hour work week also!