covering part 1 (Tail Feathers)

I started covering the tail surfaces. The rudder was first. This is the first time I am using the Stewart system Eco Bond adhesive. As usual there is a learning curve to go down. I will eventually re-cover the rudder, but I learned a few good lessons. The Eco bond is really good stuff, but it needs to be applied with a foam brush. The natural fiber paint brush I was using does not apply the adhesive evenly. This will make for a lumpy covering job. In the Stewart manual, they give a lot of good tips, one of them was the use of this disposable cup method.

Chinette plate and Dixie cup holder

this is a holder for the Eco bond adhesive. In the middle is a cut down Dixie cup that has been bonded with 5 minute Epoxy to the center of a Heavy duty Chinette paper plate. A fresh Dixie cup is used for the actual adhesive. Its placed in the Dixie Cup holder. This way it wont spill on you. about 1/3 a cup is all the adhesive you work with at a time. That's the length of out time you have available.
The Eco Bond is water soluble, but once it cures, its set for good.

pre coating the structure

The method I finally settled on is to pre-coat the entire structure and let it fully dry. The Eco Bond is heat activated. The fabric is placed into position and then ironed onto the frame with a iron set and calibrated to 200 degrees. The heat of the irons is extremely important. Its very important to use a good IR thermometer when you calibrate the Irons. The normal main shrink temp is 250 degrees, on a certified plane with heavier structure, the shrink is accomplished in three steps, 250 degrees, 300 and finally 350 degrees. that is way too much for an ultralight airframe.  This is the main reason I am recovering the rudder. I used the higher temp and I bent the trailing edge. Its slightly scalloped. All ultralights stop the shrink at 300 degrees.

Rudder

I am using a single wrap piece of cloth for the rudderThe first wrap will attach to the trailing edge The cloth will be wrapped over the trailing edge. The opposite side will wrap over the railing edge and attach to the cloth only. All ribs are also bonded,








 

Ribs being bonded

 once the adhesive dries, the fabric is tacked on using a heated iron, after everything is in place, additional Eco bond is brushed into the surface to adhere to the previous coat. Once this sets, its really on there.










 

beginning of the Horizontal

The horizontal came out really well. I used two separate pieces to cover this surface. Both pieced will over wrap the leading edge.

Finished Horizontal

So far the covering process added only 2.5 ounces, the real weigh gain will be the finish. Tomorrow I will finish the elevator and the ailerons. My buddy Ed will come by tomorrow and we will pull the wings. I can cover the R/H wing immediately, the L/H wing needs some repair on a plywood piece that was damaged during storage. But I should have both wings covered by Saturday. Then its on to the fuselage. after I cover the fuselage and finish the plane, I need to re assemble the wings and then build a root fairing. I decided it would be easier once I figure out where the fuselage fabric is placed.

Final Jobs Before covering

Merry Christmas!!   For the last 3 years, this vacation has been my chance to make real progress on my project. I had hoped to be able to take off most of the month, but we had a huge number off RFQ's ( Request for Quote) in the last month. I normally work on an advanced composite design project, unless we have quotes to do. Had my project just been my Advanced R&D project, I could have taken off. Oh well. Anyway, I got smart and bought 3) 55 gallon Barrels and set the Robin on top of them. This also gave me a chance to weigh her with the wings on. I am not going to make ultralight weight without a Ballistic Parachute. I am close, 246 lbs, but that without cover. On this plane however is a ground adjustable CGS prop that weighs 9.5 lbs. I am using that Prop to dial in a fixed pitch Spruce prop that will weigh 1.5 lbs. Subtracting that weight from the total and that gives me a weigh allowance of 16 lbs for covering. I have estimated 18 lbs. Anyway, with a Second Chantz http://www.secondchantz.com/ ballistic chute, I will be a legal Ultralight. as I mentioned earlier in my blog, by wing is 19 lbs over weight. 5 lbs of that weight is excessive resin packed into the void between the round carbon pultruded rods. The other excessive weight is the fiberglass in the spar and the leading edge. I have begun working on a redesigned wing, I do not like the current attach method either. This and the desire to reduce weight has driven me to a redesign. My new wing design will be constructed of plywood and graphite pultrusions. There will be a fixed center section, this one redesign will save 5 lbs, due to elimination of the overlapping spars. The attachment method will be more akin to the beautiful German sailplane designs I have been studying. There will be no physical attachment of the ailerons or the wing other than two main shear bolts. All fore and aft and vertical shear will be reacted by sockets and pins. The breakdown of the wing will be greatly simplified by this redesign, I would anticipate that installing the wings or breaking them down will take about 10 minutes.

up in the air

If my span was one foot longer, I couldn't build her in my shop. man I miss my old shop in Wichita!! I picked these barrels up at a local Feed store, believe it or not, but they were marked as having concentrated lime juice from Iran!!!  I thought we had an economic embargo in place for 25 years??? The scales are also shown in this view. I needed to elevate the plane so I could walk around it without ruining my back. I needed access to bottom so I could terminate the aileron cables. I designed the wire routing so that they could pass from root rib to root rib without passing through any redirection pulleys. In the root of each wing rib, I added 2 split Piper Style cable guides. The cables are being redirected less than 1/2 of a degree. Very acceptable!!! The ailerons actuate with very little friction.

Aileron Cables

Here is a view looking fwd from the tail . This area is accessible after the seat is removed. the Main wing shear pins are also shown. These ended up being 3/4"  grade 8 pins. They are modified automotive grade 8 bolts. Strength wise, automotive Grade 8 bolts are stronger than typical aircraft bolts. AN aircraft bolts are actually equivalent to Automotive grade 5 bolts, the big difference is the pitch of the thread.  The cables break at 3 AN-115 shackles with 3) 3/16" clevis pins.

cable cutout

This was a little "oops". At the limit of the bottom travel of the aileron, the turnbuckle interfered with the upper aileron fairing. 3 minutes of work with the rotary rasp and a circular sanding wheel, and all was fixed. The aileron cable pulleys are free floating and seek their own angle thru the range of aileron travel. All 4 pulley brackets are identical. The design has two cotter pins that retain the cable when the lines are slack. For inspection purposes, there will be an inspection cover in the lower covering. The Ailerons are Frise type ailerons.

The big issue with a long sailplane wing is adverse yaw. Plain hinged ailerons will generate more drag when deflected downward than upward. This is due to the dynamic pressure being greater on the lower surface than the upper. Since drag is a function of dynamic pressure, the down traveling aileron will normally have more drag that the up traveling aileron. This causes the nose to yaw in the direction opposite of the turn. The pilot must anticipate this and lead with rudder prior to staring the bank. This makes  for a poor flying airplane. Adverse yaw is usually eliminated by the use of differential bell cranks. But this would have required 1 bell crank bearing and two Heim or Rod ends per aileron. That equates to about $200 per airplane. The alternative is a Frise style aileron. I chose the Frise because of three reasons, it was lighter, cheaper and the dipping of the nose causes an increase in drag and an aerodynamic balancing force that reduces control stick forces. The German Gliders that I have been flying, have friction and aerodynamic forces so low, there is very little force required.

Elevator Tip Cap

One of the last jobs I did today was trim and bond the elevator tip cap. Tomorrow, I will add a small foam bulkhead that closes out the Horizontal and the elevator tip caps.


I have three more jobs to finish before i can start covering, i need to install the Primer tubing and install the Throttle. once they are finished, I have only to finish installing the Rudder and Vert. Fin tip cap. I held off until this week, and it turned out to be a good thing, My  Buddy Ed Gardner http://mmwauto.com/ gave me a very cool Christmas gift, one that everyone on this blog will eventually appreciate. Its a 170 degree digital Video recorder. Its so small I can mount it in the Vert. fin Tip cap. I will record my first flight and taxi tests with this.

Canopy Latch, and Windshield.

Well I am finally finished with the canopy. This is one of the last jobs I needed to complete before I start covering her.  On Saturday I was joined by Jay Swindle, Jay is a local Texan and one of my earliest Blog followers. We worked together all Saturday afternoon completing the canopy latch. Since my last blog update, I installed the Engine Primer pump. There is a small fuel port on the reed valve housing that is designed to accept an external primer. This is convenient because of the closed cowling of the engine. I decide to mount the primer on the L/H inboard longeron. To avoid removing any area in the  longeron I decided to mount the Primer on a 3/4" plywood stand off block, that block in turn was bonded to the the longeron with T-88 adhesive.

Fuel primer

The primer bracket was made from .063" 2024-T3 sheet. I bent this part on  a combination sheet metal shear, roller and brake. I bought this tool years ago when the price of steel was low. I paid one dollar a pound for this 350 lb tool.

Multi- Function brake/shear/roller

This is a view of my combination tool. in my plans drawings there is a line on every flat pattern that signifies the center line of the bend. That center line is directly in the middle of the upper radius plate. I usually measure back from one edge and offset that dimension for the width of the "V" groove. A machine square is used to square it to the face of the "V" groove. The flat patterns also account for the stretch that the part will under go when it is formed. I learned this skill by drawing flat patterns by hand on the 747 section 41 fatigue redesign program. I believe I drew over 5000 patterns. After that many, the process kind of sticks with you.

Primer Bracket and Uni Bit

One more word about the Primer bracket, and that is the process of drilling a large diameter hole in thin sheet metal. The best method I have found so far is the Step drill or Uni Bit. At $38 bucks for one bit, its a bit pricy, but well worth the price. As you can see the hole it drilled was very clean.

Canopy Centering clip

I needed 4 of these, canopy centering clips. when the canopy rotates to the closed position, these clips will center the canopy so the latch pin aligns

L/H canopy latch

Here is what I ended up with for the canopy latch. I had a design already drawn, but it was way too complicated and I didn't feel like building it. I wanted something simpler. Jay and I were brainstorming on this and we decided to take a ride to Midway Airport and see how the Germans did it on their sailplanes. What I ended up with is kind of a hybrid between the Schweitzer 1-26 and the Grob 103. There is a fwd and aft detent plate at the front of the latch handle and an adjustable home made eye bolt as the rear latch.

rear canopy latch detail

I took a 1/4" bolt and then made a lug out of 1/8' 4130 steel. I brazed the two together. I purposely made the rear post adjustable vertically to allow for adjustment to the center line of the latch pin. The latch rod by the way is 3/8 hydraulic truck brake line. I cut off a 5/16" bolt and put a 15 degree taper on the end of it. That was then brazed into the latch tube.

Canopy installed

Then it was on to the next big job, final installation of the canopy windshield. I attached the canopy with 200 Avex Countersunk pop rivets. The outside of the canopy was touch countersunk to accept the head of the rivet. The canopy installed very cleanly. There is a protective plastic covering still on the outside of the canopy. I will keep it that way until just before first flight. 

Another view of the canopy

This shows the reason for the yarmulke, the wind shield is flat wrapped with a single curvature. All compound contour is confined to the yarmulke. It also doubles as a sun shield. I'm pretty pleased at the way this came out

Canopy quick release and disconnect plug

I finished fabrication and installation of the canopy quick disconnect hinge. I started modification of the fwd turtle deck to accept a square cut out for the disconnect plug. The socket side of the disconnect cable is designed to snap into a square cutout. I decided to modify the fwd turtle deck rear bulkhead to remove the core and close out the the area of the plug. The close out has a thick build up of fiberglass doublers to make up the required thickness of the disconnect plug.

Quick disconnect hinge showing the 3/8" spring pin

This is a picture of the final installation of the quick disconnect hinge. The pin had to be split and spliced so it could be installed.

Rear view of release pin

This is a view of the release pin. I drilled and then reamed this hole to allow exactly .002" clearance. The pin removes with 7 lbs of force with no lift load. The square cutout in the canopy is the location where the disconnect cable will be located. a strain relief will be added to the cable and attached to the emergency lanyard so that it is removed the cable will automatically be disconnected

core foam removed and edges beveled.

This is the start of the bulkhead reinforcement. The core was split using the Multi- tool and then cleaned out using the same tool. The exposed foan was then bevel sanded and the exposed fiberglass was cleaned up with 100 grit sand paper. I put a piece of tape on the opposite side to cover the old hole.

close out with glass doublers

After the glass thoroughly cures I will lay out the rectangle opening for the cable plug.

Next job is the canopy patch and the emergency release handle.


The next job will be the last before covering, I need to rig thew aileron cables and set the disconnects,