Wednesday, May 4, 2016

#19 Rudder Stop Blocks

I decided the rudder mechanism needs to be adjustable. The way it is now, you have to set exactly the right angle for the rudder in neutral (no drag position) and then wrap the control cable around the hang tube and tape it in place so it's really set during construction with no easy way to adjust it once the glider has been built. Here's my idea of making it adjustable without adding heavy turnbuckles.

Replace the existing front stop (appears to be made out of Delrin plastic or something similar) with a stop that is slotted.

Wood was the only easily obtainable material for me so that's what I used in my first prototype. The cage tubing is 2 inch so I started with a 2 inch Forstner bit for $9 at my local hardware store and drilled a hole through a piece of hardwood block I had laying around. Cutting it down to something close to the original stop piece I then used a router to cut the slots for the machine screws I used. I drilled out two of the mounting holes for the original piece in order to accommodate aluminum nutserts I bought at my local hardware store.
The original stop:

Nut serts mounted in only two of the drilled out original holes

The slotted replacement stop block prior to sanding

The finished replacement stop block mounted using two machine screws.

I chose the hole set that best lined up with the middle of the range of final adjustment I was looking for on the rudder.  I got lucky and ended up with the block set right in the middle of the slots so I can adjust either way.  I'll probably tape some tell tale yarns on the rudder to make the final adustment.

Tuesday, May 3, 2016

#18 Strut Fairings

I've decided the struts need to be faired. After a lot of thinking, I decided on a foam rib approach using a NACA streamline form, finess ratio of 4.500/1.145 or 3.93. I got this by downloading the NACA 20 streamline shape data into OpenOfficeCalc (freeware version of MS Excel) and rescaling it to get something slightly over 1” thick. This gives me a rib profile that has enough of a wall thickness (just a bit over 1/16”) to be able to slip it over the 1.0” strut tube without tearing out. Here are my notes on figuring out what foam to use;
Lowe's – Dow Styrofoam TM, Square Edge Insulation board (blue)
comes in 0.55,0.78, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0 thick boards 2X8 and 4X8 sheets
Home Depot - Owens Corning Formular 150 (pink)

material density
  • Aircraft Spruce blue foam (9.0 oz/16 oz/lb)/(0.5/12x2x4 ft3) = 1.69ft3
  • Square Edge 33.85 oz/16 oz/lb/(2/12x2x4 ft3) = 1.59 lbs/ft3
  • Formular 150 = 1.3 lbs/ft3
Formular vs Square Edge compressive strength is stated at 15 vs 25psi so I'm choosing Square Edge.  I'm guessing the fairing to be approx 60% of a 1x5x44 stick and there are 14 of them (7 per side)
.6x(1x5x44)x1 ft3/1728 in3 = 1.07 ft3 of foam for all the fairings

amounts to 1.69-1.59=0.1 lbs or 1.6 oz difference between the two foams (and the Dow stuff is both cheaper and lighter) I see no advantage in using Aircraft Spruce foam not to mention it is extremely expensive.

      At 1.59lbs x 1.07 ft3 = 1.7 lbs for the fairings minus pi x 1” cut out of the middle which I'm guessing to be 50% of the fairing profile area. This would leave maybe 1.0 pound of material for the fairing plus whatever I end up using to cover it (Monofilm) and the trailing edge strip which I plan to use balsa for the initial proto.
      As it turned out, I used a rib and beam structure which is significantly lighter in weight than what I figured on here.  I never did weigh it out so do not know what the final fairing was.
The aluminum fairings (there were only 6 per side) weighed in at 34.3oz (2.14 lbs without the tape or rivets)
So, I expect roughly half the weight to do foam fairings vs aluminum and also they should be less drag.

Dow Square Edge showed no problems at 225F from the fabric iron. Should tolerate all the model iron-on films out there.
A bit of research on the internet revealed Gorilla Glue to work well in gluing foam. I tried a sample and saw the foam fail and not the glue-foam joint. Now for the fabrication process....

My idea uses ribs, leading edge and trailing edge beams glued together with a polyurethane waterproof glue marketed as Gorilla Glue and is widely available.

I decided to rough-cut a template from plywood for the ribs and then sand it to the exact profile using a vertical disc sander. The first step was to drill a 1.0” hole through the plywood. I used cabinet grade since I will need to make several hundred ribs. I then positioned the paper profile over the 1” hole as close as I could to center and traced out the pattern onto the plywood. Next I rough cut to the outside of the profile using a band saw and then carefully sanded up to the line using a disc sander. I drilled a couple holes on each side of the template and drove some smooth shank nails flush.

I bought a 1/2” router bit with a bearing on the shaft end to ride against the plywood form mounted in a cheap router table I borrowed. I had access to a hot wire set up so didn't need to make my own. I did find that I wanted to replace the nichrome wire which was too thick with a stainless steel fishing leader I ordered from Cabela's. Too small of wire cuts too slow and to large a wire transfers too much heat....trial and error.

Rough cut piece of half inch thick foam mounted onto the template.

Starting the cut

First pass complete.

Trimming off the last bit on the trailing edge

Next with the router

The finished hole

Complete rib removed from the template

I arbitrarily chose a 3 3/8ths inch spacing between ribs and fabricated both a trailing edge and leading edge beam to form a complete structure for the film covering I used. The leading edge beam was 5/8 thick and the trailing edge beam was 1 inch thick. This structure formed a strong enough frame to support the monofilm covering I used and proved to be more durable than I had anticipated for normal set-up and break-down wear and tear.
Here is the completed trailing edge form lying on the hot knife table

In this shot the block of foam is in the form held by shoving a hat pin into it through the hole I drilled in the form. This helped to keep the foam from shifting while doing the cutting.

In this shot, looking down onto the hot knife table at the form, I have just finished the first cut.

The completed beam ready to be put in the finished pile.

The leading edge beams were made using the leading edge profile and a form just like the trailing edge form.
This shot shows the strut with all the ribs in place ready for the beams to be glued in.

I used small rubber bands to hold the ribs against the beams while the glue set up. I learned later that this was not necessary and just added extra time to the fabrication process.  The glue is tacky enough to easily hold the joints together during cure.

I used a flat 2X4 with a long piece of 180 grit self adhesive sandpaper as my sanding bed to even up any topography problems that came up as a result of me not aligning the beams and ribs exactly and also to make the trailing edge a straight line.  I used monofilm applied with a hot iron exactly as in model plane covering.
This shot shows the fairing end covered.
Laying out the main sheet of monofilm to begin the covering process.

Before heat shrinking

After heat shrinking.....magic!

One note on final heat shrinking.....
I consistently had the film "stick" to the strut tubing causing a series of puckers in the middle of each bay.  I tried adding more ribs to decrease the distance between the bays with no noticeable effect.  The only thing I was able to do to reduce this problem frequency and severity was to apply double stick tape onto the strut surface between bays and then dust the tape with talcum powder just prior to applying the film.  Although this didn't completely eliminate the problem, it was significantly better and I felt well worth the extra step.

Once the fairing was completed it became clear that the router template I made to produce all the ribs had just the right size hole on it to thread the ribs onto the strut without breaking them and produced enough friction that the fairing can be rotated but will easily stay in position once I align it. I made an alignment “wrench” to do this.

It took some trial and error to figure out how much clearance I needed on each end of the fairing to clear the cable swages. The main problem is how the plans had you rig it. All of the cables are double swaged (for no clear reason) and the main swage nearest the bracket was pulled so tight (there's a drawing in the plans on this) so as to ride right up onto the bracket plate making it very hard for it to rotate and also putting the second swage a couple inches or more out onto the cable causing interference with the fairings I'm trying to install. I had to provide nearly 4 inches of clear strut on the middle positions both leading and trailing edge to keep those fairings from being ripped up on fold down. Even with the extra clearance I fold both middle negative wires to the other side of the bracket on tear down to avoid contact with the fragile fairing. As it is I fabricated a foam block about 4 inches thick for the root end of the leading and trailing edge at the lower wing panel bracket and glued velcro on the aluminum gusset and the block to hold it in place while folding the panels down. These blocks keep the wings from collapsing completely thus avoiding smashing the inboard fairings against the ribs. I still have some deformation but it's acceptable. This way I can leave the fairings in flying alignment in the collapsed transport mode without having to worry about having them move out of position by the wing ribs.

Next, I made two foam cases for each set of diagonal struts to protect their fairings during transport since it is so easy to tear the monofilm covering which is easy to repair but a nusance I prefer to avoid.

Here are a few photos of the fairings installed in Darrell's glider which I am using to train on.  Notice the two rear root struts are not faired.  As mentioned above this is necessary in order to enter the cage and handle the glider while on the ground.


I found right away that leaving both the root diagonals and rear root struts unfaired was best in the learning phase.  After one is accomplished in handling the glider in a variety of launch conditions, then adding fairing to the diagonal should not present a real problem.  Since you cannot grip the fairings (way to fragile) I can't really handle the glider without having access to the rear root struts to get into the center cage area and then lift the glider to attach the harness lifter shoulder straps I made.  I therefore left these rear root struts unfaired.   The fairings are amazingly durable.  I've crashed them, flown with the root diagonals faired and gone through enough set-ups and take-downs to convince me they will hold up fine under normal flying.  I do feel the diagonal storage cases were worth the effort to make since they are so exposed to damage when not in the airframe.  I had to provide extra clearance on several of the strut ends to avoid damage during fold down and also at each quick disconnect position where you need extra space for your hand to get the negative wires attached.

Saturday, July 25, 2015

#17 Rigging and Final Assembly

This post will be the last one for this project.  It was intended to cover the repair of an Easy Riser damaged in a training flight. Subsequent modifications to the Easy Riser is being covered in a seperate blog titled "Re-Thinking The Easy Riser" and can be found at

Ready for rigging now I've moved the right wing panels onto the frame I had bolted to the floor when I completed the pre-rigging from sheet #3.

As I put the struts in place, I recalled the problems I had noticed when learning to fly. I took great pains to patch all the tears and holes in the glider I inherited only to have the leading edge root strut bracket rivnut punch a hole right through the nice patch I had put over the previous hole. Here is a photo of that bracket “after” I drilled out the rivets, flipped it and re-installed the pop rivets.

It turns out that there is plenty of clearance now on both sides of this bracket and I get no contact with either the fabric or the gusset with the bracket in this orientation. The strut fit is not changed. If you don't do this, expect to see a nasty hole punched through the fabric by the rivnut end as shown below on Darrel's upper wing panel trailing edge which I had just patched prior to realizing what was causing it.

I found it far easier to do the tail swage first, fit the cable loop over the bracket bushing, snug up the main swage and then compress it. The plan sheet says to do the main swage first which I tried at first and right away switched to doing the tail first. Another thing I'd do different would be to thread on shrink tubing PRIOR to all swaging. When I got to the end and saw where the cable ends contact the fabric I found it necessary to tape over all the swaged cable ends. In the folded storage/transit position there was a fair amount of abrasion happening not to mention getting holes poked in my finger tips from the cable wire sticking out of the secondary swage during set-up & tear down.

In this shot I am setting the final tension on this flying wire using two vise grips held with my left hand while tightening the wire clamp with my right hand. Otherwise I'd have needed to find someone to help. This worked fine.

I made multiple trials to get the tension on all the cables just right and it took a fair amount of time to do a decent job of getting them all “just right”. My swage tool (I finally had to buy one) was a short handled Nicopress model 32 VC-VG which does both 3/32 and 1/16 swages. It required quite a bit of muscle for the 3/32 swages so I ended up cutting a pair of extension “handles” from 1 ½ inch PVC pipe. The other critical tool I was lucky enough to borrow from one of the EAA members was a Felco cable shears. This made all the cable cuts a piece of cake producing nice, clean ends.

No photos of my trials locating the control cable inside the tip of the lower wing panel. Located a hole based on how Darrel's cable was deforming the fabric and hot knifed it free-hand. Turned out fairly crappy. Should have taped a nice circle template and cut to that instead. Since this was a re-build, the bushing was already swaged onto the cable end so I had to make the hole big enough to fit the entire thing through the fabric. Rather than do an actual fabric patch (would require me to do a spot re-paint) I just used adhesive-backed sailboat Dacron patch tape which worked OK.
Next I rigged the rudder return spring exactly like I re-configured Darrel's where I removed the bungee approach specified in the UFM plans (a poor solution I felt) and installed a nutsert (that's what the guy at True Value Hardware called it).
The nutsert can be seen above laying on the wing to the right of the hole it will be installed into.

This shows the nutsert fully installed.  It is nearly flush with the tip tube surface.

I picked out a spring from the hardware store spring selection and attached it to the wing tip using two nylon washers and a small bolt.  I also picked out a steel pin, drilled it to accept a safety pin and used this as a quick connect to attach the rudder control cable during assembly.  I replaced these soon afterward with a stainless steel spring (sourced on-line through Grainger) and aluminum binding post pin (commonly available at hardware stores).

The next step was to rig the control cable which involved wrapping it around the twist grips per the plan so that the rudders come back to neutral when released.

I really liked the grip material Darrel had on his glider which was cloth handle bar tape for bicycles. I had a hard time getting anything close to long enough. The best I did was less than 10 ft so that's what I used. The underwrap was just electrical friction tape followed by the cable winding then covered by the bike tape and terminated with vinyl electrical tape on both ends.

Now I am nearly done. I got worried about the paint sticking to itself in the folded storage and transit position so I decided to wax every surface except the bottom of the lower panels using the Poly Fiber recommendation of a non-silicon based Carnuba wax which took me a good part of a day to do but I'm glad I did as you will hear about in a minute. So here's the completed glider ready to pack up and take it's second flight (recall the first one ended in disaster over 30 years ago...hence this project).

Here I am at the local test flight area the next day on the Oregon coast (Cape Kiwanda) in perfect conditions....low tide, dune to myself with a 9mph breeze right up the hill.

Although you cannot tell from this photo, the glider is sitting on a tarp I staked down in the sand so that the glider never touched the sand.  I just could not bring myself to allow that after putting all this effort into the build.
I weighed the finished glider just to have an idea how much over weight I was and it came out at 66 lbs which is about 16 lbs over. I can feel the difference just carrying the individual wing assemblies and knew I was going to have my hands full getting this thing up the dune. I was right, I made it up to about 2/3 of the way to the very top and just decided I'd be so wasted if I went any further that I'd be too exhausted to safely launch it. I was determined to not even allow it to touch the sand that when I got as far as I was going I basically took off in what felt like 10-11mph breeze. Launched fine, flew fine, rudder response was fine and the landing was easy. I could not even visualize making another climb up the dune so I packed it up and went home with a smile on my face. This makes 19 launches in an Easy Riser for me to date. I have not yet learned to reliably get my feet up onto the leading edge to assume the proper flying pilot position.  This is a critical skill in order to be in the air for any length of time and certainly at any significant altitude.  If you are interested in my experience learning to fly, please visit my other blog dedicated to the learning aspect of the Easy Riser at

I hope this helps anyone out there in building an Easy Riser as that was my original intent.  Refinement of the rigging, designing a parachute pack mount, re-design of the internal rib layout are some of the things to be covered in a follow-on blog which you can find here:

Wednesday, May 13, 2015

#16 Rudder Covering + More Masking & Painting

Since no one offered use of their paint booth last October, I was forced to wait until spring. So, here we are, April 2015 and already plenty of days warm enough to paint, however.....I ran into trouble last fall. I shot the rudders with Polybrush right over the old dope finish and then Insignia white color base coat and proceeded to mask the accent stripes. After making a masking error requiring tape removal, I found the base coat peeled off with the tape right down to the old dope finish. No point in going further. Ripped off all the covering on both rudders and set about prep'ing the frames for recovering. This pretty much shot the idea of completing the painting last fall. I found that the left rudder had actually sustained some damage once I had the covering removed so I fixed that and beefed up the aluminum ribs which are definitely the weak link in the frame structure. Here's a shot of the rudder frame leading edge rib before.
I cut out a piece of ½ inch foam from the damaged wing rib to fit inside the aluminum rudder rib. I glued it in place using Gorilla glue which is supposed to work well on this type of foam. The stiffening effect on the rib was amazing. If I build another ER, I'd use this on all the aluminum ribs in the rudders which would also allow one to rib stitch rather than rely on the dicey fabric to aluminum bond using fabric cement (without the foam insert, the rib would just collapse as you tightened the stitch knot).

I recalled covering these rudders back when I first built this kit that they were very difficult to do without many wrinkles so both these rudders were ugly anyway. I decided to try a different method this time around and built a quick frame out of 1X2 fir and attached a piece of fabric to it using an office stapler.
I cleaned up the aluminum frame, coated it with Polytak fabric cement and then place the wooden frame over the rudder structure.
A small slit for the rivnut to poke through allowed the fabric to lay down nicely onto the rudder structure. I then ran a very thin line of 50/50 cement/MEK around the entire perimeter of the rudder, rubbed it in and let it dry (std process).
I then simply cut around the perimeter leaving enough fabric to do the wrap onto the aluminum structure and got an almost wrinkle-free main area. The hard part was doing the snips and cuts to get the fabric fitted around the ends, brackets and horn. Repeated the frame process for the other side and ended up with no wrinkles after doing the final shrinking at about 300 F. Wetted out the glue on the ribs to attach fabric then applied Poly-Brush (coat #1 brushed on, coat #2 & #3 sprayed on). Same pin hole bubble issue. Just have to re-brush back over what you've just applied as you go to knock down the bubbles before the P-Brush tacks up. What you don't get will be ironed out at 225F prior to spraying.
Here are the rudders after completing all the gluing, smoothing with the iron and general detailing finishing with the first brush-on coat of Poly-Brush.

Here they are after the final sprayed on coat of Poly-Brush......

OK, on to painting. I've poly-brushed the rudders and shot the base coat of white. Two coats was sufficient. One thing I've found in getting an even coat aside from being very smooth and even on your gun passes (you need to always be aware of how far the nozzle is from the surface, what angle the spray fan is relative to your gun pass direction and how fast you move the gun along the surface). It's a tough job and was hard for me to do. I would finish a panel and then go back and look for uneveness. I would then spot spray the light areas until the whole thing looked relatively even. I tried to put on just enough color on the first coat so that the second coat was the final one. In the photo below, notice the different color masking paper on the leading edge at mid span. That stuff is the paper you use when you paint a room in your house which I suspected when I experienced bleed through. I'm not sure if it's the paper because I went to an auto paint supply shop and got their masking paper and had a little better luck but still saw it bleed through a little. I think the take away here is to DOUBLE LAYER THE MASKING PAPER OR USE A WIDE BORDER OF TAPE next to the paint line. Also helps if your technique is good enough to allow very little paint overlap onto the masking paper.  As you can see in this photo, I don't do a very good job of keeping paint off the masking paper.  I was fixing a screw up here where I forgot to take the accent stripes all the way to the root on the lower panels.  I am leaving a gap at the root on the upper panels where I will strip the paint back and glue on a fabric closure with a zipper after I'm finished.  Darrel did this on his and it works really slick.

In this next photo, I've removed a piece from the other wing panel where I had used it right in the area I was painting. You can see what happened.....bleed through! So go find your local supplier for automotive painting and get your paper from them but I'd still test it first before you commit to use it to mask an entire took me a couple hours to finish one panel and that was after I got the hang of it.

I used Reducer on a Q-tip in an attempt to mellow it out a bit with limited success. I went over the area with red but could not make it go away.

Here are some shots of the masking involved in creating a simple design scheme similar to the lines on the glider Brian Porter flew in the 1976 National meet.

The blue tape in that shot is vinyl tape used in automotive trim masking. You can form it somewhat around curves. I could not do a real tight curve successfully and ended up cutting the curves for the rudders which were much smaller radii compared to the wing panel curves.

Back in the converted RV shed with the drop-down lights for painting.

Masking the rudders.

The finished rudders ready for painting.

This next photo shows my attempt at getting an even first coat of red on the rudders. I always shoot the edges first since this is where the risk of generating drips is greatest. Making a couple light passes worked best followed with filling in the rest of the surface.

Here is a shot of the final accent stripe of gold as I am removing the masking tape around the curve. Gives you an idea of the cutting and fitting I had to do in order to obtain a nice tight curve around the bend.

One thing I did which really helped get the last little bit of paint out of my cans was to use a metal shears and cut through the lip gutter then pour out the last bit of paint and rinse with a little Reducer.

I got a couple small areas where the color pulled off the Poly-Brush surface with the masking tape. Likely some contaminate I neglected to get off prior to painting. I'll need to touch it up with a fine tip

brush later.
Here are more shots of the rudder masking for both the red and gold accent stripes. Lots of time masking and re-masking to do even simple paint schemes like I'm attempting here.

As a side note, it was 58F and raining when I shot these.  I saw no problem with the paint nor did I note any difference in spraying under these cool conditions.