#11 Patching My Trainer Easy + Finish Work on Trailer

Repaired holes in Darrel Robbin's Easy using Clear Aerothane which was recommended by the tech at Polyfiber. Aerothane is a two part polyurethane recommended as a sealing coat on light weight sails and is supposed to stick well to nitrate dope surfaces (I wiped the areas with MEK to clean them prior to patching). I needed very little Aerothane to do these patches so mixed up small amounts using a teaspoon measuring set and stirring up the two-part mix in a small cup.

The Aerothane is being used as a glue and sealant in this process. I found the best way to do the patches was to apply the Aerothane around the perimeter of the patch area and let it set for about 20 minutes while I cut the patch out of scrap cloth. It was warm and dry when I did this and after 20 minutes the Aerothane was tacky. I carefully applied the patch trying to keep wrinkles and air pockets out of the patch job. Once I had pressed it into place, I went over it with wet Aerothane to finish sealing the patched area.

On the rudder corner, I could not get the fabric to stay down after wrapping it 90 degrees and ended up using masking tape to hold it in place while the Aerothane dried. This worked well and the tape came off without a problem.

It was interesting to note that on this glider, the lower bracket for the inboard diagonal strut cut a hole in the fabric when the wing folded down. I had to patch these areas on both upper wings and it was evident that Darrel had patched them previously. I noticed the bracket on one was misaligned on the wing strut such that the bracket was rotated out of plane toward the upper panel where the tear occurred. I bent it back into plane which should make it easier to install the diagonal strut during setup as well as eliminate any contact of the bracket with the wing surface. The only other thing I could do would be to pad this area such that the wings cannot fold completely together (maybe only a half inch would easily prevent any contact).

I fabricated an elastic cord loop to replace the small bungee cord that came with the kit to provide counter force on the rudder horn. Darrel had done this on one wing but it was missing on the one I fixed.

I realized that I need to get the trailer finished now since Darrel's glider is ready to fly but I can't transport it without the trailer. Started coating the trailer bed boards with epoxy resin in prep for bolting them to the frame.

Here is a shot of the main bracket I had to make to hold down the box to the trailer tongue.

The main beam I laminated two cedar 2X6's together, screwed them and coated them with epoxy. Here they are with the brackets in place to attach to the box.

The final shot of the trailer bed ready for the box to be lowered onto it.  You can see the brackets on the back side of the main front beam that I will lag bolt to the box.

Lowered the box onto the trailer bed and secured with the custom brackets I had fabricated. This photo shows one of the brackets under the box that attach it to the main beam at the tongue.

OK, ready for a trial run on the road to see if the shock brackets and axle hardware will  hold up to the stress. I've loaded it with Darrel's glider and the spring deflection looks like I'm in the ballpark at least.

Passed the test after a 20 mile cruise. Hit some fairly good bumps to make sure the shock system was functioning. I believe I could have set a bowl of soup on the box and not spilled any.....really amazing how smooth it rode over the bumps I hit. Even a railroad crossing at 50 mph was no problem! Nothing came loose, nothing broke....I'm in business!

Next up, I need to finish the rear access door, the one I'll be opening to get the glider in and out. I picked up 3 stainless piano hinges to mount on the bottom.

You can also see the cables that holds the door in a horizontal position when open so that I can easily pull the panels out of the box onto the open door in prep for positioning them to carry over to a setup area. I also found some nice adjustable cam buckle hardware that will make it quick and easy to open and close and get a good (hopefully dustproof) seal. These shots show the door in its closed position.

Now all this hardware needs to come off again in prep for painting the entire box plus both front and rear access doors. I should probably put this off until I can get the wings finished. I'll need to talk to the tech advisor about fall weather affecting the covering process for the wing panels. I could probably get away with more weather variations painting the box than covering the wings so it would make sense to start on them first.

#10 Trailer Modifications + Acquired Trainer Easy Riser

My apologies for those following this blog.  I really did not intend to take such a long break from the project but summer got in the way and after my fiasco with the covering process I was having a hard time getting back into it.  A significant part of this project involves finishing the completely enclosed trailer shown in the very first post. I completely removed the shelf system and relocated them to a position about 4" lower that made use of all the wasted headroom over the lower wing set left by the rib camber I had not taken into consideration originally. There was also a considerable amount of epoxy/ fiberglass repair that needed to be done and a reconstruction/re-design of the end panels to accomplish a weather-resistant seal on both ends.  I also removed one of two leafs in the suspension system (the photo is after I removed the small leaf) and added shocks on both sides to smooth out the ride.The shock/springs came off a Harley Sportster mod job....still need to see if they are too stiff.

Currently I'm working on the bed that I will need to attach the box to and then I'll try out the suspension system with a full load.

Mid July I had an opportunity to inspect the covering of an Icarus II that was done by someone I knew to be a “craftsman”. I figured this would give me an idea what was possible in doing a good job of covering this type of airframe. Here are a couple of shots showing the leading edge area and the rib sag.

My conclusion after looking at this was that it is possible to get a very nice, wrinkle-free covering with very little inter-rib sag. Keep in mind that nitrate dope keeps on shrinking years after it is applied so the rib sag you see in this picture must have been near zero when the glider was covered.

In July, I flew Fort Funston and happened to meet a former Easy pilot who ended up giving me his Easy along with the car top box he built to transport it. He flew it one last time in what I guessed to be winds at the Fort over 20. He is taller than I am, maybe 6' and probably has about 25-30 pounds over me and he had all he could do to maintain control on the ground with the glider. I learned a lot by watching him fly it. He used no rudder control on the ground (said it really wasn't effective). He told me that pitch control is really all you have plus body torque to get and keep the wings level while ground handling. Once in the air flow he had a lot of pressure on each hand placed forward on the twist grips to keep the nose down. He could pull down a high wing by pushing down harder on the high side but I never saw him do anything with the rudders. I had to come in twice at his request before he launched to pull down a wing that he could not pull down on his own. Once in the air it looked really sweet.....easy, comfortable flying position and an effortless landing. He did tell me to start flying it before I put too much more time into my project to make sure I am happy with it's performance. He said the sink rate wasn't all that good. I expect I will do significantly better than he did since I am quite a bit smaller that he is. He had it rigged with a compressed air chute deployment system that a friend of his was making at the time and he used it on that last flight. I will need to rig my own system once I start flying it at high altitude sites. Here's a shot of me on the way home from the Fort with Darrel Robbins' Easy in it's car top case and my Comet on top.

Here are a couple video links to Darrel's final flight in it the day I returned to Oregon.

http://www.youtube.com/watch?v=YPUnctxRzMk

http://www.youtube.com/watch?v=Oa3H-MeA738

Keep in mind that the wind at launch was gusting over 20.

The glider itself has some tears in the sail that I will repair before taking it out. Here it is shown in it's new home (the box I built with the reconfigured shelf mod I did in June).

Had over an hour talk with Brian Porter last night on the phone where we discussed various topics including things to pay attention to in building the glider and also tips on what he found worked for him in flying it. Brian was one of the experts at flying rigid wing hang gliders back in the day. He won the Escape Country meet with the Easy Riser in 1976. He mentioned increasing the washout to a 2 5/8 inch block on the fabrication frame vs 2 ½ specified in the plans. This was thought to improve the sink rate. I asked him about covering and his comments indicated that he was able to pull a lot of spanwise tension in the cloth without dog legging the frame. No tips on how he was able to do this. It could be the fact that I tweaked the frame when I crashed is setting mine up to dog leg with even moderated spanwise tension. I am beginning to believe this is the case. If true, then my only solution is to go light on both spanwise tension and chordwise tension living with a few wrinkles or bend the frame back to straight again. He said the glider is prone to pitch sensitivity and will pop up and down in thermals.You get used to it after a while. If properly built, the glider should trim out so that once in the cage, feet on the leading edge, you should not be able to stall the wing even with your back up against the rear of the cage but this should put you at minimum sink right above a stall. You have to let your feet down to get it to stall. You can see him drop just one leg and then bring it up again as he adjusts his approach for the spot landing in the video link I'm including below. He also fabricated handles that he mounted 90 degrees off the twist grips to aid in rudder deployment. He said you'd be surprised at how tiring it is to work the twist grips for an hour. The front negative wires were replaced with 3/32 cable since they will see a large load if the wing goes negative. The plans called for 1/16. He recounted inspecting a wreckage where these cables broke when a fabric detachment occurred and caused an involuntary tuck. Deploying both rudders will pitch the nose up since they are above the center of mass in the loaded air frame. This video link to YouTube shows footage of Brian doing an approach where you can see how he moves his legs and how the glider responds as he flies into ground effect and flares.

https://www.youtube.com/watch?v=eHlsQOOt73Y

The current state of the project is both upper wing panels are ready to cover. I have the pre-shrunk material and am winding down my summertime activities. I hope to begin covering again in September. My first priority is to finish the trailer so I can move the wings when I finish them.  Without the trailer being ready, I have no way to move the wing panels to and from the shop which is about 8 miles from my house (I have no wing frame at this shop).  I am also anxious to repair the fabric on Darrel's glider so I can begin to take it to the beach and learn how to fly it before winter sets in.....decisions, decisions.

#9 Covering & Sealing With The New Material

Got the new material (now thought to be the right stuff which turns out to be a bad assumption) and re-started the covering process. The leading edge glue line I had penciled in on the first attempt was still visible so we used that to glue this bottom piece to. The bottom “blanket” of fabric was then rough cut to span length adding 6 inches of extra cloth off the tip and the root struts. The factory edge was very smooth so we just glued it on beginning at the middle and moving out toward the tip and then out to the root end. We wet glued this leading edge line meaning we applied wet glue and then immediately set the fabric in it. You can also pre-glue full strength and then come back and use 50/50 MEK/glue and set the fabric that way which I believe is what the plans spelled out. It's a real guess as to how much spanwise tension to apply. Even the moderate amount we applied created a spanwise sweep about 3 inches beginning at that internal strut. There just isn't anything in the frame to keep that from happening. After gluing the leading edge of the bottom blanket, we applied glue to the bottom rib cap strips and then came back and mashed the cloth into the half dried glue with 50/50 glue/MEK mix. Massaging this in gave fairly thorough and consistent cloth penetration with no pull up or separation. The tip and root ribs were wet glued since it was much easier to handle the cloth over wet glue at the ends of the panel. There was some detailed trimming to do at the root strut where the cloth has to be terminated. This was done with the soldering gun blade tip and basically followed the outer edge of the root gusset plate where the chafing tape stopped. Here's a shot of the finished panel prior to detailing with the iron. Most of the large area shrinking has already been done and you can see the inter-rib sag that occurred as a result.

The sag measured nearly an inch in the worst bays. I released the leading edge seam on the worst bays and relaxed it back to where there was only about ½ inch overlap left and gained back a lot of the airfoil.

 At this point I am getting the feeling that there is just too much frame distortion to expect the panels to fit together well enough to set up or fold down not to mention the inter-rib sag which looks severe to me but I continue with the sealing step anyway.  You can easily see the dog leg sweep on the leading edge caused by the fabric tension.  It starts right where you'd expect it to....at the internal diagonal rib and out to the tip.  I took the time to do some detail work most would skip such as these patches over the gusset holes. Even though I did a fair job of cutting the gusset slits, these patches really clean up each gusset position.  I drew the pattern out using a drafting compass and cut it out using a pinking shears.

Starting the sealant coat (Poly Brush in this case).

The gusset patch after sealing. It really did look better with the patch than without.

A shot of the bottom of the panel with the first coat of sealant complete.

Top of the same panel at the same state. I could have used clear Poly Brush but felt being able to see where I had been was more important which is why it is rust colored (their standard sealant color). I planned to paint the wing so this would all be under a couple coats of paint when I'm finished.

After all this, I finally verify that the original plans and kit for this glider involved applying pre-shrunk polyester dress lining material using standard aircraft fabric cement (Super Seam) and nitrate dope referred to now days as the Ceconite process (except for the fabric of course). All my effort and hours of detailing the spars using the small iron was just practice. I stripped the airframe and place an order for pre-shrunk polyester for the material used up during the first attempt at covering. I won't get back to working on recovering until September most likely. The next post will cover some of the things I'm working on this summer that are directly related to the project including reconfiguring the trailer, inspecting an old Icarus cover job and inheriting a completely finished and flyable Easy Riser during my annual trip to fly at Fort Funston near San Francisco.

#8 Covering & Sealing Using PolyFiber Fabric - oops!

The covering supplies arrived. Here is a shot of nearly $1000 worth of chemicals including the glue, the sealer, the UV paint and the top coat paint plus the thinner for these products.

I hope to have some left over that I can sell to the EAA chapter here. They go through this stuff like water. Decided to have the Tech Counselor help me do the upper left wing panel and then I'd take it from there. Started by putting anti chafing tape on all the potential rub points on the frame that would have fabric contact. I had taken a stab at what I thought would be adequate for taping over sharp areas. Not good enough per my Tech Counselor Ernie. He showed me how this needed to be done. No real tricks here, just had to think about how to best cover the topography with as little tape as possible. Here's a shot of the wing panel after I finished re-taping the root rib gussets. The rest of the panel shows what I thought would be adequate. I had to remove all of what I had done and re-do it right.

Here are some examples of what the anti chafing taping should look like if you are doing a good job of it.

The next step was to apply the leading edge filament tape. I used the directions specified in the original plans that call for three span

wise lengths spaced 3 inch center-to-center from the leading edge of 1.5” filament tape. The purpose is to help minimize the fabric droop between ribs when the fabric is tightened up during the ironing process and the coating process.  After the filament tape is applied it is really easy to bump it with a hand or something on the table or saw horse it's setting on and fold the tape onto itself. After you do this it is really hard to separate the tape. This happened multiple times to me during the process and each time I had to use MEK solvent on a paper towel to redissolve the tape glue so that I could pull it apart again. I could not completely fix an area once this happened but decided it wasn't bad enough to redo it. This shot shows it prior to several accidental collapses that had to be separated.

Next, my Tech Counselor highly recommended I cross brace the ribs midway between the trailing edge and the last row of filament tape. He supplied me with the approved material which was 1/2” wide cloth tape designed specifically for this. I don't think this was necessary since the filament tape and gluing the fabric to the ribs really doesn't allow for any movement of the ribs after the covering is complete anyway but I went ahead as instructed and did it. This shot shows me finishing up the cross bracing tape.

We got to a dead end here as soon as we had tacked down the fabric on the bottom of this wing panel. We were noticing a reluctance of this material to shrink. It became obvious the more we tried to shrink it that it was pre-shrunk polyester cloth....something you might get at a fabric store. When polyester cloth is pre-shrunk, there is about 10% of shrink left in the cloth and it takes a hot iron to get that last 10% (something around 350 F). This won't work for covering material on a "conventional"airframe because you want all of that shrink margin to get a decent, tight and smooth covered surface.  However, this is not a "conventional" airframe, far from it.  The Easy Riser airframe is extremely fragile and weak relative to the techniques and materials used on stiffer, more constrained airframes.  My tech counselor has had no experience with this type of frame so I'm back to re-reading the instructions sheets.  Once I re-read them it was apparent that pre-shrunk material was, in fact, what UFM used to cover the Easy with.  I had saved some scraps of material that I had from the initial covering I did years ago and put them to the iron set at about 300F.  There was almost no more shrinking going on at that temp.  The plans mention a very crude reference to shrinking once the cloth is in place.  It says to set the iron on "wool" and go for it.  You will know if it's too hot because it will melt the material.  So.......the Poly Fiber manual talks about 350F being the highest temp you ever want to take polyester cloth.  Beyond this, the fibers actually begin to relax and then finally melt outright.  My conclusion here is that the original kit cloth was, in fact, pre-shrunk polyester fabric which weighs in at about 1.5 oz/sq yd, significantly lighter than the lightest material you can buy from aircraft supply shops.  The method UFM describes in their plans basically talks about hand stretching the cloth as best you can and gluing it down while holding tension.  Had I read the plan instructions more closely and tested the scraps I had kept from the original material, I could have saved myself a lot of labor and expense.  Although, because my tech counselor assumed he was dealing with a standard covering process, he applied the fabric loosely when we glued the pre-shrunk material so it could not have been salvaged as the bracket holes were consequently in the wrong place.  The photos that follow show the various steps I will now be doing over again with pre-shrunk material.

This shot shows the cuts made for one of the strut gussets using a Weller soldering gun with the blade tip. This was slick and was right on the mark since we made a template pattern before making the cuts.

Here's what happens when you don't make a template and get in a hurry.

A shot showing the rough tension prior to the heat shrinking. This one is the root bay....notice how loose it is. With standard unshrunk polyester, this will shrink up tighter than a drum if you take it all the way up to 350 degrees F.

Here is the Tech Counselor starting to heat shrink the fabric. Notice how loose he strung it. His assumption was that it was standard, unshrunk polyester fabric and very soon after this concluded it was pre-shrunk fabric that I would have to strip and toss.

The next report will take me back to the beginning of the covering process where I will use standard uncertified light fabric material which I ordered from Spencer Aircraft Supply in Washington.....another ~$400 receipt.  I will then discover the airframe is way too weak to support the standard shrinking process and soon be right back to pre-shrunk polyester (basically dress lining material).

 

A separate issue that did not occur to me until after I had re-covered the airframe with the correct (pre-shrunk) cloth was the unecessary step of all the taping (anti-chafing) I meticulously did over all the gussets.  This is standard motorized aircraft construction technique but totally overkill for a foot-launched glider.  Subsequent repairs where I had to recover wing panels were all done with NO taping.  The weight savings here was not insignificant so it was well worth eliminating the taping. 

#7 Pre-Rig

When I found that neither set of wings would rig up with the original cabling and not have the rudders binding significantly, I realized I would have to re-rig the entire glider.....meaning I needed to cut ALL the rigging cables and remove them. I ended up doing this using a cutoff wheel on my ¼ inch angle grinder. I had to really be careful not to nick the brackets or tubing but it worked OK. I cut off one end of each negative wire cable leaving a cable bushing on the other end. I used two of these pieces, each with a cable bushing on the end and a cut cable end on the other and clamped them together using the electrical clamp nuts called for in the rigging part of the instructions. I end up with an adjustable cable with bushings on both ends that I used to hold the wing from folding down while I checked the upper and lower spars for parallel alignment.

The photo below shows the right wing set up on the fixture and if you look close you can make out the plumb bob off the leading edge wing joiner on the left hand side of the photo where I am checking for parallel alignment of upper and lower leading edge spars and also the 14” stagger.

You may also have noticed the tape on the floor which I used to mark all the reference points called out for on the pre-rigging sheet in the plans. Here is a shot of what I mentioned can happen in the last post if you don't watch which bolt you're using where (permanently compressed strut).

I have done a bit of sourcing research trying to find the part shown in this photo that is used throughout the Easy Riser rigging brackets. It is called a rivet nut and various other names depending on the manufacturer. The longest barrel length I could find anywhere to date is approximately 0.5 inches. Somewhere, Larry Mauro apparently sourced one with a barrel length of nearly 3/4” which doesn't seem to exist anywhere I've tried looking. He may have had it through a special order. The ½ inch ones which are readily available, are used on this glider frame in the brackets with only a single cable attached as shown here.

One of my goals in this project is to find sources for all the parts needed to make an Easy Riser from the ground up so I would like to find the longer rivet nut even if I have to find a manufacturer willing to make a custom run of them. Below is a shot showing the longer rivet nut with the half cable bushing which is what requires the barrel length to be nearly 3/4” long since a second cable bushing will need to slip onto the end of it for the quick disconnect negative wire attach point during set up.

That completes the pre-rigging. Next, I need to wrap all seven ribs on the upper left wing panel using the knot shown in the original addendum the plans included for rib stitching (which I also plan to do after attaching the fabric). Wrapping the entire length of the rib keeps the cap strip from pulling off the foam core.  This is probably most important in rough landings where the wing spars might collide with a stationary object whereas rib stitching functions to keep the fabric attached to the ribs.  The other three panels I had already finished rib wrapping from the original build. This shot shows the left upper wing panel propped up on saw horses ready for rib wrapping.

Somewhere I thought I remembered the instructions including wrapping the ribs but could find no reference to it anywhere in the large plan drawings or the rib stitching addendum. I used the same knot shown in the addendum to wrap the ribs. Here is a shot of the last knot being tied on the final rib.  I later decide this is totally redundant since the entire glider will have to be rib stitched after covering and sealing anyway which will accomplish the same thing.

Ordered the fabric glue to do a test on the frame with the old glue intact to see if it would be compatible with the new glue. The tests were good which means it will not be necessary to completely strip all the spars of the old glue. The old glue was Super Seam that came with the original kit. This was really good news since stripping all that glue would have been a real job.

The local EAA chapter has a Tech Counselor that has volunteered to help me attach the fabric to the first wing and shrink it. This requires me to get the trailer ready to haul wing panels so I have been spending most of the time working on that, hence, not much progress on the wings. My next post will include the material order list for the covering supplies I will need through the top coat paint.