Tuesday, March 5, 2019

INTRODUCTION

The entire content of this blog is dedicated entirely to the Easy Riser as a foot launched glider and not as the ultralight powered configuration.

I have been thinking about how to make the Easy Riser more easily repairable after suffering from 3 significant crashes now that required re-building at least one of the wing panels after each incident. The last crash not only bent a wing spar but also severely bent several of the strut brackets as the upper wing kept on moving forward after the lower wing hit the ground. In this blog I hope to cover ideas I have implemented in completing my own repairs on the 3 Easy Riser gliders I currently own. This will include not only what I did but also information on sourcing of parts, processes and materials.  I will divide the posts into specific parts of the project to make it easier to find what you might want to look at versus a chronology of the build process.

Gap Cover

 Cardboard pattern created by trial and error fitting.  Rotary fabric cutter made the job of cutting out the pieces easy.
 Pre-creasing seams prior to sewing made holding a straight line much easier.
 Marking the hem line prior to setting the crease using an iron.
 The finished pre-creased panels ready for Velcro and zipper

Sewing on the fuzzy side of the Velcro to the outboard edge of the gap panel.  Notice the zipper already sewn to the center edge of this panel.

The advantage to this approach makes it possible to easily disassemble the glider and also adjust the fabric tension to get a really nice smooth gap cover.

I will add a photo of the installed cover soon.

Saturday, November 3, 2018

Possible Design Changes




A front-page cover photo of Eric Wallner flying a motorized Easy Riser at Oshkosh came out in Sport Aviation magazine in 2018.  Subsequent discussions with Eric inspired me to summarize some of the design changes he made to his 1970's kit when he built it that could be considered as beneficial to the foot launched glider.  Several of the changes he made were specific to the motorized version which I will not include in this summary. I will also not mention detailing changes that I’ve already covered in my other sections in this blog and are not actual "design changes".

1. All struts shortened by 3 inches which also required the rudder planform to be changed. I do not have the pattern for his rudder but from the photos it appears to have the same, general shape.  This change will also affect the stagger measurement you make and will not be the 14 inch dimension given on the Pre-Rig plan sheet #3.

2. The wing dihedral was reduced from 6 inch offset to 4 inch offset (a 30% decrease).

3.  An anti-sweepback or drag cable was mounted internally from what I understood to be the internal leading edge strut gussets out to the trailing edge rudder bracket. I don’t know what hardware Eric used to mount this cable. I assume it was 1/16 cable.

4.  Shortened the top panel by 6 inches to allow the upper and lower tips to fold down even. This reduces the sail area and hence will affect your wing loading.

Sunday, April 15, 2018

Rigging

last update  4/1518


Brackets

Leading edge side

All non-quick disconnect cable ends use cable bushings and retainer washers vs the original rivnut/custom spacer/retainer washer assembly.
Both root quick disconnect positions use original rivnut stud brackets.
Both mid position quick disconnect positions use re-built rivnut kit brackets where the original long barrel rivnut is drilled out and replaced with a short barrel stainless rivnut. The salvaged retainer washer is used on the flying wire on the outside position.
  1. upper root - original bracket
  2. lower root - new bracket*, no rivnut, drilled for 3/16 AN bolt.  Flying wire in the outside position.
  3. upper mid - new bracket* with straight rivnut stud.  Flying wire uses cable bushing and retainer washer in outside position on bolt.
  4. lower mid - new bracket* drilled to 3/16 AN bolt.  Flying wire uses cable bushing and retainer washer in outside position on bolt. Negative wire uses cable bushing and retainer washer on inside position terminated with nyloc nut.
  5. Upper outer – new bracket* drilled to 3/16 AN bolt.  Flying wire uses cable bushing and retainer washer in outside position on bolt.
  6. Lower outer – new bracket* drilled to 3/16 AN bolt.  Flying wire uses cable bushing and retainer washer in outside position on bolt. Negative wire uses cable bushing and retainer washer on inside position terminated with nyloc nut.
  7. Upper tip – original bolt mount through leading edge spar.
  8. Wear prevention washers of .025 Lexan are installed between the strut and bracket steel on each side of each strut/bracket.
* the new bracket requires ¼ inch spacers on both sides of the 1 inch strut to achieve the required bracket gap of 1.5 inches. This enables a complete disassembly by getting rid of the permanently captured flying wire originally part of the rivnut/bracket assembly and specially tooled bracket and custom spacer.


Trailing edge side


All 3 of these brackets are drilled to 3/16 for AN3 bolts.
  1. Upper root – original bracket, new short rivnut
  2. lower root – flying wire outside positions
  3. upper mid – original bracket, new short rivnut, fly wire in outside positions
  4. lower mid – new bracket drilled 3/16 with flying wire in outside position and negative wire inside.
  5. Upper outer - new bracket drilled 3/16 with flying wire in outside position
  6. lower outer - new bracket drilled 3/16 with negative wire on inside
Materials and sources

Brackets – Local job shop fabrication. 20 gauge stainless, laser cut from author’s Draftsight dwg files created from original plan parts. Files available in “files” section of Easy Riser Yahoo group.
Retainer washers – stainless, sourced per original kit part
Cable
Cable coating -
Nico press sleeves – zinc plated sleeves will corrode. These must be tin coated. I always get these from an authorized Nicopress distributor since they are a critical component.
Shrink tubing -
Strut saddle bushings – Leading Edge Airfoils. If these become unavailable, plain nylon fender washers could easily do the job.






Saturday, January 13, 2018

Internal Wing Panel Structure

last update - 6/22/18



Jigs

1. 15.5 degree ramp and guide bar jig used for final finish sanding of LE and TE rib ends.
2. Hollow rib jig from 1/2" plywood used for locating through holes for internal strut clearance.
3.  Clamshell form to fabricate ribs.
4. raw foam blank template for hot knife cutting rib foam cores.
5. 15.5 degree rib gusset jig to set rib gusset offset.
6. rib slab cutting board used for cutting all slabs (minor & major ribs and foam fairing slabs.
7. chord dimension jig (2 each mounted on either side of each rib as they are riveted to the frame) They lock in the outside wing chord dimension of 39 7/16.

Changes needed to be made to the original kit plans to allow me to solve the severe fabric pull down between the ribs that was so hard to avoid with the original rib layout.  The lower wing panel originally had 6 ribs.  My current approach involves using 1 extra main rib on the bottom wing panels making a total of seven 1/2 inch foam/spruce cap strip main ribs.  In addition to the extra main rib, I've added 6 minor ribs constructed of 1/4 foam and balsa wood cap strips with a single side gusset to mate with the leading and trailing edge spars.  The other change I am including is the replacement of the filament tape with pinked, 1.0 inch Poly tape from Aircraft Spruce.  I am running 5 lengths spanwise with a 2" spacing on the leading edge section.  I found that strapping tape is not compatible with the application of PolyBrush fabric sealant as it causes trapped bubbles that cannot be removed.  The tape MUST be shrunk prior to covering to avoid unrecoverable puckers in the main fabric.

I have witnessed 3 partially assembled kits that all had a different chord dimension, none of which came in at the plan spec of 39 7/16.  Hence the inclusion of a chord dimension jig above.


Changes From Original plans;


Both panels:

1. Replace strapping tape with 5 spans of 1 inch Poly Tape (Aircraft Spruce)

Bottom Panel:

1.  Add one main rib for a total of 7 (spaced evenly)
2.  Add 6 minor ribs (1/4 inch) between each main rib


Top Panel:

1. Currently added 3 additional main ribs evenly spaced to avoid bracket locations.
2. Added full-length minor ribs (1/4 inch thick with a single LE & TE gusset)
3. Added 3/4 inch .035 internal strut midway between the original internal diagonal strut and the tip to help alleviate spar bowing during the covering process.


Locating holes in foam for internal struts

This was originally a challenge and now. with the addition of several minor ribs I found it necessary to come up with a process to bore these through holes.

Fabricate a template rib. Cut a scrap piece of 1 inch tubing at the angle the strut will go through at. Trace the angle cut tube end onto a 3x5 card and cut out a bit larger than the tube outline. Make two of these cards. Remove the strut and thread the first cut out card onto the strut. Next thread the template rib onto the strut and lastly thread on the second card. Tape in place after the strut is re-located to it’s installed position. Carefully remove the strut far enough so that the rib template can be taken out. Transfer the hole location onto the rib to be bored out and cut out the foam. Fine tune with half round file and/or sandpaper.


The photo here shows the template rib (this one is made from 1/2 inch plywood) located at the position of a minor rib (1/4 inch thick vs main ribs that are 1/2) that will be bored using the template rib and cards taped to it.  (notice the two temporary, removable rivets called 'Clecos" commonly used in aircraft construction).
TO BE CONTINUED

Hang Tubes

The main focus of this post is to explain how I constructed new hang tube assemblies after destroying one in my last crash.

Materials:
1. Main tubes - black anodized 2"x .035 wall 6061T6 aluminum tubing.  Source:
2. Twist grip - 2 1/4 inch
3. rudder stop - hardwood block, nutsert
4. tape wrap -

POST UNDER CONSTRUCTION

Friday, January 12, 2018

Strut Fairings

Material Sources:
1. foam - Dow Styrofoam TM, Square Edge Insulation (blue in color), building supply stores (I got this from Lowe's national chain of home improvement stores).
2. glue - Original Gorilla Glue widely available in stores and on-line.
3. covering film - Aerolite (Solite-W) – available on-line.

Special jigs:
1. strut holder - see photo (very simple to make this).  Used for both glue up and covering.

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 (length to width) of 4.500/1.145 or 3.93. This ratio just “looked” about like what I was thinking, no magic engineering. I created the full scale profile template 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 – Corning Formular 150 (pink)

material density
  • Aircraft Spruce blue foam (9.0 oz/16 oz/lb)/(0.5/12x2x4 ft3) = 1.69ft3
  • Square Edge33.85 oz/16 oz/lb/(2/12x2x4 ft3) = 1.59 lbs/ft3
  • Formular 150 1.31 lbs/ft3
Formular vs Square Edge compressive strength is stated at 15 vs 25psi so I'm choosing Square Edge.
Guess 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.
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.
THE RIBS

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 to the surface.
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….depends on your power supply.

I wanted these ribs to be ½ inch thick so I needed to cut slabs from a large, 2 inch thick stock sheet to start with.
Starting the cut


Almost complete

Ready to trim that tail

Perimeter cut done


Cutting the strut through hole

Pop it off the template for a completed rib

THE INTER-RIB BEAMS

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 jig lying on the hot knife table



In this next shot the block of foam is in the form jig 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 and hat pins to hold the ribs against the beams while the glue set up. Using glue sparingly made this unnecessary.  I also found that the Gorilla Glue gets tacky fairly quickly so one can move from one rib assembly to the next without any wait time.  It takes me about 1 full day to complete one side so for both wings I'm into 2 days to get the entire set ready to cover with the monofilm.

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 is a shot of an end piece of film I applied first before covering the main part of the fairing.

Laying out the main sheet of monofilm to begin the covering process.


Before heat shrinking

After heat shrinking.....magic!


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.




I used this "wrench" to set the fairing angles and then only found it rarely needed again since there is enough friction against the strut to keep them in position unless they are really bumped hard.

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 the cables. All of them 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 unfaired, clear strut on the middle positions for 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 is how they look installed in my trainer.  You can see the foam rib-beam structure in the backlit photo.  I have had no issues flying with these fairings and they are surprisingly durable.