Is That A Mirage?

By Michael (Augie) McKibben

I fell in love with the Mirage years ago — 1984 to be exact. I needed to replace my second RC glider, a well-worn and always reliable Gentle Lady. I had been sizing up the Sagittas, the Oly II, the Windfree, and so on, but I wanted something different, something that no one else had. And I wanted a standard or open class glider at a “low” price. Just so happens that my local hobby store had a Hi-Flight Model Products’ Mirage for about $45, as I recall, which fit into my budget perfectly, so I bought it.

Michael McKibben's Mirage

Building my first Mirage was a challenge for me as a relative newcomer. This is a big glider made almost entirely from balsa with bits of spruce and plywood. Dutifully following instructions, I built the Mirage to the best of my ability, added transparent red Monokote™ with white trim and installed the Airtronics four- channel radio from my old Gentle Lady. My Mirage flew like a dream and opened up a whole new soaring experience for me. Flying my new sailplane was a joy as I watched it dance on the rising air. My landings became less worrisome and more consistent. I felt like I had been flying for years and could hardly wait for the weekends to hunt thermals with my new Mirage!

Blaine Rawdon’s New Design

At this time, Airtronics models and a few others like the Paragon, Oly II, and Bird of Time dominated RC soaring. The Mirage introduced a design philosophy already being tested in freeflight models. Blaine Rawdon's i innovative Mirage coupled a lightly loaded wing with an airfoil designed for a wider speed range then offered by most floaters. This required a departure from conventional construction techniques. The three-piece wing was planned to minimize weight while maintaining “just enough” strength to be durable. Wing sheeting was minimized, as were tip details. Lightweight wing tips meant reduced inertial yaw and allowed nimble turning. The fuselage was kept extremely light by using balsa sides strengthened by a balsa doubler. Keeping the fuselage wide at the rear gave the stabilizer a strong base. An offset rudder is aligned with the left side of the fuse to provide a firm connection to the fuselage tube and to provide a straight and rigid pushrod run to the rudder horn. Only the right side of the horizontal stabilizer has an operating elevator, the left side is fixed. While helping to decrease the overall weight, the fixed stabilizer has an added benefit of less drag.

The result? Blaine said, “The Mirage came out very light, and the light air performance was better than hoped for. The goal of a wide speed range was realized too. An unexpected benefit of the light structure was very nimble handling. Even today, the plane is a pleasure to fly in thermals because it is so easy to maneuver into position and so easy to read. Despite a delicate appearance, the original two Mirages still fly on occasion with Bill Watson’s guidance. Simple construction and ease of repair are the keys to longevity for this design.”

The model proved its versatility and success among modelers on the West Coast. Blaine said, “The Mirage became popular for contest work… My best remembered win was Dave Thornburg’s 1979 hand launch contest at SULA’s field in Carson, CA. I think that this was the last time I beat Joe Wurts.”

Sadly, almost as soon as the Mirage came on the scene, the newer composite gliders overtook the all-wood models and pushed them aside. The Sagitta, Oly II, Paragon, and Mirage became relics. Today, however, the popularity of RES and nostalgia class models has created a resurgence of interest in “built up” gliders and once again the Mirage is in the mix. This begs the question; can a new Mirage compete against the RES type gliders of today?

Although the Mirage qualifies for the nostalgia sailplane class, with a few fairly simple modifications it can also become a potent competitor in the RES category as well. So, let’s consider a few basic changes:

  1. Replace the rubber-band wing mount with a bolt-on method.
  2. Add carbon-fiber caps to the center wing panel spars.
  3. Beef up the shear webs in the center panel.
  4. Add spoilers. This is allowed by nostalgia rules as long as you maintain the overallstructural design of the original.
  5. Wrap the joiner and joiner boxes with Kevlar.

Making these five modifications to the original Mirage design can significantly increase its strength without sacrificing the light wing loading. In addition, spoilers increase the control needed for the precision landing tasks in RES contests. You can find out more about the “Nostalgia” rules by logging onto Ray Hayes’ web site at www.skybench.com, and clicking on the “RES & Nostalgia” link.

A New Mirage Kit

Isthmus Models MirageMark Millerii of Isthmus Model Company, www.isthmusmodels.com, has produced a “short kit” of the Mirage. The kit includes laser cut parts such as the ribs, wing joiner parts and fuselage sides, the canopy tray and bulkheads. A plastic canopy is included in the kit along with a list of materials needed to complete the Mirage. To obtain the full-size plans and building instructions, Click on the “Mirage Plans” link on the Isthmus Model Company web site and look for plan set #753.

Although the Mirage is easy enough to fly and its construction is trouble-free and conventional, I would not recommend it as the first project of an absolute beginner. Its optimized structure is “just enough” and will not tolerate building errors or a major crash. Assuming the builder understands conventional balsa construction, I will by-pass that and focus instead on the following modifications.

1. Spar; laminate .007” x .375” x 48” carbon fiber to the bottoms of both top and bottom spars of the center section for a little extra strength. Carefully increase the depth of the main spar slots of the ribs to allow for the increased spar height.

2. Spoilers; place immediately behind the main spar and between the three bays just inside of the outer bays of the center panel. Use 1 1/4in x 5/16in trailing edge stock and carefully recess only the necessary ribs. In keeping with the AMA rules for nostalgia, we want to maintain the open structure of the wing design as much as possible. Use the cord and lever method for activation of the spoilers. One servo mounted in front of the main bulkhead will pull on the cord to activate both spoilers. The cord exits the bottom of the center panel from either side of the center most rib. The cord is kept in one piece to form a loop around a ball link on the servo. Punch 1/8in holes through the necessary ribs to allow for a nylon antenna tube to run the cord. Frame up the spoiler bays with 1/8in x 1/4in spruce to the rear and 1/4in x 1/4in balsa on the outside left and right of each bay. Carefully shape the top of the spoilers to match the profile of the airfoil.

3. The wing mount; split the center rib at the spar and install a 1/8in plywood joiner laminated between 1/8in vertical grain balsa for a 3/8in joiner sheer web combination. Add 1in trailing edge stock under the trailing edge sheeting of the center panel for a firm foundation for the hole required for the ¼-20 nylon bolt. The bolt is threaded into a piece of 1/4in plywood epoxied to the fuse just in front of the rear most bulkhead. Make a duplicate of the forward half of the center rib and glue both into position to create a 1/4in space that will hold a 1/4in hardwood dowel for the leading edge portion of the wing mount. After the center panel is sheeted, positioned the wing carefully and cut a 1/4in hole into the leading edge using a sharpened brass tube and the hole in the main bulkhead as a guide. Use epoxy to glue the dowel (and fill the void) in place after making sure the wing is seated perfectly and aligned. Allow the epoxy to cure fully with the wing in its correct position. The only real change in the fuselage is the main bulkhead. Create the bulkhead from 1/4in plywood. Trace its profile 1/8in shy of the canopy outline shown on the plan’s cross section. Cut 1/4in holes for the wing’s mounting dowel and spoiler cord with two 5/16in holes for the pushrods.

4. The shear webs; increase the shear web widths in the center panel. Use 3/8in vertical-grain balsa for the next three bays adjacent to the center bay. Use 1/4in for the next three bays adjacent to that and finish off with 1/8in shear webs.

5. You should make pushrods out of 3/8in balsa per the instructions. They are lighter and will not lose trim settings as temperature and humidity change. In a pinch, you could use 1/4in hard wood dowels.

6. The only change I would make to the wing’s center panel construction would be to make the turbulators out of good quality 1/8in x 1/8in spruce instead of balsa.

7. I encourage everyone to taper the trailing edge of the tips per the plans. The key to the Mirage’s maneuverability is lightweight wing tips. The plans also show scallops on the trailing edge. This is optional.

8. Move the bulkhead that forms the front of the servo bay forward 1/4in to make room for the addition of the spoiler servo. You can move this bulkhead around to make room for your particular servo arrangement.

9. Wrap the joiner and joiner boxes with Kevlar string for a little added strength.

10. The plans call for glassing the forward third of the fuselage. I opted for a technique that I really like. I used 1.5oz fiberglass cloth wetted out with water based poly-acrylic. I add 8 drops of yellow food coloring to every once of acrylic to get a match for my transparent yellow Monokote™; it takes about 5 or 6 coats to fill the weave of the cloth. This method is lighter than glassing but not as durable. But when you get a ding—and you will—just fill it in, brush on a little colored poly and it looks good as new.

Having followed the plans and added the modifications, I had only to add the radio gear and balance. I installed Hitec HS81 servos for the elevator, rudder and spoiler control, with a Hitec 555 receiver and an 1100 mah battery pack. I like a lot of control throw on my gliders, so my throws for the rudder are 2” in each direction and 1” up and down for the elevator. With all of my gear installed, I needed about 3 ounces of nose weight to balance the Mirage on the plan’s CG. I suggest you use this CG as a starting point. You can shift the balance point around after you get familiar with your new sailplane. This new Mirage is significantly stronger and ready to fly at 37.5oz. That is just 4.5oz over the typical original giving me a wing loading of 5.9oz/sq ft.

First Flight

Finally the good stuff! I brought my new Mirage to the field trimmed and balanced, gave it a once over that included a range check. Satisfied that everything was ready, I faced into a wind of 8 to 10 mph and tossed it straight and level. The Mirage quickly climbed out to about 15 feet. I needed to push the nose down to avoid stalling, but nevertheless it flew well. I adjusted the trim for the windy conditions and turned to my hi-start.

Launching the MirageWith absolute confidence in my new light air machine, I hooked my 37.5oz Mirage up to my new NSP Pinnacle L Hi-start and gave it a light toss. That first launch was like a rocket straight up as high as the line allowed! I was surprised and unprepared for the speed of the launch. At altitude my chute slid away and I headed off into the wind, rock solid and steady with very little trim adjustment necessary to keep my heading.

My 2002 Mirage is just as fun to fly as I remember. The most impressive thing about this glider is its maneuverability. The Mirage is really light on its feet. The response to control input is immediate and it telegraphs lift in classic fashion. It can fly fast to cover ground and yet fly slow enough to thermal effectively. Turns are its best feature. Stand the Mirage right up on a wing tip and pirouette around as tight as you can imagine without fear of tip stalls. You will find this ability incredibly helpful when coring a tiny thermal at low altitude. This is one glider you can safely bank hard at low altitudes. One note of caution, it is very sensitive to wing warp, especially in the tip sections. If you find that you need a lot of rudder trim to keep it flying straight, check your wing and make sure it is aligned accurately. I do like to use 1/8in to 3/16in of washout in the tips for stability in turns. If you fly a Mirage too fast, the wingtips may flutter at around 60 mph. Avoid hard launches from your hi-start and go a little easy on your winch pedal. The Mirage achieves outstanding launches without much effort.

If you are looking for a great open class Nostalgia or RES type glider, Mirage may be for you. Its light air performance is unmatched by most, and yet it is a floater with legs. You may be surprised at how it moves out when you put the nose down. The cost for most modelers will be about $110 to $120 depending on where you buy your additional balsa, less if you already have an extensive balsa collection started.

Good Luck!

Mirage Specifications

 
Parameter
Typical Original New 2002
Typical Weight (ounces) 33 37.5
Wingspan (inches) 112.5  
Wing Area (square inches) 915  
Wing Loading (ounces / square foot) 5.19 5.9
Aspect Ratio 13.96:1  
Minimum Sink 1.1 ft/sec @ 19 ft/sec  
Maximum L/D 18.5 @ 21 ft/sec  

 

 Catching the Mirage

Photo furnished by Blaine Rawdon. All rights reserved. 

i Blaine Rawdon grew up in Southern California where he started flying U-Control models at the age of eight, flying with the neighbors in San Fernando Valley’s Sepulveda Basin. U-control and free flight competed with slot cars until leaving for Amherst College in Massachusetts. There he earned a Bachelor of Art degree in Physics. He then returned to southern California to earn a Bachelor of Science in Architecture at USC. Blaine took up RC soaring and joined the San Fernando Valley Silent Flyers. There he met Bill Watson and this friendship led to work on Paul MacCready’s Gossamer Condor and Albatross as a builder and crew and then to a design position on the Solar Challenger. From there it was on to McDonnell-Douglas as a structures designer and then as an aircraft configuration designer. Blaine is now a Boeing Technical Fellow in the field of aircraft configuration design. His key accomplishments include configuration design work on the Blended Wing Body and the Pelican Ultra Large Transport Aircraft.

ii Mark Miller has played an essential role in the Mirage’s revival. I met Mark through our club, the Minnesota Radio Control Soaring Society and we have become great friends. Mark, who lives in Madison, WI, was up to our club field in Blaine, MN on a warm Saturday afternoon late last year for a little visit and some thermal duration. Mark and I started talking about the availability of built-up sailplanes and our mutual desire to see more of this type of sailplane in the market. The subject of the Mirage came up and we found that we have a similar interest in this simple and elegant glider. To my surprise, Mark took it upon himself to produce parts for a new and improved Mirage. I pestered him often and we started a collaboration o f sorts that would produce a new Mirage for the new millennium. Mark did all of the hard CAD work and research himself but he did give me the opportunity to build his first production of the Mirage short kit.