Le Fish Open Source Aerobatics Glider Wiki

Building Le Fish[]


Le Fish plans are available for free download from SlopeAerobatics.com:

The plans can be used as the basis for any of the builds described below.

Building Considerations[]

There are many different approaches to building Le Fish, and they have evolved significantly over time. The design has been built using a wide variety of techniques, and flown successfully across a broad range of weights from 16.5oz (470g) to 43oz (1220g) and more.  In all cases it is fun to fly, but when the plane has been optimized for both typical lift conditions and a pilot's flying style, Le Fish can offer a truly wonderful flying experience.

The most important considerations for a new Le Fish builder should be the following:

  1. What are the typical lift conditions the plane will be flown in?
  2. What kind of aerobatics do you want to primarily focus on? I.e. Precision, DS Acro, VTPR, Ultrabatics, etc.
  3. Do you want to be able to perform Madflight flips?

The answers to these questions will help guide selection of the build techniques, control linkages and all up weight (AUW) the builder should target to meet his/her flying goals.

Typical Lift Conditions[]

This is probably the single most important consideration a builder should contemplate before starting construction on his/her Le Fish.  What are your local flying conditions like? What is the altitude and topography of your favorite slope - is it a steep coastal cliff, or a more gently sloped alpine meadow? How strong is the wind on an average day? Does it come straight-in, or is it frequently off-center? Do you often have cycles of lift and sink as thermals come through?

Le Fish was born in Santa Barbara, California, where typical conditions range from 7-10mph (11-16kph / 3-4.5m/s) at Ellwood Mesa, our small 90ft (30m) but steep coastal bluff site, to 12-20mph (20-32kph / 5.5-8.8m/s) at the Ruins, our inland mountain site (located 3,500ft / 1,000m above sea level).  The ultralight build (sub 21oz / 600g) is absolutely better for the light beach lift than the traditional build (35oz / 1000g+), whereas the traditional build starts to perform better than the ultralight build at the mountain site when the lift hits the upper end of the normal range (around 20mph / 32kph / 8.8m/s).

So, as a general rule, if you mainly intend to fly your Le Fish in lighter conditions (12mph / 20kph / 5.5m/s or less), you should absolutely focus on building an ultralight plane (sub 21oz / 600g). If your typical conditions are stronger than 20mph / 32kph / 8.8m/s, then you will want to focus on building the plane heavier - around 1000g (35oz) or more to give satisfying performance. For conditions in between, a midweight build of around 700-850g (25-30oz), or an ultralight build could both be good solutions... depending on the flying style you wish to pursue.

Flying Styles[]

Tied and in some ways beholden to one's typical lift conditions is one's preferred flying style. In broad terms, lighter lift conditions will tend to favor a close-in, more VTPR / ultrabatic flying style, whereas stronger conditions will tend to favor "big sky" aerobatics, performed with greater speed and energy, generally (though not always) further away from the terrain and pilot. Obviously a determined and experienced pilot can to some degree overcome natural obstacles presented by the weight of their glider and the conditions they find themselves facing, but as a general rule, for day-to-day flying, the greatest satisfaction comes from having a plane that is well suited both to the conditions and the pilot's preferred flying style.

All else being equal, a heavier plane will require more lift to perform satisfying aerobatics than a light plane. It wlll generally carry more speed and energy, which can be an advantage for precision and DS aerobatics, but is generally a disadvantage for VTPR and ultrabatics. This same speed and energy means it will crash harder and often break more easily and/or more dramatically than a lighter plane. It will stall more deeply, stay locked in snaps and spins longer, and take more time to recover from same. However, a heavier plane will fly in stronger and/or offcenter lift conditions with greater ease, situations that might see an ultralight plane struggle. It will go faster and punch higher, things that are the traditional bread-and-butter of slope soaring performance, and which many pilots crave and enjoy.

An ultralight (sub 21oz / 600g) Le Fish allows the pilot to really perform in weak conditions that would not even permit a typical aerobatics glider to maintain flight. 7-8mph (11-12kph / 3-3.5m/s) of straight-in wind at a decent slope will see an ultralight Le Fish completely freed to perform pretty much any aerobatic figure the pilot can imagine. Continuous, chained precision routines can be flown in a tiny "aerobatics box" located literally in front of the pilot's face, and the full gamut of VTPR and ultrabatics stunts are at the pilot's fingertips. The ultra-low weight allows, at the pilot's discretion, the simulation of slow-motion in realtime, a tremendously uncanny sensation for both pilot and audience. A big part of the philosophy behind ultralight flying is seeing how slow, smooth and controlled your flying can become - allowing the pilot to craft extremely technical sequences of non-stop chained figures in a very small airspace, actively engaging with the terrain and surroundings in a way not open to a heavier glider.


The last question a Le Fish builder needs to answer is whether or not he or she is interested in performing Madflight - upright and inverted flips in the pitch axis. Madflight absolutely opens up a new vista of aerobatic glider performance, especially when complemented by an ultralight and ultradurable airframe (this being the core essence of the ultrabatic concept). Performing Madflight requires provisioning for a "Mad Stab" elevator - a full flying stabilizer capable of approximately 170-180* of rotation (about 85-90* each way). Creating a reliable, precise and durable Mad Stab requires that careful attention be paid to the radio programming, control linkages, and balancing of the stabilizer in order to realize best results.

Build Weights[]

Below are links to build logs and a summary of the three general classes of Le Fish builds: Ultralight, Midweight and Traditional.

There are many different ways to build Le Fish; much is left to the builder to decide. The fastest and easiest build is to use polyurethane glue (eg. Gorilla Glue) and laminating film; more compex builds - such as removable two piece wings, or more complex coverings involving Solartex and Goop, fiberglass, strapping tape, etc. will add considerably to the time required to complete the plane - but may very well be worth the effort, depending on the goals of the builder.

Ultralight Build (17-21oz / 480-600g all up weight)[]

See the How to Build a Swiss Fish thread on RCGroups for photos and discussion about this build style.

The main philosophy: "If it is light enough, it will be strong enough!"

General Build Tips:
I've arrived at a hardware solution for the ultralight Le Fish build that I'm pretty happy with as far as a general recommendation, especially for first-time Le Fish builders and/or people who don't have a lot of scratchbuilding experience.

Now, first things first: there are many, many, many ways to build a Le Fish and I'm by no means claiming this is the be-all, end-all approach that someone should follow. With that said, it's what I'm currently using, and it's proven to be durable, lightweight, and easy to install - all things that are very important for a "general consumption" type of solution.

Specialists will have their own preferences and very good reasons for same, and may feel their solutions are superior to what I'm putting forward here. They probably are, for all I know! However, I'm just trying to establish a super-easy-to-approach ground floor solution that will result in a plane with good performance, great durability and easy construction - all things I prefer when given the choice

One more disclaimer: I provide manufacturers, suppliers, and part numbers below for your convenience only. I do not have any sort of relationship with any of the suppliers mentioned, do not receive compensation from them, or otherwise. There are many places to find this stuff, I'm just trying to help establish a "known good" baseline. Feel free to substitute for equivalents based on preference, local availability, phase of the moon or whatever. IDGAF, it's your plane after all!

So, with those disclaimers out of the way, here is what I'm recommending in terms of hardware for an ultralight (17-20oz / 480-560g) build of Le Fish:


  • 1.3lb EPP for wings
  • 1.9lb EPP for fuselage
  • 6mm sheet Depron or EPP used for ailerons and tail surfaces (full-length cores with ailerons cut off and hinged works well too)
  • 1.7mil laminating film covering on entire plane, with 3mil on D-Box of wing
    • D-Box = beginning on top of the wing, wrapped from spar forward around leading edge, and back to spar on bottom
  • The film used is the Premium CP Laminating Film from Laminator Warehouse
    • Available in 500' rolls from Laminator Warehouse, or in smaller quantities from Canuck Engineering and Aloft Hobbies (amongst others).
    • Depending on the width used, about 10' - 15' of 1.7mil laminating film, and about 5' of 3mil laminating film will be enough to finish a Le Fish as well as have leftovers for repairs.
  • 0.032" x 0.310" x 72" (7.9mm x 0.8mm x 180cm) carbon fiber ribbon spar in main wing where indicated on plan, with identical ribbon spar laminated to the subtrailing edge (CSTSales.com Graphlite Carbon Fiber Rectangle Part Number T733L6)
  • No longeron in fuselage required
  • Lightening holes in wings, fuselage, tail surfaces, etc. to taste (they don't save much weight, but they do look very cool!)
  • Hitec HS-65MG or equivalent servos recommended throughout. Metal gears are a good choice for durability.
    • If using Hitec HS-65MG for the elevator servo, replace stock servo arms with Du-Bro #934 Micro Servo Arm XL for Hitec or equivalent - using the longest arm possible is important to get maximum elevator throw
  • 6V AAA NiMH Eneloop battery pack, or ~700mAh 6.6V LiFe
  • If using LiFe pack, confirm servos & receiver support the higher 6.6V voltage
    • Lithium Polymer (Lipo) chemistry NOT RECOMMENDED for Le Fish!
  • Parkflyer-sized receiver
  • 12" servo extension for elevator servo in tailboom
  • Du-Bro 1/2A Nylon Control Horns #107 or equivalent - you'll need 5 control horns in total
    • 2 for ailerons
    • 2 for elevator
    • 1 for rudder
  • Should take little to no noseweight to balance
  • Reinforce all control horn mounting points top & bottom with sheets of 1/32" plywood or fiberglass / carbon fiber equivalent. This really makes a huge difference in how positive the surfaces feel in flight, and how well they hold up to abuse.


Madslide-style all moving stabilizer capable of approximately 180º rotation on high rates

  • Elevator servo mounted in tailboom just aft of the wing trailing edge
  • 0.125" / 3.2mm carbon fiber tube for stabilizer spar / joiner (CSTSales.com Part Number T512)
  • K & S Tubing 5/32" (3.9mm) x 0.014" (0.35mm) wall aluminum or brass tubing for pivot bearing - perfect sleeve with above CF tube
  • Du-Bro #846 Micro Pull-Pull System with tailboom-mounted elevator servo is an easy and effective off-the-shelf solution that works, but there are other solutions for the intrepid scratchbuilder
  • To get maximum stabilizer travel on high rates, use the furthest out holes on the longest double-sided arm possible for your servo. Use the holes closest to the elevator surface on the control horns.
  • If using Hitec HS-65MG for the elevator servo, replace stock servo arms with Du-Bro #934 Micro Servo Arm XL for Hitec or equivalent.
    • The wider the servo arm, the easier it is to get maximum throw on the elevator - around 170-180º of travel is the minimum for performing tight flips.
  • Setup a low rate with reduced throws for normal flying, as well as a high rate with full throw and maximum exponential (make sure the expo you use softens the feel around center!)


Servos mounted similar to the Aeromod Coquillaj, in fuselage directly in front of wing, offset slightly below the wing centerline.

  • Two options for light, durable pushrods that are easy to build:
    • Option 1: 0.070" (1.8mm) solid carbon fiber rod (CSTSales Part Number T320) glued with medium CA or epoxy to a Du-Bro Mini Nylon Clevis #227 at the aileron surface, and connected to Du-Bro EZ-Connector #121 at aileron servo arm.
      • Can sleeve over this with additional 0.125" (3.2mm) carbon fiber tube as used for the Madstab elevator pivot for additional stiffness at small weight penalty.
    • Option 2: 0.079" (2mm) solid high modulus carbon fiber rod (CSTSales Part Number THM321) glued at both ends with medium CA or epoxy to a Du-Bro 2mm Threaded Coupler #695 with a Du-Bro Mini Nylon Clevis #227


  • Mount servo in canopy area between wing leading edge and battery pack.
  • Du-Bro 30" Micro Pushrod #852 is a durable, lightweight and simple solution - run down the middle of the fuselage between the two halves, exiting approximately 2-3" in front of the rudder hinge line.

Laminating Film:
The "New Stuff" CP Premium Laminating Film comes from Laminator Warehouse in 500' rolls - essentially, a lifetime supply for one builder. Since there's a two roll minimum, I'd encourage you to do a group buy with friends and club mates

There are also various suppliers providing this same laminating film on a per-foot basis. This can be a great choice for your first build. Approximately 15' of 1.7mil and 5' of 3mil will be sufficient - although it depends entirely on the width of film being offered by your supplier. If in doubt, get more than you think you'll need - it's very handy to have on hand for repairs, and you may, like many others, be so impressed by its quality that you'll want to cover more of your builds with it.

There are five widths of 1.7mil and 3mil available:
http://www.laminatorwarehouse.com/la...ss_Film_100691 http://www.laminatorwarehouse.com/la...ss_Film_101066

I like using the widest widths of lam film available (27"), which gives you the most options for shapes and covering approaches. Many of the per-foot suppliers sell narrower widths, which are also fine, you'll just have to do more overlaps and will need more footage to cover the whole plane versus going with the wider film.

Laminating film is extremely inexpensive, and it's great to have more on hand for repairs, so err on the side of ordering too much - you'll wind up using it one way or another!

Midweight Build (25-30oz / 700-850g all up weight)[]

French Le Fish build thread on Jivaro-Models (in French but has lots of photos)

Summary of Midweight Build:

  • Balsa ailerons and tail surfaces
  • 1.7mil or 3mil laminating film covering, extra reinforcements to taste
  • 8mm x 1mm carbon fiber ribbon spar in main wing, with another 8mm x 1mm carbon fiber ribbon spar subtrailing edge.
    • Additional wing joiner reinforcement recommended; doubling up the 8mm x 1mm ribbon spar in the center 30" of the wing could be a solution.
  • Fuselage longeron to taste; recommended if a pull-pull elevator and/or rudder are used.
  • Lightening holes in wings, fuselage, tail surfaces, etc. to taste (they don't save much weight, but they do look very cool!)
  • Hitec HS-65MG or equivalent servos
    • Hitec HS-85MG or equivalent if higher speeds intended
  • 6V AAA or AA battery pack, or 6.6V LiFe equivalent
    • If using LiFe pack, confirm servos & receiver support high voltage
  • Small receiver

Traditional Build (35-40oz / 1000-1150g all up weight)[]

Le Fish Build Log - 60" Aerobatic EPP Slope Prototype thread on RCGroups

Summary of Traditional Build:

  • Balsa ailerons and tail surfaces
  • Covering Options:
    • Laminating film:
      • 3mil or 5mil laminating film on entire glider
    • Goop/Ultracote/Solartex/Strapping Tape build:
      • Strapping tape on wing center panel, leading edges, fuselage, etc. underneath covering
      • Ultracote or equivalent on wings and tail;
      • Thinned Goop on bare fuselage foam, then again on top of fuselage covering and wing leading edges
      • Solartex on fuselage, finished with thinned Goop on top
  • Spars as supplied in the Leading Edge Gliders kit
  • Fuselage longeron as supplied in the Leading Edge Gliders kit
  • Hitec HS-85MG or equivalent if higher speeds intended
  • 6V AAA or AA battery pack, or 6.6V LiFe equivalent
    • If using LiFe pack, confirm servos & receiver support high voltage