Airfield Models - Design and Build Contest 2006-2007

Antonio Carlos Martins' Hyperbolic Lady II

May 02, 2015

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Antonio Carlos Martins' Hyperbolic Lady II 2nd Place 2006-2007 Design & Build Contest

Antonio Carlos Martins' Hyperbolic Lady II

Photo Copyright Antonio Carlos Martins


Airfield Models ( Specifications and Equipment

Wing Span: 78.74"
Chord: 9"
Wing Area: 713 square inches
Aspect Ratio: 8.75:1
Weight: 21 ounces
Wing Loading: 4.25 oz./sq. ft.
Length: 46.5" from back of propeller to elevator hinge line
Motor: Hacker A20 20L
Speed Controller: Castle Creation Phoenix 25
Battery: 1300mAh, 3S
Transmitter: Futaba 6EXA
Receiver: Futaba 127DF
Servos (2): Elevator, Rudder Way Point 19g

The spoiler is activated by putting the Esc on rear mode.  With the engine running at 10% and a prop on rear there's a lot of drag.

Editor's Note:  I asked Antonio to clarify the spoiler activation. This is his reply:

I used an ESC named Mamba from Castle Creation with rear function.  It is plugged into the throttle channel of the receiver.  Settings are as follows:

  • Throttle and trim fully forward (up) is full forward throttle.
  • Throttle closed with trim fully forward is motor stop.
  • Throttle closed and trim fully back (down) allows 10% reverse throttle.  This means airbrake using the engine.

But this is forbidden on FAI concept in F5J .

I make models for me, not for competition so I developed this use for the ESC.



The Hyperbolic Lady II is Antonio's entry in the Airfield Models 2006-2007 Design and Build Contest.  I've never seen a model from Antonio that I didn't like.  This one is no exception.

Antonio's first language is Portuguese.  He translated the article to English and did a much better job than if I tried to translate English to Portuguese.  Some of the article didn't translate well so I exercised my editorial prerogative to help clarify things.

Text, photos and linked photos that follow are Copyright Antonio Carlos Martins


About the Hyperbolic Lady II

The name comes from the elliptical wing made in hyperbolic system.  In fact it is a redesign of a old model with the same wing in plan view.

This new model takes many things into consideration:

  • A powerful out-runner motor, the Hacker.
  • Lithium Polymer Batteries in 3S
  • Vertical climb
  • A reasonably glide ratio, let's say 1:26
  • Low sink ratio

And most important, be a constructive model as simple as possible to build having only limitations that a modeler live with.



The fuselage is pod and boom style.

The balsa pod is carved from a box of 3/16" medium balsa sheet and reinforced internally with 1/16 plywood.

Finished with a thin cloth of fiberglass, and a finishing resin for reinforcement giving it a "lacquered" effect.

To make a rolled fuselage all you need is a good  mold.  A snooker baton is perfect.

The process is as follows:

Make a shallow chamfer along one edge of the balsa sheet.  A 10:1 bevel is about right.

Cover the baton with saran wrap.  Wet the balsa with water having a small amount of dish detergent.

Begin to curve the balsa sheet around the baton.  Hold the balsa in place using quality tape spaced about 4" between pieces.

Because the snooker baton is a cone, all you have to do is pull the balsa tube to obtain a round circle.

If some torsion (twists) occur you can turn the balsa tube until a perfect line is obtained with no twists.

Let the tube dry for a minimum of 24 hours (longer is better).

After the tube is fully dry, use thin CA glue to glue the joint taking care not to glue the tape to the tube.

Do not remove the cone from the mold at this time.  Use fine sandpaper to sand the tube as smooth as possible.  Go ahead and finish sand the tube at this time.

Fiberglass the tube using light (0.5 or 0.75 oz. cloth).  Apply a second coat of resin.  Finish sand the resin after the second coat is fully cured.

Remove the balsa cone from the snooker baton when you are satisfied and that's it.



The wings are conventional construction having false ribs to better support the covering.  Balsa for the ribs was selected to provide good performance (light weight) and longevity.   Spruce spars were used.


Tail group

The tail is the lightest I have ever designed.  I chose to have a full elevator (all-moving) and place the rudder at extreme of the fuselage.

The result is a very docile glider with enough power to climb in seconds.  The model responds with very good authority to all commands.

I have plans available if you like the model.

Antonio Carlos Martins




The Hyperbolic Lady II is a beautiful model.  Unfortunately, it's very difficult for me to judge because there aren't enough construction photos.  That really hurt Antonio in this contest.

The model is all wood with the exception of the stabilizer mounts which appear to be cut from fiberglass board.  The fuselage finish appears to be fiberglass cloth and resin.  From what I can see this is a project for intermediate to advanced craftsmen.  While the lines are simple and elegant, building the model will require some wood working skills beyond putting together a box and sanding the sides flat.

The fuselage is pod and boom style.  Antonio built a tapered boom by rolling balsa over a snooker baton (billiard cue).  The boom fairs into the fuselage nicely so that the pod flows into the boom instead of just turning into one.  I really like the finished result, but I'd like more photos to see more detail of how he attached the boom.  However, he did me and possibly many others a big favor in providing details of how he made the rolled balsa tail-boom. 

The center section of the wing is constant chord.  Antonio put some effort into cutting a set of ribs to make elliptical wing tip panels.  The vertical stabilizer and all-moving horizontal stabilizer also have an elliptical shape to them to give the model a lot of flowing curves overall.

Antonio is a very competent and confident builder.  He is probably the type of builder who knows he can build anything he can think of and just has to decide if he actually wants to do it or not.

Congratulations for giving flight to another of your ideas, Antonio.  My only request is that you please document your models better.  Construction photos motivate and encourage people to build.



William Rahiser's BR1 Sailplane
Antonio Amado's Submarine MK II

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