F!R Building instructions
Here is Tony Hebb's design. There will also be a kit version available from www.indoorbalsa.net Nothing difficult here. Build the model and then 'improve' it by trying to build each component a bit lighter.
Building Notes - 35 cm Entry level (Jan 2012)
The purpose of this model is to provide a step on from, say, a Gyminnie Cricket that will provide excellent duration times whilst remaining easy to build. I say easy - but having built the prototype and tried to keep everything within the bounds of what a normal modeller will have available I realise that this is still difficult, but hey, you can build this model without milligram scales, a digital thickness gauge or a sophisticated balsa stripper.
Kits will be available from www.indoorbalsa.net
As your confidence and skills grow you can build new, lighter components whilst still remaining within a recognised duration class.
You will need the following tools:-
A metal straight edge, preferably 24”
Modelling knife
Carbon steel razor blades
Razor Plane
Pins
Balsa cement - ideally 80% Ambroid/20% cellulose or acetone. If not available use UHU from the yellow and Black tubes, again thinned 50% with above.
Small round nosed and needle nosed pliers
Small side cutters
Fine sandpaper contact glued to a balsa block about 1.5” x 4”
From a material viewpoint you’ll also need:-
A “Dual” prop bearing for EZB model from SAMS or Flitehook.
.013” piano wire or .013” steel guitar string
Film covering
Indoor quality 1/32, 1/16 (.063”)and 3/32 balsa, ideally in the 5 to 6 pound range.
Indoor .013” balsa for the prop blades, 4 to 5 pound C grain good
You might consider buying one of the EZB kits that are available and using the wood from it.
Build Notes.
First of all I am not trying to give a blow by blow construction account. Please, please find and read Larry Coslick’s Hobby Shopper EZB article (Indoor News and Views) - he does this far better than I can and I still reference it today!
What I shall do is describe how to put this model together with as little fuss as possible and still get a decent duration model out of the other end - you will not use these construction techniques much in your indoor future!
Wing and Tailplane.
Measurements - 1/16 sheet is .063”, make 2 reference strips, one half this (.030”) and one 3/4 (.045”) just by eye is quite good enough. These will allow you to gauge the finished ribs and spar thicknesses quite well.
Put a new blade in your razor plane and adjust it so that it takes the finest continuous shaving possible.
Cut a piece of 1/16 sheet about 8” long by 1” wide. Mark across the top surface with a felt pen - lightly.
Take 3 shavings off the sheet starting at 2”from the tip, then at 4” and finally 6”, just let the plane do the work, no pressing down, then lightly sand the sheet to give a smooth taper to about .045 at the tip.
Cut 4 spars off the sheet, cut the taper (.063 at the root) by eye so the spar is about .045 at the tip, pair up the spars and sand to match along the length. Best to straighten up the edge of the spar sheet after each pair of spars to keep the grain along the spar. Cut diagonal joints at the centre, pre glue then cement together, press against a straight edge to keep the bottom flat.
To make the ribs cut a template from stiff card, you can sand it smooth and if necessary a bit of superglue will harden up the edge. Break a razor blade in two and put some tape across the broken edge to hold it by. Use your .045” measure and a good eye to slice off 5 ribs from the 1/32 sheet.
Stick ¼” squares of sellotape over the plan where the glue joints fall, then pin pieces of straight edged balsa to outline the wing frame. Set the spars in position, holding them in place with soft balsa “clamps”, don’t pin the spars directly. You should pre glue all joints. I attach the ribs first at the leading edge, then cut to length using a NEW piece of razor blade and glue to the trailing edge.
The tailplane is the same, except of course the spars are thinner (taper from .045 down to .030) - the ribs can be a little thinner too. Note the offset on the centre rib.
Covering is OK with Pennyplane film or lighter(eg. OS film), there are various articles describing the techniques available on-line. It’s really not that difficult and so much better than condenser paper.
Finally cut and glue the spars on the wing and tail to form the dihedral breaks, make a few “rugby post” jigs to help keep things flat, makes life easy and doesn’t take much making.
Motor Stick and boom.
Cut the ¼ wide MS from light, stiff 3/32 sheet, reduce the front and rear to 3/16 by taking a few shavings off with the razor plane, sand it smooth, go on you can even round off the corners ever so lightly! Make the boom from 3/16 x 1/16 at the motor hook tapering to 1/8 x 1/32 at tailplane TE) - worth the effort though, this is an important piece of the model, needs to be as light and stiff as you can make it. Emphasis on the latter!
The wing posts are 1/16 square rounded (rotate gently between two pieces of sandpaper glued to a couple of flat pieces of balsa) - you only really need to round the ends. Make them a nice snug fit in the 1/16 tissue tubes. Something a little smaller diameter (about .045+) for the tail posts will be fine.
Glue the boom to the MS with a ¼” overlap joint; make sure it’s straight along the bottom edge.
Next add the front bearing with 2 to 3 degrees left thrust, 0 degrees downthrust, then add the rear motor hook. Add some tissue reinforcement to both these metal to wood joints for security.
To mount the posts I glue one in place first, then use the completed wing/tail to mark the location of the other. Finally put the tubes on the posts and with the wing propped up at the right height glue the tubes to the LE and TE spars. Make sure the wing/tail surfaces are flat at this point. When you glue the tail tubes in place build in about 3/8” tail tilt (port tip high) to help the left turn. Let the joints dry thoroughly before handling!
Propeller.
Ideally buy some light .013” C grain sheet for the blades and make as per the Hobby Shopper article, otherwise its sand down from 1/32 - a bit of a task I know.
Form the blades wet over a bottle as per the Bob Bailey article for the Gyminnie Cricket on the BMFA we site - I’d recommend just a 10 degree offset and use a larger diameter bottle (than standard wine one!) for a former to avoid over cambering the blades. Using a pitch jig is better but needs more work to produce, for this size prop. the bottle method is OK. Attach the blades to the propeller spar with 20” pitch.
Prop spar - use slightly harder balsa than for other components. Make two halves, tapering as for the wing spars to match them and join at centre with scarf joint. Form prop hook, push shaft through spar at scarf joint and bend a U at the front end. Attach with cement or thin cyano, making sure shaft is at right angles to spar. Attach blades to spar using cement as for other joints.
Prop pitch set by making tip angles about 28 - 30 degrees to shaft (make sure both are the same!).
The prop. is the heart of a duration model and time spent here will be well rewarded.
Flying.
This model is going to climb like a homesick angel, so for a typical sports hall and to speed up the trimming process I’d recommend using a 1/3 motor with a 2/3 spacer - make it from hard balsa or a bamboo skewer with 20g wire ends. The size and weight of your motor (and therefore spacer) is going to be dependent on the finished weight of your model, my model weighs in at 1.25g and a full motor in the region of 1g is OK. Try about .050” thick rubber to start with. The motor is made to 1/3 weight and 1/3 distance between prop. hook and rear hook.
Hang the motor (+spacer if using) between the prop. and the rear hook and check that the model balances around the indicated CG, if not add blue tack or similar to make it do so.
The wing is set at zero incidence and the tail at -2 or 3 degrees to start with. Put on a couple of hundred turns and try it, aim to fly nose up with a left turning circle of 15 to 20’ and enjoy.
Conclusion.
I hope that you’ll be able to get someone to help with the model as this makes all the difficult bits much simpler and they will have access to wood, rubber, scales etc. that makes everything so much easier. You can go it alone but eventually you have to fly the thing somewhere anyway, so why not get in touch up front?
Once you’ve made a model if you want to improve it there are many areas to try. It’ll probably be heavier than you’d like, now is the time to get fussier about weight and stiffness of the balsa you use. The spars can definitely be reduced, but remember it has to support the final weight of the model! Try to get a model built at around 1.0gm. The propeller blades can easily be made from .010” balsa or even try a built up propeller! Using OS film for covering will also save 100mg or so - I find this easier to use in fact as it seems to have less static charge. Or how about a rolled motor stick?
All part of the challenge.....have fun!
The purpose of this model is to provide a step on from, say, a Gyminnie Cricket that will provide excellent duration times whilst remaining easy to build. I say easy - but having built the prototype and tried to keep everything within the bounds of what a normal modeller will have available I realise that this is still difficult, but hey, you can build this model without milligram scales, a digital thickness gauge or a sophisticated balsa stripper.
Kits will be available from www.indoorbalsa.net
As your confidence and skills grow you can build new, lighter components whilst still remaining within a recognised duration class.
You will need the following tools:-
A metal straight edge, preferably 24”
Modelling knife
Carbon steel razor blades
Razor Plane
Pins
Balsa cement - ideally 80% Ambroid/20% cellulose or acetone. If not available use UHU from the yellow and Black tubes, again thinned 50% with above.
Small round nosed and needle nosed pliers
Small side cutters
Fine sandpaper contact glued to a balsa block about 1.5” x 4”
From a material viewpoint you’ll also need:-
A “Dual” prop bearing for EZB model from SAMS or Flitehook.
.013” piano wire or .013” steel guitar string
Film covering
Indoor quality 1/32, 1/16 (.063”)and 3/32 balsa, ideally in the 5 to 6 pound range.
Indoor .013” balsa for the prop blades, 4 to 5 pound C grain good
You might consider buying one of the EZB kits that are available and using the wood from it.
Build Notes.
First of all I am not trying to give a blow by blow construction account. Please, please find and read Larry Coslick’s Hobby Shopper EZB article (Indoor News and Views) - he does this far better than I can and I still reference it today!
What I shall do is describe how to put this model together with as little fuss as possible and still get a decent duration model out of the other end - you will not use these construction techniques much in your indoor future!
Wing and Tailplane.
Measurements - 1/16 sheet is .063”, make 2 reference strips, one half this (.030”) and one 3/4 (.045”) just by eye is quite good enough. These will allow you to gauge the finished ribs and spar thicknesses quite well.
Put a new blade in your razor plane and adjust it so that it takes the finest continuous shaving possible.
Cut a piece of 1/16 sheet about 8” long by 1” wide. Mark across the top surface with a felt pen - lightly.
Take 3 shavings off the sheet starting at 2”from the tip, then at 4” and finally 6”, just let the plane do the work, no pressing down, then lightly sand the sheet to give a smooth taper to about .045 at the tip.
Cut 4 spars off the sheet, cut the taper (.063 at the root) by eye so the spar is about .045 at the tip, pair up the spars and sand to match along the length. Best to straighten up the edge of the spar sheet after each pair of spars to keep the grain along the spar. Cut diagonal joints at the centre, pre glue then cement together, press against a straight edge to keep the bottom flat.
To make the ribs cut a template from stiff card, you can sand it smooth and if necessary a bit of superglue will harden up the edge. Break a razor blade in two and put some tape across the broken edge to hold it by. Use your .045” measure and a good eye to slice off 5 ribs from the 1/32 sheet.
Stick ¼” squares of sellotape over the plan where the glue joints fall, then pin pieces of straight edged balsa to outline the wing frame. Set the spars in position, holding them in place with soft balsa “clamps”, don’t pin the spars directly. You should pre glue all joints. I attach the ribs first at the leading edge, then cut to length using a NEW piece of razor blade and glue to the trailing edge.
The tailplane is the same, except of course the spars are thinner (taper from .045 down to .030) - the ribs can be a little thinner too. Note the offset on the centre rib.
Covering is OK with Pennyplane film or lighter(eg. OS film), there are various articles describing the techniques available on-line. It’s really not that difficult and so much better than condenser paper.
Finally cut and glue the spars on the wing and tail to form the dihedral breaks, make a few “rugby post” jigs to help keep things flat, makes life easy and doesn’t take much making.
Motor Stick and boom.
Cut the ¼ wide MS from light, stiff 3/32 sheet, reduce the front and rear to 3/16 by taking a few shavings off with the razor plane, sand it smooth, go on you can even round off the corners ever so lightly! Make the boom from 3/16 x 1/16 at the motor hook tapering to 1/8 x 1/32 at tailplane TE) - worth the effort though, this is an important piece of the model, needs to be as light and stiff as you can make it. Emphasis on the latter!
The wing posts are 1/16 square rounded (rotate gently between two pieces of sandpaper glued to a couple of flat pieces of balsa) - you only really need to round the ends. Make them a nice snug fit in the 1/16 tissue tubes. Something a little smaller diameter (about .045+) for the tail posts will be fine.
Glue the boom to the MS with a ¼” overlap joint; make sure it’s straight along the bottom edge.
Next add the front bearing with 2 to 3 degrees left thrust, 0 degrees downthrust, then add the rear motor hook. Add some tissue reinforcement to both these metal to wood joints for security.
To mount the posts I glue one in place first, then use the completed wing/tail to mark the location of the other. Finally put the tubes on the posts and with the wing propped up at the right height glue the tubes to the LE and TE spars. Make sure the wing/tail surfaces are flat at this point. When you glue the tail tubes in place build in about 3/8” tail tilt (port tip high) to help the left turn. Let the joints dry thoroughly before handling!
Propeller.
Ideally buy some light .013” C grain sheet for the blades and make as per the Hobby Shopper article, otherwise its sand down from 1/32 - a bit of a task I know.
Form the blades wet over a bottle as per the Bob Bailey article for the Gyminnie Cricket on the BMFA we site - I’d recommend just a 10 degree offset and use a larger diameter bottle (than standard wine one!) for a former to avoid over cambering the blades. Using a pitch jig is better but needs more work to produce, for this size prop. the bottle method is OK. Attach the blades to the propeller spar with 20” pitch.
Prop spar - use slightly harder balsa than for other components. Make two halves, tapering as for the wing spars to match them and join at centre with scarf joint. Form prop hook, push shaft through spar at scarf joint and bend a U at the front end. Attach with cement or thin cyano, making sure shaft is at right angles to spar. Attach blades to spar using cement as for other joints.
Prop pitch set by making tip angles about 28 - 30 degrees to shaft (make sure both are the same!).
The prop. is the heart of a duration model and time spent here will be well rewarded.
Flying.
This model is going to climb like a homesick angel, so for a typical sports hall and to speed up the trimming process I’d recommend using a 1/3 motor with a 2/3 spacer - make it from hard balsa or a bamboo skewer with 20g wire ends. The size and weight of your motor (and therefore spacer) is going to be dependent on the finished weight of your model, my model weighs in at 1.25g and a full motor in the region of 1g is OK. Try about .050” thick rubber to start with. The motor is made to 1/3 weight and 1/3 distance between prop. hook and rear hook.
Hang the motor (+spacer if using) between the prop. and the rear hook and check that the model balances around the indicated CG, if not add blue tack or similar to make it do so.
The wing is set at zero incidence and the tail at -2 or 3 degrees to start with. Put on a couple of hundred turns and try it, aim to fly nose up with a left turning circle of 15 to 20’ and enjoy.
Conclusion.
I hope that you’ll be able to get someone to help with the model as this makes all the difficult bits much simpler and they will have access to wood, rubber, scales etc. that makes everything so much easier. You can go it alone but eventually you have to fly the thing somewhere anyway, so why not get in touch up front?
Once you’ve made a model if you want to improve it there are many areas to try. It’ll probably be heavier than you’d like, now is the time to get fussier about weight and stiffness of the balsa you use. The spars can definitely be reduced, but remember it has to support the final weight of the model! Try to get a model built at around 1.0gm. The propeller blades can easily be made from .010” balsa or even try a built up propeller! Using OS film for covering will also save 100mg or so - I find this easier to use in fact as it seems to have less static charge. Or how about a rolled motor stick?
All part of the challenge.....have fun!