Quorneng's build blog

If Eric has one then so can I!

I was challenged on the RCME web site to build a 25" span Frog Wren as a RC glider - twin rudders and all!

The challenger was hoping to keep his below 4oz - the original (free flight) was only 1.25oz!

With nowhere to fly a true glider (other than by tow line) I though I would make it powered as well but also keep below 4 oz and just for good measure without using dedicated micro 'all in one' components.

You can see where this was going - Depron!
A very nice plan is down loadable from here

The wing.

Just 9 pieces (top and bottom skins and a spar web all in 2mm Depron. The spar flange is actually a lightweight tissue strip glued onto the top and bottom surface. It weighs 0.44oz.
The tailplane, elevator and rudders.

To keep weigh to a minimum I chose a pull/pull closed loop using 1.7lb mono filament fishing line.
The 3.7g elevator and rudder servos glued together as a block.

The rudder lines run down the top of the fuselage, out along the tailplane leading, around the front of the fin to the rudder horn.

Then to the rudder trailing edge, across to the other side and similarly back to the other side of the rudder servo arm.

And it works

The complete airframe and servos weighs 1.15oz

Should be ok for under 4oz.

wooooooot! bout time you had a build, looking good good Simon

PS to be like Eric you would have to grow a beard

Ha!
I didn't say I want to be like Eric only to have my 'own' build blog.

A bit more progress.
The 7g motor mounted on the balsa nose block.

Those are 12BA screws!
The motor faired in with Depron and a 5x3 prop.

It is amazing how heavy even 7g feels when it is added to the end of a 25g fuselage!

The battery box.

It adds considerable stiffness to the fuselage and also gives local reinforcement where you hold it for launch.

The Depron 'Motor' Wren complete in my normal lightweight colours of Classic Red detail and unpainted Depron.

It weighs 3¹ /4 oz with a 500mAh 2s LiPo.
It can be easily lifted by its wing tips which means it should be ok for a loop.
Just need the right weather.

Maiden today was not at all successful!
Climbed gently away but slowly started rolling to the right, the rudder had no effect, and it went into a spiral dive. No damage.

So quickly made 'stick on' rudder extensions to almost double their area.

It helped in as much as the roll to right was controlled but I could not stop the resulting roll to the left so it spiralled in the other way.
Nose slightly crushed.

Those twin fins may have been ok for a lightweight glider but with a prop on the front it appears the directional stability is very poor and the original rudders have little or no effect.

So before the next attempt:
Nose shortened by 1/2" to reduce the side area ahead of the CofG
3 degrees down thrust added
Battery moved forward 6mm to bring the CofG to 27% chord.
Taller 'Lancaster' shape fins and rudders of greater area.

Its all good fun!

I doff my cap to you sir. A lovely little model and I'm sure you'll get her flying just right

The shortened nose and revised fins.

Down thrust has been added.

A comparison of the new and old fins.

The original glider had a lifting section tailplane which not only placed the CofG at nearly 50% chord but also required rather more wing incidence than normal to achieve longitudinal stability.
As I am using a symmetrical section tailplane I have sanded the top of the fuselage to reduce the incidence a touch.
The total weight is unchanged as the extra material in the fins has been matched by the reduction in the shortened nose.
The battery has also been moved to bring the CofG forward.

Now of course the weather is horrible!

Despite Sarah's jibe "about time I did another build" the Frog Wren is actually just a 'filler' job.
The most complex recent build has been the Glasflugel H201 Libelle glider.
The original was an early fibreglass 15m glider that at the the time had a superb performance.

I set my self the task of building a true scale version but in Depron and with a motor in the nose.
Like most glass ships it has very 'skinny' high aspect ratio wings which were going to a real challenge in Depron particularly as I was not going to use carbon reinforcement.
First job to build the fuselage in 3mm Depron.

No internal structure just formers and planking.

Once the RH half was complete the cockpit internals were added and the other side was built onto it.

Finally the fin and tailplane were added.

Here I did allow myself a small piece of carbon rod to connect the elevator halves.
The next problem was the wings. To scale they are 2.1m. The longest balsa I have available is 3ft meaning the wing was going to have to be built in 3 pieces although ultimately to be permanently joined as a one piece wing.

Despite Sarah's jibe "about time I did another build"

la la la! still a build looks good though simon

Eric
I had employed Depron 'planking' on both the Skyray and the Natter although this was the first time I had tried a complete 1/2 fuselage.

The Libelle wing presented a further problem.
The full size used a relatively thick 18% Wortman wing section specifically designed for use with fibreglass to keep the wing stresses low. At the time carbon was not available.
Such a thick wing section would be very inefficient at the small chords (just 2 inches at the tip) of the high aspect ratio wing however the shape of the cockpit canopy would look 'wrong' as it passes over the wing if a typical model glider 10% thickness was used.
As the wing was to be built in 3 pieces the solution was to use the true scale section at the root but reduce it to just 10% by the start of the outer wing panels. The short centre section would thus be quite a complex shape as it would also include the dihedral angles.
The wing uses a broad (1") 1mm hard balsa spar set flush with the wing surface but mounted on a Depron box structure acting as the shear web. The same structure I had developed for the 2m Depron wing for my Big Dragon.

The completed centre section positioned on the fuselage.

The long outer wing panels use the same type of structure but the balsa flange tapers to just 1mm wide at the tip.

The 10% thin Wortman section is retained all the way to the tip.
The wing is so thin that even a 3.7g servo has to be mounted flush with both the top and bottom wing surface.

With the aileron servo installed the top rear skin can be added.

This picture shows just how 'skinny' the Libelle wing really is when compared to the similar span to the Easy Fly ST330 I restored last year.

It is just as well the Libelle should weigh less than half as much

"wow"
i love the way this is coming together.

i have to use depron on a build soon i think.

It is a terrific build i am watching with interest as those so so slim wings are built, a real eye opener you depron boys are giving.

Sorry to jump about a bit but the Depron Frog Wren is proving difficult.
I tried some simple glides without a prop which did at least show it glides reasonable well and straight but even with the taller fins the rudders still have very little effect. You can see it yaw a bit with full rudder but with very little induced roll so little change in direction or correction to bring up a low wing.
This lack of roll could be due to either a lack of dihedral, as Eric pointed out, or simply insufficient rudder power. With twin fins there is little prop wash directly over the rudders.
So first to test the rudder authority with a big, probably over size, single fin and rudder.

It can then be progressively cut down to find an adequate minimum.
If the proves to be of a similar area to the twin fins I will refit them but with fixed rudders and use ailerons instead for roll and direction control.

Depending on how well the Depron Wren eventually flies will determine whether I proceed on my original intention and build a balsa and tissue powered Frog Wren.