Hi everyone,

Call it nostalgia, if you will. Oldies sometimes get the urge to start a project for old times sake.
The Yellow Bird is one such. 55 years old now. Published by Alan Webber in Aeromodeller in 1961!

When we were kids, about 50 years ago, all the NCC Air Wing cadets used to fly Yellow Birds off catapults. We used to watch in envy, as we couldn't afford one. Boy, did they fly well!

Now plans available on outerzone.co.uk, thanks to steve WMD.

To build a really good chuck glider, you need contest grade balsa. Or 6oz/sqft.
My 3mm sheet is 9oz/sqft, or 50% overweight.
But Webber says in his article that there's no need to build it lighter than his.
His 20" plan says 1.55oz, or say 44gms.
So a 15" version (about 50% wing area) needs to be in 20-25gms range...

Originally in 20" and 13" versions. Mine is 15".
Reason? On my iPad the span is 15cm. So easy to fix sizes without printing the plan!
And the last 3mm sheet i had is only 3" wide. Just right for 15"span.

The 15"x3" is already too heavy...

Is anyone interested in such stuff, or am i just talking to myself?

For good performance, one needs wings with low inertia, ie, light wingtips.
That means sanding a taper in the wing blank, from 3mm at root to about 1.5mm at tip.
Not so easy!
Have to keep the 7.5" semi span 7.5" from the edge of the drawing board and sand it till the outer edge is half the thickness.

Then you have to draw an ellipse,
And cut it...

Quote from: K K Iyer on December 25, 2016, 09:06:11 PM
Hi everyone,

Call it nostalgia, if you will. Oldies sometimes get the urge t


Is anyone interested in such stuff, or am i just talking to myself?

i am

good choice KK

the Yellow Bird has powerful nostalgia for me too. 

following your build.

Built one, but not well 

Second model after Bobni

All the best Iyer sir, after nearly 50 years, I'll finally learn how it's meant to be done 

Seems like I've struck some chords!

Even a small and simple model gives enough opportunity to test one's workmanship.
Little things like jhaadu teeli LE reinforcement.
String edging on TE and around the perimeter of the stab.

Still had sawdust sawed from my RCTLG build of 2-3 years ago
Tried dope+sawdust as a gain filler. Too lumpy. Good for filling cracks, gaps in joints etc, but not for filling the fine grain.
Went back to dope+talcum powder. Still doing something wrong. Perhaps first coat should have been thick and rubbed on. Now four coats done with 400 grit sanding, but grain still shows. Added 1.5gms to 13.5gms raw.

Dremel sanding disc next?

I think you should have covered with tissue

Correct!
Should have told me earlier 
Dope+talc adding too much weight...

Couldn't locate plain tissue in any shop. The kite paper available seems a bit too crisp. And too shiny on one side. Perhaps paper towel from the kitchen roll.

Had some real Jap tissue saved for over 25 years.
But last when I went to Lucknow, found it eaten by termites.
Along with kits of a Mills 1.3 powered freeflight Chipmunk, Mercury Marvin 1.5cc CL, Keil Kraft Comet catapult glider, Guillow Cessna, Solarbo balsa etc.
And LPs like Abbey Road, Sgt Pepper, L Shankar Double Violin etc with original covers.
Had to set fire to the lot.

Hope to meet them again when its time for me to be set afire...
Nostalgia aint IS what it used to be, after all.

There is an aerodynamics reason (other than nostalgia), for picking this model.

One of the current chuck/catapult glider theories is that you need LESS  pitch stability, so that the mdel can stall, and roll, at the top.

This Yellow Bird has 4 times the horizontal tail volume coefficient, compared to what I've been using last few years.

Is this good? Is it bad?

Inputs welcome...

There are more subtleties in this 55 year old design.

The plan says to steam warp the port wing so that the LE is 1/16" higher at the polyhedral joint.
Since the chord there is about 2", it means about 0.5 degree washin.

What this does is that
At launch (high speed, low angle of attack) there is a significant difference in lift between the port and starboard wings, with not much difference in drag. Resulting in strong right roll.
Later in the glide (low speed, high AOA) the lift difference is small, and the drag differential is larger. Resulting in yaw to left. (That's how chucks fly traditionally, right roll on launch, left circle glide)

But it also means washin at the tip. So is it a good option?

Or better to keep the panel flat, and add a wedge below the port wing inboard of the poly break?
(My usual preference)

Looking for inputs from theoretical and/or experimental perspectives.

See condition after six coats!

What am I doing wrong?

Are you sanding to flush between coats?

normal household acrylic emulsion makes a very good sanding sealer


apply one coat .... let dry for about 6 hrs (it is water based)

sand with fine sandpaper .... it sands like chalk and totally fills the grain.
for best results - do the final sanding with some news paper
you can use nitrocellulose clear / paint on top

try on a scrap piece to convince yourself

Iyer sir for doping you can use nc clear lacquer mix with nc thinner

@gaurang.1972,
I had posted the same advice on the forum a few months ago 
Thanks anyway.

@saikat sir,
Dope+talc seems to be working after i increased the talc amount.
But added significant weight!
Will try your suggestion in next build.

@sanjayrai55 sir,
Yes sir. Sanded each coat till i got basal joint arthritis in thumb 

Regards to all three.

Sorry sir I don't read your former post but I was also do it for my tiny tot and other gliders sorry for inconvenience

Finish is only 'chalega' standard. Pity.
Fuselage using strip cut from window beading.
Nearly done. Hope to do test glides tomorrow, and full launches on Sunday.

@gaurang.1972
No inconvenience at all.
There is no harm if correct info (like you gave) is posted in more than one thread. After all everyone doesn't read every thread.
So cheers!

Despite all the care taken, wing incidence found to be slightly negative. (1st pic)
Guess eyes too old for accurate eyeballing!
No option but to cut the (remarkably solid) wing/fuse joint. Had to use a razor saw.
Cut a thin wedge off the wing mount.
Now the slope of the chord relative to the stab is 5mm in 300mm. (2nd pic)
Or 1 in 60, which should be 1 degree if i remember my maths

Is this low enough to avoid looping at launch and still high enough to pull out from dives?

Request input from anyone who can guide, as don't want to be cutting the wing/fuse joint again...

Can you believe this?
The fuselage broke because there was a knot in it 
Moral: do not test glide inside house!

Moral: don't use moulding. Leads to knotty problems

Thanks for your 'moral' support 

Next question.
Should i splint the wood fuselage with CF? Or build a fresh CF boom fuselage?
Have to decide tonight, else can't test tomorrow.

Awaiting (possible) input on incidence/decalage from sanjayrai55, saikat, flyingboxcar, rcpilotacro, sundaram, VC, glidiator, and other experts/old timers i may have missed/ not come across...

Buildnew

Forget joint or this time the problem won't be knotty, but put you out of joint

@sanjayrai55,
Sir,
Yeh joint hee mujhe pareshan kar raha hai!

KK,

Been following your build log.
HLG / CLG is next on my list of to do.
Have you checked the articles on the site
Amaglider.com

Some very good articles on techniques to build  gliders that can really fly.

Have so.e yellow Bird kits from Aurora Models I bought about 5 years ago. Guess it is the same bird. Have built one but not really tested them out in real trimming flights.

In fact when I saw that for glider duration competition the 2min was the benchmark I felt no one would be able to cross that as the record is just about a minute.
The Rubber power could have been 2 mins as that I'd attainable.
Just my thoughts.

Incidentally ÀMAI is planning the first Indoor Nationals in April in Delhi (Sonepat).
Would be great if we have a large participation.