It all started like this.
On the Vintage & Old Timers forum on RCGroups, some senior members run a ‘build off’ once in 6 months. There is a theme selected by participants, and everyone tries to build an appropriate model in the next 6 months. The prize for completing it is the participant’s own model. So everyone who completes has his own new model as a prize! There’s also a vote for the most popular build.
Those who fail to complete can participate in the next CAP (Complete A Project)

The theme for the second half of this year was EAR (Early Age Revisit). Participants were to build a model that they really desired in their early age, but never built for some reason or the other.

In the 1960s, I flew towline gliders, Cox or Mills powered free flights, and Frog/AM 1.5cc powered control line models. Later progressed to Enya .19, OS .20 powered Peacemakers...

Couldn’t even imagine a 35 glow powered Nobler or Thunderbird!

But one of my friends had an OS Pet powered Control Line Graupner UltraStunter.
Another had a Control Line Mercury Marvin.

I knew back then that one day, sooner or later, I’d build these models.

The time has come.

So I downloaded the Mercury Marvin plan from OuterZone, and got it printed. The cost of printing it full size (Rs 70) was far more than I expected.

I’m converting it to RC and electric power.

I’ve cut out the ribs, and fabricated the leading edge and spars.

If anyone is interested, I’ll post pics as my build proceeds...

Here’s the plan...

Made a ply template for the ribs...

Deterioration in workmanship due to age is apparent...

Some improvement with the help of a sanding block...

Here is the original instructions booklet...
https://outerzone.co.uk/download_file.asp?planID=7458&FileType=Supp&Filename=Marvin_CL_Mercury_oz7458_instructions.pdf

Some observations about the control line model, while thinking of RC and electric power conversion.

1. Flew at 50mph. Or 75fps. On 40’ lines., or a 250’ circle. That is 3.3 secs per lap. Was it really so fast?
As far as I can recollect after 40 years, my OS20 powered Peacemaker couldn’t have been under 5 sec on 50’ lines.
2. 75fps on a 6” pitch prop means 150 rps, or 9000 rpm, or 10500rpm on 5” pitch. Probably ran at much higher rpm to drag the lines along
3. July 1956 Model Aircraft review (Sceptreflight.com) of the AM10 diesel shows 0.1 bhp (80w) at 10500rpm, and 1.2 bhp (100 w) at 14000.
4. Weighed 10-12oz all up

So it could do the stunt pattern, lines and all, at say 150 watts/lb...

Without the lines, perhaps 100w/lb would suffice

That AM10 weighed 3oz, so with tank and fuel, say 150gms

So an 80gm 2s 1000mah lipo, with a 30 gm motor plus Esc and 2-3 9gm servos may be enough?

I’m planning on aileron, elevator, throttle. No rudder.

What motor, prop, Esc, Lipo would be suitable for this RC version?

Interesting, very interesting

Assume 12 oz, about 350 gm

RCB's PRO C 2822 KV 1200 gives:
● Get 350gms Thrust
PROP – 8x4E
Lipo – 2cell 7.4V
ESC - 20 amp

My calculations show at 7000 RPM, 7.4 V, the thrust is 10.3 oz, absorbed power (by prop) is 35 W

Assuming 70% efficiency (prop + motor) current draw is ~ 7 A

So 1000 mah LiPo will last 1/7 X 60 = ~ 8.5 minutes at full power

If you use a 3S battery, more weight, but also more thrust! (if needed)

Mr Iyer,
Congratulations on such a great project. Marvin was a second step  at our NCC. Loved it. Converting it to electric RC would be terrific.

for airplanes around 12 ozs i have successfully used Hacker A20-22L, 20 amp esc and on a 3s lipo around 1000 mah. Just sharing. here are the details: http://www.flybrushless.com/motor/view/255.
A bit costly but mine has lasted 10 years with a couple nose dives crashes.

Anyways, wish you the best on your project. will watch this thread closely.

Some progress atlast...

Trailing Edge top sheet attached with PVA glue and taped down to drawing board edge to ensure no warps.

  Subscribed...

I guess old age brings its own problems .
Forgot to bevel the edge of the bottom TE sheeting.
So on gluing on the top TE sheet, I got a reflexed TE.

To correct that, painted the top TE with water and the bottom with dope.

Found that the dope was dark brown, having got impregnated with rust. Rusty dope I last used over 40 years ago...

But it cured the problem. At least on the starboard side (pic 1)
But not on the Port side (pic 2)

Crawling along at a snail’s pace...
Added centre section webbing.
Then some unnecessary stuff.
Added perimeter to tips to ensure adequate contact patch for covering.
Then finding it wider than needed, chamfered the inner edge.
Utterly unnecessary.
Will add servo mount plates and centre section sheeting between dinner and bedtime. Hopefully.

Getting better...

What a joy it is to cut those corners with the Dremel...

Bottom open till servos stuck on with double sided tape...

Once you start the Dremel, it’s not easy to stop...

Sad to cut the wing in two.
Wanted a bit of dihedral to avoid a droopy look.

As of now,
231 views on RCI,
1823 on RCG!

Coming along well!

Nice one sir.

Thanks folks, but it gets worse!

First trial with Doculam. Disaster.
Then did another tip in Chinese film, to check if I still remembered how.

Just use monokote!

Excellent progress, KK Iyer sir.

Me too extremely slow with the woodwork, even though it is laser-cut kit build.
My current problem is the engine mount...drilling precise vertical holes thru' beams are a big challenge.

Before starting on the fuselage, one last rethink.

Unthrottled OS Pet .09 (circa 1960), or EMax CF2822 (~150w on 3s, presumably 100w on 2s...)

Views?

I have about 10 such 300ml bottles of half used glow fuel with the castor oil separated.
So inclined towards electric, even though my lipos, 6 yrs old on average, are a bit bloated, but should manage 10A(10c)...

For years, nay, decades, I’ve tried and failed to get a mirror finish.
I’ve tried dope and balsa dust (saved religiously by wife in the ‘fine sawdust can’)
I’ve tried grey filler putty
The best I’ve done is with 18gsm glass cloth and Bob Smith Finish Cure epoxy (Smooth, but hardly mirror finish)
But I want to do it without glass/epoxy.

On a recent US visit, got some Mod Podge and some Spackle.
Don’t know what to do with the Mod Podge, and the spackle says ‘not for use as a skim film’

Somehow, one thing I never did was to cover sheet balsa surfaces with dope, then tissue with thinner.

Request suggestions for a nice finish on the Marvin fuselage and empennage (while waiting for 38 micron doculam for the wing)
Rai saheb said ‘Just use monokote’
But all I have is a 5m roll of Green.
Really want translucent silver on wings, silver on fuselage bottom half, black on fuselage top half...

Throw them all away! Fuel first. Either get the ingredients and mix a fresh batch, or buy 5% Falcon Fuel 1 litre

You don't need 'precise holes'  Drill them slightly oversize eg for a 3 mm bolt use a 3.2 mm drill etc. Use a Nyloc nut for simple and assured retaining

(Iyer sir, sorry for interrupting your thread)

Drill on an aluminium template first. CA it to the mount. Then use it as a guide to drill through mount.

One advantage of oversize holes is that you can adjust side/down thrust 

Traced outline to make some internal changes...

Was away 1st to 7th, Pondicherry and Chennai, family meet and a wedding.
Got sick due to lousy air from AC in Chennai hotel.
Still not fully recovered even after 5 days of antibiotics.

Deadline to fly the Marvin is 31st (effectively last Sunday, 29th)

So started on the fuselage...

Take care! All the best

Sent from my motorola one power using Tapatalk

Some progress...
Going to bed now.

I wish I could come to your place and learn some balsa lessons. Great work sir.

@manu,
Most welcome any time.
Where are you now and what are you doing? In Sendhwa? Update me on Whatsapp.
Merry Christmas to you and your family.

Here’s a pic of progress today.

I am in Delhi, sir.

Took hours of work to modify a glow engine spinner to fit over the collet/spinner prop mount of the electric motor. Had to cut off 9mm from motor shaft.
A few more hours to blend the nose into the spinner.

I guess with age, its taking me an hour to get 10 minutes of work done.

My Lipos are also aging and getting puffed. After six years I got lazy and let them remain unused at full charge instead of at 3.85v for storage. The result is they come down from 12.4v to ~10v even at 10C (10amps draw).
With a 9x4.7 prop, showing 100watts (10a x 10v) at full throttle. (60watts on 8x4 prop)
Hope that will be enough, and that the finished weight stays well below 1lb/450gms...

Thanks to a past thermal soaring world champion and author (Sundancer on RCG), I discovered Doculam. What a pleasure.
At par with discovering dope some 55 years ago, the first Cox Babe Bee 50 years ago, then Monokote 40 years ago and CA glue 30 years ago.

Learnt how to use it with very little error by exercising patience and low heat.
When I hurried it a bit and turned the heat up more than I intended, got 2-3 small holes.
But that taught me how to patch.

Had doubts about being able to cover with tissue over the doculam.
So tried on one wingtip bottom with some several year old yellow tissue (the white I had seemed too stiff)
Remembered Sundancer mentioning somewhere to draw the tissue across a pan of water.
Really pleased with the result. Not perfect, but 9/10.

This is the way to get that vintage dope and tissue look on vintage models, with puncture resistance added by the Doculam.

Doubt if anyone is interested in such vintage stuff, but I carry on due to my own vintage!

I had bought some heat shrinkable adhesive-backed lamination (low heat melt) to try with thermocole. Is Doculam something similar? ( I haven't yet used it, but tried on a small area - seemed OK)

This is the product -  https://www.amazon.in/gp/product/B07N85GCR9/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

Same/similar. Doculam is a name like Monokote, that has become generic.

Do you first cover with tissue, then laminate?

Laminate first.

What is the "pan of water" for then?

To drag the tissue over so that one side gets wet.
The laminated surface is doped, then the tissue is laid on wet. While wet, it’s brushed through with thinner.
Well that’s the theory. My experience limited to only one wing tip so far!
Here’s a pic of one tip with only laminate, and one with tissue too.

Canopy/hatch.
Toothpick pegs at the back, magnet pair in front.
Took more effort than I expected, to get right.

Doculam glazing?

Almost ready, but not quite.

It’s 11pm on 31st Dec, so time for bed!

Happy New Year to all our forum members.

Happy New Year and Happy Landings all

Humidity was over 90% last two days.
As soon as it went below 70, added some talc and thinner to the dope, and did the fin, stab, elevator and flaps.
Decided to hinge before tissue cover.
Top hinge line. On the elevators used the 27micron doculam below and in the V.
Top hinge far thicker doculam.

Then got a doubt. What if the thick doculam is too stiff? Will it crack? Etc.
So on the flaps/ailerons used the fine doculam on both sides.
As insurance, added 4 of 2x2mm hinges of the thick doculam per wing.

So far so good.
Till I came back from walking the dog, and stepped on the top cowl that was lying on the floor.
I’ve CA’d it together. Will make another if needed.

Bad news yesterday, I’m afraid.
Applied green tissue to turtledeck.
First, it bled.
Then when it was dry, it just peeled off!
And left a stain.

I fear I may have to resort to paint or Monokote, something I wanted to avoid.

But it wasn’t the tissues fault, it was mine.
Looks like the dope coat was too thin, and the thinner too copious.
Maybe the dope got dissolved and thin enough to be completely absorbed by the (wet) tissue, which then on drying just peeled right off like an onion skin!

Tried again. Thick coat of dope, thinned just enough to keep the brush from sticking to the wood, and tissue applied DRY. Then brushed through with absolutely minimum thinner.

Seems to have worked.

@saikat sir,
Where are you?
Eagerly await your advice.
Regards

I had some degree of success adding Universal Stainer to the "Dope"  (actually NC Clear lacquer)

It sagged initially, but after some days was fully taut

Sirji, never knew that you do stick and tissue models too!

I started my aeromodelling life with several Bobnis!

These are Guillows kits

where you find Dope

"  "Dope"  (actually NC Clear lacquer) "  Use Duco with Duco thinner

Auto paint shops.
Try to get Duco, as suggested by Rai saheb.

If not possible, you can get dope (ask for NC Clear) loose from auto paint shops / auto painters.

Got some a few years ago, Rs 60 for 200ml in a new tin. Used a bit for my Pilatus Porter, Druine Turbulent and Iambus. But when I opened it now, the tin had rusted, turning the dope a dark brown.

So this time I took a glass jar and got 200ml. For Rs 50!

Thinner is available from hardware shops in 500ml plastic bottles.
Cost me Rs 80 last time. But this stuff absorbs water from the air. When I tried it now, it turned the dope milky. So I got a new bottle. Rs 51 this time!

But why do you need dope? Are you planning to build old style stick and tissue models?
If so, welcome to the small group of people still using dope. Do post your build log.

BTW, are you in Bhopal? Have we met? Sorry if I’ve forgotten.
Some flyers from Bhopal often come with Tanmay to the Creative Flyers RC Airfield in Indore.
Are you one of them?

Sorry sir .We never met . those people expert flyer, i am an aeromodeller and still learning flying .Also i stick with my Bhopal now try to find new air field .our every field occupied international cricket players, car learner , and above all kite flyer (patang baj). whenever i will come to indore i will meet you.
with regards.
Arvind khare 

Nearly done. Only control horns and pushrods pending.

Had lot of problems with the tissue/dope finish.
Found out what was wrong.
The thinner was making the dope blush. It wasn’t the humidity. It was the thinner itself.
Went to the auto paint shop from where I got the NC Clear Lacquer (dope)
Showed them the (industrial) thinner I used, and how it turned the dope milky.
The guy there dipped his finger in my thinner, sniffed it, and said this is a chemical. Called Methanol!
That just blew me away.

He sold me another 250ml of dope, 500ml of auto quality thinner, and a 1” brush.
For Rs 130 total.
The new stuff is just fine. Even if it couldn’t erase all earlier blemishes.

Moral: Don’t use industrial thinner. Duco available on the net for about 250/litre.

That's a fine covering job! 

Looking Real Good now. All that experiments (dope, tissue, etc) all paying off clearly. Awaiting your maiden video

Can't take my eyes off it. Superb sir.