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Dec 20, 2010, 11:22 PM
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DH 94 Moth Minor, I.M.A. Ltd, FF to RC conversion.


Tiger Moths are really good flying aircraft in all sizes. So when I heard about the monoplane called the Moth Minor in 1994, I was intrigued. It is not simply a Tiger Moth with one wing removed, but a project by De Havilland to replace the Moth series of biplanes, simpler to build, similar flying traits, using less power. Concieved as a low cost trainer and basic civil airplane, it was farily remarkable in the final result. Not only basic transportation, but aerobatic certified.

Designed to be made quick in a production line method, only 140 or so were actually built before World War II caused production line changes to support the war effort. Not a real fancy looker, but beauty is in the eye of the beholder. Reminds me of Ryans, PT's, and Miles types.

So finding the Web site in the UK devoted to models sold by International Model Aircraft, Ltd, under the name of FROG, made me put on the thinking cap. Designed and sold in the 1940's and maybe early 1950's, these Free Flight designs just call out to be micro conversions.

Like the original Moth Minor, simple design, few parts, and quick construction was calling my name.
Last edited by Freddie B; Dec 27, 2010 at 11:46 PM.
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Dec 20, 2010, 11:34 PM
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Freddie B's Avatar
So the International Model Aircraft, Ltd, models you need to check out this great website. Spend some time going through the designs. Many could be enlarged to make some really cool projects. Sheet foam construction or Balsa could be used depending on your preferance.

I.M.A. Ltd planes, FROG Series, on website Hose of Frog Here:

http://www.houseoffrog.co.uk/

The DH 94 Moth Minor Plan is under the link to 'Rubber Powered Scale Models' here:

http://www.houseoffrog.co.uk/senior_scale.htm

If you are in the United States or elsewhere that A4 paper is not standard, use letter size paper as the plans were scanned with plenty of margin around the edges to work out very well. Just turn off any scaling, or shrink to fit options.

I printed out my sheets, some cut and paste, here is what the full size plans came out like. Along with very few parts to cut, 3 sheets printed out, ribs, formers, nose block, and tail pieces.

Fred

Fred
Dec 20, 2010, 11:49 PM
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Freddie B's Avatar
At around 22" wingspan, the DH 94 Moth Minor Model is roughly 1/20th scale.

I am opting for balsa construction, tissue covering, some modifications to make this Free flight plan into an RC electric conversion. Sheet foam would be an easy one with this design but it's been awhile since I created some good old balsa dust.

The plan and parts are very simple, and since there is no kit to buy and wait for I can get a quick start. If you have feared starting from scratch and cutting your own parts, this would be a good entry plane. Cutting your own parts goes quick and you have better control over final fit and finish.

I will use:

Spectrum AR6400 receiver.
Brushed Spectrum gearbox with the UM 51 motor.
Prop to be determined after final weight measurement.
3 channel R/E/T control.
Spectrum (e-flight, parkzone) or Turnigy single cell lipos in the 110-150mah range.

After the maiden I may build an aileron wing too, as it would be easy to switch between the two for 4 channel control.

No greif now over going brushless! I figure even at 22", given the 'slender' long aspect ratio wing, this bird should be light enough to perform well on stock gear, minimal investment. UM 51 gearbox and prop specs say up to 60 gram airframe, and even the older Sukhoi gearbox should be good up to 50 grams.
Dec 21, 2010, 12:01 AM
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So without delay I started cutting out parts!

My first modification is going to be to the nose area, starting with Former #7. The PZ gearbox will fit in this build, tight. S I am enlarging Former #7 by 1/16" on both sides, which needs the top cowel radius to be elarged by 1/16" too. A simple coin, circle template, compass, etc fixed up the paper patern pronto!

I like to cut the parts slightly oversize from the plan, put a little glue stick on the rear, fix it to my wood, and cut/sand to the lines. Peel the paper off, and lightly sand. On the ribs I also use glue stick to put two pieces of wood together and cut 2 matching ribs at once. Speeds things up.
Last edited by Freddie B; Dec 21, 2010 at 12:25 AM.
Dec 21, 2010, 12:07 AM
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The only other mods to the nose now are formers #8, and #9 need to be slightly bigger to mate to former #7. These parts are so amall that sanding to size is easy, so I used my Former #7 to trace a larger #8, and #9 the same basic size.
Dec 21, 2010, 12:17 AM
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I've been sharing a tip lately, but it hasn't caught on too fast, so here we go again.

Elmer's Rubber Cement. School glue. About $1.35 regular price, yet I have found it as cheap as $0.39 cents a bottle near back to school time.

Ever need to laminate some parts, balsa, foam, sandpaper to wood blocks, etc. Elmer's Rubber Cement is a great contact cement.

Elmer's is foam safe too! Yes it has yet to melt any foam I've used it on.

Basic, contact cement is placed on both parts. Let dry (Elmer's dries fast). A couple minutes on balsa, 5-10 on foam and other solid surfaces. Once dry, press together. But aim close because there is no taking them apart!

I used it here to laminate the nose formers, but also decided to make my formers from balsa plywood. 2 sheets of 1/32" balsa laminated cross grain. Very optional, but I love the added strength and minimal weight of this process. I don't break formers working on my builds this way.

Fred
Dec 21, 2010, 12:21 AM
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Last item tonight.

I am not using fancy contest grade balsa stock that has been in my vault for 30 years here.

As a free flight conversion I am not worried about the extra weight my balsa has in medium to harder grades. The plane needs to support more weight that the free flight original.

Another thing I like about the FROG designs, they use a little bit 'thicker' stock in areas, giving some added strength yet this alows some weight reduction in simpler structures. A sort of give take thing that helps in build time and handling strengths.

Fred
Dec 21, 2010, 01:16 AM
free flight or micro RC ???
g_kandylakis's Avatar
a welcome change in terms of subject and building method...

At 1/20 scale you should be fine with your setup, no worry about the motor.

Will be watching your progress,

George
Dec 21, 2010, 12:57 PM
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Freddie B's Avatar
Thanks George. The airframe and gear should be in the ball park of the Parkzone planes I'd guess, only somewhat larger, but not a lot. Depends how much I decide to add to make it stronger in areas if I opt for a hatch. I will be making the wing removable, as the design already has, but with pin and bolt instead of rubber bands.

Fred
Dec 21, 2010, 06:31 PM
Registered User
I am a BIG Dehavilland fan! I'm pretty excited about finding this build thread. Right now I'm about 2/3's through a Dumas Tiger Moth with a brushless mod. I've already downloaded the plans your working from, and can't wait to see where you go with it all.

I use the Elmer's Rubber Cement for cutting balsa and ply from patterns too, but would have never guessed the "contact cement" option with it. That's a nice bit of info to have. May use that, as I have to laminate another thickness of balsa to the firewall in my Moth. Every build thread I read I learn something new. That's just the first one in this thread.

David
Dec 21, 2010, 08:11 PM
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Dorme's Avatar
Watch out in the use of Elmer's glue. It is not permanent (easily pulls apart) and weighs more than CA or white glue. It is an excellent glue for transferring parts from paper to balsa (ribs, formers) and then removing the paper, and as you stated, good for attaching sandpaper to blocks.
Dec 21, 2010, 09:49 PM
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cd_webb,

I so agree that De Havilland planes are right up there with any out there. Your Tiger Moth conversion will be very cool indeed.

Dorme,

I have a FFF Bluecore wing that folded over spar, laminated at the trailing edge, and it's held strong for over 3 years. My sanding blocks take quite a bit of effort to R&R the sandpaper, so I use the 3X brand (3M I think) since the backing is more 'cloth-like'. Havn't had anything de-laminate by doing the 'contact' cement thing which is coat both sides, let dry, then press together. When you say 'not permanent', did you apply the parts together while still wet?


Fred
Dec 21, 2010, 10:33 PM
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Thought I'd share a couple photos.

I decided to get the nose block done and out of the way, say 90%. It will still have some final sanding when mounted and at the lower edge when the lower block gets attached.

I laminated former #8 & #9 together. I made 'former' #10, the ring, from a lamination of 1/64 plywood, and 1/16" balsa. Glued this to the #8/#9 sandwich. This alows for a very firm, strong front edge, that sands well to control shaping, and to keep ding damage to nill or nothing!

So that I could keep them seperate from former #7 until it is mounted to the framework, I made tiny dowel from 2mm toothpicks as seen in the photo. Parts slip on and off, no slop.

Then with some sandpaper glued to a 7/16" Dia dowel (with Elmer's ) I sanded the nose block to fairly finished shape by using a photo of a full scale Moth Minor downloaded from the internet.

Fred
Dec 21, 2010, 10:51 PM
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Freddie B's Avatar
OK, the tail group on this design is simple, basic, 1/16" sheet stock. This works really well, and is fairly light. Stable firm stock is best, or a cross lamination near the tips would help prevent warping.

A good couple of coats of your favorite sealer, some thinned paint/dope, etc is all that would be required to finish them up.

BUT!

I wanted to create my tail group with more 'air' in it, and cover with tissue like the rest of the airframe. There are many ways to do this, from built up edges, ribs, to the style I'm going for, Laminated.

I used a 3mm depron foam sheet for my form. I simply traced a line inside the tail patterns about the thickness my laminations would end up at. and cut it to shape there.

I tried the crayon/wax coating for releasing the parts when dry. Didn't work out so well and I craked my first set at the radius removing them. So I did a second set, this time using vinyl trim tape on the foam, and laminated to the shinny outside side.

First set I used medium weight 1/32" stock, stripped to 3/32" wide, 3 pieces. Soaked them in water, wiped carpenters glue to the edges, place all pieces together, and did the gently pulling, stretching, stack around the form, taping as I went. Let dry 6-24 hours.

On the second set I decided to go with 4 laminations because my balsa behaved more like medium-soft stock, the tight radius in the corners, and so I can sand them a lot for final shape, and retain great strength.

Fred
Dec 21, 2010, 11:03 PM
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Went ahead and cut out the rest of the parts to make this a 'Kit'.

All told about 1 1/2 to 2 hours, but I work slow. I like to make everything as precise and smooth as possible, What can I say, I was a precision machinist in my earlier life!

Stripped some wood stock using my Master Airscrew stripper, more than enough for this build, and maybe another!

The MAS stripper used to #@!"# me off. Then I read a tip that you set the #11 blade so it only goes through a little more than 1/2 way of the sheet thickness. Strip along one side, turn the sheet over, strip along that side, and you get good straight stripped stock without the blade wandering. Simple and brillant. Another 1/2 hour to strip the wood.

So a picture of my 'Kit', and don't forget the laminations for the tail group could be simple, solid, flat sheet stock.

Not much to it, is there! Told you these desings were simple and straight forward.

Fred


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