Dumas Zero (As a trainer)

[Konrad]

This Zero is being used to reintroduce my brother to the dynamic art of flying models. He is an accomplished modeler building exquisite static scale models. He often adds details that only god can see.

Here we choose the Dumas Zero because it is laser cut, low wing, short nosed and has a tapered wing. Other than the laser cutting all these add up to a difficult model to fly.  It will force me to use all the tricks I know to get this project to fly. I feel this will make a great model to expose a person to flying models assuming they have supervision. To be sure it would make a horrible model to teach oneself!

First was to sand off the laser char. I think this char often detracts from any light finish. (This was to be a green camouflage finish. More on that later).

The next trick that never seems to be mentioned in the manuals is to pre-twist the wing saddles. This is in my opinion critical particularly with designs with such radical changes  in the fuselage to wing junction.  We heated the saddles in a microwave oven for about 15seconds after wetting the saddles with water. While the saddles were still hot twisted the saddles to the shape we expected they would need to be. 

While the saddles cooled we thinned the keels and the ID of the formers aft of the CG to be about 1/2 to a 1/3 the as cut size. We built the fuselage per the plans with the keels only using Titebond glue. We forced dried this in the microwave to drive off the moisture. With the formers in place and supported on the keels we placed the pre-shaped saddles on the formers. Using tape (not pins) we again forced dried the glue in the microwave

With the weight credits from thinning  of the keels and formers we  added some filler to support the rear mounting of the canopy.

As the Zero is a very short nosed aircraft and the Dumas Zero has an enlarged stabilizer we added nose weight in the way of balsa filler.

This is only the second or third model I've covered in Esaki tissue. Wow, what a game changer! It is much like what covering with wet silkspan is to covering in dry domestic tissue. It really is nice to use the properties of the material to the fullest.  With wet Esaki we were able to cover the bottom of this compound curved fuselage from center keel to side keel in one piece.

[Konrad]

Some of you might have noticed that I'm doing this old school with nitrate dope. I didn't want to add to the learning curve my ignorance on covering with the "New" water based adhesives and sealants such as those from Deluxe Material.

I'm really impressed with the quality of the covering job my brother did. While I did about 60% of the covering on this model (demonstrating the tecniques) he did the same process on the other half of the model. I can say that I can't tell which piece he applied verses the pieces I applied.

What I'm dealing with is the browning of the nitrate dope. You might see this as dope stains. In the past I rarely had this issue, if ever. What is posted is the condition of the covering right after the Esaki has dried. I'm hoping that this staining will blend with the application of the classic 50/50 thinner and dope sealant. Do you guys use more than one coat of 50/50 on Esaki? I recall using 2 or more coats on domestic tissue. (Another weight saving from using Esaki tissue).

So here is the story for the "yellow Zero". like I said my brother builds exquisite scale models. Building this stand way off flying scale model was a bit troublesome to his esthetic eye. He then realized that Aurora models in the 60's came out with a Yellow Zero. I think that as a teenager he build one and left it yellow. So this is drawing back on his experience as a youth on that plastic model build so many decades ago.

What I want to ask is how do you guys apply tissue markings to models? How is the chalking process done? Are the marking applied dry or wet? Are they applied now or after the tissue is sealed? I think I'll ask these question in the technique section of the forum.

[TheLurker]

What I want to ask is how do you guys apply tissue markings to models?

That's a question that will get you n² answers where n is the number of modellers you ask

My preferred technique is...

After covering & doping

EzeDoped models.  Paint the surface with thinned glue stick (I use a nylon 4O brush) following the centre of the item's shape but not out to the borders of the item. Stick it in place then paint a little more thinned glue stick under the edges to seal them.

Cellulose doped models.  Tack the item (letter/number) with down with either dots of thinned glue stick or a few dots of thinners. Then flood/paint the item with more thinners.  When the thinners has gone off a very thin coat of very dilute (20% or less by volume) non-shrinking dope to seal it.

I've not used nitrate dope for umm, errr, well a very long time.  I'd hope it would behave as cellulose dope, but I don't know.  May be worth making up a test panel and trying it out.

Chalking.  Mike Kelly is your man for that I think. 

Novel choice of scheme. I heartily approve.

How did you twist the wing saddles? Did you bend them to follow the curve of the fuselage or warp them to induce washout/in? 

[Jmk89]

How is the chalking process done?

Here are links to two items from the NFFS website :
Pastel Chalk

Pan Pastels

[Konrad]

What I want to ask is how do you guys apply tissue markings to models?

That's a question that will get you n² answers where n is the number of modellers you ask

...

How did you twist the wing saddles? Did you bend them to follow the curve of the fuselage or warp them to induce washout/in?

So true about the ways to skin a cat ( my apologies to the cat).

I did it the manly way! I just held the hot saddles between my fingers. I still have calluses from when I was a working man. But I like the idea of slowly wrapping them around a broomstick.

[Konrad]

I know this was a typo. But the warping of the saddles was done only to aid in the construction of the fuselage. There was no intended aerodynamic improvement (trimming aid, wash-out/wash-in).

[Konrad]

Wow, it's been about 2 months since I was last here. In that time the Zero has come to life. I like that my brother kept the build light hearted. Here he was masking the canopy with yellow masking tape (Frog brand) in preparation for applying a latex mask. The mask looked great at 5 feet and as there is a high probability that the model will be damaged during flight testing he left the masking tape as the framing.

I have to say I'm really impressed at how well the model looks. I think a lot of this can be traced to the use of old time materials like Esaki Tissue and nitrate dope. But equally it was the time my brother spent sanding.

We did try some 24 test flights, but it really was too windy! Two issue came up. First was that the Zero needed a lot of right and down thrust. Here I'm show that I'm reworking the front bulkhead to add 4.5mm (5°) shim. The second issue is that I can't keep the S hook on the prop shaft. When I get a chance I'll take detail photos and ask for help on troubleshooting.

Some spec's are that the model is 34.8 grams ready to fly with a bit less than 5 grams of nose weight. Power is from 4 strands of 2.6mm x 1mm rubber that are 1.5 time the length of the hook to peg distance, driving a 7" Peck Polymers prop.

[Konrad]

Any ideas as to why it appears that the S hook climbs (bunches) forward and slips through the prop hook! This has happened 3 times with a wound motor (200 turns). Here is the configuration of the S hook and prop hook.

[Piecost]

My experience is that a rigid ring on the motor will tend to climb the reverse S hook and even orientate 90 degrees to the axis of rotation. Try using a neoprene O-Ring on the motor instead; it will deform and wrap onto the hook.

[Konrad]

That's exactly what is happening. This is the first time I've experienced this. Do you have a source for the "O" rings?

[MKelly]

Check the plumbing or faucet repair aisle at Lowes or Home Depot. I get mine there, they have a variety of useful sizes.

Mike

[Jmk89]

In Australia they are called O-rings and they are replacement parts in taps (what our Murrican frenz call faucets), etc.  They come in a variety of sizes.  Choose a size that your motor fits through comfortably leaving just enough space for you to slide it onto the prop hook.

[Jmk89]

Here's a picture from our local hardware depot in Australia (Bunnings) - this set costs a few $A.  You can get sets all the one size if you want

[Piecost]

Make sure that you test that the O Ring is strong enough before using on your model. For example; IIRC a 1.5mm thickness O Ring was not strong enough for four strands of 1/8" Rubber.

[Piecost]

I don't know why Crocket hooks; rigid hooks used on Wakefield and Coupe models, do not experience the same problem. I guess that it is due to their  motors not being longer than the propeller to peg length. Perhaps someone  can confirm.