Le Piaf 1/2A - RC Groups
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Sep 06, 2017, 12:20 AM
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Le Piaf 1/2A


Hi everybody,

This building thread is about a French 1/2A model still famous over here.

When I left Canada in 1978 I had built and crashed at maiden flight a CG 1/2A Skylane, a Mark Models Windfree, a HoB 1/2A Mustang and a custom designed 1/2A. I still didn't know how to fly and was in desperation (what a highly dramatized story, I hope you love it ).

The 1/2A craze had not struck France and everybody laughed at me when I said I was looking forward to building a RC model motorized by a .049 Cox engine (my budget was very low back then and I had already spent most of my money buying a reliable Robbe German radio). "Monsieur, le model will never fly with such a small moteur".

Some time later, in 1979, an indigenous modeler, Patrick Nicolas, who used to write articles for a French RC magazine, leaned over the pond and heard about all this 1/2A craze. He decided to design a very simple 1/2A named Piaf (sparrow). Hundreds of Piaf have then been built. Patrick Nicolas also designed a 1/2A bipe, "MiniBip".

As far as I know the Piaf and the MiniBip are the only 1/2A designed in France.

A fellow classmate, who also happened to be a modeler, had built and flown the Piaf and gave me P. Nicolas' article. So I built the Piaf and learned to fly.
Last edited by Paul_BB; Sep 08, 2017 at 01:29 AM.
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Sep 06, 2017, 01:36 AM
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A full scale plan of the Piaf exists (attached below) but is not convenient and the airfoil seems ridiculous. Moreover, the fuselage profile is slightly different from the one that appeared in the French magazine. This is a sacrilege.

So I was commited to draw my own plan when Gene Rock offered to help me out. Gene had in store a completely flat bottomed Clark Y type airfoil, exactly the kind required for this model.
Last edited by Paul_BB; Sep 18, 2017 at 05:52 AM.
Sep 06, 2017, 11:42 PM
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Here is the plan of Le Piaf.

Compared to the original Piaf we have made a number of changes.

1- The centre sheeting of the original Piaf sticks out of the wing surface because the ribs beneath are of the same thickness than the other ribs. We have corrected this cosmetic default.

2- The wing dihedral brace has been removed and replaced by a butt join and a fiberglass strip. It is much more convenient to sand a half wing than a whole wing.

3- A tail skid has been added.

4- The dihedral has been reduced from 18 to 12░ in order to prevent excess Dutch roll.

5- The piece of plywood that holds the landing gear to the fuselage bottom has been widened.

6- The ill-defined completely flat Clark Y type airfoil of the original Piaf has been replaced by a completely flat Clark Y type airfoil developed by Gene.

Because of these modifications and to avoid any copyright issues, we have renamed the "Piaf" "Le Piaf".
Last edited by Paul_BB; Sep 16, 2017 at 11:59 PM. Reason: New version of the plan
Sep 08, 2017, 02:30 AM
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Wing: rib shaping


I used some cardboard for the rib templates. The template upper and lower surfaces have been hardened with CA glue.

There are three sorts of ribs:
- 2 ribs R1 5mm thick for the half wing roots under the center sheeting
- 2 ribs R2 1.5mm thick under the center sheeting
- 18 ribs R3 1.5mm thick

Oh! And we also need two 3mm R3 ribs for the wing tips.

Plywood templates are more appropriate but require more time to shape. Being careful and for such a small model, in my view cardboard rib templates are more than adequate. CA hardened surfaces are as strong as plywood. The only inconvenient is that these templates do bend if care is not taken.

Note: don't forget to leave 1 mm of balsa fore and aft of the ribs because they will be glued into notches in the LE and TE.
Last edited by Paul_BB; Sep 11, 2017 at 04:32 AM.
Sep 09, 2017, 09:50 AM
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Wing: trailing edge shaping


To shape the trailing edge I cut two balsa strips 17mm wide and 60cm long from some 8mm thick balsa sheet of medium density. The thickness of the trailing edge is only 6mm but I had the 8mm sheet on hand.

The trailing edge is shaped by wedging it between two piano wires of respectively 1mm and 6mm of diameter (I used a 6mm aluminum tube that I had at hand).
I glued the wire and the tube on a strip of wood using CA glue.
Note: I stuck one of the TE stick between the wire and the tube before gluing them to eliminate any slack.

I started off shaping the TE using a plane, then 40 grit sandpaper, 80 and finally 120.

My prayers for those living in Florida.
Last edited by Paul_BB; Sep 09, 2017 at 10:05 AM.
Sep 11, 2017, 04:25 AM
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Wing construction


Photo 1: I made notches for the ribs in the leading edge and the trailing edge. I had previously taped the LE and TE together. The notches are a little over 1mm deep and a little less than 1.5mm wide. Warning ! The root rib is 5 mm thick! The notches must be perpendicular to the LE and TE.

Photo 2: I pinned the lower spar resting against a steel ruler. The spar must be straight!

Photo 3: I used a balsa template (hard and thick) to fix the leading edge and the trailing edge with respect to the spar, and not a rib, because of the notches that are not necessarily of the same depth.

Photo 4: I glued the two parts of the lower central sheeting against the LE, the lower spar and the TE.

Photo 5: I glued the ribs, which is very easy and quick because of the notches, then the upper spar once the glue had dried.

Photo 6: I glued the balsa braces against the spars. Attention, the braces must not be flush with the wing surface, but shorter than the wing thickness. This will be more aesthetic. For this purpose and for each box (excepted for the first wing box due to the lower sheeting) I put some thin cardboard on the building board against the spar before gluing the corresponding brace (see photo).


Note: I use plain slow drying white glue everywhere I can excepted in places that will be sanded (specifically the sheeting). In this case I use UHU Hart. Because I can clean the latter with acetone and because I find it easy to sand. But to each his own.
Last edited by Paul_BB; Sep 13, 2017 at 09:42 AM.
Sep 13, 2017, 09:42 AM
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Wing construction


Photo 1: gluing of the upper central sheeting (two parts in front of and behind the upper spar). I chose a balsa dense enough to resist the pressure of the fastening rubber bands.

Photo 2: squaring up of the tip ribs.

Photo 3: squaring up of the root ribs that will be later on beveled to a 6░ angle.

Photo 4: gluing of the 3mm wing tips.

Photo 5: gluing of the triangle braces at the wing tips (two triangles at the end of each half wing).
Sep 13, 2017, 01:51 PM
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Looks like your project is coming along nicely! It's always a pleasure to watch your building prowess.

As soon as I can free up some time, I'm going to build a geared twin .049, "Twin-Bee" engine. - http://www.ebay.com/itm/Build-a-Cox-...QAAOxyThVTYE~C

I was thinking this might be a cute plane for it if I scaled it up a bit, say 25-30% or so. I could it "Le Gros Piaf" . Anyway, It'll go on my list of possible candidates.

Mike
Last edited by CryHavoc; Sep 13, 2017 at 01:56 PM.
Sep 13, 2017, 10:47 PM
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Hey Paul, I agree with CH Mike, nice airplane and build ! Your final CAD plan is quite nice, too ! So does a flat bottomed Clark Y perform slow and gentle ? Just curious.... Mike
Sep 14, 2017, 12:29 AM
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Quote:
Originally Posted by CryHavoc
Looks like your project is coming along nicely! It's always a pleasure to watch your building prowess.

As soon as I can free up some time, I'm going to build a geared twin .049, "Twin-Bee" engine. - http://www.ebay.com/itm/Build-a-Cox-...QAAOxyThVTYE~C

I was thinking this might be a cute plane for it if I scaled it up a bit, say 25-30% or so. I could it "Le Gros Piaf" . Anyway, It'll go on my list of possible candidates.

Mike
Thanks Mike. Wow this geared Twin-Bee is incredible. One good think about this simple Le Piaf model is that you have an easy access to the engine.
Last edited by Paul_BB; Sep 14, 2017 at 12:57 AM.
Sep 14, 2017, 12:49 AM
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Quote:
Originally Posted by ms62tn
Hey Paul, I agree with CH Mike, nice airplane and build ! Your final CAD plan is quite nice, too ! So does a flat bottomed Clark Y perform slow and gentle ? Just curious.... Mike
Hi Mike thanks for the kind words. The CAD plan has been drawn by Gene Rock. We worked together but he gave this plan the "RCM touch". All praises go to him.

As a matter of fact a standard Clark Y performs very well for low Reynolds numbers. This fact is known by model sailplane pilots. Now we have better airfoils thanks to Pr Mark Drela, but the Clark Y stands on its own merits. This was a surprise when it was discovered because the Clark Y was designed in 1922!

The flat bottom Clark Y is slightly less competitive but has this great advantage to lie flat on the building board. Thus the lower wing sheeting can be pinned down first on the building board and then the ribs glued onto it.
Last edited by Paul_BB; Sep 14, 2017 at 02:54 AM.
Sep 14, 2017, 06:21 PM
I'd rather be flying.....
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Hi Paul -

Your Le Piaff build is really looking nice ! And, very historical..... I have a Twin Cox .049 i could post a picture if you like ? It is a factory built unit from Thompson Products Brooklyn, NY USA...

Best regards,

jeff
Sep 14, 2017, 11:58 PM
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Quote:
Originally Posted by JeffMac
...I have a Twin Cox .049 i could post a picture if you like ? It is a factory built unit from Thompson Products Brooklyn, NY USA...
Hi Jeff thanks, yes please post the picture, I'm curious about this engine.
Sep 15, 2017, 06:13 AM
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Photo 1: sanding of the leading edge. That's the big thing. I use templates, different grades of sandpaper glued on a flat surface. This is when you are happy to work on a half wing at the time. I have drawn a line on the leading edge representing the origin of the airfoil. Line that should not be erased.

Photo 2: center sheeting sanding. I use acetone to remove excess UHU Hart glue before sanding. Generally speaking I wipe with acetone everywhere I find this glue, this eases the sanding.

Photo 3: slight sanding of the upper wing surface, in the area of the spar.

Photo 4: wing tip sanding.
Sep 16, 2017, 01:35 AM
I'd rather be flying.....
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Thompson Tee Pee .098 RC


Hi Paul-

Here are photos of my Thompson Products .098 RC.... it is very well made and uses a separate fuel tank rather than the Cox tanks. the first owner told me he flew it on a semi-scale Sikorski flying boat a few times in the late 1960s....

I have not ran it but enjoy having this one

Best regards,

jeff


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